Little red dot (galaxy)

A little red dot galaxy (center) in false color
False-color stamps of 20 little red dot galaxies

Little red dots (LRDs) are a class of small, red-tinted galaxies discovered by the James Webb Space Telescope.[1][2][3] Their discovery was published in March 2024, and they are currently poorly understood.[4] They appear to have existed between 0.6 and 1.6 billion years after the Big Bang, from 13.2 to 12.2 billion years ago.[1]

LRDs were first selected by photometric methods because they are blue in ultraviolet and red in the optical spectrum.[4] But soon, 80% of them were found to have very broad Balmer emission lines, suggesting that they are active galactic nuclei (AGN) and host supermassive black holes at their center.[5]

However, LRDs also exhibit properties that are difficult to explain within the AGN scenario. For example, they have a flat infrared spectrum[6] and lack x-ray detection.[7][8] LRDs also show very weak time variability, often seen in AGN observation.[9]

Several models have been proposed to explain the observed properties of LRDs.[10][11][12] The shape of the ultraviolet spectrum can be explained by the scattered AGN light[10][11] or by the gray dust extinction law.[12]

The gas in LRDs spins extremely fast, at around 3,000 km/h, when the typical gas flow is around 300 km/h.[1] Some scientists argue that the gas is accelerated to these extreme speeds by spinning, supermassive black holes; it has also been argued that LRDs are extremely compact to spin at their speeds.[1] Most are also small, usually around 2% of the radius of the Milky Way.[3]

Likely local analogues of LRDs were discovered in a sample of Green Pea Galaxies (GP). These are broad-line AGN hosting Green Peas (BLGP) with V-shaped rest-frame UV-to-optical SEDs. Seven such V-shaped BLGPs were identified. These V-shaped BLGPs host over-massive black holes.[13]

References

  1. ^ a b c d Boyle, Rebecca (2024-10-09). "The 'Beautiful Confusion' of the First Billion Years Comes Into View". Quanta Magazine. Retrieved 2024-10-18.
  2. ^ "Little Red Dots: Stars or Black Holes?". NASA Space News. 2024-09-09. Retrieved 2024-10-18.
  3. ^ a b Pacucci, Fabio; Conversation, The. "Hidden, compact galaxies in the distant universe—searching for the secrets behind the little red dots". phys.org. Retrieved 2024-10-18.
  4. ^ a b Matthee, Jorryt; Naidu, Rohan P.; Brammer, Gabriel; Chisholm, John; Eilers, Anna-Christina; Goulding, Andy; Greene, Jenny; Kashino, Daichi; Labbe, Ivo; Lilly, Simon J.; Mackenzie, Ruari; Oesch, Pascal A.; Weibel, Andrea; Wuyts, Stijn; Xiao, Mengyuan (March 2024). "Little Red Dots: An Abundant Population of Faint Active Galactic Nuclei at z ∼ 5 Revealed by the EIGER and FRESCO JWST Surveys". The Astrophysical Journal. 963 (2): 129. arXiv:2306.05448. Bibcode:2024ApJ...963..129M. doi:10.3847/1538-4357/ad2345. ISSN 0004-637X.
  5. ^ Greene, Jenny E.; Labbe, Ivo; Goulding, Andy D.; Furtak, Lukas J.; Chemerynska, Iryna; Kokorev, Vasily; Dayal, Pratika; Volonteri, Marta; Williams, Christina C.; Wang 王, Bingjie 冰洁; Setton, David J.; Burgasser, Adam J.; Bezanson, Rachel; Atek, Hakim; Brammer, Gabriel (2024-03-01). "UNCOVER Spectroscopy Confirms the Surprising Ubiquity of Active Galactic Nuclei in Red Sources at z > 5". The Astrophysical Journal. 964 (1): 39. arXiv:2309.05714. Bibcode:2024ApJ...964...39G. doi:10.3847/1538-4357/ad1e5f. ISSN 0004-637X.
  6. ^ Williams, Christina C.; Alberts, Stacey; Ji, Zhiyuan; Hainline, Kevin N.; Lyu, Jianwei; Rieke, George; Endsley, Ryan; Suess, Katherine A.; Sun, Fengwu; Johnson, Benjamin D.; Florian, Michael; Shivaei, Irene; Rujopakarn, Wiphu; Baker, William M.; Bhatawdekar, Rachana (2024-06-01). "The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8". The Astrophysical Journal. 968 (1): 34. arXiv:2311.07483. Bibcode:2024ApJ...968...34W. doi:10.3847/1538-4357/ad3f17. ISSN 0004-637X.
  7. ^ Ananna তনিমা তাসনিম, Tonima Tasnim অনন্যা; Bogdán, Ákos; Kovács, Orsolya E.; Natarajan, Priyamvada; Hickox, Ryan C. (2024-07-01). "X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?". The Astrophysical Journal Letters. 969 (1): L18. arXiv:2404.19010. Bibcode:2024ApJ...969L..18A. doi:10.3847/2041-8213/ad5669. ISSN 2041-8205.
  8. ^ Yue, Minghao; Eilers, Anna-Christina; Ananna, Tonima Tasnim; Panagiotou, Christos; Kara, Erin; Miyaji, Takamitsu (2024-10-01). "Stacking X-Ray Observations of "Little Red Dots": Implications for Their Active Galactic Nucleus Properties". The Astrophysical Journal Letters. 974 (2): L26. arXiv:2404.13290. Bibcode:2024ApJ...974L..26Y. doi:10.3847/2041-8213/ad7eba. ISSN 2041-8205.
  9. ^ Kokubo, Mitsuru; Harikane, Yuichi (2024). "Challenging the AGN scenario for JWST/NIRSpec broad Hα emitters/Little Red Dots in light of non-detection of NIRCam photometric variability and X-ray". arXiv:2407.04777 [astro-ph.GA].
  10. ^ a b Kocevski, Dale D.; Onoue, Masafusa; Inayoshi, Kohei; Trump, Jonathan R.; Arrabal Haro, Pablo; Grazian, Andrea; Dickinson, Mark; Finkelstein, Steven L.; Kartaltepe, Jeyhan S.; Hirschmann, Michaela; Aird, James; Holwerda, Benne W.; Fujimoto, Seiji; Juneau, Stéphanie; Amorín, Ricardo O. (2023-09-01). "Hidden Little Monsters: Spectroscopic Identification of Low-mass, Broad-line AGNs at z > 5 with CEERS". The Astrophysical Journal Letters. 954 (1): L4. arXiv:2302.00012. Bibcode:2023ApJ...954L...4K. doi:10.3847/2041-8213/ace5a0. ISSN 2041-8205.
  11. ^ a b Labbe, Ivo; Greene, Jenny E.; Bezanson, Rachel; Fujimoto, Seiji; Furtak, Lukas J.; Goulding, Andy D.; Matthee, Jorryt; Naidu, Rohan P.; Oesch, Pascal A.; Atek, Hakim; Brammer, Gabriel; Chemerynska, Iryna; Coe, Dan; Cutler, Sam E.; Dayal, Pratika (2023). "UNCOVER: Candidate Red Active Galactic Nuclei at 3 < z < 7 with JWST and ALMA". arXiv:2306.07320 [astro-ph.GA].
  12. ^ a b Li, Zhengrong; Inayoshi, Kohei; Chen, Kejian; Ichikawa, Kohei; Ho, Luis C. (2024). "Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows". arXiv:2407.10760 [astro-ph.GA].
  13. ^ Lin, Ruqiu; Zheng, Zhen-Ya; Jiang, Chunyan; Yuan, Fang-Ting; Ho, Luis C.; Wang, Junxian; Jiang, Linhua; Rhoads, James E.; Malhotra, Sangeeta (2024-12-11). "Discovery of Local Analogs to JWST's Little Red Dots". arXiv:2412.08396 [astro-ph].

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