REVIEW 9 cited by
The Small Sizes and High Implied Densities of `Little Red Dots' with Balmer Breaks Could Explain Their Broad Emission Lines Without an AGN
Not yet reviewed by Pith; the record is open.
This paper has not been read by Pith yet. Machine review is queued; the pith claim, tier, and objections will appear here once it completes.
SPECIMEN: schema-true, not a live event
T0 review · schema-true
One-sentence machine reading of the paper's core claim.
pith:XXXXXXXX · record.json · timestamp
The Small Sizes and High Implied Densities of `Little Red Dots' with Balmer Breaks Could Explain Their Broad Emission Lines Without an AGN
abstract
Early JWST studies found an apparent population of massive, compact galaxies at redshifts $z\gtrsim7$. Recently three of these galaxies were shown to have prominent Balmer breaks, demonstrating that their light at $\lambda_{\rm rest} \sim 3500$ $\r{A}$ is dominated by a stellar population that is relatively old ($\sim$200 Myr). All three also have broad H$\beta$ emission with $\sigma > 1000 \,\rm km s^{-1}$, a common feature of such `little red dots'. From S\'ersic profile fits to the NIRCam images in F200W we find that the stellar light of galaxies is extremely compact: the galaxies have half-light radii of $r_{\rm e}\sim$ 100 pc, in the regime of ultra compact dwarfs in the nearby Universe. Their masses are uncertain, as they depend on the contribution of possible light from an AGN to the flux at $\lambda_{\rm rest}>5000$ $\r{A}$. If the AGN contribution is low beyond the Balmer break region, the masses are $M_* \sim 10^{10}-10^{11}\mathrm{M}_{\odot}$, and the central densities are higher than those of any other known galaxy population by an order of magnitude. Interestingly, the implied velocity dispersions of $\sim$1500 kms$^{-1}$ are in very good agreement with the measured H$\beta$ line widths. We suggest that some of the broad lines in `little red dots' are not due to AGNs but simply reflect the kinematics of the galaxies, and speculate that the galaxies are observed in a short-lived phase where the central densities are much higher than at later times. We stress, however, that the canonical interpretation of AGNs causing the broad H$\beta$ lines also remains viable.
Forward citations
Cited by 9 Pith papers
-
Misaligned or chaotic? A strong break of axial symmetry in the local LRD J1025 revealed with VLT/FORS2 spectropolarimetry
The local Little Red Dot J1025 shows a 48° polarisation-angle offset between continuum and broad H-alpha, requiring broken axial symmetry.
-
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.
-
Discovery of Multiply Ionized Iron Emission Powered by an Active Galactic Nucleus in a z~7 Little Red Dot
The z=6.68 Little Red Dot THRILS 46403 shows a 4.5 sigma [FeVII] line, the first robust coronal-line detection among z>5 LRDs, plus narrow Balmer absorption, supporting an AGN with direct sightlines to gas at or beyon...
-
Characterizing the roles of transitory obscured phases and inner torus in shaping the fractions of obscured AGN at cosmic noon
Pure evolutionary AGN light curves can only reproduce cosmic-noon obscured fractions if the visible phase is tuned by luminosity or if a long-lived torus is added; starbursts and mergers alone cannot.
-
MEGA: Spectrophotometric SED Fitting of Little Red Dots Detected in JWST MIRI
Standard AGN and star-forming templates cannot fully reproduce the SEDs of eight MIRI-detected little red dots; dense-gas models plus extra hot dust partly work but fail on UV and narrow emission lines.
-
A "Black Hole Star" Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots
A source 660 million years after the Big Bang is interpreted as a black hole star with a dust-free dense gas atmosphere, implying Little Red Dots have black hole masses overestimated by orders of magnitude.
-
The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?
A z=2.6 hyperluminous dust-obscured galaxy with an LRD-like SED hosts a ~10^10.2 Msun black hole, while the origin of its blue UV excess is left ambiguous.
-
SEEDZ: Rapid Galaxy Assembly as a Pathway to Supermassive Stars, Dense Stellar Environments and Massive Black Hole Seeds
Rapid halo growth in SEEDZ simulations enables heavy black hole seed formation via supermassive stars at a comoving number density of 0.1 cMpc^{-3} by z=10, with most seeds in near-solar metallicity gas.
-
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.
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.