SQuIGG$\vec{L}$E: Observational Evidence of Low Ongoing Star Formation Rates in Gas-Rich Post-Starburst Galaxies
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2025
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| author | Zhu, Pengpei Suess, Katherine A. Kriek, Mariska Setton, David J. Bezanson, Rachel Donofrio, Vincenzo Feldmann, Robert Goulding, Andy D. Greene, Jenny E. Narayanan, Desika Spilker, Justin |
| author_facet | Zhu, Pengpei Suess, Katherine A. Kriek, Mariska Setton, David J. Bezanson, Rachel Donofrio, Vincenzo Feldmann, Robert Goulding, Andy D. Greene, Jenny E. Narayanan, Desika Spilker, Justin |
| contents | ALMA observations have shown that candidate "post-starburst" galaxies (PSBs) at z$\sim$0.6 can retain significant molecular gas reservoirs. These results would imply that -- unlike many model predictions -- galaxies can shut down their star formation before their cold gas reservoirs are depleted. However, these studies inferred star formation rates (SFRs) either from [O II] line fluxes or from spectral energy distribution modeling, and could have missed large dust-obscured contributions to the SFRs. In this study, we present Keck/NIRES observations of 13 massive ($\mathrm{M_*}\gtrsim \times 10^{11} \,\, \mathrm{M_\odot}$) PSBs, which allow us to estimate $\mathrm{Hα}$ SFRs in these gas-rich post-starburst galaxies. We confirm the previously inferred low SFRs for the majority of the sample: 11/13 targets show clear $\mathrm{Hα}$ absorption, with minimal infilling indicating dust-corrected SFRs of $<4.1 \,\mathrm{M_\odot\, yr^{-1}}$. These SFRs are notably low given the large $\mathrm{H_2}$ reservoirs ($\sim 1-5 \times 10^{10} \,\, \mathrm{M_\odot}$) present in 5/13 of these galaxies, placing them significantly offset from star-forming galaxies on the Kennicutt-Schmidt relation for star-forming galaxies. The [N II]/H$α$ ratios of all 13 PSBs imply contributions from non-star-forming ionization mechanisms (e.g., AGN, shocks, or hot evolved stars) to their $\mathrm{Hα}$ emission, suggesting that even these low ongoing SFRs may be overestimated. These low $\mathrm{Hα}$ SFRs, dust-corrected using A$_v$ estimates from SED fitting, confirm that these galaxies are very likely quiescent and, thus, that galaxies can quench before their cold gas reservoirs are fully depleted. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2501_16459 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | SQuIGG$\vec{L}$E: Observational Evidence of Low Ongoing Star Formation Rates in Gas-Rich Post-Starburst Galaxies Zhu, Pengpei Suess, Katherine A. Kriek, Mariska Setton, David J. Bezanson, Rachel Donofrio, Vincenzo Feldmann, Robert Goulding, Andy D. Greene, Jenny E. Narayanan, Desika Spilker, Justin Astrophysics of Galaxies ALMA observations have shown that candidate "post-starburst" galaxies (PSBs) at z$\sim$0.6 can retain significant molecular gas reservoirs. These results would imply that -- unlike many model predictions -- galaxies can shut down their star formation before their cold gas reservoirs are depleted. However, these studies inferred star formation rates (SFRs) either from [O II] line fluxes or from spectral energy distribution modeling, and could have missed large dust-obscured contributions to the SFRs. In this study, we present Keck/NIRES observations of 13 massive ($\mathrm{M_*}\gtrsim \times 10^{11} \,\, \mathrm{M_\odot}$) PSBs, which allow us to estimate $\mathrm{Hα}$ SFRs in these gas-rich post-starburst galaxies. We confirm the previously inferred low SFRs for the majority of the sample: 11/13 targets show clear $\mathrm{Hα}$ absorption, with minimal infilling indicating dust-corrected SFRs of $<4.1 \,\mathrm{M_\odot\, yr^{-1}}$. These SFRs are notably low given the large $\mathrm{H_2}$ reservoirs ($\sim 1-5 \times 10^{10} \,\, \mathrm{M_\odot}$) present in 5/13 of these galaxies, placing them significantly offset from star-forming galaxies on the Kennicutt-Schmidt relation for star-forming galaxies. The [N II]/H$α$ ratios of all 13 PSBs imply contributions from non-star-forming ionization mechanisms (e.g., AGN, shocks, or hot evolved stars) to their $\mathrm{Hα}$ emission, suggesting that even these low ongoing SFRs may be overestimated. These low $\mathrm{Hα}$ SFRs, dust-corrected using A$_v$ estimates from SED fitting, confirm that these galaxies are very likely quiescent and, thus, that galaxies can quench before their cold gas reservoirs are fully depleted. |
| title | SQuIGG$\vec{L}$E: Observational Evidence of Low Ongoing Star Formation Rates in Gas-Rich Post-Starburst Galaxies |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2501.16459 |