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ATCA Legacy Project Expression of Interest: WALLABY@ATCA
Title:
Au t h o r s : Point of contact:

WALLABY@ATCA
L i s t e r S t a v e l e y - S m i t h , B Д r b e l Ko r i b a l s k i , P a o l o S e r r a , To b i a s We s t m e i e r ( o n b e h a l f o f t h e WA L L A B Y t e a m ) To b i a s We s t m e i e r

Scientific Aims
The aims of the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) are to discover and examine the distribution and neutral hydrogen (H) properties of up to 500,0001 galaxies out to a redshift of 0.26 (equivalent to a look-back time of ~ 3 Gyr) in order to study: (1) galaxy formation and the missing satellite problem in the Local Group, (2) evo lution and star-formation in galaxies, (3) mergers and interactions in galaxies, (3) the H mass function and its variation with galaxy density, (4) physical processes governing the distribution and evolution of cool gas at low redshift, (5) cosmological parameters relating to gas-rich galaxies, and (6) the nature of the cosmic web. WALLABY will provide the largest, most homogeneous H sample of galaxies. It will have a flux sensitivity some 20 times better than the H Parkes All-Sky Survey (HIPASS), at a ve locity resolution some 4 times better, and will detect 20 times more galaxies than the re cently completed ALFALFA survey with six times better spatial resolution. WALLABY will detect dwarf galaxies (MH = 108 M) out to a distance of 60 Mpc, massive galaxies (MH = 6в109 M) to 500 Mpc, and super-H massive galaxies like Malin 1 (MH = 5в1010 M) to the survey `edge' of 1 Gpc. The driving motivation for WALLABY@ATCA is to provide a regular stream of follow-up H (and continuum) observations of noteworthy WALLABY discoveries. These discoveries will include: (1) the extrema of the galaxy population such as `dark' galaxies [2] and H-massive galaxies, which guide our understanding of galaxy formation and evolution; (2) new gas-rich Local Group galaxies [3] whose dynamical characteristics will allow us to better de fine the sphere of influence of the early ionizing cocoon and hot halo of the Milky Way; (3) new local Volume galaxies [4] which will allow us to measure the faintest end of the H mass function [5]; (4) new interacting systems in a variety of environments (field, group, cluster), which will allow us to quantify the relative influence of physical effects such as tidal and ram-pressure forces and its variation with density [6][7]. WALLABY@ATCA would only observe a small fraction of `interesting' WALLABY discover ies. We expect around 1% of WALLABY discoveries to merit follow-up observations; how ever, the time requested in Table 1 (3000 h) is only sufficient to observe 1 in 2000 discoveries. Nonetheless, this would significantly leverage ASKAP science and give rise to a new stream 1 Based on nominal ASKAP telescope specifications and requested time allocation [1]. 1


of value-added scientific publications in a than is possible by writing hundreds of would significantly advance the scientific JVLA and MeerKAT, which would otherwi

larger, better managed and coordinated approach disconnected PI-driven proposals. This in turn, utility of ATCA over other facilities such as the se have superior performance.

Since the point-source sensitivities of ASKAP and ATCA are similar at 1.4 GHz, what advantages does WALLABY@ATCA offer over WALLABY itself? Firstly, ASKAP is a survey in strument, and it would be a waste of its survey capability to re-observe a single area of sky for the observation of a single object. Secondly, the ATCA is re-configurable and can offer three times the resolution of ASKAP in its most extended configuration (WALLABY is lim ited to processing data from the 2-km ASKAP core) or 400 times the column density sensi tivity in its least extended configuration. As shown in Table 1, we do not expect any significant time request until 2017OCTS, or later according to the current ASKAP timeline.
Table 1: Requested ATCA observational parameters for WALLABY@ATCA

Area of sky LST range Frequency CABB mode Array configuration Observing strategy

Sensitivity Observing time Resources Team expertise

Declination < -20° 0 to 2 4 h 1200 to 1430 MHz CFB 1M­0.5k, CFB 64M­32k All (H75 to 6km) 12-hour synthesis of a single source, or small number of sources, at a time Typically 2.7 mJy/beam per 6.6 km/s channel (4в12 h), corresponding to 35 K (6-km configuration) or 2.3 mJy/beam per 6.6 km/s channel (1в12 h), corresponding to 22 mK (H75 configuration), according to ATCA sensitivity calculator (robust -1) 3000 h total at 300 h per semester from 2017OCTS The WALLABY team consists of 124 members, including an earlyscience active core of at least 30 members and students Good knowledge of spectral-line processing

References
[ [ [ [ [ [ [ 1 2 3 4 5 6 7 ] ] ] ] ] ] ] Duffy et al. 2012, MNRAS, 426, 3385 Janowiecki et al. 2015, ApJ, 801, 96 Ryan-Weber et al. 2008, MNRAS, 384, 535 Giovanelli et al. 2013, AJ, 146, 15 Martin et al. 2010, ApJ, 723, 1359 Spekkens et al. 2014, ApJ, 795, L5 Wetzel et al. 2013, MNRAS, 432, 336

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