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Khochfar, Sadegh

Publications and source records attributed to Khochfar, Sadegh.

QUOTAS: A New Research Platform for the Data-driven Discovery of Black Holes

We present QUOTAS, a novel research platform for the data-driven investigation of supermassive black hole (SMBH) populations. While SMBH data—observations and simulations—have grown in complexity and abundance, our computational environments and tools have not matured commensurately to exhaust opportunities for discovery. To explore the BH, host galaxy, and parent dark matter halo connection—in this pilot version—we assemble and colocate the high-redshift, z > 3 quasar population alongside simulated data at the same cosmic epochs. As a first demonstration of the utility of QUOTAS, we investigate correlations between observed Sloan Digital Sky Survey (SDSS) quasars and their hosts with those derived from simulations. Leveraging machine-learning algorithms (ML), to expand simulation volumes, we show that halo properties extracted from smaller dark-matter-only simulation boxes successfully replicate halo populations in larger boxes. Next, using the Illustris-TNG300 simulation that includes baryonic physics as the training set, we populate the larger LEGACY Expanse dark-matter-only box with quasars, and show that observed SDSS quasar occupation statistics are accurately replicated. First science results from QUOTAS comparing colocated observational and ML-trained simulated data at z3 are presented. QUOTAS demonstrates the power of ML, in analyzing and exploring large data sets, while also offering a unique opportunity to interrogate theoretical assumptions that underpin accretion and feedback models. QUOTAS and all related materials are publicly available at the Google Kaggle platform. (The full data set—observational data and simulation data—are available at: https://www.kaggle.com/ and the codes are available at:https://www.kaggle.com/datasets/quotasplatform/quotas)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Growth of First Galaxies: Impacts of Star Formation and Stellar Feedback

Recent observations have detected galaxies at high-redshift z∼6--11, and revealed the diversity of their physical properties, from normal star-forming galaxies to starburst galaxies. To understand the properties of these observed galaxies, it is crucial to understand the star formation (SF) history of high-redshift galaxies under the influence of stellar feedback. In this work, we present the results of cosmological hydrodynamic simulations with zoom-in initial conditions, and investigate the formation of the first galaxies and their evolution toward observable galaxies at z∼6. We focus on three different galaxies that end up in halos with masses M{sub h}=2.4×10{sup 10} h{sup −1} M{sub ⊙} (Halo-10), 1.6×10{sup 11} h{sup −1} M{sub ⊙} (Halo-11), and 0.7×10{sup 12} h{sup −1} M{sub ⊙} (Halo-12) at z = 6. Our simulations also probe the impacts of different subgrid assumptions, i.e., SF efficiency and cosmic reionization, on SF histories in the first galaxies. We find that SF occurs intermittently due to supernova (SN) feedback at z≳10, and then it proceeds more smoothly as the halo mass grows at lower redshifts. Galactic disks are destroyed due to SN feedback, while galaxies in simulations with no feedback or lower SF efficiency models can sustain a galactic disk for long periods ≳10 Myr. The expulsion of gas at the galactic center also affects the inner dark matter density profile for a short period. Our simulated galaxies in Halo-11 and Halo-12 reproduce the SF rates and stellar masses of observed Lyα emitters at z∼7--8 fairly well given the observational uncertainties.

79 ASTRONOMY AND ASTROPHYSICS↗

The spectral evolution of the first Galaxies. III. Simulated James Webb Space Telescope spectra of reionization-epoch galaxies with Lyman continuum leakage

Using four different suites of cosmological simulations, we generate synthetic spectra for galaxies with different Lyman-continuum escape fractions (f (esc)) at redshifts $z\approx 7$–9, in the rest-frame wavelength range relevant for the James Webb Space Telescope (JWST) NIRSpec instrument. By investigating the effects of realistic star formation histories and metallicity distributions on the EW(Hβ)–β diagram (previously proposed as a tool for identifying galaxies with very high f (esc)), we find that neither of these effects are likely to jeopardize the identification of galaxies with extreme Lyman-continuum leakage. Based on our models, we expect that essentially all $z\approx 7\mbox{--}9$ galaxies that exhibit rest-frame $\mathrm{EW}({\rm{H}}\beta )\lesssim 30$ Å to have ${f}_{\mathrm{esc}}\gt 0.5$. Incorrect assumptions concerning the ionizing fluxes of stellar populations or the dust properties of $z\gt 6$ galaxies can in principle bias the selection, but substantial model deficiencies of this type should at the same time be evident from offsets in the observed distribution of $z\gt 6$ galaxies in the EW(Hβ)–β diagram compared to the simulated distribution. Such offsets would thereby allow JWST/NIRSpec measurements of these observables to serve as input for further model refinement.

79 ASTRONOMY AND ASTROPHYSICS↗

CONNECTION BETWEEN DYNAMICALLY DERIVED INITIAL MASS FUNCTION NORMALIZATION AND STELLAR POPULATION PARAMETERS

We report on empirical trends between the dynamically determined stellar initial mass function (IMF) and stellar population properties for a complete, volume-limited sample of 260 early-type galaxies from the ATLAS{sup 3D} project. We study trends between our dynamically derived IMF normalization α{sub dyn} ≡ (M/L){sub stars}/(M/L){sub Salp} and absorption line strengths, and interpret these via single stellar population-equivalent ages, abundance ratios (measured as [α/Fe]), and total metallicity, [Z/H]. We find that old and alpha-enhanced galaxies tend to have on average heavier (Salpeter-like) mass normalization of the IMF, but stellar population does not appear to be a good predictor of the IMF, with a large range of α{sub dyn} at a given population parameter. As a result, we find weak α{sub dyn}-[α/Fe] and α{sub dyn} –Age correlations and no significant α{sub dyn} –[Z/H] correlation. The observed trends appear significantly weaker than those reported in studies that measure the IMF normalization via the low-mass star demographics inferred through stellar spectral analysis.

79 ASTRONOMY AND ASTROPHYSICS↗