Eight low-redshift Little Red Dots identified in DESI DR1 exhibit broad Balmer lines, steep decrements, compact shapes, and negligible variability, with a number density roughly 10,000 times lower than at z>4.
SPURS: Evidence for Clumpy Neutral Envelopes and Ionized IGM Surrounding Little Red Dots in Abell 2744 from Ultra-Deep Rest-UV Spectroscopy
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abstract
Rest-frame ultraviolet (UV) spectra of Little Red Dots (LRDs) often show Ly$\alpha$ emission. Along with broad Balmer emission, LRDs are expected to produce broad Ly$\alpha$ emission. However, the large column density of neutral gas invoked to explain the Balmer break should significantly redshift and further broaden the Ly$\alpha$ line, making it challenging to detect without sensitive, moderate-resolution spectra. We present ultra-deep (29 hours) G140M JWST/NIRSpec observations covering the rest-UV of two LRDs in Abell2744 from the SPURS Cycle 4 Large Program. One of our targets is Abell2744-QSO1, a gravitationally-lensed LRD at $z=7.04$ with faint UV emission (M$_{\rm UV}=-16.9$), and the other source (UNCOVER-2476) is newly-confirmed at $z=4.02$ with a very bright UV continuum (M$_{\rm UV}=-19.6$). We find that Abell2744-QSO1 has a broad Ly$\alpha$ profile, along with narrow CIV, FeII$\lambda1786$, and OI$\lambda1302$ emission. The Ly$\alpha$ profile suggests an origin similar to the broad H$\alpha$, but the line is considerably less redshifted than expected from existing dense gas models. We show that the line profile can be explained if the dense neutral gas is clumpy, allowing Ly$\alpha$ to escape by scattering off of the clump surfaces. We find that UNCOVER-2476 has narrow [NeIV] emission, indicating either a hard radiation field or shocks. We confirm two close neighbors with Ly$\alpha$ emission around Abell2744-QSO1, indicating it traces a dense environment that may have ionized its surrounding IGM. We suggest that LRDs may preferentially trace bubbles carved by their dense environments, contributing to the prevalence of Ly$\alpha$ in the population.
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New JWST pure-parallel imaging over 400 arcmin² yields UV luminosity functions at z~7.5-10 consistent with pre-JWST models and significant clustering of bright galaxies implying they occupy more massive halos than previously modeled.
Little red dots are the dust-reddened, high-inclination counterparts of little blue dots under a super-Eddington unification model, with luminosity-dependent fractions peaking near 20% and obscured systems showing systematically higher black hole masses due to selection.
High-redshift AGN emitting UHE protons up to 10^19 eV generate a 50 PeV cosmogenic neutrino bump consistent with IceCube data from their JWST-measured average properties without fine-tuning.
Non-LTE wind atmosphere models computed with CMFGEN reproduce the SED and Balmer decrement of most Little Red Dots when dust-attenuated with Av ~2, while predicting Fe II, O I, and Ca lines, but struggle to produce both a genuine Balmer break and strong lines simultaneously.
citing papers explorer
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A new sample of Little Red Dots at $z<0.45$ in DESI DR1: Broad Balmer lines, low ionization spectrum and no variability
Eight low-redshift Little Red Dots identified in DESI DR1 exhibit broad Balmer lines, steep decrements, compact shapes, and negligible variability, with a number density roughly 10,000 times lower than at z>4.
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BEACON: JWST NIRCam Pure-parallel Imaging Survey. III. Constraints on the UV LF and the Clustering of z~7-14 Galaxies
New JWST pure-parallel imaging over 400 arcmin² yields UV luminosity functions at z~7.5-10 consistent with pre-JWST models and significant clustering of bright galaxies implying they occupy more massive halos than previously modeled.
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Little red dots as obscured little blue dots: relative abundances, luminosities, and black-hole masses
Little red dots are the dust-reddened, high-inclination counterparts of little blue dots under a super-Eddington unification model, with luminosity-dependent fractions peaking near 20% and obscured systems showing systematically higher black hole masses due to selection.
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Ultrahigh-energy cosmogenic neutrino emissions in the high-redshift universe
High-redshift AGN emitting UHE protons up to 10^19 eV generate a 50 PeV cosmogenic neutrino bump consistent with IceCube data from their JWST-measured average properties without fine-tuning.
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Non-LTE atmosphere models of very luminous sources and their applicability to Little Red Dots, quasi-stars, and similar objects
Non-LTE wind atmosphere models computed with CMFGEN reproduce the SED and Balmer decrement of most Little Red Dots when dust-attenuated with Av ~2, while predicting Fe II, O I, and Ca lines, but struggle to produce both a genuine Balmer break and strong lines simultaneously.