arXiv subjects

Teodora-Elena Bulichi

Publications and source records attributed to Teodora-Elena Bulichi.

9 recordsLinked to original sources

arXiv2026

MEOW: The increase in the obscured AGN fraction in mid-infrared from 0 < z < 6 with JWST MIRI

Obscured active galactic nuclei (AGN) are often invoked to explain the rapid emergence of young quasars at high redshift and are crucial for building a complete census of AGN activity and black hole growth. The advent of the James Webb Space Telescope (JWST) extends the discovery space for obscured AGN into the mid-infrared (mid-IR) with unprecedented precision through reprocessed dust emission. In this work, we use deep JWST Mid-Infrared Instrument (MIRI) imaging from the MIRI Early Obscured AGN Wide Survey (MEOW), together with existing JWST Near Infrared Camera (NIRCam), spectroscopic, and Hubble Space Telescope imaging data, to identify a previously unrecognized population of obscured AGN out to z ~ 6. Using spectral energy distribution (SED) modeling of the MIRI-detected sources, we identify 883 AGN over an area of ~ 131 arcmin2 and construct the AGN bolometric luminosity function, including both obscured and unobscured sources, across five redshift bins. We find an excess in AGN abundance relative to UV-selected AGN luminosity functions, indicating a substantial obscured population missed by optical/UV surveys, with the inferred obscured fraction increasing with redshift and reaching ~ 98-99% in our highest-redshift bin, 4.5 < z < 6. We also find higher AGN abundances and obscured fractions than X-ray-based studies, consistent with a previously unrecognized population of heavily obscured, Compton-thick AGN revealed by mid-IR selection. These results suggest that a large fraction of supermassive black hole growth at early times occurs during heavily obscured phases largely inaccessible at other wavelengths.

astro-ph.GA↗

arXiv2026

Introducing the Lumina project: large-volume radiation-hydrodynamic simulations of the epochs of hydrogen and helium reionization

Understanding how galaxies and active galactic nuclei (AGN) jointly drive the reionization of the intergalactic medium (IGM) across cosmic time remains a major challenge in cosmology. We present Lumina, a large-volume radiation-hydrodynamic simulation that self-consistently follows the coupled evolution of the intergalactic medium, galaxies, and AGN through HI, HeI, and HeII reionization down to redshift $z=3$. Lumina evolves a cosmological volume of comoving side length $L_{\mathrm{box}}=500\,\mathrm{cMpc}$ with $2\times 6000^{3}$ resolution elements, corresponding to baryonic and dark-matter mass resolutions of $3.6\times 10^{6}\,\text{M}_{\odot}$ and $1.9\times 10^{7}\,\text{M}_{\odot}$, respectively. The simulation uses the moving-mesh code AREPO, combining the IllustrisTNG galaxy-formation model with a GPU-accelerated M1 radiation-transport solver in six frequency bins. The initial conditions employ separate transfer functions for baryons and dark matter and include their relative streaming velocity. Lumina predicts a late, predominantly stellar-driven hydrogen reionization, with the median sub-volume fully ionized by $z\approx 5.2$ and residual neutral HI patches persisting until $z\approx 4.75$. HeII reionization is driven self-consistently by AGN and is nearly complete by $z=3$. The simulation yields a Thomson-scattering optical depth in excellent agreement with Planck, an IGM thermal history and photoionization background broadly consistent with observational constraints, and a clear late-time thermal boost associated with HeII reionization. Its galaxy population remains consistent with the original IllustrisTNG project, while the larger volume improves statistics for rare objects, large-scale environments, and cosmic variance, enabling forward modelling of observables linking HI and HeII topologies to the evolving galaxy and AGN populations.

astro-ph.CO↗

arXiv2026

The MIRI Early Obscured-AGN Wide Survey (MEOW): A Population of Hidden AGN at $z \gtrsim 5$ Revealed by JWST/MIRI Imaging

We present the MIRI Early Obscured-AGN Wide Survey (MEOW), a JWST/MIRI imaging survey designed to detect dust-obscured active galactic nuclei (AGN) across cosmic time, with a particular focus on the high-redshift universe at $z \gtrsim 5$. MEOW observes the GOODS-N and GOODS-S fields with 43 pointings covering 95 arcmin$^2$ with the F1000W and F2100W filters, reaching depths of 0.5 and 3.6 $μ$Jy ($5σ$), respectively. Using spectral energy distribution (SED) modeling combining MEOW photometry with archival HST, JWST/NIRCam, and SCUBA-2 data, we identify a sample of 16 MIRI-selected AGN at $z = 4.5$--$7.2$ (12 spectroscopically confirmed), spanning bolometric luminosities of $L_{\rm bol} = 10^{44.6}$--$10^{46.4}$~erg~s$^{-1}$. Twelve of the 16 AGN are newly identified in this work, including at least five narrow-line AGN representing the obscured population to which broad-line spectroscopic searches are insensitive. Two broad-line AGN exhibit markedly different mid-infrared emission properties, consistent with one being a little red dot (LRD) and the other either a typical AGN or an LRD with unusually strong hot-dust emission. The MIRI-selected AGN bolometric luminosity function at $z = 4.5$--$6$ yields number densities comparable to those of broad-line AGN and LRDs, suggesting that obscured AGN contribute significantly to the total AGN census at these epochs. The narrow-line AGN reside in diverse host environments, with evidence for both circumnuclear and host-galaxy-scale obscuration, pointing to multiple physical mechanisms at work. These results establish JWST/MIRI imaging as an indispensable component of a multi-faceted approach to a complete census of early supermassive black hole growth.

astro-ph.GA↗

arXiv2026

The Lumina Project: Intergalactic Clumping and Recombination Sinks

Recombinations during the Epoch of Reionization are intrinsically inhomogeneous, with different regions of the intergalactic medium contributing unevenly depending on their density, temperature, ionization state, and spatial patchiness. We combine the high- and medium-resolution 95.5 cMpc Thesan-1 andh Thesan-2 runs with the significantly larger 500 cMpc Lumina simulation to measure clumping factors and recombination rates consistently across different resolutions and box sizes. We consider the standard ionized hydrogen clumping factor, $C_{\rm HII} \equiv \langle n_{\rm HII}^2\rangle/\langle n_{\rm HII}\rangle^2$, and a recombination-weighted clumping factor, $C_{\rm rec}$. Despite differences in resolution, volume, and reionization history, the simulations show an approximately universal clumping evolution at the 10-20% level when parametrized by the global ionized fraction $x_{\rm HII}$ rather than by redshift. Across all simulations, $C_{\rm rec}$ remains systematically below $C_{\rm HII}$, with the discrepancy increasing toward lower redshift as photoheating suppresses recombinations. In \lumina, the density-only prescription overpredicts the instantaneous recombination rate by factors of 1.29 at $z\approx8$ and 1.84 at $z\approx5$, and the cumulative recombination count by a factor of 1.45 by $z\approx5$. Mapping the recombination budget in the joint overdensity-temperature plane reveals that the dominant recombination ridges closely follow simple analytic thermal equilibrium bands. Finally, we introduce a phase-space recombination integral and define a phase-space clumping factor, $C_{\rm ps}(Δ,T)$, which isolates the intrinsic recombination enhancement associated with ionization structure and thermal state at fixed overdensity and temperature.

astro-ph.GA↗

arXiv2026

The Lumina Project: The Demographics of Active Galactic Nuclei from Quasars to Little Red Dots at $z\geq 3$

High-redshift active galactic nuclei (AGN) serve as powerful probes of early black-hole growth, galaxy formation, and the evolving intergalactic medium (IGM). In this work, we use Lumina, a cosmological radiation-hydrodynamic simulation spanning the epochs of hydrogen and helium reionization, which combines a large $(500\,{\rm cMpc})^3$ volume with $2\times 6000^3$ resolution elements, to explore high-redshift AGN. The simulation self-consistently follows hundreds of millions of galaxies and supermassive black holes (SMBHs), together with their impact on the ionization and thermal state of the IGM. We exploit this uniquely large dynamic range to predict multi-band AGN luminosity functions (LFs) at $z \geq 3$, from hard X-rays to the mid-infrared. These predictions encompass both moderately luminous quasars and the faint ``Little Red Dots'' (LRDs) uncovered by JWST. We develop an empirical model that maps simulated SMBHs onto observed AGN using bolometric and extinction/absorption corrections for canonical AGN and LRDs, and in which SMBHs with $M_{\rm BH}\leq 10\,M_{\rm seed} \sim 10^{7}\,{\rm M}_{\odot}$ stay in the LRD phase with a duty cycle of $30\%$. This simple framework reproduces the observed LFs and clustering of LRDs. Meanwhile, the pre-JWST quasar LF constraints are recovered, although we find that a $\sim 0.3$ dex log-normal scatter in bolometric luminosity is required to reproduce the bright end. We place the simulated AGN population in the cosmological context by quantifying the redshift evolution of AGN and LRD number densities, and their contributions to the integrated BH mass densities. The same AGN population is the dominant driver for the HeII reionization modelled self-consistently in Lumina. This empirical AGN model paves the way for general population-synthesis models of high-redshift AGN, including LRDs, in a unified cosmological framework.

astro-ph.GA↗

arXiv2025

High-redshift AGN population in radiation-hydrodynamics simulations

High-redshift active galactic nuclei (AGN) have long been recognized as key probes of early black hole growth and galaxy evolution. However, modeling this population remains difficult due to the wide range of luminosities and black hole masses involved, and the high computational costs of capturing the hydrodynamic response of gas and evolving radiation fields on-the-fly. In this study, we present a new suite of simulations based on the IllustrisTNG galaxy formation framework, enhanced with on-the-fly radiative transfer, to examine AGN at high redshift (z > 5) in a protocluster environment extracted from the MillenniumTNG simulation. We focus on the co-evolution of black holes and their host galaxies, as well as the radiative impact on surrounding intergalactic gas. The model predicts that black holes form in overdense regions and lie below the local black hole-stellar mass relation, with stellar mass assembly preceding significant black hole accretion. Ionizing photons are primarily produced by stars, which shape the morphology of ionized regions and drive reionization. Given the restrictive black hole growth in the original IllustrisTNG model, we reduce the radiative efficiency from 0.2 to 0.1, resulting in higher accretion rates for massive black holes, more bursty growth, and earlier AGN-driven quenching. However, the resulting AGN remain significantly fainter than observed high-redshift quasars. As such, to incorporate this missing population, we introduce a quasar boosted model, in which we artificially boost the AGN luminosity. This results in strong effects on the surrounding gas, most notably a proximity effect, and large contributions to He ionization.

astro-ph.GA↗

arXiv2024

How galaxy properties vary with filament proximity in the SIMBA simulations

We explore the dependence of global galaxy properties in the SIMBA simulation as a function of distance from filaments identified using DisPerSe. We exclude halos with mass $M_h>10^{13}M_\odot$ to mitigate the impact of group and cluster environments. Galaxies near filaments are more massive and have more satellites, which we control for by examining deviations from best-fit scaling relations. At $z=0$, star formation (SF) is significantly suppressed within $\lesssim 100$ kpc of filaments, more strongly for satellites, indicating substantial pre-processing in filaments. By $z=2$, the trend is weak and if anything indicates an increase in SF activity close to filaments. The suppression at $z\lesssim 1$ is accompanied by lowered \HI fractions, and increased metallicities, quenched fractions, and dispersion-dominated systems. $H_2$ fractions are not strongly suppressed when controlling for stellar mass, suggesting that star formation efficiency drives the drop in SF. By comparing amongst different SIMBA feedback variant runs, we show that the majority of SF suppression owes to filamentary shock-heating, but there is a non-trivial additional effect from AGN feedback. When looking around massive ($M_h>10^{13}M_\odot$) halos, those galaxies near filaments behave somewhat differently, indicating that filaments provide an additional environmental effect relative to halos. Finally, we compare SIMBA results to EAGLE and IllustrisTNG at $z=0$, showing that all models predict SF suppression within $\lesssim 100$ kpc of filaments, nonetheless, detailed differences may be observationally testable.

astro-ph.GA↗

arXiv2023

Expanding on the Fundamental Metallicity Relation in Dwarf Galaxies with MUSE

The mass-metallicity relation (MZR) represents one of the most important scaling relations in the context of galaxy evolution, comprising a positive correlation between stellar mass and metallicity (Z). The fundamental metallicity relation (FMR) introduces a new parameter, the star formation rate (SFR), in the dependence. While several studies found that Z is anti-correlated with the SFR at fixed mass, the validity of this statement has been questioned extensively and no widely-accepted consensus has been reached yet. With this work, we investigate the FMR in nine nearby, spatially-resolved, dwarf galaxies, using gas diagnostics on integral-field spectroscopic data of the Multi Unit Spectroscopic Explorer (MUSE), pushing such investigations to lower galaxy masses and higher resolutions. We find that both the MZR and FMR exhibit different behaviours within different star forming regions of the galaxies. We find that the SFR surface density - metallicity anti-correlation is tighter in the low-mass galaxies of our sample. For all the galaxies considered, we find a SFR surface density - stellar mass surface density correlation. We propose that the main reason behind these findings is connected to the accretion mechanisms of the gas fuelling star formation -- low-mass, metal-poor galaxies accrete pristine gas from the intergalactic medium, while in more massive and metal-enriched systems the gas responsible for star formation is recycled from previous star forming episodes.

astro-ph.GA↗

arXiv2022

Nuclear star cluster formation in star-forming dwarf galaxies

Nuclear star clusters (NSCs) are massive star clusters found in all types of galaxies from dwarfs to massive galaxies. Recent studies show that while low-mass NSCs in dwarf galaxies ($M_\text{gal} < 10^{9} M_\odot$) form predominantly out of the merger of globular clusters (GCs), high-mass NSCs in massive galaxies have assembled most of their mass through central enriched star formation. So far, these results of a transition in the dominant NSC formation channel have been based on studies of early-type galaxies and massive late-type galaxies. Here, we present the first spectroscopic analysis of a sample of nine nucleated late-type dwarf galaxies with the aim of identifying the dominant NSC formation pathway. We use integral-field spectroscopy data obtained with the Multi Unit Spectroscopic Explorer (MUSE) instrument to analyse the ages, metallicities, star formation histories, and star formation rates of the NSCs and their surroundings. Our sample includes galaxies with stellar masses $M_\text{gal} = 10^7 - 10^9 M_\odot$ and NSC masses $M_\text{NSC} = 6 \times 10^4 - 6 \times 10^{6} M_\odot$. Although all NSC spectra show emission lines, this emission is not always connected to star formation within the NSC, but rather to other regions along the line-of-sight. The NSC star formation histories reveal that metal-poor and old populations dominate the stellar populations in five NSCs, possibly stemming from the inspiral of GCs. The NSCs of the most massive galaxies in our sample show significant contributions from young and enriched populations that indicate additional mass growth through central star formation. Our results support previous findings of a transition in the dominant NSC formation channel with galaxy mass, showing that the NSCs in low-mass galaxies predominantly grow through the inspiral of GCs, while central star formation can contribute to NSC growth in more massive galaxies.

astro-ph.GA↗