Neutral Hydrogen in Galaxy Groups

Virginia KilbornSwinburne University of Technology

Duncan Forbes (Swinburne)Baerbel Koribalski (ATNF)David Barnes (Melbourne)Nuria McKay (Liverpool)Carole Mundell (Liverpool)Ruth Musgrave (Swinburne)

The 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

The GEMS HI Survey

• 17 groups surveyed in HI at Parkes using the 13 beam multibeam receiver

• Field of view 5.5 x 5.5o

• Velocity resolution ~1.6 km/s • Bandwidth ~2500 km/s• Spatial resolution 14.5 arcmin• Sensitivity MHI ~108-109 Msun

HI Group Details

• Groups in our sample: NGC 524, 720, 1332, 1400, 1566, 1792/1808, 3783, 3923, 4636, 7144, 7176, 7714, 1052, 3557, 5044, IC 1459 & Grus group.

• Data reduced using the aips++ routines “livedata” and “gridzilla” (as with HIPASS), producing 3-D HI datacubes

• Data search conducted visually by 2 people (hope to supplement this with automated search in future)

• Sixteen groups searched to date: ~10% new group members / group found

GEMS Groups Details NGC 1566

NGC 5044

NGC 3783

NGC 1808

Distance

21Mpc

33 Mpc

36 Mpc

17 Mpc

Survey HI mass limit

~2x108

Msun

~6 x108

Msun

~8x108

Msun ~108 Msun

Members 26 89

36

7

HI detections

13(15)

23 13(18)

7

New group members

2 9 4 0

X-rays Galaxy

Group

Group

None

The NGC 1566 Group

NGC 1566

NGC 5044

NGC 3783

NGC 1808

Distance

21Mpc

33 Mpc

36 Mpc

17 Mpc

Survey HI mass limit

~2x108

Msun

~6 x108

Msun

~8x108

Msun ~108 Msun

Members 26 89

36

7

HI detections

13(15)

23 13(18)

7

New group members

2 9 4 0

X-rays Galaxy

Group

Group

None

NGC 1566 - HI DistributionLSBG F157-081

APMBGC157+016+068

The NGC 5044 Group

NGC 1566

NGC 5044

NGC 3783

NGC 1808

Distance

21Mpc

33 Mpc

36 Mpc

17 Mpc

Survey HI mass limit

~2x108

Msun

~6 x108

Msun

~8x108

Msun ~108 Msun

Members 26 89

36

7

HI detections

13(15)

23 13(18)

7

New group members

2 9 4 0

X-rays Galaxy

Group

Group

None

NGC 5044 - HI DistributionMckay et al. 2004, astro-ph/0405241

The NGC 3783 Group

NGC 1566

NGC 5044

NGC 3783

NGC 1808

Distance

21Mpc

33 Mpc

36 Mpc

17 Mpc

Survey HI mass limit

~2x108

Msun

~6 x108

Msun

~8x108

Msun ~108 Msun

Members 26 89

36

7

HI detections

13(15)

23 13(18)

7

New group members

2 9 4 0

X-rays Galaxy

Group

Group

None

NGC 3783 - HI Distribution

NGC 1792/1808 Group

NGC 1566

NGC 5044

NGC 3783

NGC 1808

Distance

21Mpc

33 Mpc

36 Mpc

17 Mpc

Survey HI mass limit

~2x108

Msun

~6 x108

Msun

~8x108

Msun ~108 Msun

Members 26 89

36

7

HI detections

13(15)

23 13(18)

7

New group members

2 9 4 0

X-rays Galaxy

Group

Group

None

NGC1792/1808 HI distribution

HI deficiency in group galaxies?

• Several studies have indicated HI deficiencies in cluster galaxies and compact groups (eg Solanes et al. 2001, ApJ 548, 97; Verdes-Montenegro et al. 2001, A&A 377, 812)

• 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 (eg: Solanes et al. 1996, ApJ 461, 609; Haynes & Giovanelli 1984, AJ 89, 758)

Expected HI content of late-type galaxies

• Used the HIPASS Bright Galaxy Catalogue (BGC; Koribalski et al. 2004, AJ, 128, 16) - HI selected galaxies

• Divided the ~800 late-type galaxies into optical morphological type

• Fit linear regression to relationship between optical diameter and HI mass for each morphology

• Use these fit lines to determine expected HI mass (with upper and lower limits) for the group galaxies to determine whether they have a typical HI content

NGC 5044

HI content of group galaxies

NGC 1792/1808

NGC 1566

NGC 1566 Group

NGC 1566 & NGC 5044 HI Content and Deficiency

No overall HI deficiency for the NGC 1566 groupHowever, two group members display

deficiencies - NGC 1515 (12) &

NGC 1536 (2)

NGC 5044 group - one late-type with HI

deficiency, ESO 576-G 017 (9)

+ Why do these galaxies contain less HI than expected?- Previous gravitational interactions?- Ram pressure stripping from IGM?

+ Need higher resolution observations to study the HI distribution of these galaxies.+ Expect to find more examples of HI deficiency in the other 13 groups

NGC 1566 group

Summary-17 Groups observed for the GEMS HI survey-Find ~10% new group members - thus

providing a more complete view of the groups

-Found a number of ‘new’ dwarf galaxies, and some possible HI clouds

-No systematic HI deficiency seen in the late-type members of the groups, although several examples of individual galaxies being deficient

-HI deficient galaxies not found in the centre of the groups where the intra-group x-ray emission is (eg n5044)

-What is the history of these galaxies? Need to find more examples to complete the picture.