The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82
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| Format: | Preprint |
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2025
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| author | Wang, Jian-Fa Gao, Yu Tan, Qing-Hua Jiang, Xue-Jian Ji, Li Zhang, Zhi-Yu Wang, Jun-Zhi Wang, Jun-Feng Greve, R. Thomas Jiang, Yan Bemis, Ashley Brinks, Elias Chung, Aeree Currie, J. Malcolm de Grijs, Richard Fang, Taotao Ho, C. Luis Lee, Bumhyun Matsushita, Satoki Michałowski, Michał Pak, Soojong Poojon, Panomporn Rawlings, G. Mark Saintonge, Amelie Sun, Yi-Chen Zhou, Jing |
| author_facet | Wang, Jian-Fa Gao, Yu Tan, Qing-Hua Jiang, Xue-Jian Ji, Li Zhang, Zhi-Yu Wang, Jun-Zhi Wang, Jun-Feng Greve, R. Thomas Jiang, Yan Bemis, Ashley Brinks, Elias Chung, Aeree Currie, J. Malcolm de Grijs, Richard Fang, Taotao Ho, C. Luis Lee, Bumhyun Matsushita, Satoki Michałowski, Michał Pak, Soojong Poojon, Panomporn Rawlings, G. Mark Saintonge, Amelie Sun, Yi-Chen Zhou, Jing |
| contents | We present observations of HCN J=4-3 and HCO^+ J=4-3 lines obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey, combined with archival HCN J=1-0 and HCO^+ J=1-0 data from the Green Bank Telescope, to study the spatial distribution and excitation conditions of dense molecular gas in the disk of M82. We detect HCN J=4-3 and HCO^+ J=4-3 emission within the central region (< 500 pc) of the galaxy, while the J=1-0 emission lines exhibit a more extended spatial distribution (> 700 pc). The dense gas shows a clear double-lobed structure in both spatial distribution and kinematics, with the HCN and HCO^+ J=4-3 lines in the southwest lobe blueshifted by ~ 40 km/s relative to the J=1-0 lines. The HCN J=4-3/1-0 and HCO^+ J=4-3/1-0 line-luminosity ratios range from 0.09 to 0.53 and from 0.14 to 0.87, respectively, with mean values of 0.18 +/- 0.04 and 0.36 +/- 0.06. The HCN ratio is lower than the typical average observed in nearby star-forming galaxies, whereas the HCO^+ ratio is comparatively higher, suggesting that the high-J HCN emission in M82 is significantly sub-thermally excited. Spatially, the peak values of the J=4-3/1-0 ratios are found in the northwest region of M82, coinciding with the galaxy-scale outflow. Elevated HCN/HCO^+ ratios are also detected in roughly the same area, potentially tracing local excitation enhancements driven by the outflow. The HCN/HCO^+ J=4-3 ratio across all detected regions ranges from 0.19 to 1.07 with a mean value of 0.41 +/- 0.11, which is significantly lower than the average J=1-0 ratio of 0.76 +/- 0.08. Both ratios are significantly lower than the average values observed in nearby star-forming galaxies, which could be related to the relatively low gas density and the presence of an extended photo-dissociation region in M82. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_20479 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82 Wang, Jian-Fa Gao, Yu Tan, Qing-Hua Jiang, Xue-Jian Ji, Li Zhang, Zhi-Yu Wang, Jun-Zhi Wang, Jun-Feng Greve, R. Thomas Jiang, Yan Bemis, Ashley Brinks, Elias Chung, Aeree Currie, J. Malcolm de Grijs, Richard Fang, Taotao Ho, C. Luis Lee, Bumhyun Matsushita, Satoki Michałowski, Michał Pak, Soojong Poojon, Panomporn Rawlings, G. Mark Saintonge, Amelie Sun, Yi-Chen Zhou, Jing Astrophysics of Galaxies We present observations of HCN J=4-3 and HCO^+ J=4-3 lines obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey, combined with archival HCN J=1-0 and HCO^+ J=1-0 data from the Green Bank Telescope, to study the spatial distribution and excitation conditions of dense molecular gas in the disk of M82. We detect HCN J=4-3 and HCO^+ J=4-3 emission within the central region (< 500 pc) of the galaxy, while the J=1-0 emission lines exhibit a more extended spatial distribution (> 700 pc). The dense gas shows a clear double-lobed structure in both spatial distribution and kinematics, with the HCN and HCO^+ J=4-3 lines in the southwest lobe blueshifted by ~ 40 km/s relative to the J=1-0 lines. The HCN J=4-3/1-0 and HCO^+ J=4-3/1-0 line-luminosity ratios range from 0.09 to 0.53 and from 0.14 to 0.87, respectively, with mean values of 0.18 +/- 0.04 and 0.36 +/- 0.06. The HCN ratio is lower than the typical average observed in nearby star-forming galaxies, whereas the HCO^+ ratio is comparatively higher, suggesting that the high-J HCN emission in M82 is significantly sub-thermally excited. Spatially, the peak values of the J=4-3/1-0 ratios are found in the northwest region of M82, coinciding with the galaxy-scale outflow. Elevated HCN/HCO^+ ratios are also detected in roughly the same area, potentially tracing local excitation enhancements driven by the outflow. The HCN/HCO^+ J=4-3 ratio across all detected regions ranges from 0.19 to 1.07 with a mean value of 0.41 +/- 0.11, which is significantly lower than the average J=1-0 ratio of 0.76 +/- 0.08. Both ratios are significantly lower than the average values observed in nearby star-forming galaxies, which could be related to the relatively low gas density and the presence of an extended photo-dissociation region in M82. |
| title | The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2506.20479 |