Velocity Dispersion Of Galaxies Research Articles

Cosmological Test of an Ultraviolet Origin of Dark Energy

The accelerated expansion of the Universe is impressively well described by a cosmological constant. However, the observed value of the cosmological constant is much smaller than expected based on quantum field theories. Recent efforts to achieve consistency in these theories have proposed a relationship between Dark Energy and the most compact objects, such as black holes (BHs). However, experimental tests are very challenging to devise and perform. In this article, we present a testable model with no cosmological constant in which the accelerated expansion can be driven by black holes. The model couples the expansion of the Universe (the Friedmann equation) with the mass function of cosmological halos (using the Press–Schechter formalism). Through the observed link between halo masses and BH masses, one thus gets a coupling between the expansion rate of the Universe and the BHs. We compare the predictions of this simple BH model with SN1a data and find poor agreement with observations. Our method is sufficiently general to allow us to also test a fundamentally different model, also without a cosmological constant, where the accelerated expansion is driven by a new force proportional to the internal velocity dispersion of galaxies. Surprisingly enough, this model cannot be excluded using the SN1a data.

The splashback radius and the radial velocity profile of galaxy clusters in IllustrisTNG

We used 1697 clusters of galaxies from the TNG300-1 simulation (mass M200c > 1014 M⊙ and redshift range 0.01 ≤ z ≤ 1.04) to explore the physics of the cluster infall region. We used the average radial velocity profile derived from simulated galaxies, vrad(r), and the average velocity dispersion of galaxies at each redshift, σv(r), to explore cluster-centric dynamical radii that characterize the cluster infall region. We revisited the turnaround radius, the limiting outer radius of the infall region, and the radius where the infall velocity has a well-defined minimum. We also explored two new characteristic radii: (i) the point of inflection of vrad(r) that lies within the velocity minimum, and (ii) the smallest radius where σv(r) = |vrad(r)|. These two, nearly coincident, radii mark the inner boundary of the infall region where radial infall ceases to dominate the cluster dynamics. Both of these galaxy velocity based radii lie within 1σ of the observable splashback radius. The minimum in the logarithmic slope of the galaxy number density is an observable proxy for the apocentric radius of the most recently accreted galaxies, the physical splashback radius. The two new dynamically derived radii relate the splashback radius to the inner boundary of the cluster infall region.

Do ultra diffuse galaxies with rich globular clusters systems have overly massive haloes?

ABSTRACT Some Ultra Diffuse Galaxies (UDGs) appear to host exceptionally rich globular cluster (GC) systems compared to normal galaxies of the same stellar mass. After re-examining these claims, we focus on a small sample of UDGs from the literature that have both rich GC systems (NGC >20) and a measured galaxy velocity dispersion. We find that UDGs with more GCs have higher dynamical masses and that GC-rich UDGs are dark matter dominated within their half-light radii. We extrapolate these dynamical masses to derive total halo masses assuming cuspy and cored mass profiles. We find reasonable agreement between halo masses derived from GC numbers (assuming the GC number–halo mass relation) and from cored halo profiles. This suggests that GC-rich UDGs do not follow the standard stellar mass–halo mass relation, occupying overly massive cored haloes for their stellar mass. A similar process to that invoked for some Local Group dwarfs, of early quenching, may result in GC-rich UDGs that have failed to form the expected mass of stars in a given halo (and thus giving the appearance of overly an massive halo). Simulations that correctly reproduce the known properties of GC systems associated with UDGs are needed.

Fundamental scaling relationships revealed in the optical light curves of tidal disruption events

ABSTRACT We present fundamental scaling relationships between properties of the optical/UV light curves of tidal disruption events (TDEs) and the mass of the black hole that disrupted the star. We have uncovered these relations from the late-time emission of TDEs. Using a sample of 63 optically selected TDEs, the latest catalogue to date, we observed flattening of the early-time emission into a near-constant late-time plateau for at least two-thirds of our sources. Compared to other properties of the TDE light curves (e.g. peak luminosity or decay rate) the plateau luminosity shows the tightest correlation with the total mass of host galaxy (p-value of 2 × 10−6, with a residual scatter of 0.3 dex). Physically this plateau stems from the presence of an accretion flow. We demonstrate theoretically and numerically that the amplitude of this plateau emission is strongly correlated with black hole mass. By simulating a large population (N = 106) of TDEs, we determine a plateau luminosity-black hole mass scaling relationship well described by $\log _{10} \left({{M_{\bullet }}/M_\odot }\right) = 1.50 \log _{10} \left({ L_{\rm plat}}/10^{43} \, {\rm erg\, s^{-1}}\right) + 9.0$ (here Lplat is measured at 6 × 1014 Hz in the rest frame). The observed plateau luminosities of TDEs and black hole masses in our large sample are in excellent agreement with this simulation. Using the black hole mass predicted from the observed TDE plateau luminosity, we reproduce the well-known scaling relations between black hole mass and galaxy velocity dispersion. The large black hole masses of 10 of the TDEs in our sample allow us to provide constraints on their black hole spins, favouring rapidly rotating black holes. Finally, we also discover two significant correlations between early time properties of optical TDE light curves (the g-band peak luminosity and radiated energy) and the TDEs black hole mass.

Spurious heating of stellar motions by dark matter particles in cosmological simulations of galaxy formation

ABSTRACT We use two cosmological simulations to study the impact of spurious heating of stellar motions within simulated galaxies by dark matter (DM) particles. The simulations share the same numerical and subgrid parameters, but one used a factor of 7 more DM particles. Many galaxy properties are unaffected by spurious heating, including their masses, star formation histories, and the spatial distribution of their gaseous baryons. The distribution and kinematics of stellar and DM particles, however, are affected. Below a resolution-dependent virial mass, $M_{200}^{\rm spur}$, galaxies have higher characteristic velocities, larger sizes, and more angular momentum in the simulation with lower DM mass resolution; haloes have higher central densities and lower velocity dispersions. Above $M_{200}^{\rm spur}$, galaxies and haloes have similar properties in both runs. The differences arise due to spurious heating, which transfers energy from DM to stellar particles, causing galaxies to heat up and haloes to cool down. The value of $M_{200}^{\rm spur}$ can be derived from an empirical disc heating model, and coincides with the mass below which the predicted spurious velocity dispersion exceeds the measured velocity dispersion of simulated galaxies. We predict that galaxies in the $100^3\, {\rm Mpc}^3$eagle run and IllustrisTNG-100 are robust to spurious collisional effects at their half-mass radii provided $M_{200}^{\rm spur}\approx 10^{11.7}\, {\rm M_\odot }$; for the $25^3\, {\rm Mpc}^3$eagle run and IllustrisTNG-50, we predict $M_{200}^{\rm spur}\approx 10^{11}\, {\rm M_\odot }$. Suppressing spurious heating at smaller/larger radii, or for older/younger stellar populations, requires haloes to be resolved with more/fewer DM particles.

A new framework for understanding the evolution of early-type galaxies

Context. We have recently suggested that the combination of the scalar virial theorem (Ms ∝ Reσ2) and the L = L0′σβ law, with L0′ and β changing from galaxy to galaxy (and with time), can provide a new set of equations valid for investigating the evolution of early-type galaxies. These equations are able to account for the tilt of the fundamental plane and to explain the observed distributions of early-type galaxies in all its projections. Aims. In this paper we analyze the advantages offered by these equations, derive the β and L0′ parameters for real and simulated galaxies, and demonstrate that depending on the value of β galaxies can move only along some permitted directions in the fundamental plane projections. Then we show that simple galaxy models that grow in mass by infall of gas and form stars with a star formation rate depending on the stellar velocity dispersion nicely reproduce the observed distributions of early-type galaxies in the fundamental plane projections and yield βs that agree with the measured values. Methods. We derive the mutual relationships among the stellar mass, effective radius, velocity dispersion, and luminosity of early-type galaxies as a function of β and calculate the coefficients of the fundamental plane. Then, using the simple infall models, we show that the star formation history of early-type galaxies is compatible with the σ-dependent star formation rate, and that both positive and negative values of β are possible in a standard theory of galaxy evolution. Results. The parameter β(t) offers a new view of the evolution of early-type galaxies. In brief, it gives a coherent interpretation of the fundamental plane and of the motions of galaxies in its projections; it is the fingerprint of their evolution; it measures the degree of virialization of early-type galaxies; and finally it allows us to infer their evolution in the near past.

ALMA hints at the presence of turbulent disk galaxies at z > 5

Context. High-redshift galaxies are expected to be more turbulent than local galaxies because of their smaller size and higher star formation and thus stronger feedback from star formation, frequent mergers events, and gravitational instabilities. However, this scenario has recently been questioned by the observational evidence of a few galaxies at z ∼ 4 − 5 with a gas velocity dispersion similar to what is observed in the local population. Aims. Our goal is to determine whether galaxies in the first billion years of the Universe have already formed a dynamically cold rotating disk similar to the local counterparts. Methods. We studied the gas kinematic of 22 main-sequence star-forming galaxies at z > 5 and determined their dynamical state by estimating the ratio of the rotational velocity and of the gas velocity dispersion. We mined the ALMA public archive and exploited the [C II] and [O III] observations to perform a kinematic analysis of the cold and warm gas of z > 5 main-sequence galaxies. We compared our results with what was found in the local and distant Universe and investigated the evolution of the gas velocity dispersion with redshift. We also compared the observations with theoretical expectations to assess the main driver of the gas turbulence at z > 5. Results. The gas kinematics of the high-z galaxy population observed with ALMA is consistent within the errors with rotating but turbulent disks. We indeed infer a velocity dispersion that is systematically higher by 4–5 times than the local galaxy population and the z ∼ 5 dust-obscured galaxies reported in the literature. The difference between our results and those reported at similar redshift can be ascribed to the systematic difference in the galaxy properties in the two samples: the disks of massive dusty galaxies are dynamically colder than the disks of dust-poor galaxies. The comparison with the theoretical predictions suggests that the main driver of the velocity dispersion in high-redshift galaxies is the gravitational energy that is released by the transport of mass within the disk. Finally, we stress that future deeper ALMA high-angular resolution observations are crucial to constrain the kinematic properties of high-z galaxies and to distinguish rotating disks from kiloparsec-scale mergers.

Abell 1201: detection of an ultramassive black hole in a strong gravitational lens

ABSTRACTSupermassive black holes (SMBHs) are a key catalyst of galaxy formation and evolution, leading to an observed correlation between SMBH mass MBH and host galaxy velocity dispersion σe. Outside the local Universe, measurements of MBH are usually only possible for SMBHs in an active state: limiting sample size and introducing selection biases. Gravitational lensing makes it possible to measure the mass of non-active SMBHs. We present models of the $z$ = 0.169 galaxy-scale strong lens Abell 1201. A cD galaxy in a galaxy cluster, it has sufficient ‘external shear’ that a magnified image of a $z$ = 0.451 background galaxy is projected just ∼1 kpc from the galaxy centre. Using multiband Hubble Space Telescope imaging and the lens modelling software PYAUTOLENS, we reconstruct the distribution of mass along this line of sight. Bayesian model comparison favours a point mass with MBH = 3.27 ± 2.12 × 1010 M⊙ (3σ confidence limit); an ultramassive black hole. One model gives a comparable Bayesian evidence without an SMBH; however, we argue this model is nonphysical given its base assumptions. This model still provides an upper limit of MBH ≤ 5.3 × 1010 M⊙, because an SMBH above this mass deforms the lensed image ∼1 kpc from Abell 1201’s centre. This builds on previous work using central images to place upper limits on MBH, but is the first to also place a lower limit and without a central image being observed. The success of this method suggests that surveys during the next decade could measure thousands more SMBH masses, and any redshift evolution of the MBH−σe relation. Results are available at https://github.com/Jammy2211/autolens_abell_1201.

A common origin for the fundamental plane of quiescent and star-forming galaxies in the EAGLE simulations

ABSTRACT We use the EAGLE cosmological simulations to perform a comprehensive and systematic analysis of the z = 0.1 fundamental plane (FP), the tight relation between galaxy size, mass, and velocity dispersion. We first measure the total mass and velocity dispersion (including both random and rotational motions) within the effective radius to show that simulated galaxies obey a total mass FP that is very close to the virial relation ($\lt 10{{\ \rm per\ cent}}$ deviation), indicating that the effects of non-homology are weak. When we instead use the stellar mass, we find a strong deviation from the virial plane, which is driven by variations in the dark matter content. The dark matter fraction is a smooth function of the size and stellar mass, and thereby sets the coefficients of the stellar mass FP without substantially increasing the scatter. Hence, both star-forming and quiescent galaxies obey the same FP, with equally low scatter ($0.02\,$dex). We employ simulations with a variable stellar initial mass function (IMF) to show that IMF variations have a modest additional effect on this FP. Moreover, when we use luminosity-weighted mock observations of the size and spatially integrated velocity dispersion, the inferred FP changes only slightly. However, the scatter increases significantly, due to the luminosity-weighting and line-of-sight projection of the velocity dispersions, and measurement uncertainties on the half-light radii. Importantly, we find significant differences between the simulated FP and observations, which likely reflects a systematic difference in the stellar mass distributions. Therefore, we suggest the stellar mass FP offers a simple test for cosmological simulations, requiring minimal post-processing of simulation data.

Spectroscopic Confirmation of Two X-Ray Diffuse and Massive Galaxy Clusters at Low Redshift

We present MMT spectroscopic observations of two massive galaxy cluster candidates at redshift z ∼ 0.07 that show extended and diffuse X-ray emission in the ROSAT All-Sky Survey (RASS) images. The targets were selected from a previous catalog of 303 newly identified cluster candidates with the similar properties using the intracluster medium emission. Using the new MMT Hectospec data and Sloan Digital Sky Survey archival spectra, we identify a number of member galaxies for the two targets and confirm that they are galaxy clusters at z = 0.079 and 0.067, respectively. The size of the two clusters, calculated from the distribution of the member galaxies, is roughly 2 Mpc in radius. We estimate cluster masses using three methods based on their galaxy number overdensities, galaxy velocity dispersions, and X-ray emission. The overdensity-based masses are (6 ∼ 8) × 1014 M ⊙, comparable to the masses of large clusters at low redshift. The masses derived from velocity dispersions are significantly lower, likely due to their diffuse and low concentration features. Our result suggests the existence of a population of large clusters with very diffuse X-ray emission that has been missed by most previous searches using the RASS images. If most of the 303 candidates in the previous catalog are confirmed to be real clusters, this may help to reduce the discrepancy of cosmological results between the cosmic microwave background and galaxy cluster measurements.

Dark matter and dark energy denote the gravitation of the expanding universe

We reason that it is the gravitation of all ordinary matter, extending from the dense distant past to the sparse present, rather than dark matter, that shows up in galaxy rotation and velocity dispersion. Likewise, we argue that it is this gradient in the gravitational energy due to the expansion, rather than dark energy, that explains Type 1a supernovae brightness vs. redshift data. Our conclusions follow from statistical mechanics, the thermodynamic theory based on the atomistic axiom that everything comprises quanta. In line with the Einstein field equations, the vacuum quanta embodying gravitation, geometrized as spacetime, equate in dynamic balance to the quanta embodying the substance of the stress–energy tensor. In accordance with quantum field theory, the proposed ground-state field of paired light quanta complies with Bose–Einstein statistics and assumes an excited state around a particle.

Spatial Distribution of Dark Matter in and Around Galaxy Clusters Traced by Galaxies, Gas, and Intracluster Stars in a Simulated Universe

To understand how well galaxies, gas, and intracluster stars trace dark matter in and around galaxy clusters, we use the IllustrisTNG cosmological hydrodynamical simulation and compare the spatial distribution of dark matter with that of baryonic components in clusters. To quantify the global morphology of the density distribution of each component in clusters, we fit an ellipse to the density contour of each component and derive shape parameters at different radii. We find that the ellipticity of dark matter is better correlated with that of galaxy mass-weighted number density, rather than with that of galaxy number density or galaxy velocity dispersion. We thus use the galaxy mass-weighted number density map as representative of the galaxy maps. Among three different density maps from galaxies, gas, and intracluster stars, the ellipticity of dark matter is best reproduced by that of the galaxy map over the entire radii. The virialized galaxy clusters show a better correlation of spatial distribution between dark matter and other components than the unvirialized clusters, suggesting that it requires some time for each component to follow the spatial distribution of dark matter after merging events. Our results demonstrate that galaxies are still good tracers of dark matter distribution even in the nonlinear regime corresponding to the scales in and around galaxy clusters, being consistent with the case where galaxies trace well the matter distribution on cosmologically large scales.

X-ray studies of the Abell 3158 galaxy cluster with eROSITA

Context. The most nearby clusters are the best places for studying physical and enrichment effects in the faint cluster outskirts. The Abell 3158 cluster (A3158), located at z = 0.059, is quite extended with a characteristic radius r200 = 23.95 arcmin. The metal distribution in the outskirts of this cluster has previously been studied with XMM-Newton. In 2019, A3158 was observed as a calibration target in a pointed observation with the eROSITA telescope on board the Spektrum-Roentgen-Gamma mission. Bright large clusters, such as A3158, are ideal for studying the metal distribution in the cluster outskirts, along with the temperature profile and morphology. With the deeper observation time of the eROSITA telescope, these properties can now be studied in greater detail and at larger radii. Furthermore, bright nearby clusters are ideal X-ray instrumental cross-calibration targets as they cover a large fraction of the detector and do not vary in time. Aims. We first compare the temperature, metal abundance, and normalisation profiles of the cluster from eROSITA with previous XMM-Newton and Chandra data. Following this calibration work, we investigate the temperature and metallicity of the cluster out to almost r200, measure the galaxy velocity dispersion, and determine the cluster mass. Furthermore, we search for infalling clumps and background clusters in the field. Methods. We determined 1D temperature, abundance, and normalisation profiles from both eROSITA and XMM-Newton data as well as 2D maps of temperature and metal abundance distribution from eROSITA data. The velocity dispersion was determined and the cluster mass was calculated from the mass–velocity dispersion (M200−συ) relation. Galaxy density maps were created to enable a better understanding of the structure of the cluster and the outskirts. Results. The overall (i.e. in the range 0.2−0.5r500) temperature was measured to be 5.158 ± 0.038 keV. The temperature, abundance, and normalisation profiles of eROSITA all agree to within a confidence level of about 10% with those we determined using XMM-Newton and Chandra data, and they are also consistent with the profiles published previously by the X-COP project. The cluster morphology and surface brightness profile of cluster Abell 3158 appear to be regular at a first glance. Clusters that have such profiles typically are relaxed and host cool cores. However, the temperature profile and map show that the cluster lacks a cool core, as was noted before. Instead, an off-centre cool clump lies to the west of the central cluster region, as reported previously. These are indications that the cluster may be undergoing some sloshing and merger activity. Furthermore, there is a bow-shaped edge near the location of the cool gas clump west of the cluster centre. Farther out west of the X-ray images of A3158, an extension of gas is detected. This larger-scale extension is described here for the first time. The gas metallicity (~0.2 solar) measured in the outskirts (»r500) is consistent with an early-enrichment scenario. The velocity dispersion of the cluster member galaxies is measured to be 1058 ± 41 kms−1 based on spectroscopic redshifts of 365 cluster member galaxies and the total mass is determined as M200,c = 1.38 ± 0.25 × 1015 M⊙. The mass estimate based on the X-ray temperature is significantly lower at M200 = 6.20 ± 0.75 × 1014 M⊙, providing further indications that merger activity boosts the velocity dispersion and/or biases the temperature low. An extended X-ray source located south of the field of view also coincides with a galaxy overdensity with spectroscopic redshifts in the range 0.05 < z < 0.07. This source further supports the idea that the cluster is undergoing merger activity. Another extended source located north of the field of view is detected in X-rays and coincides with an overdensity of galaxies with spectroscopic redshifts in the range of 0.070 < z < 0.077. This is likely a background cluster that is not directly related to A3158. Additionally, the known South Pole Telescope cluster SPT-CL J0342-5354 at z = 0. 53 was detected.

A machine learning approach to infer the accreted stellar mass fractions of central galaxies in the TNG100 simulation

ABSTRACT We propose a random forest (RF) machine learning approach to determine the accreted stellar mass fractions (facc) of central galaxies, based on various dark matter halo and galaxy features. The RF is trained and tested using 2710 galaxies with stellar mass log10M*/M⊙ > 10.16 from the TNG100 simulation. Galaxy size is the most important individual feature when calculated in 3-dimensions, which becomes less important after accounting for observational effects. For smaller galaxies, the rankings for features related to merger histories increase. When an entire set of halo and galaxy features are used, the prediction is almost unbiased, with root-mean-square error (RMSE) of ∼0.068. A combination of up to three features with different types (galaxy size, merger history, and morphology) already saturates the power of prediction. If using observable features, the RMSE increases to ∼0.104, and a combined usage of stellar mass, galaxy size plus galaxy concentration achieves similar predictions. Lastly, when using galaxy density, velocity, and velocity dispersion profiles as features, which approximately represent the maximum amount of information extracted from galaxy images and velocity maps, the prediction is not improved much. Hence, the limiting precision of predicting facc is ∼0.1 with observables, and the multicomponent decomposition of galaxy images should have similar or larger uncertainties. If the central black hole mass and the spin parameter of galaxies can be accurately measured in future observations, the RMSE is promising to be further decreased by ∼20 per cent.

Cosmological Parameter Estimation Using Current and Future Observations of Strong Gravitational Lensing

The remarkable development of cosmology benefits from the increasingly improved measurements of cosmic distances, including absolute distances and relative distances. In recent years, however, the emerged cosmological tensions have motivated us to explore independent and precise late-universe probes. The two observational effects of strong gravitational lensing (SGL), the velocity dispersions of lens galaxies and the time delays between multiple images can provide measurements of relative and absolute distances, respectively, and their combination makes it possible to break the degeneracies between cosmological parameters and enable tight constraints on them. In this paper, we combine the observed 130 SGL systems with velocity-dispersion measurements and 7 SGL systems with time-delay measurements to constrain dark-energy cosmological models. It is found that the combination of the two effects does not significantly break the degeneracies between cosmological parameters as expected. However, with the simulations of 8000 SGL systems with well-measured velocity dispersions and 55 SGL systems with well-measured time delays based on the forthcoming LSST survey, we find that the combination of two effects can significantly break the parameter degeneracies, and make the constraint precision of cosmological parameters meet the standard of precision cosmology. We conclude that the observations of SGL will become a useful late-universe probe for precisely measuring cosmological parameters.

Please Repeat: Strong Lensing of Gravitational Waves as a Probe of Compact Binary and Galaxy Populations

Abstract Strong gravitational lensing of gravitational wave sources offers a novel probe of both the lens galaxy and the binary source population. In particular, the strong lensing event rate and the time-delay distribution of multiply imaged gravitational-wave binary coalescence events can be used to constrain the mass distribution of the lenses as well as the intrinsic properties of the source population. We calculate the strong lensing event rate for a range of second- (2G) and third-generation (3G) detectors, including Advanced LIGO/Virgo, A+, Einstein Telescope (ET), and Cosmic Explorer (CE). For 3G detectors, we find that ∼0.1% of observed events are expected to be strongly lensed. We predict detections of ∼1 lensing pair per year with A+, and ∼50 pairs per year with ET/CE. These rates are highly sensitive to the characteristic galaxy velocity dispersion, σ *, implying that observations of the rates will be a sensitive probe of lens properties. We explore using the time-delay distribution between multiply imaged gravitational-wave sources to constrain properties of the lenses. We find that 3G detectors would constrain σ * to ∼21% after 5 yr. Finally, we show that the presence or absence of strong lensing within the detected population provides useful insights into the source redshift and mass distribution out to redshifts beyond the peak of the star formation rate, which can be used to constrain formation channels and their relation to the star formation rate and delay-time distributions for these systems.

The environmental dependence of the stellar velocity dispresion of active galactic nucleus (AGN) host galaxies and dependence of the clustering properties of AGN host galaxies on the stellar velocity dispersion

We use two volume-limited active galactic nucleus (AGN) host galaxy samples constructed by Deng & Wen [47], and explore the environmental dependence of the stellar velocity dispersion in these two volume-limited AGN host galaxy samples. In the luminous volume-limited AGN host galaxy sample, the stellar velocity dispersion of AGN host galaxies apparently depends on local environments: AGN host galaxies with large stellar velocity dispersion exist preferentially in high density regime, while AGN host galaxies with small stellar velocity dispersion are located preferentially in low density regions. But in the faint volume-limited AGN host galaxy sample, this dependence is fairly weak. We also examine the dependence of the clustering properties of AGN host galaxies on the stellar velocity dispersion by cluster analysis, and find that in the luminous volume-limited AGN host galaxy sample, AGN host galaxies with small stellar velocity dispersion preferentially form isolated galaxies, close pairs and small groups, while AGN host galaxies with large stellar velocity dispersion preferentially inhabit the dense groups and clusters. In the faint volume-limited AGN host galaxy sample, although the fraction of isolated galaxies with small stellar velocity dispersion is apparently higher than the one with large stellar velocity dispersion, the trend in the luminous volume-limited sample is very difficultly observed. This likely is due to the galaxy number of the faint volume-limited AGN host galaxy sample being too small to ensure an ideal statistical analysis.

Revisiting the Lensed Fraction of High-redshift Quasars

Abstract The observed lensed fraction of high-redshift quasars (∼0.2%) is significantly lower than previous theoretical predictions (≳4%). We revisit the lensed fraction of high-redshift quasars predicted by theoretical models, where we adopt recent measurements of galaxy velocity dispersion functions (VDFs) and explore a wide range of quasar luminosity function (QLF) parameters. We use both analytical methods and mock catalogs, which give consistent results. For ordinary QLF parameters and the depth of current high-redshift quasar surveys (m z ≲ 22), our model suggests a multiply imaged fraction of F multi ∼ 0.4%–0.8%. The predicted lensed fraction is ∼1%–6% for the brightest z s ∼ 6 quasars (m z ≲ 19), depending on the QLF. The systematic uncertainties of the predicted lensed fraction in previous models can be as large as 2–4 times and are dominated by the VDF. Applying VDFs from recent measurements decreases the predicted lensed fraction and relieves the tension between observations and theoretical models. Given the depth of current imaging surveys, there are ∼15 lensed quasars at z s > 5.5 detectable over the sky. Upcoming sky surveys like the Legacy Survey of Space and Time survey and the Euclid survey will find several tens of lensed quasars at this redshift range.

Individual element sensitivity for stellar evolutionary isochrones

ABSTRACT Stellar evolution calculations with variable abundance ratios were used to gauge the effects on temperatures, luminosities, and lifetimes in various phases. The individual elements C, N, O, Mg, Si, and Fe were included. Most of the effect relevant to integrated light models is contained in the temperature variable, as opposed to the time-scale or luminosity. We derive a recipe for including abundance-sensitive temperature effects that is applicable to existing isochrone grids. The resultant enhanced isochrones are incorporated into composite stellar population models and compared with galaxy data from the Sloan Digital Sky Survey. A severe oxygen–age degeneracy is apparent, 2–3 Gyr per 0.1 dex in [O/R], where R represents a heavy element such as Fe. Over the range of early-type galaxy velocity dispersion, the spans of all abundance ratios are reduced but the age range increases and becomes systematically older. Allowing Fe-peak elements the freedom to vary accentuates this increase of age span. Overall, these results sharpen the age–mass correlation known as downsizing but decrease the steepness of abundance ratio gradients. Both of these observations, in turn, imply a more robust contribution from gas-free mergers in the histories of typical elliptical galaxies.

The Three Hundred–NIKA2 Sunyaev–Zeldovich Large Program twin samples: Synthetic clusters to support real observations

The simulation database of The Three Hundred Project has been used to pick synthetic clusters of galaxies with properties close to the observational targets of the NIKA2 camera Sunyaev–Zeldovich (SZ) Large Program. Cross–matching of cluster parameters such as mass and redshift of the cluster in the two databases has been implemented to generate the so–called twin samples for the Large Program. This SZ Large Program is observing a selection of galaxy clusters at intermediate and high redshift (0:5 < z < 0:9), covering one order of magnitude in mass. These are SZ–selected clusters from the Planck and Atacama Cosmology Telescope catalogs, wherein the selection is based on their integrated Compton parameter values, Y500: the value of the parameter within the characteristics radius R500. The Three Hundred hydrodynamical simulations provide us with hundreds of clusters satisfying these redshift, mass, and Y500 requirements. In addition to the standard post-processing analysis of the simulation, mock observational maps are available mimicking X–ray, optical, gravitational lensing, radio, and SZ observations of galaxy clusters. The primary goal of employing the twin samples is to compare different cluster mass proxies from synthetic X–ray, SZ effect and optical maps (via the velocity dispersion of member galaxies and lensing κ-maps) of the clusters. Eventually, scaling laws between different mass proxies and the cluster mass will be cross–correlated to reduce the scatter on the inferred mass and the mass bias will be related to various physical parameters.