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    We present a suite of 16 high-resolution hydrodynamic simulations of an isolated dwarf galaxy (gaseous and stellar disc plus a stellar bulge) within an initially cuspy dark matter (DM) halo, including self-interactions between the DM particles; as well as stochastic star formation and subsequent supernova feedback (SNF), implemented using the stellar feedback model SMUGGLE. The simulations start from identical initial conditions, and we regulate the strength of DM self-interactions and SNF by systematically varying the self-interacting DM (SIDM) momentum transfer cross-section and the gas density threshold for star formation. The DM halo forms a constant density core of similar size and shape for several combinations of those two parameters. Haloes with cores that are formed due to SIDM (adiabatic cusp-core transformation) have velocity dispersion profiles that are closer to isothermal than those of haloes with cores that are formed due to SNF in simulations with bursty star formation (impulsive cusp-core transformation). Impulsive SNF can generate positive stellar age gradients and increase random motion in the gas at the centre of the galaxy. Simulated galaxies in haloes with cores that were formed adiabatically are spatially more extended, with stellar metallicity gradients that are shallower (at late times) than those of galaxiesmore »in other simulations. Such observable properties of the gas and the stars, which indicate either an adiabatic or an impulsive evolution of the gravitational potential, may be used to determine whether observed cores in DM haloes are formed through DM self-interactions or in response to impulsive SNF.

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    The nebular recombination line H α is widely used as a star formation rate (SFR) indicator in the local and high-redshift Universe. We present a detailed H α radiative transfer study of high-resolution isolated Milky-Way and Large Magellanic Cloud simulations that include radiative transfer, non-equilibrium thermochemistry, and dust evolution. We focus on the spatial morphology and temporal variability of the H α emission, and its connection to the underlying gas and star formation properties. The H α and H β radial and vertical surface brightness profiles are in excellent agreement with observations of nearby galaxies. We find that the fraction of H α emission from collisional excitation amounts to fcol ∼ 5–$10{{\ \rm per\ cent}}$, only weakly dependent on radius and vertical height, and that scattering boosts the H α luminosity by $\sim 40{{\ \rm per\ cent}}$. The dust correction via the Balmer decrement works well (intrinsic H α emission recoverable within 25 per cent), though the dust attenuation law depends on the amount of attenuation itself both on spatially resolved and integrated scales. Important for the understanding of the H α–SFR connection is the dust and helium absorption of ionizing radiation (Lyman continuum [LyC] photons), which are about $f_{\rm abs}\approx 28{{\ \rm per\ cent}}$ and $f_{\rm He}\approx 9{{\ \rmmore »per\ cent}}$, respectively. Together with an escape fraction of $f_{\rm esc}\approx 6{{\ \rm per\ cent}}$, this reduces the available budget for hydrogen line emission by nearly half ($f_{\rm H}\approx 57{{\ \rm per\ cent}}$). We discuss the impact of the diffuse ionized gas, showing – among other things – that the extraplanar H α emission is powered by LyC photons escaping the disc. Future applications of this framework to cosmological (zoom-in) simulations will assist in the interpretation of spectroscopy of high-redshift galaxies with the upcoming James Webb Space Telescope.

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    We post-process galaxies in the IllustrisTNG simulations with skirt radiative transfer calculations to make predictions for the rest-frame near-infrared (NIR) and far-infrared (FIR) properties of galaxies at z ≥ 4. The rest-frame K- and z-band galaxy luminosity functions from TNG are overall consistent with observations, despite ${\sim}0.5\, \mathrm{dex}$ underprediction at z = 4 for MK ≲ −25 and Mz ≲ −24. Predictions for the JWST MIRI observed galaxy luminosity functions and number counts are given. Based on theoretical estimations, we show that the next-generation survey conducted by JWST can detect 500 (30) galaxies in F1000W in a survey area of $500\, {\rm arcmin}^{2}$ at z = 6 (z = 8). As opposed to the consistency in the UV, optical, and NIR, we find that TNG, combined with our dust modelling choices, significantly underpredicts the abundance of most dust-obscured and thus most luminous FIR galaxies. As a result, the obscured cosmic star formation rate density (SFRD) and the SFRD contributed by optical/NIR dark objects are underpredicted. The discrepancies discovered here could provide new constraints on the sub-grid feedback models, or the dust contents, of simulations. Meanwhile, although the TNG predicted dust temperature and its relations with IR luminosity and redshiftmore »are qualitatively consistent with observations, the peak dust temperature of z ≥ 6 galaxies are overestimated by about $20\, {\rm K}$. This could be related to the limited mass resolution of our simulations to fully resolve the porosity of the interstellar medium (or specifically its dust content) at these redshifts.

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    Direct collapse black holes (BHs) are promising candidates for producing massive z ≳ 6 quasars, but their formation requires fine-tuned conditions. In this work, we use cosmological zoom simulations to study systematically the impact of requiring: (1) low gas angular momentum (spin), and (2) a minimum incident Lyman–Werner (LW) flux in order to form BH seeds. We probe the formation of seeds (with initial masses of $M_{\rm seed} \sim 10^4\!-\!10^6\, \mathrm{M}_{\odot }\, h^{-1})$ in haloes with a total mass >3000 × Mseed and a dense, metal-poor gas mass >5 × Mseed. Within this framework, we find that the seed-forming haloes have a prior history of star formation and metal enrichment, but they also contain pockets of dense, metal-poor gas. When seeding is further restricted to haloes with low gas spins, the number of seeds formed is suppressed by factors of ∼6 compared to the baseline model, regardless of the seed mass. Seed formation is much more strongly impacted if the dense, metal-poor gas is required to have a critical LW flux (Jcrit). Even for Jcrit values as low as 50J21, no $8\times 10^{5}~\mathrm{M}_{\odot }\, h^{-1}$ seeds are formed. While lower mass ($1.25\times 10^{4},1\times 10^{5}~\mathrm{M}_{\odot }\, h^{-1}$) seeds do form, they are strongly suppressed (by factors of ∼10–100) comparedmore »to the baseline model at gas mass resolutions of $\sim 10^4~\mathrm{M}_{\odot }\, h^{-1}$ (with even stronger suppression at higher resolutions). As a result, BH merger rates are also similarly suppressed. Since early BH growth is dominated by mergers in our models, none of the seeds are able to grow to the supermassive regime ($\gtrsim 10^6~\mathrm{M}_{\odot }\, h^{-1}$) by z = 7. Our results hint that producing the bulk of the z ≳ 6 supermassive BH population may require alternate seeding scenarios that do not depend on the LW flux, early BH growth dominated by rapid or super-Eddington accretion, or a combination of these possibilities.

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  5. ABSTRACT Galaxy mergers are known to host abundant young massive cluster (YMC) populations, whose formation mechanism is still not well-understood. Here, we present a high-resolution galaxy merger simulation with explicit star formation and stellar feedback prescriptions to investigate how mergers affect the properties of the interstellar medium and YMCs. Compared with a controlled simulation of an isolated galaxy, the mass fraction of dense and high-pressure gas is much higher in mergers. Consequently, the mass function of both molecular clouds and YMCs becomes shallower and extends to higher masses. Moreover, cluster formation efficiency is significantly enhanced and correlates positively with the star formation rate surface density and gas pressure. We track the orbits of YMCs and investigate the time evolution of tidal fields during the course of the merger. At an early stage of the merger, the tidal field strength correlates positively with YMC mass, λtid ∝ M0.71, which systematically affects the shape of the mass function and age distribution of the YMCs. At later times, most YMCs closely follow the orbits of their host galaxies, gradually sinking into the centre of the merger remnant due to dynamical friction, and are quickly dissolved via efficient tidal disruption. Interestingly, YMCs formed during the firstmore »passage, mostly in tidal tails and bridges, are distributed over a wide range of galactocentric radii, greatly increasing their survivability because of the much weaker tidal field in the outskirts of the merger system. These YMCs are promising candidates for globular clusters that survive to the present day.« less
    Free, publicly-accessible full text available June 3, 2023
  6. ABSTRACT We compare the star-forming main sequence (SFMS) of galaxies – both integrated and resolved on 1 kpc scales – between the high-resolution TNG50 simulation of IllustrisTNG and observations from the 3D-HST slitless spectroscopic survey at z ∼ 1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2–1 dex between observed and simulated main-sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M*> 1010 M⊙, by ∼10–40 per cent, after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M*> 1010.5 M⊙, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In contrast, the original Illustris simulation and a variantmore »TNG run without black hole kinetic wind feedback, do not reproduce the central SFR profile suppression seen in data. In TNG, inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates.« less
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    ABSTRACT We present the radial gas-phase, mass-weighted metallicity profiles and gradients of the TNG50 star-forming galaxy population measured at redshifts z = 0–3. We investigate the redshift evolution of gradients and examine relations between gradient (negative) steepness and galaxy properties. We find that TNG50 gradients are predominantly negative at all redshifts, although we observe significant diversity among these negative gradients. We determine that the gradients of all galaxies grow more negative with redshift at a roughly constant rate of approximately $-0.02\ \mathrm{dex\, kpc^{-1}}/\Delta z$. This rate does not vary significantly with galaxy mass. We observe a weak negative correlation between gradient (negative) steepness and galaxy stellar mass at z < 2. However, when we normalize gradients by a characteristic radius defined by the galactic star formation distribution, we find that these normalized gradients do not vary significantly with either stellar mass or redshift. We place our results in the context of previous simulations and show that TNG50 high-redshift gradients are more negative than those of models featuring burstier feedback, which may further highlight high-redshift gradients as important discriminators of galaxy formation models. We also find that z = 0 and z = 0.5 TNG50 gradients are consistent with the gradientsmore »observed in galaxies at these redshifts, although the preference for flat gradients observed in redshift z ≳ 1 galaxies is not present in TNG50. If future JWST (James Webb Space Telescope) and ELT (Extremely Large Telescope) observations validate these flat gradients, it may indicate a need for simulation models to implement more powerful radial gas mixing within the ISM (interstellar medium), possibly via turbulence and/or stronger winds.« less
  8. Abstract Deciphering the formation of supermassive black holes (SMBHs) is a key science goal for upcoming observational facilities. In many theoretical channels proposed so far, the seed formation depends crucially on local gas conditions. We systematically characterize the impact of a range of gas-based black hole seeding prescriptions on SMBH populations using cosmological simulations. Seeds of mass Mseed ∼ 103–106 M⊙ h−1 are placed in haloes that exceed critical thresholds for star-forming, metal-poor gas mass and halo mass (defined as $\tilde{M}_{\mathrm{sf,mp}}$ and $\tilde{M}_{\mathrm{h}}$, respectively, in units of Mseed). We quantify the impact of these parameters on the properties of z ≥ 7 SMBHs. Lower seed masses produce higher black hole merger rates (by factors of ∼10 and ∼1000 at z ∼ 7 and z ∼ 15, respectively). For fixed seed mass, we find that $\tilde{M}_{\mathrm{h}}$ has the strongest impact on the black hole population at high redshift (z ≳ 15, where a factor of 10 increase in $\tilde{M}_{\mathrm{h}}$ suppresses merger rates by ≳ 100). At lower redshift (z ≲ 15), we find that $\tilde{M}_{\mathrm{sf,mp}}$ has a larger impact on the black hole population. Increasing $\tilde{M}_{\mathrm{sf,mp}}$ from 5–150 suppresses the merger rates by factors of ∼8 at z ∼ 7–15. This suggests that themore »seeding criteria explored here could leave distinct imprints on LISA merger rates. In contrast, AGN luminosity functions are much less sensitive to seeding criteria, varying by factors ≲ 2 − 3 within our models. Such variations will be challenging to probe even with future sensitive instruments such as Lynx or JWST. Our study provides a useful benchmark for development of seed models for large-volume cosmological simulations.« less