Where is the neutral atomic gas in Hickson groups?*
Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, 18080 Granada, Spain
2 Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA e-mail: firstname.lastname@example.org
3 University of Delaware, Newark, Delaware, USA e-mail: email@example.com
4 Max-Planck-Institut für Radioastronomie Auf dem Hügel 69, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
5 Instituto de Astrofísica de Andalucía, CSIC Apdo. Correos 3004, 18080 Granada, Spain e-mail: email@example.com
6 Instituto de Astrofísica de Andalucía, CSIC Apdo. Correos 3004, 18080 Granada, Spain e-mail: firstname.lastname@example.org
Corresponding author: L. Verdes-Montenegro, email@example.com
Accepted: 8 August 2001
We have analyzed the total HI contents of 72 Hickson compact groups of galaxies (HCGs) and the detailed spatial distributions and kinematics of HI within a subset of 16 groups using the high angular resolution observations obtained with the VLA in order to investigate a possible evolutionary scenario for these densest systems in the present day galaxy hierarchy. For the more homogeneous subsample of 48 groups, we found a mean HI deficiency of , which corresponds to 40% of the expected HI for the optical luminosities and morphological types of the member galaxies. The individual galaxies show larger degrees of deficiency than the groups globally, (24% of the expected HI), due in most cases to efficient gas stripping from individual galaxies into the group environment visible in the VLA maps. The degree of deficiency is found to be similar to the central galaxies of Virgo and Coma cluster, and Coma I group, in spite of the significantly different characteristics (number of galaxies, velocity dispersion) of these environments. It does not seem plausible that a significant amount of extended HI has been missed by the observations. Hence phase transformation of the atomic gas should explain the HI deficiency. The groups richer in early type galaxies or more compact with larger velocity dispersions show a weak tendency to be more HI deficient. The detection rate of HCGs at X-ray wavelengths is larger for HI deficient groups, although the hot gas distribution and hence its origin is only known for a few cases. In the evolutionary scenario we propose, the amount of detected HI would decrease further with evolution, by continuous tidal stripping and/or heating. The H2 content also tends to be lower than expected for the galaxies in HI deficient groups, this may suggest that the HI stripping by frequent tidal interaction breaks the balance between the disruption of molecular clouds by star formation and the replenishment from the ambient HI.
Key words: galaxies: interactions / galaxies: kinematics and dynamics / galaxies: evolution / galaxies: structure / galaxies: ISM / radio lines: galaxies
This work is partially based on observations made with the VLA operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc., ALFOSC, which is owned by the Instituto de Astrofísica de Andalucía (IAA, CSIC) and operated at the Nordic Optical Telescope (NOT) under agreement between IAA and the NBIfA of the Astronomical Observatory of Copenhagen, and 1.5 m telescope of the Observatorio de Sierra Nevada, Granada, Spain, which is operated by the IAA (CSIC).
© ESO, 2001