More is better: Strong constraints on the stellar properties of LEGA-C z  ∼  1 galaxies with Prospector

¹ STAR Institute, Université de Liège, Quartier Agora, Allée du six Aout 19c, B-4000 Liege, Belgium
² Sterrenkundig Observatorium Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium
³ Max-Planck Institut für Astronomie Königstuhl, D-69117 Heidelberg, Germany
⁴ Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy
⁵ Department of Physics and Astronomy and PITT PACC, University of Pittsburgh, Pittsburgh, PA 15260, USA
⁶ Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA
⁷ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁸ Cavendish Laboratory – Astrophysics Group, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK
⁹ Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802, USA
¹⁰ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
¹¹ Institute for Computational and Data Sciences, The Pennsylvania State University, University Park, PA 16802, USA
¹² Institute of Astrophysics, National Taiwan University, Taipei 10617, Taiwan
¹³ Department of Physics and Center for Theoretical Physics, National Taiwan University, Taipei 10617, Taiwan
¹⁴ Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan

^⋆ Corresponding author; angelos.nersesian@uliege.be

Received: 18 October 2024
Accepted: 5 February 2025

Abstract

Aims. We present the stellar properties of 2908 galaxies (1208 quiescent and 1700 star forming) at 0.6 < z < 1.0 from the Large Early Galaxy Astrophysics Census (LEGA-C) survey. We emphasize the importance of high signal-to-noise, high spectral resolution spectroscopy in the inference of stellar population properties of galaxies.

Methods. We estimated the galaxy properties with the Bayesian spectral energy distribution (SED) framework Prospector. We fit spectroscopy and broadband photometry together, drawn from the LEGA-C DR3 and UltraVISTA catalogs, respectively.

Results. We report a positive correlation between light-weighted ages and stellar velocity dispersion (σ_⋆). The trend with σ_⋆ is weaker for the mass-weighted ages and stellar metallicity (Z_⋆). At fixed σ_⋆, we find a tentative correlation between Z_⋆ and stellar age. On average, quiescent galaxies are characterized by high Z_⋆; they are ∼1.1 Gyr older, less dusty, and have steeper dust attenuation slopes (due to a lower optical depth) compared to star-forming galaxies. Conversely, star-forming galaxies are characterized by significantly higher dust optical depths and shallower (grayer) attenuation slopes. Low-mass (high-mass) star-forming galaxies have lower (higher) Z_⋆, while their stellar populations are on average younger (older). A key pragmatic result of our study is that a linear-space metallicity prior is preferable to a logarithmic-space one when using photometry alone, as the latter biases the posteriors downward.

Conclusions. Spectroscopy greatly improves stellar population measurements and is required to provide meaningful constraints on age, metallicity, and other properties. Pairing spectroscopy with photometry helps to resolve the dust–age–metallicity degeneracy. Spectroscopic data yield more accurate mass- and light-weighted ages, with ages inferred from photometry alone suffering such large uncertainties that their utility is limited. Stellar metallicities are constrained by our spectroscopy, but precise measurements remain challenging (and impossible with photometry alone), particularly in the absence of Mg and Fe lines redward of 5000 Å in the observed spectrum.