706 research outputs found
Large-Scale Structures Behind the Southern Milky Way from Observations of Partially Obscured Galaxies
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 < l < 340, |b| < 10. 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/s connecting to the Hydra
and Antlia clusters, a shallow extended supercluster in Vela (~ 6000km/s), and
a nearby (4882 km/s), very massive (M ~ 2-5 10^15 Msun), rich Coma-like cluster
which seems to constitute the previously unidentified center of the Great
Attractor. The innermost part of the Milky Way where the foreground obscuration
in the blue is 5mag, respectively HI-column densities greater than 6 10^21 /
cm^2 remains fully opaque. In this approximately 8 degrees 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.Comment: Presented at the Multibeam Workshop on ``HI in the Local Universe'',
Sydney, May 13-15 1996. Accepted 2.11.1996 for publication by PASA.
Latex-file with 4 encapsulated postscript files. Version with original
figures available at
http://www.atnf.csiro.au/~lstavele/13beam/proceedings/korteweg/korteweg.htm
Extragalactic Large-Scale Structures behind the Southern Milky Way. IV. Redshifts Obtained with MEFOS
Abbreviated: 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.Comment: 11 pages, 7 figures; accepted for publication in A&A. Tables 1 and 2
will be available in electronic format at the CDS. Figure 1 at full
resolution, and both tables are available at
http://mensa.ast.uct.ac.za/~pwoudt/data/H4462/
A catalogue of galaxies behind the southern Milky Way. - II. The Crux and Great Attractor regions (l = 289deg - 338deg)
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).Comment: 19 pages, 16 figures, accepted for publication in A&A. Tables will
shortly be available in electronic version at the CDS. Full resolution
(colour) copies of Figures 1, 2, 3 and 16 are available at
http://mensa.ast.uct.ac.za/~pwoud
Parkes HI observations of galaxies behind the southern Milky Way. II. The Crux and Great Attractor regions (l ~ 289 degree to 338 degree)
As part of our programme to map the large-scale distribution of galaxies
behind the southern Milky Way, we observed 314 optically-selected,
partially-obscured galaxies in the Zone of Avoidance (ZOA) in the Crux and
Great Attractor (GA) regions. The observations were conducted with the Parkes
64m radio telescope, in a single-pixel pointed mode, reaching an rms noise
level of typically 2-6 mJy over the velocity search range of 400<v<10500km/s. A
total of 162 galaxies were detected. This can be explained by the prominence of
the GA overdensity in the survey regions, which leads to a relatively higher
fraction of nearby galaxies. It is also evident from the quite narrow velocity
distribution (largely confined to 3000-6000km/s) and deviates significantly
from the expectation of a uniform galaxy distribution for the given sensitivity
and velocity range. No systematic differences were found between detections and
non-detections, in terms of latitude, foreground extinction, or environment,
except for the very central part of the rich Norma cluster, where hardly any
galaxies were detected. A detailed investigation of the HI content of the
galaxies reveals strong HI deficiency at the core of the Norma cluster (within
about a 0.4 Abell radius), similar to what has been found in the Coma cluster.
The redshifts obtained by this observing technique result in a substantial
reduction of the so-called redshift ZOA. This is obvious when analysing the
large-scale structure of the new HI data in combination with data from optical
ZOA redshift surveys. The lower latitude detections provide further evidence of
the extension of the Norma Wall, across the ZOA, in particular its bending
towards the Cen-Crux clusters above the Galactic plane at slightly higher
redshift, rather than a straight continuation towards the Centaurus clusters.Comment: 30 pages, 11 figures, including aa.cls; accepted by A
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