Observed Scaling Relations Research Articles

The role of dry mergers in shaping the scaling relations of galaxies

In the context of the hierarchical formation of galaxies, we investigated the role played by mergers in shaping the scaling relations of galaxies, that is the projections of their fundamental plane onto the and planes. To this end, based on the scalar virial theorem, we developed a simple theory of multiple dry mergers to read both the large-scale simulations and the companion scaling relations. The aim was to compare the results of this approach with the observational data and with two of the most recent and detailed numerical cosmo-hydro-dynamical simulations: Illustris-TNG and EAGLE (Evolution and Assembly of GaLaxies and their Environments). We derived these scaling relations for the galaxies of the Mapping Nearby Galaxies at APO (MaNGA) and Wide-field Imaging of Nearby Galaxy-Clusters Survey (WINGS) databases and compared them with the observational data, the numerical simulations, and the results of our simple theory of dry mergers. The multiple dry merging mechanism is able to explain all the main characteristics of the observed scaling relations of galaxies, such as slopes, scatters, curvatures, and zones of exclusion. The distribution of galaxies in these planes is continuously changing across time because of the merging activity and other physical processes, such as star formation, quenching, and energy feedback. The simple merger theory presented here yields the correct distribution of galaxies in the main scaling relations at all cosmic epochs. The precision is comparable with that obtained by the modern cosmo-hydro-dynamical simulations, with the advantage of providing a rapid exploratory response on the consequences engendered by different physical effects.

The supermassive black hole population from seeding via collisions in nuclear star clusters

The coexistence of nuclear star clusters (NSCs) and supermassive black holes (SMBHs) in galaxies with stellar masses of ∼ 10^ M_⊙, scaling relations between their properties and the properties of the host galaxy (e.g., M_ NSC stellar -M_ galaxy stellar and M_ BH -M_ galaxy stellar ), and the fact that NSCs seem to take on the role of SMBHs in less massive galaxies (and vice versa in the more massive ones) suggest that the origin of NSCs and SMBHs is related. In this study we implemented an `in situ' NSC formation scenario in which NSCs are formed in the center of galaxies due to star formation in the accumulated gas. We explored the impact of the free parameter A_ res, which regulates the amount of gas transferred to the NSC reservoir and thus plays a crucial role in shaping the cluster's growth. Simultaneously, we included a black hole (BH) seed formation recipe based on stellar collisions within NSCs in the semi-analytic model Galacticus to explore the resulting population of SMBHs. We determined the parameter space of the NSCs that form a BH seed and find that in initially more compact NSCs, the formation of these BH seeds is more favorable. This leads to the formation of light, medium, and heavy BH seeds, which eventually reach masses of up to ∼ 10^9 M_⊙ and is comparable to the observed SMBH mass function at masses above $10^8$ M_⊙. Additionally, we compared the resulting population of NSCs with a NSC mass function derived from the stellar mass function of galaxies from the GAMA survey at z<0.06, finding a good agreement in terms of shape. We also find a considerable overlap in the observed scaling relations between the NSC mass, the stellar mass of the host galaxy, and the velocity dispersion, which is independent of the value of A_ res. However, the chi-square analysis suggests that the model requires further refinement to achieve better quantitative agreement.

Generic Elasticity of Thermal, Underconstrained Systems.

Athermal (i.e., zero-temperature) underconstrained systems are typically floppy, but they can be rigidified by the application of external strain, which is theoretically well understood. Here and in the companion paper [C. T. Lee and M. Merkel, Phys. Rev. E 110, 064147 (2024)PRESCM2470-004510.1103/PhysRevE.110.064147], we extend this theory to finite temperatures for a very broad class of underconstrained systems. In the vicinity of the athermal transition point, we derive from first principles expressions for elastic properties such as isotropic tension t and shear modulus G on temperature T, isotropic strain ϵ, and shear strain γ, which we confirm numerically. These expressions contain only three parameters: entropic rigidity κ_{S}, energetic rigidity κ_{E}, and a parameter b_{ϵ} describing the interaction between isotropic and shear strain, which can be determined from the microstructure of the system. Our results imply that in underconstrained systems, entropic and energetic rigidity interact like two springs in series. This also allows for a simple explanation of the previously numerically observed scaling relation t∼G∼T^{1/2} at ϵ=γ=0. Our work unifies the physics of systems as diverse as polymer fibers and networks, membranes, and vertex models for biological tissues.

Dark energy survey year 3 results: miscentring calibration and X-ray-richness scaling relations in redMaPPer clusters

ABSTRACT We use Dark Energy Survey Year 3 (DES Y3) clusters with archival XMM–Newton and Chandra X-ray data to assess the centring performance of the redMaPPer cluster finder and to measure key richness observable scaling relations. We find that 10–20 per cent of redMaPPer clusters are miscentred, both when comparing to the X-ray peak position and to the visually identified central cluster galaxy. We find no significant difference in miscentring in bins of low versus high richness or redshift. The dominant reasons for miscentring include masked or missing data and the presence of other bright galaxies in the cluster. For half of the miscentred clusters, the correct central was one of the possible centrals identified by redMaPPer, while for ∼40 per cent of miscentred clusters, the correct central is not a redMaPPer member mostly due to masking. Additionally, we fit scaling relations of X-ray temperature and luminosity with richness. We find a TX–λ scatter of $0.21\pm 0.01$. While the scatter in TX–λ is consistent in redshift bins, we find modestly different slopes, with high-redshift clusters displaying a somewhat shallower relation. Splitting based on richness, we find a marginally larger scatter for our lowest richness bin, 20 < λ < 40. We note that the robustness of the scaling relations at lower richnesses is limited by the unknown selection function, but at λ > 75, we detect nearly all of the clusters falling within existing X-ray pointings. The X-ray properties of detected, serendipitous clusters are generally consistent with those of targeted clusters.

Potency–Magnitude Scaling Relations and a Unified Earthquake Catalog for the Western United States

Abstract Quantifying the size of earthquakes is a foundational task in seismology, and over the years several magnitude scales have been developed. Of these, only scales based on seismic moment or potency can properly characterize changes in event size without saturation. Here, we develop empirical potency–magnitude scaling relations for earthquakes in the western United States, allowing us to translate instrumental magnitude estimates into uniform measures of earthquake size. We use synthetic waveforms to validate the observed scaling relations and to provide additional insight into the differences between instrumental and physics-based magnitude scales. Each earthquake in our catalog is assigned a clustering designation distinguishing mainshocks from triggered seismicity, along with a potency-based magnitude estimate that is comparable to moment magnitude and that can be easily converted into other magnitude scales as needed. The developed catalog and associated scaling relations have broad applications for fundamental and applied studies of earthquake processes and hazards.

Overview and public data release of the augmented Auriga Project: cosmological simulations of dwarf and Milky Way-mass galaxies

ABSTRACT We present an extended suite of the Auriga cosmological gravo-magnetohydrodynamical ‘zoom-in’ simulations of 40 Milky Way-mass haloes and 26 dwarf galaxy–mass haloes run with the moving-mesh code arepo. Auriga adopts the Lambda cold dark matter cosmogony and includes a comprehensive galaxy formation physics model following the coupled cosmic evolution of dark matter, gas, stars, and supermassive black holes which has been shown to produce numerically well-converged galaxy properties for Milky Way-mass systems. We describe the first public data release of this augmented suite of Auriga simulations, which includes raw snapshots, group catalogues, merger trees, initial conditions, and supplementary data, as well as public analysis tools with worked examples of how to use the data. To demonstrate the value and robustness of the simulation predictions, we analyse a series of low-redshift global properties that compare well with many observed scaling relations, such as the Tully–Fisher relation, the star-forming (SF) main sequence, and H i gas fraction/disc thickness. Finally, we show that SF gas discs appear to build rotation and velocity dispersion rapidly for $z\gtrsim 3$ before they ‘settle’ into ever-increasing rotation-dispersion ratios ($V/\sigma$). This evolution appears to be in rough agreement with some kinematic measurements from H$\alpha$ observations, and demonstrates an application of how to utilize the released data.

Multiphase characterization of AGN winds in five local type-2 quasars

We present MEGARA integral field unit (IFU) observations of five local type-2 quasars (QSO2s, z ∼ 0.1) from the Quasar Feedback (QSOFEED) sample. These active galactic nuclei (AGN) have bolometric luminosities of 1045.5 − 46 erg s−1 and stellar masses of ∼1011 M⊙. The LR-V grating of MEGARA allows us to explore the kinematics of the ionized gas through the [O III]λ5007 Å emission line. The nuclear spectra of the five QSO2s, extracted in a circular aperture of ∼1.2″ (∼2.2 kpc) in diameter, matching the resolution of these seeing-limited observations, show signatures of high velocity winds in the form of broad (full width at half maximum, 1300 ≤ FWHM ≤ 2240 km s−1) and blueshifted components. We found that four out of the five QSO2s present outflows that we can resolve with our seeing-limited data, and they have radii ranging from 3.1 to 12.6 kpc. In the case of the two QSO2s with extended radio emission, we found that it is well aligned with the outflows, suggesting that low-power jets might be compressing and accelerating the ionized gas in these radio-quiet QSO2s. In the four QSO2s with spatially resolved outflows, we measured ionized mass outflow rates of 3.3–6.5 M⊙ yr−1 when we used [S II]-based densities, and of 0.7–1.6 M⊙ yr−1 when trans-auroral line-based densities were considered instead. We compared them with the corresponding molecular mass outflow rates (8–16 M⊙ yr−1), derived from CO(2–1) ALMA observations at 0.2″ resolution. The cold molecular outflows carry more mass than their ionized counterparts. However, both phases show lower outflow mass rates than those expected from observational scaling relations where uniform assumptions on the outflow properties were adopted. This might be indicating that the AGN luminosity is not the only driver of massive outflows and/or that these relations need to be rescaled using accurate outflow properties (i.e., electron density and radius). We did not find a significant impact of the outflows on the global star formation rates when considering the energy budget of the molecular and ionized outflows together. However, spatially resolved measurements of recent star formation in these targets are needed in order to evaluate this fairly, considering the dynamical timescales of the outflows, of 3–20 Myr for the ionized gas and 1–10 Myr for the molecular gas.

MIGHTEE-H i: the MH i – M* relation over the last billion years

ABSTRACT We study the $M_{\rm H\, {\small {I}}}-M_{\star }$ relation over the last billion years using the MIGHTEE-H i sample. We first model the upper envelope of the $M_{\rm H\, {\small {I}}}-M_{\star }$ relation with a Bayesian technique applied to a total number of 249 H i-selected galaxies, without binning the data sets, while taking account of the intrinsic scatter. We fit the envelope with both linear and non-linear models, and find that the non-linear model is preferred over the linear one with a measured transition stellar mass of log10(M⋆/M⊙) = 9.15 ± 0.87, beyond which the slope flattens. This finding supports the view that the lack of H i gas is ultimately responsible for the decreasing star formation rate observed in the massive main-sequence galaxies. For spirals alone, which are biased towards the massive galaxies in our sample, the slope beyond the transition mass is shallower than for the full sample, indicative of distinct gas processes ongoing for the spirals/high-mass galaxies from other types with lower stellar masses. We then create mock catalogues for the MIGHTEE-H i detections and non-detections with two main galaxy populations of late- and early-type galaxies to measure the underlying $M_{\rm H\, {\small {I}}}-M_{\star }$ relation. We find that the turnover in this relation persists whether considering the two galaxy populations as a whole or separately. We note that an underlying linear relation could mimic this turnover in the observed scaling relation, but a model with a turnover is strongly preferred. Measurements on the logarithmic average of H i masses against the stellar mass are provided as a benchmark for future studies.

Disk Galaxies Are Self-similar: The Universality of the H i-to-Halo Mass Ratio for Isolated Disks

Observed scaling relations in galaxies between baryons and dark matter global properties are key to shed light on the process of galaxy formation and on the nature of dark matter. Here, we study the scaling relation between the neutral hydrogen (H i) and dark matter mass in isolated rotationally supported disk galaxies at low redshift. We first show that state-of-the-art galaxy formation simulations predict that the H i-to-dark-halo mass ratio decreases with stellar mass for the most massive disk galaxies. We then infer dark matter halo masses from high-quality rotation curve data for isolated disk galaxies in the local Universe and report on the actual universality of the H i-to-dark halo mass ratio for these observed galaxies. This scaling relation holds for disks spanning a range of 4 orders of magnitude in stellar mass and 3 orders of magnitude in surface brightness. Accounting for the diversity of rotation curve shapes in our observational fits decreases the scatter of the H i-to-dark halo mass ratio while keeping it constant. This finding extends the previously reported discrepancy for the stellar-to-halo mass relation of massive disk galaxies within galaxy formation simulations to the realm of neutral atomic gas. Our result reveals that isolated galaxies with regularly rotating extended H i disks are surprisingly self-similar up to high masses, which hints at mass-independent self-regulation mechanisms that have yet to be fully understood.

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

I(cm)z, a semi-analytic model for the thermodynamic properties in galaxy clusters: Calibrations with mass and redshift, and implication for the hydrostatic bias

Context. In the self-similar scenario for galaxy cluster formation and evolution, the thermodynamic properties of the X-ray emitting plasma can be predicted in their dependencies on the halo mass and redshift only. However, several departures from this simple self-similar scenario have been observed. Aims. We show how our semi-analytic model i(cm)z, which modifies the self-similar predictions through two temperature-dependent quantities, the gas mass fraction fg = f0Tf1Ezfz and the temperature variation fT = t0Tt1Eztz, can be calibrated to incorporate the mass and redshift dependencies. Methods. We used a published set of 17 scaling relations to constrain the parameters of the model. We were subsequently able to make predictions as to the slope of any observed scaling relation within a few percent of the central value and about one σ of the nominal error. Contextually, the evolution of these scaling laws was also determined, with predictions within 1.5σ and within 10 percent of the observational constraints. Relying on this calibration, we have also evaluated the consistency of the predictions on the radial profiles with some observational datasets. For a sample of high-quality data (X-COP), we were able to constrain a further parameter of the model, the hydrostatic bias b. Results. By calibrating the model versus a large set of X-ray scaling laws, we have determined that (i) the slopes of the temperature dependence are f1 = 0.403 (±0.009) and t1 = 0.144 (±0.017); and that (ii) the dependence upon Ez are constrained to be fz = −0.004 (±0.023) and tz = 0.349 (±0.059). These values, which are inserted in the scaling laws that propagate the mass and redshift dependence to the integrated quantities, permit one to estimate directly how the normalizations of a given quantity QΔ changes as a function of the mass (or temperature) and redshift halo in the form QΔ ∼ MaMEzaz ∼ TaT EzaTz, which is in very good agreement with the current observational constraints. When applied to the best spatially resolved data, we obtained estimates of the hydrostatic bias b that are lower than, but still comparable with, the results obtained by other, more standard, means. We conclude that the calibrated semi-analytic model i(cm)z is able to make valuable predictions on the slope and redshift evolution of the X-ray scaling laws, and on the expected radial behavior of the thermodynamic quantities, including any possible hydrostatic bias.

The Origin of the Relation Between Stellar Angular Momentum and Stellar Mass in Nearby Disk-dominated Galaxies

The IllustrisTNG simulations reproduce the observed scaling relation between the stellar specific angular momentum (sAM) j s and mass M s of central galaxies. We show that the local j s–M s relation develops at z ≲ 1 in disk-dominated galaxies. We provide a simple model that describes well such a connection between halos and galaxies. The index of 0.55 of the j s–M s relation comes from the product of the indices of the , , and j s ∝ j tot relations, where j tot and M tot are the overall sAM and mass of the halo, respectively. A non-negligible deviation from tidal torque theory, which predicts , should be included. This model further suggests that the stellar-to-halo mass ratio of disk galaxies increases monotonically following a nearly power-law function that is consistent with the latest dynamical measurements. Biased collapse, in which galaxies form from the inner and lower sAM portion of their parent halos, has a minor effect at low redshifts. The retention factor of angular momentum reaches ∼1 in disk galaxies with strong rotations, and it correlates inversely with the mass fraction of the spheroidal component, which partially explains the morphological dependence of the j s–M s relation.

Modelling the host galaxies of binary compact object mergers with observational scaling relations

ABSTRACT The merger rate density evolution of binary compact objects and the properties of their host galaxies carry crucial information to understand the sources of gravitational waves. Here, we present galaxy$\mathcal {R}$ate, a new code that estimates the merger rate density of binary compact objects and the properties of their host galaxies, based on observational scaling relations. We generate our synthetic galaxies according to the galaxy stellar mass function. We estimate the metallicity according to both the mass–metallicity relation (MZR) and the fundamental metallicity relation (FMR). Also, we take into account galaxy–galaxy mergers and the evolution of the galaxy properties from the formation to the merger of the binary compact object. We find that the merger rate density changes dramatically depending on the choice of the star-forming galaxy main sequence, especially in the case of binary black holes (BBHs) and black hole neutron star systems (BHNSs). The slope of the merger rate density of BBHs and BHNSs is steeper if we assume the MZR with respect to the FMR, because the latter predicts a shallower decrease of metallicity with redshift. In contrast, binary neutron stars (BNSs) are only mildly affected by both the galaxy main sequence and metallicity relation. Overall, BBHs and BHNSs tend to form in low-mass metal-poor galaxies and merge in high-mass metal-rich galaxies, while BNSs form and merge in massive galaxies. We predict that passive galaxies host at least ∼5–10 per cent, ∼15–25 per cent, and ∼15–35 per cent of all BNS, BHNS, and BBH mergers in the local Universe.

The galactic dust-up: modelling dust evolution in FIRE

ABSTRACT Recent strides have been made developing dust evolution models for galaxy formation simulations but these approaches vary in their assumptions and degree of complexity. Here, we introduce and compare two separate dust evolution models (labelled ‘Elemental’ and ‘Species’), based on recent approaches, incorporated into the gizmo code and coupled with fire-2 stellar feedback and interstellar medium physics. Both models account for turbulent dust diffusion, stellar production of dust, dust growth via gas-dust accretion, and dust destruction from time-resolved supernovae, thermal sputtering in hot gas, and astration. The ‘Elemental’ model tracks the evolution of generalized dust species and utilizes a simple, ‘tunable’ dust growth routine, while the ‘Species’ model tracks the evolution of specific dust species with set chemical compositions and incorporates a physically motivated, two-phase dust growth routine. We test and compare these models in an idealized Milky Way-mass galaxy and find that while both produce reasonable galaxy-integrated dust-to-metals (D/Z) ratios and predict gas-dust accretion as the main dust growth mechanism, a chemically motivated model is needed to reproduce the observed scaling relation between individual element depletions and D/Z with column density and local gas density. We also find the inclusion of theoretical metallic iron and O-bearing dust species are needed in the case of specific dust species in order to match observations of O and Fe depletions, and the integration of a sub-resolution dense molecular gas/CO scheme is needed to both match observed C depletions and ensure carbonaceous dust is not overproduced in dense environments.

Seismic modelling and observations of rainfall

Rainfall is a key driver of geomorphological processes ranging from impacting drops that lead to the small-scale dislodgement of soil particles to large-scale morphogenic floods and rainfall-induced hillslope processes. Although rainfall has been identified in seismic records, the associated power spectral density and its quantitative relation to the underlying physical processes have not yet been studied. Here, we analyze nearly 2 years of combined seismic and optical disdrometer measurements, where the latter enables the drop-based quantification of rainfall physical properties. Our measurements confirm the broadband observation of ground velocity power spectral density due to rainfall, allowing the seismic identification of rainfall at intensities as low as 1 mm/h. Seismic power, P, shows a power-law scaling with rainfall intensity, I, and kinetic energy, E: P∝I2.1 and P∝E1.6. The observed scaling relations are consistent between the three monitored sites although there are absolute differences in seismic power of about 1 order of magnitude, which are likely due to variability in landcover and subsurface seismic properties. With a physical model, we demonstrate that the observed power-law relations are set by an underlying linear relation between seismic power and rainfall impulse power, and that the associated exponent values of I and E are due to the covariance of the raindrop size distribution with the total number of drops. The largest raindrop fractions, whose relative contribution increases with rainfall intensity, dominate the seismic signal where, in our case, 90% of the seismic power is attributed to drops larger than 3 mm. Using our model, we estimate the contributing area of rainfall to seismic observations to be within a radial distance of ∼5–25 m. The spatially integrated nature of the seismic measurements and their sensitivity to large raindrops, which control the disaggregation and the mobilization of soil particles, make seismic records well-suited for the investigation of soil erosion processes. More generally, our work provides a basis for the temporally-resolved seismic quantification of rainfall that drives the dynamics of various hydro-geomorphological processes.

High-resolution synthetic UV-submm images for Milky Way-mass simulated galaxies from the ARTEMIS project

ABSTRACT We present redshift-zero synthetic dust-aware observations for the 45 Milky Way-mass simulated galaxies of the ARTEMIS project, calculated with the skirt radiative transfer code. The post-processing procedure includes components for star-forming regions, stellar sources, and diffuse dust. We produce and publicly release realistic high-resolution images for 50 commonly used broad-band filters from ultraviolet to submillimetre wavelengths and for 18 different viewing angles. We compare the simulated ARTEMIS galaxies to observed galaxies in the DustPedia data base with similar stellar mass and star formation rate, and to synthetic observations of the simulated galaxies of the Auriga project produced in previous work using a similar post-processing technique. In all cases, global galaxy properties are derived using SED fitting. We find that, similar to Auriga, the post-processed ARTEMIS galaxies generally reproduce the observed scaling relations for global fluxes and physical properties, although dust extinction at FUV/UV wavelengths is underestimated and representative dust temperatures are lower than observed. At a resolved scale, we compare multiwavelength non-parametric morphological properties of selected disc galaxies across the data sets. We find that the ARTEMIS galaxies largely reproduce the observed morphological trends as a function of wavelength, although they appear to be more clumpy and less symmetrical than observed. We note that the ARTEMIS and Auriga galaxies occupy adjacent regions in the specific star formation versus stellar mass plane, so that the synthetic observation data sets supplement each other.

Gamma Rays from Fast Black-hole Winds

Abstract Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersion of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. In this work we use data from the Fermi Large Area Telescope to search for the γ-ray emission from galaxies with an ultrafast outflow (UFO): a fast (v ∼ 0.1 c), highly ionized outflow, detected in absorption at hard X-rays in several nearby active galactic nuclei (AGN). Adopting a sensitive stacking analysis we are able to detect the average γ-ray emission from these galaxies and exclude that it is due to processes other than UFOs. Moreover, our analysis shows that the γ-ray luminosity scales with the AGN bolometric luminosity and that these outflows transfer ∼0.04% of their mechanical power to γ-rays. Interpreting the observed γ-ray emission as produced by cosmic rays (CRs) accelerated at the shock front, we find that the γ-ray emission may attest to the onset of the wind–host interaction and that these outflows can energize charged particles up to the transition region between galactic and extragalactic CRs.

The baryon cycle of Seven Dwarfs with superbubble feedback

We present results from a high-resolution, cosmological, ΛCDM simulation of a group of field dwarf galaxies with the “superbubble” model for clustered SN feedback, accounting for thermal conduction and cold gas evaporation. We compared our results to a previous simulation which has the same initial condition and galaxy formation physics (other than SN feedback), but adopts a delayed-cooling model for supernova. The simulated luminous galaxies have blue colors, low star formation efficiencies and metallicities, and high cold gas content, reproducing the observed scaling relations of dwarf galaxies in the Local Volume. Bursty star formation histories and superbubble-driven outflows lead to the formation of kpc-size dark matter (DM) cores when stellar masses reaches M* > 106 M⊙, similar to previous findings. However, the superbubble model appears more effective in destroying DM cusps than the delayed-cooling model in the previous study, reflecting a higher coupling efficiency of SN energy with the ISM. On larger scale, superbubble-driven outflows have a more moderate impact: galaxies have higher gas content, more extended stellar discs, and a smaller metal-enriched region in the circumgalactic medium (CGM). The two halos with Mvir ∼ 109 M⊙, which formed ultra-faint dwarf galaxies with the delayed-cooling mode, remain dark due to the different impact of metal-enriched galactic winds from two nearby luminous galaxies, indicating that the formation of faint dwarfs is highly dependent on feedback and environmental effects. The column density distributions of H I, Si II, C IV and O VI as a function of the scaled impact parameter (b/Rvir) are in good agreement with recent observations of CGM around isolated dwarf galaxies. While H I is ubiquitous with a covering fraction of unity within the CGM, low and intermediate ions like Si II and C IV are less extended (typically confined within 0.2 − 0.3 Rvir), and non-detections are common. O VI is more extended with column density N(O VI) ≳ 1013.5 cm−2 within Rvir, but its mass is only 11% of the total CGM oxygen budget, as the diffuse CGM is highly ionised by the UV background. Superbubble feedback produces C IV and O VI column densities that are an order of magnitude higher than those in the previous study using delayed-cooling feedback. Thus, the CGM and DM cores are most sensitive probes of feedback mechanisms.

The role of mergers and gas accretion in black hole growth and galaxy evolution

We use a semi-analytic galaxy formation model to study the co-evolution of supermassive black holes (SMBHs) with their host galaxies. Although the coalescence of SMBHs is not important, the quasar-mode accretion induced by mergers plays a dominant role in the growth of SMBHs. Mergers play a more important role in the growth of SMBH host galaxies than in the SMBH growth. It is the combined contribution from quasar mode accretion and mergers to the SMBH growth and the combined contribution from starburst and mergers to their host galaxy growth that determine the observed scaling relation between the SMBH masses and their host galaxy masses. We also find that mergers are more important in the growth of SMBH host galaxies compared to normal galaxies which share the same stellar mass range as the SMBH host galaxies.

Brightest Cluster Galaxies and Intracluster Light: Their Mass Distribution in the Innermost Regions of Groups and Clusters

Abstract We improve the model presented in Contini & Gu that describes the radial mass distribution of brightest cluster galaxies (BCGs) and the diffuse component also known as intracluster light (ICL), by assuming that the global BCG+ICL radial mass distribution follows the sum of three profiles: Jaffe and exponential profiles for the bulge and disk of the BCG, respectively, and a modified version of an NFW profile for the ICL. We take advantage of a wide sample of BCG+ICL systems simulated with our state-of-the-art semianalytic model to (a) investigate the reliability of our BCG+ICL distribution by looking at several scaling relations between the BCG+ICL stellar mass within different apertures and the total BCG+ICL/halo mass, at different redshifts; (b) make a prediction of the distance where the radial distribution transitions from BCG to ICL dominated. We find that our model nicely reproduces all the observed scaling relations investigated at the present time with a compelling degree of precision, but slightly biased low with respect to observations at higher redshifts (z ≳ 0.5). The transition radius predicted by our model is in good agreement with recent observational results, and spans a range between ∼15 kpc and ∼100 kpc. It mostly depends on the morphology of the BCG, whether it is bulge or disk dominated, on the amount of ICL with respect to the bulge and/or disk, and on the dynamical state of the group/cluster.