The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots
A significant fraction of little red dots (LRDs) exhibit nearby extended emission of unknown origin. If physically associated with the LRD, this component may trace stellar emission from an off-center host galaxy, neighboring companions, or nebular gas illuminated by the active nucleus. We investiga...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/2041-8213/adee0a |
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| author | Chang-Hao Chen Luis C. Ho Ruancun Li Kohei Inayoshi |
| author_facet | Chang-Hao Chen Luis C. Ho Ruancun Li Kohei Inayoshi |
| author_sort | Chang-Hao Chen |
| collection | DOAJ |
| description | A significant fraction of little red dots (LRDs) exhibit nearby extended emission of unknown origin. If physically associated with the LRD, this component may trace stellar emission from an off-center host galaxy, neighboring companions, or nebular gas illuminated by the active nucleus. We investigate the detailed spectral energy distribution (SED) of the extended emission near four LRDs in the JWST UNCOVER and MegaScience surveys. We accurately decompose the extended emission from the dominant point source by simultaneously fitting the images in eight broadband and nine medium-band filters. After considering both the results from photometric redshift fitting and the probability of galaxies at different redshifts overlapping, we confirm that the off-center blobs in three sources are physically associated with the LRDs, with two of them showing strong [O iii ] λλ 4959, 5007 emission captured by the medium-band filters. While the SEDs of all three blobs can be modeled assuming star-forming galaxies with stellar mass ∼10 ^8 M _⊙ , the exceptionally strong [O iii ] emission of two sources is best interpreted as pure nebular emission from low-density ( n < 10 cm ^−3 ), low-metallicity ( Z ≈ 0.05−1 Z _⊙ ) gas photoionized by the ultraviolet radiation from the nearby LRD. Adopting LRD halo masses constrained by clustering measurements and theoretical considerations, we estimate a typical baryonic halo mass accretion rate of ∼2−9 M _⊙ yr ^−1 . If the halo accretion rate is sustained to z = 4 and stars form with an efficiency of 10%, the accreted gas would build a galaxy with stellar mass ∼10 ^9 M _⊙ , potentially rendering them spatially resolved at lower redshift. |
| format | Article |
| id | doaj-art-c86803c4257e470bbc3979c97a21c85a |
| institution | Kabale University |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-c86803c4257e470bbc3979c97a21c85a2025-08-20T03:59:41ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019891L1210.3847/2041-8213/adee0aThe Physical Nature of the Off-center Extended Emission Associated with the Little Red DotsChang-Hao Chen0https://orcid.org/0009-0003-4721-177XLuis C. Ho1https://orcid.org/0000-0001-6947-5846Ruancun Li2https://orcid.org/0000-0001-8496-4162Kohei Inayoshi3https://orcid.org/0000-0001-9840-4959Kavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of China; Department of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of ChinaKavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of China; Department of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of ChinaKavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of China; Department of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of ChinaKavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of China; Department of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of ChinaA significant fraction of little red dots (LRDs) exhibit nearby extended emission of unknown origin. If physically associated with the LRD, this component may trace stellar emission from an off-center host galaxy, neighboring companions, or nebular gas illuminated by the active nucleus. We investigate the detailed spectral energy distribution (SED) of the extended emission near four LRDs in the JWST UNCOVER and MegaScience surveys. We accurately decompose the extended emission from the dominant point source by simultaneously fitting the images in eight broadband and nine medium-band filters. After considering both the results from photometric redshift fitting and the probability of galaxies at different redshifts overlapping, we confirm that the off-center blobs in three sources are physically associated with the LRDs, with two of them showing strong [O iii ] λλ 4959, 5007 emission captured by the medium-band filters. While the SEDs of all three blobs can be modeled assuming star-forming galaxies with stellar mass ∼10 ^8 M _⊙ , the exceptionally strong [O iii ] emission of two sources is best interpreted as pure nebular emission from low-density ( n < 10 cm ^−3 ), low-metallicity ( Z ≈ 0.05−1 Z _⊙ ) gas photoionized by the ultraviolet radiation from the nearby LRD. Adopting LRD halo masses constrained by clustering measurements and theoretical considerations, we estimate a typical baryonic halo mass accretion rate of ∼2−9 M _⊙ yr ^−1 . If the halo accretion rate is sustained to z = 4 and stars form with an efficiency of 10%, the accreted gas would build a galaxy with stellar mass ∼10 ^9 M _⊙ , potentially rendering them spatially resolved at lower redshift.https://doi.org/10.3847/2041-8213/adee0aEarly universeHigh-redshift galaxiesActive galactic nucleiAGN host galaxies |
| spellingShingle | Chang-Hao Chen Luis C. Ho Ruancun Li Kohei Inayoshi The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots The Astrophysical Journal Letters Early universe High-redshift galaxies Active galactic nuclei AGN host galaxies |
| title | The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots |
| title_full | The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots |
| title_fullStr | The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots |
| title_full_unstemmed | The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots |
| title_short | The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots |
| title_sort | physical nature of the off center extended emission associated with the little red dots |
| topic | Early universe High-redshift galaxies Active galactic nuclei AGN host galaxies |
| url | https://doi.org/10.3847/2041-8213/adee0a |
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