The ALMaQUEST Survey XII: Dense Molecular Gas as traced by HCN and HCO$^{+}$ in Green Valley Galaxies
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2024
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| author | Lin, Lihwai Pan, Hsi-An Ellison, Sara L. Harada, Nanase Jimenez-Donaire, Maria J. French, K. Decker Baker, William M. Hsieh, Bau-Ching Koyama, Yusei Lopez-Coba, Carlos Michiyama, Tomonari Rowlands, Kate Sanchez, Sebastian F. Thorp, Mallory |
| author_facet | Lin, Lihwai Pan, Hsi-An Ellison, Sara L. Harada, Nanase Jimenez-Donaire, Maria J. French, K. Decker Baker, William M. Hsieh, Bau-Ching Koyama, Yusei Lopez-Coba, Carlos Michiyama, Tomonari Rowlands, Kate Sanchez, Sebastian F. Thorp, Mallory |
| contents | We present ALMA observations of two dense gas tracers, HCN(1-0) and HCO$^{+}$(1-0), for three galaxies in the green valley and two galaxies on the star-forming main sequence with comparable molecular gas fractions as traced by the CO(1-0) emissions, selected from the ALMaQUEST survey. We investigate whether the deficit of molecular gas star formation efficiency (SFE$_{\rm mol}$) that leads to the low specific star formation rate in these green valley galaxies is due to a lack of dense gas (characterized by the dense gas fraction $f_{\rm dense}$) or the low star formation efficiency of dense gas (SFE$_{\rm dense}$). We find that SFE$_{\rm mol}$ as traced by the CO emissions, when considering both star-forming and retired spaxels together, is tightly correlated with SFE$_{\rm dense}$ and depends only weakly on $f_{\rm dense}$. The specific star formation rate (sSFR) on kpc scales is primarily driven by SFE$_{\rm mol}$ and SFE$_{\rm dense}$, followed by the dependence on $f_{\rm mol}$, and is least correlated with $f_{\rm dense}$ or the dense-to-stellar mass ratio ($R_{\rm dense}$). When compared with other works in the literature, we find that our green valley sample shows lower global SFE$_{\rm mol}$ as well as lower SFE$_{\rm dense}$ while exhibiting similar dense gas fractions when compared to star-forming and starburst galaxies. We conclude that the star formation of the 3 green valley galaxies with a normal abundance of molecular gas is suppressed mainly due to the reduced SFE$_{\rm dense}$ rather than the lack of dense gas. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2401_05976 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The ALMaQUEST Survey XII: Dense Molecular Gas as traced by HCN and HCO$^{+}$ in Green Valley Galaxies Lin, Lihwai Pan, Hsi-An Ellison, Sara L. Harada, Nanase Jimenez-Donaire, Maria J. French, K. Decker Baker, William M. Hsieh, Bau-Ching Koyama, Yusei Lopez-Coba, Carlos Michiyama, Tomonari Rowlands, Kate Sanchez, Sebastian F. Thorp, Mallory Astrophysics of Galaxies We present ALMA observations of two dense gas tracers, HCN(1-0) and HCO$^{+}$(1-0), for three galaxies in the green valley and two galaxies on the star-forming main sequence with comparable molecular gas fractions as traced by the CO(1-0) emissions, selected from the ALMaQUEST survey. We investigate whether the deficit of molecular gas star formation efficiency (SFE$_{\rm mol}$) that leads to the low specific star formation rate in these green valley galaxies is due to a lack of dense gas (characterized by the dense gas fraction $f_{\rm dense}$) or the low star formation efficiency of dense gas (SFE$_{\rm dense}$). We find that SFE$_{\rm mol}$ as traced by the CO emissions, when considering both star-forming and retired spaxels together, is tightly correlated with SFE$_{\rm dense}$ and depends only weakly on $f_{\rm dense}$. The specific star formation rate (sSFR) on kpc scales is primarily driven by SFE$_{\rm mol}$ and SFE$_{\rm dense}$, followed by the dependence on $f_{\rm mol}$, and is least correlated with $f_{\rm dense}$ or the dense-to-stellar mass ratio ($R_{\rm dense}$). When compared with other works in the literature, we find that our green valley sample shows lower global SFE$_{\rm mol}$ as well as lower SFE$_{\rm dense}$ while exhibiting similar dense gas fractions when compared to star-forming and starburst galaxies. We conclude that the star formation of the 3 green valley galaxies with a normal abundance of molecular gas is suppressed mainly due to the reduced SFE$_{\rm dense}$ rather than the lack of dense gas. |
| title | The ALMaQUEST Survey XII: Dense Molecular Gas as traced by HCN and HCO$^{+}$ in Green Valley Galaxies |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2401.05976 |