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1. A Unified Model for the Coevolution of Galaxies and Their Circumgalactic Medium: The Relative Roles of Turbulence and Atomic Cooling Physics

   https://doi.org/10.3847/1538-4357/acf3ea  

   Pandya, Viraj ; Fielding, Drummond B. ; Bryan, Greg L. ; Carr, Christopher ; Somerville, Rachel S. ; Stern, Jonathan ; Faucher-Giguère, Claude-André ; Hafen, Zachary ; Anglés-Alcázar, Daniel ; Forbes, John C. ( October 2023 , The Astrophysical Journal)

   The circumgalactic medium (CGM) plays a pivotal role in regulating gas flows around galaxies and thus shapes their evolution. However, the details of how galaxies and their CGM coevolve remain poorly understood. We present a new time-dependent two-zone model that self-consistently tracks not just mass and metal flows between galaxies and their CGM but also the evolution of the global thermal and turbulent kinetic energy of the CGM. Our model accounts for heating and turbulence driven by both supernova winds and cosmic accretion as well as radiative cooling, turbulence dissipation, and halo outflows due to CGM overpressurization. We demonstrate that, depending on parameters, the CGM can undergo a phase transition (“thermalization”) from a cool, turbulence-supported phase to a virial-temperature, thermally supported phase. This CGM phase transition is largely determined by the ability of radiative cooling to balance heating from supernova winds and turbulence dissipation. We perform an initial calibration of our model to the FIRE-2 cosmological hydrodynamical simulations and show that it can approximately reproduce the baryon cycles of the simulated halos. In particular, we find that, for these parameters, the phase transition occurs at high redshift in ultrafaint progenitors and at low redshift in classicalM_vir∼ 10¹¹M_⊙dwarfs, while Milky Way–mass halos undergo the transition atz≈ 0.5. We see a similar transition in the simulations though it is more gradual, likely reflecting radial dependence and multiphase gas not captured by our model. We discuss these and other limitations of the model and possible future extensions.

    

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2. Probing the CGM of low-redshift dwarf galaxies using FIRE simulations

   https://doi.org/10.1093/mnras/staa3322  

   Li, Fei ; Rahman, Mubdi ; Murray, Norman ; Hafen, Zachary ; Faucher-Giguère, Claude-André ; Stern, Jonathan ; Hummels, Cameron B ; Hopkins, Philip F ; El-Badry, Kareem ; Kereš, Dušan ( November 2020 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Observations of ultraviolet (UV) metal absorption lines have provided insight into the structure and composition of the circumgalactic medium (CGM) around galaxies. We compare these observations with the low-redshift (z ≤ 0.3) CGM around dwarf galaxies in high-resolution cosmological zoom-in runs in the FIRE-2 (Feedback In Realistic Environments) simulation suite. We select simulated galaxies that match the halo mass, stellar mass, and redshift of the observed samples. We produce absorption measurements using trident for UV transitions of C iv, O vi, Mg ii, and Si iii. The FIRE equivalent width (EW) distributions and covering fractions for the C iv ion are broadly consistent with observations inside 0.5Rvir, but are underpredicted for O vi, Mg ii, and Si iii. The absorption strengths of the ions in the CGM are moderately correlated with the masses and star formation activity of the galaxies. The correlation strengths increase with the ionization potential of the ions. The structure and composition of the gas from the simulations exhibit three zones around dwarf galaxies characterized by distinct ion column densities: the discy interstellar medium, the inner CGM (the wind-dominated regime), and the outer CGM (the IGM accretion-dominated regime). We find that the outer CGM in the simulations is nearly but not quite supported by thermal pressure, so it is not in hydrostatic equilibrium, resulting in halo-scale bulk inflow and outflow motions. The net gas inflow rates are comparable to the star formation rate of the galaxy, but the bulk inflow and outflow rates are greater by an order of magnitude, with velocities comparable to the virial velocity of the halo. These roughly virial velocities (${\sim } 100 \, \rm km\, s^{-1}$) produce large EWs in the simulations. This supports a picture for dwarf galaxies in which the dynamics of the CGM at large scales are coupled to the small-scale star formation activity near the centre of their haloes. 

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3. Dust Temperature Uncertainties Hamper the Inference of Dust and Molecular Gas Masses from the Dust Continuum Emission of Quiescent High-redshift Galaxies

   https://doi.org/10.3847/2041-8213/ac951d  

   Cochrane, R. K. ; Hayward, C. C. ; Anglés-Alcázar, D. ( November 2022 , The Astrophysical Journal Letters)

   Single flux density measurements at observed-frame submillimeter and millimeter wavelengths are commonly used to probe dust and gas masses in galaxies. In this Letter, we explore the robustness of this method to infer dust mass, focusing on quiescent galaxies, using a series of controlled experiments on four massive halos from the Feedback in Realistic Environments project. Our starting point is four star-forming central galaxies at seven redshifts betweenz= 1.5 andz= 4.5. We generate modified quiescent galaxies that have been quenched for 100 Myr, 500 Myr, or 1 Gyr prior to each of the studied redshifts by reassigning stellar ages. We derive spectral energy distributions for each fiducial and modified galaxy using radiative transfer. We demonstrate that the dust mass inferred is highly dependent on the assumed dust temperature,T_dust, which is often unconstrained observationally. Motivated by recent work on quiescent galaxies that assumedT_dust∼ 25 K, we show that the ratio between dust mass and 1.3 mm flux density can be higher than inferred by up to an order of magnitude, due to the considerably lower dust temperatures seen in non-star-forming galaxies. This can lead to an underestimation of dust mass (and, when submillimeter flux density is used as a proxy for molecular gas content and gas mass). This underestimation is most severe at higher redshifts, where the observed-frame 1.3 mm flux density probes rest-frame wavelengths far from the Rayleigh–Jeans regime, and hence depends superlinearly on dust temperature. We fit relations between ratios of rest-frame far-infrared flux densities and mass-weighted dust temperature that can be used to constrain dust temperatures from observations and hence derive more reliable dust and molecular gas masses.

    

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4. The gravitational field of X-COP galaxy clusters

   https://doi.org/10.1051/0004-6361/202142507  

   Eckert, D. ; Ettori, S. ; Pointecouteau, E. ; van der Burg, R. F. ; Loubser, S. I. ( June 2022 , Astronomy & Astrophysics)

   The mass profiles of massive dark matter halos are highly sensitive to the nature of dark matter and potential modifications of the theory of gravity on large scales. The Λ cold dark matter (CDM) paradigm makes strong predictions on the shape of dark matter halos and on the dependence of the shape parameters on halo mass, such that any deviation from the predicted universal shape would have important implications for the fundamental properties of dark matter. Here we use a set of 12 galaxy clusters with available deep X-ray and Sunyaev–Zel’dovich data to constrain the shape of the gravitational field with an unprecedented level of precision over two decades in radius. We introduce a nonparametric framework to reconstruct the shape of the gravitational field under the assumption of hydrostatic equilibrium and compare the resulting mass profiles to the expectations of Navarro–Frenk–White (NFW) and Einasto parametric mass profiles. On average, we find that the NFW profile provides an excellent description of the recovered mass profiles, with deviations of less than 10% over a wide radial range. However, there appears to be more diversity in the shape of individual profiles than can be captured by the NFW model. The average NFW concentration and its scatter agree very well with the prediction of the ΛCDM framework. For a subset of systems, we disentangle the gravitational field into the contribution of baryonic components (gas, brightest cluster galaxy, and satellite galaxies) and that of dark matter. The stellar content dominates the gravitational field inside ∼0.02 R 500 but is responsible for only 1–2% of the total gravitational field inside R 200 . The total baryon fraction reaches the cosmic value at R 200 and slightly exceeds it beyond this point, possibly indicating a mild level of nonthermal pressure support (10 − 20%) in cluster outskirts. Finally, the relation between observed and baryonic acceleration exhibits a complex shape that strongly departs from the radial acceleration relation in spiral galaxies, which shows that the aforementioned relation does not hold at the galaxy-cluster scale. 

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5. The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

   https://doi.org/10.3847/2041-8213/acf85b  

   Chen, Hsiao-Wen ; Qu, Zhijie ; Rauch, Michael ; Chen, Mandy C. ; Zahedy, Fakhri S. ; Johnson, Sean D. ; Schaye, Joop ; Rudie, Gwen C. ; Boettcher, Erin ; Cantalupo, Sebastiano ; et al ( September 2023 , The Astrophysical Journal Letters)

   This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshiftz≈ 0.4–1. Through spectrally resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small asl_cl∼ 1 pc and density lower thann_H= 10⁻³cm⁻³are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperatureTand the nonthermal motionsb_NT, independent of the ionization models. On average,b_NTis found to increase withl_clfollowing$b_{\mathrm{NT}}\propto l_{\mathrm{cl}}^{0.3}$over three decades in spatial scale froml_cl≈ 1 pc tol_cl≈ 1 kpc. Attributing the observedb_NTto turbulent motions internal to the clumps, the best-fitb_NT–l_clrelation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass ofϵ≈ 0.003 cm²s⁻³and a dissipation timescale of ≲100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferredϵis comparable to what is found in Civabsorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

    

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