On the Tidal Dependence of Galaxy Properties

TL;DR

This study investigates how galaxy properties relate to their tidal environment and local density, revealing a scale-dependent correlation that peaks at about 2 h^{-1} Mpc, consistent across observations and simulations.

Contribution

It identifies a specific smoothing scale where galaxy property correlations with environment are maximized, linking tidal ellipticity to local density effects in galaxy formation.

Findings

Correlation between galaxy properties and environment depends on smoothing scale.

Optimal scale (~2 h^{-1} Mpc) maximizes color-density correlation.

Simulation results agree with observational findings, with some differences in strength.

Abstract

Using volume-limited samples drawn from The Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we measure the tidal environment of galaxies, which we characterize by the ellipticity e of the potential field calculated from the smoothed spatial number density 1 + {\delta} of galaxies. We analyze if galaxy properties, including color, Dn4000, concentration and size correlate with e, in addition to depending on 1 + {\delta}. We find that there exists a transition smoothing scale at which correlations/anti-correlations with e reverse. This transition scale is well represented by the distance to the 3rd- nearest-neighbor of a galaxy in a volume limited sample with Mr < -20 which has a distribution peaked at ~ 2 h-1Mpc. We further demonstrate that this scale corresponds to that where the correlation between the color of galaxies and environmental density 1+{\delta} is the strongest. For this optimal smoothing R0 no additional correlations with e are observed. The apparent dependence on tidal ellipticity e at other smoothing scales Rs can be viewed as a geometric effect, arising from the cross correlation be- tween (1+{\delta}o) and e(Rs). We perform the same analysis on numerical simulations with semi-analytical modeling (SAM) of galaxy formation. The e dependence of the galaxy properties shows similar behavior to that in the SDSS, although the color-density cor- relation is significantly stronger in the SAM. The 'optimal adaptive smoothing scale' in the SAM is also closely related to the distance to the 3rd-nearest-neighbor of a galaxy, and its characteristic value is consistent with, albeit slightly smaller than for SDSS.