NoSOCS in SDSS – V. Red disc and blue bulge galaxies across different environments

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 ≤ 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 ∼ 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.

MORPHOLOGY AND THE COLOR–MASS DIAGRAM AS CLUES TO GALAXY EVOLUTION AT z ∼ 1

“…The disks span the color-mass diagram, but there is no bimodality to suggest a rapid transition through the green valley. This is in agreement with other recent studies of the star formation histories of low redshift disk galaxies (Wolf et al 2009;Masters et al 2010;Tojeiro et al 2013;Lopes et al 2016). …”

“…We found that is indeed the case, shown by Figure 8. The offset of asymmetry between the blue elliptical peak and the red elliptical peak is evidence that there is at least a significant fraction of blue ellipticals that are associated with mergers, agreeing with recent findings (Smethurst et al 2015;Lopes et al 2016). By visual inspection, it was clear that the galaxies with A > 0.15 were significantly asymmetric.…”

“…Additionally, some spheroidal galaxies could trickle down from the red sequence after a spontaneous burst of star formation, perhaps after a minor merger. Recent studies investigating this population have not converged on a single evolutionary scenario for the blue bulge population, but have found evidence that there are contributions from both major mergers as well as 'rejuvination' (Smethurst et al 2015;Tojeiro et al 2013;Lopes et al 2016).…”

NoSOCS in SDSS – VI. The environmental dependence of AGN in clusters and field in the local Universe

“…Discrepancies among different studies are generally explained by the use of different samples (in terms of luminosity and mass, and wavelength selection), and environment definitions. Regarding the use of AGN selected in different wavelengths the environmental dependence and triggering mechanism for AGN selected in the radio may be different from optical and mid-IR selected AGN (Satyapal et al 2014;Ellison et al 2015), as well as X-rays (Martini et al 2013;Goulding et al 2014).…”

Galaxy And Mass Assembly (GAMA): blue spheroids within 87 Mpc

“…They neither find any evidence suggesting inside-out growth scenario which could turn BSphs to large disks, nor do they see any disk growth around BSphs (but see Graham, Dullo, & Savorgnan 2015;Graham, Ciambur, & Savorgnan 2016;Graham et al 2017, for an alternative view). Lopes et al (2016) also investigated a sample of low-z galaxies in various environments. Their analysis suggests that while highly-asymmetric BSphs may originate in mergers, the star formation histories of BSphs are likely to be heterogenous.…”