分类： 天文学 >> 天文学 提交时间： 2023-02-19
K. Decker French
Adam Smercina
Kate Rowlands
Akshat Tripathi
Ann I. Zabludoff
J. D. Smith
Desika Narayanan
Yujin Yang
Yancy Shirley
Katey Alatalo
摘要： The molecular gas in galaxies traces both the fuel for star formation and the processes that can enhance or suppress star formation. Observations of the molecular gas state can thus point to when and why galaxies stop forming stars. In this study, we present ALMA observations of the molecular gas in galaxies evolving through the post-starburst phase. These galaxies have low current star formation rates, regardless of the SFR tracer used, with recent starbursts ending within the last 600 Myr. We present CO (3-2) observations for three post-starburst galaxies, and dense gas HCN/HCO+/HNC (1-0) observations for six (four new) post-starburst galaxies. The post-starbursts have low excitation traced by the CO spectral line energy distribution (SLED) up to CO (3-2), more similar to early-type than starburst galaxies. The low excitation indicates that lower density rather than high temperatures may suppress star formation during the post-starburst phase. One galaxy displays a blueshifted outflow traced by CO (3-2). MaNGA observations show that the ionized gas velocity is disturbed relative to the stellar velocity field, with a blueshifted component aligned with the molecular gas outflow, suggestive of a multiphase outflow. Low ratios of HCO+/CO, indicating low fractions of dense molecular gas relative to the total molecular gas, are seen throughout post-starburst phase, except for the youngest post-starburst galaxy considered here. These observations indicate that the impact of any feedback or quenching processes may be limited to low excitation and weak outflows in the cold molecular gas during the post-starburst phase.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Justin Atsushi Otter
Kate Rowlands
Katherine Alatalo
Ho-Hin Leung
Vivienne Wild
Yuanze Luo
Andreea O. Petric
Elizaveta Sazonova
David V. Stark
Timothy Heckman
Timothy A. Davis
Sara Ellison
K. Decker French
William Baker
Asa F. L. Bluck
Lauranne Lanz
Lihwai Lin
Charles Liu
Carlos López Cobá
Karen L. Masters
摘要： Post-starburst galaxies (PSBs) have recently and rapidly quenched their star-formation, thus they are an important way to understand how galaxies transition from star-forming late-types to quiescent early-types. The recent discovery of large cold gas reservoirs in PSBs calls into question the theory that galaxies must lose their gas to become quiescent. Optical Integral Field Spectroscopy (IFS) surveys have revealed two classes of PSBs: central PSBs with central quenching regions and ring PSBs with quenching in their outskirts. We analyze a sample of 13 nearby (z < 0.1) PSBs with spatially resolved optical IFS data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey and matched resolution Atacama Large (sub-)Millimeter Array (ALMA) observations of $^{12}$CO(1-0). Disturbed stellar kinematics in 7/13 of our PSBs and centrally concentrated molecular gas is consistent with a recent merger for most of our sample. In galaxies without merger evidence, alternate processes may funnel gas inwards and suppress star-formation, which may include outflows, stellar bars, and minor mergers or interactions. The star-formation efficiencies of the post-starburst regions in nearly half our galaxies are suppressed while the gas fractions are consistent with star-forming galaxies. AGN feedback may drive this stabilization, and we observe AGN-consistent emission in the centers of 5/13 galaxies. Finally, our central and ring PSBs have similar properties except the ionized and molecular gas in central PSBs is more disturbed. Overall, the molecular gas in our PSBs tends to be compact and highly disturbed, resulting in concentrated gas reservoirs unable to form stars efficiently.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yuanze Luo
Kate Rowlands
Katherine Alatalo
Elizaveta Sazonova
Abdurro'uf
Timothy Heckman
Anne M. Medling
Susana E. Deustua
Kristina Nyland
Lauranne Lanz
Andreea O. Petric
Justin A. Otter
Susanne Aalto
Sabrina Dimassimo
K. Decker French
John S. Gallagher
Joel C. Roediger
Sofia Stepanoff
摘要： We present a multiwavelength study of IC 860, a nearby post-starburst galaxy at the early stage of transitioning from blue and star-forming to red and quiescent. Optical images reveal a galaxy-wide, dusty outflow originating from a compact core. We find evidence for a multiphase outflow in the molecular and neutral gas phase from the CO position-velocity diagram and NaD absorption features. We constrain the neutral mass outflow rate to be ~0.5 M$_{\odot}/$yr, and the total hydrogen mass outflow rate to be ~12 M$_{\odot}$/yr. Neither outflow component seems able to escape the galaxy. We also find evidence for a recent merger in the optical images, CO spatial distribution, and kinematics, and evidence for a buried AGN in the optical emission line ratios, mid-IR properties, and radio spectral shape. The depletion time of the molecular gas reservoir under the current star formation rate is ~7 Gyr, indicating that the galaxy could stay at the intermediate stage between the blue and red sequence for a long time. Thus the timescales for a significant decline in star formation rate ("quenching") and gas depletion are not necessarily the same. Our analysis supports the quenching picture where outflows help suppress star formation by disturbing rather than expelling the gas and shed light on possible ongoing activities in similar quenching galaxies.
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