Recalibrating the cosmic star formation history Wilkins, Stephen M; Lovell, Christopher C; Stanway, Elizabeth R
Monthly notices of the Royal Astronomical Society,
12/2019, Letnik:
490, Številka:
4
Journal Article
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ABSTRACT
The calibrations linking observed luminosities to the star formation rate (SFR) depend on the assumed stellar population synthesis model, initial mass function, star formation and metal ...enrichment history, and whether reprocessing by dust and gas is included. Consequently the shape and normalization of the inferred cosmic star formation history is sensitive to these assumptions. Using v2.2.1 of the Binary Population and Spectral Synthesis (bpass) model we determine a new set of calibration coefficients for the ultraviolet, thermal infrared, and hydrogen recombination lines. These ultraviolet and thermal infrared coefficients are 0.15–0.2 dex higher than those widely utilized in the literature while the H α coefficient is ∼0.35 dex larger. These differences arise in part due to the inclusion binary evolution pathways but predominantly reflect an extension in the IMF to 300 M⊙ and a change in the choice of reference metallicity. We use these new coefficients to recalibrate the cosmic star formation history, and find improved agreement between the integrated cosmic star formation history and the in situ measured stellar mass density as a function of redshift. However, these coefficients produce new tension between SFR densities inferred from the ultraviolet and thermal infrared and those from H α.
ABSTRACT
We introduce the First Light And Reionisation Epoch Simulations (FLARES), a suite of zoom simulations using the EAGLE model. We resimulate a range of overdensities during the Epoch of ...Reionization (EoR) in order to build composite distribution functions, as well as explore the environmental dependence of galaxy formation and evolution during this critical period of galaxy assembly. The regions are selected from a large $(3.2 \, \mathrm{cGpc})^{3}$ parent volume, based on their overdensity within a sphere of radius 14 h−1 cMpc. We then resimulate with full hydrodynamics, and employ a novel weighting scheme that allows the construction of composite distribution functions that are representative of the full parent volume. This significantly extends the dynamic range compared to smaller volume periodic simulations. We present an analysis of the galaxy stellar mass function (GSMF), the star formation rate distribution function (SFRF), and the star-forming sequence (SFS) predicted by FLARES, and compare to a number of observational and model constraints. We also analyse the environmental dependence over an unprecedented range of overdensity. Both the GSMF and the SFRF exhibit a clear double-Schechter form, up to the highest redshifts (z = 10). We also find no environmental dependence of the SFS normalization. The increased dynamic range probed by FLARES will allow us to make predictions for a number of large area surveys that will probe the EoR in coming years, carried out on new observatories such as Roman and Euclid.
ABSTRACT
Matching the number counts of high-z submillimetre-selected galaxies (SMGs) has been a long-standing problem for galaxy formation models. In this paper, we use 3D dust radiative transfer to ...model the submm emission from galaxies in the simba cosmological hydrodynamic simulations, and compare predictions to the latest single-dish observational constraints on the abundance of 850 μm-selected sources. We find good agreement with the shape of the integrated 850 μm luminosity function, and the normalization is within 0.25 dex at >3 mJy, unprecedented for a fully cosmological hydrodynamic simulation, along with good agreement in the redshift distribution of bright SMGs. The agreement is driven primarily by simba’s good match to infrared measures of the star formation rate (SFR) function between z = 2 and 4 at high SFRs. Also important is the self-consistent on-the-fly dust model in simba, which predicts, on average, higher dust masses (by up to a factor of 2.5) compared to using a fixed dust-to-metals ratio of 0.3. We construct a light-cone to investigate the effect of far-field blending, and find that 52 per cent of sources are blends of multiple components, which makes a small contribution to the normalization of the bright end of the number counts. We provide new fits to the 850 μm luminosity as a function of SFR and dust mass. Our results demonstrate that solutions to the discrepancy between submm counts in simulations and observations, such as a top-heavy initial mass function, are unnecessary, and that submillimetre-bright phases are a natural consequence of massive galaxy evolution.
Abstract
We present results on the morphological and structural evolution of a total of 3956 galaxies observed with JWST at 1.5 <
z
< 6.5 in the JWST CEERS observations that overlap with the CANDELS ...EGS field. This is the biggest visually classified sample observed with JWST yet, ∼20 times larger than previous studies, and allows us to examine in detail how galaxy structure has changed over this critical epoch. All sources were classified by six individual classifiers using a simple classification scheme aimed at producing disk/spheroid/peculiar classifications, whereby we determine how the relative number of these morphologies has evolved since the Universe’s first billion years. Additionally, we explore structural and quantitative morphology measurements using
Morfometryka
, and show that galaxies with
M
*
> 10
9
M
⊙
at
z
> 3 are not dominated by irregular and peculiar structures, either visually or quantitatively, as previously thought. We find a strong dominance of morphologically selected disk galaxies up to
z
= 6 in this mass range. We also find that the stellar mass and star formation rate densities are dominated by disk galaxies up to
z
∼ 6, demonstrating that most stars in the Universe were likely formed in a disk galaxy. We compare our results to theory to show that the fraction of types we find is predicted by cosmological simulations, and that the Hubble Sequence was already in place as early as one billion years after the Big Bang. Additionally, we make our visual classifications public for the community.
Characterising and identifying galaxy protoclusters Lovell, Christopher C; Thomas, Peter A; Wilkins, Stephen M
Monthly notices of the Royal Astronomical Society,
03/2018, Letnik:
474, Številka:
4
Journal Article
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Abstract
We study the characteristics of galaxy protoclusters using the latest L-galaxies semi-analytic model. Searching for protoclusters on a scale of ∼10 cMpc gives an excellent compromise between ...the completeness and purity of their galaxy populations, leads to high distinction from the field in overdensity space, and allows accurate determination of the descendant cluster mass. This scale is valid over a range of redshifts and selection criteria. We present a procedure for estimating, given a measured galaxy overdensity, the protocluster probability and its descendant cluster mass for a range of modelling assumptions, particularly taking into account the shape of the measurement aperture. This procedure produces lower protocluster probabilities compared to previous estimates using fixed size apertures. The relationship between active galactic nucleus (AGN) and protoclusters is also investigated and shows significant evolution with redshift; at z ∼ 2, the fraction of protoclusters traced by AGN is high, but the fraction of all AGNs in protoclusters is low, whereas at z ≥ 5 the fraction of protoclusters containing AGN is low, but most AGNs are in protoclusters. We also find indirect evidence for the emergence of a passive sequence in protoclusters at z ∼ 2, and note that a significant fraction of all galaxies reside in protoclusters at z ≥ 2, particularly the most massive.
Abstract
We employ the very large cosmological hydrodynamical simulation BlueTides to investigate the predicted properties of the galaxy population during the epoch of reionization (z > 8). BlueTides ...has a resolution and volume ((400/h ≈ 577)3 cMpc3) providing a population of galaxies that is well matched to depth and area of current observational surveys targeting the high-redshift Universe. At z = 8, BlueTides includes almost 160 000 galaxies with stellar masses >108 M⊙. The population of galaxies predicted by BlueTides closely matches observational constraints on both the galaxy stellar mass function and far-UV (150 nm) luminosity function. Galaxies in BlueTides are characterized by rapidly increasing star formation histories. Specific star formation rates decrease with redshift though remain largely insensitive to stellar mass. As a result of the enhanced surface density of metals, more massive galaxies are predicted to have higher dust attenuation resulting in a significant steepening of the observed far-UV luminosity function at high luminosities. The contribution of active supermassive black holes (SMBHs) to the UV luminosities of galaxies with stellar masses 109–10 M⊙ is around 3 per cent on average. Approximately 25 per cent of galaxies with M
* ≈ 1010 M⊙ are predicted to have active SMBHs that contribute >10 per cent of the total UV luminosity.
ABSTRACT
JWST is set to transform many areas of astronomy, one of the most exciting is the expansion of the redshift frontier to z > 10. In its first year, alone JWST should discover hundreds of ...galaxies, dwarfing the handful currently known. To prepare for these powerful observational constraints, we use the First Light And Reionization Epoch simulations (flares) to predict the physical and observational properties of the z > 10 population of galaxies accessible to JWST. This is the first time such predictions have been made using a hydrodynamical model validated at low redshift. Our predictions at z = 10 are broadly in agreement with current observational constraints on the far-UV luminosity function and UV continuum slope β, though the observational uncertainties are large. We note tension with recent constraints z ∼ 13 from Harikane et al. (2021) – compared to these constraints, flares predicts objects with the same space density should have an order-of-magnitude lower luminosity, though this is mitigated slightly if dust attenuation is negligible in these systems. Our predictions suggest that in JWST’s first cycle alone, around 600 galaxies should be identified at z > 10, with the first small samples available at z > 13.
Nebular-line emission during the Epoch of Reionization Wilkins, Stephen M; Lovell, Christopher C; Fairhurst, Ciaran ...
Monthly notices of the Royal Astronomical Society,
04/2020, Letnik:
493, Številka:
4
Journal Article
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ABSTRACT
Nebular emission lines associated with galactic H ii regions carry information about both physical properties of the ionized gas and the source of ionizing photons as well as providing the ...opportunity of measuring accurate redshifts and thus distances once a cosmological model is assumed. While nebular-line emission has been extensively studied at lower redshift there are currently only few constraints within the epoch of reionization (EoR; z > 6), chiefly due to the lack of sensitive near-IR spectrographs. However, this will soon change with the arrival of the Webb Telescope providing sensitive near-IR spectroscopy covering the rest-frame UV and optical emission of galaxies in the EoR. In anticipation of Webb, we combine the large cosmological hydrodynamical simulation BlueTides with photoionization modelling to predict the nebular emission-line properties of galaxies at z = 8 → 13. We find good agreement with the, albeit limited, existing direct and indirect observational constraints on equivalent widths though poorer agreement with luminosity function constraints.
We present powderday (available at https://github.com/dnarayanan/powderday), a flexible, fast, open-source dust radiative transfer package designed to interface with both idealized and cosmological ...galaxy formation simulations. powderday builds on fsps stellar population synthesis models, and hyperion dust radiative transfer, and employs yt to interface between different software packages. We include our stellar population synthesis modeling on the fly, allowing significant flexibility in the assumed stellar physics and nebular line emission. The dust content follows either simple observationally motivated prescriptions (i.e., constant dust-to-metals ratios, or dust-to-gas ratios that vary with metallicity), direct modeling from galaxy formation simulations that include dust physics, as well as a novel approach that includes the dust content via learning-based algorithms from the simba cosmological galaxy formation simulation. Active galactic nuclei (AGNs) can additionally be included via a range of prescriptions. The output of these models are broadband (912 -1 mm) spectral energy distributions (SEDs), as well as filter-convolved monochromatic images. powderday is designed to eliminate last-mile efforts by researchers that employ different hydrodynamic galaxy formation models and seamlessly interfaces with gizmo, arepo, gasoline, changa, and enzo. We demonstrate the capabilities of the code via three applications: a model for the star formation rate-infrared luminosity relation in galaxies (including the impact of AGNs), the impact of circumstellar dust around AGB stars on the mid-infrared emission from galaxy SEDs, and the impact of galaxy inclination angle on dust attenuation laws.
ABSTRACT
We present a random forest (RF) framework for predicting circumgalactic medium (CGM) physical conditions from quasar absorption line observables, trained on a sample of Voigt profile-fit ...synthetic absorbers from the simba cosmological simulation. Traditionally, extracting physical conditions from CGM absorber observations involves simplifying assumptions such as uniform single-phase clouds, but by using a cosmological simulation we bypass such assumptions to better capture the complex relationship between CGM observables and underlying gas conditions. We train RF models on synthetic spectra for H i and selected metal lines around galaxies across a range of star formation rates, stellar masses, and impact parameters, to predict absorber overdensities, temperatures, and metallicities. The models reproduce the true values from simba well, with normalized transverse standard deviations of 0.50–0.54 dex in overdensity, 0.32–0.54 dex in temperature, and 0.49–0.53 dex in metallicity predicted from metal lines (not H i), across all ions. Examining the feature importance, the RF indicates that the overdensity is most informed by the absorber column density, the temperature is driven by the line width, and the metallicity is most sensitive to the specific star formation rate. Alternatively examining feature importance by removing one observable at a time, the overdensity and metallicity appear to be more driven by the impact parameter. We introduce a normalizing flow approach in order to ensure the scatter in the true physical conditions is accurately spanned by the network. The trained models are available online.
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