HI in Galaxy Groups

HI in Galaxy Groups

Virginia KilbornSwinburne University of

Technology

Duncan Forbes Baerbel Koribalski

Sarah Brough David Barnes

GEMS HI Survey

Aims:

• To investigate the interplay between hot and cold gas in groups

• To study the evolutionary history of the groups and the part evolution plays in gas content of the groups

• To study gas removal mechanisms in low-density parts of the Universe

• To find new group members, and possible HI clouds

HI in GEMS groups

• 16 groups were observed at Parkes using the multibeam receiver - 5.5x5.5 degree fields

• Groups have varying x-ray properties– 8 have intra-group X-ray emission– 6 have X-rays from central group galaxy– 2 undetected in X-rays

• The 16 groups lie between 1000-3000 km/s (~13-40 Mpc)

• Detection limit for HI is around 5x108 M

• Number of group members varies from ~10 to >150 - very diverse range of groups

HI Findings

• Total Galaxies detected: 210• Uncatalogued HI detections:14 (7 %)• New redshifts: 8 (5 %)• HI Clouds: 1 definite, 3+ candidates• Total new group members: (10 %)

• Also - added in 6dFGS galaxies for further group members

Groups with intra-group X-ray emission

Intra-group X-rays II

Intra-group X-rays III

Groups with central galaxy X-ray emission

Galaxy X-rays II

Groups with no detected X-ray emission

Lack of central HIOthers

LX

LX and HI distribution

TX and HI concentration

Lack of central HIOthers

Spiral fraction vs Tx

Group HI deficiency?• Several studies have indicated HI

deficiencies in cluster galaxies and compact groups

• Would like to see if this extends to loose groups

• What is the mechanism - can RAM pressure stripping work in a low IGM environment or are interactions more important?

• Firstly - need to determine expected HI mass for a galaxy of given optical morphology

• Morphology, combined with optical diameter good indicator

• We use both optical sample and BGC to make predictions for NGC 1566 group (spiral and late-type galaxies)

Result: No HI deficiency for the NGC 1566 group

Several members display Individual deficiency - NGC 1515 (12) & NGC 1536 (2)

Kilborn et al. 2005

HI ‘clouds’ in groups

• How common are HI clouds without visible stars in galaxy groups?

•What is the formation Scenario? –interactions culminating in HI stripping–Ram pressure stripping–Primordial?

•HI clouds in our GEMS groups - –One confirmed cloud in NGC 3783 group–One possible cloud in same group–Plus several candidates in the NGC 5044 group

Oosterloo & van Gorkom, astro-ph/0505397Minchin et al 2005 1993

NGC 3783 Group

NGC 3783

MHI = 5x109M

MHI = 1010M

ATCA HI map and DSSII R-band

Keck R-band imageKeck B-band image

NGC 5044 HI cloud candidates

Conclusions

• New group members found in HI surveys of groups (~1-2 per galaxy group)

• Some groups lack HI in central regions - correlated with TX

• HI clouds - at least one in our study, several more candidates. Likely formation scenario: tidal debris

Future Work• Statistical analysis of HI content

of the groups• High resolution ATCA HI obs of

cloud candidates• 2dF redshifts for galaxies in

N3783 cloud fields• HI deficiency of group galaxies?• SFR of group galaxies