Extragalactic Large-Scale Structures behind the Southern Milky Way. -- II. Redshifts Obtained at the SAAO in the Crux Region

In our systematic optical galaxy search behind the southern Milky Way, 3760 (mostly unknown) galaxies with diameters D > 0.2 arcminutes were identified in the Crux region (287 < l < 318 degrees, |b| < 10 degrees, Woudt & Kraan-Korteweg 1997). Prior to this investigation, only 65 of these galaxies had known redshifts. In order to map the galaxy distribution in redshift space we obtained spectra for 226 bright (B_J < 18.0 mag) objects with the 1.9m telescope of the South African Astronomical Observatory (SAAO). Two main structures crossing the Galactic Plane in the Crux region have now become clear. A narrow, nearby filament from (l,b) = (340 deg, -25 deg) 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 km/s. 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.Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, LaTex, 6 encapsulated postscript figures, requires l-aa.sty and epsf.sty. Original figures and tables are available upon request (E-mail: [email protected]

The Norma cluster (ACO3627): II. The near infrared K_s-band luminosity function

A deep K_s-band photometric catalogue of galaxies at the core of the rich, nearby Norma cluster (ACO3627) is presented. The survey covers about 45 by 45 square arcmin (slightly less than 1/3 Abell radius), which corresponds to approx. 0.8 Mpc^2 at the adopted distance (v_cmb/H0) of 70 Mpc of this cluster. The survey is estimated to be complete to a magnitude of M_Ks <~ -19.5 mag. This extends into the dwarf regime, 6 magnitudes below M_Ks*. The catalogue contains 390 objects, 235 of which are classified as likely or definite galaxies and 155 as candidate galaxies. The Ks-band luminosity function (LF) is constructed from the photometric sample, using a spectroscopic subsample to correct for fore- and background contamination. We fit a Schechter function with a characteristic magnitude of M_Ks* = -25.39 \pm 0.80 mag and faint-end slope of alpha = -1.26 \pm 0.10 to the data. The shape of the LF is similar to those found in previous determinations of the cluster LF, in both optical and near infrared. The Schechter parameters agree well with those of recent field LFs, suggesting that both the shape of the bright end and the faint end slope are relatively insensitive to environment.Comment: 18 pages, 6 figures, 8 tables (includes full photometric catalogue as appendix), accepted for publication in MNRA

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

High Speed Photometry of SDSS J013701.06-091234.9

We present high speed photometry of the Sloan Digital Sky Survey cataclysmic variable SDSS J013701.06-091234.9 in quiescence and during its 2003 December superoutburst. The orbital modulation at 79.71\pm0.01 min is double humped; the superhump period is 81.702\pm0.007 min. Towards the end of the outburst late superhumps with a period of 81.29\pm0.01 min were observed. We argue that this is a system of very low mass transfer rate, and that it probably has a long outburst interval.Comment: 5 pages, 8 figures. Accepted for publication in MNRA

X-ray and optical observations of the unique binary system HD49798/RXJ0648.0-4418

We report the results of XMM-Newton observations of HD49798/RXJ0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P=13.2 s) and has a dynamically measured mass of 1.28+/-0.05 M_sun. Its X-ray emission consists of a strongly pulsed, soft component, well fit by a blackbody with kT~40 eV, accounting for most of the luminosity, and a fainter hard power-law component (photon index ~1.6). A luminosity of ~10^{32} erg/s is produced by accretion onto the white dwarf of the helium-rich matter from the wind of the companion, which is one of the few hot sub-dwarfs showing evidence of mass-loss. A search for optical pulsations at the South African Astronomical Observatory 1.9-m telescope gave negative results. X-rays were detected also during the white dwarf eclipse. This emission, with luminosity 2x10^{30} erg/s, can be attributed to HD 49798 and represents the first detection of a hot sub-dwarf star in the X-ray band. HD49798/RXJ0648.0-4418 is a post-common envelope binary which most likely originated from a pair of stars with masses ~8-10 M_sun. After the current He-burning phase, HD 49798 will expand and reach the Roche-lobe, causing a higher accretion rate onto the white dwarf which can reach the Chandrasekhar limit. Considering the fast spin of the white dwarf, this could lead to the formation of a millisecond pulsar. Alternatively, this system could be a Type Ia supernova progenitor with the appealing characteristic of a short time delay, being the descendent of relatively massive stars.Comment: Accepted for publication on The Astrophysical Journa