2007, QUEST 3, 3-7
This article is directed at the general public. It describes some of the amazing discoveries made in the previously concealed skies of the Zone of Avoidance, a large area of the sky that is obscured from our view by the dust and stars of the disk of our own Galaxy.
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2007, Mon. Not, Roy. Ast. Soc., in press
A detailed dynamical analysis of the nearby rich Norma cluster (ACO 3627) is presented. From radial velocities of 296 cluster members, we find a mean velocity of 4871 +/- 54 km/s and a velocity dispersion of 925 km/s. The mean velocity of the E/S0 population (4979 +/- 85 km/s) is offset with respect to that of the S/Irr population (4812 +/- 70 km/s) by `Delta' v = 164 km/s in the cluster rest frame. This offset increases towards the core of the cluster. The E/S0 population is free of any detectable substructure and appears relaxed. Its shape is clearly elongated with a position angle that is aligned along the dominant large-scale structures in this region, the so-called Norma wall. The central cD galaxy has a very large peculiar velocity of 561 km/s which is most probably related to an ongoing merger at the core of the cluster. The spiral/irregular galaxies reveal a large amount of substructure; two dynamically distinct subgroups within the overall spiral-population have been identified, located along the Norma wall elongation. The dynamical mass of the Norma cluster within its Abell radius is 1 - 1.1 x 10^15 h^-1_73 M_Sun. One of the cluster members, the spiral galaxy WKK 6176 which recently was observed to have a 70 kpc X-ray tail, reveals numerous striking low-brightness filaments pointing away from the cluster centre suggesting strong interaction with the intracluster medium.
arXiv:0706.2227, Full text (pdf)
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2007, in Galaxies in the Local Volume, eds. B. Koribalski & H. Jerjen, Astrophys. & Space Sci., in press
The Parkes deep HI ZOA survey has been extended between 2002 and 2004 towards higher latitudes in the Galactic Bulge region. This area of extreme star crowding and high extinction levels remains impenetrable at any other waveband regime. Preliminary results of the 3 dimensional distribution based on the combined HI-surveys will be presented. It will focus on the extent and "content" of the Local Void as outlined by these HI surveys, followed by a discussion of the properties of the few galaxies detected in the Local Void in comparison them to properties of the Parkes ZOA HI survey as a whole.
arXiv:0710.1795, Full text (pdf)
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2007, in Galaxies in the Local Volume, eds. B. Koribalski & H. Jerjen, Astrophys. & Space Sci., in press
The large-scale dynamics of galaxies in the Local Universe is dominated by the Great Attractor. At its core sits the Norma cluster (the nearest rich cluster) which allows a close-up view of possible galaxy transformation processes that might occur in such very dense environments. The spiral galaxy WKK6176 - close to the centre of the Norma cluster - reveals a plethora of evidence for strong interactions with the intracluster medium shows multiple filamentary structures/streams aligned with the recently detected X-ray tail. After' a discussion the properties of the Norma cluster itself, we will present deep multiwavelength (BVRJHKs) imaging, optical spectroscopy and galaxy evolutionary models (GALEV) of this interesting WKK6176.
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2007, Astron. Astrophys. 466, 481-499
The highly obscured radio-bright galaxy PKS1343-601 (l=309.7, b=+1.8) has been suspected to mark the centre of a hitherto unknown cluster in the Great Attractor region. As such it presents an ideal region for a search of galaxies in the near-infrared (NIR) and an in-depth study of their colours as a function of extinction. A visual search of a ~30 square-degree area centered on this radio galaxy on images of the NIR DENIS survey (IJK) revealed 83 galaxies (including two AGNs) and 39 possible candidates. Of these, 49 are also listed in the 2MASS Extended Source Catalog 2MASX. Taking the IRAS/DIRBE extinction values (Schlegel et al. 1998) at face value, the absorption in the optical (A_B) ranges from ~2m to over 100m across the Galactic Plane. Comparing the detections with other systematic surveys, we conclude that this search is highly complete up to the detection limits of the DENIS survey and certainly surpasses any automatic galaxy finding algorithm applied to crowded areas. The NIR galaxy colours from the 7arcsec aperture were used as a probe to measure total Galactic extinction. A comparison with the IRAS/DIRBE Galactic reddening maps suggests that the IRAS/DIRBE values result in a slight overestimate of the true extinction at such low Galactic latitudes; the inferred extinction from the galaxy colours corresponds to about 87% of the IRAS/DIRBE extinctions. Although this determination still shows some scatter, it proves the usefulness of NIR surveys for calibrating the IRAS/DIRBE maps in the extinction range of 2m < A_B < 12m.
astro-ph/0607108, Full text (pdf)
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2007, IAU Transactions, Vol. 26A, Reports on Astronomy 2002-2005, eds. O. Engvold, Cambridge: Cambridge University Press, pp. 281-289
This report gives a brief overview of some of the activities and developments in extragalactic research over the past three years.
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2007, Astron. J. 133, 979-986
We report on the discovery of two spiral galaxies located behind the southern Milky Way, within the least explored region of the Great Attractor. They lie at 317, -0.5 deg galactic, where obscuration from Milky Way stars and dust exceeds 13 to 15 mag of visual extinction. The galaxies were the most prominent of a set identified using mid-infrared images of the low-latitude (|b| < 1 deg) Spitzer Legacy program GLIMPSE. Follow-up HI radio observations reveal that both galaxies have redshifts that place them squarely in the Norma Wall of galaxies, which appears to extend diagonally across the Galactic Plane from Norma in the south to Centaurus & Vela in the north. We report on the near-infrared, mid-infrared and radio properties of these newly discovered galaxies, and discuss their context in the larger view of the Great Attractor. The work presented here demonstrates that mid-infrared surveys open up a new window to study galaxies in the Zone of Avoidance.
Full text (pdf) , astro-ph/0611397
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2006, Mon. Not, Roy. Ast. Soc. 369, 1741-1754
We report the discovery of a very HI-massive disk galaxy, HIZOA J0836-43, at a velocity of v_hel = 10689 km/s, corresponding to a distance of 148 Mpc (assuming H_0=75 km/s/Mpc). It was found during the course of a systematic HI survey of the southern Zone of Avoidance (|b| < 5 deg) with the multibeam system at the 64m Parkes radio telescope. Follow-up observations with the Australia Telescope Compact Array (ATCA) reveal an extended HI disk. We derive an HI mass of 7.5 x 10^10 Msun. Using the HI radius, we estimate a total dynamical mass of 1.4 x 10^12 Msun, similar to the most massive known disk galaxies such as Malin 1. HIZOA J0836-43 lies deep in the Zone of Avoidance (l, b = 262.48 deg, -1.64 deg) where the optical extinction is very high, A_B = 9.8. However, in the near-infrared wavebands, where the extinction is considerably lower, HIZOA J0836-43 is clearly detected by both DENIS and 2MASS. Deep AAT near-infrared (Ks and H-band) images show that HIZOA J0836-43 is an inclined disk galaxy with a prominent bulge (scale length 2.5 arcsec or 1.7 kpc), and an extended disk (scale length 7 arcsec or 4.7 kpc) which can be traced along the major axis out to a radius of 20 arcsec or 13.4 kpc (at 20 mag/arcsec^2 in Ks). The HI disk is much more extended, having a radius of 66 kpc at 1 Msun/pc^2. Detections in the radio continuum at 1.4 GHz and at 60 micron (IRAS) are consistent with HIZOA J0836-43 forming stars at a rate of ~35 Msun/yr. We compare the properties of HIZOA J0836-43 with those of the most HI-massive galaxies currently known, UGC 4288, UGC 1752 and Malin 1, all of which are classified as giant low surface brightness galaxies.(abridged)
Full text (pdf) , astro-ph/0604108
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2006, Mon. Not. Roy. Ast. Soc, 369, 1131-1142
To further our understanding of the Great Attractor (GA), we have undertaken a redshift survey using the 2dF on the AAT. Clusters and filaments in the GA region were targeted with 25 separate pointings resulting in approximately 2600 new redshifts. Targets included poorly studied X-ray clusters from the CIZA catalogue as well as the Cen-Crux and PKS 1343-601 clusters, both of which lie close to the classic GA centre. For nine clusters in the region, we report velocity distributions as well as virial and projected mass estimates. The virial mass of CIZA J1324.7-5736, now identified as a separate structure from the Cen-Crux cluster, is found to be ~3x10^14 M_sun, in good agreement with the X-ray inferred mass. In the PKS 1343-601 field, five redshifts are measured of which four are new. An analysis of redshifts from this survey, in combination with those from the literature, reveals the dominant structure in the GA region to be a large filament, which appears to extend from Abell S0639 (l=281\deg, b=+11\deg) to (l~5\deg, b~-50\deg), encompassing the Cen-Crux, CIZA J1324.7-5736, Norma and Pavo II clusters. Behind the Norma Cluster at cz~15000 km/s, the masses of four rich clusters are calculated. These clusters (Triangulum-Australis, Ara, CIZA J1514.6-4558 and CIZA J1410.4-4246) may contribute to a continued large-scale flow beyond the GA. The results of these observations will be incorporated into a subsequent analysis of the GA flow.
Full text (pdf) , astro-ph/0603692
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2005,``From Cosmological Structures to the Milky Way'', Reviews in Modern Astronomy 18, ed. S. Röser, (New York: Wiley), p. 48-75
This paper provides an update to the review on extragalactic large-scale structures uncovered in the Zone of Avoidance (ZOA) by Kraan-Korteweg & Lahav 2000, in particular in the Great Attractor region. Emphasis is given to the penetration of the ZOA with the in 2003 released NIR 2MASX Catalog. The distribution is little affected by the foreground dust. Galaxies can be identified to extinction levels of over A(B) < 10m except in the wider Galactic Bulge region (see Fig. 9) where star density is a strong delimiting factor. The shape of the NIR-ZOA is quite asymmetric due to Galactic features such as spiral arms and the Bulge, something that should not be ignored when using NIR samples for studies such as dipole determinations.
Results are presented from the deep blind HI ZOA survey performed with the Multibeam Receiver at the Parkes telescope (v < 12700km/s). The distribution of the roughly one thousand discov ered spiral galaxies in the optically and NIR impenetratable part of the ZOA clearly depict the prominence of the Norma Supercluster. With the optically identified galaxies in the ZOA, a picture emerges that bears a striking resemblance to the Coma cluster in the Great Wall: the rich Norma cluster (ACO 3627) lies within a great-wall like structure that can be traced at the redshift range of the cluster over 90dg on the sky, with two foreground filaments - reminiscent of the legs in the famous stick man - that merge in an overdensity at slightly lower redshifts around the radio galaxy PKS 1343-601 (see Figs. 14 & 16). (abridged)
Full text (ps.gz) , astro-ph/0502217
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2005, Astron. J. 129, 220-238
We present the results of the northern extension of the HI Parkes Zone of Avoidance Survey, a blind HI survey utilizing the multibeam receiver on the Parkes 64-m telescope. In the two regions studied here, l=36 to 52 deg. and l=196 to 212 deg., |b|<5 deg., we have detected 77 HI galaxies, twenty of which have been previously detected in HI. The survey has a median rms noise of 6.0 mJy/beam and is complete to a mean flux density of 22 mJy. We have searched for multiwavelength counterparts to the 77 galaxies detected here: 19, 27, and 11 have a likely optical, 2MASS, and IRAS cataloged counterpart, respectively. A further 16 galaxies have likely visible counterparts on the Digitized Sky Survey. The detection of these 77 galaxies allows a closer inspection of the large-scale structures in these regions. We see several filaments crossing the Galactic plane, one of which appears to be the continuation of a sine-wave like feature that can be traced across the whole southern sky. An analysis of the HI mass function suggests that the regions studied here may be underdense. One particularly noteworthy galaxy is HIZOA J0630+08 (l,b = 203 deg., -0.9 deg.) with a velocity of 367 km/s. We suggest that it belongs to the nearby Orion Group which includes a small number of dwarf galaxies. The newly detected galaxies improve our understanding of the properties of several voids, such as the Orion, Gemini, and Canis Major Voids.
Full text (pdf) , astro-ph/0409570
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2005, ``Nearby Large-Scale Structures and the Zone of Avoidance'', eds. A.P. Fairall & P.A. Woudt, A.S.P. Conf. Ser. 329, 119-132
Galaxies uncovered in the Zone of Avoidance (ZOA) with deep optical searches are compared to the distribution of objects in the 2MASS Extended Source Catalog (2MASX). While the galaxy density of optical surveys is strongly correlated to the dust content, and become ineffective in uncovering the galaxy distribution at A_B > 3.0 mag, this effect is much less severe in the NIR. Galaxies can be identified in 2MASS at optical extinction layers of over 10mag. However, star density has been found to be the dominant limiting factor in the NIR in the wider Galactic Bulge region (see Fig. 4) where optical surveys still do quite well.
Systematic positional offsets have also been found between objects in the 2MASX and the optical ZOA as well as other galaxy catalogs. These seem to have their origin in the astrometric reference frame used by these surveys as well as different fitting algorithms when determining positions (details are given in the Appendix). The astrometric offsets between 2MASX and more recent galaxy catalogs (or on the Digitized Sky Survey remeasured positions) are of the order of 1 - 1.5 arcsec, comparable to the relative dispersion in positions between these surveys. Still, it is advisable to take this effect into account when combining galaxies from different catalogs for observational purposes.
Full text (pdf) , astro-ph/0409391
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2005, ``Nearby Large-Scale Structures and the Zone of Avoidance'', eds. A.P. Fairall & P.A. Woudt, A.S.P. Conf. Ser. 329, 147-158
Deep J, H and Ks photometry of the low Galactic latitude Norma cluster has been obtained with the 1.4-m Infrared Survey Facility (IRSF) and with SOFI on the NTT. Together with spectroscopy taken at the Anglo-Australian Observatory using 2dF, the near-infrared Fundamental Plane of the Norma cluster will be used to determine the distance to this cluster and to assess its location within the Great Attractor overdensity. Potential systematic uncertainties related to the determination of peculiar velocities in the Zone of Avoidance are discussed in some detail. In particular the effects (uncertainties, systematics and scatter) of extinction and star-crowding on the derived magnitudes at low latitudes are investigated in great detail. We present a first look at the emerging Ks-band Fundamental Plane of the Norma cluster. We expect an uncertainty of ~ 3% (~ 150 km/s at the distance of the Norma cluster) in our final Fundamental Plane distance estimate based on 76 galaxies.
Full text (pdf), astro-ph/0410725
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2005, ``Nearby Large-Scale Structures and the Zone of Avoidance'', eds. A.P. Fairall & P.A. Woudt, A.S.P. Conf. Ser. 329, 159-166
Motivated by the possibility that the highly obscured (A_B = 12 mag) radio galaxy PKS 1343-601 at (l,b,cz) = (309.7, +1.8, 3872km/s) might constitute the center of a heavily obscured cluster in the Great Attractor region, we have imaged about 2 x 2 degree of the core of this prospective cluster in the I-band using the WFI at the ESO 2.2m telescope at La Silla. We were able to identify 49 galaxies and 6 uncertain galaxy candidates. Although their distribution does not resemble a centrally condensed, massive cluster, its appearance -- severely influenced by the strong dust gradient across our surveyed region - is entirely consistent with a cluster.
Full text (pdf) , astro-ph/0406044
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2005, ``Nearby Large-Scale Structures and the Zone of Avoidance'', eds. A.P. Fairall & P.A. Woudt, A.S.P. Conf. Ser. 329, 167-176
We present results of a search for galaxies around the highly obscured giant radio galaxy PKS1343-601 using the near-infrared DENIS survey. We compare our findings with surveys in the B-band, at the 21cm line emission, and with 2MASS. Recession velocities of galaxies in this area suggest a low-velocity-dispersion group or cluster of galaxies including an X-ray confirmed Seyfert 2. The colours of the galaxies have been used to examine the extinctions in this low-latitude area where IRAS/DIRBE estimates are unreliable. We find the true extinction to be roughly 15% lower than the IRAS/DIRBE extinctions.
Full text, astro-ph/0407019
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2005, ``Nearby Large-Scale Structures and the Zone of Avoidance'', eds. A.P. Fairall & P.A. Woudt, A.S.P. Conf. Ser. 329, 199-208
The 64-m Parkes telescope, equipped with the 21-cm multibeam receiver, has completed a sensitive survey (typically 6 mJy/beam rms) for HI galaxies in the Zone of Avoidance (ZOA) accessible to the telescope, 196 < l < 52deg, and |b| < ~5deg. While galaxy candidate inspection is not yet quite complete, and final number not yet determined, the survey has yielded about 1000 galaxies. The data, in the form of three-dimensional datacubes, have been inspected by eye, and candidate lists assembled, and about half have now been checked for reality, and accepted into the final catalog. The distributions on the sky and in redshift space are presented, showing galaxies belonging to previously-known structures, and newly-discovered features. Of the 469 confirmed HI galaxies, 191 have a NIR source within 6arcmin in the 2MASS Extended Source Catalog, but the incidence of NIR counterparts is a strong function of longitude: in the low obscuration, low stellar surface density Puppis region, 131 of the 186 HI galaxies have 2MASS counterparts (70%), while in the Galactic bulge region, only 6 of the 155 HI detections have a 2MASS extended source coincident (4%). This is attributable to the HI survey's ability to detect galaxies even in regions of high foreground stellar surface density.
Full text (ps.gz), astro-ph/0406517
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2005, ``Maps of the Cosmos'', IAU Symp. 216, eds. M. Colless, L. Staveley-Smith & R. Stathakis, ASP, 203-210
A first analysis of a deep blind HI survey covering the southern Zone of Avoidance plus an extension towards the north (196 < l < 52 deg) obtained with the Multibeam receiver at the 64m Parkes telescope reveals slightly over a thousand galaxies within the latitude completeness limit of |b| < 5deg. The characteristics and the uncovered large-scale structures of this survey are described, in particular the prominence of the Norma Supercluster, the possible cluster around PKS 1343-601 (both in the Great Attractor region), as well as the Local Void and the clustering in the Puppis region. In this blind HI survey, HIZOA J0836-43, one of the most massive spiral galaxies known to date was discovered (M(HI) = 7.3 10^10 Msun M(tot) = 1.1 10^12 Msun; Ho = 75 km/s/Mpc). Although of similar mass as Malin 1-like objects, this galaxy does not share their typical low-surface brightness properties but seems an exceptionally massive but normal, high-surface brightness, star-forming galaxy.
Full text (pdf), astro-ph/0311129
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2004, Astron. J. 128, 16-46
We present the HIPASS Bright Galaxy Catalog (BGC) which contains the 1000 HI-brightest galaxies in the southern sky as obtained from the HI Parkes All-Sky Survey (HIPASS). The selection of the brightest sources is based on their HI peak flux density (Speak > 116 mJy) as measured from the spatially integrated HIPASS spectrum. The derived HI masses range from about 10^7 to 4 x 10^10 Msun. While the BGC (z < 0.03) is complete in Speak, only a subset of about 500 sources can be considered complete in integrated HI flux density (FHI > 25 JY km/s). The HIPASS BGC contains a total of 158 new redshifts and yields no evidence for a population of "free-floating" intergalactic HI clouds without associated optical counterparts. HIPASS provides a clear view of the local large-scale structure. The dominant features in the sky distribution of the BGC are the Supergalactic Plane and the Local Void. In addition, one can clearly see the Centaurus Wall which connects via the Hydra and Antlia clusters to the Puppis filament. Some previously hardly noticed galaxy groups stand out quite distinctively in the HI sky distribution. Several new structures are seen for the first time, not only behind the Milky Way.
Full text (pdf) , astro-ph/0404436
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2004, Astron. Astrophys. 415, 9-18
As part of our efforts to unveil extragalactic large-scale structures behind the southern Milky Way, we here present redshifts for 764 galaxies in the Hydra/Antlia, Crux and Great Attractor region (266deg < l < 338deg, |b| < 10deg), obtained with the Meudon-ESO Fibre Object Spectrograph (MEFOS) at the 3.6-m telescope of ESO. The observations are part of a redshift survey of partially obscured galaxies recorded in the course of a deep optical galaxy search behind the southern Milky Way. A total of 947 galaxies have been observed, a small percentage of the spectra (N=109, 11.5%) were contaminated by foreground stars, and 74 galaxies (7.8%) were too faint to allow a reliable redshift determination. With MEFOS we obtained spectra down to the faintest galaxies of our optical galaxy survey, and hence probe large-scale structures out to larger distances (v <~ 30000 km/s) than our other redshift follow-ups. The most distinct large-scale structures revealed in the southern Zone of Avoidance are discussed in context to known structures adjacent to the Milky Way.
Full text (pdf) , astro-ph/031195
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2003, Astron. J. 126, 2362-2367
We have obtained VLA and optical follow-up observations of the low-velocity H I source HIZSS 3 discovered by Henning et al. (2000) and Rivers (2000) in a survey for nearby galaxies hidden by the disk of the Milky Way. Its radio characteristics are consistent with this being a nearby (~1.8 Mpc) low-mass dwarf irregular galaxy (dIm). Our optical imaging failed to reveal a resolved stellar population, but did detect an extended H-alpha emission region. The location of the H-alpha source is coincident with a partially-resolved H I cloud in the 21-cm map. Spectroscopy confirms that the Halpha source has a similar radial velocity to that of the H I emission at this location, and thus we have identified an optical counterpart. The Halpha emission (100 pc in diameter and with a luminosity of 1.4 10^{38}erg/s) is characteristic of a single H II region containing a modest population of OB stars. The galaxy's radial velocity and distance from the solar apex suggests that it is not a Local Group member, although a more accurate distance is needed to be certain. The properties of HIZSS 3 are comparable to those of GR 8, a nearby dIm with a modest amount of current star formation. Further observations are needed to characterize its stellar population, determine the chemical abundances, and obtain a more reliable distance estimate.
Full text (pdf), astro-ph/0308080
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2003, Astron. J. 125, 2842-2858
We present a new accurate measurement of the HI mass function of galaxies from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the highest HI peak flux densities in the southern hemisphere (Koribalski et al. 2003). This sample spans nearly four orders of magnitude in HI mass (from log M_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected galaxies to date. We develop a bivariate maximum likelihood technique to measure the space density of galaxies, and show that this is a robust method, insensitive to the effects of large scale structure. The resulting HI mass function can be fitted satisfactorily with a Schechter function with faint-end slope alpha=-1.30. This slope is found to be dependent on morphological type, with later type galaxies giving steeper slopes. We extensively test various effects that potentially bias the determination of the HI mass function, including peculiar motions of galaxies, large scale structure, selection bias, and inclination effects, and quantify these biases. The large sample of galaxies enables an accurate measurement of the cosmological mass density of neutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies contribute only 15% to this value, consistent with previous findings.
Full text (pdf), astro-ph/0302440
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2003, in ``Galaxy Evolution: Theory and Observations'', Rev. Mexicana Astron. Astrof. (Serie de Conf.), 17, 37
A large part of the Great Attractor (GA) region is hidden by the Milky Way. The mapping of structures (clusters as well as voids) in this region is important, however, for the understanding of this massive overdensity and its dynamics. We discuss our observing program of the Norma cluster (ACO 3627), a rich cluster at the core of the GA, as well as first results from an I-band survey centered on PKS1343-601, a strong, but heavily obscured radio continuum source that seems to constitute the center of yet another rich cluster in the GA region.
Full text (pdf)
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2002, Astron. Astrophys. 391, 887-902
As part of our program to map the large-scale distribution of galaxies behind the Milky Way, we used the Parkes 210 ft (64 m) radio telescope for pointed HI observations of a sample of low surface-brightness (due to heavy obscuration) spiral galaxies selected from the deep optical Zone of Avoidance (ZOA) galaxy catalog in the Hydra/Antlia region (Kraan-Korteweg 2000a). Searching a simultaneous velocity range of either 300 to 5500 km/s or 300 to 10500 km/s to an rms level of typically 2 - 4 mJy resulted in detections in 61 of the 139 pointings, leading to a total of 66 detections (an additional detection was made in a reference position, and two other pointings revealed two and four independent signals respectively). Except for 2 strong HI emitters identified in the shallow Zone of Avoidance HI survey (Henning et al. 2000), all HI detections are new. An analysis of the properties of the observed and detected galaxies prove that pointed HI observations of highly obscured galaxies allow the tracing of a population of nearby, intrinsically large and bright spiral galaxies that otherwise would not be recovered. The new data identified a previously unrecognized nearby group at l=287.5, b=-9.5, V=1700 km/s, the continuation of the Hydra/Antlia filament on the opposite side of the Galactic plane, and helped to delimit a distinct void in the ZOA centered at 2000 km/s.
Full text (pdf), astro-ph/0206197
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2002, Astron. J. 124, 1954-1974
The HI Parkes All-Sky Survey (HIPASS) is a blind 21-cm survey for extragalactic neutral hydrogen, covering the whole southern sky. The HIPASS Bright Galaxy Catalog (BGC; Koribalski et al. 2002) is a subset of HIPASS and contains the 1000 HI-brightest (peak flux density) galaxies. Here we present the 138 HIPASS BGC galaxies, which had no redshift measured prior to the Parkes multibeam HI surveys. Of the 138 galaxies, 87 are newly cataloged. Newly cataloged is defined as no optical (or infrared) counterpart in the NASA/IPAC Extragalactic Database. Using the Digitized Sky Survey we identify optical counterparts for almost half of the newly cataloged galaxies, which are typically of irregular or magellanic morphological type. Several HI sources appear to be associated with compact groups or pairs of galaxies rather than an individual galaxy. The majority (57) of the newly cataloged galaxies lie within ten degrees of the Galactic Plane and are missing from optical surveys due to confusion with stars or dust extinction. This sample also includes newly cataloged galaxies first discovered in the HI shallow survey of the Zone-of-Avoidance (Henning et al. 2000). The other 30 newly cataloged galaxies escaped detection due to their low surface brightness or optical compactness. Only one of these, HIPASS J0546-68, has no obvious optical counterpart as it is obscured by the Large Magellanic Cloud. We find that the newly cataloged galaxies with |b| > 10 are generally lower in HI mass and narrower in velocity width compared with the total HIPASS BGC. In contrast, newly cataloged galaxies behind the Milky Way are found to be statistically similar to the entire HIPASS BGC. In addition to these galaxies, the HIPASS BGC contains four previously unknown HI clouds.
Full text (pdf), astro-ph/0206447
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2001, Astron. Astrophys. 380, 441-459
In this second paper of the catalogue series of galaxies behind the southern Milky Way, we report on the deep optical galaxy search in the Crux region (289deg <= l <= 318deg and -10deg < b <= 10deg) and the Great Attractor region (316deg <= l <= 338deg and -10deg <= b <= 10deg). The galaxy catalogues are presented, a brief description of the galaxy search given, as well as a discussion on the distribution and characteristics of the uncovered galaxies. A total of 8182 galaxies with major diameters D >= 0.2 arcmin were identified in this ~850 square degree area: 3759 galaxies in the Crux region and 4423 galaxies in the Great Attractor region. Of the 8182 galaxies, 229 (2.8%) were catalogued before in the optical (3 in radio) and 251 galaxies have a reliable (159), or likely (92) cross-identification in the IRAS Point Source Catalogue (3.1%). A number of prominent overdensities and filaments of galaxies are identified. They are not correlated with the Galactic foreground extinction and hence indicative of extragalactic large-scale structures. Redshifts obtained at the South African Astronomical Observatory (SAAO) for 518 of the newly catalogued galaxies in the Crux and Great Attractor regions (Fairall et al. 1998; Woudt et al. 1999) confirm distinct voids and clusters in the area here surveyed. With this optical galaxy search, we have reduced the width of the optical `Zone of Avoidance' for galaxies with extinction-corrected diameters larger than 1.3 arcmin from extinction levels A_B >= 1.0 mag to A_B >= 3.0 mag: the remaining optical Zone of Avoidance is now limited by |b| <= 3deg (see Fig. 16).
Full text (ps.gz), astro-ph/0110464,
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2001, Astron. Astrophys. 369, 432-440
ATCA 21 cm HI observations of the rich galaxy cluster ACO 3627 in the Great Attractor region are presented. Three fields of 30' diameter located within one Abell radius of ACO 3627 were observed with a resolution of 15'' and an rms noise of ~ 1 mJy/beam. Only two galaxies were detected in these fields. We compare their HI distribution to new optical R-band images and discuss their velocity fields. The first galaxy is a gas-rich unperturbed spiral whereas the second shows a peculiar HI distribution. The estimated 3-sigma HI mass limit of our observations is about 7 x 10^8 M_o for a line width of 150 km/s. The non-detection of a considerable number of luminous spiral galaxies indicates that the spiral galaxies are HI deficient. The low detection rate is comparable to the HI deficient Coma cluster (Bravo-Alfaro et al. 2000). ACO 3627 is a bright X-ray cluster. We therefore suspect that ram pressure stripping is responsible for the HI deficiency of the bright cluster spirals.
astro-ph/0102200,
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2001, Mon. Not. Roy. Ast. Soc. 322, 486-498
The acquisition of HI Parkes All Sky Survey (HIPASS) southern sky data commenced at the Australia Telescope National Facility's Parkes 64-m telescope in 1997 February, and was completed in 2000 March. HIPASS is the deepest HI survey yet of the sky south of declination +2 deg, and is sensitive to emission out to 170 Mpc (Ho=75) The characteristic root mean square noise in the survey images is 13.3 mJy. This paper describes the survey observations, which comprise 23 020 eight-degree scans of 9-min duration, and details the tech- niques used to calibrate and image the data. The processing algorithms are successfully designed to be statistically robust to the presence of interference signals, and are particular to imaging point (or nearly point) sources. Specifically, a major improvement in image quality is obtained by designing a median-gridding algorithm which uses the median estimator in place of the mean estimator.
Full text (pdf)
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2000, Lecture Notes in Physics, "GTO Lectures on Astrophysics", eds. D. Page and J. Hirsch, (Springer: Heidelberg), p301-344
Dust and stars in the plane of the Milky Way create a "Zone of Avoidance" in the extragalactic sky. Galaxies are distributed in gigantic labyrinth formations, filaments and great walls with occasional dense clusters. They can be traced all over the sky, except where the dust within our own galaxy becomes too thick - leaving about 25% of the extragalactic sky unaccounted for. Our Galaxy is a natural barrier which constrains the studies of large-scale structures in the Universe, the peculiar motion of our Local Group of galaxies and other streaming motions (cosmic flows) which are important for understanding formation processes in the Early Universe and for cosmological models. Only in recent years have astronomers developed the techniques to peer through the disk and uncover the galaxy distribution in the Zone of Avoidance. I present the various observational multi-wavelength procedures (optical, far infrared, near infrared, radio and X-ray) that are currently being pursued to map the galaxy distribution behind our Milky Way. Particular emphasis is given to discoveries in the Great Attractor region -- a from streaming motions predicted huge overdensity centered behind the Galactic Plane. The recently unveiled massive rich cluster A3627 seems to constitute the previously unidentified core of the Great Attractor.
astro-ph/0006199
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2000, in "Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe in HI", ASP Conf. Ser. 218, eds. R.C. Kraan-Korteweg, P.A. Henning, H. Andernach, 193-201
A deep optical galaxy search behind the southern Milky Way and a subsequent redshift survey of the identified obscured galaxies traces clusters and superclusters into the deepest layers of Galactic foreground extinction (A_B <= 3^m - 5^m). In the Great Attractor region, we have identified a low-mass cluster (the Centaurus-Crux cluster) at (l, b, v, sigma) = (305.5deg, +5.5deg, 6214 km/s, 472 km/s) and found that ACO 3627 (the Norma cluster) at (l, b, v, sigma) = (325.3deg, -7.2deg, 4844 km/s, 848 km/s) is the most massive cluster in the Great Attractor region known to date. It is comparable in virial mass, richness and size to the well-known but more distant Coma cluster. The Norma cluster most likely marks the bottom of the potential well of the Great Attractor. It is located at the intersection of two main large-scale structures, the Centaurus Wall and the Norma supercluster. The flow field observed around the Great Attractor probably is caused by the confluence of these two massive structures.
astro-ph/0006126
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2000, in "Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe in HI", ASP Conf. Ser. 218, eds. R.C. Kraan-Korteweg, P.A. Henning, H. Andernach, 207-214
A blind HI survey using the Parkes telescope at |b| < 5deg 300 < l < 332 deg has so far revealed 305 galaxies, most of which were previously unknown. These galaxies are used to map out the distribution of filaments and voids out to 10^4 km/s. A preliminary measurement of the galaxy overdensity suggests only a moderate overdensity is present, and that the excess mass (above the background density) is about 2 10^15 Omega_0 Msun. This is below the mass predicted in POTENT reconstructions of the local velocity field, and implies that the `Great Attractor' (GA) is not as massive as these reconstructions indicate, or does not lie hidden in the region investigated.
Full text (ps.gz), astro-ph/0009223
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2000, in "Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe in HI", ASP Conf. Ser. 218, eds. R.C. Kraan-Korteweg, P.A. Henning, H. Andernach, 19-26
Dust and stars in the Milky Way create a ``Zone of Avoidance'' (ZOA) in the distribution of optically visible galaxies of about 25% of the sky. To reduce this gap, optical searches for partially obscured galaxies have been performed. The status of these deep searches, in particular their completeness as a function of foreground extinction are discussed. Using existing sky surveys, over 50000 previously unknown galaxies have been identified. The surveys cover practically the whole ZOA. It is shown that these surveys are complete for galaxies with extinction-corrected diameters D^o ge 1.3 arcmin to extinction levels of A_B le 3.0 mag. Incorporating these new data in a whole-sky map of galaxies complete to D^o ge 1.3 arcmin finds the ZOA reduced by a factor of about 2 to 2.5, respectively from extinction levels of A_B = 1.0 mag to A_B = 3.0 mag (see Fig.~4).
astro-ph/0006121
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2000, in "Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe in HI", ASP Conf. Ser. 218, eds. R.C. Kraan-Korteweg, P.A. Henning, H. Andernach, 35-41
An optical search of the Scorpius region -- close to the Galactic bulge -- has revealed some 1400 partially-obscured galaxies. Redshifts have been obtained for nearly a hundred of these objects. Preliminary indications of large-scale structures are reported.
astro-ph/0006120
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2000, The Astronomy and Astrophysics Review 10, 211-261
Due to the foreground extinction of the Milky Way, galaxies appear increasingly fainter the closer they lie to the Galactic Equator, creating a "zone of avoidance" of about 25% in the distribution of optically visible galaxies. A "whole-sky" map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor region.
Various dynamically important structures behind the Milky Way have only recently been made ``visible'' through dedicated deep surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and X-ray) for galaxies in the Zone of Avoidance are reviewed, including a discussion on the limitations and selection effects of these partly complementary approaches. The uncovered and suspected large-scale structures are summarized. Reconstruction methods of the density field in the Zone of Avoidance are described and the resulting predictions compared with observational evidence. The comparison between reconstructed density fields and the observed galaxy distribution allow derivations of the density and biasing parameters Omega_0 and b.
astro-ph/0005501, Full text (ps.gz)
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2000, in "Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe in HI", ASP Conf. Ser. 218, eds. R.C. Kraan-Korteweg, P.A. Henning, H. Andernach, 119-127
We discuss the possibilities of extragalactic large-scale studies behind the Zone of Avoidance (ZOA) using complementary multi-wavelength data from optical, systematic blind HI , and near-infrared (NIR) surveys. Applying these data to the NIR Tully-Fisher relation permits the mapping of the peculiar velocity field across the ZOA. Here, we present results of a comparison of galaxies identified in the rich low-latitude cluster Abell 3627 in the B-band with NIR (DENIS) data, and cross-identifications of galaxies detected with the blind Parkes HI Multibeam survey with NIR data - many of which are optically invisible.
astro-ph/0005447
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2000, Astron. J. 119, 2686-2698
A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212 < l < 36 deg, |b| leq 5 deg), has been made with the 21cm multibeam receiver on the Parkes 64~m radiotelescope. The survey, sensitive to normal spiral galaxies to a distance of about 40 Mpc and more nearby dwarfs, detected 110 galaxies. Of these, 67 have no counterparts cataloged in the NASA/IPAC Extragalactic Database. In general, the uncataloged galaxies lie behind thicker obscuration than do the cataloged objects. All of the newly-discovered galaxies have HI flux integrals more than an order of magnitude lower than the Circinus galaxy. The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg \& Huchtmeier 1992), and the Local Void remains empty. The HI mass function derived for the sample is satisfactorily fit by a Schechter function with parameters alpha = 1.51 +- 0.12, Phi = 0.006 +- 0.003, and log(M*) = 9.7 +- 0.10.
astro-ph/0003245
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2000, Publ. Astron. Soc. Australia 17, 6-12
Due to the foreground extinction of the Milky Way, galaxies become increasingly faint as they approach the Galactic Equator creating a ``zone of avoidance'' (ZOA) in the distribution of optically visible galaxies of about 25%. A ``whole-sky'' map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor (GA) region. The current status of deep optical galaxy searches behind the Milky Way and their completeness as a function of foreground extinction will be reviewed. It has been shown that these surveys - which in the mean time cover the whole ZOA (Fig. 2) - result in a considerable reduction of the ZOA from extinction levels of A_B = 1.0 mag (Fig. 1) to A_B = 3.0 mag (Fig. 2). In the remaining, optically opaque ZOA, systematic HI surveys are powerful in uncovering galaxies, as is demonstrated for the GA region with data from the full sensitivity Parkes Multibeam HI survey (300 < l < 332 deg, |b| < 5.5 deg, Fig. 4).
astro-ph/9910572
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2000, Astron. Astrophys. Suppl. Ser. 141, 123-140
A deep optical galaxy search in the southern Milky Way - aimed at reducing the width of the Zone of Avoidance - revealed 3279 galaxy candidates above the diameter limit of D > 0.2 arcmin, of which only 112 (3.4%) were previously catalogued. The surveyed region (266 < l < 296 and -10 < b < +8) lies in the extension of the Hydra and Antlia clusters - where a supercluster is suspected - and in the approximate direction of the dipole anisotropy in the Cosmic Microwave Background radiation. Here we present the optical properties of the unveiled galaxies such as positions, diameters, magnitudes, morphological types, including a detailed discussion on the quality of these data and the completeness limits as a function of the foreground dust extinction. For 127 of the 227 positional matches in the IRAS PSC, a reliable cross-identification could be found. Several distinct overdensities and filaments of galaxies can be identified that are apparently uncorrelated with the Galactic foreground extinction hence the probable signature of extragalactic large-scale structures. This catalog constitutes the first part in a series of five equally conducted optical searches for galaxies in the southern Milky Way (245 < l < 350). With these surveys, the entire Zone of Avoidance will have been covered by means of visual inspection. The catalogs build the basis for various spectroscopic and photometric follow-up programs which eventually will allow a thorough analyse of the galaxy distribution in redshift space and the peculiar velocity fields within the Zone of Avoidance, as well an an improved understanding of the Galactic foreground extinction.
astro-ph/9910455,
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2000, Astron. J. 119, 1627-1637
We report on a blind neutral hydrogen survey for galaxies using the 21 cm multibeam receiver on the Parkes 64 m telescope. The surveyed region covers |b|<=5 deg in the zone of avoidance (ZOA) from Galactic longitude 308 - 332 deg. The survey represents the first phase of a blind HI survey covering the southern ZOA (l=212 deg to 36 deg). We have detected HI in 42 galaxies above a 3 sigma limit of 60 mJy. The galaxies detected in this survey have velocities out to 6000 km s-1 and HI masses in the range 4x10^7 to 3x10^10 Msun (Ho=75). Only eight of the 42 galaxies have velocities previously measured. A further nine galaxies appear to have optical counterparts in the Woudt's 1998 catalog. In total, 16 of the galaxies appear to be associated with IRAS sources, although only three of these are without optical counterparts. The estimated median extinction for the 20 galaxies with optical or IR counterparts is AB=3.8 mag. For the 22 galaxies with no counterparts, the estimated median extinction is AB=5.6 mag. The distribution of galaxies is suggestive of a connection between the Centaurus supercluster above the Galactic plane and the Pavo-Indus supercluster beneath the plane. No previously hidden concentrations of galaxies were found.
Full text (ps.gz)
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2000, in "Cosmic Flows" workshop, A.S.P. Conf. Ser. 201, eds. S. Courteau, M. Strauss, and J. Willick (ASP: San Francisco), p. 88-91
The nature and extent of the Great Attractor (GA) has been the subject of much debate in the past decade, partly due to the fact that a large fraction of the GA overdensity is hidden by the southern Milky Way. Based on our deep optical galaxy search behind the southern Milky Way and a subsequent redshift survey we discovered that the Norma cluster (ACO 3627) in the GA region is a very massive cluster of galaxies. The cluster is comparable in size, richness and mass to the Coma cluster. It is located at the intersection of two distinct large structures, the Centaurus Wall and the Norma Supercluster. The velocity flow fields in the GA region are most likely caused by the confluence of these two massive structures where the Norma cluster constitutes its previously unseen but predicted core. The possibility that another, heavily obscured and yet uncharted rich cluster might form part of the GA overdensity is also discussed.
astro-ph/9909094
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1999

1999, Astron. Astrophys. 352, 39-48
In the third of a series of papers on large-scale structures behind the southern Milky Way, we report here on redshifts obtained at the South African Astronomical Observatory (SAAO) in the Great Attractor region (318deg < l < 340deg, |b| <= 10deg, Woudt 1998). This region encompasses the peak in the reconstructed mass density field, associated with the Great Attractor (Kolatt et al. 1995, Dekel et al. 1998) and covers the crossing of the Supergalactic Plane with the Galactic Plane.
We have obtained reliable redshifts for 309 galaxies in the Great Attractor region with the ``Unit'' spectrograph (first with a Reticon, then with a CCD detector) at the 1.9-m telescope of the SAAO.
We realise here, that the Great Attractor region is dominated by ACO 3627 (hereafter referred to as the Norma cluster), a highly obscured, nearby and massive cluster of galaxies close to the plane of the Milky Way (l,b,v) = (325.3deg, -7.2deg, 4844 km/s) (Kraan-Korteweg et al. 1996, Woudt 1998). Previous redshift surveys in the GA region have failed to gauge the significance of the Norma cluster, primarily due to the diminishing effects of the Galactic foreground extinction on the partially obscured galaxies. In the absence of the obscuring effects of the Milky Way, the Norma cluster would have appeared as prominent as the well-known Coma cluster, but nearer in redshift-space. This cluster most likely marks the bottom of the potential well of the Great Attractor (Woudt 1998).
astro-ph/9911274
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1999, Astroph. J 524, 612-622
We have commenced a 21-cm survey of the entire southern sky (delta < 0 degrees, -1200 km/s < v < 12700 km/s) which is ''blind'', i.e. unbiased by previous optical information. In the present paper we report on the results of a pilot project which is based on data from this all-sky survey. The project was carried out on an area of 600 square degrees centred on the nearby Centaurus A (Cen A) group of galaxies at a mean velocity of v ~ 500 km/s. This was recently the subject of a separate and thorough optical survey. We found 10 new group members to add to the 21 galaxies already known in the Cen A group: five of these are previously uncatalogued galaxies, while five were previously catalogued but not known to be associated with the group. We found optical counterparts for all the HI detections, most of them intrinsically very faint low surface brightness dwarfs. The new group members add approximately 6% to the HI mass of the group and 4% to its light. The HI mass function, derived from all the known group galaxies in the interval 10^7 Msun of HI to 10^9 Msun of HI, has a faint-end slope of 1.30 +/- 0.15, allowing us to rule out a slope of 1.7 at 95% confidence. Even if the number in the lowest mass bin is increased by 50%, the slope only increases to 1.45 +/- 0.15.
astro-ph/9906146
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1999, Publ. Astron. Soc. Australia 16, 53-59
Various dynamically important extragalactic large-scale structures in the local Universe lie behind the Milky Way. Most of these structures (predicted and unexpected) have only recently been made ``visible'' through dedicated deep surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and X-ray) for galaxies in the Zone of Avoidance (ZOA) will be reviewed and the uncovered and suspected large-scale structures summarised. Particular emphasis is given to the Great Attractor region where the existence of yet another cluster is suspected (Woudt 1998). Predictions from reconstructions of the density field in the ZOA are discussed and compared with observational evidence. Although no major structures are predicted out to about v < 10000 km/s for which no observational evidence exists, the comparison between reconstructed density fields and the observed galaxy distribution remain important as they allow derivations of the density and biasing parameters.
Full text (pdf) , astro-ph/9901419
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1999, Publ. Astron. Soc. Australia 16, 48-52
The Dwingeloo Obscured Galaxies Survey (DOGS) is a 21-cm blind survey for galaxies hidden in the northern "Zone of Avoidance" (ZOA): the portion of the optical extragalactic sky which is obscured by dust in the Milky Way. Like the Parkes southern hemisphere ZOA survey, the DOGS project is designed to reveal hidden dynamically important nearby galaxies and to help "fill in the blanks" in the local large scale structure. To date, 36 galaxies have been detected by the Dwingeloo survey; 23 of these were previously unknown (no corresponding sources recorded in the NASA Extragalactic Database (NED)). Among the interesting detections are 3 nearby galaxies in the vicinity of NGC 6946 and 11 detections in the Supergalactic plane crossing region. VLA follow-up observations have been conducted for several of the DOGS detections.
Full text (pdf) , astro-ph/9903443
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1999, Publ. Astron. Soc. Australia 16, 42-47
Roughly 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various surveys are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from (different) limitations and selection effects. We illustrate the promise of using a multi-wavelength approach for extragalactic large-scale studies behind the ZOA, i.e. a combination of three surveys -- optical, systematic blind HI and near-infrared (NIR), which will allow the mapping of the peculiar velocity field in the ZOA through the NIR Tully-Fisher relation. In particular, we present here the results of cross-identifying HI-detected galaxies with the DENIS NIR survey, and the use of NIR colours to determine foreground extinctions.
Full text (pdf), Full text
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1999, Publ. Astron. Soc. Australia 16, 35-37
The HI Parkes Zone of Avoidance Survey is a 21 cm blind search with the multibeam receiver on the 64-m radiotelescope, looking for galaxies hidden behind the southern Milky Way. The first, shallow (15 mJy rms) phase of the survey has uncovered 107 galaxies, two-thirds of which were previously unknown. The addition of these galaxies to existing extragalactic catalogs allows the connectivity of a very long, thin filament across the Zone of Avoidance within 3500 km/s to become evident. No local, hidden, very massive objects were uncovered. With similar results in the north (The Dwingeloo Obscured Galaxies Survey) our census of the most dynamically important HI-rich nearby galaxies is now complete, at least for those objects whose HI profiles are not totally buried in the Galactic HI signal. Tests are being devised to better quantify this remaining ZOA for blind HI searches. The full survey is ongoing, and is expected to produce a catalog of thousands of objects when it is finished.
Full text (pdf), astro-ph/9904024
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1999, Astron. Astrophys. Suppl. Ser. 135, 255-271
A radio spectroscopic driftscan survey in the 21cm line with the Nancay Radio Telescope of 0.08 steradians of sky in the direction of the constellation Canes Venatici covering a heliocentric velocity range of -350 < V_hel < 2350 km/s produced 53 spectral features, which was further reduced to a sample of 33 reliably detected galaxies by extensive follow-up observations. With a typical noise level of rms = 10 mJy after Hanning smoothing, the survey is - depending on where the detections are located with regard to the center of the beam - sensitive to M(HI)=1-2x10^8 Msun at 23 Mpc and to M(HI)=4-8x10^7 Msun throughout the CVn Groups (Ho=100). The survey region had been previously examined on deep optical plates by Binggeli et al. 1990 and contains loose groups with many gas-rich galaxies as well as voids. No galaxies that had not been previously identified in these deep optical surveys were uncovered in our HI survey, neither in the groups nor the voids. The implication is that no substantial quantity of neutral hydrogen contained in gas-rich galaxies has been missed in these well-studied groups. All late-type members of our sample are listed in the Fisher and Tully (1981b) optically selected sample of nearby late-type galaxies; the only system not contained in Fisher and Tullys' Catalog is the S0 galaxy NGC 4203. Within the well-sampled CVn group volume with distances corrected for flow motions, the HI mass function is best fitted with the Zwaan et al. (1997) HI mass function (alpha=-1.2) scaled by a factor of f=4.5 in account of the locally overdense region.
astro-ph/9811096
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1999, in "The Low Surface Brightness Universe", IAU Coll 171, eds. J.I. Davies et al., A.S.P. Conf. Ser. p.103-110
The systematic mapping of obscured and optically invisible galaxies behind the Milky Way through complementary surveys are important in arriving at the whole-sky distribution of complete galaxy samples and therewith for our understanding of the dynamics in the local Universe. In this paper, a status report is given of the various deep optical, near infrared (NIR), and systematic blind HI-surveys in the Zone of Avoidance, including a discussion on the limitations and selection effects inherent to the different multi-wavelength surveys and first results.
astro-ph/9711001
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1998, ESO/ATNF Workshop on "Looking Deep in the Southern Sky" eds. R. Morganti and W. Couch, Springer, 23-28
About 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various approaches are presently being employed to uncover the galaxy distribution in this Zone of Avoidance (ZOA). Results as well as the different limitations and selection effects from these multi-wavelengths explorations are being discussed. Galaxies within the innermost part of the Milky Way - typically at a foreground obscuration in the blue of A_B > 5mag and |b| < 5 deg - remain particularly difficult to uncover except for HI-surveys: the Galaxy is fully transparent at the 21cm line and HI-rich galaxies are easy to trace. We will report here on the first results from the systematic blind HI-search (v < 12700 km/s) in the southern Zone of Avoidance which is currently being conducted with the Parkes Multibeam (MB) Receiver.
astro-ph/9804066
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1998, Scientific American, Octobre issue, p.50-57
Over a fifth of the universe is hidden from view, blocked by dust and stars in the disk of our galaxy. But over the past few years, astronomers have found ways to peek through the murk.
On a dark night, far from city lights, we can clearly see the disk of our galaxy shimmering as a broad band across the sky. This diffuse glow is the direct light emitted by hundreds of billions of stars as well as the indirect starlight scattered by dust grains in interstellar space. We are located about 28,000 light-years from the center of the galaxy in the midst of this disk. But although the Milky Way may be a glorious sight, it is a constant source of frustration for astronomers who study the universe beyond our galaxy. The disk blocks light from a full 20 percent of the cosmos, and it seems to be a very exciting 20 percent.
Somewhere behind the disk, for example, are crucial parts of the two biggest structures in the nearby universe: the Perseus-Pisces supercluster of galaxies and the "Great Attractor," a gargantuan agglomeration of matter whose existence has been inferred from the motions of thousands of galaxies through space. Observations also show a tantalizing number of bright and nearby galaxies in the general direction of the disk, suggesting there are many others that go unseen. Without knowing what lies in our blind spot, researchers cannot fully map the matter in our corner of the cosmos. This in turn prevents them from settling some of the most important questions in cosmology: How large are cosmic structures? How did they form? What is the total density of matter in the universe?
SciAm Oct. 1998
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1998, Astron. J. 116, 2717-2727
We present the first results of a blind HI survey for galaxies in the southern Zone of Avoidance with a multibeam receiver on the Parkes telescope. This survey is eventually expected to catalog several thousand galaxies within Galactic latitude |b| < 5 deg, mostly unrecognised before due to Galactic extinction and confusion. We present here results of the first three detections to have been imaged with the Australia Telescope Compact Array (ATCA). The galaxies all lie near Galactic longitude 325 deg and were selected because of their large angular sizes, up to 1.3 deg. Linear sizes range from 53 to 108 kpc. The first galaxy is a massive 5.7 x 10^11 Msun disk galaxy with a faint optical counterpart, SGC 1511.1-5249. The second is probably an interacting group of galaxies straddling the Galactic equator. No optical identification is possible. The third object appears to be an interacting pair of low column density galaxies, possibly belonging to an extended Circinus or Centaurus A galaxy group. No optical counterpart has been seen despite the predicted extinction (A_B=2.7 - 4.4 mag) not being excessive. We discuss the implications of the results, in particular the low HI column densities (~ 10^19 atoms/cm^2) found for two of the three galaxies.
Full text (ps.gz)
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1998, 3rd Euroconference on "The Impact of Near Infrared Surveys on Galactic and Extragalactic Astronomy", eds. N. Epchtein, Kluwer: Dordrecht, p. 209-220
About 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various approaches are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from (different) limitations and selection effects. We investigated the potential of using the DENIS NIR survey for studies of galaxies behind the obscuration layer of our Milky Way and for mapping the Galactic extinction. As a pilot study, we recovered DENIS I-, J- and K-band images of heavily obscured but optically still visible galaxies. We determined the I-, J- and K-band luminosity function of galaxies on three DENIS strips that cross the center of the nearby, low-latitude, rich cluster Abell 3627. The resulting extinction-corrected I-J and J-K colours of these cluster galaxies compare well with that of an unobscured cluster. We searched for and identified galaxies at latitudes where the Milky Way remains fully opaque (|b| < 5deg and A_B < 4-5 mag) - in a systematic search as well as around positions of galaxies detected with the blind HI-survey of the ZOA currently conducted with the Multibeam Receiver of the Parkes Radiotelescope.
astro-ph/9711226
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1998, Astron. Astrophys. 338, 8-14
ACO 3627 is a rich, nearby cluster of galaxies at the core of the Great Attractor. Although it lies at the low galactic latitude of b = -7.2deg where the galactic extinction is significant, its proximity makes it a good candidate for studies of environmental effects on its members. Here, we report on a multi-wavelength study of a Seyfert 1 galaxy at 30 arcmin from the centre of ACO 3627. Its Seyfert nature was discovered spectroscopically and confirmed in X-rays. We have obtained B_J and R_C CCD photometry as well as J, H, K and L aperture photometry at the SAAO, low and high resolution spectroscopy (ESO and SAAO), 21 cm line observations (Parkes Observatory) and X-ray ROSAT PSPC data.
The Seyfert 1 galaxy is of morphology SBa(r). It has a nearby companion (dS0). A consistent value for the galactic extinction of A_B = 1.6 mag could be determined. The nucleus of the Seyfert galaxy is very blue with a strong (B_J - R_C) colour gradient in the inner 2.5 arcsec. The extinction-corrected near-infrared colours of WKK 6092 are typical of a Seyfert 1 galaxy, likewise its X-ray spectrum. The galaxy has a very low HI flux. This could be explained by its morphology, but also - due to its very central position within the rich Norma cluster - to ram pressure stripping.
astro-ph/9804052
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1998, Mon. Not. Roy. Astron. Soc. 299, 24-30
Motivated by recent discoveries of nearby galaxies in the Zone of Avoidance, we conducted a pilot study of galaxy candidates at low Galactic latitude, near Galactic longitude l ~ 135deg, where the Supergalactic Plane is crossed by the Galactic Plane. We observed with the 1m Wise Observatory in the I-band 18 of the `promising' candidates identified by visual examination of Palomar red plates by Hau et al. (1995). A few candidates were also observed in R or B bands, or had spectroscopic observations performed at the Isaac Newton Telescope and at the Wise Observatory. Our study suggests that there are probably 10 galaxies in this sample. We also identify a probable Planetary Nebula. The final confirmation of the nature of these sources must await the availability of full spectroscopic information. The success rate of about 50% in identifying galaxies at Galactic latitude |b| <5 deg indicates that the ZOA is a bountiful region to discover new galaxies.
astro-ph/9707345
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1998, Astron. J. 115, 584-591
Our Galaxy blocks a significant portion of the extragalactic sky from view, hampering studies of large-scale structure. This produces an incomplete knowledge of the distribution of galaxies, and, assuming galaxies trace mass, of the gravity field. Further, just one unrecognized, nearby massive galaxy could have large influence over the Milky Way's motion with respect to the Cosmic Microwave Background. Diligent surveys in the optical and infrared wavebands can find galaxies through moderate Galactic gas and dust, but close to the Galactic Plane, only radio surveys are effective. The entire northern Zone of Avoidance is being searched at 21 cm for galaxies using the Dwingeloo 25-m telescope. A shallow search for nearby, and/or massive galaxies has been completed, yielding five objects. Two of these galaxies were previously unknown, and although they are not likely members of the Local Group, are part of the nearby Universe. A deeper search continues, which will produce a flux-limited catalog of hidden galaxies. This portion of the survey is one-third complete, and has detected about 40 objects to date. Based on present understanding of the HI mass function, the complete survey should uncover 50 - 100 galaxies.
astro-ph/9711001
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1998, Astron. Astrophys. Suppl. Ser. 127, 463-470
In our systematic optical galaxy search behind the southern Milky Way, 3760 (mostly unknown) galaxies with diameters D > 0.2 arcmin were identified in the Crux region (287deg < l < 318deg, |b| < 10deg, Woudt & Kraan-Korteweg 1997). In order to map the galaxy distribution in redshift space we obtained spectra for 226 bright (B_J < 18.0mag) objects with the 1.9m telescope of the South African Astronomical Observatory (SAAO). Redshifts could be determined for 209 objects, of which 173 have good signal-to-noise ratios. Of the 36 tentative redshifts, four are confirmed through independent values in the literature. The redshifts of three objects indicate them to be galactic of origin. In addition, 26 redshifts have have been measured in the Hydra-Antlia region investigated earlier (Kraan-Korteweg, Fairall & Balkowski 1995), of which one is a tentative estimate. Two main structures crossing the Galactic Plane in the Crux region have now become clear. A narrow, nearby filament from (l, b) = (340deg, -25deg) to the Centaurus cluster can be traced. This filament runs almost parallel to the extension of the Hydra-Antlia clusters found earlier and is part of what we have earlier termed the ``Centaurus Wall'' extending in redshift-space between 0 < v < 6000 km/s (Fairall & Paverd 1995). The main outcome of this survey however, is the recognition of another massive extended structure between 4000 < v < 8000 k/ms. This broad structure, dubbed the Norma Supercluster (Woudt et al. 1997), runs nearly parallel to the Galactic Plane from Vela to ACO 3627 (its centre) from where it continues to the Pavo cluster. This massive structure is believed to be associated with the Great Attractor. The survey has furthermore revealed a set of cellular structures, similar to those seen in redshift space at higher galactic latitudes, but never before seen so clearly behind the Milky Way.
astro-ph/9705152
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1998, Astron. Astrophys. Suppl. Ser. 127, 397-408
Sensitive 21cm HI line observations were performed for 23 dwarf members and possible members of the nearby M81 group of galaxies, including five objects of a clustering of extremely low-surface brightness objects of unknown nature. With the Nancay decimetric radio telescope the radial velocity range of -529 to 1826 km/s was searched to an rms noise of ~3-5 mJy. Only three objects were detected. However, their high radial velocities (between 600 and 1150 km/s) show them to lie behind the M81 group. These three objects, classified as dS0: (UGC 4998) and Im (Kar 1N and UGC 5658), have HI masses of 0.5, 2.0 and 2.5 10^8 Msun, for the assumed distance of 4 Mpc, and HI mass-to-blue light ratios of 0.05, 0.91 and 0.22 Msun/LBsun, respectively. Considering that half of the observed objects are classified as irregular dwarfs, hence expected to be relatively gas-rich, the resulting detection rate of about 1/3 is quite low. However, the mean redshift and velocity dispersion of the M81 group ( = 101 km/s, sigma=114 km/s) suggest that the HI emission of low velocity HI-rich members of the M81 group may still remain hidden within the strong Galactic HI emission (typically -150 < v < 115 km/s) or, for the 6 dwarf candidates in the immediate vicinity of M81, overshadowed by the very extended HI envelope encompassing M81, M82, NGC 3077, and NGC 2976 (-280 < v < 355 km/s).
astro-ph/9706081
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1997, XVIIth Moriond Astrophysics Meeting on ``Extragalactic Astronomy in the Infrared'', eds. Trinh Xuan Thuan et al., Eds Frontieres (Gif-sur-Yvette), 381-386
We investigated the potential of using DENIS for studies of galaxies behind the obscuration layer of our Milky Way, and mapping the Galactic extinction. As a pilot study, we examined DENIS I-, J-, and K-band images of heavily obscured galaxies from a deep optical (B_J-band) galaxy survey in the Zone of Avoidance. We tried to uncover additional galaxies at latitudes where the Milky Way remains fully opaque, i.e. we conducted a `blind' search at |b| < 5deg and A_B > 4-5 mag. Furthermore, we determined the I, J and K magnitudes of galaxies in the low-latitude, nearby, rich cluster Abell 3627 and compared the resulting colour-colour diagram with that of an unobscured cluster.
astro-ph/9706093
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1997, Publ. Astron. Soc. Australia 14, 37-44 Driftscan methods are highly efficient, stable techniques for conducting extragalactic surveys in the 21 cm line of neutral hydrogen. Holding the telescope still while the beam scans the sky at the sidereal rate produces exceptionally stable spectral baselines, increased stability for RFI signals, and excellent diagnostic information about system performance. Data can be processed naturally and efficiently by grouping long sequences of spectra into an image format, thereby allowing thousands of individual spectra to be calibrated, inspected and manipulated as a single data structure with standard tools that already exist in astronomical software. The behaviour of spectral standing waves (multi-path effects) can be appraised and excised in this environment, making observations possible while the Sun is up. The method is illustrated with survey data from Arecibo and Nancay.
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1997, Publ. Astron. Soc. Australia 14, 15-20
We report here on extragalactic large-scale structures uncovered by a deep optical survey for galaxies behind the southern Milky Way. Systematic visual inspection of the ESO/SRC-survey revealed over 10000 previously unknown galaxies in the region 265 to 340 degrees. With subsequently obtained redshifts of more than 10% of these galaxies, new structures across the Milky Way are unveiled, such as a filament at 2500 km per sec connecting to the Hydra and Antlia clusters, a shallow extended supercluster in Vela (6000 km/sec), and a nearby (4882 km per sec), very massive, rich Coma-like cluster which seems to constitute the previously unidentified centre of the Great Attractor. The innermost part of the Milky Way remains fully opaque. In this approximately 8 degree wide strip, the forthcoming blind HI survey with the multi-beam system at Parkes will provide the only tool to unveil this part of the extragalactic sky.
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1997, Experimental Astronomy 7, 65-85
We are describing a new multi-fibre positioner, MEFOS, that was in general use at the La Silla Observatory, and implemented at the prime focus of the ESO 3.6 m telescope. It is an arm positioner using 29 arms in a one degree field. Each arm is equipped with an individual viewing system for accurate setting and carries two spectroscopic fibres, one for the astronomical object and the other one for the sky recording needed for sky subtraction. The spectral fibres intercept 2.5 arcsec on the sky and run from the prime focus to the Cassegrain, where the B&C spectrograph is located. After describing the observational procedure, we present the first scientific results.
astro-ph/9612204
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1997 in ``Dark and Visible Matter in Galaxies and Cosmological Implications'', eds. M. Persic and P. Salucci, A.S.P. Conf. Ser.117, 373-379
The nature and the extent of the Great Attractor has been the subject of much debate, not in the least due to the unfortunate position of its central part being behind the Milky Way. We here present the latest results from our deep optical galaxy search in the southern Milky Way. A full view of the southern hemisphere is emerging, revealing ACO 3627 as the most prominent concentration of galaxies in the southern sky. Our follow-up spectroscopic observations support the idea that ACO 3627 is the dominant component of a ``great wall''-structure, similar to Coma in the (northern) Great Wall.
astro-ph/9610179
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1996, Astron. Astrophys. 315, 549-554
Spectroscopic observations have been carried out for eleven objects believed to be planetary nebulae on the basis of their optical appearance. They were discovered in an ongoing deep search for galaxies in the Southern Milky Way (Kraan-Korteweg & Woudt 1994). The objects were observed with the 1.9m telescope of the South African Astronomical Observatory during our program for obtaining redshifts of obscured galaxies in the ``Zone of Avoidance''. Of the eleven objects, three proved too faint for a definite classification, four were galaxies with radial velocities between v=3920 km/s and v=14758 km/s, but four were confirmed as planetary nebulae (PNE). Their relative line strengths and radial velocities have been determined. The PNE are on average fairly large (23''-30''). Two of them (PNG 298.3+06.7 and PNG 323.6-04.5) were previously unknown; for these we show H_alpha and [OIII] images.
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1996, ApJ 467, 168-174
The cluster A3627 was recently recognized to be a very massive, nearby cluster in a galaxy survey close to the Galactic plane. We are reporting on ROSAT PSPC observations of this object, which confirm that the cluster is indeed very massive. The X-ray emission detected from the cluster extends over almost 10 in radius. The X-ray image is not spherically symmetric and shows indications of an ongoing cluster merger. Because of the strong interstellar absorption, the spectral analysis and the gas temperature determination are difficult. The data are consistent with an overall gas temperature in the range 5- 10 keV. There are signs of temperature variations in the merger region. A mass estimate based on the X-ray data yields values of 0.4-2.2 x 10^15^ M_sun if extrapolated to the virial radius of 3 h^-1^_50 Mpc. In the ROSAT energy band (0.1-2.4 keV) the cluster emission yields a flux of about 2 x 10^-10^ ergs s^-1^ cm^-2^, which makes A3627 the sixth brightest cluster in the ROSAT All Sky Survey. The cluster was missed in earlier X-ray surveys because it was confused with a neighboring X-ray bright, galactic X-ray binary (1H 1556-605). The large X-ray flux makes A3627 an important target for future studies.
astro-ph/9602140
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1996, Mon. Not. Roy. Astron. Soc. 280, 537-549
We present new optical observations of the nearby barred spiral galaxy Dwingeloo 1 (Dw1) obtained with the Isaac Newton, William Herschel and Wise telescopes. Dw1 lies at Galactic coordinates (l=138.52, b=-0.11) and it is heavily obscured by dust and gas in the Milky Way. We infer that Dw1 is of morphological type SBb or SBc (T=4), has an inclination i~=50 deg, a position angle PA~=110 deg, and a recession velocity relative to the Milky Way V_MW=256+/-9 km/s. The measured total apparent magnitudes of Dw1 are V=14.0+/-0.5, R=12.2+/-0.2 and I=10.7+/-0.2. The extinction estimate towards Dw1 is highly uncertain. The extinction in the B band, derived from Galactic HI column density measurements, is A_B~=5.8. Estimated from Galactic 100-mum emission, the extinction is A_B~=4.3, while the reddened colours of Dw1 yield an estimate of A_B~=10.4. Assuming A_B=5.8, Tully-Fisher relations in the I and R bands lead to a distance estimate for Dw1 of D~=300 km/s. However, for the derived range of extinction estimates 4.3<~A_B<~10.4, the distance varies from 100 to 500 km/s. We also report the detection of numerous HII regions associated with Dw1, and present data from the Infrared Astronomical Satellite (IRAS) archive.
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1996, Astron. Astrophys. 309, 687-701
We present observations made with the Westerbork Synthesis Radio Telescope of HI emission from Dwingeloo 1, a nearby barred spiral discovered during the Dwingeloo Obscured Galaxies Survey for galaxies hidden in the Zone of Avoidance, and of Dwingeloo 2, a small galaxy discovered in the beam of these WSRT observations. The WSRT data reveal the position of the dynamical center of Dw1, its systemic LSR velocity, its total (projected) width in velocity, its inclination on the sky, and its integrated HI flux, as well as details of the velocity field and gas distribution. Dw1 is the nearest grand-design barred spiral system, and is probably amongst the ten largest galaxies closer than about 5Mpc. We report here also the discovery of Dwingeloo 2, a small galaxy located within the WSRT primary beam as pointed to Dw1. In view of its angular and kinematic proximity to Dw1, Dw2 may well be a companion to the larger system. The two galaxies are probably both members of the group containing Maffei 1 & 2 and IC342 and may influence the peculiar motions within that group and the morphology of its individual members.
astro-ph/9511020
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1996, Nature 379, 519-521
Our deep survey for partially-obscured galaxies behind the southern Milky Way reveals that the cluster A3627 at Galactic coordinates l=325, b=-7 - which lies 9 degrees from the most recently predicted centre of the Great Attractor - would be seen to be the most prominent cluster in the southern hemisphere, were its galaxies not obscured by the dust and stars of the Milky Way. Our follow-up redshift observations find this rich cluster to be very massive (5 10^15 M_sun). Its overall properties are, in fact, comparable to the well-studied Coma cluster. With a mean redshift of v(obs)=4882 km/s, A3627 is the nearest known rich cluster in the Universe. Moreover, A3627 seems to be the dominant peak of a larger supercluster or great wall. Its location in redshift space close to the core of the Great Attractor mass excess suggests that A3627 is at the bottom of its potential well.
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1994, Nature 372, 77-79
The disk of the Milky Way contains a lot of gas and dust, which obscures about 20% of the extragalactic sky. Galaxies hidden behind the Milky Way may have an important influence on the dynamics of the Local Group and its peculiar motion relative to the cosmic microwave background radiation. Here we report the discovery of a large spiral galaxy, which we call Dwingeloo 1, during the course of a search for emission from atomic hydrogen (HI) associated with galaxies hidden by the disk of the Milky Way -- such emission is not obscured by the disk if the velocity of the emission differs from that of the local gas. The new galaxy seems to be associated with the group containing IC342 and the Maffei galaxies, and a subsequent optical image suggests that it is of type SBb. The detection of Dwingeloo 1 early in the course of this survey suggests that many more galaxies hidden behind the Milky Way remain to be discovered.

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