Spatially-Resolved Star Formation Main Sequence of Galaxies in the CALIFA Survey

TL;DR

This study uses spatially-resolved spectroscopic data from 306 CALIFA survey galaxies to analyze the star formation main sequence at local scales, revealing a tight correlation with small scatter across different galaxy types.

Contribution

It demonstrates that the star formation main sequence can be recovered from spatially-resolved properties, providing new insights into galaxy star formation at sub-galactic scales.

Findings

High correlation with small scatter (0.23 dex) in local SFR and stellar mass surface densities.

The spatially-resolved relation has a slope of 0.72 ± 0.04.

Identification of a retired galaxy sequence related to old stellar populations.

Abstract

The "main sequence of galaxies" $-$ defined in terms of the total star formation rate $\psi$ vs. the total stellar mass $M_*$ $-$ is a well-studied tight relation that has been observed at several wavelengths and at different redshifts. All earlier studies have derived this relation from integrated properties of galaxies. We recover the same relation from an analysis of spatially-resolved properties, with integral field spectroscopic (IFS) observations of 306 galaxies from the CALIFA survey. We consider the SFR surface density in units of log(M$_{\odot}$ yr$^{-1}$ Kpc$^{-2}$) and the stellar mass surface density in units of log(M$_{\odot}$ Kpc$^{-2}$) in individual spaxels which probe spatial scales of 0.5-1.5 Kpc. This local relation exhibits a high degree of correlation with small scatter ($\sigma = 0.23$ dex), irrespective of the dominant ionisation source of the host galaxy or its integrated stellar mass. We highlight: $(i)$ the integrated star formation main sequence formed by galaxies whose dominant ionisation process is related to star formation, for which we find a slope of 0.81 $\pm 0.02$; (ii) the spatially-resolved relation obtained with the spaxel analysis, we find a slope of 0.72 $\pm 0.04$; (iii) for the integrated main sequence we identified also a sequence formed by galaxies that are dominated by an old stellar population, which we have called the retired galaxies sequence.