Early-Type (E, S0) Galaxies in the Catalog of Isolated Galaxies (KIG)

TL;DR

This study reclassifies early-type isolated galaxies using modern surveys, investigates their companions, and compares their mass-to-light ratios, revealing differences in their dynamical evolution compared to late-type galaxies.

Contribution

It provides a revised classification of isolated early-type galaxies and analyzes their companion systems and mass ratios using new survey data.

Findings

Number of E- and S0-type galaxies reduced to 91.

Found 90 companions around 45 host galaxies.

Mass-to-light ratio for galaxy-companion systems is consistent with previous estimates.

Abstract

We use the data of modern digital sky surveys (PanSTARRS-1, SDSS) combined with HI-line and far ultraviolet (GALEX) surveys to reclassify 165 early-type galaxies from the Catalog of Isolated Galaxies (KIG). As a result, the number of E- and S0-type galaxies reduced to 91. Our search for companions of early-type KIG galaxies revealed 90 companions around 45 host galaxies with line-of-sight velocity differences $|dV| < 500$ km s$^{-1}$ and linear projected separations $R_{p} < 750$ kpc. We found no appreciable differences in either integrated luminosity or color of galaxies associated with the presence or absence of close neighbors. We found a characteristic orbital mass-to-luminosity ratio for 26 systems "KIG galaxy--companion" to be $M_{\odot}/L_{K} = (74\pm26) M_{\odot}/L_{\odot}$, which is consistent with the $M_{\rm orb}/L_{K}$ estimates for early-type isolated galaxies in the 2MIG catalog ($63 M_{\odot}/L_{\odot}$), and also with the $M_{\rm orb}/L_{K}$ estimates for E- and S0-type galaxies in the Local Volume: $38\pm22$ (NGC 3115), $82\pm26$ (NGC 5128), $65\pm20$ (NGC 4594). The high halo-to-stellar mass ratio for E- and S0-type galaxies compared to the average $(20\pm3) M_{\odot}/L_{\odot}$ ratio for bulgeless spiral galaxies is indicative of a significant difference between the dynamic evolution of early- and late-type galaxies.