Orbital Dependence of Galaxy Properties in Satellite Systems of Galaxies

TL;DR

This study analyzes how satellite galaxy properties depend on their orbital motion and distance from host galaxies, revealing differences in distribution, speed, and color between prograde and retrograde satellites using SDSS data.

Contribution

It provides the first comprehensive analysis of satellite galaxy orbital directions and their impact on properties like distribution, velocity, and color in a large SDSS sample.

Findings

Prograde satellites are nearly as numerous as retrograde ones.

Velocity distributions are symmetric with median near zero km/s.

Radial distribution varies significantly between prograde and retrograde satellites.

Abstract

We study the dependence of satellite galaxy properties on the distance to the host galaxy and the orbital motion using the SDSS data. From SDSS DR7 we find 3515 isolated satellite systems of galaxies at z<0.03 that contain 8904 satellite galaxies. Using this sample we construct a catalog of 635 satellites associated with 215 host galaxies whose spin directions are determined by our inspection of the SDSS color images and/or by spectroscopic observations in the literature. We divide satellite galaxies into prograde and retrograde orbit subsamples depending on their orbital motion respect to the spin direction of the host. We find that the number of galaxies in prograde orbit is nearly equal to that of retrograde orbit galaxies: the fraction of satellites in prograde orbit is 50+/-2%. The velocity distribution of satellites with respect to their hosts is found almost symmetric: the median bulk rotation of satellites is -1+/- 8 km/s. It is found that the radial distribution of early-type satellites in prograde orbit is strongly concentrated toward the host while that of retrograde ones shows much less concentration. We also find the orbital speed of late-type satellites in prograde orbit increases as the projected distance to the host (R) decreases while the speed decreases for those in retrograde orbit. At R less than 0.1 times the host virial radius the orbital speed decreases in both prograde and retrograde orbit cases. Prograde satellites are on average fainter than retrograde satellites for both early and late morphological types. The u-r color becomes redder as R decreases for both prograde and retrograde orbit late-type satellites. The differences between prograde and retrograde orbit satellites may be attributed to their different origin or the different strength of physical processes that they have experienced through hydrodynamic interactions with their host galaxies.