The GEMS Project and Collapsed Groups Duncan Forbes Swinburne University

Galaxies in LowDensity Environments Duncan Forbes Swinburne University

Motivation Groups poorly studied relative to clusters Suppression occurs at group-like densities (2dF, SDSS) What is the timescale ? Are galaxies in groups pre-processed ? What is the physical mechanism ?

Physical Processes in Groups Ram pressure stripping Interactions & Harassment Mergers Group tidal field Strangulation/Suffocation Overlapping dark matter halos

People…in Crete Trevor Ponman, Trevor Miles, Habib Khosroshahi, Louise Nolan (Birmingham) Frazer Pearce (Nottingham) Warrick Couch (UNSW) Ewan O’Sullivan (CfA) Sarah Brough, Robert Proctor, Virginia Kilborn (Swinburne)...a loose group of people studying loose groups of galaxies

GEMS Group Evolution Multi-wavelength Study Aim: to understand how the group environment affects galaxy evolution and how groups themselves evolve. Method: multi-wavelength data and mock catalogues.

GEMS People Swinburne Forbes, Kilborn, Brough, 2 new PhD students Birmingham (Ponman) Nottingham (Pearce) UNSW (Couch) ATNF (Koribalski)

GEMS Sample Selection Catalogues of Galaxy Groups 14 < D < 43 Mpc ROSAT PSPC 10,000sec => 60 nearby groups with a range of X-ray properties, ie dynamically young groups with no IGM to virialised old groups with a hot, dense IGM. Includes both compact and loose groups.

GEMS Dataset ROSAT imaging (1.5 degrees) Wide-field optical imaging (0.5 degrees) Parkes HI mapping (5.5 degrees) ATCA HI follow-up 6dFGS spectra XMM/Chandra imaging Mock catalogues

X-ray Imaging

X-ray Imaging 60 Groups T X, L X, Z to R 500 Osmond & Ponman 2004

L X ~T X 4 Osmond & Ponman 2004 Revised

Halo Stripping ? Helsdon etal Isolated BGGs

Optical Imaging 30 Groups B,R,I filters

Structural Properties Khosroshahi etal R/R virial

Luminosity Functions Miles etal Low L X groups Low sigma Lots of spirals Current merging Pre-virialised

HI Imaging 16 Groups mapped with the Parkes multibeam instrument over 5.5 degrees Mass limit of ~ 10 8 M sun 2x deeper than HIPASS survey 10x better velocity resolution than HIPASS 15 arcmin beam (hence ATCA followup)

NGC 3783 Group

New Galaxies In 17 groups searched to date: 30 new group galaxies (~ 10% new) 20 new redshifts 10 not optically catalogued a few potential HI clouds M ~ 10 8 M sun IGM HI is rare, but some tidal bridges => small effect on LF faint end => `missing satellites’ are not HI clouds (CenA group: a few M ~ 10 6 M sun HI clouds)

New Galaxy in NGC 5044 group M HI = 10 9 M sun V = 2750 km/s M HI /L B = 1.7 McKay etal 2004

Virial Radius Calculate R virial for groups using σ or T X ? Statistical problems calculating σ for low N systems Systematic bias in σ Physical reasons for a low σ (dynamical friction, orientation effects) Xrays only probe small fraction of virial radius => use both σ and T X !

NGC 1566 group no IGM R virial (σ)

NGC 5044 group

NGC 3783 group

Isolated Galaxies Early-type galaxy, V < 9,000 km/s, B < 14 No neighbours within: 700 km/s 0.67 Mpc in plane of the sky 2 B mags (factor of 6 in mass) Formation? old, undisturbed recent merger collapsed group (“fossil”)

Hermits Swinburne Forbes, Reda, Proctor Harvard (O’Sullivan) Durham (Hau)

Colour-magnitude Relation

Fundamental Plane Deviant galaxies have young stellar populations and/or disturbed morphology

FP – Kappa style

Radial Kinematics

Collapsed Groups ? Typical isolated galaxy M B = -20.5, L X /L B = 30 One potential collapsed group: NGC 1132 M B = -22.0, log L X = 43.0 erg/s, L X /L B = 32 ΔM 12 = 2.2, featureless morphology, old stellar population

Future Work Stellar population analysis, eg NGC 821 Focus on `transition’ galaxies, ie E + disk = spiral eg NGC 821 HI in isolated ellipticals, ie 10% detected in HIPASS Measuring dark halo mass, eg via dwarfs or Xrays

NGC 821 Proctor et al. 2005

Future Work Stellar population analysis, eg NGC 821 Focus on `transition’ galaxies, ie E + disk = spiral eg NGC 821 HI in isolated ellipticals, ie 10% detected in HIPASS Measuring dark halo mass, eg via dwarfs or Xrays

NGC 4555 O’Sullivan & Ponman 2005

Web sites astronomy.swin.edu.au/dforbes (5-9 Dec. 2005, Chile)

Conclusions Xray halos of ellipticals not stripped Optical LF dip in young, low L X groups HI mapping probes dynamical processes Many group galaxies beyond R virial Most isolated ellipticals obey scaling relations, and are not collapsed groups