Function Of Star Formation Rate Research Articles

X-ray stacking reveals average SMBH accretion properties of star-forming galaxies and their cosmic evolution over 4 ≲ z ≲ 7

ABSTRACT With an X-ray stacking analysis of $\simeq 12\, 000$ Lyman-break galaxies (LBGs) using the Chandra Legacy Survey image, we investigate average supermassive black hole (SMBH) accretion properties of star-forming galaxies (SFGs) at 4 ≲ z ≲ 7. Although no X-ray signal is detected in any stacked image, we obtain strong 3σ upper limits for the average black hole accretion rate (BHAR) as a function of star formation rate (SFR). At z ∼ 4 (5) where the stacked image is deeper, the 3σ BHAR upper limits per SFR are ∼1.5 (1.0) dex lower than the local black hole-to-stellar mass ratio, indicating that the SMBHs of SFGs in the inactive (BHAR $\lesssim 1 \, \mathrm{M}_\odot$ yr−1) phase are growing much more slowly than expected from simultaneous evolution. We obtain a similar result for BHAR per dark halo accretion rate. QSOs from the literature are found to have ∼1 dex higher SFRs and ≳ 2 dex higher BHARs than LBGs with the same dark halo mass. We also make a similar comparison for dusty starburst galaxies and quiescent galaxies from the literature. A duty-cycle corrected analysis shows that for a given dark halo, the SMBH mass increase in the QSO phase dominates over that in the much longer inactive phase. Finally, a comparison with the TNG300, TNG100, SIMBA100, and EAGLE100 simulations finds that they overshoot our BHAR upper limits by ≲ 1.5 dex, possibly implying that simulated SMBHs are too massive.

Early Growth of the Star Formation Rate Function in the Epoch of Reionization: An Approach with Rest-frame Optical Emissions

We present a star formation rate function (SFRF) at z ∼ 6 based on star formation rates (SFRs) derived by spectral energy distribution fitting on data from rest-frame UV to optical wavelengths of galaxies in the CANDELS GOODS-South and North fields. The resulting SFRF shows an excess compared to the previous estimations by using rest-frame UV luminosity functions (LFs) corrected for the dust attenuation and is comparable to that estimated from a far-infrared LF. This suggests that the number density of dust-obscured intensively star-forming galaxies at z ∼ 6 has been underestimated in the previous approach based only on rest-frame UV observations. We parameterize the SFRF using the Schechter function and obtain the best-fit parameter of the characteristic SFR (SFR*) when the faint-end slope and characteristic number density are fixed. The best-fit SFR* at z ∼ 6 is comparable to that at z ∼ 2, when the cosmic star formation activity reaches its peak. Together with SFRF estimations with a similar approach using rest-frame UV to optical data, the SFR* is roughly constant from z ∼ 2 to ∼6 and may decrease above z ∼ 6. Since the SFR* is sensitive to the high-SFR end of the SFRF, this evolution of SFR* suggests that the high-SFR end of the SFRF grows rapidly during the epoch of reionization and reaches a similar level observed at z ∼ 2.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

We use a complete set of deep narrow-band imaging data for 384 galaxies gathered during the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) to derive the first Hα luminosity function of the Virgo cluster within its virial radius. The data, which are sensitive to the emission of a single O-early B ionising star, allow us to cover the whole dynamic range of the Hα luminosity function (1036 ≤ L(Hα)≤1042 erg s−1). After they are corrected for [NII] contamination and dust attenuation, the data are used to derive the star formation rate function in the range 10−4 ≲ SFR ≲ 10 M⊙ yr−1. These luminosity functions are derived for gas-rich and gas-poor systems and for objects belonging to the different substructures of the Virgo cluster. They are then compared to those derived at other frequencies or using different tracers of star formation in Virgo, in other nearby and high-z clusters, in the field, and finally to those predicted by the IllustrisTNG cosmological hydrodynamical simulations (TNG50 and TNG100). The Hα luminosity function of the Virgo cluster is fairly flat (α = −1.07 when fitted with a Schechter function) in the range 1038.5 ≲ L(Hα)≲1040.5 erg s−1, and it abruptly decreases at lower luminosities. When compared to those derived for other nearby clusters and for the field, the slope and the characteristic luminosity of the Schechter function change as a function of the dynamical mass of the system, of the temperature of the X-rays gas, and of the dynamical pressure exerted on the interstellar medium of galaxies moving at high velocity within the intracluster medium. All these trends can be explained in a scenario in which the activity of star formation of galaxies is reduced in massive clusters due to their hydrodynamical interaction with the surrounding medium, suggesting once again that ram-pressure stripping is the dominant mechanism affecting galaxy evolution in local clusters of dynamical mass Mcluster ≳ 1014 M⊙. The comparison with the IllustrisTNG cosmological hydrodynamical simulations shows a more pronounced decrease at the faint end of the distribution. If the Virgo cluster is representative of typical nearby clusters of similar mass, this difference suggests that the stripping process in simulated galaxies in these environments is more efficient than observed.

PAH Emission from Star-forming Galaxies in JWST Mid-infrared Imaging of the Lensing Cluster SMACS J0723.3-7327

The mid-infrared spectra of star-forming galaxies (SFGs) are characterized by characteristic broad polycyclic aromatic hydrocarbon (PAH) emission features at 3–20 μm. As these features are redshifted, they are predicted to dominate the flux at specific mid-infrared wavelengths, leading to substantial redshift-dependent color variations in broadband photometry. The advent of JWST for the first time allows the study of this effect for normal SFGs. Based on spectral energy distribution templates, we here present tracks in mid-infrared (4.4, 7.7, 10, 15, and 18 μm) color–color diagrams describing the redshift dependence of SFG colors. In addition, we present simulated color–color diagrams by populating these tracks using the cosmic star formation history and the star formation rate function. Depending on redshift, we find that SFGs stand out in the color–color diagrams by several magnitudes. We provide the first observational demonstration of this effect for galaxies detected in the JWST Early Release Observations of the field toward the lensing cluster SMACS J0723.3−7327. While the distribution of detected galaxies is consistent with the simulations, the numbers are substantially boosted by lensing effects. The PAH emitter with the highest spectroscopic redshift, detected in all bands, is a multiply imaged galaxy at z = 1.45. There is also a substantial number of cluster members that do not exhibit PAH emission except for one SFG at z = 0.38. Future wider-field observations will further populate mid-infrared color–color diagrams and provide insight into the evolution of typical SFGs.

Non-universal stellar initial mass functions: large uncertainties in star formation rates at z ≈ 2–4 and other astrophysical probes

ABSTRACT We explore the assumption, widely used in many astrophysical calculations, that the stellar initial mass function (IMF) is universal across all galaxies. By considering both a canonical broken-power-law IMF and a non-universal IMF, we are able to compare the effect of different IMFs on multiple observables and derived quantities in astrophysics. Specifically, we consider a non-universal IMF that varies as a function of the local star formation rate, and explore the effects on the star formation rate density (SFRD), the extragalactic background light, the supernova (both core-collapse and thermonuclear) rates, and the diffuse supernova neutrino background. Our most interesting result is that our adopted varying IMF leads to much greater uncertainty on the SFRD at $z \approx 2-4$ than is usually assumed. Indeed, we find an SFRD (inferred using observed galaxy luminosity distributions) that is a factor of $\gtrsim 3$ lower than canonical results obtained using a universal IMF. Secondly, the non-universal IMF we explore implies a reduction in the supernova core-collapse rate of a factor of $\sim 2$, compared against a universal IMF. The other potential tracers are only slightly affected by changes to the properties of the IMF. We find that currently available data do not provide a clear preference for universal or non-universal IMF. However, improvements to measurements of the star formation rate and core-collapse supernova rate at redshifts $z \gtrsim 2$ may offer the best prospects for discernment.

The Sample of Red Supergiants in 12 Low-mass Galaxies of the Local Group

Abstract This work establishes the most complete sample of red supergiants (RSGs) in 12 low-mass galaxies (WLM, IC 10, NGC 147, NGC 185, IC 1613, Leo A, Sextans B, Sextans A, NGC 6822, Pegasus Dwarf, SMC, and LMC) of the Local Group, which forms a solid basis to study the properties of RSGs as well as the star formation rate and initial mass function of the galaxies. After removing the foreground dwarf stars by their obvious branch in the near-infrared color–color diagram ( J − H 0 / H − K 0 ) with the UKIRT/WFCAM and 2MASS photometry as well as the Gaia/EDR3 measurements of proper motion and parallax, RSGs are identified from their location in the color–magnitude diagram J − K 0 / K 0 of the member stars of the specific galaxy. A total of 2190 RSGs are found in 10 dwarf galaxies, and additionally, 4823 and 2138 RSGs are found in LMC and SMC, respectively. The locations of the tip of the red giant branch in the J − K 0 / K 0 diagram are determined to serve as an indicator of the metallicity and distance modulus of the galaxies.

The Evolving Interstellar Medium of Star-forming Galaxies, as Traced by Stardust*

Abstract We analyze the far-infrared (FIR) properties of ∼5000 star-forming galaxies at z < 4.5, drawn from the deepest, super-deblended catalogs in the GOODS-N and COSMOS fields. We develop a novel panchromatic spectral energy distribution fitting algorithm, Stardust, that models the emission from stars, active galactic nuclei (AGNs), and infrared dust emission, without relying on energy balance assumptions. Our code provides robust estimates of the UV−optical and FIR physical parameters, such as the stellar mass (M *), dust mass (M dust), infrared luminosities (L IR) arising from AGN and star formation activity, and the average intensity of the interstellar radiation field (〈U〉). Through a set of simulations we quantify the completeness of our data in terms of M dust, L IR, and 〈U〉 and subsequently characterize the distribution and evolution of these parameters with redshift. We focus on the dust-to-stellar mass ratio (f dust), which we parameterize as a function of cosmic age, stellar mass, and specific star formation rate. The f dust is found to increase by a factor of 10 from z = 0 to z = 2 and appears to remain flat at higher z, mirroring the evolution of the gas fraction. We also find a growing fraction of warm to cold dust with increasing distance from the main sequence, indicative of more intense interstellar radiation fields, higher star formation efficiencies, and more compact star-forming regions for starburst galaxies. Finally, we construct the dust mass functions (DMFs) of star-forming galaxies up to z = 1 by transforming the stellar mass function to DMF through the scaling relations derived here. The evolution of f dust and the recovered DMFs are in good agreement with the theoretical predictions of the Horizon-AGN and IllustrisTNG simulations.

GALEX UV Catalog of Low-redshift Galaxies for Estimating Transient Rates

AbstractDetection of transients such as supernovae (SNe) and kilonovae (KNe) in early phase has recently become important for understanding the progenitor properties and multi-messenger astronomy. Predicting which galaxy has the higher probability of hosting the transient events would help detect the early phase of the events and get information on their progenitors. The SN and KN rates are known to be a function of star formation rate (SFR) and stellar mass of the host galaxy. The SFR of a galaxy can be estimated from ultraviolet (UV) luminosity. However, the UV magnitudes have been derived carefully only for a limited number of nearby galaxies. Here, we introduce GALEX galaxy catalog of all-sky UV brightness of low redshift galaxies. To do so, we derive the UV photometry of galaxies in the GLADE catalog using the GALEX AIS images, supplemented by GALEX NGS and MIS data. From the near-UV (NUV) and far-UV (FUV) magnitudes, we calculate the SFRs of the galaxies, which will further be useful for estimating the SN and KN rate. The results are compared with previous GALEX UV catalog of galaxies. There will be an updated catalog based on this catalog for calculating KN rate of the galaxies in the future work.

Star Formation Rate Function at z ∼ 4.5: An Analysis from Rest UV to Optical

Abstract We present a star formation rate function (SFRF) at z ∼ 4.5 based on photometric data from the rest UV to optical of galaxies in the CANDELS GOODS-South field using spectral energy distribution (SED) fitting. We evaluate the incompleteness of our sample and correct for it to properly compare the SFRF in this study with those estimated based on other probes. The SFRF is obtained down to ∼10 M ⊙ yr−1, and it shows a significant excess compared to that estimated from the UV luminosity function and dust correction based on the UV spectral slope. As compared with the UV-based SFRF, the number density is larger by ∼1 dex at a fixed SFR, or the best-fit Schechter parameter of the characteristic SFR, SFR*, is larger by ∼1 dex. We extensively examine several assumptions on SED fitting to see the robustness of our result and find that the excess still exists even if the assumptions change such as star formation histories, dust extinction laws, and a one- or two-component model. By integrating our SFRF to 0.22 M ⊙ yr−1, the cosmic star formation rate density (CSFRD) at this epoch is calculated to be 4.53 − 0.87 + 0.94 × 10 − 2 M ⊙ yr − 1 Mpc − 3 , which is ∼0.25 dex larger than the previous measurement based on UV observations. We also find that galaxies with intensive star formation (>10 M ⊙ yr−1) occupy most of the CSFRD (∼80%), suggesting that star formation activity at this epoch is dominated by intensively star-forming galaxies.

Population III star explosions and Planck 2018 data

We investigate the effect of the population III (Pop III) stars supernova explosion (SN) on the high redshifts reionization history using the latest Planck data. It is predicted that massive Pop III stars $(130\text{ }\text{ }{M}_{\ensuremath{\bigodot}}\ensuremath{\le}M\ensuremath{\le}270\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$ explode energetically at the end of their stellar life as pair-instability supernovae (PISNe). In the explosion, supernova remnants grow as hot ionized bubbles and enhance the ionization fraction in the early stage of the reionization history. This enhancement affects the optical depth of the cosmic microwave background (CMB) and generates the additional anisotropy of the CMB polarization on large scales. Therefore, analyzing the Planck polarization data allows us to examine the Pop III star SNe and the abundance of their progenitors, massive Pop III stars. In order to model the supernova(SN) contribution to reionization, we introduce a new parameter $\ensuremath{\zeta}$, which relates to the abundance of the SNe to the collapse fraction of the Universe. Using the Markov chain Monte Carlo method with the latest Planck polarization data, we obtain the constraint on our model parameter, $\ensuremath{\zeta}$. Our constraint tells us that observed CMB polarization is consistent with the abundance of PISNe predicted from the star formation rate and initial mass function of Pop III stars in recent cosmological simulations. We also suggest that combining further observations on the late reionization history, such as high redshift quasi-stellar object (QSO) observations, can provide tighter constraints and important information on the nature of Pop III stars.

ALMA Lensing Cluster Survey: Bright [C ii] 158 μm Lines from a Multiply Imaged Sub-L ⋆ Galaxy at z = 6.0719

Abstract We present bright [C ii] 158 μm line detections from a strongly magnified and multiply imaged (μ ∼ 20–160) sub–L * ( M UV = − 19.75 − 0.44 + 0.55 ) Lyman-break galaxy (LBG) at z = 6.0719 ± 0.0004, drawn from the ALMA Lensing Cluster Survey (ALCS). Emission lines are identified at 268.7 GHz at ≥8σ exactly at the positions of two multiple images of the LBG, behind the massive galaxy cluster RXCJ0600−2007. Our lens models, updated with the latest spectroscopy from VLT/MUSE, indicate that a sub region of the LBG crosses the caustic, and is lensed into a long (∼6″) arc with a local magnification of μ ∼ 160, for which the [C ii] line is also significantly detected. The source plane reconstruction resolves the interstellar medium (ISM) structure, showing that the [C ii] line is co-spatial with the rest-frame UV continuum at a scale of ∼300 pc. The [C ii] line properties suggest that the LBG is a rotation-dominated system, whose velocity gradient explains a slight difference in redshifts between the whole LBG and its sub-region. The star formation rate (SFR)–L [CII] relations, for whole and sub-regions of the LBG, are consistent with those of local galaxies. We evaluate the lower limit of the faint-end of the [C ii] luminosity function at z = 6, finding it to be consistent with predictions from semi-analytical models and from the local SFR–L [CII] relation with a SFR function at z = 6. These results imply that the local SFR–L [CII] relation is universal for a wide range of scales, including the spatially resolved ISM, the whole region of the galaxy, and the cosmic scale, even in the epoch of reionization.

Reproducing submillimetre galaxy number counts with cosmological hydrodynamic simulations

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.

Main-sequence Scatter is Real: The Joint Dependence of Galaxy Clustering on Star Formation and Stellar Mass

Abstract We present new measurements of the clustering of stellar-mass-complete samples of ∼40,000 SDSS galaxies at z ∼ 0.03 as a joint function of stellar mass and specific star formation rate (sSFR). Our results confirm what Coil et al. find at z ∼ 0.7: galaxy clustering is a stronger function of sSFR at fixed stellar mass than of stellar mass at fixed sSFR. We also find that galaxies above the star-forming main sequence (SFMS) with higher sSFR are less clustered than galaxies below the SFMS with lower sSFR, at a given stellar mass. A similar trend is present for quiescent galaxies. This confirms that main-sequence scatter, and scatter within the quiescent sequence, is physically connected to the large-scale cosmic density field. We compare the resulting galaxy bias versus sSFR, and relative bias versus sSFR ratio, for different galaxy samples across 0 < z < 1.2 to mock galaxy catalogs based on the empirical galaxy evolution model of Behroozi et al. This model fits PRIMUS and DEEP2 clustering data well at intermediate redshift, but agreement with SDSS is not as strong. We show that increasing the correlation between galaxy SFR and halo accretion rate at z ∼ 0 in the model substantially improves agreement with SDSS data. Mock catalogs suggest that central galaxies contribute substantially to the dependence of clustering on sSFR at a given stellar mass and that the signal is not simply an effect of satellite galaxy fraction differences with sSFR. Our results are highly constraining for galaxy evolution models and show that the stellar-to-halo mass relation depends on sSFR.

The intrinsic SFRF and sSFRF of galaxies: comparing SDSS observation with IllustrisTNG simulation

The star formation rate function (SFRF) and specific star formation rate function (sSFRF) from observations are impacted by the Eddington bias, due to uncertainties in the estimated star formation rate (SFR). We develop a novel method to correct the Eddington bias and obtain the intrinsic SFRF and sSFRF from the Sloan Digital Sky Survey (SDSS) Data Release 7. The intrinsic SFRF is in good agreement with measurements from previous data in the literature that relied on UV SFRs but its high star-forming end is slightly lower than the corresponding IR and radio tracers. We demonstrate that the intrinsic sSFRF from SDSS has a bimodal form with one peak found at sSFR ∼ 10−9.7 yr−1 representing the star-forming objects while the other peak is found at sSFR ∼ 10−12 yr−1 representing the quenched population. Furthermore, we compare our observations with the predictions from the IllustrisTNG and Illustris simulations and affirm that the “TNG” model performs much better than its predecessor. However, we show that the simulated SFRF and CSFRD of TNG simulations are highly dependent on resolution, reflecting the limitations of the model and today’s state-of-the-art simulations. We demonstrate that the bimodal, two peaked sSFRF implied by the SDSS observations does not appear in TNG regardless of the adopted box-size or resolution. This tension reflects the need for inclusion of an additional efficient quenching mechanism in the TNG model.

The specific star formation rate function at different mass scales and quenching: a comparison between cosmological models and SDSS

ABSTRACT We present the eddington bias corrected specific star formation rate function (sSFRF) at different stellar mass scales from a sub-sample of the Sloan Digital Sky Survey Data Release DR7 (SDSS), which is considered complete both in terms of stellar mass (M⋆) and star formation rate (SFR). The above enable us to study qualitatively and quantitatively quenching, the distribution of passive/star-forming galaxies and perform comparisons with the predictions from state-of-the-art cosmological models, within the same M⋆ and SFR limits. We find that at the low-mass end (${M_{\star }} = 10^{9.5}\!-\!10^{10} \, {\rm M_{\odot }}$) the sSFRF is mostly dominated by star-forming objects. However, moving to the two more massive bins (${M_{\star }} = 10^{10}\!-\!10^{10.5} \, {\rm M_{\odot }}$ and ${M_{\star }} = 10^{10.5}\!-\!10^{11} \, {\rm M_{\odot }}$) a bi-modality with two peaks emerges. One peak represents the star-forming population, while the other describes a rising passive population. The bi-modal form of the sSFRFs is not reproduced by a range of cosmological simulations (e.g. Illustris, EAGLE, Mufasa, and IllustrisTNG) which instead generate mostly the star-forming population, while a bi-modality emerges in others (e.g. L-Galaxies, Shark, and Simba). Our findings reflect the need for the employed quenching schemes in state-of-the-art models to be reconsidered, involving prescriptions that allow ‘quenched galaxies’ to retain a small level of SF activity (sSFR = ${\rm 10^{-11} \, }$–${\rm 10^{-12} \, {\rm yr^{-1}}}$) and generate an adequate passive population/bi-modality even at intermediate masses (${M_{\star }} = 10^{10}\!-\!10^{10.5} \, {\rm M_{\odot }}$).

Gas accretion regulates the scatter of the mass–metallicity relation

ABSTRACT In this paper, we take advantage of the GAlaxy Evolution and Assembly (GAEA) semi-analytic model to analyse the origin of secondary dependencies in the local galaxy mass–gas metallicity relation. Our model reproduces quite well the trends observed in the local Universe as a function of galaxy star formation rate and different gas-mass phases. We show that the cold gas content (whose largest fraction is represented by the atomic gas phase) can be considered as the third parameter governing the scatter of the predicted mass–metallicity relation, in agreement with the most recent observational measurements. The trends can be explained with fluctuations of the gas accretion rates: a decrease of the gas supply leads to an increase of the gas metallicity due to star formation, while an increase of the available cold gas leads to a metallicity depletion. We demonstrate that the former process is responsible for offsets above the mass–metallicity relation, while the latter is responsible for deviations below the mass–metallicity relation. In low- and intermediate-mass galaxies, these negative offsets are primarily determined by late gas cooling dominated by material that has been previously ejected due to stellar feedback.

Cosmology-insensitive estimate of IGM baryon mass fraction from five localized fast radio bursts

ABSTRACT Five fast radio bursts (FRBs), including three apparently non-repeating ones, FRB 180924, FRB 181112, and FRB 190523, and two repeaters, FRB 121102 and FRB 180916.J0158+65, have already been localized so far. We apply a method developed recently by us to these five localized FRBs to give a cosmology-insensitive estimate of the fraction of baryon mass in the intergalactic medium, fIGM. Using the measured dispersion measure (DM) and luminosity distance dL data (inferred from the FRB redshifts and dL of Type Ia supernovae at the same redshifts) of the five FRBs, we constrain the local $f_{\rm IGM} = 0.84^{+0.16}_{-0.22}$ with no evidence of redshift dependence. This cosmology-insensitive estimate of fIGM from FRB observations is in excellent agreement with previous constraints using other probes. Moreover, using the three apparently non-repeating FRBs only we get a little looser but consistent result: $f_{\rm IGM} = 0.74^{+0.24}_{-0.18}$. In these two cases, reasonable estimations for the host galaxy DM contribution (DMhost) can be achieved by modelling it as a function of star formation rate. The constraints on both fIGM and DMhost are expected to be significantly improved with the rapid progress in localizing FRBs.

Testing galaxy formation simulations with damped Lyman-α abundance and metallicity evolution

ABSTRACT We examine the properties of damped Lyman-α absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: simba and technicolor dawn. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multifrequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Ly α forest mean transmission at z > 5. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at z ≥ 3, and both reproduce the observed neutral hydrogen cosmological mass density, $\Omega _{\rm H\, \small{I}}(z)$. However, the DLA abundance and metallicity distribution are sensitive to the galactic outflows’ feedback and the UVB amplitude. Adopting a strong UVB and/or slow outflows underproduces the observed DLA abundance, but yields broad agreement with the observed DLA metallicity distribution. By contrast, faster outflows eject metals to larger distances, yielding more metal-rich DLAs whose observational selection may be more sensitive to dust bias. The DLA metallicity distribution in models adopting an H2-regulated star formation recipe includes a tail extending to [M/H] ≪ −3, lower than any DLA observed to date, owing to curtailed star formation in low-metallicity galaxies. Our results show that DLA observations play an important role in constraining key physical ingredients in galaxy formation models, complementing traditional ensemble statistics such as the stellar mass and star formation rate functions.

Effects of metallicity on high-mass X-ray binary formation

ABSTRACT The heating of the intergalactic medium in the early, metal-poor Universe may have been partly due to radiation from high-mass X-ray binaries (HMXBs). Previous investigations on the effect of metallicity have used galaxies of different types. To isolate the effects of metallicity on the production of HMXBs, we study a sample consisting only of 46 blue compact dwarf galaxies covering metallicity in the range 12+log(O/H) of 7.15–8.66. To test the hypothesis of metallicity dependence in the X-ray luminosity function (XLF), we fix the XLF form to that found for near-solar metallicity galaxies and use a Bayesian method to constrain the XLF normalization as a function of star formation rate for three different metallicity ranges in our sample. We find an increase by a factor of 4.45 ± 2.04 in the XLF normalization between the metallicity ranges 7.1–7.7 and 8.2–8.66 at a statistical significance of 99.79 per cent. Our results suggest that HMXB production is enhanced at low metallicity, and consequently that HMXBs may have contributed significantly to the reheating of the early Universe.

Merging Rates of Compact Binaries in Galaxies: Perspectives for Gravitational Wave Detections

Abstract We investigate the merging rates of compact binaries in galaxies and the related detection rate of gravitational wave (GW) events with AdvLIGO/Virgo and with the Einstein Telescope. To this purpose, we rely on three basic ingredients: (i) the redshift-dependent galaxy statistics provided by the latest determination of the star formation rate functions from UV+far-IR/(sub)millimeter/radio data; (ii) star formation and chemical enrichment histories for individual galaxies, modeled on the basis of observations; and (iii) compact remnant mass distribution and prescriptions for merging of compact binaries from stellar evolution simulations. We present results for the intrinsic birth rate of compact remnants, the merging rates of compact binaries, GW detection rates, and GW counts, attempting to differentiate the outcomes among black hole–black hole, neutron star–neutron star, and black hole–neutron star mergers and to estimate their occurrence in disk and spheroidal host galaxies. We compare our approach with the one based on cosmic star formation rate density and cosmic metallicity, exploited by many literature studies; the merging rates from the two approaches are in agreement within the overall astrophysical uncertainties. We also investigate the effects of galaxy-scale strong gravitational lensing of GW in enhancing the rate of detectable events toward high redshift. Finally, we discuss the contribution of undetected GW emission from compact binary mergers to the stochastic background.