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| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2504.08032 |
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| _version_ | 1866913788421210112 |
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| author | Ma, Yilun Greene, Jenny E. Setton, David J. Goulding, Andy D. Annunziatella, Marianna Fan, Xiaohui Kokorev, Vasily Labbe, Ivo Li, Jiaxuan Lin, Xiaojing Marchesini, Danilo Matthee, Jorryt Robbins, Luke Sajina, Anna Sawicki, Marcin Telford, O. Grace |
| author_facet | Ma, Yilun Greene, Jenny E. Setton, David J. Goulding, Andy D. Annunziatella, Marianna Fan, Xiaohui Kokorev, Vasily Labbe, Ivo Li, Jiaxuan Lin, Xiaojing Marchesini, Danilo Matthee, Jorryt Robbins, Luke Sajina, Anna Sawicki, Marcin Telford, O. Grace |
| contents | Little red dots (LRDs) are a population of red, compact objects discovered by JWST at $z>4$. At $4<z<8$, they are roughly 100 times more abundant than UV-selected quasars. However, their number density is uncertain at $z<4$ due to the small sky coverage and limited blue wavelength coverage of JWST. We present our ground-based search for LRDs at $2\lesssim z\lesssim4$, combining ultra-deep Hyper Suprime-Cam photometry and various (near-)infrared surveys within a total area of $\sim3.1\,\mathrm{deg^{2}}$. We find that for LRDs with $M_{5500}<-22.5$, their number density declines from $\sim10^{-4.5}\,\mathrm{cMpc^{-3}}$ at $z>4$ to $\sim10^{-5.3}\,\mathrm{cMpc^{-3}}$ at $2.7<z<3.7$ and $\sim10^{-5.7}\,\mathrm{cMpc^{-3}}$ at $1.7<z<2.7$. We also present the Magellan/FIRE spectrum of our first followed-up candidate, DEEP23-z2LRD1 at $z_\mathrm{spec}=2.26$, as a proof of concept for our sample selection. Similar to high-redshift LRDs, the spectrum of DEEP23-z2LRD1 exhibits broad H$α$ emission with $\mathrm{FWHM}\approx2400\,\mathrm{km\,s^{-1}}$ and with nearly symmetric narrow H$α$ absorption. Additionally, DEEP23-z2LRD1 has extremely narrow [OIII] lines with $\mathrm{FWHM}\approx140\,\mathrm{km\,s^{-1}}$, suggesting the presence of an accreting black hole in a low-mass host galaxy. Limited by the angular resolution of ground-based surveys, we emphasize that spectroscopic follow-ups are required to characterize the contamination fraction of this sample and pin down LRD number density at $z<4$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_08032 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Counting Little Red Dots at $z<4$ with Ground-based Surveys and Spectroscopic Follow-up Ma, Yilun Greene, Jenny E. Setton, David J. Goulding, Andy D. Annunziatella, Marianna Fan, Xiaohui Kokorev, Vasily Labbe, Ivo Li, Jiaxuan Lin, Xiaojing Marchesini, Danilo Matthee, Jorryt Robbins, Luke Sajina, Anna Sawicki, Marcin Telford, O. Grace Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics High Energy Astrophysical Phenomena Little red dots (LRDs) are a population of red, compact objects discovered by JWST at $z>4$. At $4<z<8$, they are roughly 100 times more abundant than UV-selected quasars. However, their number density is uncertain at $z<4$ due to the small sky coverage and limited blue wavelength coverage of JWST. We present our ground-based search for LRDs at $2\lesssim z\lesssim4$, combining ultra-deep Hyper Suprime-Cam photometry and various (near-)infrared surveys within a total area of $\sim3.1\,\mathrm{deg^{2}}$. We find that for LRDs with $M_{5500}<-22.5$, their number density declines from $\sim10^{-4.5}\,\mathrm{cMpc^{-3}}$ at $z>4$ to $\sim10^{-5.3}\,\mathrm{cMpc^{-3}}$ at $2.7<z<3.7$ and $\sim10^{-5.7}\,\mathrm{cMpc^{-3}}$ at $1.7<z<2.7$. We also present the Magellan/FIRE spectrum of our first followed-up candidate, DEEP23-z2LRD1 at $z_\mathrm{spec}=2.26$, as a proof of concept for our sample selection. Similar to high-redshift LRDs, the spectrum of DEEP23-z2LRD1 exhibits broad H$α$ emission with $\mathrm{FWHM}\approx2400\,\mathrm{km\,s^{-1}}$ and with nearly symmetric narrow H$α$ absorption. Additionally, DEEP23-z2LRD1 has extremely narrow [OIII] lines with $\mathrm{FWHM}\approx140\,\mathrm{km\,s^{-1}}$, suggesting the presence of an accreting black hole in a low-mass host galaxy. Limited by the angular resolution of ground-based surveys, we emphasize that spectroscopic follow-ups are required to characterize the contamination fraction of this sample and pin down LRD number density at $z<4$. |
| title | Counting Little Red Dots at $z<4$ with Ground-based Surveys and Spectroscopic Follow-up |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2504.08032 |