ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies
We present ^12 CO( J = 1 – 0) mapping observations over ∼1/2 of the optical disk of 12 nearby galaxies from the Fundamental CO 1–0 Transition Survey of nearby galaxies (FACTS), using the ALMA Total Power array. Variations in the ^12 CO( J = 2 − 1)/ ^12 CO( J = 1 − 0) line ratio r _21 are investig...
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2025-01-01
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| author | Shinya Komugi Tsuyoshi Sawada Jin Koda Fumi Egusa Fumiya Maeda Akihiko Hirota Amanda M. Lee |
| author_facet | Shinya Komugi Tsuyoshi Sawada Jin Koda Fumi Egusa Fumiya Maeda Akihiko Hirota Amanda M. Lee |
| author_sort | Shinya Komugi |
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| description | We present ^12 CO( J = 1 – 0) mapping observations over ∼1/2 of the optical disk of 12 nearby galaxies from the Fundamental CO 1–0 Transition Survey of nearby galaxies (FACTS), using the ALMA Total Power array. Variations in the ^12 CO( J = 2 − 1)/ ^12 CO( J = 1 − 0) line ratio r _21 are investigated. The luminosity-weighted r _21 of the 11 sample galaxies ranges from 0.52 to 0.69 with an average of 0.61. We use position–velocity diagrams along the major axis and tilted ring models to separate the normal rotating galactic disk from kinematic outliers that deviate from pure circular rotation. We find that r _21 is systematically higher in outliers compared to the disk. We compare r _21 between SA, SAB, and SB galaxies, and find no significant difference in the average r _21 depending on the presence of galactic bars. We find, however, that the radial gradient in r _21 is bimodal, where a group containing all SA galaxies prefer constant or very shallow r _21 gradients out to 40% of the optical radius, while another group containing all SB galaxies have a steep r _21 gradient, decreasing by ∼20% before 40% of the optical radius, which also corresponds to the radius of the stellar bar. After this radius, these galaxies become consistent with a constant or shallow trend in r _21 . The large scale trend in r _21 can have implications for how we interpret observations made solely in the ^12 CO( J = 2 − 1) line. |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-7680a39736ff4a9c94e84941fdb290132025-02-07T16:19:38ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01980112610.3847/1538-4357/ada6b5ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby GalaxiesShinya Komugi0https://orcid.org/0009-0007-2493-0973Tsuyoshi Sawada1https://orcid.org/0000-0002-0588-5595Jin Koda2https://orcid.org/0000-0002-8762-7863Fumi Egusa3https://orcid.org/0000-0002-1639-1515Fumiya Maeda4https://orcid.org/0000-0002-8868-1255Akihiko Hirota5https://orcid.org/0000-0002-0465-5421Amanda M. Lee6https://orcid.org/0000-0001-8254-6768Division of Liberal Arts, Kogakuin University , 2665-1 Nakano-cho, Hachioji, Tokyo 192-0015, Japan ; [email protected]; National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Department of Physics and Astronomy, Stony Brook University , Stony Brook, NY 11794-3800, USANational Astronomical Observatory of Japan , Los Abedules 3085 Office 701, Vitacura, Santiago 763 0414, Chile; Joint ALMA Observatory , Alonso de Córdova 3107, Vitacura, Santiago 763 0355, ChileDepartment of Physics and Astronomy, Stony Brook University , Stony Brook, NY 11794-3800, USAInstitute of Astronomy, Graduate School of Science, The University of Tokyo , 2-21-1 Osawa, Mitaka, Tokyo 181-0015, JapanResearch Center for Physics and Mathematics, Osaka Electro-Communication University , 18-8 Hatsucho, Neyagawa, Osaka, 572-8530, JapanNational Astronomical Observatory of Japan , Los Abedules 3085 Office 701, Vitacura, Santiago 763 0414, Chile; Joint ALMA Observatory , Alonso de Córdova 3107, Vitacura, Santiago 763 0355, ChileDepartment of Physics and Astronomy, Stony Brook University , Stony Brook, NY 11794-3800, USAWe present ^12 CO( J = 1 – 0) mapping observations over ∼1/2 of the optical disk of 12 nearby galaxies from the Fundamental CO 1–0 Transition Survey of nearby galaxies (FACTS), using the ALMA Total Power array. Variations in the ^12 CO( J = 2 − 1)/ ^12 CO( J = 1 − 0) line ratio r _21 are investigated. The luminosity-weighted r _21 of the 11 sample galaxies ranges from 0.52 to 0.69 with an average of 0.61. We use position–velocity diagrams along the major axis and tilted ring models to separate the normal rotating galactic disk from kinematic outliers that deviate from pure circular rotation. We find that r _21 is systematically higher in outliers compared to the disk. We compare r _21 between SA, SAB, and SB galaxies, and find no significant difference in the average r _21 depending on the presence of galactic bars. We find, however, that the radial gradient in r _21 is bimodal, where a group containing all SA galaxies prefer constant or very shallow r _21 gradients out to 40% of the optical radius, while another group containing all SB galaxies have a steep r _21 gradient, decreasing by ∼20% before 40% of the optical radius, which also corresponds to the radius of the stellar bar. After this radius, these galaxies become consistent with a constant or shallow trend in r _21 . The large scale trend in r _21 can have implications for how we interpret observations made solely in the ^12 CO( J = 2 − 1) line.https://doi.org/10.3847/1538-4357/ada6b5Galaxy disksMolecular gasCO line emission |
| spellingShingle | Shinya Komugi Tsuyoshi Sawada Jin Koda Fumi Egusa Fumiya Maeda Akihiko Hirota Amanda M. Lee ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies The Astrophysical Journal Galaxy disks Molecular gas CO line emission |
| title | ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies |
| title_full | ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies |
| title_fullStr | ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies |
| title_full_unstemmed | ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies |
| title_short | ALMA FACTS. II. Large Scale Variations in the 12CO(J = 2 – 1) to 12CO(J = 1 – 0) Line Ratio in Nearby Galaxies |
| title_sort | alma facts ii large scale variations in the 12co j 2 1 to 12co j 1 0 line ratio in nearby galaxies |
| topic | Galaxy disks Molecular gas CO line emission |
| url | https://doi.org/10.3847/1538-4357/ada6b5 |
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