EARLY-TYPE GALAXY ARCHEOLOGY: AGES, ABUNDANCE RATIOS, AND EFFECTIVE TEMPERATURES FROM FULL-SPECTRUM FITTING

By C. Conroy, G. Graves, P. V. van Dokkum. 2013

169 citations recorded by the source corpus.

The stellar populations of galaxies hold vital clues to their formation histories. In this paper we present results based on modeling stacked spectra of early-type galaxies drawn from the Sloan Digital Sky Survey as a function of velocity dispersion, σ, from 90 km s−1 to 300 km s−1. The spectra are of extremely high quality, with typical signal-to-noise ratio of 1000 Å−1, and a wavelength coverage of 4000 Å −8800 Å. Our population synthesis model includes variation in 16 elements from C to Ba, a two-component star formation history, the shift in effective temperature, Δ Teff, of the stars with respect to a solar metallicity isochrone, and the stellar initial mass function, among other parameters. In our approach we fit the full optical spectra rather than a select number of spectral indices and are able to, for the first time, measure the abundances of the elements V, Cr, Mn, Co, and Ni from the integrated light of distant galaxies. Our main results are as follows: (1) light-weighted stellar ages range from 6–12 Gyr from low to high σ; (2) [Fe/H] varies by less than 0.1 dex across the entire sample; (3) Mg closely tracks O, and both increase from ≈0.0 at low σ to ∼0.25 at high σ; Si and Ti show a shallower rise with σ, and Ca tracks Fe rather than O; (4) the iron peak elements V, Cr, Mn, and Ni track Fe, while Co tracks O, suggesting that Co forms primarily in massive stars; (5) C and N track O over the full sample and [C/Fe] and [N/Fe] exceed 0.2 at high σ; and (6) the variation in Δ Teff with total metallicity closely follows theoretical predictions based on stellar evolution theory. This last result is significant because it implies that we are robustly solving not only for the detailed abundance patterns but also the detailed temperature distributions (i.e., isochrones) of the stars in these galaxies. A variety of tests reveal that the systematic uncertainties in our measurements are probably 0.05 dex or less. Our derived [Mg/Fe] and [O/Fe] abundance ratios are 0.05–0.1 dex lower than most previous determinations. Under the conventional interpretation that the variation in these ratios is due to star formation timescale variations, our results suggest longer star formation timescales for massive early-type galaxies than previous studies. Detailed chemical evolution models are necessary in order to translate the abundance ratio distributions of these galaxies into constraints on their formation histories. Alternatively, these data may provide useful constraints on the nucleosynthetic pathways for elements whose production is not well understood.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/254440abe3e69c30534992fc61c55a17792dbec8

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Instrumentation

Citations in the corpus

A BUDGET AND ACCOUNTING OF METALS AT z ∼ 0: RESULTS FROM THE COS-HALOS SURVEY (2013, result): “We note that the normalization of this relation has decreased as the reference models have improved (Arrigoni et al. 2010; Conroy et al. 2013).”
THE UNIVERSAL RELATION OF GALACTIC CHEMICAL EVOLUTION: THE ORIGIN OF THE MASS–METALLICITY RELATION (2014, background): “A correlation between stellar mass and metallicity is observed not only in gas but also stars (Gallazzi et al. 2005; Kudritzki et al. 2012; Kirby et al. 2013; Conroy et al. 2013; Hosek et al. 2014).”
De re metallica: the cosmic chemical evolution of galaxies (2018, unknown): “…& Charlot, 2003; Conroy et al., 2009; Leitherer, 2014; Chevallard & Charlot, 2016; Wilkinson et al., 2017; Cappellari, 2017, among many others), see Conroy (2013) for a recent review, and http://www.sedfitting.org (by 10 Maiolino R., Mannucci F. T. Budavari, D. Dale, B. Groves and J. Walcher) for…”
The stellar IMF in early-type galaxies from a non-degenerate set of optical line indices (2013, background): “A full spectral fitting approach can help to further investigate possible IMF variations with galaxy masses and to trace the complete star formation history of a galaxy (Conroy et al. 2013).”