SQuIGG$\vec{L}$E: Spatially resolved NIRSpec Pa$α$ reveals that the most CO-luminous, $z\sim0.7$ post-starburst galaxies exhibit falling---but still active---star formation behind optically thick dust
Abstract
One of the fundamental uncertainties in the study of galaxies at the interface between star formation and quiescence--post-starburst galaxies--is their instantaneous star formation rate. While these galaxies appear quiescent in the rest UV-optical, many of the youngest systems are highly CO luminous, implying dense molecular gas, and potentially star formation. However, their instantaneous star formation rates have proved elusive, as measurements with rest-optical emission lines or UV-to-IR SED fitting yield order-of-magnitude uncertainty. Here, we present JWST/NIRSpec G395M/170LP integral field spectroscopy of the three most CO-luminous massive galaxies in the SQuIGG$\vec{L}$E survey, spatially resolving Pa$α$/Br$γ$/Br$β$ to map the dust-corrected star formation rate. We find that these galaxies host star formation rates of $27-80$ $M_\odot \ \mathrm{yr^{-1}}$, though $\sim30-40\%$ of the emission may arise from non-star-forming ionization (AGN or shocks), implied by high [FeII]/Pa$α$ in central spaxels. We also find effective $A_{\mathrm{Pa}α}\sim1$ and individual $\sim700$ pc spaxels with $A_{\mathrm{Paα}}\sim2$, implying significant dust obscuration of nebular regions that contribute little to the rest-optical lines. These galaxies are not consistent with total quiescence; the measured star formation rates place these galaxies on or above the main sequence. However, their star formation rates \textit{are} significantly lower ($\sim0.5-1$ dex) than the peak star formation rates inferred from spectrophotometric fitting. We propose that the CO luminous post-starburst phase represents the last gasp of star formation in galaxies on the rapid quenching pathway, and that dust-obscured star formation, outflows, and (speculatively) an uncertain CO-to-H2 conversion reconcile their gas exhaustion with observed timescales of fading.
Authors 16
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Affiliation as printed
Department of Astrophysical Sciences , Princeton University , 4 Ivy Lane , Princeton , NJ 08544 , USA
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Affiliation as printed
Department of Astrophysical Sciences , Princeton University , 4 Ivy Lane , Princeton , NJ 08544 , USA
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Affiliation as printed
Department of Physics and Astronomy and PITT PACC , University of Pittsburgh , Pittsburgh , PA 15260 , USA
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University of Colorado Boulder
Affiliation as printed
Department for Astrophysical & Planetary Science , University of Colorado , Boulder , CO 80309 , USA
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Affiliation as printed
Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy , Texas A&M University , 4242 TAMU , College Station , TX 77843-4242 , US
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Affiliation as printed
Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy , Texas A&M University , 4242 TAMU , College Station , TX 77843-4242 , US
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Affiliation as printed
Department of Astronomy , University of Geneva , Chemin Pegasi 51 , Versoix CH-1290 , Switzerland
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Affiliation as printed
Department of Astrophysics , Universität Zürich , Winterthurerstrasse 190 , Zurich CH-8057 , Switzerland
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Affiliation as printed
Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy , Texas A&M University , 4242 TAMU , College Station , TX 77843-4242 , US
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Affiliation as printed
Department of Astrophysical Sciences , Princeton University , 4 Ivy Lane , Princeton , NJ 08544 , USA
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory , Leiden University , P.O. Box 9513 , 2300 RA Leiden , The Netherlands
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Rochester Institute of Technology
Affiliation as printed
Laboratory for Multiwavelength Astrophysics , School of Physics and Astronomy , Rochester Institute of Technology , 84 Lomb Memorial Drive , Rochester , NY 14623 , USA
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Affiliation as printed
Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy , Texas A&M University , 4242 TAMU , College Station , TX 77843-4242 , US
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Affiliation as printed
Department of Astronomy , University of Florida , 211 Bryant Space
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University of Illinois Urbana-Champaign · National Center for Supercomputing Applications
Affiliation as printed
Center for AstroPhysical Surveys , National Center for Supercomputing Applications , 1205 West Clark Street , Urbana , IL 61801 , USA
University of Illinois Urbana-Champaign Department of Astronomy , University of Illinois , 1002 W. Green St. , Urbana , IL 61801 , USA
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