HST/WFC3 Grism Observations of z ∼ 1 Clusters: Evidence for Rapid Outside-in Environmental Quenching from Spatially Resolved Hα Maps
Jasleen Matharu, Adam Muzzin, Gabriel Brammer, Erica J. Nelson, Matthew W. Auger, P. C. Hewett, R. F. J. van der Burg, Michael L. Balogh, R. Demarco, Danilo Marchesini, Allison Noble, Gregory Rudnick, Arjen van der Wel, Gillian Wilson, H. K. C. Yee
Abstract
Abstract We present and publicly release ( www.gclasshst.com ) the first spatially resolved H α maps of star-forming cluster galaxies at z ∼ 1, made possible with the Wide Field Camera 3 (WFC3) G141 grism on the Hubble Space Telescope (HST). Using a similar but updated method to 3D-HST in the field environment, we stack the H α maps in bins of stellar mass, measure the half-light radius of the H α distribution, and compare it to the stellar continuum. The ratio of the H α to stellar continuum half-light radius, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>R</mml:mi> <mml:mo stretchy="false">[</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> <mml:mrow> <mml:mo stretchy="false">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo stretchy="false">]</mml:mo> <mml:mo>=</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> <mml:mo>,</mml:mo> <mml:mi>Cont</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:mfrac> </mml:mstyle> </mml:math> , is smaller in the clusters by (6 ± 9)%, but statistically consistent within 1 σ uncertainties. A negligible difference in R [H α /C] with environment is surprising, given the higher quenched fractions in the clusters relative to the field. We postulate that the combination of high quenched fractions and no change in R [H α /C] with environment can be reconciled if environmental quenching proceeds rapidly. We investigate this hypothesis by performing similar analysis on the spectroscopically confirmed, recently quenched cluster galaxies. 87% have H α detections, with star formation rates 8 ± 1 times lower than star-forming cluster galaxies of similar stellar mass. Importantly, these galaxies have an R [H α /C] that is (81 ± 8)% smaller than coeval star-forming field galaxies at fixed stellar mass. This suggests the environmental quenching process occurred outside-in. We conclude that disk truncation due to ram pressure stripping is occurring in cluster galaxies at z ∼ 1, but more rapidly and/or efficiently than in z ≲ 0.5 clusters, such that the effects on R [H α /C] become observable just after the cluster galaxy has recently quenched.