Future ASKAP Studies of the Local Volume

The Australian SKA Pathfinder (ASKAP) will be a powerful instrument for performing large-scale surveys of galaxies. Its frequency range and large field of view makes it especially useful for an all-sky survey of Local Volume galaxies, and will probably increase the number of known galaxies closer than 10 Mpc by a factor of two and increase, by at least an order of magnitude, the number detected in HI. Implications for our knowledge of the HI mass function for the very faintest galaxies and for the structure and dynamics of the Local Volume are discussed.Comment: 4 pages, 2 figures. To appear in 'Galaxies in the Local Volume' (Sydney, July 2007), eds. B. Koribalski & H. Jerjen, Astrophys. & Space Scienc

HI Science with the Square Kilometre Array

The Square Kilometre Array (SKA) will be a formidable instrument for the detailed study of neutral hydrogen (HI) in external galaxies and in our own Galaxy and Local Group. The sensitivity of the SKA, its wide receiver bands, and the relative freedom from radio frequency interference at the SKA sites will allow the imaging of substantial number of high-redshift galaxies in HI for the first time. It will also allow imaging of galaxies throughout the Local Volume at resolutions of <100 pc and detailed investigations of galaxy disks and the transition between disks, halos and the intergalactic medium (IGM) in the Milky Way and external galaxies. Together with deep optical and millimetre/sub-mm imaging, this will have a profound effect on our understanding of the formation, growth and subsequent evolution of galaxies in different environments. This paper provides an introductory text to a series of nine science papers describing the impact of the SKA in the field of HI and galaxy evolution. We propose a nested set of surveys with phase 1 of the SKA which will help tackle much of the exciting science described. Longer commensal surveys are discussed, including an ultra-deep survey which should permit the detection of galaxies at z=2, when the Universe was a quarter of its current age. The full SKA will allow more detailed imaging of even more distant galaxies, and allow cosmological and evolutionary parameters to be measured with exquisite precision.Comment: 9 pages, 1 figure, accepted by Proceedings of Science as the HI Overview Chapter for "Advancing Astrophysics with the Square Kilometre Array

Cosmological surveys with the Australian Square Kilometre Array Pathfinder

This is a design study into the capabilities of the Australian Square Kilometre Array Pathfinder in performing a full-sky low redshift neutral hydrogen survey, termed WALLABY, and the potential cosmological constraints one can attain from measurement of the galaxy power spectrum. We find that the full sky survey will likely attain 0.6 million redshifts which, when combined with expected Planck CMB data, will constrain the Dark Energy equation of state to 20%, representing a coming of age for radio observations in creating cosmological constraints.Comment: 10 pages, 6 figures, accepted in PASA, updated to match published versio

Cosmological Forecasts for Combined and Next Generation Peculiar Velocity Surveys

Peculiar velocity surveys present a very promising route to measuring the growth rate of large-scale structure and its scale dependence. However, individual peculiar velocity surveys suffer from large statistical errors due to the intrinsic scatter in the relations used to infer a galaxy's true distance. In this context we use a Fisher Matrix formalism to investigate the statistical benefits of combining multiple peculiar velocity surveys. We find that for all cases we consider there is a marked improvement on constraints on the linear growth rate $f\sigma_{8}$. For example, the constraining power of only a few peculiar velocity measurements is such that the addition of the 2MASS Tully-Fisher survey (containing only $\sim2,000$ galaxies) to the full redshift and peculiar velocity samples of the 6-degree Field Galaxy Survey (containing $\sim 110,000$ redshifts and $\sim 9,000$ velocities) can improve growth rate constraints by $\sim20\%$. Furthermore, the combination of the future TAIPAN and WALLABY+WNSHS surveys has the potential to reach a $\sim3\%$ error on $f\sigma_{8}$, which will place tight limits on possible extensions to General Relativity. We then turn to look at potential systematics in growth rate measurements that can arise due to incorrect calibration of the peculiar velocity zero-point and from scale-dependent spatial and velocity bias. For next generation surveys, we find that neglecting velocity bias in particular has the potential to bias constraints on the growth rate by over $5\sigma$, but that an offset in the zero-point has negligible impact on the velocity power spectrum.Comment: 24 pages, 11 figures, 7 tables. Accepted for publication in MNRA

Dynamics and star formation activity of CG J1720-67.8 unveiled through integral field spectroscopy and radio observations

CG J1720-67.8 is an ultra compact group of several galaxies with a low velocity dispersion, and displaying the hallmarks of mutual interaction and possible tidal dwarf galaxy formation. In hierarchical models, the system is a possible precursor to a massive elliptical galaxy. In this paper, we use new optical integral field spectroscopic and radio observations to investigate the evolutionary status of the group in more detail: global star-formation rates are estimated using H$\alpha$ and 1.4 GHz radio continuum measurements; H {\sc i} observations provide an upper limit to the global neutral gas content; optical broadband colours and spectra provide ages and stellar mass estimates for the tidal dwarf candidates; the bidimensional H$\alpha$ velocity field is used to trace the kinematics of the group and its members, which are compared with numerical simulations of galaxy encounters. The observations suggest a model in which multiple interactions have occurred, with the latest strong encounter involving at least two major components within the last 200 Myr. Debris from the encounter fuels ongoing star formation at the global level of $\sim20$ M$_{\odot}$ yr$^{-1}$, with self-gravity within the tidal tail possibly providing a mechanism to enhance the star formation rate of the tidal dwarf candidates, with bursts of star-formation in clumps of mass $\sim2\times 10^7$ M$_{\odot}$ appearing within the last 10 Myr. The amount of time required for final merging of all group components remains uncertain.Comment: 22 pages, 16 figures. Accepted for publication in MNRA

Detection of Carbon Monoxide within the Magellanic Bridge

The Mopra 22m and SEST 15m telescopes have been used to detect and partially map a region of 12CO(1-0) line emission within the Magellanic Bridge, a region lying between the Large and Small Magellanic Clouds. The emission appears to be embedded in a cloud of neutral hydrogen, and is in the vicinity of an IRAS source. The CO emission region is found to have a 60um/100um flux density ratio typical for 12CO(1-0) detections within the SMC, although it has a significantly lower 12CO brightness and velocity width. These suggest that the observed region is of a low metallicity, supporting earlier findings that the Magellanic Bridge is not as evolved as the SMC and Magellanic Stream, which are themselves of a lower metallicity than the Galaxy. Our observations, along with empirical models based on SMC observations, indicate that the radius of the detected CO region has an upper limit of ~16 pc. This detection is, to our knowledge, the first detection of CO emission from the Magellanic Bridge and is the only direct evidence of star formation through molecular cloud collapse in this region.Comment: 8 pages, 6 Figures. LaTeX. Accepted for publication by MNRA

The Column Density Distribution Function at z=0 from HI Selected Galaxies

We have measured the column density distribution function, f(N), at z=0 using 21-cm HI emission from galaxies selected from a blind HI survey. f(N) is found to be smaller and flatter at z=0 than indicated by high-redshift measurements of Damped Lyman-alpha (DLA) systems, consistent with the predictions of hierarchical galaxy formation. The derived DLA number density per unit redshift, dn/dz =0.058, is in moderate agreement with values calculated from low-redshift QSO absorption line studies. We use two different methods to determine the types of galaxies which contribute most to the DLA cross-section: comparing the power law slope of f(N) to theoretical predictions and analysing contributions to dn/dz. We find that comparison of the power law slope cannot rule out spiral discs as the dominant galaxy type responsible for DLA systems. Analysis of dn/dz however, is much more discriminating. We find that galaxies with log M_HI < 9.0 make up 34% of dn/dz; Irregular and Magellanic types contribute 25%; galaxies with surface brightness > 24 mag arcsec^{-2} account for 22% and sub-L* galaxies contribute 45% to dn/dz. We conclude that a large range of galaxy types give rise to DLA systems, not just large spiral galaxies as previously speculated.Comment: 13 pages, low resolution figures in the appendix, MNRAS accepte

Local Column Density Distribution Function from HI selected galaxies

The cross-section of sky occupied by a particular neutral hydrogen column density provides insight into the nature of Lyman-alpha absorption systems. We have measured this column density distribution at z=0 using 21-cm HI emission from a blind survey. A subsample of HI Parkes All Sky Survey (HIPASS) galaxies have been imaged with the Australia Telescope Compact Array (ATCA). The contribution of low HI mass galaxies 10^7.5 to 10^8 M_solar is compared to that of M_star (10^10 to 10^10.5 M_solar) galaxies. We find that the column density distribution function is dominated by low HI mass galaxies with column densities in the range 3x10^18 to 2x10^20 cm^-2. This result is not intuitively obvious. M_star galaxies may contain the bulk of the HI gas, but the cross-section presented by low HI mass galaxies 10^7.5 to 10^8 M_solar is greater at moderate column densities. This result implies that moderate column density Lyman-alpha absorption systems may be caused by a range of galaxy types and not just large spiral galaxies as originally thought.Comment: 5 pages, including 1 figure. To appear in "Extragalactic Gas at Low Redshift" (ASP Conf. Series, Weymann Conf.