Early-type galaxies in the SDSS

TL;DR

This study analyzes nearly 9000 early-type galaxies from SDSS, revealing their scaling relations, chemical properties, and evolutionary trends, and finds that their characteristics are consistent with passive evolution over the past 9 billion years.

Contribution

It provides a comprehensive analysis of the scaling relations, chemical abundances, and evolution of early-type galaxies using a large SDSS sample, including mock catalog validation.

Findings

Scaling relations are consistent across g*, r*, i*, z* bands.

Higher redshift galaxies are bluer and slightly more luminous, indicating passive evolution.

Galaxies in dense regions show slight differences in the Fundamental Plane.

Abstract

A sample of nearly 9000 early-type galaxies, in the redshift range 0.01<z<0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The sample was used to study how early-type galaxy observables, including luminosity L, effective radius R, surface brightness I, color, and velocity dispersion V, are correlated with one another. Measurement biases are understood with mock catalogs which reproduce all of the observed scaling relations. At any given redshift, the intrinsic distribution of luminosities, sizes and velocity dispersions in our sample are all approximately Gaussian. In the r* band L ~ V^3.91, L ~ R^1.58, R ~ I^(-0.75), and the Fundamental Plane relation is R ~ V^(1.49) I^(-0.75). These relations are approximately the same in the g*, i* and z* bands. At fixed luminosity, the mass-to-light ratio scales as M/L ~ L^0.14. The g*-r* color scales as V^0.25. Color also correlates with magnitude and size, but these correlations are entirely due to the L-V and R-V relations. Chemical evolution and star formation histories are investigated using co-added spectra of similar objects in our sample. Chemical abundances correlate primarily with velocity dispersion. At fixed V, the higher redshift population is bluer, is weaker in Mg2, and is stronger in Hbeta than the population nearby. In addition, the population at higher redshifts is slightly more luminous. These differences are consistent with that of a passively evolving population which formed the bulk of its stars about 9 Gyrs ago. The Fundamental Plane suggests that galaxies in dense regions are slightly different from those in less dense regions, but the co-added spectra and color--magnitude relations show no statistically significant dependence on environment.