NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-08-17 T06:49:52 PDT
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For refcode 2015MNRAS.450.3874A:
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Copyright by Royal Astronomical Society. 2015MNRAS.450.3874A Evidence of boosted ^13^CO/^12^CO ratio in early-type galaxies in dense environments Alatalo, Katherine; Crocker, Alison F.; Aalto, Susanne; Davis, Timothy A.; Nyland, Kristina; Bureau, Martin; Duc, Pierre-Alain; Krajnovic, Davor; Young, Lisa M. Abstract. We present observations of ^13^CO(1-0) in 17 Combined Array for Research in Millimeter Astronomy ATLAS^3D^ early-type galaxies (ETGs), obtained simultaneously with ^12^CO(1-0) observations. The ^13^CO in six ETGs is sufficiently bright to create images. In these six sources, we do not detect any significant radial gradient in the ^13^CO/^12^CO ratio between the nucleus and the outlying molecular gas. Using the ^12^CO channel maps as 3D masks to stack the ^13^CO emission, we are able to detect 15/17 galaxies to >3sigma (and 12/17 to at least 5sigma) significance in a spatially integrated manner. Overall, ETGs show a wide distribution of ^13^CO/^12^CO ratios, but Virgo cluster and group galaxies preferentially show a ^13^CO/^12^CO ratio about two times larger than field galaxies, although this could also be due to a mass dependence, or the CO spatial extent (R_CO_/R_e_). ETGs whose gas has a morphologically settled appearance also show boosted ^13^CO/^12^CO ratios. We hypothesize that this variation could be caused by (i) the extra enrichment of gas from molecular reprocessing occurring in low-mass stars (boosting the abundance of ^13^C to ^12^C in the absence of external gas accretion), (II) much higher pressure being exerted on the mid-plane gas (by the intracluster medium) in the cluster environment than in isolated galaxies, or (III) all but the densest molecular gas clumps being stripped as the galaxies fall into the cluster. Further observations of ^13^CO in dense environments, particularly of spirals, as well as studies of other isotopologues, should be able to distinguish between these hypotheses. Key words: galaxies: clusters: general, galaxies: elliptical and lenticular, cD, galaxies: ISM
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