The Global and Radial Stellar Mass Assembly of Milky Way-sized Galaxies

Abstract

We study the global and radial stellar mass assembly of eight zoomed-in MW-sized galaxies produced in Hydrodynamics cosmological simulations. The disk-dominated galaxies (4) show a fast initial stellar mass growth in the innermost parts, driven mostly by in-situ SF, but since z ∼ 2 − 1 the SF enters in a long-term quenching phase. The outer regions follow this trend but more gentle as more external they are. As the result, the radial stellar mass growth is highly inside-out due to both the inside-out structural growth and inside-out SF quenching. The half-mass radius evolves fast; for instance, R 0.5 (z = 1)< 0.5R 0.5 (z = 0). Two other runs resemble lenticular galaxies. One shows also a pronounced inside-out growth and the other one presents a nearly uniform radial mass assembly. The other two galaxies suffered late major mergers. Their normalized radial mass growth histories (MGHs) are nearly close among them but with periods of outside-in assembly during or after the mergers. For all the simulations, the archaeological radial MGHs calculated from the z = 0 stellar-particles age distribution are similar to the current MGHs, which evidences that the mass assembly by ex-situ stars and the radial mass transport do not change significantly their radial mass distributions. Our results agree qualitatively with observational inferences from the fossil record method applied to a survey of local galaxies and from look-back observations of progenitors of MW-sized galaxies. However, the inside-out growth mode is more pronounced and the R 0.5 growth is faster in simulations than in observational inferences.

Optical integral field spectroscopy observations applied to simulated galaxies: testing the fossil record method

“…The archaeological histories are conceptually similar to what is obtained from IFS observations by applying the fossil record method. For a formal definition of these different histories and their respective determinations for the Sp8D and Sp6L galaxies, see Appendix C. We remark that both the current (real) and archaeological radial MGHs are very similar for the simulated galaxies Sp8D and Sp6L, which shows that mergers and radial mass transport do not significantly change their radial mass distributions (Avila-Reese et al 2018).…”

“…For the main goal of this paper, we need well-resolved simulated galaxies. This is the case of the suite of eight zoomin cosmological simulations presented in Colín et al (2016) and Avila-Reese et al (2018). The simulations correspond to Milky Way-sized galaxies chosen to be in relatively isolated halos today.…”

“…This MGH takes into account the stellar mass between two snapshots that is added by in-situ star formation (M ,in−situ), acquired from outside (M ,in), lost (by radial mass transport, M ,out), and the mass lost by stellar winds (M ,ml ), that is, ∆M = M ,in−situ + M ,in − M ,out − M ,ml (Eq. 1 in Avila-Reese et al 2018). The insitu MGH takes into account only the stellar mass formed in-situ and the mass lost by stellar winds, without considering the amount of stellar mass acquired from outside or lost previously, i.e., it does not take into account the terms M ,in and M ,out.…”

SDSS-IV MaNGA – an archaeological view of the cosmic star formation history

“…Sánchez et al 2014;Sánchez-Menguiano et al 2016;Belfiore et al 2016;Sánchez-Menguiano et al 2017). The inside-out quenching process has also been seen in cosmological simulations of galaxy evolution (Tacchella et al 2016;Avila-Reese et al 2018) and observed at high-redshift (e.g. Tacchella et al 2015) .…”

SDSS-IV MaNGA: spatially resolved star formation histories and the connection to galaxy physical properties

“…The radial migration of stars could play an in important role in the observed spatial distribution of stars of different ages. Avila-Reese et al (2018) used simulations of Milky-Way like galaxies to show that the radial distribution of stellar mass growth is mostly from in-situ star formation, and that radial stellar mass migration does not significantly change the distribution of stellar mass in a galaxy. However in low mass galaxies (M * < 10 9.6 M ), inflows and outflows of gas can cause strong radial migration of stars, with young stars experiencing the strongest short-timescale migration.…”