NoSOCS in SDSS. V. Red Disc and Blue Bulge Galaxies Across Different Environments

TL;DR

This study examines how environment influences the properties of red discs and blue bulges in galaxies, revealing environmental effects, mass dependence, and possible evolutionary pathways through detailed analysis of galaxy samples in clusters and fields.

Contribution

It provides new insights into the environmental dependence and evolutionary processes of red discs and blue bulges, highlighting the role of stellar mass and slow quenching mechanisms.

Findings

Red discs become redder in denser environments, especially within virial radii.

Quenching timescale estimated at approximately 2-3 Gyr.

Blue bulges show signs of mergers and asymmetric features.

Abstract

We investigated the typical environment and physical properties of "red discs" and "blue bulges", comparing those to the "normal" objects in the blue cloud and red sequence. Our sample is composed of cluster members and field galaxies at $z \le 0.1$, so that we can assess the impact of the local and global environment. We find that disc galaxies display a strong dependence on environment, becoming redder for higher densities. This effect is more pronounced for objects within the virial radius, being also strong related to the stellar mass. We find that local and global environment affect galaxy properties, but the most effective parameter is stellar mass. We find evidence for a scenario where "blue discs" are transformed into "red discs" as they grow in mass and move to the inner parts of clusters. From the metallicity differences of red and blue discs, and the analysis of their star formation histories, we suggest the quenching process is slow. We estimate a quenching time scale of $\sim $ 2$-$3 Gyr. We also find from the sSFR$-$M$_*$ plane that "red discs" gradually change as they move into clusters. The "blue bulges" have many similar properties than "blue discs", but some of the former show strong signs of asymmetry. The high asymmetry "blue bulges" display enhanced recent star formation compared to their regular counterparts. That indicates some of these systems may have increased their star formation due to mergers. Nonetheless, there may not be a single evolutionary path for these blue early-type objects.