Search

The advent of new sub-millimetre (sub-mm) observational facilities has stimulated the desire to model the sub-mm line emission of galaxies within cosmological galaxy formation models. This is typically done by applying sub-resolution recipes to describe the properties of the unresolved interstellar medium (ISM). While there is freedom in how one implements sub-resolution recipes, the impact of various choices has yet to be systematically explored. We combine a semi-analytic model of galaxy formation with chemical equilibrium networks and numerical radiative transfer models and explore how different choices for the sub-resolution modelling affect the predicted CO, [C  i ], and [C  ii ] emission of galaxies. A key component for a successful model includes a molecular cloud mass–size relation and scaling for the ultraviolet and cosmic ray radiation field that depend on local ISM properties. Our most successful model adopts a Plummer radial density profile for gas within molecular clouds. Different assumptions for the clumping of gas within molecular clouds and changes in the molecular cloud mass distribution function hardly affect the CO, [C  i ], and [C  ii ] luminosities of galaxies. At fixed star formation rate, the [C  ii ]–SFR ratio of galaxies scales inversely with the pressure acting on molecular clouds, increasing the molecular clouds density and hence decreasing the importance of [C  ii ] line cooling. We find that it is essential that a wide range of sub-mm emission lines arising in vastly different phases of the ISM are used as model constraints in order to limit the freedom in sub-grid choices. [ABSTRACT FROM AUTHOR]

Knowledge of the number density of Ha emitting galaxies is vital for assessing the scientific impact of the Euclid and Wide Field Infrared Survey Telescope (WFIRST) missions. In this work, we present predictions from a galaxy formation model, GALACTICUS, for the cumulative number counts of Ha-emitting galaxies. We couple GALACTICUS to three different dust attenuation methods and examine the counts using each method. A χ² minimisation approach is used to compare the model predictions to observed galaxy counts and calibrate the dust parameters. We find that weak dust attenuation is required for the GALACTICUS counts to be broadly consistent with the observations, though the optimum dust parameters return large values for χ², suggesting that further calibration of GALACTICUS is necessary. The model predictions are also consistent with observed estimates for the optical depth and the Ha luminosity function. Finally, we present forecasts for the redshift distributions and number counts for two Euclidlike and one WFIRST-like surveys. For a Euclid-like survey with redshift range of 0.9 ≤ z ≤ 1.8 and Ha + [N II] blended flux limit of 2 × 10-16 erg s-1 cm-2, we predict a number density between 3900 and 4800 galaxies per square degree. For a WFIRST-like survey with redshift range of 1 ≤ z ≤ 2 and blended flux limit of 1 × 10-16 erg s-1 cm-2, we predict a number density between 10 400 and 15 200 galaxies per square degree. [ABSTRACT FROM AUTHOR]

Star-forming clumps have been found to significantly influence the star formation of gas-rich |$z\gt 1$| galaxies. Using public data from JWST /NIRCam (Cosmic Evolution Survey; COSMOS-Web) and Atacama Large (sub-)Millimeter Array (ALMA; Fiber-Multi Object Spectrograph or FMOS-COSMOS survey), we study a sample of 32 massive (⁠|$\gt 10^{10.5}\, \rm {\rm M}_{\odot }$|⁠) main-sequence galaxies at |$z_{\rm spec}\sim 1.5$| with |$\sim 0.3\, \rm kpc$| resolution. We create composite morphological models consisting of bulge, disc, and clumps to fully 'deconstruct' the galaxy images. With the resulting measurements of the flux and size of these components, we find the following: (i) the combined contribution of clumps is 1–30 per cent towards the net star formation of the host while contributing 1–20 per cent to its stellar mass. The clumps show a correlation between their stellar mass and star formation rate (SFR), but have an increased specific SFR relative to the star formation main-sequence, with offsets ranging from |$0 \lesssim \Delta \log \rm sSFR \lesssim 0.4$|⁠. They feature star formation surface densities of |$10^{-2}-10^{2}\, \rm {\rm M}_{\odot }\, yr^{ -1}\, kpc^{-2}$|⁠ , consistent with values observed in both local star-forming and starburst galaxies. (ii) The detected clumps span a large range of characteristic sizes (⁠|$r_{e} \sim 0.1 - 1\, \rm kpc$|⁠) and stellar masses (⁠|$\sim 10^{8.0-9.5}\, \rm {\rm M}_{\odot }$|⁠). We estimate a mass–size relation (⁠|$r_{e} \propto \rm M_{\star }^{\, 0.52 \pm 0.07}$|⁠) along with a stellar mass function (slope, |$\alpha = - 1.85 \pm 0.19$|⁠), both suggesting a hierarchical nature similar to that expected in star-forming regions in local galaxies. (iii) Our measurements agree with the properties of stellar clumps in |$z\gtrsim 1$| lensed systems, bridging the gap between lensed and unlensed studies by detecting structures at sub-kpc scales. (iv) Clumps are found to be preferentially located along spiral features visible primarily in the residual rest frame near-IR images. In conclusion, we present an observation-based, coherent picture of star-forming clumps in galaxies at |$z \gt 1$|⁠. [ABSTRACT FROM AUTHOR]

We present new free-form and hybrid mass reconstructions of the galaxy cluster lens MACS J0416.1 |$-$| 2403 at |$z=0.396$| using the lens inversion method GRALE. The reconstructions use 237 spectroscopically confirmed multiple images from Bergamini et al. (2023) as the main input. Our primary model reconstructs images to a positional accuracy of 0.191 arcsec, thus representing one of the most precise reconstructions of this lens to date. Our models find broad agreement with previous reconstructions, and identify two |$\sim 10^{12}\, {\rm M}_{\odot }$| light-unaffiliated substructures. We focus on two highly magnified arcs: Spock and Mothra. Our model features a unique critical curve structure around the Spock arc with 2 crossings. This structure enables sufficient magnification across this arc to potentially explain the large number of transients as microlensing events of supergiant stars. Additionally, we develop a model of the millilens substructure expected to be magnifying Mothra, which may be a binary pair of supergiants with |$\mu \sim 6000$|⁠. This model accounts for flexibility in the millilens position while preserving the observed flux and minimizing image position displacements along the Mothra arc. We constrain the millilens mass and core radius to |$\lesssim 10^6 {\rm M}_{\odot }$| and |$\lesssim 17$|  pc, respectively, which would render it one of the smallest and most compact substructures constrained by lensing. If the millilens is dominated by wave dark matter, the axion mass is constrained to be |$\lesssim 3.0 \times 10^{-21}$|  eV. Further monitoring of this lens with JWST will uncover more transients, permitting tighter constraints on the structure surrounding these two arcs. [ABSTRACT FROM AUTHOR]

The current paradigm for the co-evolution of galaxies and their supermassive black holes postulates that dust-obscured active galactic nuclei (AGNs) represent a transitional phase towards a more luminous and unobscured state. However, our understanding of dusty AGNs and their host galaxies at early cosmic times is inadequate due to observational limitations. Here, we present JWST observations of CID-931, an X-ray-detected AGN at a spectroscopic redshift of |$z_{\rm spec}=4.91$|⁠. Multiband NIRCam imaging from the COSMOS-Web program reveals an unresolved red core, similar to JWST-discovered dusty AGNs. Strikingly, the red core is surrounded by at least eight massive star-forming clumps spread over |${1{^{\prime \prime}_{.}}6} \approx 10\,\,{\rm kpc}$|⁠ , each of which has a stellar mass of |$10^9$| – |$10^{10}\, M_{\odot }$| and a radius of |$\sim$| 0.1–1 kpc. The whole system amounts to |$10^{11}\, M_{\odot }$| in stellar mass, higher than typical star-forming galaxies at the same epoch. In this system, gas inflows and/or complex merger events may trigger clump formation and AGN activity, thus leading to the rapid formation of a massive galaxy hosting a supermassive black hole. Future follow-up observations will provide new insights into the evolution of the galaxy–black hole relationship during such transitional phases in the early universe. [ABSTRACT FROM AUTHOR]