Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

Abstract

We analyze the optical continuum of star-forming galaxies in SDSS by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass-star formation rate and the stellar mass-gas-phase metallicity relations, respectively. We also fit linear combinations of single burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass-stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase-metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

L-GALAXIES 2020: Spatially resolved cold gas phases, star formation, and chemical enrichment in galactic discs

“…Overall, we find a good correspondence between our model results and the SDSS data over the three orders of magnitude in stellar mass considered. At low masses, the slope of our model MZ * R matches that of the Zahid et al (2017) relations fairly well, although the normalisation is a factor of ∼2 above the observed mass-weighted relation. Nonetheless, it is encouraging to see convergence to a similar value of Z * at higher mass, where star-formation histories, weighting differences, and spectral fitting issues are all likely to be better constrained in observations.…”

“…Okamoto et al 2017). The data provided by Zahid et al (2017), which only consider starforming systems, are therefore likely a fairer comparison to our model relation.…”

“…14 shows the relation between stellar mass and stellar metallicity (the MZ * R) at z = 0 for star-forming galaxies in our new model (the solid and dashed red lines) and for that of Henriques et al (2015) (the red dotted line). For comparison, observational results from Zahid et al (2017), are shown as green and purple circles (for luminosity-weighted and mass-weighted measurements, respectively). These are derived using full spectral fitting of M * -binned stacks of ∼ 200, 000 SDSS-DR7 and utilise stellar absorption lines to determine Z * .…”

Low Metallicities and Old Ages for Three Ultra-diffuse Galaxies in the Coma Cluster

“…We note that the data points from Zahid et al (2017) and Gallazzi et al (2005) in Figure 12 represent the total metallicities instead of iron abundances of galaxies in their samples. The large scatter of the MZR from Gallazzi et al Figure 11.…”

“…The top left panel of Figure 12 shows the locations of DF7, DF44, and DF17 on the MZR relative to other populations, including dwarf galaxies in the Local Group (Kirby et al 2013; gray dots), early-type galaxies stacked in stellar mass bins (Conroy et al 2014) (green), star-forming galaxies in SDSS (Zahid et al 2017), and the MZR from Gallazzi et al (2005), which covers both star-forming and quiescent SDSS galaxies (light blue). We note that the data points from Zahid et al (2017) and Gallazzi et al (2005) in Figure 12 represent the total metallicities instead of iron abundances of galaxies in their samples.…”