Quenching depends on morphologies: implications from the ultraviolet-optical radial color distributions in Green Valley Galaxies

TL;DR

This study investigates how residual star formation in green valley galaxies varies with morphology by analyzing UV-optical color distributions, revealing different star formation patterns in early- and late-type galaxies and implications for galaxy quenching processes.

Contribution

It provides new insights into the radial distribution of star formation in green valley galaxies based on UV-optical colors, highlighting morphology-dependent quenching signatures.

Findings

Early-type galaxies have flat colors out to R90, with some showing blue cores indicating central star formation.

Late-type galaxies exhibit uniform color profiles with a red bulge and blue disk.

Approximately 50% of early-type galaxies have centrally concentrated star formation, confirmed by spectroscopy.

Abstract

In this Letter, we analyse the radial UV-optical color distributions in a sample of low redshift green valley (GV) galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation distribute in these galaxies. We find that the dust-corrected $u-r$ colors of early-type galaxies (ETGs) are flat out to $R_{90}$, while the colors turn blue monotonously when $r>0.5R_{50}$ for late-type galaxies (LTGs). More than a half of the ETGs are blue-cored and have remarkable positive NUV$-r$ color gradients, suggesting that their star formation are centrally concentrated; the rest have flat color distributions out to $R_{90}$. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that $\sim$50 % ETGs have EW(H$\rm \alpha$)$>6.0$ \AA. For the LTGs, 95% of them show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable "blue-cored" and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general picture that quenching first occur in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.