Companions around the nearest luminous galaxies: Segregation and selection effects

Abstract

Using the "Updated Nearby Galaxy Catalog", we consider different properties of companion galaxies around luminous hosts in the Local Volume. The data on stellar masses, linear diameters, surface brightnesses, HI-richness, specific star formation rate (sSF R), and morphological types are discussed for members of the nearest groups, including the Milky Way and M 31 groups, as a function of their separation from the hosts. Companion galaxies in groups tend to have lower stellar masses, smaller linear diameters and fainter mean surface brightnesses as the distance to their host decreases. The hydrogen-to-stellar mass ratio of the companions increases with their linear projected separation from the dominant luminous galaxy. This tendency is more expressed around the bulge-dominated hosts. While linear separation of the companions decreases, their mean sSF R becomes lower, accompanied with the increasing sSF R scatter. Typical linear projected separation of dSphs around the bulge-dominated hosts, 350 kpc, is substantially larger than that around the disk-dominated ones, 130 kpc. This difference probably indicates the presence of larger hot/warm gas haloes around the early-type host galaxies. The mean fraction of dSph (quenched) companions in 11 the nearest groups as a function of their projected separation Rp can be expressed as f (E) = 0.55 − 0.69 × Rp. The fraction of dSphs around the Milky Way and M 31 looks much higher than in other nearby groups because the quenching efficiency dramatically increases towards the ultra-low mass companions. We emphasize that the observed properties of the Local Group are not typical for other groups in the Local Volume due to the role of selection effects caused by our location inside the Local Group.

Environmental quenching of low-mass field galaxies

“…We then compute the quenched fraction, f quench , as a function of host-centric distance (see the grey shaded regions in Figures 2, 3, and 4). Our measured quenched fraction within the Local Volume is in good agreement with the observed fraction of earlytype galaxies in the vicinity of other nearby massive hosts (Karachentsev & Kudrya 2015).…”

Morphological properties of galaxies in different Local Volume environments

“…However, there is not any further growth seen at higher Θ1 (possibly due to galaxy distance errors comparable to the virial radius of a group). Similar behaviour of a quenched fraction of satellites around the nearby luminous galaxies has been also noticed by Karachentsev & Kudrya (2015) and Fillingham et al (2018).…”

Newly discovered dwarf galaxies in the MATLAS low density fields

“…Observations of dwarfs in nearby groups and clusters show that dwarf galaxies follow a morphology-density relation similar to massive galaxies, such that dEs are preferentially located in denser environments and dIrrs in lower density environments (Dressler 1980;Ferguson & Sandage 1990;Grebel et al 2003;Skillman et al 2003;Côté et al 2009;Weisz et al 2011;Karachentsev & Kudrya 2015). However, it is unclear if a group (or more dense) environment is a necessary condition to establish the morphology-density relation, or if it also exists around isolated host galaxies.…”

“…Several deep optical imaging observing programs have begun collecting data in recent years, either for the express purpose of detecting new dwarf galaxies or with this as a secondary science goal. These include large sky surveys such as the Panoramic Survey Telescope and RApid Response System (PAN-STARRS1; Chambers et al 2016), the Dark Energy Survey (DES; The Dark Energy Survey Collaboration 2005), Survey of the MAgellanic Stellar History (SMASH; Nidever et al 2017), and the VLT Survey Telescope AT-LAS (Shanks et al 2015), as well as deep imaging projects of the regions around nearby massive galaxies such as the Dwarf Galaxy Survey with Amateur Telescopes (DGSAT; Martínez-Delgado et al 2010), the Giant Galaxies, Dwarfs, and Debris Survey (GGADDS; Ludwig et al 2012), the Tief Belichtete Galaxien project (Karachentsev et al 2015), and observations taken with the Dragonfly Telephoto Array Abraham & van Dokkum 2014). Deep imaging programs of nearby clusters, such as the Next Generation Virgo cluster Survey (NGVS; Ferrarese et al 2012) and the Next Generation Fornax Survey (NGFS; Muñoz et al 2015) are also revealing fainter dwarf populations that were previously missed.…”