Dwarf Galaxies in the Coma Cluster: II. Spectroscopic and Photometric Fundamental Planes

TL;DR

This study extends the fundamental plane analysis to faint dwarf galaxies in the Coma cluster, revealing increased scatter, color correlations, and insights into mass-to-light ratios and star formation effects.

Contribution

It provides the first detailed fundamental plane analysis for dwarf galaxies in Coma, extending to fainter magnitudes and incorporating spectroscopic and photometric data.

Findings

Scatter about the FP increases for fainter galaxies.

Bluer dwarf galaxies show larger residuals from the FP.

Mass-to-light ratio is insensitive to mass in faint dwarfs.

Abstract

We present a study of the fundamental plane, FP, for a sample of 71 dwarf galaxies in the core of Coma cluster in magnitude range $-21 < M_I <-15$. Taking advantage of high resolution DEIMOS spectrograph on Keck II for measuring the internal velocity dispersion of galaxies and high resolution imaging of HST/ACS, which allows an accurate surface brightness modeling, we extend the fundamental plane (FP) of galaxies to $\sim$1 magnitude fainter luminosities than all the previous studies of the FP in Coma cluster. We find that, the scatter about the FP depends on the faint-end luminosity cutoff, such that the scatter increases for fainter galaxies. The residual from the FP correlates with the galaxy colour, with bluer galaxies showing larger residuals from FP. We find $M/L \propto M^{-0.15\pm0.22}$ in F814W-band indicating that in faint dwarf ellipticals, the $M/L$ ratio is insensitive to the mass. We find that less massive dwarf ellipticals are bluer than their brighter counterparts, possibly indicating ongoing star formation activity. Although tidal encounters and harassment can play a part in removing stars and dark matter from the galaxy, we believe that the dominant effect will be the stellar wind associated with the star formation, which will remove material from the galaxy resulting in larger $M/L$ ratios. We attribute the deviation of a number of faint blue dwarfs from the FP of brighter ellipticals to this effect. We also study other scaling relations involving galaxy photometric properties including the photometric plane. We show that, compared to the FP, the scatter about the photometric plane is smaller at the faint end.