Stellar masses, sizes, and radial profiles for 465 nearby early-type galaxies: an extension to the Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G)

TL;DR

This paper extends the Spitzer Survey of Stellar Structure in Galaxies by adding 465 early-type galaxies, providing detailed near-infrared profiles, derived properties, and scaling relations to improve understanding of galaxy structures.

Contribution

It presents a comprehensive data release and analysis of early-type galaxies within the S$^{4}$G, including surface photometry and scaling relations, filling a bias in the original survey.

Findings

ETGs are more massive and concentrated than LTGs.

Good agreement with previous mass--size and mass--concentration relations.

Subtle differences among ETG sub-types.

Abstract

The Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G) is a detailed study of over 2300 nearby galaxies in the near-infrared (NIR), which has been critical to our understanding of the detailed structures of nearby galaxies. Because the sample galaxies were selected only using radio-derived velocities, however, the survey favored late-type disk galaxies over lenticulars and ellipticals. A follow-up Spitzer survey was conducted to rectify this bias, adding 465 early-type galaxies (ETGs) to the original sample, to be analyzed in a manner consistent with the initial survey. We present the data release of this ETG extension, up to the third data processing pipeline (P3): surface photometry. We produce curves of growth and radial surface brightness profiles (with and without inclination corrections) using reduced and masked Spitzer IRAC 3.6$\mu$m and 4.5$\mu$m images produced through Pipelines 1 and 2, respectively. From these profiles, we derive the following integrated quantities: total magnitudes, stellar masses, concentration parameters, and galaxy size metrics. We showcase NIR scaling relations for ETGs among these quantities. We examine general trends across the whole S$^{4}$G and ETG extension among our derived parameters, highlighting differences between ETGs and late-type galaxies (LTGs). ETGs are, on average, more massive and more concentrated than LTGs, and also show subtle distinctions among ETG morphological sub-types. We also derive the following scaling relations and compare with previous results in visible light: mass--size (both half-light and isophotal), mass--concentration, mass--surface brightness (central, effective, and within 1 kpc), and mass--color. We find good agreement with previous works, though some relations (e.g., mass--central surface brightness) will require more careful multi-component decompositions to be fully understood.