Publications (3)0 Total impact
ABSTRACT: We have conducted an HI 21 cm emission-line survey using the Parkes 20cm
multibeam instrument and the Australia Telescope Compact Array (ATCA) of six
loose groups of galaxies chosen to be analogs to the Local Group. The goal of
this survey is to make a census of the HI-rich galaxies and high-velocity
clouds (HVCs) within these groups and compare these populations with those in
the Local Group. The Parkes observations covered the entire volume of each
group with a rms M(HI) sensitivity of 4-10x10^5 M(sun) per 3.3 km/s channel.
All potential sources detected in the Parkes data were confirmed with ATCA
observations at ~2' resolution and the same M(sun) sensitivity. All the
confirmed sources have associated stellar counterparts; no starless HI
clouds--HVC analogs--were found in the six groups. In this paper, we present a
description of the survey parameters, its sensitivity and completeness. Using
the population of compact HVCs (CHVCs) around the Milky Way as a template
coupled with the detailed knowledge of our survey parameters, we infer that our
non-detection of CHVC analogs implies that, if similar populations exist in the
six groups studied, the CHVCs must be clustered within 90 kpc of group
galaxies, with average M(HI) < 4x10^5 M(sun) at the 95% confidence level. The
corollary is that the same must apply to Milky Way CHVCs. This is consistent
with our previous results from a smaller sample of groups, and in accordance
with recent observational and theoretical constraints from other authors. These
results confirm that there is very little neutral matter around galaxies, and
that any substantial reservoir of baryons must be in other phases.
ABSTRACT: We present the results of our HI survey of six loose groups of galaxies analogous to the Local Group. The survey was conducted using the Parkes telescope and the Australia Telescope Compact Array to produce a census of all the gas-rich galaxies and potential analogs to the high-velocity clouds (HVCs) within these groups down to M(HI)<10^7 M(sun) as a test of models of galaxy formation. We present the HI mass function and halo mass function for these analogous groups and compare them with the Local Group and other environments. We also demonstrate that our non-detection of HVC analogs in these groups implies that they must have low HI masses and be clustered tightly around galaxies, including around our own Milky Way, and are not distributed throughout the Local Group.
ABSTRACT: of Scientific Justification (will be made publicly available for accepted proposals): Cosmological evolution is mapped using tracers of star formation. Usually the selection of tracers is biased by stellar luminosity. We propose to determine star formation properties of a sample selected free of the stellar bias: by gas content from the HiPASS survey. Since an interstellar medium is a prerequisite for star formation, our survey will uniformly sample all galaxies that could form stars, and hence provide a fair view of the local star formation demographics. The sample will consist of the 500 HiPASS galaxies, each of which will be imaged in Hff and the stellar continuum. Integrated, this yields the local star formation rate density, which will be used as benchmark to estimate the bias in other Hff samples. This survey will also provide high resolution images of the star formation morphology over a wide range of galaxies, particularly towards irregular dwarfs which are often missed in other studies. The Hi content of galaxies combined with the SFR will be used to predict the evolution of the Hi mass function and the epoch when the cosmological gas tank runs dry.