Massive quiescent galaxies grow in size after they stop forming stars — but the effects of the environment on how they grow is debated. In field environments, the growth happens through 2 channels: minor mergers that build an extended low-density envelope, and/or new arrivals (recently-quenched larger galaxies dropping into the quiescent population) inflating the median size without any individual galaxy growing. However, is it true in the dense regions like galaxy clusters?
Using the same CLAUDS+HSC pipeline I built for George et al., 2024 (George et al., 2024), I compared quiescent galaxies (QGs) in the cores of massive clusters (HSC-SSP cluster catalogues) with field galaxies at matched mass and redshift. The result, in ApJ 2025: environment significantly impacts QG size evolution, with QGs in cluster cores generally showing different size-mass relations (SMR) but similar size growth compared to field galaxies. QGs inthe densest cluster environments are consistently found to be smaller in size compared to their counterparts in the field. This difference is more pronounced in the rest-frame UV light. Cluster QGs are typically smaller than field counterparts at a given mass due to dense, high-velocity environments, yet they grow in size by accretion and environmental quenching of “newcomer” galaxies.
Published in ApJ 987, 45 (2025) (George et al., 2025).
Redshift evolution of the characteristic sizes of cluster and field QGs in rest-frame UV and optical wavelengths. Re are characteristic sizes of log M = 10.7 galaxies and are taken from the SMR fits. The best-fitting power-law functions are plotted as solid curves, with their uncertainties shown as shaded regions. Left: The first panel compares the size evolution of field QGs in UV (orange squares) and optical (maroon diamonds). The second panel compares the same for cluster QGs in UV (red pentagons) and optical (brown circles). Right: The first panel depicts the size evolution of field and cluster QGs in the rest-frame UV and the second panel illustrates the same in the rest-frame optical. The rest of the details are the same as in the left panels.
References
2025
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Effects of Environment on the Size Evolution of Quiescent Galaxies: Comparing Galaxies in Clusters and in the Field at Two Rest-frame Wavelengths
Angelo George, Ivana Damjanov, Marcin Sawicki, and 7 more authors
The Astrophysical Journal, 2025
Milky Way-mass quiescent galaxies in cluster cores are smaller than their field counterparts, and the difference is more pronounced in the rest-frame UV than in the optical.
2024
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Two rest-frame wavelength measurements of galaxy sizes at z<1: the evolutionary effects of emerging bulges and quenched newcomers
Angelo George, Ivana Damjanov, Marcin Sawicki, and 6 more authors
Monthly Notices of the Royal Astronomical Society, 2024
Comparing rest-frame UV and optical sizes of galaxies in COSMOS reveals that the apparent size growth of quiescent galaxies since z ∼ 1 is driven mainly by minor mergers and in part by the arrival of newly quenched, larger systems. The size evolution of star-forming galaxies is shaped by the bulge growth.
