How Massive are Massive Compact Galaxies?

TL;DR

This study examines how assumptions in spectral energy distribution modeling influence stellar mass estimates of massive compact galaxies at z~2.3, revealing they are significantly smaller than local counterparts regardless of modeling choices.

Contribution

It systematically evaluates the impact of different SED modeling assumptions, including stellar populations and IMF, on mass estimates of high-redshift compact galaxies.

Findings

Mass estimates vary by up to 0.18 dex with different models.

Two-component models can increase mass estimates by 0.08 to 0.22 dex.

Galaxies are 3-9 times smaller than local mass-size relation, regardless of assumptions.

Abstract

Using a sample of nine massive compact galaxies at z ~ 2.3 with rest-frame optical spectroscopy and comprehensive U through 8um photometry we investigate how assumptions in SED modeling change the stellar mass estimates of these galaxies, and how this affects our interpretation of their size evolution. The SEDs are fit to Tau-models with a range of metallicities, dust laws, as well as different stellar population synthesis codes. These models indicate masses equal to, or slightly smaller than our default masses. The maximum difference is 0.16 dex for each parameter considered, and only 0.18 dex for the most extreme combination of parameters. Two-component populations with a maximally old stellar population superposed with a young component provide reasonable fits to these SEDs using the models of Bruzual & Charlot (2003); however, using models with updated treatment of TP-AGB stars the fits are poorer. The two-component models predict masses that are 0.08 to 0.22 dex larger than the Tau-models. We also test the effect of a bottom-light IMF and find that it would reduce the masses of these galaxies by 0.3 dex. Considering the range of allowable masses from the Tau-models, two-component fits, and IMF, we conclude that on average these galaxies lie below the mass-size relation of galaxies in the local universe by a factor of 3-9, depending on the SED models used.