Little red dot (astronomical object)

stamps of 6 little red dots with redshift given LRDs were first selected by photometric methods because they are blue in ultraviolet and red in the optical spectrum. Active galactic nuclei are defined as small regions in the centers of galaxies that emit copious amounts of energy in the form of bright jets and winds. Scientists study the properties of AGNs to better understand supermassive black hole formation and how they contribute to the structure and dynamics of LRDs. This region is also known as the accretion disk. The gas in LRDs spins extremely fast. observing rapid gas orbits of roughly a strong indicator of black hole accretion. and little X-ray emission has been detected. LRDs also show very weak time variability, while high variability is often seen in AGN observation. == Observed properties ==

Several models have been proposed to explain the observed properties of LRDs. The shape of the ultraviolet spectrum can be explained by the scattered AGN light Research has shown that LRDs do not commonly exist at lower redshifts. One possible reason for this observation is "inside-out growth." When a galaxy evolves and expands outward from its nucleus at lower redshifts, a decreasing amount of gas is deposited near the accreting black hole. Thus, the black hole sheds its outer gas layers, becomes bluer, and is no longer categorized as an LRD. From a sample of 99 LRDs analyzed for morphology, 69 were predominantly compact without extended components, with the other 30 with more complex morphologies. Of these complex galaxies, 50% showed multiple associated components, and the rest showed highly asymmetric structures, with indications of a composite nature. It is hypothesized from this analysis that LRDs may be a product of galaxy interactions and mergers, with potential evidence to suggest early stages of galaxy and black hole growth. These suspected young black holes are among the smallest recorded, at 105 - 107 solar masses. 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 SED. Seven such V-shaped BLGPs were identified from a sample size of 2,190. These V-shaped BLGPs host over-massive black holes. == RUBIES ==

/MSA pointings in the UDS and EGS fields. Purple pointings correspond to the first half of observations in January to March 2024. Background images show the NIRCam F444W image mosaics, primarily constructed from public imaging of the CEERS and PRIMER surveys. The outline of the PRIMER MIRI imaging footprint for the UDS is shown in pink. RUBIES, the "Red Unknowns: Bright Infrared Extragalactic Survey", is a JWST program led by Anna de Graaff and Gabriel Brammer that observed ~300 "very red sources" in the Ultra Deep Survey (UDS) and Extended Groth Strip (EGS) fields. Research conducted in association with RUBIES program has found that sources of a selected group (2 < z < 5) have a majority of massive quiescent galaxies, which is 10 times the original estimated value. The program has also found that observed LRDs have much lower levels of hot and cold gas than models would suggest, pointing away from the possibilities of AGNs or star-forming galaxies, although this is still debated. == Notable LRDs ==

The Cliff (RUBIES-UDS-154183) is an LRD confirmed to be a broad-line active galactic nucleus (BLAGN) with the red-shift z = 9.288. It is the highest red-shift AGN known. CAPERS-LRD-z9 exhibits a prominent Balmer break and "provides strong evidence in support of the 'dense-gas-enshrouded AGN'" explanation. These unusual Balmer jumps are notable properties of LDRs, causing difficulties in observations and spectroscopic analysis. Some LDRs exhibit a symmetrical density distribution of electron scattering, thus a gaseous envelope absorbing nebular spectra is a credible possibility. RUBIES-BLAGN-1 RUBIES-BLAGN-1 is an LRD which is "an unusually bright LRD (zspec = 3.1) observed as part of the RUBIES program. This LRD exhibits broad emission lines (FWHM ~ 4000 km s−1), a blue UV continuum, a clear Balmer break, and a red continuum sampled out to rest-frame 4 μm with MIRI." J1007_AGN The LRD J1007_AGN has a red-shift z = 7.3, and is "embedded in an overdensity of eight nearby galaxies". Abell 2744-QSO1 Abell 2744-QSO1 is an LRD with z = 7.04. It was described as a "naked" black hole, because very few stars are in its vicinity. MoM-BH*-1 MoM-BH*-1 is a prominent LRB described as "a higher-redshift analogue of The Cliff". == Further reading ==