Satellite galaxies around present-day massive ellipticals

Abstract

Using the spectroscopic New York University Value-Added Galaxy Catalogue and the photometric photo-z catalogues of the Sloan Digital Sky Survey Data Release 7, we have explored the satellite distribution around ∼1000 massive (M ⋆ 2×10 11 M ⊙ ) visually classified elliptical galaxies down to a satellite mass ratio of 1:400 (i.e. 5×10 8 M sat 2×10 11 M ⊙ ). Our host galaxies were selected to be representative of a mass complete sample. The satellites of these galaxies were searched within a projected radial distance of 100 kpc to their hosts. We have found that only 20-23 per cent of the massive ellipticals have at least a satellite down to a mass ratio 1:10. This number increases to 45-52 per cent if we explore satellites down to 1:100 and is >60-70 per cent if we go further down to 1:400. The average projected radial distance of the satellites to their hosts for our whole sample down to 1:400 is ∼59 kpc (which can be decreased at least down to 50 kpc if we account for incompleteness effects). The number of satellites per galaxy host only increases very mildly at decreasing the satellite mass. The fraction of mass which is contained in the satellites down to a mass ratio of 1:400 is 8 per cent of the total mass contained by the hosts. Satellites with a mass ratio from 1:2 to 1:5 (with ∼28 per cent of the total mass of the satellites) are the main contributor to the total satellite mass. If the satellites eventually infall into the host galaxies, the merger channel will be largely dominated by satellites with a mass ratio down to 1:10 (as these objects have 68 per cent of the total mass in satellites).

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

“…Our results are compatible with Mármol-Queraltó et al (2012 and, more recently, with Ruiz et al (2014), who characterised the population of satellites around massive ellipticals (M 2 × 10 11 M ). They find that on average, there is about one satellite around each central galaxy, down to a mass ratio 1/100.…”

Galaxy and Mass Assembly (GAMA): probing the merger histories of massive galaxies via stellar populations

“…Furthermore, a number count analysis supported the idea that mass ratios closer to ∼1:3 dominate this growth channel in massive galaxies. An extension of this study to a very large sample of low-z galaxies from Sloan Digital Sky Survey (SDSS) (Ruiz, Trujillo & Mármol-Queraltó 2014) confirmed that mass ratios in the region 1:5 are more important than minor merging systems (typically defined by mass ratios below 1:10).…”

Understanding the size growth of massive galaxies through stellar populations

“…mass ratio above 0.3). We also show in the figure the low-redshift estimates derived from the SDSS dataset by Ruiz et al (2014). Note that the fractional growth rate via merging stays approximately constant, at ΔM/M ∼10% per Gyr.…”

“…Note the preponderance of the major merging component ratios in the expected growth. The data points at z=0 (labelled SDSS) correspond to the analysis of Ruiz et al (2014). Adapted from Ferreras et al 2014. …”