Cosmic Star Formation Rate Density Research Articles

The Hα and [O iii] λ5007 Luminosity Functions of 1.2 < z < 1.9 Emission-line Galaxies from Hubble Space Telescope (HST) Grism Spectroscopy

Euclid and the Roman Space Telescope (Roman) will soon use grism spectroscopy to detect millions of galaxies via their Hα and [O iii] λ5007 emission. To better constrain the expected galaxy counts from these instruments, we use a vetted sample of 4239 emission-line galaxies from the 3D Hubble Space Telescope survey to measure the Hα and [O iii] λ5007 luminosity functions between 1.16 < z < 1.90; this sample is ∼4 times larger than previous studies at this redshift. We find very good agreement with previous measurements for Hα, but for [O iii], we predict a higher number of intermediate-luminosity galaxies than from previous works. We find that, for both lines, the characteristic luminosity, , increases monotonically with redshift, and use the Hα luminosity function to calculate the epoch’s cosmic star formation rate density. We find that Hα-visible galaxies account for ∼81% of the epoch’s total star formation rate, and this value changes very little over the 1.16 < z < 1.56 redshift range. Finally, we derive the surface density of galaxies as a function of limiting flux and find that previous predictions for galaxy counts for the Euclid Wide Survey are unchanged, but there may be more [O iii] galaxies in the Roman High Latitude Survey than previously estimated.

An Ultra-deep Multiband Very Large Array (VLA) Survey of the Faint Radio Sky (COSMOS-XS): New Constraints on the Cosmic Star Formation History

We make use of ultra-deep 3 GHz Karl G. Jansky Very Large Array (VLA) observations of the COSMOS field from the multiband COSMOS-XS survey to infer radio luminosity functions (LFs) of star-forming galaxies (SFGs). Using ∼1300 SFGs with redshifts out to z ∼ 4.6, and fixing the faint and bright end shape of the radio LF to the local values, we find a strong redshift trend that can be fitted by pure luminosity evolution with the luminosity parameter given by α L ∝ (3.40 ± 0.11) − (0.48 ± 0.06)z. We then combine the ultra-deep COSMOS-XS data set with the shallower VLA-COSMOS 3 GHz large project data set over the wider COSMOS field in order to fit for joint density+luminosity evolution, finding evidence for significant density evolution. By comparing the radio LFs to the observed far-infrared and ultraviolet (UV) LFs, we find evidence of a significant underestimation of the UV LF by 22% ± 14% at high redshift (3.3 < z < 4.6, integrated down to ). We derive the cosmic star formation rate density (SFRD) by integrating the fitted radio LFs and find that the SFRD rises up to z ∼ 1.8 and then declines more rapidly than previous radio-based estimates. A direct comparison between the radio SFRD and a recent UV-based SFRD, where we integrate both LFs down to a consistent limit (), reveals that the discrepancy between the radio and UV LFs translates to a significant (∼1 dex) discrepancy in the derived SFRD at z > 3, even assuming the latest dust corrections and without accounting for optically dark sources.

The evolution of the galaxy UV luminosity function at redshifts z ≃ 8 – 15 from deep JWST and ground-based near-infrared imaging

ABSTRACT We reduce and analyse the available JWST ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range z = 8 − 15. This yields a new estimate of the evolution of UV luminosity density (ρUV), and hence cosmic star formation rate density (ρSFR) out to within &amp;lt;300 Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power law (rather than a Schechter) function up to z ∼ 10, and that the LF and the resulting derived ρUV (and thus ρSFR), continues to decline gradually and steadily up to z ∼ 15 (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). We provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at z ≥ 12, one of which appears to set a new redshift record as an apparently robust galaxy candidate at z ≃ 16.4, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe.

The ALMA REBELS survey: the dust-obscured cosmic star formation rate density at redshift 7

ABSTRACT Cosmic dust is an essential component shaping both the evolution of galaxies and their observational signatures. How quickly dust builds up in the early Universe remains an open question that requires deep observations at (sub-)millimetre wavelengths to resolve. Here, we use Atacama Large Millimeter Array observations of 45 galaxies from the Reionization Era Bright Emission Line Survey (REBELS) and its pilot programs, designed to target [C ii] and dust emission in UV-selected galaxies at z ∼ 7, to investigate the dust content of high-redshift galaxies through a stacking analysis. We find that the typical fraction of obscured star formation fobs = SFRIR/SFRUV+IR depends on stellar mass, similar to what is observed at lower redshift, and ranges from fobs ≈ 0.3 − 0.6 for galaxies with log10(M⋆/M⊙) = 9.4–10.4. We further adopt the z ∼ 7 stellar mass function from the literature to extract the obscured cosmic star formation rate density (SFRD) from the REBELS survey. Our results suggest only a modest decrease in the SFRD between 3 ≲ z ≲ 7, with dust-obscured star formation still contributing ${\sim}30{{\ \rm per\ cent}}$ at z ∼ 7. While we extensively discuss potential caveats, our analysis highlights the continued importance of dust-obscured star formation even well into the epoch of reionization.

Astroparticle Constraints from the Cosmic Star Formation Rate Density at High Redshift: Current Status and Forecasts for JWST

We exploit the recent determination of the cosmic star formation rate (SFR) density at high redshifts z≳4 to derive astroparticle constraints on three common dark matter (DM) scenarios alternative to standard cold dark matter (CDM): warm dark matter (WDM), fuzzy dark matter (ψDM) and self-interacting dark matter (SIDM). Our analysis relies on the ultraviolet (UV) luminosity functions measured from blank field surveys by the Hubble Space Telescope out to z≲10 and down to UV magnitudes MUV≲−17. We extrapolate these to fainter yet unexplored magnitude ranges and perform abundance matching with the halo mass functions in a given DM scenario, thus, obtaining a redshift-dependent relationship between the UV magnitude and the halo mass. We then computed the cosmic SFR density by integrating the extrapolated UV luminosity functions down to a faint magnitude limit MUVlim, which is determined via the above abundance matching relationship by two free parameters: the minimum threshold halo mass MHGF for galaxy formation, and the astroparticle quantity X characterizing each DM scenario (namely, particle mass for WDM and ψDM, and kinetic temperature at decoupling TX for SIDM). We perform Bayesian inference on such parameters using a Monte Carlo Markov Chain (MCMC) technique by comparing the cosmic SFR density from our approach to the current observational estimates at z≳4, constraining the WDM particle mass to mX≈1.2−0.4(−0.5)+0.3(11.3) keV, the ψDM particle mass to mX≈3.7−0.4(−0.5)+1.8(+12.9.3)×10−22 eV, and the SIDM temperature to TX≈0.21−0.06(−0.07)+0.04(+1.8) keV at 68% (95%) confidence level. Finally, we forecast how such constraints will be strengthened by upcoming refined estimates of the cosmic SFR density if the early data on the UV luminosity function at z≳10 from the James Webb Space Telescope (JWST) will be confirmed down to ultra-faint magnitudes.

Public Release of A-SLOTH: Ancient Stars and Local Observables by Tracing Halos

The semianalytical model a-sloth (Ancient Stars and Local Observables by Tracing Halos) is the first public code that connects the formation of the first stars and galaxies to observables. After several successful projects with this model, we publish the source code (https://gitlab.com/thartwig/asloth) and describe the public version in this paper. The model is based on dark matter merger trees that can either be generated based on Extended Press–Schechter theory or be imported from dark matter simulations. On top of these merger trees, a-sloth applies analytical recipes for baryonic physics to model the formation of both metal-free and metal-poor stars and the transition between them with unprecedented precision and fidelity. a-sloth samples individual stars and includes radiative, chemical, and mechanical feedback. It is calibrated based on six observables, such as the optical depth to Thomson scattering, the stellar mass of the Milky Way and its satellite galaxies, the number of extremely metal-poor stars, and the cosmic star formation rate density at high redshift. a-sloth has versatile applications with moderate computational requirements. It can be used to constrain the properties of the first stars and high-z galaxies based on local observables, predicts properties of the oldest and most metal-poor stars in the Milky Way, can serve as a subgrid model for larger cosmological simulations, and predicts next-generation observables of the early universe, such as supernova rates or gravitational wave events.

Implications of the cosmological 21-cm absorption profile for high-redshift star formation and deep JWST surveys

ABSTRACT Apart from its anomalously large depth, the cosmological 21-cm absorption signal measured by the EDGES collaboration also has a shape that is distinctly different from theoretical predictions. Models with non-traditional components such as super-adiabatic baryonic cooling or an excess radio background (ERB) explain the depth of the observed profile, but still conspicuously fail to explain its shape. In this paper, we quantify the requirements imposed by the EDGES measurement on sources of Ly α and X-ray photons in the presence of ERB at cosmic dawn. In extreme cases, the Ly α and X-ray emissivities require to be enhanced by up to an order of magnitude relative to traditional models. Furthermore, this enhancement needs to be active only for a short duration. We find that under conventional assumptions for the cosmic star formation rate density (SFRD), standard stellar populations are incapable of meeting these conditions. Only highly unusual models of massive metal-free stars seem to provide a possible mechanism. Conversely, if the sources of Ly α and X-ray photons are compelled to have standard properties, the EDGES measurement puts strong demands on the cosmic SFRD. This provides interesting falsifiable predictions for high-redshift galaxy surveys enabled by the James Webb Space Telescope (JWST). We derive predictions for galaxy UV luminosity functions and number densities, and show that a deep JWST survey with a limiting UV magnitude of mUV, lim = 32 would potentially be able to rule out the predictions enforced by the EDGES measurement.

On the simultaneous modelling of dust and stellar populations for interpretation of galaxy properties

ABSTRACT The physical properties of galaxies are encoded within their spectral energy distribution and require comparison with models to be extracted. These models must contain a synthetic stellar population and, where infrared data are to be used, also consider prescriptions for energy reprocessing and re-emission by dust. While many such models have been constructed, there are few analyses of the impact of stellar population model choice on derived dust parameters, or vice versa. Here, we apply a simple framework to compare the impact of these choices, combining three commonly used stellar population synthesis models and three dust emission models. We compare fits to the ultraviolet to far-infrared spectral energy distributions of a validation sample of infrared-luminous galaxies. We find that including different physics, such as binary stellar evolution, in the stellar synthesis model can introduce biases and uncertainties in the derived parameters of the dust and stellar emission models, largely due to differences in the far-ultraviolet emission available for reprocessing. This may help to reconcile the discrepancy between the cosmic star formation rate and stellar mass density histories. Notably the inclusion of a dusty stellar birth cloud component in the dust emission model provides more flexibility in accommodating the stellar population model, as its re-emission is highly sensitive to the ultraviolet radiation field spectrum and density. Binary populations favour a longer birth cloud dissipation time-scale than is found when assuming only single star population synthesis.

Insufficient Gas Accretion Caused the Decline in Cosmic Star-formation Activity Eight Billion Years Ago

Measurements of the atomic hydrogen (Hi) properties of high-redshift galaxies are critical to understanding the decline in the star formation rate (SFR) density of the universe after its peak ≈8–11 Gyr ago. Here, we use ≈510 hr of observations with the upgraded Giant Metrewave Radio Telescope to measure the dependence of the average Hi mass of star-forming galaxies at z = 0.74–1.45 on their average stellar mass and redshift by stacking their Hi 21 cm emission signals. We divide our sample of 11,419 main-sequence galaxies at z = 0.74–1.45 into two stellar-mass (M *) subsamples, with M * > 1010 M ⊙ and M * < 1010 M ⊙, and obtain clear detections, at >4.6σ significance, of the stacked Hi 21 cm emission in both subsamples. We find that galaxies with M * > 1010 M ⊙, which dominate the decline in the cosmic SFR density at z ≲ 1, have Hi reservoirs that can sustain their SFRs for only a short period, 0.86 ± 0.20 Gyr, unless their Hi is replenished via accretion. We also stack the Hi 21 cm emission from galaxies in two redshift subsamples, at z = 0.74–1.25 and z = 1.25–1.45, again obtaining clear detections of the stacked Hi 21 cm emission signals, at >5.2σ significance in both subsamples. We find that the average Hi mass of galaxies with 〈M *〉 ≈ 1010 M ⊙ declines steeply over a period of ≈1 billion years, from (33.6 ± 6.4) × 109 M ⊙ at 〈z〉 ≈ 1.3 to (10.6 ± 1.9) × 109 M ⊙ at 〈z〉 ≈ 1.0, i.e., by a factor ≳3. We thus find direct evidence that accretion of Hi onto star-forming galaxies at z ≈ 1 is insufficient to replenish their Hi reservoirs and sustain their SFRs, thus resulting in the decline in the cosmic SFR density 8 billion years ago.

Searching Far and Long. I. Pilot ALMA 2 mm Follow-up of Bright Dusty Galaxies as a Redshift Filter

A complete census of dusty star-forming galaxies (DSFGs) at early epochs is necessary to constrain the obscured contribution to the cosmic star formation rate density (CSFRD); however, DSFGs beyond z ∼ 4 are both rare and hard to identify from photometric data alone due to degeneracies in submillimeter photometry with redshift. Here, we present a pilot study obtaining follow-up Atacama Large Millimeter Array (ALMA) 2 mm observations of a complete sample of 39 850 μm-bright dusty galaxies in the SSA22 field. Empirical modeling suggests 2 mm imaging of existing samples of DSFGs selected at 850 μm—1 mm can quickly and easily isolate the “needle in a haystack” DSFGs that sit at z > 4 or beyond. Combining archival submillimeter imaging with our measured ALMA 2 mm photometry (1σ ∼ 0.08 mJy beam−1 rms), we characterize the galaxies’ IR spectral energy distributions (SEDs) and use them to constrain redshifts. With available redshift constraints fit via the combination of six submillimeter bands, we identify 6/39 high-z candidates each with >50% likelihood to sit at z > 4, and find a positive correlation between redshift and 2 mm flux density. Specifically, our models suggest the addition of 2 mm to a moderately constrained IR SED will improve the accuracy of a millimeter-derived redshift from Δz/(1 + z) = 0.3 to Δz/(1 + z) = 0.2. Our IR SED characterizations provide evidence for relatively high-emissivity spectral indices (〈β〉 = 2.4 ± 0.3) in the sample. We measure that especially bright (S 850μ m > 5.55 mJy) DSFGs contribute ∼10% to the cosmic-averaged CSFRD from 2 < z < 5, confirming findings from previous work with similar samples.

A New Estimate of the Cosmic Star Formation Density from a Radio-selected Sample, and the Contribution of H-dark Galaxies at z ≥ 3

Abstract The star formation rate density (SFRD) history of the universe is well constrained up to redshift z ∼ 2. At earlier cosmic epochs, the picture has been largely inferred from UV-selected galaxies (e.g., Lyman-break galaxies; LBGs). However, the inferred star formation rates of LBGs strongly depend on the assumed dust extinction correction, which is not well constrained at high z, while observations in the radio domain are not affected by this issue. In this work we measure the SFRD from a 1.4 GHz selected sample of ∼600 galaxies in the GOODS-N field up to redshift ∼3.5. We take into account the contribution of active galactic nuclei from the infrared-radio correlation. We measure the radio luminosity function, fitted with a modified Schechter function, and derive the SFRD. The cosmic SFRD shows an increase up to z ∼ 2 and then an almost flat plateau up to z ∼ 3.5. Our SFRD is in agreement with those from other far-IR/radio surveys and a factor 2 higher than those from LBG samples. We also estimate that galaxies lacking a counterpart in the HST/WFC3 H-band (H-dark) make up ∼25% of the ϕ-integrated SFRD relative to the full sample at z ∼ 3.2, and up to 58% relative to LBG samples.

GOLDRUSH. IV. Luminosity Functions and Clustering Revealed with ∼4,000,000 Galaxies at z ∼ 2–7: Galaxy–AGN Transition, Star Formation Efficiency, and Implication for Evolution at z &gt; 10

Abstract We present new measurements of rest-UV luminosity functions and angular correlation functions from 4,100,221 galaxies at z ∼ 2–7 identified in the Subaru/Hyper Suprime-Cam survey and CFHT Large Area U-band Survey. The obtained luminosity functions at z ∼ 4–7 cover a very wide UV luminosity range of ∼ 0.002 – 2000 L UV * combined with previous studies, confirming that the dropout luminosity function is a superposition of the active galactic nucleus (AGN) luminosity function dominant at M UV ≲ −24 mag and the galaxy luminosity function dominant at M UV ≳ −22 mag, consistent with galaxy fractions based on 1037 spectroscopically identified sources. Galaxy luminosity functions estimated from the spectroscopic galaxy fractions show the bright-end excess beyond the Schechter function at ≳2σ levels, possibly made by inefficient mass quenching, low dust obscuration, and/or hidden AGN activity. By analyzing the correlation functions at z ∼ 2–6 with HOD models, we find a weak redshift evolution (within 0.3 dex) of the ratio of the star formation rate (SFR) to the dark matter accretion rate, SFR / M ̇ h , indicating the almost constant star formation efficiency at z ∼ 2–6, as suggested by our earlier work at z ∼ 4–7. Meanwhile, the ratio gradually increases with decreasing redshift at z &lt; 5 within 0.3 dex, which quantitatively reproduces the cosmic SFR density evolution, suggesting that the redshift evolution is primarily driven by the increase of the halo number density due to the structure formation, and the decrease of the accretion rate due to the cosmic expansion. Extrapolating this calculation to higher redshifts assuming the constant efficiency suggests a rapid decrease of the SFR density at z &gt; 10 with ∝ 10−0.5(1+z), which will be directly tested with the James Webb Space Telescope.

The Physical Properties of Luminous z ≳ 8 Galaxies and Implications for the Cosmic Star Formation Rate Density from ∼0.35 deg2 of (Pure-)Parallel HST Observations*

Abstract We present the largest systematic, Hubble Space Telescope (HST)–based search to date for luminous z ≳ 8 galaxy candidates using ∼1267 arcmin2 of (pure-)parallel observations from a compilation of 288 random sightlines with Advanced Camera for Surveys and Wide Field Camera 3 observations, derived from the (Super)Brightest of Reionizing Galaxies (SuperBoRG) data set and together representing a factor ∼1.12× larger than existing space-based data sets. Using near-infrared (NIR) color cuts and careful photo-z analyses, we find 31 z ≳ 8 galaxy candidates over 29 unique sightlines, and derive global galaxy properties such as UV magnitudes and continuum slopes, sizes, and rest-frame optical properties (e.g., star formation rates (SFRs), stellar masses, A v). Taking advantage of the (pure-)parallel nature of our data set—making it one of the most representative thus far—and derived SFRs, we evaluate the cosmic SFR density for the bright end of the UV luminosity function (LF) at z ∼ 8–10 and test the validity of luminosity-function-derived results using a conversion factor. We find that our method yields comparable results to those derived with LFs. Furthermore, we present follow-up observations of five (Super)BoRG targets with the Keck Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) instrument, finding no evidence of Lyα in &gt;3 hr of Y-band observations in either, consistent with a largely neutral medium at z ∼ 8. Our results offer a definitive HST legacy on the bright end of the LF and provide a valuable benchmark as well as targets for follow-up with the James Webb Space Telescope.

Energy functions of fast radio bursts derived from the first CHIME/FRB catalogue

ABSTRACT Fast radio bursts (FRBs) are mysterious millisecond pulses in radio, most of which originate from distant galaxies. Revealing the origin of FRBs is becoming central in astronomy. The redshift evolution of the FRB energy function, i.e. the number density of FRB sources as a function of energy, provides important implications for the FRB progenitors. Here, we show the energy functions of FRBs selected from the recently released Canadian Hydrogen Intensity Mapping Experiment (CHIME) catalogue using the Vmax method. The Vmax method allows us to measure the redshift evolution of the energy functions as it is without any prior assumption on the evolution. We use a homogeneous sample of 164 non-repeating FRB sources, which are about one order of magnitude larger than previously investigated samples. The energy functions of non-repeating FRBs show Schechter function-like shapes at z ≲ 1. The energy functions and volumetric rates of non-repeating FRBs decrease towards higher redshifts similar to the cosmic stellar-mass density evolution: there is no significant difference between the non-repeating FRB rate and cosmic stellar-mass density evolution with a 1 per cent significance threshold, whereas the cosmic star-formation rate scenario is rejected with a more than 99 per cent confidence level. Our results indicate that the event rate of non-repeating FRBs is likely controlled by old populations rather than young populations that are traced by the cosmic star-formation rate density. This suggests old populations, such as old neutron stars and black holes, as more likely progenitors of non-repeating FRBs.

High-redshift predictions from IllustrisTNG – III. Infrared luminosity functions, obscured star formation, and dust temperature of high-redshift galaxies

ABSTRACT 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 redshift 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.

Extensive Lensing Survey of Optical and Near-infrared Dark Objects (El Sonido): HST H-faint Galaxies behind 101 Lensing Clusters

Abstract We present a Spitzer/IRAC survey of H-faint (H 160 ≳ 26.4, &lt; 5σ) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of ∼648 arcmin2 (effectively ∼221 arcmin2 in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 μm; median CH2 = 22.46 ± 0.11 AB mag) that lack robust HST/WFC3-IR F160W counterparts. The most remarkable source in our sample, namely ES-009 in the field of Abell 2813, is the brightest H-faint galaxy at 4.5 μm known so far (CH2 = 20.48 ± 0.03 AB mag). We show that the H-faint sources in our sample are massive (median M star = 1010.3±0.3 M ⊙), star-forming (median star formation rate = 100 − 40 + 60 M ⊙ yr−1), and dust-obscured (A V = 2.6 ± 0.3) galaxies around a median photometric redshift of z = 3.9 ± 0.4. The stellar continua of 14 H-faint galaxies can be resolved in the CH2 band, suggesting a median circularized effective radius (R e,circ; lensing corrected) of 1.9 ± 0.2 kpc and &lt;1.5 kpc for the resolved and whole samples, respectively. This is consistent with the sizes of massive unobscured galaxies at z ∼ 4, indicating that H-faint galaxies represent the dusty tail of the distribution of a wider galaxy population. Comparing with the ALMA dust continuum sizes of similar galaxies reported previously, we conclude that the heavy dust obscuration in H-faint galaxies is related to the compactness of both stellar and dust continua (R e,circ ∼ 1 kpc). These H-faint galaxies make up 16 − 7 + 13 % of the galaxies in the stellar-mass range of 1010 − 1011.2 M ⊙ at z = 3 ∼ 5, contributing to 8 − 4 + 8 % of the cosmic star formation rate density in this epoch and likely tracing the early phase of massive galaxy formation.

A deep radio view of the evolution of the cosmic star formation rate density from a stellar-mass-selected sample in VLA-COSMOS

ABSTRACT We present the 1.4 GHz radio luminosity functions (RLFs) of galaxies in the Cosmic Evolution Survey (COSMOS) field, measured above and below the 5σ detection threshold, using a Bayesian model-fitting technique. The radio flux densities from Very Large Array (VLA)-COSMOS 3-GHz data are extracted at the position of stellar-mass-selected galaxies. We fit a local RLF model, which is a combination of active galactic nuclei and star-forming galaxies (SFGs), in 10 redshift bins with a pure luminosity evolution model. Our RLF exceeds previous determinations at low radio luminosities at z &amp;lt; 1.6 with the same radio data, due to our ability to directly constrain the knee and faint-end slope of the RLF. Beyond z ∼ 2, we find that the SFG part of the RLF exhibits a negative evolution (L* moves to lower luminosities) due to the decrease in low stellar-mass galaxies in our sample at high redshifts. From the RLF for SFGs, we determine the evolution in the cosmic star formation rate density (SFRD), which we find to be consistent with the established behaviour up to z ∼ 1 using far-infrared data, but exceeds that from the previous radio-based work for the reasons highlighted above. Beyond z ∼ 1.5 the cosmic SFRD declines. We note that the relation between radio luminosity and star formation rate is crucial in measuring the cosmic SFRD from radio data at z &amp;gt; 1.5. We investigate the effects of stellar mass on the total RLF by splitting our sample into low (108.5 ≤ M/M⊙ ≤ 1010) and high ($M\gt 10^{10}\, \mathrm{M}_{\odot }$) stellar-mass subsets. We find that the SFRD is dominated by sources in the high stellar masses bin, at all redshifts.

The nature of hyperluminous infrared galaxies

Context. Hyperluminous infrared galaxies (HLIRGs) are shown to have been more abundant in early epochs. The small samples used in earlier studies are not sufficient to draw robust statistical conclusions regarding the physical properties and the power sources of these extreme infrared (IR) bright galaxies. Aims. We make use of multi-wavelength data of a large HLIRG sample to derive the main physical properties, such as stellar mass, star formation rate (SFR), volume density, and the contribution to the cosmic stellar mass density and the cosmic SFR density. We also study the black hole (BH) growth rate and its relationship with the SFR of the host galaxy. Methods. We selected 526 HLIRGs in three deep fields (Boötes, Lockman-Hole, and ELAIS-N1) and adopted two spectral energy distribution (SED) fitting codes: CIGALE, which assumes energy balance, and CYGNUS, which is based on radiative transfer models and does not adopt an energy balance principle. We used two different active galactic nucleus (AGN) models in CIGALE and three AGN models in CYGNUS to compare results that were estimated using different SED fitting codes and a range of AGN models. Results. The stellar mass, total IR luminosity, and AGN luminosity agree well among different models, with a typical median offset of 0.1 dex. The SFR estimates show the largest dispersions (up to 0.5 dex). This dispersion has an impact on the subsequent analysis, which may suggest that the previous contradictory results could partly have been due to the different choices in methods. HLIRGs are ultra-massive galaxies, with 99% of them having stellar masses larger than 1011 M⊙. Our results reveal a higher space density of ultra-massive galaxies than what was found by previous surveys or predicted via simulations. We find that HLIRGs contribute more to the cosmic SFR density as redshift increases. In terms of BH growth, the two SED fitting methods provide different results. We can see a clear trend in whereby SFR decreases as AGN luminosity increases when using CYGNUS estimates. This may possibly imply quenching by AGN in this case, whereas this trend is much weaker when using CIGALE estimates. This difference is also influenced by the dispersion between SFR estimates obtained by the two codes.

The Observed Cosmic Star Formation Rate Density Has an Evolution that Resembles a Γ(a, bt) Distribution and Can Be Described Successfully by Only Two Parameters

Abstract A debate is emerging regarding the recent inconsistent results of different studies for the cosmic star formation rate density (CSFRD) at high-z. We employ UV and IR data sets to investigate the SFR function (SFRF) at z ∼ 0–9. We find that the SFRFs derived from the dust-corrected UV (UVcorr) data contradict those from IR on some key issues because they are described by different distributions (Schechter versus double power law), imply different physics for galaxy formation (UVcorr data suggest an SFR limit/strong mechanism that diminish the number density of highly star-forming systems with respect to IR) and compare differently with the stellar mass density evolution obtained from spectral energy distribution fitting (UVcorr is in agreement, while IR differs up to 0.5 dex). However, both tracers agree on a constant CSFRD evolution at z ∼ 1–4 and point to a plateau instead of a peak. In addition, using both indicators, we demonstrate that the evolution of the observed CSFRD can be described by only two parameters and a function that has the form of a Gamma distribution (Γ(a, bt)). In contrast to previous parameterizations used in the literature, our framework connects the parameters to physical properties such as the SFR depletion time and cosmic baryonic gas density. The build-up of stellar mass occurs in Γ(a, bt) distributed steps and is the result of gas consumption up to the limit at which no eligible gas for SF at t = ∞ remains, resulting in a final cosmic stellar mass density of ∼ 0.5 × 10 9 M ⊙ Mpc 3 .

Normal, dust-obscured galaxies in the epoch of reionization.

Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6 (refs. 1-3), during the so-called epoch of reionization. While a few of these UV-identified galaxies revealed substantial dust reservoirs4-7, very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies8-12 and companions of rare quasars13,14. These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at z > 6 is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at z = 3-6 (refs. 15,16). However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star-forming galaxies at z = 6.6813 ± 0.0005 and z = 7.3521 ± 0.0005. These objects are not detected in existing rest-frame UV data and were discovered onlythrough their far-infrared [C II] lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at z ≈ 7. This population of heavily dust-obscured galaxies appears to contribute 10-25% to the z > 6 cosmic star formation rate density.