UVCANDELS: The role of dust on the stellar mass-size relation of disk galaxies at 0.5 $\leq z \leq$ 3.0

TL;DR

This study uses ultraviolet and optical imaging to analyze the size and dust effects on disk galaxies across redshifts 0.5 to 3, revealing dust's significant role in size measurements and challenging the inside-out growth interpretation.

Contribution

It demonstrates that dust attenuation can explain size differences in galaxy measurements, questioning previous inside-out growth assumptions.

Findings

Dust can account for size differences at z=2.

The stellar mass-size relation is steeper in UV than optical.

Massive, dusty galaxies drive the size relation slope.

Abstract

We use the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields (UVCANDELS) to measure half-light radii in the rest-frame far-UV for $\sim$16,000 disk-like galaxies over $0.5\leq z \leq 3$. We compare these results to rest-frame optical sizes that we measure in a self-consistent way and find that the stellar mass-size relation of disk galaxies is steeper in the rest-frame UV than in the optical across our entire redshift range. We show that this is mainly driven by massive galaxies ($\gtrsim10^{10}$M$_\odot$), which we find to also be among the most dusty. Our results are consistent with the literature and have commonly been interpreted as evidence of inside-out growth wherein galaxies form their central structures first. However, they could also suggest that the centers of massive galaxies are more heavily attenuated than their outskirts. We distinguish between these scenarios by modeling and selecting galaxies at $z=2$ from the VELA simulation suite in a way that is consistent with UVCANDELS. We show that the effects of dust alone can account for the size differences we measure at $z=2$. This indicates that, at different wavelengths, size differences and the different slopes of the stellar mass-size relation do not constitute evidence for inside-out growth.