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The Host Galaxy (If Any) of the Little Red Dots
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The Host Galaxy (If Any) of the Little Red Dots
abstract
We investigate the host galaxy properties of eight little red dots (LRDs) selected from the JWST UNCOVER survey, applying a new technique ({\tt\string GalfitS}) to simultaneously fit the morphology and spectral energy distribution using multi-band NIRCam images covering $\sim 1-4\,\mu {\rm m}$. We detect the host galaxy in only one LRD, MSAID38108 at $z = 4.96$, which has a stellar mass of $\log (M_*/M_{\odot}) = 8.66^{+0.24}_{-0.23}$, an effective radius $R_e=0.66^{+0.08}_{-0.05}$ kpc, and a S\'ersic index $n=0.71^{+0.07}_{-0.08}$. No host emission centered on the central point source is found in the other seven LRDs. We derive stringent upper limits for the stellar mass of a hypothetical host galaxy by conducting realistic mock simulations that place high-redshift galaxy images under the LRDs. Based on the black hole masses estimated from the broad H$\alpha$ emission line, the derived stellar mass limits are at least a factor of 10 lower than expected from the $z \approx 0$ scaling relation between black hole mass and host galaxy stellar mass. Intriguingly, four of the LRDs (50\% of the sample) show extended, off-centered emission, which is particularly prominent in the bluer bands. The asymmetric emission of two sources can be modeled as stellar emission, but the nature of the other two is unclear.
Forward citations
Cited by 9 Pith papers
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What you see is what you get: empirically measured bolometric luminosities of Little Red Dots
Directly integrating the observed spectra of two Little Red Dots shows the bolometric luminosity is dominated by rest-frame optical light, lowering implied black hole masses to about 10^5 to 10^7 solar masses.
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Hidden in Pixels I: Discovery of dual "little red dots" indicates excess clustering on kilo-parsec scales
Four dual LRD candidates at z~5.5 with kpc separations show 20-30x excess sub-arcsec clustering versus extrapolated AGN ACF, implying merger-driven SMBH growth.
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ATLAS. II. Extremely High Incidence of Balmer Line Absorption with Predominant Blueshifts in LRDs: Statistical Insights through Comparison with Type 1 AGNs
Balmer-line absorption occurs in ~35% (14/40) of JWST little-red-dot AGNs, roughly 850x the rate in SDSS type-1 AGNs, with mostly slow blueshifted absorber velocities.
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Reduced Incidence of Little Red Dots at z < 3 from Number Density and Halo Mass Evolution
LRDs transition from underdense low-halo-mass environments at z>4 to typical galaxy conditions by z~3.5, with halo growth leading to larger sizes and SED changes that explain their disappearance at lower redshifts.
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Reduced Incidence of Little Red Dots at z < 3 from Number Density and Halo Mass Evolution
Little red dots shift from underdense, low-halo-mass environments at z>4 to ordinary galaxy environments by z~3.5, explaining their declining abundance at z<3.
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Quenching of X-ray emission in little red dots by both Compton-thick gas and high accretion rates
X-ray non-detection of little red dots requires both Compton-thick gas columns (~1e25 cm^-2) and intrinsically weak X-ray emission with bolometric correction k_bol,X ≳ 30.
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Quenching of X-ray emission in little red dots by both Compton-thick gas and high accretion rates
LRDs require Compton-thick gas at moderate metallicity plus high accretion rates producing weak X-rays to explain their non-detection, implying they are not chemically pristine.
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Undermassive Hosts of $z = 4-6 $ AGN from JWST/NIRCam Image Decomposition with CONGRESS, FRESCO, and JADES
Faint AGN hosts at z≈4–6 look 1–2 dex less massive after image decomposition, pushing their black-hole-to-stellar-mass ratios to ~0.01–1.48, above the local relation.
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Little Red reionization factories
LRDs may drive cosmic reionization: tidal fields are said to funnel intergalactic hydrogen into colliding streams at LRD sites, igniting starbursts that ionize the gas.
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