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.