Work

Small and Complex. I. The Three-component Structure of z ∼ 0 Massive Compact Quiescent Galaxies

Year: 2026

Type: article

Abstract: We investigate the morphology and structural properties of 246 massive compact quiescent galaxies (MCGs; log M ⋆ ∼ 10 –11, σ e ∼ 150–350 km s −1 , R e ∼ 0.7–2.5 kpc) at z ∼ 0, selected as outliers in the stellar mass–velocity dispersion and velocity dispersion–size relations, using g -, r -, and i -band Hyper Suprime-Cam images. We compare them to a control sample of average-sized quiescent galaxies (CSGs) matched in stellar mass, star formation rate, redshift, and g − i color. Both samples are dominated by S0 galaxies, comprising 93% of MCGs and 71% of CSGs, while ellipticals account for 4% and 11%, respectively. The fraction of interacting or morphologically disturbed systems is low in both samples (13% for MCGs and 16% for CSGs). Multicomponent decompositions of the g - and r -band images show that 75% of MCGs require a three-component model (bulge, disk, and envelope), while 21% are best fit by two components and 4% by a single Sérsic profile. Two-component MCGs are preferentially low-inclination systems, suggesting that the three-component fraction represents a lower limit. In contrast, only 7% of CSGs exhibit a comparable three-component structure. Bars are present in 29% of CSGs but are absent in MCGs. For three-component systems, MCGs and CSGs have similar bulge ( R e = 0.39 versus 0.45 kpc) and envelope ( R e = 6.4 versus 5.8 kpc) sizes, while MCG disks are significantly more compact ( R e = 1.9 versus 3.3 kpc). The envelope component shows a broad ellipticity distribution ( ϵ Envelope ∼ 0.0–0.6), which we interpret as corresponding to either a stellar halo or a thick disk.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/ae9e25