Catalogues of isolated galaxies, isolated pairs, and isolated triplets in the local Universe

Abstract

Context. The construction of catalogues of galaxies and the a posteriori study of galaxy properties in relation to their environment have been hampered by scarce redshift information. The new 3-dimensional (3D) surveys permit small, faint, physically bound satellites to be distinguished from a background-projected galaxy population, giving a more comprehensive 3D picture of the surroundings. Aims. We aim to provide representative samples of isolated galaxies, isolated pairs, and isolated triplets for testing galaxy evolution and secular processes in low density regions of the local Universe, as well as to characterise their local and large-scale environments. Methods. We used spectroscopic data from the tenth data release of the Sloan Digital Sky Survey (SDSS-DR10) to automatically and homogeneously compile catalogues of 3702 isolated galaxies, 1240 isolated pairs, and 315 isolated triplets in the local Universe (z ≤ 0.080). To quantify the effects of their local and large-scale environments, we computed the projected density and the tidal strength for the brightest galaxy in each sample. Results. We find evidence of isolated pairs and isolated triplets that are physically bound at projected separations up to d ≤ 450 kpc with radial velocity difference ∆ ≤ 160 km s −1 , where the effect of the companion typically accounts for more than 98% of the total tidal strength affecting the central galaxy. For galaxies in the catalogues, we provide their positions, redshifts, and degrees of relation with their physical and large-scale environments. The catalogues are publicly available to the scientific community. Conclusions. For isolated galaxies, isolated pairs, and isolated triplets, there is no difference in their degree of interaction with the large-scale structure (up to 5 Mpc), which may suggest that they have a common origin in their formation and evolution. We find that most of them belong to the outer parts of filaments, walls, and clusters, and generally differ from the void population of galaxies.

The effect of local and large-scale environments on nuclear activity and star formation

“…We use the sample of isolated galaxies and isolated pairs compiled by Argudo-Fernández et al (2015b) from the SDSS-DR10 (Ahn et al 2014). Isolated galaxies and central galaxies in the pairs (the brightest of the pair by definition) are selected in a volume-limited sample redshift range 0.005 ≤ z ≤ 0.080, with 11 ≤ m r ≤ 15.7, where m r is the SDSS model magnitude in the r-band.…”

“…This criterion allows the second galaxy in the pair to be at least 2 orders of magnitude fainter within the range of spectroscopic completeness of the SDSS main galaxy sample at m r,Petrosian < 17.77 mag (Strauss et al 2002). Argudo-Fernández et al (2015b) used a three-dimensional isolation criterion, based on projected distances on the sky and redshift. The systems are isolated with no neighbours in a volume of 1 Mpc projected distance within a line-of-sight velocity difference of ∆ ≤ 500 km s −1 .…”

On the influence of the environment on galactic chemical abundances

“…To select the isolated galaxies, a criterion based on a selection in a projected distance -velocity difference space is usually employed. However, different numerical values for such criteria are adopted in the literature (e.g., Fuse et al 2012;Argudo-Fernández et al 2015;Spector & Brosch 2016;Lacerna et al 2016). We have chosen to use the isolation criteria from Lacerna et al (2016).…”

“…It was noted above that different numerical values of the peculiar galactic velocities V p were adopted in different studies (e.g., Fuse et al 2012;Argudo-Fernández et al 2015;Spector & Brosch 2016;Lacerna et al 2016). Above we considered the case of V p = 1000 km s −1 .…”

Isolated Galaxies versus Interacting Pairs with MaNGA

“…The sample of isolated galaxies used in this study is selected from the SDSS-based catalogue of Isolated Galaxies (SIG; [10]), which provided a representative sample of SDSS-selected isolated galaxies for testing galaxy evolution and secular processes in low density regions of the local Universe. These galaxies are isolated with no physical neighbours within a volume of ∆ ≤ 500 km·s −1 and d ≤ 1 Mpc projected radius, where ∆ is the absolute value of the line-of-sight velocity difference between the galaxy and its neighbours.…”