The evolution of galaxies resolved in space and time: an inside-out growth view from the CALIFA survey

TL;DR

This study uses spatially resolved spectral data from the CALIFA survey to analyze how massive galaxies grow their stellar mass inside-out over time, revealing mass-dependent growth patterns and a transition in growth modes for lower mass galaxies.

Contribution

It provides the first spatially and temporally resolved analysis of stellar mass assembly in a large sample of galaxies, demonstrating inside-out growth and a mass-dependent transition in growth modes.

Findings

Massive galaxies grow inside-out with faster inner and outer growth in more massive ones.

A maximum spheroidal growth rate occurs at a stellar mass of ~10^10 Msun.

Galaxies below ~10^10 Msun show outside-in growth patterns.

Abstract

The growth of galaxies is one of the key problems in understanding the structure and evolution of the universe and its constituents. Galaxies can grow their stellar mass by accretion of halo or intergalactic gas clouds, or by merging with smaller or similar mass galaxies. The gas available translates into a rate of star formation, which controls the generation of metals in the universe. The spatially resolved history of their stellar mass assembly has not been obtained so far for any given galaxy beyond the Local Group. Here we demonstrate how massive galaxies grow their stellar mass inside-out. We report the results from the analysis of the first 105 galaxies of the largest to date three-dimensional spectroscopic survey of galaxies in the local universe (CALIFA). We apply the fossil record method of stellar population spectral synthesis to recover the spatially and time resolved star formation history of each galaxy. We show, for the first time, that the signal of downsizing is spatially preserved, with both inner and outer regions growing faster for more massive galaxies. Further, we show that the relative growth rate of the spheroidal component, nucleus and inner galaxy, that happened 5-7 Gyr ago, shows a maximum at a critical stellar mass ~10^10 Msun. We also find that galaxies less massive than ~10^10 Msun show a transition to outside-in growth, thus connecting with results from resolved studies of the growth of low mass galaxies.