Little red dot (galaxy) explained

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.

LRDs were first selected by photometric methods because they are blue in ultraviolet and red in the optical spectrum. 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 or by the gray dust extinction law.

The gas in LRDs spins extremely fast, at around 3,000 km/h, when the typical gas flow is around 300 km/h. 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. Most are also small, usually around 2% of the radius of the Milky Way.

Further reading

Notes and References

  1. Web site: Boyle . Rebecca . 2024-10-09 . The 'Beautiful Confusion' of the First Billion Years Comes Into View . 2024-10-18 . Quanta Magazine . en.
  2. Web site: 2024-09-09 . Little Red Dots: Stars or Black Holes? . 2024-10-18 . NASA Space News . en-US.
  3. Web site: Pacucci . Fabio . Conversation . The . Hidden, compact galaxies in the distant universe—searching for the secrets behind the little red dots . 2024-10-18 . phys.org . en.
  4. 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 . 10.3847/1538-4357/ad2345 . free . 2306.05448 . 2024ApJ...963..129M . 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 . 10.3847/1538-4357/ad1e5f . free . 2309.05714 . 2024ApJ...964...39G . 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 . 10.3847/1538-4357/ad3f17 . free . 2311.07483 . 2024ApJ...968...34W . 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 . 10.3847/2041-8213/ad5669 . free . 2404.19010 . 2024ApJ...969L..18A . 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 . 10.3847/2041-8213/ad7eba . free . 2404.13290 . 2024ApJ...974L..26Y . 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 . 2407.04777 . astro-ph.GA.
  10. 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 . 10.3847/2041-8213/ace5a0 . free . 2302.00012 . 2023ApJ...954L...4K . 2041-8205.
  11. 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 . 2306.07320 . astro-ph.GA.
  12. Li . Zhengrong . Inayoshi . Kohei . Chen . Kejian . Ichikawa . Kohei . Ho . Luis C. . 2024 . Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows . 2407.10760 . astro-ph.GA.

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