1. Neutral Hydrogen in Galaxy Groups
Duncan Forbes (Swinburne)
Baerbel Koribalski (ATNF)
David Barnes (Melbourne)
Nuria McKay (Liverpool)
Carole Mundell (Liverpool)
Ruth Musgrave (Swinburne)
Virginia Kilborn
Swinburne University of Technology

2. 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

3. 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 ~ Msun
Note: sensitivity is twice or more that of HIPASS, and about 10 times better vel resolution (1.6 vs 13km/s).

4. 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
Note: groups between km/s - close enough for good sensitivity, far enough away to not be confused with local emission, and be easier to cover spatially.

5. GEMS Groups Details 21Mpc 33 Mpc 36 Mpc 17 Mpc 26 89 36 7 13(15) 23
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)
New group members 2 9 4
X-rays
Galaxy
Group
None
Mention: - groups chosen to present here have a variety of sizes, member numbers, and x-ray emission
- HI mass limit - determined on distance to group, and RMS of cube (100 km/s velocity width)

6. The NGC 1566 Group 21Mpc 33 Mpc 36 Mpc 17 Mpc 26 89 36 7 13(15) 23
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)
New group members 2 9 4
X-rays
Galaxy
Group
None

7. NGC HI Distribution
LSBG F
APMBGC

8. The NGC 5044 Group 21Mpc 33 Mpc 36 Mpc 17 Mpc 26 89 36 7 13(15) 23
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)
New group members 2 9 4
X-rays
Galaxy
Group
None
Put in mckay reference…

9. NGC 5044 - HI Distribution Mckay et al. 2004, astro-ph/0405241
add in HI contour pic here of nurias galaxy
**how much info is added to this cluster? Ie total mass of all c/f mass already detected
Note: new galaxies give an extra 30% HI mass
Gal #5 is RC , all the others are new detections

10. The NGC 3783 Group 21Mpc 33 Mpc 36 Mpc 17 Mpc 26 89 36 7 13(15) 23
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)
New group members 2 9 4
X-rays
Galaxy
Group
None

11. NGC HI Distribution
Note: #8 is a new group member, no previous r/s known ESO 320-G013
#2 is a previously unknown galaxy

12. NGC 1792/1808 Group 21Mpc 33 Mpc 36 Mpc 17 Mpc 26 89 36 7 13(15) 23
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)
New group members 2 9 4
X-rays
Galaxy
Group
None

13. NGC1792/1808 HI distribution
Insert some galaxy pictures here

14. 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)

15. 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

16. HI content of group galaxies
NGC 1792/1808
NGC 1566
NGC 5044
Note: couldn’t do this for n3783 due to so many interacting galaxies. . .

17. NGC 1566 & NGC 5044 HI Content and Deficiency
NGC 1566 group
NGC 1566 Group
No overall HI deficiency for the NGC 1566 group
+ 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
However, two group members display
deficiencies -
NGC 1515 (12) &
NGC 1536 (2)
Insert 1566 hi def graph here
NGC 5044 group - one late-type with HI deficiency,
ESO 576-G 017 (9)

18. 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.