YV Annual General Meeting CEO Report Ross Kilborn September 2010.
WALLABY SWG3 The influence of environment on the HI content of galaxies Virginia Kilborn Bunker Bay,...
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Transcript of WALLABY SWG3 The influence of environment on the HI content of galaxies Virginia Kilborn Bunker Bay,...
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WALLABY SWG3
The influence of environment on the HI content of galaxies
Virginia KilbornBunker Bay, Nov, 2009
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SWG3: Galaxy Environments (groups, interactions/mergers)
Ben Bekhti, Blake, Bouchard, Buyle, Colless, English, Henning, Jerjen, Jozsa, Juette, Karachentsev, Kerp, Kilborn, Koribalski, Kraan-Korteweg, Lopez-Sanchez, Meurer, Oosterloo, Popping, Radchaudhury, Rhee, Saikia, Spekkens, van der Hulst, Westmeier, Wilcots, Winkel, Wong
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Effect of Environment
• We know that environment affects the evolution of galaxies:– Galaxies in clusters were bluer at high redshift compared to z~0 -
evolution of galaxies in clusters? Galaxies in clusters are redder and older than the field (e.g. Butcher & Oemler)
– Galaxies in clusters are more likely to be early-type (e.g. Dressler 1980).
– Similar effects recently seen in the less-dense group environment
•How will ASKAP be able to investigate these effects?– Observations of the removal of HI from galaxies (gas stripping) – Frequency and environment of galaxy mergers– Extra-galactic HI (in dense, and low-density environments)– Evolution of HI content of galaxies from z~0.5 to z~0– HI mass function in different environments (Zwaan et al.)
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Stripping the HI from galaxies
• What are the main methods to strip gas from galaxies?
– Harassment - frequent, high-speed encounters in clusters– Strangulation - gradual gas-loss from a galaxy into the potential well
of a cluster or group– Ram pressure stripping– Tidal interactions
• In particular, these last 2 effects can be seen in high-resolution HI observations
Chung 2007
Vollmer et al 2004
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Investigating gas stripping without mapping
• The closest few to ten thousand galaxies will be mapped well enough to see tidal and ram pressure stripping effects in the imaging
• The other 100s of thousand galaxies will be unresolved - how to test if they are losing gas?
• Use the optical properties to determine the expected HI content of a galaxy of a particular optical classification (or some other classification scheme)
• This requires accurate matching of HI detection with optical catalogues, and homogeneous optical data
• A good project for SkyMapper
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Previous “HI deficiency” measures
• In the mid-80s, Haynes and Giovanelli looked at defHI in clusters, finding HI deficient spirals near the centres of a number of clustersdefHI = MHI(expected) - MHI (obs)
• Their “expected HI mass” based on the relationship of a few tens of galaxies of each optical classification
• In 2005, new “expected HI mass” relations determined using HIPASS BGC - over 100 galaxies in each relationship
• This data applied to galaxy group work, and found that there are HI deficient galaxies in groups too - so its not just clusters that are stripping HI from galaxies
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HI deficiency in groups: comparison with X-ray and v
• HI def in groups - can’t be due to ram pressure stripping (entirely) as:– HI def galaxies found in groups without X-rays– No relationship seen between HI def fraction and X-ray
emission/velocity dispersion of groups
clustersclusters
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Global galaxy evolution• Until now, deep HI studies have concentrated on
particular structures- clusters, and more recently groups and filaments
• ASKAP will make it possible to study galaxy evolution across the continuum of all environments
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Ryder et al. 2002
Giovanelli et al. 2006, in prep
Kilborn et al 2000
English et al. 2009
Oosterloo & van Gorkum 08