Gaia Gaspar

In the black hole star (BH ^* ) framework, the characteristic V-shaped spectral energy distribution of little red dots (LRDs) is produced by an accreting BH embedded in a dense neutral-gas envelope with a near-unity covering factor. This envelope reprocesses the radiation and emits as a ∼5000 K blackbody, producing the optical continuum in LRDs. Meanwhile, the ultraviolet (UV) is powered by a low-mass, dust-free, metal-poor host. The BH ^* scenario is promising but has yet to undergo detailed testing; conducting a self-consistent UV-to-optical spectral-fitting analysis of LRDs would provide a robust assessment of the model. In this work, we tested the BH ^* scenario by fitting the full JWST/NIRSpec PRISM spectrum of “The Cliff” ( z _spec = 3.55), an LRD that played a pivotal role in the development of the BH ^* model. We find that a Bagpipes fit that allows stellar, nebular, active galactic nucleus (AGN), and blackbody components naturally yields a BH ^* -like solution for The Cliff, even with broad priors. Our method allows us to characterize its host despite it remaining unresolved in JWST imaging. From the continuum, we infer the host to be low-mass (log M _★ / M _⊙ ∼ 7.7), star-forming, metal-poor, and affected by non-negligible dust attenuation ( A _V ∼ 0.5 mag) acting on both stellar and nebular components. Higher stellar masses (up to log M _★ / M _⊙ ∼ 8.1) and attenuations (up to A _V ∼ 1 mag) are obtained depending on the assumed dust attenuation law. Modest AGN UV leakage is consistently allowed – and sometimes preferred – by the code but remains weak and not robustly constrained, with both AGN+host and host-dominated UV scenarios yielding statistically equivalent fits. The star formation history of the host is relatively smooth, with the galaxy already assembling log M _★ / M _⊙ ∼ 7 about 200 Myr before z _spec = 3.55. The BH-to- M _★ ratio consistently exceeds the values expected from BH–host scaling relations, especially at recent times. This tension may indicate either inaccurate estimates of the BH properties or non-coeval BH–host evolution in this LRD.

Little red dots (LRDs) are a heterogeneous class of objects, and several scenarios have been proposed for their physical nature and evolution. While these theories have been tested on individual LRDs using limited spectral features, a systematic Bayesian analysis of the LRD population incorporating the different models across a broad wavelength range is still lacking. We conducted a consistent ultraviolet (UV)-to-optical continuum fitting analysis of 99 LRDs at 2 < z < 6 using JWST/NIRSpec PRISM spectroscopy. Employing a modified version of the code Bagpipes , including blackbody (BB) emission affected by Balmer absorption, stellar and nebular emission attenuated by dust, and an active galactic nucleus (AGN) component, we assessed the performance of the black hole star (BH ^∗ ) model in describing the LRD population. We adopted broad priors and therefore did not impose any specific physical scenario. Our results show that only ∼4% of LRDs with statistically robust solutions (81 objects in total) are best fit by a BH ^∗ in the optical and a host galaxy in the UV. About 9% of the LRDs show BB-dominated optical continua, but lack a stellar component or exhibit AGN UV leakage. Most LRDs are dominated by stellar and/or AGN emission in the optical, with a minor BB contribution. When we adopted a prior that disfavored a strong AGN continuum to enforce BH ^∗ -like solutions, the percentage of BH ^∗ systems increased to ∼35%, highlighting the strong degeneracy between a BH ^∗ solution and alternative scenarios. Even when BH ^∗ -like solutions were enforced, many LRDs still required a stellar-dominated optical continuum. This might indicate limitations in the BH ^∗ model, as further supported by independent evidence, such as the detection of high-ionization emission lines in some LRDs.

The little red dot (LRD) paradigm comprises three main unknowns that are intrinsically connected: (1) What is the nature of these sources? (2) How do they form? (3) How do they evolve? Larger spectroscopic samples and high-resolution data are needed to delve deeper into the mechanisms governing these sources. Understanding their formation and evolution requires identifying the rise and fall of the key features that characterize these systems, such as their compactness and “V”-shaped spectral energy distributions. In this work, we present a galaxy system nicknamed “The Stingray” that was identified in the Canadian NIRISS Unbiased Cluster Survey (CANUCS). This group contains three sources at z _spec = 5.12, including an active galactic nucleus (AGN), a Balmer break galaxy, and a star-forming satellite. The latter resembles a building blocks system in which interactions boost stellar mass and black hole mass growth beyond what is expected from secular processes alone. The AGN in this system exhibits features indicative of a transitional object, bridging a normal AGN and an LRD phase. These features include a blue rest-frame UV slope, compact size, and a broad H α line (all of which are characteristic of LRDs), but a flatter rest-frame optical slope compared to that observed in LRDs. The features in this source point to the emergence or fading of an LRD, potentially triggered by environmental effects.

The main sequence of star-forming galaxies (SFGMS or MS) is a fundamental scaling relation that provides a global framework for studying galaxy formation and evolution, as well as an insight into the complex star formation histories (SFHs) of individual galaxies. In this work, we combine large-area pre-JWST surveys (COSMOS2020, CANDELS), which probe high- M _★ sources (> 10 ⁹ M _⊙ ), with SHARDS/CANDELS FAINT and JWST data from CANUCS, CEERS, JADES, and UNCOVER, to obtain a high- z , star formation rate (SFR) and stellar mass ( M _★ ) complete sample spanning both high- and low- M _★ regimes. Completeness in both M _★ and the SFR is key to avoiding biases introduced by low-mass, highly star-forming objects. Our combined dataset is 80% complete down to 10 ^7.6 M _⊙ at z ∼ 1 (10 ^8.8 M _⊙ at z ∼ 9). The overall intrinsic MS slope (based on the SFR ₁₀₀ and M _★ derived with Dense Basis and nonparametric SFHs) shows little evolution up to z ∼ 5, with values ∼0.7 − 0.8. The slope in the low- M _★ regime becomes steeper than that in the high- M _★ end at least up to z ∼ 5, but the strength of this change is highly dependent on the assumptions made on the symmetry of the uncertainties in M _★ and SFR. If real, the steepening suggests reduced star formation efficiency or declining gas content with decreasing M _★ . The transition between the low- M _★ regime and the canonical MS occurs around 10 ^9.5 M _⊙ , independent of z . This critical value may coincide with the assembly of galaxies’ disks, which can provide a mechanism for self-regulation that stabilizes them against feedback. The intrinsic scatter is compatible with canonical estimates, also at low- M _★ , ranging from 0.2 − 0.3 dex. This is indicative of rapid variations in star formation being averaged out over ≲100 Myr.

We present the first data release of the Canadian NIRISS Unbiased Cluster Survey (CANUCS), a JWST Cycle 1 GTO program targeting five lensing clusters and flanking fields in parallel (A370, MACS0416, MACS0417, MACS1149, and MACS1423; survey area ∼100 arcmin ² ), with NIRCam imaging, NIRISS slitless spectroscopy, and NIRSpec prism multiobject spectroscopy. Fields centered on cluster cores include imaging in eight bands from 0.9–4.4 μ m, alongside continuous NIRISS coverage from 1.15–2 μ m, while the NIRCam flanking fields provide five wide-band and nine medium-band filters for exceptional spectral sampling, all to ∼29 mag _AB . We also present JWST in Technicolor, a Cycle 2 follow-up GO program targeting three CANUCS clusters (A370, MACS0416, and MACS1149). The Technicolor program adds NIRISS slitless spectroscopy in F090W to the cluster fields while adding eight wide-, medium-, and narrowband filters to the flanking fields. This provides NIRCam imaging in all wide- and medium-band filters over ∼30 arcmin ² . This paper describes our data reduction and photometry methodology. We release NIRCam, NIRISS, and Hubble Space Telescope imaging, point-spread functions (PSFs), PSF-matched imaging, photometric catalogs, and photometric and spectroscopic redshifts. We provide lens models and stellar population parameters in up to 19 filters for ∼53,000 galaxies in the cluster fields, and ∼44,000 galaxies in up to 29 filters in the flanking fields. We further present 733 NIRSpec spectra and redshift measurements up to z = 10.8. Comparing against our photometric redshifts, we find catastrophic outlier rates of only 4%–7% and scatter of σ _NMAD of 0.01–0.03.

We present a spectroscopic analysis of a broad-line active galactic nucleus (AGN) selected as a little red dot (LRD) at z = 5.3 behind the Bullet cluster (Bz5.3) based on JWST/NIRCam and NIRSpec data. The detection of strong Fe ii , O i , and Ca ii triplet emission lines, along with the evidence of broad Balmer lines, provides strong evidence of a broad-line region (BLR) and an accreting supermassive black hole. Notably, we report the first detection of the λ 1304 bump (i.e., a blend of O i λ 1304 and Si ii ) at high redshift, a feature commonly seen in local AGNs but not yet reported in the early Universe. The O i λ 1304/ λ 8446 photon ratio provides an independent measurement of dust attenuation in galaxies. In Bz5.3, this ratio is highly suppressed (0.1–0.3), implying significant internal dust extinction, with estimated dust attenuation A _V ∼ 0.4–1.0. We identify Ly β fluorescence as the dominant excitation mechanism of the low-ionization lines, with additional contributions from collisional excitation. High O i λ 8446 equivalent width and weak O i λ 7774 support this interpretation. The detection of iron emission, whether from broad permitted or narrow forbidden lines, supports the presence of a stratified BLR, as also recently proposed in local LRDs. Photoionization modeling of O i λ 8446 and Ca ii further suggests the coexistence of multiple gas phases with distinct densities and ionization states, highlighting the complexity of the BLR. Bz5.3 thus offers a rare window into early AGN activity and BLR physics at early times.

We report the discovery of a z ∼ 7 group of galaxies that contains two little red dots (LRDs) just 3.3 kpc apart, along with three potential satellite galaxies, as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). The spectral energy distributions (SEDs) of this LRD pair show evidence of a Balmer break, consistent with a recent (∼100 Myr) quenching of star formation. In contrast, the satellites are compatible with a recent-onset (∼100 Myr), ongoing burst of star formation. LRD1’s SED is consistent with a dust-free active galactic nucleus (AGN) being the source of the UV excess in the galaxy. The optical continuum would be powered by the emission from an obscured post-starburst and the AGN at a subdominant level. LRD2’s SED is more ambiguous, but it could also be indicative of a dust-free AGN. In this scenario, these LRDs would be massive (M_⋆ ∼ 10¹⁰ M_⊙) and dusty (A(V) > 1 mag) and the three satellites would be lower-mass objects (M_⋆ ∼ 10^8 − 9 M_⊙) subject to low dust attenuations. The proximity of the two LRDs suggests that their interaction is responsible for their recent star formation histories, which can be interpreted as environmental bursting and quenching in the epoch of reionization.

In this paper we analyse a sample of 46 barred galaxies of MaNGA. Our goal is to investigate the stellar kinematics of these galaxies and obtain their rotation curves. Additionally, we aim to derive the total stellar and dynamical masses, as well as the maximum rotation velocity, in order to examine their distributions and scaling relations. Using the Pipe3D dataproducts publicly available we obtained the rotation curves, which were fitted considering two components of an axisymmetric Miyamoto-Nagai gravitational potential. We found a wide range of the maximum rotation velocities (117 - 340 km s -1 ), with a mean value of 200 km s -1 . In addition we found that the total stellar and dynamical masses are in the range of log(M star /M sun ) = 10.1 - 11.5, with a mean value of log(M star /M sun ) = 10.8, and log(M dyn /M sun ) = 10.4 - 12.0, with a mean value of log(M dyn /M sun ) = 11.1, respectively. We found a strong correlation between dynamical mass and maximum velocity, between maximum velocity and magnitude, and between stellar mass and maximum velocity. According to these results, barred galaxies exhibit similar behaviour to that of normal spiral galaxies with respect to these relations, as well as in terms of the distribution of their dynamical mass and maximum rotation velocity. Ho we ver, we found that the distribution of stellar masses of barred galaxies is statistically different from other samples including non-barred galaxies. Finally, analysing the galaxies that show nuclear activity, we find no difference with the rotation curves of normal galaxies.

NGC 4945 harbors one of the nearest active galactic nuclei (AGNs), which allows us to reach high spatial resolution with current observational facilities. The Seyfert 2 nucleus is deeply obscured by an edge-on disk with A _V ∼ 14, requiring infrared observations to study circumnuclear structures and the interstellar medium. In this work, we present an imaging and long-slit spectroscopic study of the nuclear region with a spatial resolution of 6.5 pc, based on Flamingos-2 (F2) and T-ReCS data taken at the Gemini South observatory. We report subarcsecond photometric measurements of the nucleus in J, H, and K _s filters, and at larger apertures. We do not detect nuclear variability. The nuclear spectra confirm that even in the K band the AGN emission-line features are completely obscured by dust. We detect a circumnuclear disk in the K band as well as in the mid-infrared N and Q _abands, with a radial scale length of ∼120 pc. The disk shows knots mostly in a ring-like arrangement that has been previously detected with Paα observations from the Hubble Space Telescope, indicating that these are deeply embedded, massive young star clusters. We present here the spectrum of one of the brightest unresolved objects (R < 5 pc), which we identify as a super star cluster candidate with M K s − 16.6 ± 0.4 . For the circumnuclear region, a detailed rotation curve allows us to measure a nuclear mass of M = (4.4 ± 3) × 10⁶ M _⊙ within a radius of ∼6.5 pc. We also report the detection of hot dust (∼1000 K) out to a nuclear distance of 80 pc measured along the semimajor axis.