Resolved stellar population properties of PHANGS-MUSE galaxies

Abstract

Analyzing resolved stellar populations across the disk of a galaxy can provide unique insights into how that galaxy assembled its stellar mass over its lifetime. Previous work at ∼1 kpc resolution has already revealed common features in the mass buildup (e.g., inside-out growth of galaxies). However, even at approximate kpc scales, the stellar populations are blurred between the different galactic morphological structures such as spiral arms, bars and bulges. Here we present a detailed analysis of the spatially resolved star formation histories (SFHs) of 19 PHANGS-MUSE galaxies, at a spatial resolution of ∼100 pc. We show that our sample of local galaxies exhibits predominantly negative radial gradients of stellar age and metallicity, consistent with previous findings, and a radial structure that is primarily consistent with local star formation, and indicative of inside-out formation. In barred galaxies, we find flatter metallicity gradients along the semi-major axis of the bar than along the semi-minor axis, as is expected from the radial mixing of material along the bar during infall. In general, the derived assembly histories of the galaxies in our sample tell a consistent story of inside-out growth, where low-mass galaxies assembled the majority of their stellar mass later in cosmic history than high-mass galaxies (also known as “downsizing”). We also show how stellar populations of different ages exhibit different kinematics. Specifically, we find that younger stellar populations have lower velocity dispersions than older stellar populations at similar galactocentric distances, which we interpret as an imprint of the progressive dynamical heating of stellar populations as they age. Finally, we explore how the time-averaged star formation rate evolves with time, and how it varies across galactic disks. This analysis reveals a wide variation of the SFHs of galaxy centers and additionally shows that structural features become less pronounced with age.

The TYPHOON Stellar Population Synthesis Survey. I. The Young Stellar Population of the Great Barred Spiral NGC 1365

“…Since the galaxy is characterized by strong star formation activity, the blue sensitivity of TYPHOON is an advantage and allows for a good characterization of the properties of its young stellar population. This will provide important information extending the work and the results obtained recently within the comprehensive ESO Very large Telescope (VLT) PHANGS-MUSE survey (Emsellem et al 2022;Pessa et al 2023).…”

“…We note that central stellar metallicities of NGC 1365 have already been studied within two surveys using the ESO VLT IFU MUSE, the TIMER (Gadotti et al 2019;Bittner et al 2020;Gadotti et al 2020), and the PHANGS (Emsellem et al 2022) survey. Both surveys do not distinguish between the metallicities of the young and old populations and provide only an average over the total population but also indicate a drop of total metallicity toward the center (Bittner 2021;Pessa et al 2023). From the result we obtained, we learn that this drop is caused by a strong burst of the formation of a very young population of low metallicity.…”

“…The final set of our SSP spectra is then adjusted to the TYPHOON spectral resolution. Because of the low TYPHOON spectral resolution, we do not consider the line-broadening effects of stellar velocity dispersion, which has been measured, for instance, by Bittner et al (2020) and Pessa et al (2023).…”

“…For our population synthesis analysis, we use the spectral range of 4000-7070 Å where the flux-calibrated spectra have the best signal. Compared to the range of 4800-7000 Å used in the PHANGS-MUSE study by Pessa et al (2023) this is an important blueward extension that enables a more accurate characterization of the young stellar population.…”

“…Spectroscopic studies of galaxies with integral field units (IFU) have become an important tool in investigating the evolution of galaxies. Spatially resolved maps of their chemical composition, stellar ages, star formation rates, and gas properties provide unique information about the complex physical processes affecting galaxy evolution (see, for instance, Westmoquette et al 2011;Sánchez-Blázquez et al 2014;Bittner et al 2020;Carrillo et al 2020;Parikh et al 2021;Emsellem et al 2022;Pessa et al 2023;Thainá-Batista et al 2023). Usually, because of the relatively small field of view of the available IFUs (of the order of 1′) this work has mostly been concentrated on galaxies with small angular size or only central regions.…”