Where is the neutral atomic gas in Hickson groups?

Abstract

Abstract. 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 DefHI = 0.40 ± 0.07, 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, DefHI = 0.62 ± 0.09 (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.

H i debris in the IC 1459 galaxy group

“…It also allows us to derive both the H i and total mass distributions of galaxies and groups, pin-point the locations of likely star formation in the galaxy outskirts and tidal dwarf galaxies in the densest H i debris. Although the phenomena related to galaxy interactions in groups and clusters are expected to be relatively common (e.g., Verdes-Montenegro et al 2001;Bekki et al 2005a,b;Chung et al 2009;English et al 2010;Serra et al 2012;Wolfinger et al 2013;Serra et al 2015) the need for high sensitivity to extended structures as well as suitable velocity and angular resolution make them difficult to detect and study in detail. Future H i observations with SKA Pathfinders such as ASKAP, Apertif and MeerKat (see Koribalski 2015) will allow deep H i imaging of many galaxy groups and clusters near and far.…”

“…Many detailed H i studies, ranging from galaxies in close pairs (e.g., Gordon et al 2001;Koribalski & Dickey 2004;Koribalski & López-Sánchez 2009;Sengupta et al 2015), compact groups Koribalski et al 2003;Serra et al 2012), Hickson compact groups (Hickson 1982;Verdes-Montenegro et al 2001), loose groups (Kilborn et al 2009;Pisano et al 2011) and clusters (Chung et al 2009) have been carried out. The stripped gas may be found as tidal tails, filaments, and plumes near the interacting galaxies, e.g.…”

A mid-IR study of Hickson compact groups

“…Even though only a few HCGs have been mapped in detail in neutral hydrogen, single-dish measurements reveal that they are generally deficient in HI with a median mass of M HI ∼ 2.2 × 10 10 M , two times less than what is observed in loose groups (Williams & Rood 1987;Verdes-Montenegro et al 2001). However, the molecular gas content of their individual galaxies, as traced by the CO emission, is similar to that of interacting pairs and starburst galaxies (Leon et al 1998).…”

Two formation channels of ultra-compact dwarf galaxies in Hickson compact groups

“…The group's angular diameter is about 6 . This group is in an earlier evolutionary stage, as indicated by the low number of optical signs of galaxy interaction (Mendes de Oliveira & Hickson 1994), its longer crossing time ( 0.2 t Hubble ), high spiral fraction (Hickson et al 1992) and Hi content (Verdes-Montenegro et al 2001). This group shows no signs of intragroup light, where most of the optical luminosity is concentrated on its brightest galaxy (NGC 1199).…”