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Aims. We provide an in-depth analysis of the COSMOS-Web ring, an Einstein ring at z ≈ 2 that we serendipitously discovered during the data reduction of the COSMOS-Web survey and that could be the most distant lens discovered to date. Methods. We extracted the visible and near-infrared photometry of the source and the lens from more than 25 bands. We combined these observations with far-infrared detections to study the dusty nature of the source and we derived the photometric redshifts and physical properties of both the lens and the source with three different spectral energy distribution (SED) fitting codes. Using JWST/NIRCam images, we also produced two lens models to (i) recover the total mass of the lens, (ii) derive the magnification of the system, (iii) reconstruct the morphology of the lensed source, and (iv) measure the slope of the total mass density profile of the lens. Results. We find the lens to be a very massive elliptical galaxy at z = 2.02 ± 0.02 with a total mass within the Einstein radius of Mtot(<θEin = (3.66 ± 0.36) × 1011M⊙ and a total stellar mass of M⋆ = 1.37−0.11+0.14 × 1011 M⊙. We also estimate it to be compact and quiescent with a specific star formation rate below 10−13 yr. Compared to stellar-to-halo mass relations from the literature, we find that the total mass of the lens within the Einstein radius is consistent with the presence of a dark matter (DM) halo of total mass Mh = 1.09−0.57+1.46 × 1013 M⊙. In addition, the background source is a M⋆ = (1.26 ± 0.17) × 1010M⊙ star-forming galaxy (SFR ≈ (78 ± 15) M⊙ yr) at z = 5.48 ± 0.06. The morphology reconstructed in the source plane shows two clear components with different colors. Dust attenuation values from SED fitting and nearby detections in the far infrared also suggest that the background source could be at least partially dust-obscured. Conclusions. We find the lens at z ≈ 2. Its total, stellar, and DM halo masses are consistent within the Einstein ring, so we do not need any unexpected changes in our description of the lens such as changing its initial mass function or including a non-negligible gas contribution. The most likely solution for the lensed source is at z ≈ 5.5. Its reconstructed morphology is complex and highly wavelength dependent, possibly because it is a merger or a main sequence galaxy with a heterogeneous dust distribution. [ABSTRACT FROM AUTHOR]

We investigate how the recovery of galaxy star formation rates (SFRs) using energy-balance spectral energy distribution (SED) fitting codes depends on their recent star formation histories (SFHs). We use the magphys and prospector codes to fit 6706 synthetic SEDs of simulated massive galaxies at 1 < z < 8 from the Feedback in Realistic Environments project. We identify a previously unknown systematic error in the magphys results due to bursty star formation: the derived SFRs can differ from the truth by as much as 1 dex, at large statistical significance (>5σ), depending on the details of their recent SFH. SFRs inferred using prospector with non-parametric SFHs do not exhibit this trend. We show that using parametric SFHs (pSFHs) causes SFR uncertainties to be underestimated by a factor of up to 5×. Although this undoubtedly contributes to the significance of the systematic, it cannot explain the largest biases in the SFRs of the starbursting galaxies, which could be caused by details of the stochastic prior sampling or the burst implementation in the magphys libraries. We advise against using pSFHs and urge careful consideration of starbursts when SED modelling galaxies where the SFR may have changed significantly over the last ∼100 Myr, such as recently quenched galaxies, or those experiencing a burst. This concern is especially relevant, e.g. when fitting JWST observations of very high redshift galaxies. [ABSTRACT FROM AUTHOR]

Author(s): D. P. Marrone (corresponding author) [1]; J. S. Spilker [1]; C. C. Hayward [2, 3]; J. D. Vieira [4]; M. Aravena [5]; M. L. N. Ashby [3]; M. B. [...]

Recent works have suggested that energy balance spectral energy distribution (SED) fitting codes may be of limited use for studying high-redshift galaxies for which the observed ultraviolet and far-infrared emission are offset (spatially 'decoupled'). It has been proposed that such offsets could lead energy balance codes to miscalculate the overall energetics, preventing them from recovering such galaxies' true properties. In this work, we test how well the SED fitting code magphys can recover the stellar mass, star formation rate (SFR), specific SFR, dust mass, and luminosity by fitting 6706 synthetic SEDs generated from four zoom-in simulations of dusty, high-redshift galaxies from the FIRE project via dust continuum radiative transfer. Comparing our panchromatic results (using wavelengths 0.4–500 μm, and spanning 1 < z < 8) with fits based on either the starlight (⁠|$\lambda _\mathrm{eff} \le 2.2\, \mu$| m) or dust (⁠|$\ge 100\, \mu$| m) alone, we highlight the power of considering the full range of multiwavelength data alongside an energy balance criterion. Overall, we obtain acceptable fits for 83 per cent of the synthetic SEDs, though the success rate falls rapidly beyond z ≈ 4, in part due to the sparser sampling of the priors at earlier times since SFHs must be physically plausible (i.e. shorter than the age of the universe). We use the ground truth from the simulations to show that when the quality of fit is acceptable, the fidelity of magphys estimates is independent of the degree of UV/FIR offset, with performance very similar to that previously reported for local galaxies. [ABSTRACT FROM AUTHOR]

Context. How galaxies form, assemble, and cease their star formation is a central question within the modern landscape of galaxy evolution studies. These processes are indelibly imprinted on the galaxy stellar mass function (SMF), and its measurement and understanding is key to uncovering a unified theory of galaxy evolution. Aims. We present constraints on the shape and evolution of the galaxy SMF, the quiescent galaxy fraction, and the cosmic stellar mass density across 90% of the history of the Universe from z = 7.5 → 0.2 as a means to study the physical processes that underpin galaxy evolution. Methods. The COSMOS survey is an ideal laboratory for studying representative galaxy samples. Now equipped with deeper and more homogeneous near-infrared coverage exploited by the COSMOS2020 catalog, we leverage the large 1.27 deg2 effective area to improve sample statistics and understand spatial variations (cosmic variance) – particularly for rare, massive galaxies – and push to higher redshifts with greater confidence and mass completeness than previous studies. We divide the total stellar mass function into star-forming and quiescent subsamples through NUVrJ color-color selection. The measurements are then fit with single- and double-component Schechter functions to infer the intrinsic galaxy stellar mass function, the evolution of its key parameters, and the cosmic stellar mass density out to z = 7.5. Finally, we compare our measurements to predictions from state-of-the-art cosmological simulations and theoretical dark matter halo mass functions. Results. We find a smooth, monotonic evolution in the galaxy stellar mass function since z = 7.5, in general agreement with previous studies. The number density of star-forming systems have undergone remarkably consistent growth spanning four decades in stellar mass from z = 7.5 → 2 whereupon high-mass systems become predominantly quiescent ("downsizing"). Meanwhile, the assembly and growth of low-mass quiescent systems only occurred recently, and rapidly. An excess of massive systems at z ≈ 2.5 − 5.5 with strikingly red colors, with some being newly identified, increase the observed number densities to the point where the SMF cannot be reconciled with a Schechter function. Conclusions. Systematics including cosmic variance and/or active galactic nuclei contamination are unlikely to fully explain this excess, and so we speculate that they may be dust-obscured populations similar to those found in far infrared surveys. Furthermore, we find a sustained agreement from z ≈ 3 − 6 between the stellar and dark matter halo mass functions for the most massive systems, suggesting that star formation in massive halos may be more efficient at early times. [ABSTRACT FROM AUTHOR]

Without active galactic nucleus (AGN) feedback, simulated massive, star-forming galaxies become too compact relative to observed galaxies at z ≲ 2. In this paper, we perform high-resolution re-simulations of a massive (⁠|$M_{\star }\sim 10^{11}\, \rm {{\rm M}_{\odot }}$|⁠) galaxy at z ∼ 2.3, drawn from the Feedback in Realistic Environments (FIRE) project. In the simulation without AGN feedback, the galaxy experiences a rapid starburst and shrinking of its half-mass radius. We experiment with driving mechanical AGN winds, using a state-of-the-art hyper-Lagrangian refinement technique to increase particle resolution. These winds reduce the gas surface density in the inner regions of the galaxy, suppressing the compact starburst and maintaining an approximately constant half-mass radius. Using radiative transfer, we study the impact of AGN feedback on the magnitude and extent of the multiwavelength continuum emission. When AGN winds are included, the suppression of the compact, dusty starburst results in lowered flux at FIR wavelengths (due to decreased star formation) but increased flux at optical-to-near-IR wavelengths (due to decreased dust attenuation, in spite of the lowered star formation rate), relative to the case without AGN winds. The FIR half-light radius decreases from ∼1 to |$\sim 0.1\, \rm {kpc}$| in |$\lesssim 40\, \rm {Myr}$| when AGN winds are not included, but increases to |$\sim 2\, \rm {kpc}$| when they are. Interestingly, the half-light radius at optical-NIR wavelengths remains approximately constant over |$35\, \rm {Myr}$|⁠ , for simulations with and without AGN winds. In the case without winds, this occurs despite the rapid compaction, and is due to heavy dust obscuration in the inner regions of the galaxy. This work highlights the importance of forward-modelling when comparing simulated and observed galaxy populations. [ABSTRACT FROM AUTHOR]

Recent years have seen growing interest in post-processing cosmological simulations with radiative transfer codes to predict observable fluxes for simulated galaxies. However, this can be slow, and requires a number of assumptions in cases where simulations do not resolve the interstellar medium (ISM). Zoom-in simulations better resolve the detailed structure of the ISM and the geometry of stars and gas; however, statistics are limited due to the computational cost of simulating even a single halo. In this paper, we make use of a set of high-resolution, cosmological zoom-in simulations of massive (⁠|$M_{\star }\gtrsim 10^{10.5}\, \rm {M_{\odot }}$| at z = 2), star-forming galaxies from the FIRE suite. We run the skirt radiative transfer code on hundreds of snapshots in the redshift range 1.5 < z < 5 and calibrate a power-law scaling relation between dust mass, star formation rate, and |$870\, \mu \rm {m}$| flux density. The derived scaling relation shows encouraging consistency with observational results from the sub-millimetre-selected AS2UDS sample. We extend this to other wavelengths, deriving scaling relations between dust mass, stellar mass, star formation rate, and redshift and sub-millimetre flux density at observed-frame wavelengths between |$\sim \! 340$| and |$\sim \! 870\, \mu \rm {m}$|⁠. We then apply the scaling relations to galaxies drawn from EAGLE, a large box cosmological simulation. We show that the scaling relations predict EAGLE sub-millimetre number counts that agree well with previous results that were derived using far more computationally expensive radiative transfer techniques. Our scaling relations can be applied to other simulations and semi-analytical or semi-empirical models to generate robust and fast predictions for sub-millimetre number counts. [ABSTRACT FROM AUTHOR]

We present Gemini-S and Spitzer -IRAC optical-through-near-IR observations in the field of the SPT2349-56 proto-cluster at z = 4.3. We detect optical/IR counterparts for only 9 of the 14 submillimetre galaxies (SMGs) previously identified by ALMA in the core of SPT2349-56. In addition, we detect four z ∼ 4 Lyman-break galaxies (LBGs) in the 30 arcsec-diameter region surrounding this proto-cluster core. Three of the four LBGs are new systems, while one appears to be a counterpart of one of the nine observed SMGs. We identify a candidate brightest cluster galaxy (BCG) with a stellar mass of |$(3.2^{+2.3}_{-1.4})\times 10^{11}$|  M⊙. The stellar masses of the eight other SMGs place them on, above, and below the main sequence of star formation at z ≈ 4.5. The cumulative stellar mass for the SPT2349-56 core is at least (12.2 ± 2.8) × 1011 M⊙, a sizeable fraction of the stellar mass in local BCGs, and close to the universal baryon fraction (0.19) relative to the virial mass of the core (1013 M⊙). As all 14 of these SMGs are destined to quickly merge, we conclude that the proto-cluster core has already developed a significant stellar mass at this early stage, comparable to z = 1 BCGs. Importantly, we also find that the SPT2349-56 core structure would be difficult to uncover in optical surveys, with none of the ALMA sources being easily identifiable or constrained through g, r , and i colour selection in deep optical surveys and only a modest overdensity of LBGs over the more extended structure. SPT2349-56 therefore represents a truly dust-obscured phase of a massive cluster core under formation. [ABSTRACT FROM AUTHOR]

The galaxy size–stellar mass and central surface density–stellar mass relationships are fundamental observational constraints on galaxy formation models. However, inferring the physical size of a galaxy from observed stellar emission is non-trivial due to various observational effects, such as the mass-to-light ratio variations that can be caused by non-uniform stellar ages, metallicities, and dust attenuation. Consequently, forward-modelling light-based sizes from simulations is desirable. In this work, we use the skirt   dust radiative transfer code to generate synthetic observations of massive galaxies (⁠|$M_{*}\sim 10^{11}\, \rm {M_{\odot }}$| at z  = 2, hosted by haloes of mass |$M_{\rm {halo}}\sim 10^{12.5}\, \rm {M_{\odot }}$|⁠) from high-resolution cosmological zoom-in simulations that form part of the Feedback In Realistic Environments project. The simulations used in this paper include explicit stellar feedback but no active galactic nucleus (AGN) feedback. From each mock observation, we infer the effective radius (R e), as well as the stellar mass surface density within this radius and within |$1\, \rm {kpc}$| (Σe and Σ1, respectively). We first investigate how well the intrinsic half-mass radius and stellar mass surface density can be inferred from observables. The majority of predicted sizes and surface densities are within a factor of 2 of the intrinsic values. We then compare our predictions to the observed size–mass relationship and the Σ1− M ⋆ and Σe− M ⋆ relationships. At z  ≳ 2, the simulated massive galaxies are in general agreement with observational scaling relations. At z  ≲ 2, they evolve to become too compact but still star forming, in the stellar mass and redshift regime where many of them should be quenched. Our results suggest that some additional source of feedback, such as AGN-driven outflows, is necessary in order to decrease the central densities of the simulated massive galaxies to bring them into agreement with observations at z  ≲ 2. [ABSTRACT FROM AUTHOR]

Change history: In this Letter, the Acknowledgements section should have included the following sentence: 'The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.'. This omission has been corrected online., Author(s): T. B. Miller [sup.1] [sup.2] , S. C. Chapman [sup.1] [sup.3] [sup.4] , M. Aravena [sup.5] , M. L. N. Ashby [sup.6] , C. C. Hayward [sup.6] [sup.7] , [...]

We present the implementation and the first results of cosmic ray (CR) feedback in the Feedback In Realistic Environments (FIRE) simulations. We investigate CR feedback in non-cosmological simulations of dwarf, sub- L ⋆ starburst, and L ⋆ galaxies with different propagation models, including advection, isotropic, and anisotropic diffusion, and streaming along field lines with different transport coefficients. We simulate CR diffusion and streaming simultaneously in galaxies with high resolution, using a two-moment method. We forward-model and compare to observations of γ-ray emission from nearby and starburst galaxies. We reproduce the γ-ray observations of dwarf and L ⋆ galaxies with constant isotropic diffusion coefficient |$\kappa \sim 3\times 10^{29}\, {\rm cm^{2}\, s^{-1}}$|⁠. Advection-only and streaming-only models produce order of magnitude too large γ-ray luminosities in dwarf and L ⋆ galaxies. We show that in models that match the γ-ray observations, most CRs escape low-gas-density galaxies (e.g. dwarfs) before significant collisional losses, while starburst galaxies are CR proton calorimeters. While adiabatic losses can be significant, they occur only after CRs escape galaxies, so they are only of secondary importance for γ-ray emissivities. Models where CRs are 'trapped' in the star-forming disc have lower star formation efficiency, but these models are ruled out by γ-ray observations. For models with constant κ that match the γ-ray observations, CRs form extended haloes with scale heights of several kpc to several tens of kpc. [ABSTRACT FROM AUTHOR]

We present the first detailed study of the spatially resolved dust continuum emission of simulated galaxies at 1 <  z  < 5. We run the radiative transfer code skirt on a sample of submillimetre-bright galaxies drawn from the Feedback In Realistic Environments (FIRE) project. These simulated galaxies reach Milky Way masses by z  = 2. Our modelling provides predictions for the full rest-frame far-ultraviolet-to-far-infrared spectral energy distributions of these simulated galaxies, as well as 25-pc resolution maps of their emission across the wavelength spectrum. The derived morphologies are notably different in different wavebands, with the same galaxy often appearing clumpy and extended in the far-ultraviolet yet an ordered spiral at far-infrared wavelengths. The observed-frame 870- |$\mu$| m half-light radii of our FIRE-2 galaxies are |${\sim} 0.5\rm {-}4\, \rm {kpc}$|⁠ , consistent with existing ALMA observations of galaxies with similarly high redshifts and stellar masses. In both simulated and observed galaxies, the dust continuum emission is generally more compact than the cold gas and the dust mass, but more extended than the stellar component. The most extreme cases of compact dust emission seem to be driven by particularly compact recent star formation, which generates steep dust temperature gradients. Our results confirm that the spatial extent of the dust continuum emission is sensitive to both the dust mass and star formation rate distributions. [ABSTRACT FROM AUTHOR]

Submillimetre galaxies (SMGs) are some of the most luminous star-forming galaxies in the Universe; however, their properties remain hard to determine due to the difficulty of identifying their optical/near-infrared counterparts. One of the key steps to determining the nature of SMGs is measuring a redshift distribution representative of the whole population. We do this by applying statistical techniques to a sample of 761 850 μm sources from the Submillimetre Common User Bolometer Array 2 Cosmology Legacy Survey observations of the UKIDSS Ultra-Deep Survey (UDS) field. We detect excess galaxies around >98.4 per cent of the 850 μm positions in the deep UDS catalogue, giving us the first 850 μm selected sample to have virtually complete optical/near-infrared redshift information. Under the reasonable assumption that the redshifts of the excess galaxies are representative of the SMGs themselves, we derive a median SMG redshift of z = 2.05 ± 0.03, with 68 per cent of SMGs residing between 1.07 < z < 3.06. We find an average of 1.52 ± 0.09 excess K-band galaxies within 12 arcsec of an 850 μm position, with an average stellar mass of 2.2 ± 0.1 × 1010 M⊙. Whilst the vast majority of excess galaxies are star forming, 8.0 ± 2.1 per cent have passive rest-frame colours and are therefore unlikely to be detected at submillimetre wavelengths even in deep interferometry. We show that brighter SMGs lie at higher redshifts, and use our SMG redshift distribution - along with the assumption of a universal far-infrared Spectral Energy Distribution (SED) - to estimate that SMGs contribute around 30 per cent of the cosmic star formation rate density between 0.5 < z < 5.0. [ABSTRACT FROM AUTHOR]

Context: The observed spatial scale of the radio continuum emission from star-forming galaxies can be used to investigate the spatial extent of active star formation, constrain the importance of cosmic-ray transport, and examine the effects of galaxy interactions. Aims: We determine the radio size distribution of a large sample of 152 submillimetre galaxies (SMGs) in the COSMOS field that were pre-selected at 1.1 mm, and later detected with the Atacama Large Millimetre/submillimetre Array (ALMA) in the observed-frame 1.3 mm dust continuum emission at a signal-to-noise ratio (S/N) of ≥5. Methods: We used the deep, subarcsecond-resolution (1σ = 2.3μJy beam-1;." 75) centimetre radio continuum observations taken by the Karl G. Jansky Very Large Array (VLA)-COSMOS 3 GHz Large Project. Results: One hundred and fifteen of the 152 target SMGs (76% ± 7%) were found to have a 3 GHz counterpart (≥ 4.2σ), which renders the radio detection rate notably high. The median value of the deconvolved major axis full width at half maximum (FWHM) size at 3 GHz is derived to be 0."59 ± 0."05, or 4.6 ± 0.4 kpc in physical units, where the median redshift of the sources is z = 2.23 ± 0.13 (23% are spectroscopic and 77% are photometric values). The radio sizes are roughly log-normally distributed, and they show no evolutionary trend with redshift, or difference between different galaxy morphologies. We also derived the spectral indices between 1.4 and 3 GHz, and 3 GHz brightness temperatures for the sources, and the median values were found to be α1.4GHz3GHz = -0.67 (Sν ∝ να) and TB = 12.6 ± 2 K. Three of the target SMGs, which are also detected with the Very Long Baseline Array (VLBA) at 1.4 GHz (AzTEC/C24b, 61, and 77a), show clearly higher brightness temperatures than the typical values, reaching TB(3 GHz) > 104.03 K for AzTEC/C61. Conclusions: The derived median radio spectral index agrees with a value expected for optically thin non-thermal synchrotron radiation, and the low median 3 GHz brightness temperature shows that the observed radio emission is predominantly powered by star formation and supernova activity. However, our results provide a strong indication of the presence of an active galactic nucleus in the VLBA and X-ray-detected SMG AzTEC/C61 (high TB and an inverted radio spectrum). The median radio-emitting size we have derived is ~ 1.5-3 times larger than the typical far-infrared dust-emitting sizes of SMGs, but similar to that of the SMGs' molecular gas component traced through mid-J line emission of carbon monoxide. The physical conditions of SMGs probably render the diffusion of cosmic-ray electrons inefficient, and hence an unlikely process to lead to the observed extended radio sizes. Instead, our results point towards a scenario where SMGs are driven by galaxy interactions and mergers. Besides triggering vigorous starbursts, galaxy collisions can also pull out the magnetised fluids from the interacting disks, and give rise to a taffy-like synchrotron-emitting bridge. This provides an explanation for the spatially extended radio emission of SMGs, and can also cause a deviation from the well-known infrared-radio correlation owing to an excess radio emission. Nevertheless, further high-resolution observations are required to examine the other potential reasons for the very compact dust-emitting sizes of SMGs, such as the radial dust temperature and metallicity gradients. [ABSTRACT FROM AUTHOR]

Establishing the stellar masses, and hence specific star-formation rates of submillimetre galaxies is crucial for determining the role of such objects in the cosmic history of galaxy/star formation. However, there is as yet no consensus over the typical stellar masses of submillimetre galaxies, as illustrated by the widely differing results reported from recent optical-infrared studies of submillimetre galaxies with spectroscopic redshifts z ≃ 2-3. Specifically, even for the same set of submillimetre galaxies, the reported average stellar masses have ranged over an order of magnitude, from ≃5 × 1010 M☉ to ≃5 × 1011 M☉. Here we study how different methods of analysis can lead to such widely varying results. We find that, contrary to recent claims in the literature, potential contamination of IRAC 3-8 μm photometry from hot dust associated with an active nucleus is not the origin of the published discrepancies in derived stellar masses. Instead, we expose in detail how inferred stellar mass depends on assumptions made in the photometric fitting, and quantify the individual and cumulative effects of different choices of initial mass function, different "brands" of evolutionary synthesis models, and different forms of assumed star-formation history. We review current observational evidence for and against these alternatives as well as clues from the hydrodynamical simulations, and conclude that, for the most justifiable choices of these model inputs, the average stellar mass of luminous (S 850 ≳ 5mJy) submillimetre galaxies is ≃2 × 1011 M☉ to within a factor ≃2. We also check and confirm that this number is perfectly reasonable in the light of the latest measurements of the dynamical masses of these objects (≃2-6×1011 M☉ from CO (1-0) observations), and the evolving stellar mass function of the overall galaxy population. Galaxy stellar masses of this order imply that the average specific star-formation rate of submillimetre galaxies is comparable to that of other star-forming galaxies at z > 2, at 2-3 Gyr-1. This supports the view that, while rare outliers may be found at any stellar mass, most submillimetre galaxies simply form the top end of the "main-sequence" of star-forming galaxies at these redshifts. Conversely, this argues strongly against the viewpoint, frequently simply asserted in the literature, that submillimetre galaxies are extreme pathological objects, of little relevance in the cosmic history of star-formation. [ABSTRACT FROM AUTHOR]