Comparing dynamical and photometric-stellar masses of early-type galaxies atz ~ 1

Abstract

Aims. The purpose of this study is to explore the relationship between galaxy stellar masses, based on multiwavelength photometry spectral template fitting and dynamical masses based on published velocity dispersion measurements, for a sample of 48 early-type galaxies at z ∼ I with HST/ACS morphological information. Methods. We determine photometric-stellar masses and perform a quantitative morphological analysis of cluster and field galaxies at redshift 0.6 < z < 1.2, using ground- and space-based multiwavelength data available on the GOODS-S field and on the field around the X-ray luminous cluster RDCS 1252.9-2927 at z = 1.24. We use multi-band photometry over 0.4-8 μm from HST/ACS, VLT/ISAAC and Spiher/IRAC to estimate photometric-stellar masses using Composite Stellar Population (CSP) templates computed with PEGASE.2 (Fioc & Rocca-Volmerange 1997) models. We compare stellar masses with those obtained using CSPs built with Bruzual & Charlot (2003, MNRAS, 344, 1000; BC03) and Maraston (2005, MNRAS, 362, 799; M05) models. We then compare photometric-stellar mass and dynamical mass estimates as a function of morphological parameters obtained from HST/ACS imaging. Results. Based on our sample, which spans the mass range log M phot ≃ [10, 11.5], we find that 1) PEGASE.2, BC03, M05 yield consistent photometric-stellar masses for early-type galaxies at z ∼ I with a small scatter (0.15 dex rms); 2) adopting a Kroupa IMF, photometric-stellar masses match dynamical mass estimates for early-type galaxies with an average offset of 0.27 dex; 3) assuming a constant IMF, increasing dark matter fraction with the increasing galaxy mass can explain the observed trend; 4) we observe that early-type galaxies with significant disk components (Sa/Sab) or with signs of dynamical interaction tend to have the largest deviation from a one-to-one M dyn vs. M phot relation.