H$\alpha$ and Continuum Sizes with the HST/WFC3 G141 Grism: Outside-In Quenching for $z=1.0-1.4$ Fast Quenchers?

TL;DR

This study examines the size evolution of star-forming regions in rapidly quenching galaxies at redshifts 1.0-1.4, revealing mostly uniform star formation decline but some evidence of outside-in quenching.

Contribution

It provides the first detailed size measurements of Hα and continuum emission in high-redshift quenching galaxies, highlighting diverse quenching mechanisms.

Findings

Most galaxies show homogeneous star formation decline.

A subset exhibits outside-in quenching signatures.

Results suggest environmental factors may influence quenching modes.

Abstract

We investigate the evolution of the physical extent of star formation of $M_{\star}>10^9~M_{\odot}$ rapidly-quenching galaxies at $z=1.0-1.4$. We measure the galaxy H$\alpha$ and stellar continuum sizes from their HST/WFC3 G141 grism spectroscopy and connect the galaxy sizes to time on their evolutionary delayed-$\tau$ tracks determined in Noirot et al. (2022). Most galaxies (10/13) have non-evolving H$\alpha$-to-continuum size-ratios consistent with unity within the measurement uncertainties, suggesting an homogeneous decline of star-formation in these galaxies despite a rapid shut-down of their star formation. On the other hand, a handful (3/13) show statistically smaller H$\alpha$ sizes compared to the stellar continuum as they age and approach the blue-cloud/red-sequence transition region. This suggests an outside-in shut-down of the star-formation (potentially driven by environmental mechanisms) in these rapidly evolving galaxies as they move from the blue cloud towards the red sequence.