Stellar systems in the direction of the Hickson Compact Group 44

Abstract

Context. In spite of the numerous studies of low-luminosity galaxies in different environments, there is still no consensus about their formation scenario. In particular, a large number of galaxies displaying extremely low-surface brightnesses have been detected in the last year, and the nature of these objects is under discussion. Aims. In this paper we report the detection of two extended low-surface brightness (LSB) objects (µ eff g ′ ≃ 27 mag) found, in projection, next to NGC 3193 and in the zone of the Hickson Compact Group (HCG) 44, respectively. Methods. We analyzed deep, high-quality, GEMINI-GMOS images with ELLIPSE within IRAF in order to obtain their brightness profiles and structural parameters. We also search for the presence of globular clusters (GC) in these fields. Results. We have found that, if these LSB galaxies were at the distances of NGC 3193 and HCG 44, they would show sizes and luminosities similar to those of the ultra-diffuse galaxies (UDGs) found in the Coma cluster and other associations. In that case, their sizes would be rather larger than those displayed by the Local Group dwarf spheroidal (dSph) galaxies. We have detected a few unresolved sources in the sky zone occupied by these galaxies showing colors and brightnesses typical of blue globular clusters. Conclusions. From the comparison of the properties of the galaxies presented in this work, with those of similar objects reported in the literature, we have found that LSB galaxies display sizes covering a quite extended continous range (r eff ∼ 0.3 − 4.5 kpc), in contrast to "normal" early-type galaxies, which shows r eff ∼ 1.0 kpc with a low dispersion. This fact might be pointing to different formation processes for both types of galaxies.

Detection of a Large Population of Ultradiffuse Galaxies in Massive Galaxy Clusters: Abell S1063 and Abell 2744

“…Since the recent revival of the UDGs in Coma (van Dokkum et al 2015;Koda et al 2015), the number of the known UDGs keeps increasing. The UDGs are found from the lowdensity regions to the high density environments such as galaxy clusters (Mihos et al 2015;Yagi et al 2016;Smith Castelli et al 2016;van der Burg et al 2016;Martin et al 2016;Merritt et al 2016;Bellazzini et al 2017;Román & Trujillo 2017a,b).…”

Ultra-diffuse galaxies outside clusters: clues to their formation and evolution

“…We want to expand such discussion further and explore which kind of structures (groups or clusters) are more favorable for the formation of UDGs. Initially, clusters were considered the natural place for finding UDGs; however, there is increasing evidence (first noted by Román & Trujillo (2017) and recently by Merritt et al (2016); see also: Ordenes-Briceño et al (2016);Smith Castelli et al (2016)) that UDGs are also found outside clusters. The existence of UDGs in the field has also been motivated theoretically by Di Cintio et al (2017).…”

(Almost) Dark Galaxies in the ALFALFA Survey: Isolated H i-bearing Ultra-diffuse Galaxies

“…But UDGs also appear to exist outside of clusters. Martínez-Delgado et al (2016) report the discovery of a UDG in the Pisces-Perseus Filament, and Merritt et al (2016) andSmith Castelli et al (2016) report the discovery of UDGs in group environments. Román & Trujillo (2017a) statistically estimate the distribution of UDGs around Abell 168, and suggest that more than 50% of UDGs could exist outside of the cluster environment.…”