SDSS-IV MaNGA: radial gradients in stellar population properties of early-type and late-type galaxies

Taniya Parikh,Brett H Andrews,Claudia Maraston,Daniel Thomas,Niv Drory,Grecco Oyarzun,Kyle B Westfall,Nicholas Fraser Boardman

doi:10.1093/mnras/stab449

Abstract

ABSTRACT We derive ages, metallicities, and individual element abundances of early- and late-type galaxies (ETGs and LTGs) out to 1.5 Re. We study a large sample of 1900 galaxies spanning 8.6–11.3 log M/M⊙ in stellar mass, through key absorption features in stacked spectra from the SDSS-IV/MaNGA survey. We use mock galaxy spectra with extended star formation histories to validate our method for LTGs and use corrections to convert the derived ages into luminosity- and mass-weighted quantities. We find flat age and negative metallicity gradients for ETGs and negative age and negative metallicity gradients for LTGs. Age gradients in LTGs steepen with increasing galaxy mass, from −0.05 ± 0.11 log Gyr/Re for the lowest mass galaxies to −0.82 ± 0.08 log Gyr/Re for the highest mass ones. This strong gradient–mass relation has a slope of −0.70 ± 0.18. Comparing local age and metallicity gradients with the velocity dispersion σ within galaxies against the global relation with σ shows that internal processes regulate metallicity in ETGs but not age, and vice versa for LTGs. We further find that metallicity gradients with respect to local σ show a much stronger dependence on galaxy mass than radial metallicity gradients. Both galaxy types display flat [C/Fe] and [Mg/Fe], and negative [Na/Fe] gradients, whereas only LTGs display gradients in [Ca/Fe] and [Ti/Fe]. ETGs have increasingly steep [Na/Fe] gradients with local σ reaching 6.50 ± 0.78 dex/log km s−1 for the highest masses. [Na/Fe] ratios are correlated with metallicity for both galaxy types across the entire mass range in our sample, providing support for metallicity-dependent supernova yields.

Highlights

Stellar population analysis is a powerful tool for extracting physical parameters from galaxy spectra, often referred to as extragalactic archaeology
Considerable progress is required on the modelling to be able to accurately determine such parameters for late-type galaxies (LTGs), we present this work as an indication of detailed stellar population signatures in spiral galaxies
The same is true locally within galaxies, independent of mass and type since the local σ gradients are consistent with the global relations. These results are consistent with P19 for early-type galaxies (ETGs) and we show that the same is true for LTGs

Summary

Introduction

Stellar population analysis is a powerful tool for extracting physical parameters from galaxy spectra, often referred to as extragalactic archaeology. Results can be obtained via modelling the full spectrum (Cid Fernandes et al 2005; Ocvirk et al 2006; Koleva et al 2009; Conroy, Graves & van Dokkum 2014; Cappellari 2017; Goddard et al 2017; Wilkinson et al 2017; Conroy et al 2018) or absorption index measurements (Trager et al 2000; Proctor & Sansom 2002; Thomas et al 2005; Schiavon 2007; Thomas et al 2010; Johansson, Thomas & Maraston 2012) which respond to a combination of stellar population parameters. Gradients provide information on internal processes such as stellar migration, inflow of pristine gas into galaxies, and outflows of enriched material via supernovae and stellar winds into the interstellar medium (ISM) (see Maiolino & Mannucci 2019, for a review)

Methods

Results

Discussion

Conclusion