Descrizione
Roberta Tripodi
INAF - Osservatorio Astronomico di Roma
New colors for black holes in the early Universe: spectroscopic insights from Little Red Dots
In this talk, I will focus on CANUCS-LRD-z8.6, one of the highest-redshift spectroscopically confirmed LRD at z = 8.6319, which hosts an accreting SMBH and shows broad Hβ, high-ionization UV lines (e.g., CIV, NIV), very low metallicity (Z < 0.1 Zsun), and a BH mass exceeding that expected from its host. These properties suggest accelerated SMBH growth relative to the galaxy (Tripodi+25, Nat. Comm., 16, 9830).
I will also introduce JWST/NIRCam+NIRSpec results on Bz5.3, a broad-line AGN at z = 5.3 behind the Bullet Cluster (Tripodi+25, ApJL,994, L6). Strong Fe II, O I, and Ca II triplet lines, along with broad Balmer emission, confirm the presence of a stratified broad-line region (BLR). Remarkably, we report the first high-redshift detection of the λ1304 bump (O I + Si II), commonly observed in local AGNs. I will also discuss the implications on the excitation mechanisms of the BLR based on low-ionization line diagnostics. Photoionization modeling also reveals multiple gas phases in the BLR with diverse densities and ionization states. Finally, I will discuss the potential role of environment in shaping the evolution of LRDs based on the latest available JWST observations, and I will present an empirical classification of the spectroscopic diversity of LRDs (Perez-Gonzalez, RT incl, 2026; arXiv:2602.20247).
Fabio Pacucci
Center for Astrophysics - Harvard & Smithsonian
THE LITTLE RED DOTS ARE DIRECT COLLAPSE BLACK HOLES
The discovery by JWST of a substantial population of compact "Little Red Dots" (LRDs) presents a major puzzle: their observed spectra defy standard astrophysical interpretations. Here, we show that LRD spectra are naturally reproduced by emission from an accreting Direct Collapse Black Hole (DCBH). Using radiation-hydrodynamic simulations, we follow the growth of the DCBH seed via a dense, compressionally heated, collisionally ionized accretion flow. The model self-consistently reproduces the screen responsible for the observed Balmer absorption, while allowing UV/optical emission to partially escape, along with reprocessed infrared radiation. Crucially, this structure is not a blackbody and requires no stellar contribution: the UV continuum originates entirely from reprocessed DCBH radiation, attenuated only by a small amount of dust with an extinction curve consistent with high-redshift galaxies. This single framework simultaneously explains the key observational puzzles of LRDs: (a) weak X-ray emission, (b) metal and high-ionization lines alongside absent star-formation features, (c) overmassive black holes, (d) compact morphology, (e) abundance and redshift evolution -- linking them directly to pristine atomic-cooling halos, (f) long-lived ($>100$ Myr), slowly variable phases driven by radiation pressure. Our findings indicate that JWST is witnessing the widespread formation of heavy black hole seeds in the early Universe.
Federica Loiacono
INAF - Osservatorio di Astrofisica e Scienze dello Spazio
THE ABUNDANCE OF LITTLE RED DOTS FROM COSMIC DAWN TO NOON
The James Webb Space Telescope discovered a class of active galactic nuclei (AGNs) missed by previous selections. A fraction of these sources, dubbed "little red dots" (LRDs), show properties that are at odds with “classical” AGNs, and their nature is matter of intense debate. Most of these objects have been found at z > 4. At cosmic dawn (z ~ 6) they are ∼ 1-2 dex more abundant than X-ray and UV-selected AGNs at z ∼ 5 − 7 with similar bolometric luminosity. According to some theories, LRDs may represent the early, rapid growth stages of newly formed black hole (BH) seeds. In this scenario, the abundance of LRDs rapidly decreases from cosmic dawn to cosmic noon, where it is expected to fall short of that of standard AGNs by ∼ 3 dex.
In this talk I will compare the number density of LRDs at cosmic dawn to that at z~2-3, with the latter based on a sample of spectroscopically confirmed LRDs. I will show that this population is still abundant at cosmic noon, with their space density being only a factor of 2-3 lower than that of UV-selected quasars with comparable luminosity. A similar trend is observed in terms of BH masses. This result suggests that the formation of BH seeds can be efficient from cosmic dawn down to cosmic noon.
Laura Bisigello
INAF - Osservatorio Astronomico di Padova
THE QUEST FOR LOW-z LRDs
Since its launch, the James Webb Space Telescope (JWST) has uncovered a puzzling population of sources characterised by a compact morphology, “v-shaped" spectra, and broad hydrogen emission lines. The nature of these "Little Red Dots" (LRDs) remains highly debated, largely due to the challenges of observing them at high redshifts (z > 4). Current theoretical models disagree, for example, regarding the host galaxy's contribution to the observed spectral energy distribution at different wavelengths. Identifying LRDs at lower redshifts (z < 4) is therefore critical to resolve their host galaxies, establishing stringent multi-wavelength constraints, and, moreover, to trace their cosmic evolution. I will provide an overview of the current search for low-z LRDs, highlighting also recent results from wide-area surveys such as Euclid.
Chair: Andrea Ferrara
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Tripodi, Roberta (Istituto Nazionale di Astrofisica (INAF))07/05/26, 11:10
In this talk, I will focus on CANUCS-LRD-z8.6, one of the highest-redshift spectroscopically confirmed LRD at z = 8.6319, which hosts an accreting SMBH and shows broad Hβ, high-ionization UV lines (e.g., CIV, NIV), very low metallicity (Z < 0.1 Zsun), and a BH mass exceeding that expected from its host. These properties suggest accelerated SMBH growth relative to the galaxy (Tripodi+25, Nat....
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Pacucci, Fabio (Center for Astrophysics | Harvard & Smithsonian)07/05/26, 11:28
The discovery by JWST of a substantial population of compact "Little Red Dots" (LRDs) presents a major puzzle: their observed spectra defy standard astrophysical interpretations. Here, we show that LRD spectra are naturally reproduced by emission from an accreting Direct Collapse Black Hole (DCBH). Using radiation-hydrodynamic simulations, we follow the growth of the DCBH seed via a dense,...
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Loiacono, Federica (Istituto Nazionale di Astrofisica (INAF))07/05/26, 11:46
The James Webb Space Telescope discovered a class of active galactic nuclei (AGNs) missed by previous selections. A fraction of these sources, dubbed "little red dots" (LRDs), show properties that are at odds with “classical” AGNs, and their nature is matter of intense debate. Most of these objects have been found at z > 4. At cosmic dawn (z ~ 6) they are ∼ 1-2 dex more abundant than X-ray and...
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Bisigello, Laura (Università di Padova)07/05/26, 12:03
Since its launch, the James Webb Space Telescope (JWST) has uncovered a puzzling population of sources characterised by a compact morphology, “v-shaped" spectra, and broad hydrogen emission lines. The nature of these "Little Red Dots" (LRDs) remains highly debated, largely due to the challenges of observing them at high redshifts (z > 4). Current theoretical models disagree, for example,...
Go to contribution page