Baryonic Component Research Articles

The baryon census and the mass-density of stars, neutral gas, and hot gas as a function of halo mass

Abstract We study the stellar, neutral gas content within halos over a halo mass range 1010to1015.5M⊙ and hot X-ray gas content over a halo mass range 1012.8to1015.5M⊙ in the local universe. We combine various empirical datasets of stellar, H i and X-ray observations of galaxies, groups and clusters to establish fundamental baryonic mass vs halo mass scaling relations. These scaling relations are combined with halo mass function to obtain the baryon densities of stars, neutral gas and hot gas (T > 106K), as a function of halo mass. We calculate the contributions of the individual baryonic components to the cosmic baryon fraction. Cosmic stellar mass density ($\Omega _\text{star}=2.09^{+0.21}_{-0.18} \times 10^{-3}$), cosmic H i mass density ($\Omega _\rm{H\,{\small I}}=0.49^{+0.25}_{-0.12} \times 10^{-3}$) and cosmic neutral gas mass density ($\Omega _\text{neutral gas}=0.71^{+0.39}_{-0.18} \times 10^{-3}$) estimates are consistent with previous more direct method measurements of these values, thereby establishing the veracity of our method. We also give an estimate of the cosmic hot plasma density ($\Omega _\text{hot gas}=2.58^{+2.1}_{-0.66} \times 10^{-3}$).

The Imprint of Dark Matter on the Galactic Acceleration Field

Measurements of the accelerations of stars enabled by time-series extreme-precision spectroscopic observations, pulsar timing, and eclipsing binary stars in the solar neighborhood offer insights into the mass distribution of the Milky Way that do not rely on traditional equilibrium modeling. Given the measured accelerations, we can determine a total mass density and infer the amount of dark matter (DM) by accounting for the mass in stars, gas, and dust. Leveraging FIRE-2 simulations of Milky Way–mass galaxies we compare vertical acceleration profiles between cold DM (CDM) and self-interacting DM (SIDM) with a constant cross section of 1 cm2 g−1 across three halos with diverse assembly histories. Notably, significant asymmetries in vertical acceleration profiles near the midplane at fixed radii are observed in both CDM and SIDM, particularly in halos recently affected by mergers with satellites of Sagittarius/SMC-like masses or greater. These asymmetries offer a unique window into exploring the merger history of a galaxy. We show that SIDM halos manifest a more oblate shape and consistently exhibit higher local stellar and DM densities and steeper vertical acceleration gradients, up to 10%–30% steeper near the solar neighborhood. However, similar magnitude changes can arise from azimuthal variations in the baryonic components at a fixed radius and external influences like mergers, making it difficult to distinguish between CDM and SIDM using acceleration measurements in a single galaxy.

A quantitative comparison between velocity dependent SIDM cross-sections constrained by the gravothermal and isothermal models

ABSTRACT One necessary step for probing the nature of self-interacting dark matter (SIDM) particles with astrophysical observations is to pin down any possible velocity dependence in the SIDM cross-section. Major challenges for achieving this goal include eliminating, or mitigating, the impact of the baryonic components and tidal effects within the dark matter halos of interest – the effects of these processes can be highly degenerate with those of dark matter self-interactions at small scales. In this work, we select 9 isolated galaxies and brightest cluster galaxies (BCGs) with baryonic components small enough such that the baryonic gravitational potentials do not significantly influence the halo gravothermal evolution processes. We then constrain the parameters of Rutherford and Møller scattering cross-section models with the measured rotation curves and stellar kinematics through the gravothermal fluid formalism and isothermal method. Cross-sections constrained by the two methods are consistent at $1\sigma$ confidence level, but the isothermal method prefers cross-sections greater than the gravothermal approach constraints by a factor of $\sim 3$.

Dark Matter Distribution in Milky Way analog Galaxies

Our current understanding of how dark matter (DM) is distributed within the Milky Way (MW) halo, particularly in the solar neighborhood, is based on either careful studies of the local stellar orbits, model assumptions on the global shape of the MW halo, or from direct acceleration measurements. In this work, we undertake a study of external galaxies, with the intent of providing insight into the DM distribution in MW-analog galaxies. For this, we carefully select a sample of galaxies similar to the MW, based on maximum atomic hydrogen (H i) rotational velocity ( vmax,HI=200–280 km s−1) and morphological type (Sab–Sbc) criteria. With a need for deep, highly resolved H i, our resulting sample is composed of five galaxies from the VLA Imaging of Virgo in Atomic Gas (VIVA) survey and The H i Nearby Galaxy Survey (THINGS). To perform our baryonic analysis, we use deep mid-IR images at 3.6 and 4.5 μm from the Spitzer Survey of Stellar Structures in Galaxies (S4G). Based on the dynamical three-dimensional modeling software 3D-Based Analysis of Rotating Objects via Line Observations (3D-BAROLO), we construct rotation curves (RCs) and derive the gas and stellar contributions from the galaxy's gaseous and stellar disks' mass surface density profiles. Through a careful decomposition of their RCs into their baryonic (stars, gas) and DM components, we isolate the DM contribution by using a Markov Chain Monte Carlo-based approach. Based on the Sun's location and the MW’s R 25, we define the corresponding location of the solar neighborhood in these systems. We put forward a window for the DM density (ρ dm = 0.21–0.55 GeV cm−3) at these galactocentric distances in our MW analog sample, consistent with the values found for the MW’s local DM density, based on more traditional approaches found in the literature.

The Galaxy–Galaxy Strong Lensing Cross Section and the Internal Distribution of Matter in ΛCDM Substructure

Strong gravitational lensing offers a powerful probe of the detailed distribution of matter in lenses, while magnifying and bringing faint background sources into view. Observed strong lensing by massive galaxy clusters, which are often in complex dynamical states, has also been used to map their dark matter (DM) substructures on smaller scales. Deep high-resolution imaging has revealed the presence of strong lensing events associated with these substructures, namely galaxy-scale sub-halos. However, an inventory of these observed galaxy–galaxy strong lensing (GGSL) events is noted to be discrepant with state-of-the-art ΛCDM simulations. Cluster sub-halos appear to be over-concentrated compared to their simulated counterparts yielding an order-of-magnitude higher value of GGSL. In this paper, we explore the possibility of resolving this observed discrepancy by redistributing the mass within observed cluster sub-halos in ways that are consistent within the ΛCDM paradigm of structure formation. Lensing mass reconstructions from data provide constraints on the mass enclosed within apertures and are agnostic to the detailed mass profile within them. Therefore, as the detailed density profile within cluster sub-halos currently remains unconstrained by data, we are afforded the freedom to redistribute the enclosed mass. We investigate if rearranging the mass to a more centrally concentrated density profile helps alleviate the GGSL discrepancy. We report that refitting cluster sub-halos to the ubiquitous ΛCDM-motivated Navarro–Frenk–White profile, and further modifying them to include significant baryonic components, does not resolve this tension. A resolution to this persisting GGSL discrepancy may require more careful exploration of alternative DM models.

Dynamical modelling and the origin of gas turbulence in z ∼ 4.5 galaxies

Context. In recent years, a growing number of regularly rotating galaxy discs have been found at z ≥ 4. Such systems provide us with the unique opportunity to study the properties of dark matter (DM) halos at these early epochs, the turbulence within the interstellar medium and the evolution of scaling relations. Aims. Here, we investigate the dynamics of four gas discs in galaxies at z ∼ 4.5 observed with ALMA in the [CII] 158 μm fine-structure line. We aim to derive the structural properties of the gas, stars and DM halos of the galaxies and to study the mechanisms driving the turbulence in high-z discs. Methods. We decomposed the rotation curves into baryonic and DM components within the extent of the [CII] discs, that is, 3 to 5 kpc. Furthermore, we used the gas velocity dispersion profiles as a diagnostic tool in investigating the mechanisms driving the turbulence in the discs. Results. We obtain total stellar, gas and DM masses in the ranges of log(M/M⊙) = 10.3 − 11.0, 9.8 − 11.3, and 11.2 − 13.3, respectively. We find dynamical evidence in all four galaxies for the presence of compact stellar components conceivably, stellar bulges. The turbulence present in the galaxies appears to be primarily driven by stellar feedback, negating the necessity for large-scale gravitational instabilities. Finally, we investigate the position of our galaxies in the context of local scaling relations, in particular the stellar-to-halo mass and Tully–Fisher analogue relations.

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Resolving the hot and ionized Universe through the Sunyaev-Zeldovich effect

An omnipresent feature of the multi-phase “cosmic web” — the large-scale filamentary backbone of the Universe — is that warm/hot (≳ 105 K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale intergalactic filaments, to the Mpc intracluster medium (ICM), all the way down to the circumgalactic medium (CGM) surrounding individual galaxies, on scales from ∼ 1 kpc up to their respective virial radii (∼ 100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the Sunyaev-Zeldovich (SZ) effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and next-generation (sub)millimeter facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity, or all of the above. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to degree scales) and we employ detailed theoretical forecasts to determine the key instrumental constraints for achieving our goals.

Euclid preparation

The Euclid photometric survey of galaxy clusters stands as a powerful cosmological tool, with the capacity to significantly propel our understanding of the Universe. Despite being subdominant to dark matter and dark energy, the baryonic component of our Universe holds substantial influence over the structure and mass of galaxy clusters. This paper presents a novel model that can be used to precisely quantify the impact of baryons on the virial halo masses of galaxy clusters using the baryon fraction within a cluster as a proxy for their effect. Constructed on the premise of quasi-adiabaticity, the model includes two parameters, which are calibrated using non-radiative cosmological hydrodynamical simulations, and a single large-scale simulation from the Magneticum set, which includes the physical processes driving galaxy formation. As a main result of our analysis, we demonstrate that this model delivers a remarkable 1% relative accuracy in determining the virial dark matter-only equivalent mass of galaxy clusters starting from the corresponding total cluster mass and baryon fraction measured in hydrodynamical simulations. Furthermore, we demonstrate that this result is robust against changes in cosmological parameters and against variation of the numerical implementation of the subresolution physical processes included in the simulations. Our work substantiates previous claims regarding the impact of baryons on cluster cosmology studies. In particular, we show how neglecting these effects would lead to biased cosmological constraints for a Euclid-like cluster abundance analysis. Importantly, we demonstrate that uncertainties associated with our model arising from baryonic corrections to cluster masses are subdominant when compared to the precision with which mass–observable (i.e. richness) relations will be calibrated using Euclid and to our current understanding of the baryon fraction within galaxy clusters.

Project Dinos I: A joint lensing–dynamics constraint on the deviation from the power law in the mass profile of massive ellipticals

ABSTRACT The mass distribution in massive elliptical galaxies encodes their evolutionary history, thus providing an avenue to constrain the baryonic astrophysics in their evolution. The power-law assumption for the radial mass profile in ellipticals has been sufficient to describe several observables to the noise level, including strong lensing and stellar dynamics. In this paper, we quantitatively constrained any deviation, or the lack thereof, from the power-law mass profile in massive ellipticals through joint lensing–dynamics analysis of a large statistical sample with 77 galaxy–galaxy lens systems. We performed an improved and uniform lens modelling of these systems from archival Hubble Space Telescope imaging using the automated lens modelling pipeline dolphin. We combined the lens model posteriors with the stellar dynamics to constrain the deviation from the power law after accounting for the line-of-sight lensing effects, a first for analyses on galaxy–galaxy lenses. We find that the Sloan Lens ACS Survey lens galaxies with a mean redshift of 0.2 are consistent with the power-law profile within 1.1σ (2.8σ) and the Strong Lensing Legacy Survey lens galaxies with a mean redshift of 0.6 are consistent within 0.8σ (2.1σ), for a spatially constant (Osipkov–Merritt) stellar anisotropy profile. We adopted the spatially constant anisotropy profile as our baseline choice based on previous dynamical observables of local ellipticals. However, spatially resolved stellar kinematics of lens galaxies are necessary to differentiate between the two anisotropy models. Future studies will use our lens models to constrain the mass distribution individually in the dark matter and baryonic components.

A distinct radial acceleration relation across the brightest cluster galaxies and galaxy clusters

Recent studies reveal a radial acceleration relation (RAR) in galaxies, which illustrates a tight empirical correlation connecting the observational acceleration and the baryonic acceleration with a characteristic acceleration scale. However, a distinct RAR has been revealed on brightest cluster galaxy (BCG) cluster scales with a seventeen-times-larger acceleration scale due to the gravitational lensing effect. In this work, we systematically explore the acceleration and mass correlations between dynamical and baryonic components in 50 BCGs. To investigate the dynamical RAR in BCGs, we derived their dynamical accelerations from the stellar kinematics using the Jeans equation through Abel inversion and adopted the baryonic mass from Sloan Digital Sky Survey photometry. We explored the spatially resolved kinematic profiles with the largest integral field spectroscopy (IFS) data collected by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. Our results demonstrate that the dynamical RAR in BCGs is consistent with the lensing RAR on BCG-cluster scales as well as a larger acceleration scale. This finding may imply that BCGs and galaxy clusters have fundamental differences from field galaxies. We also find a mass correlation, but it is less tight than the acceleration correlation.

Probing the small-scale structure of the intergalactic medium with ESPRESSO: spectroscopy of the lensed QSO UM673

ABSTRACT The gravitationally lensed quasar J014516.6-094517 at z = 2.719 has been observed with the ESPRESSO instrument at the ESO VLT to obtain high-fidelity spectra of the two images A and B with a resolving power R = 70 000. At the redshifts under investigation (2.1 ≲ z ≲ 2.7), the Lyman forests along the two sightlines are separated by sub-kiloparsec physical distances and exhibit a strong correlation. We find that the two forests are indistinguishable at the present level of signal-to-noise ratio and do not show any global velocity shift, with the cross-correlation peaking at Δv = 12 ± 48 $\rm m~s^{-1}$. The distribution of the difference in velocity of individual Ly α features is compatible with a null average and a mean absolute deviation of 930 $\rm m~s^{-1}$. Significant differences in NH i column density are not detected, putting a limit to the RMS fluctuation in the baryon density on ≲1 proper kpc scales of Δρ/ρ ≲ 3 per cent. On the other hand, metal lines show significant differences both in velocity structure and in column density. A toy model shows that the difference in velocity of the metal features between the two sightlines is compatible with the motions of the baryonic component associated with dark matter haloes of typical mass M ≃ 2 × 1010 M⊙, also compatible with the observed incidence of the metal systems. The present observations confirm the feasibility of the Sandage test of the cosmic redshift drift with high-fidelity spectroscopy of the Lyman forest of distant, bright quasars, but also provide an element of caution about the intrinsic noise associated with the usage of metal features for the same purpose.

MUSE-ALMA Haloes X: the stellar masses of gas-rich absorbing galaxies

ABSTRACT The physical processes by which gas is accreted onto galaxies, transformed into stars, and then expelled from galaxies are of paramount importance to galaxy evolution studies. Observationally constraining each of these baryonic components in the same system, however, is challenging. Furthermore, simulations indicate that the stellar mass of galaxies is a key factor influencing CGM properties. Indeed, absorption lines detected against background quasars offer the most compelling way to study the cold gas in the circumgalactic medium (CGM). The MUSE-ALMA Haloes survey is composed of quasar fields covered with VLT/MUSE observations, comprising 32 H i absorbers at 0.2 < z < 1.4 and 79 associated galaxies, with available or upcoming molecular gas measurements from ALMA. We use a dedicated 40-orbit HST UVIS and IR WFC3 broad-band imaging campaign to characterize the stellar content of these galaxies. By fitting their spectral energy distribution, we establish they probe a wide range of stellar masses: 8.1 < log (M*/M⊙) < 12.4. Given their star formation rates, most of these objects lie on the main sequence of galaxies. We also confirm a previously reported anticorrelation between the stellar masses and CGM hydrogen column density N (H i), indicating an evolutionary trend where higher mass galaxies are less likely to host large amounts of H i gas in their immediate vicinity up to 120 kpc. Together with other studies from the MUSE-ALMA Haloes survey, these data provide stellar masses of absorber hosts, a key component of galaxy formation and evolution, and observational constraints on the relation between galaxies and their surrounding medium.

The Tully–Fisher relation from SDSS-MaNGA: physical causes of scatter and variation at different radii

ABSTRACT The stellar mass Tully–Fisher relation (STFR) and its scatter encode valuable information about the processes shaping galaxy evolution across cosmic time. However, we are still missing a proper quantification of the STFR slope and scatter dependence on the baryonic tracer used to quantify rotational velocity, on the velocity measurement radius and on galaxy integrated properties. We present a catalogue of stellar and ionized gas (traced by H$\rm {\alpha }$ emission) kinematic measurements for a sample of galaxies drawn from the MaNGA Galaxy Survey, providing an ideal tool for galaxy formation model calibration and for comparison with high-redshift studies. We compute the STFRs for stellar and gas rotation at 1, 1.3 and 2 effective radii (Re). The relations for both baryonic components become shallower at 2Re compared to 1Re and 1.3Re. We report a steeper STFR for the stars in the inner parts (≤1.3Re) compared to the gas. At 2Re, the relations for the two components are consistent. When accounting for covariances with integrated v/σ, scatter in the stellar and gas STFRs shows no strong correlation with: optical morphology, star formation rate surface density, tidal interaction strength or gas accretion signatures. Our results suggest that the STFR scatter is driven by an increase in stellar/gas dispersional support, from either external (mergers) or internal (feedback) processes. No correlation between STFR scatter and environment is found. Nearby Universe galaxies have their stars and gas in statistically different states of dynamical equilibrium in the inner parts (≤1.3Re), while at 2Re the two components are dynamically coupled.

In pursuit of giants

The physical mechanisms that link the termination of star formation in quiescent galaxies and the evolution of their baryonic components, stars, and the interstellar medium (ISM; dust, gas, and metals) are poorly constrained beyond the local Universe. In this work, we characterise the evolution of the dust content in 545 quiescent galaxies observed at 0.1 < z < 0.6 as part of the hCOSMOS spectroscopic redshift survey. This is, to date, the largest sample of quiescent galaxies at intermediate redshifts for which the dust, stellar, and metal abundances are consistently estimated. We analyse how the crucial markers of a galaxy dust life cycle, such as specific dust mass (Mdust/M⋆), evolve with different physical parameters, namely gas-phase metallicity (Zgas), time since quenching (tquench), stellar mass (M⋆), and stellar population age. We find morphology to be an important factor in the large scatter in Mdust/M⋆ (∼2 orders of magnitude). Quiescent spirals exhibit strong evolutionary trends of specific dust mass with M⋆, stellar age, and galaxy size, in contrast to the little to no evolution experienced by ellipticals. When transitioning from solar to super-solar metallicities (8.7 ≲ 12 + log(O/H)≲9.1), quiescent spirals undergo a reversal in Mdust/M⋆, indicative of a change in dust production efficiency. By modelling the star formation histories of our objects, we unveil a broad dynamical range of post-quenching timescales (60 Myr < tquench < 3.2 Gyr). We show that Mdust/M⋆ is highest in recently quenched systems (tquench < 500 Myr), but its further evolution is non-monotonic, as a consequence of different pathways for dust formation, growth, or removal on various timescales. Our data are best described by simulations that include dust growth in the ISM. While this process is prevalent in the majority of galaxies, for ∼15% of objects we find evidence of additional dust content acquired externally, most likely via minor mergers. Altogether, our results strongly suggest that prolonged dust production on a timescale of 0.5 − 1 Gyr since quenching may be common in dusty quiescent galaxies at intermediate redshifts, even if their gas reservoirs are heavily exhausted (i.e. cold gas fraction < 1 − 5%).

Formation of the hydrogen line 21-cm in Dark Ages and Cosmic Dawn: dependences on cosmology and first light

ABSTRACT We analyse the formation of the redshifted hyperfine structure line 21-cm of hydrogen atom in the Dark Ages, Cosmic Dawn, and Reionization epochs. The evolution of the global differential brightness temperature in this line was computed to study its dependence on the values of cosmological parameters and physical conditions in the intergalactic medium. Variations of the depth of the Dark Ages absorption line at z ∼ 80 with variations of the cosmological parameters Ωb, Ωcdm, ΩΛ, ΩK, and H0 are studied. The standard model with post-Planck parameters predicts a value of the differential brightness temperature in the centre of the absorption line ∼30–50 mK. The profile of this line can be quite another in the non-standard cosmological models, which include the annihilating or decaying dark matter, a primordial stochastic magnetic field, etc. It can be shallower or be an emission bump instead of an absorption trough. It is also shown that the position and depth of the Cosmic Dawn absorption line formed at 10 < z < 30, due to the Wouthuysen–Field effect, is mainly defined by the spectral energy distribution of the first sources of light. If reionization occurs at zri = 7 ± 1, then the differential brightness temperature in the centre of this line is ∼80 mK. During the reionization, the emission with an amplitude of ∼20 mK is possible. It is also shown that the temperature, density, and degree of ionization of the baryonic component are decisive in calculating the intensity of the 21-cm absorption/emission line from these epochs.

The information on halo properties contained in spectroscopic observations of late-type galaxies

ABSTRACT Rotation curves are the key observational manifestation of the dark matter distribution around late-type galaxies. In a halo model context, the precision of constraints on halo parameters is a complex function of properties of the measurements as well as properties of the galaxy itself. Forthcoming surveys will resolve rotation curves to varying degrees of precision, or measure their integrated effect in the $\mathrm{H}\, \small {\rm I}$ linewidth. To ascertain the relative significance of the relevant quantities for constraining halo properties, we study the information on halo mass and concentration as quantified by the Kullback–Leibler divergence of the kinematics-informed posterior from the uninformative prior. We calculate this divergence as a function of the different types of spectroscopic observation, properties of the measurement, galaxy properties, and auxiliary observational data on the baryonic components. Using the SPARC (Spitzer Photometry & Accurate Rotation Curves) sample, we find that fits to the full rotation curve exhibit a large variation in information gain between galaxies, ranging from ~1 to ~11 bits. The variation is predominantly caused by the vast differences in the number of data points and the size of velocity uncertainties between the SPARC galaxies. We also study the relative importance of the minimum $\mathrm{H}\, \small {\rm I}$ surface density probed and the size of velocity uncertainties on the constraining power on the inner halo density slope, finding the latter to be significantly more important. We spell out the implications of these results for the optimization of galaxy surveys aiming to constrain galaxies’ dark matter distributions, highlighting the need for precise velocity measurements.

The GMRT archive atomic gas survey – II. Mass modelling and dark matter halo properties across late-type spirals

ABSTRACT Studying the kinematics and mass modelling of galaxies from H i 21 cm data provides valuable insights into the properties of both the baryonic components and the dark matter halo in nearby galaxies. Despite many observational studies, mass modelling of galaxies remains challenging due to different limitations. For example, most of the previous studies involving mass modelling are based on rotation curves derived from 2D velocity fields from H i or H α spectroscopic observation which are often affected by beam smearing and projection effect. However, kinematic modelling done by fitting the ‘Tilted ring model’ to 3D data cube is not affected by these issues. In this study, we present and compare 3D kinematic modelling of a pilot sample of 11 galaxies from the GMRT archive atomic gas survey (GARCIA) using two different publicly available pipelines. We model the observed H i rotation curve using 3.6-μm infrared data and SDSS r-band data for stellar contribution, H i surface density profile for gas, and Navarro–Frenk–White profile for dark matter halo; and employ the Markov chain Monte Carlo optimization method for parameter estimation. Further, to validate our analysis, we revisit important scaling relations, e.g. the Mgas–Mstar relation, Mstar–Mhalo relation, Mgas–Mhalo relation and Baryonic Tully–Fisher relation. The scaling relations from our analysis are broadly consistent with that reported in the literature. A larger sample of galaxies from GARCIA in the near future will allow studying these scaling relations in greater details.

Properties and observables of massive galaxies in self-interacting dark matter cosmologies

ABSTRACT We use hydrodynamic cosmological simulations to test the differences between cold and self-interacting dark matter models (CDM and SIDM) in the mass range of massive galaxies (1012 < M200/M⊙ h−1 < 1013.5). We consider two SIDM models: one with constant cross-section $\sigma /m_{\chi } = 1\, \mathrm{cm^2 \, g^{-1}}$ and one where the cross-section is velocity-dependent. Despite a weak trend in mass, we find that with the inclusion of baryons the differences between SIDM and CDM density profiles observed in the dark-matter-only case are almost erased. We also search for signatures of SIDM in the distribution of strong lensing Einstein radii and find that the distributions derived from CDM and SIDM hydro runs are both comparable to observational samples of strong lenses. We find that, looking at the total matter distribution, the interplay between self-interactions and baryons can greatly reduce the expected differences between CDM and SIDM models at this mass scale, making the discrimination between these DM models challenging. However, looking at the dark matter/baryonic fractions in the inner region of the haloes we show that the deviations of SIDM from CDM can still be found considering these components separately. These results highlight that one of the most promising paths to discriminate between CDM and SIDM is to focus on techniques able to distinguish between the dark matter and baryonic components in galaxies and clusters.

Probing the hot circumgalactic medium of external galaxies in X-ray absorption II: a luminous spiral galaxy at z ≈ 0.225

ABSTRACT The circumgalactic medium (CGM) is the most massive baryonic component of a spiral galaxy, shock heated to about 106 K for an $\rm L^{\star }$ galaxy. The CGM of the Milky Way has been well-characterized through X-ray absorption line spectroscopy. However, the paucity of bright background sources makes it challenging to probe the CGM of external galaxies. Previously, using broad O vi absorption as a signpost, we successfully detected the CGM of one galaxy in X-rays. Here we report on the detection of the O vii K α absorption line at the redshift of a spiral galaxy at z ≈ 0.225, using 1.2 Ms of Chandra observations. This is a robust detection, clearly showing the presence of the hot gas. The mass in the hot phase is at least an order of magnitude larger than that in the cooler phases detected in the UV. The presence of hot gas 116 h−1 kpc from the centre of this galaxy provides credence to the existence of the extended CGM of the Milky Way. There has been a report of the detection of O vii absorption from the warm-hot intergalactic medium in this sightline, using stacking analysis on older data set. We argue that the absorption line is from the CGM of the z ≈ 0.225 galaxy instead.

The Three Hundred Project: the evolution of physical baryon profiles

ABSTRACT The distribution of baryons provides a significant way to understand the formation of galaxy clusters by revealing the details of its internal structure and changes over time. In this paper, we present theoretical studies on the scaled profiles of physical properties associated with the baryonic components, including gas density, temperature, metallicity, pressure and entropy as well as stellar mass, metallicity and satellite galaxy number density in galaxy clusters from z = 4 to z = 0 by tracking their progenitors. These mass-complete simulated galaxy clusters are coming from The Three Hundred with two runs: Gizmo-SIMBA and Gadget-X. Through comparisons between the two simulations, and with observed profiles that are generally available at low redshift, we find that (1) the agreements between the two runs and observations are mostly at outer radii r ≳ 0.3r500, in line with the self-similarity assumption. While Gadget-X shows better agreements with the observed gas profiles in the central regions compared to Gizmo-SIMBA; (2) the evolution trends are generally consistent between the two simulations with slightly better consistency at outer radii. In detail, the gas density profile shows less discrepancy than the temperature and entropy profiles at high redshift. The differences in the cluster centre and gas properties imply different behaviours of the AGN models between Gadget-X and Gizmo-SIMBA, with the latter, maybe too strong for this cluster simulation. The high-redshift difference may be caused by the star formation and feedback models or hydrodynamics treatment, which requires observation constraints and understanding.