Browsing by Author "Davé, Romeel"
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Item Boundless baryons: how diffuse gas contributes to anisotropic tSZ signal around simulated three hundred clusters(Oxford University Press, 2023) Davé, Romeel; Lokken, Martine; Cui, WeiguangUpcoming advances in galaxy surveys and cosmic microwave background data will enable measurements of the anisotropic distribution of diffuse gas in filaments and superclusters at redshift z = 1 and beyond, observed through the thermal Sunyaev–Zel’dovich (tSZ) effect. These measurements will help distinguish between different astrophysical feedback models, account for baryons that appear to be ‘missing’ from the cosmic census, and present opportunities for using locally anisotropic tSZ statistics as cosmological probes. This study seeks to guide such future measurements by analysing whether diffuse intergalactic gas is a major contributor to anisotropic tSZ signal in THE THREE HUNDRED GIZMO-SIMBA hydrodynamic simulations. We apply multiple different halo boundary and temperature criteria to divide concentrated from diffuse gas at z = 1, then create mock Compton- y maps for the separated components. The maps from 98 simulation snapshots are centred on massive galaxy clusters, oriented by the most prominent filament axis in the galaxy distribution, and stacked. Results vary significantly depending on the definition used for diffuse gas, indicating that assumptions should be clearly defined when claiming observations of the warm-hot intergalactic medium. In all cases, the diffuse gas is important, contributing 25–60 per cent of the tSZ signal in the far field (>4 h−1 comoving Mpc) from the stacked clusters. The gas 1–2 virial radii from halo centres is especially key. Oriented stacking and environmental selections help to amplify the signal from the warm-hot intergalactic medium, which is aligned but less concentrated along the filament axis than the hot halo gas.Item Breaking baryon-cosmology degeneracy with the electron density power spectrum(IOP Publishing, 2022) Nicola, Andrina; Villaescusa-Navarro, Francisco; Davé, RomeelUncertain feedback processes in galaxies affect the distribution of matter, currently limiting the power of weak lensing surveys. If we can identify cosmological statistics that are robust against these uncertainties, or constrain these effects by other means, then we can enhance the power of current and upcoming observations from weak lensing surveys such as DES, Euclid, the Rubin Observatory, and the Roman Space Telescope. In this work, we investigate the potential of the electron density auto-power spectrum as a robust probe of cosmology and baryonic feedback.Item Ceers key paper. I. An early look into the first 500myr of galaxy formation with jwst(American Astronomical Society, 2023) Finkelstein, Steven L.; Bagley, Micaela B.; Davé, RomeelWe present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin2 , to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z ∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the z ∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at MUV ∼ −20 appears to evolve very little from z ∼ 9 to 11. We also find that the abundance (surface density [arcmin−2 ]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role.Item Cosmic sands: the origin of dusty, star-forming galaxies in the epoch of reionization(The astrophysical journal, 2023) Davé, Romeel; Lower, Sidney; Narayanan, DesikaWe present the Cosmic Sands suite of cosmological zoom-in simulations based on the simba galaxy formation model in order to study the buildup of the first massive and dusty galaxies in the early universe. Residing in the most massive halos, we find that the compact proto-massive galaxies undergo nearly continuous mergers with smaller subhalos, boosting star formation rates (SFRs) and the buildup of stellar mass. The galaxies are already appreciably chemically evolved by z = 7, with modeled dust masses comparable to those inferred from observations in the same epoch, except for the most extreme systems. We track gas accretion onto the galaxies to understand how extreme SFRs can be sustained by these early systems. We find that smooth gas accretion can maintain SFRs above 250 M · yr-1, but to achieve SFRs that boost galaxies well above the main sequence, a larger perturbation like a gas-rich major merger is necessary to trigger a starburst episode. Post-processing the Cosmic Sands simulations with dust RT, we find that, while the infrared luminosities of the most-dust-rich galaxies are comparable to local ULIRGs, they are substantially dimmer than classical z = 2 submillimeter galaxies. We end with a discussion on the possible reasons for this discrepancy at the highest masses and the future work we intend to carry out to study the chemical enrichment of the earliest dusty galaxies.Item The diversity and variability of star formation histories in models of galaxy evolution(2020-07-25) Davé, Romeel; Iyer, Kartheik; Tacchella, SandroUnderstanding the variability of galaxy star formation histories (SFHs) across a range of time-scales provides insight into the underlying physical processes that regulate star formation within galaxies. We compile the SFHs of galaxies at z = 0 from an extensive set of models, ranging from cosmological hydrodynamical simulations (Illustris, IllustrisTNG, Mufasa, Simba, EAGLE), zoom simulations (FIRE-2, g14, and Marvel/Justice League), semi-analytic models (Santa Cruz SAM) and empirical models (UniverseMachine), and quantify the variability of these SFHs on different time-scales using the power spectral density (PSD) formalism. We find that the PSDs are well described by broken power laws, and variability on long time-scales (1 Gyr) accounts for most of the power in galaxy SFHs. Most hydrodynamical models show increased variability on shorter time-scales (300 Myr) with decreasing stellar mass. Quenching can induce ∼0.4−1 dex of additional power on time-scales >1 Gyr. The dark matter accretion histories of galaxies have remarkably self-similar PSDs and are coherent with the in situ star formation on time-scales >3 Gyr. There is considerable diversity among the different models in their (i) power due to star formation rate variability at a given time-scale, (ii) amount of correlation with adjacent time-scales (PSD slope), (iii) evolution of median PSDs with stellar mass, and (iv) presence and locations of breaks in the PSDs. The PSD framework is a useful space to study the SFHs of galaxies since model predictions vary widely. Observational constraints in this space will help constrain the relative strengths of the physical processes responsible for this variability.Item Effects of active galactic nucleus feedback on cold gas depletion and quenching of central galaxies(American Astronomical Society, 2022-12-27) Davé, Romeel; Ma, Wenlin; Liu, KexinWe investigate the influence of active galactic nucleus (AGN) feedback on the galaxy cold gas content and its connection to galaxy quenching in three hydrodynamical simulations of Illustris, IllustrisTNG, and SIMBA. By comparing to the observed atomic and molecular neutral hydrogen measurements for central galaxies, we find that Illustris overpredicts the cold gas masses in star-forming galaxies and significantly underpredicts them for quenched galaxies. IllustrisTNG performs better in this comparison than Illustris, but quenched galaxies retain too much cold gas compared with observations. SIMBA shows good agreement with observations, by depleting the global cold gas reservoir for quenched galaxies. We find that the discrepancies in IllustrisTNG are caused by its weak kinetic AGN feedback that only redistributes the cold gas from the inner disks to the outer regions and reduces the inner cold gas densities. It agrees with observations much better when only the cold gas within the stellar disk is considered to infer the star formation rates. From dependences of the cold gas reservoir on the black hole mass and Eddington ratio, we find that the cumulative energy release during the black hole growth is the dominant reason for the cold gas depletion and thus the galaxy quenching. We further measure the central stellar surface density within 1 kpc (Σ1) for the high-resolution run of IllustrisTNG and find a tight correlation between Σ1 and black hole mass. It suggests that the observed decreasing trend of cold gas mass with Σ1 is also a reflection of the black hole growth.Item Efficient long-range active galactic nuclei (agns) feedback affects the low-redshift lyα forest(American Astronomical Society, 2023) Tillman, Megan Taylor; Burkhart, Blakesley; Davé, RomeelActive galactic nuclei (AGNs) feedback models are generally calibrated to reproduce galaxy observables such as the stellar mass function and the bimodality in galaxy colors. We use variations of the AGN feedback implementations in the IllustrisTNG (TNG) and SIMBA cosmological hydrodynamic simulations to show that the low-redshift Lyα forest can provide constraints on the impact of AGN feedback. We show that TNG overpredicts the number density of absorbers at column densities NHI < 1014 cm−2 compared to data from the Cosmic Origins Spectrograph (in agreement with previous work), and we demonstrate explicitly that its kinetic feedback mode, which is primarily responsible for galaxy quenching, has a negligible impact on the column density distribution (CDD) of absorbers. In contrast, we show that the fiducial SIMBA model, which includes AGN jet feedback, is the preferred fit to the observed CDD of the z = 0.1 Lyα forest across 5 orders of magnitude in column density. We show that the SIMBA results with jets produce a quantitatively better fit to the observational data than the SIMBA results without jets, even when the ultraviolet background is left as a free parameter.Item Finding universal relations in Subhalo properties with artificial intelligence(The Astrophysical Journal, 2022) Davé, RomeelWe use a generic formalism designed to search for relations in high-dimensional spaces to determine if the total mass of a subhalo can be predicted from other internal properties such as velocity dispersion, radius, or star formation rate. We train neural networks using data from the Cosmology and Astrophysics with MachinE Learning Simulations project and show that the model can predict the total mass of a subhalo with high accuracy: more than 99% of the subhalos have a predicted mass within 0.2 dex of their true value. The networks exhibit surprising extrapolation properties, being able to accurately predict the total mass of any type of subhalo containing any kind of galaxy at any redshift from simulations with different cosmologies, astrophysics models, subgrid physics, volumes, and resolutions, indicating that the network may have found a universal relation. We then use different methods to find equations that approximate the relation found by the networks and derive new analytic expressions that predict the total mass of a subhalo from its radius, velocity dispersion, and maximum circular velocity. We show that in some regimes, the analytic expressions are more accurate than the neural networks. The relation found by the neural network and approximated by the analytic equation bear similarities to the virial theorem.Item Galaxy cold gas contents in modern cosmological hydrodynamic simulations(Oxford University Press, 2020-07-03) Davé, Romeel; Crain, Robert; Stevens, AdamWe present a comparison of galaxy atomic and molecular gas properties in three recent cosmological hydrodynamic simulations, namely SIMBA, EAGLE, and IllustrisTNG, versus observations from z ∼ 0 to 2. These simulations all rely on similar subresolution prescriptions to model cold interstellar gas that they cannot represent directly, and qualitatively reproduce the observed z ≈ 0 H I and H2 mass functions (HIMFs and H2MFs, respectively), CO(1–0) luminosity functions (COLFs), and gas scaling relations versus stellar mass, specific star formation rate, and stellar surface density μ∗, with some quantitative differences. To compare to the COLF, we apply an H2-to-CO conversion factor to the simulated galaxies based on their average molecular surface density and metallicity, yielding substantial variations in αCO and significant differences between models. Using this, predicted z = 0 COLFs agree better with data than predicted H2MFs. Out to z ∼ 2, EAGLE’s and SIMBA’s HIMFs and COLFs strongly increase, while IllustrisTNG’s HIMF declines and COLF evolves slowly. EAGLE and SIMBA reproduce high-LCO(1–0) galaxies at z ∼ 1–2 as observed, owing partly to a median αCO(z = 2) ∼ 1 versus αCO(z = 0) ∼ 3. Examining H I, H2, and CO scaling relations, their trends with M∗ are broadly reproduced in all models, but EAGLE yields too little H I in green valley galaxies, IllustrisTNG and SIMBA overproduce cold gas in massive galaxies, and SIMBA overproduces molecular gas in small systems. Using SIMBA variants that exclude individual active galactic nucleus (AGN) feedback modules, we find that SIMBA’s AGN jet feedback is primarily responsible by lowering cold gas contents from z ∼ 1 → 0 by suppressing cold gas in M∗ 1010 M galaxies, while X-ray feedback suppresses the formation of high-μ∗ systemsItem Imprints of temperature fluctuations on the z ∼ 5 Lyman-α forest: a view from radiation-hydrodynamic simulations of reionization(Oxford academic, 2019) Davé, RomeelReionization leads to large spatial fluctuations in the intergalactic temperature that can persist well after its completion. We study the imprints of such fluctuations on the z ∼ 5 Ly α forest flux power spectrum using a set of radiation-hydrodynamic simulations that model different reionization scenarios. We find that large-scale coherent temperature fluctuations bring ∼20–60 per cent extra power at k ∼ 0.002 s km−1, with the largest enhancements in the models where reionization is extended or ends the latest. On smaller scales (k 0.1 s km−1), we find that temperature fluctuations suppress power by 10 per cent. We find that the shape of the power spectrum is mostly sensitive to the reionization mid-point rather than temperature fluctuations from reionization’s patchiness. However, for all of our models with reionization mid-points of z ≤ 8 (z ≤ 12), the shape differences are 20 per cent (40 per cent) because of a surprisingly well-matched cancellation between thermal broadening and pressure smoothing that occurs for realistic thermal histories. We also consider fluctuations in the ultraviolet background, finding their impact on the power spectrum to be much smaller than temperature fluctuations at k 0.01 s km−1. Furthermore, we compare our models to power spectrum measurements, finding that none of our models with reionization mid-points of z < 8 is strongly preferred over another and that all of our models with mid-points of z ≥ 8 are excluded at 2.5σ. Future measurements may be able to distinguish between viable reionization models if they can be performed at lower k or, alternatively, if the error bars on the high-k power can be reduced by a factor of 1.5.Item The origin and evolution of Lyα blobs in cosmological galaxy formation simulations(IOP Publishing Ltd, 2021) Davé, Romeel; Kimock, B; Narayanan, DHigh-redshift Lyα blobs (LABs) are an enigmatic class of objects that have been the subject of numerous observational and theoretical investigations. It is of particular interest to determine the dominant power sources for their luminosity, as direct emission from H ii regions, cooling gas, and fluorescence due to the presence of active galactic nuclei (AGNs) can all contribute significantly. In this paper, we present the first theoretical model to consider all of these physical processes in an attempt to develop a model for the origin of LABs. This is achieved by combining a series of high-resolution cosmological zoom-in simulations with ionization and Lyα radiative transfer models. We find that massive galaxies display a range of Lyα luminosities and spatial extents (which strongly depend on the limiting surface brightness used) over the course of their lives, though regularly exhibit luminosities and sizes consistent with observed LABs. The model LABs are typically powered from a combination of recombination in star-forming galaxies, as well as cooling emission from gas associated with accretion. When AGNs are included in the model, the fluorescence caused by active galactic nucleus-driven ionization can be a significant contributor to the total Lyα luminosity as well. Within our modeled mass range, there are no obvious threshold physical properties that predict the appearance of LABs, and only weak correlations of the luminosity with the physical properties of the host galaxy.Item The origin of the dust extinction curve in milky way-like galaxies(Oxford University Press, 2021) Davé, Romeel; Vogelsberger, M.; Li, Q; Torrey, P.; Narayanan, D.We develop a cosmological model for the evolution of dust grains in galaxies with a distribution of sizes in order to understand the origin of the Milky Way dust extinction curve. Our model considers the formation of active dust in evolved stars, growth by accretion and coagulation, and destruction processes via shattering, sputtering, and astration in the ISM of galaxies over cosmic time. Our main results follow. Galaxies in our cosmological model with masses comparable to the Milky Way's at z ∼0 exhibit a diverse range of extinction laws, though with slopes and bump strengths comparable to the range observed in the Galaxy. The progenitors of the Milky Way have steeper slopes and only flatten to slopes comparable to the Galaxy at z ∼1. This owes to increased grain growth rates at late times/in high-metallicity environments driving up the ratio of large to small grains, with a secondary dependence on the graphite-to-silicate ratio evolution. The UV bump strengths depend primarily on the graphite-to-silicate ratio, and remain broadly constant in MW-like galaxies between z = 3 and z = 0, though show slight variability. Our models span comparable regions of bump-slope space as sightlines in the Galaxy do, though there is a lack of clear relationship between the model slopes and bump strengths owing to variations among galaxies in the graphite-to-silicate ratio. Our model provides a novel framework to study the origins and variations of dust extinction curves in galaxies over cosmic time. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Item The vandels survey: The star-formation histories of massive quiescent galaxies at 1.0 < z < 1.3(Oxford Academics, 2019) Davé, Romeel; Carnall, A. C.; McLure, R. J.We present a Bayesian full-spectral-fitting analysis of 75 massive (M∗>1010.3M⊙) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the BAGPIPES code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of 1.48+0.34−0.39 Gyr per decade in mass, although this shows signs of flattening at M∗>1011M⊙Item X-ray emission from hot gas in galaxy groups and clusters in SIMBA(Oxford University Press, 2020-08-31) Davé, Romeel; Robson, DylanWe examine X-ray scaling relations for massive haloes (M500 > 1012.3 M) in the SIMBA galaxy formation simulation. The X-ray luminosity, LX versus M500 has power-law slopes ≈5 3 and ≈8 3 above and below 1013.5 M, deviating from the self-similarity increasingly to low masses. TX − M500 is self-similar above this mass, and slightly shallower below it. Comparing SIMBA to observed TX scalings, we find that LX, LX-weighted [Fe/H], and entropies at 0.1R200 (S0.1) and R500 (S500) all match reasonably well. S500 − TX is consistent with self-similar expectations, but S0.1 − TX is shallower at lower TX, suggesting the dominant form of heating moves from gravitational shocks in the outskirts to non-gravitational feedback in the cores of smaller groups. SIMBA matches observations of LX versus central galaxy stellar mass M∗, predicting the additional trend that star-forming galaxies have higher LX(M∗). Electron density profiles for M500 > 1014 M haloes show a ∼0.1R200 core, but the core is larger at lower masses. TX are reasonably matched to observations, but entropy profiles are too flat versus observations for intermediate-mass haloes, with Score ≈ 200–400 keV cm2. SIMBA’s [Fe/H] profile matches observations in the core but overenriches larger radii. We demonstrate that SIMBA’s bipolar jet AGN feedback is most responsible for increasingly evacuating lower-mass haloes, but the profile comparisons suggest this may be too drastic in the inner regions.