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As gravitational wave detections increase the number of observed compact binaries (consisting of neutron stars or blacks), we begin to probe the different conditions producing these binaries. Most studies of compact remnant formation focus either on stellar collapse from the evolution of field binary stars in gas-free environments or the formation of stars in clusters where dynamical interactions capture the compact objects, forming binaries. But a third scenario exists. In this paper, we study the fate of massive stars formed, accrete gas, and evolve in the dense disks surrounding supermassive black holes. We calculate the explosions produced and compact objects formed by the collapse of these massive stars. Nucleosynthetic yields may provide an ideal, directly observable, diagnostic of the formation and fate of these stars in active galactic nuclei. We present a first study of the explosive yields from these stars, comparing these yields with the observed nucleosynthetic signatures in the disks around supermassive stars with quasars. We show that, even though these stars tend to form black holes, their rapid rotation leads to disks that can eject a considerable amount of iron during the collapse of the star. The nucleosynthetic yields from these stars can produce constraints on the number of systems formed in this manner, but further work is needed to exploit variations from the initial models presented in this paper., Comment: 15 pages, 17 figures

The James Webb Space Telescope (JWST) has uncovered a new population of candidate broad-line AGN emerging in the early Universe, named ''little red dots'' (LRDs) because of their compactness and red colors at optical wavelengths. LRDs appear to be surprisingly abundant ($\approx 10^{-5}\,\mathrm{cMpc}^{-3}$) given that their inferred bolometric luminosities largely overlap with the ones of the UV-luminous quasars identified at high $z$ in wide-field spectroscopic surveys. In this work, we investigate how the population of LRDs and/or other UV-obscured AGN relates to the one of unobscured, UV-selected quasars. By comparing their number densities, we infer an extremely large and rapidly evolving obscured:unobscured ratio, ranging from $\approx20:1$ at $z\approx4$ to $\approx2300:1$ at $z\approx7$, and possibly extending out to very high ($\approx10^{47}\,\mathrm{erg}\,\mathrm{s}^{-1}$) bolometric luminosities. This large obscured:unobscured ratio is incompatible with the UV-luminous duty cycle measured for unobscured quasars at $z\approx4-6$, suggesting that LRDs are too abundant to be hosted by the same halos as unobscured quasars. This implies that either (a) the bolometric luminosities of LRDs are strongly overestimated (possibly because LRDs are dominated by stellar galaxy light) or (b) LRDs follow different scaling relations than the ones of UV-selected quasars, representing a new population of accreting SMBHs emerging in the early Universe. A direct comparison between the clustering of LRDs and the one of faint UV-selected quasars will ultimately confirm these findings, and shed light on key properties of LRDs such as their host mass distribution and duty cycle. We provide a mock analysis for the clustering of LRDs and show that it is feasible with current and upcoming JWST surveys., Comment: 15 pages. Submitted to MNRAS

We separately assess elemental abundances in AGNs' broad and narrow emission line regions (BLR and NLR), based on a critical assessment of published results together with new photoionization models. We find 1) He/H enhancements in some AGN, exceeding what can be explained by normal chemical evolution and confirm 2) super-solar {\alpha} abundance, though to a lesser degree than previously reported. We also reaffirm 3) a N/O ratio consistent with secondary production; 4) solar or slightly sub-solar Fe abundance; and 5) red-shift independent metallicity, in contrast with galactic chemical evolution. We interpret 6) the larger metallicity in the BLR than NRL in terms of an in situ stellar evolution and pollution in AGN discs (SEPAD) model. We attribute: a) the redshift independence to the heavy element pollutants being disposed into the disc and accreted onto the central supermassive black hole (SMBH); b) the limited He excess to the accretion-wind metabolism of a top-heavy population of evolving massive main sequence stars; c) the super-solar CNO enrichment to the nuclear synthesis during their post-main-sequence evolution; d) the large N/O to the byproduct of multiple stellar generations; and e) the Mg, Si, and Fe to the ejecta of type II supernovae in the disc. These results provide supporting evidence for f) ongoing self-regulated star formation, g) adequate stellar luminosity to maintain marginal gravitational stability, h) prolific production of seeds and i) dense coexistence of subsequently-grown residual black hole populations in AGN discs., Comment: 17 pages, 8 figures, accepted for publication in MNRAS

We propose a solution to the problem of accretion disc sizes in active galactic nuclei being larger when measured by reverberation mapping than predicted by theory. Considering blackbody reprocessing on a disc with thickness profile $H(r)$, our solution invokes a steep rim or rippled structures irradiated by the central lamp-post. We model the continuum lags and the faint and bright disc spectral energy distribution (SED) in the best-studied case NGC 5548 (black hole mass $M = 7\times10^{7} M_\odot$, disc inclination $i=45^\circ$). With the lamp-post off, the observed disc SED requires a low accretion rate ($\dot{M} \sim 0.0014 M_\odot$/yr) and high prograde black hole spin ($a \sim 0.93$). Reprocessing on the thin disc gives time lags increasing with wavelength but 3 times smaller than observed. Introducing a steep $H(r)$ rim, or multiple crests, near $r = 5$ light days, reprocessing on their steep centre-facing slopes increases temperatures from $\sim1500$ K to $\sim6000$ K and this increases optical lags to match the lag data. Most of the disc surface maintains the cooler $T\propto r^{-3/4}$ temperature profile that matches the SED. The bright lamp-post may be powered by magnetic links tapping the black hole spin. The steep rim occurs near the sublimation radius for dust in the disc, as in the "failed disc wind model" for broad-line clouds. Lens-Thirring torques aligning the disc and black hole spin may also raise a warp and associated waves. In both scenarios, the small density scale height implied by the inferred value of $H(r)$ suggests possible marginal gravitational instability in the disc., Comment: 17 pages, 7 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society