Hα and Continuum Sizes with the HST/WFC3 G141 GRISM: Outside-in Quenching for z = 1.0–1.4 Fast Quenchers

Abstract

We investigate the evolution of the physical extent of star formation of M ⋆ > 109 M ⊙ rapidly quenching galaxies at z = 1.0–1.4. We measure the galaxy Hα and stellar continuum sizes from their HST/WFC3 G141 grism spectroscopy and connect the galaxy sizes to time on their evolutionary delayed–τ tracks determined in Noirot et al. Most galaxies (10/13) have non-evolving Hα-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 Hα 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 toward the red sequence.