Comparing galaxy populations in compact and loose groups of galaxies

Abstract

Aims. This paper is part of a series in which we systematically compare the properties of galaxies in compact groups, loose groups, and the field. In this paper we focus our study on the age and star formation in galaxies. Methods. For galaxies in selected samples of compact groups, loose groups, and field galaxies, we compare the distributions of D n (4000) as an age indicator and the specific star formation rate as an indicator of on-going star formation. We analyse the dependence of these parameters on galaxy type and stellar mass and, for group galaxies, their dependence on the dynamic state of the system. We study the relative fraction of galaxies dominated by old stellar populations as a function of galaxy stellar mass. We perform a similar analysis for galaxies that have high specific star formation rates. Results. Galaxies in compact groups have, on average, older stellar populations than their loose-group or field counterparts. Earlytype galaxies in compact groups formed their stars and depleted their gas content more rapidly than in the other environments. We have found evidence of two populations of late-type galaxies in dynamically old compact groups: one with normal specific star formation rates and another with markedly reduced star formation. Conclusions. Processes that transform galaxies from star forming to quiescent act upon galaxies faster and more effectively in compact groups. The unique characteristics of compact groups make them an extreme environment for galaxies, where the transition to quiescence occurs rapidly.

Secondary Infall in the Seyfert’s Sextet: A Plausible Way Out of the Short Crossing Time Paradox

“…6 in this paper with Fig. 6 in Sánchez et al (2015) suggests that the underlying stellar populations of H79a and H79b are old (i.e., with luminosity-weighted age 10 9.5 yrs), but prolonged star-formation activity over the last several Myr might be present (e.g., Coenda et al 2015;Sánchez et al 2015).…”

The $-12$ mag dip in the galaxy luminosity function of Hickson Compact Groups

“…These studies suggest a rapid evolution from star-forming to quiescent galaxies in compact groups. Coenda et al (2015) compared galaxies in compact groups and loose groups and found that there were two populations of late-type galaxies in compact groups, one with normal star formation rates and another with low star formation rates. If such a partition occurs preferentially along the galaxy mass/luminosity, the significant dip of HCGs could be related to the populations of late-type galaxies.…”

The Occurrence of Compact Groups of Galaxies through Cosmic Time

“…Coenda et al (2012) found a significantly larger fraction of red and early-type galaxies in CGs, as compared to loose groups, while Martínez et al (2013) established that brightest group galaxies in CGs are brighter, more massive, larger, redder, and more frequently classified as elliptical compared to their counterparts in loose groups. Coenda et al (2015) found that CGs include a late-type population with markedly reduced sSFRs compared to loose groups and field populations. The fraction of quiescent galaxies (i.e., not actively star-forming, independent of the average age of the stellar population) in CGs is higher than in the field or loose-group population (Coenda et al 2015;Lenkić et al 2016).…”

“…Coenda et al (2015) found that CGs include a late-type population with markedly reduced sSFRs compared to loose groups and field populations. The fraction of quiescent galaxies (i.e., not actively star-forming, independent of the average age of the stellar population) in CGs is higher than in the field or loose-group population (Coenda et al 2015;Lenkić et al 2016). Farhang et al (2017) compared CGs to fossil groups in the Millennium Simulation, finding that some, but not all, CGs eventually turn into fossil systems.…”