Search

The number of identified fast radio bursts (FRBs) will continue to increase rapidly with current and planned future facilities. Strongly lensed FRBs are also expected to be found, which can provide precise time delays and thus have rich applications in cosmology and fundamental physics. However, the radio signal of lensed FRBs will be deflected by the plasma in lens galaxies in addition to the deflection by gravity. Such deflections by both gravity and plasma will cause frequency-dependent time delays, which are different from the dispersion delay and the geometric delay caused by gravitational lensing. Depending on the lensing and plasma models, the frequency–time-delay relationship of the lensed images can show distinguishing behaviours either between the multiple images or from the dispersion relation. Such phenomena cannot be neglected in future studies, especially at low radio frequencies, as plasma exists in lens galaxies in general. More importantly, such information provides not only a potential way to search for lensed FRBs but also constraints on the mass and plasma distributions in lens galaxies. In particular, plasma may make the missing central images observable at low radio frequencies. [ABSTRACT FROM AUTHOR]

Early-type galaxies (ETGs) possess total density profiles close to isothermal, which can lead to non-Gaussian line-of-sight velocity dispersion (LOSVD) under anisotropic stellar orbits. However, recent observations of local ETGs in the MASSIVE Survey reveal outer kinematic structures at 1.5 R eff (effective radius) that are inconsistent with fixed isothermal density profiles; the authors proposed varying density profiles as an explanation. We aim to verify this conjecture and understand the influence of stellar assembly on these kinematic features through mock ETGs in IllustrisTNG. We create mock Integral-Field-Unit observations to extract projected stellar kinematic features for 207 ETGs with stellar mass |$M_{\ast }\geqslant 10^{11} \, \mathrm{M_{\odot}}$| in TNG100-1. The mock observations reproduce the key outer (1.5 R eff) kinematic structures in the MASSIVE ETGs, including the puzzling positive correlation between velocity dispersion profile outer slope γouter and the kurtosis h 4's gradient. We find that h 4 is uncorrelated with stellar orbital anisotropy beyond R eff; instead, we find that the variations in γouter and outer h 4 (a good proxy for h 4 gradient) are both driven by variations of the density profile at the outskirts across different ETGs. These findings corroborate the proposed conjecture and rule out velocity anisotropy as the origin of non-Gaussian outer kinematic structure in ETGs. We also find that the outer kurtosis and anisotropy correlate with different stellar assembly components, with the former related to minor mergers or flyby interactions while the latter is mainly driven by major mergers, suggesting distinct stellar assembly origins that decorrelates the two quantities. [ABSTRACT FROM AUTHOR]

The stellar mass-to-light ratio gradient in SDSS r -band ∇(M */ L r ) of a galaxy depends on its mass assembly history, which is imprinted in its morphology and gradients of age, metallicity, and stellar initial mass function (IMF). Taking a MaNGA sample of 2051 galaxies with stellar masses ranging from 109 to 1012 M ⊙ released in SDSS DR15, we focus on face-on galaxies, without merger and bar signatures, and investigate the dependence of the 2D ∇(M */ L r ) on other galaxy properties, including M */ L r -colour relationships by assuming a fixed Salpeter IMF as the mass normalization reference. The median gradient is ∇ M */ L r ∼ −0.1 (i.e. the M */ L r is larger at the centre) for massive galaxies, becomes flat around M * ∼ 1010 M ⊙ and change sign to ∇ M */ L r ∼ 0.1 at the lowest masses. The M */ L r inside a half-light radius increases with increasing galaxy stellar mass; in each mass bin, early-type galaxies have the highest value, while pure-disc late-type galaxies have the smallest. Correlation analyses suggest that the mass-weighted stellar age is the dominant parameter influencing the M */ L r profile, since a luminosity-weighted age is easily affected by star formation when the specific star formation rate (sSFR) inside the half-light radius is higher than 10−3 Gyr−1. With increased sSFR gradient, one can obtain a steeper negative ∇(M */ L r ). The scatter in the slopes of M */ L -colour relations increases with increasing sSFR, for example, the slope for post-starburst galaxies can be flattened to 0.45 from the global value 0.87 in the M */ L versus g − r diagram. Hence converting galaxy colours to M */ L should be done carefully, especially for those galaxies with young luminosity-weighted stellar ages, which can have quite different star formation histories. [ABSTRACT FROM AUTHOR]

We present a method to compute the magnification of a finite source star lensed by a triple lens system based on the image boundary (contour integration) method. We describe a new procedure to obtain continuous image boundaries from solutions of the tenth-order polynomial obtained from the lens equation. Contour integration is then applied to calculate the image areas within the image boundaries, which yields the magnification of a source with uniform brightness. We extend the magnification calculation to limb-darkened stars approximated with a linear profile. In principle, this method works for all multiple lens systems, not just triple lenses. We also include an adaptive sampling and interpolation method for calculating densely covered light curves. The C++ source code and a corresponding python interface are publicly available. [ABSTRACT FROM AUTHOR]

Galactic model plays an important role in the microlensing field, not only for analyses of individual events but also for statistics of the ensemble of events. However, the Galactic models used in the field vary, and some are unrealistically simplified. Here, we tested three Galactic disc dynamic models; the first is a simple standard model that was widely used in this field, the second model considers the radial dependence of the velocity dispersion, and the last model employs the asymmetric drift in the disc velocity distribution. We found that for a typical lens mass |$M_{\rm L}=0.5\, {\rm M}_\odot$|⁠ , the two new dynamical models predict |$\sim 16{{\ \rm per\ cent}}$| or |$\sim 5{{\ \rm per\ cent}}$| less long-time-scale events (e.g. microlensing time-scale t E > 300 d) and |$\sim 5{{\ \rm per\ cent}}$| and |$\sim 3.5{{\ \rm per\ cent}}$| more short-time-scale events (t E < 3 d) than the standard model. Moreover, the microlensing event rate as a function of Einstein radius θE or microlensing parallax πE also shows some model dependence (a few per cent). The two new models also have an impact on the total microlensing event rate. This result will also to some degree affect the Bayesian analysis of individual events, but overall, the impact is small. However, we still recommend that modellers should be more careful when choosing the Galactic model, especially in statistical works involving Bayesian analyses of a large number of events. Additionally, we find the asymptotic power-law behaviours in both θE and πE distributions, and we provide a simple model to understand them. [ABSTRACT FROM AUTHOR]

We analyse the kinematics and spatial distribution of 15 599 fundamental-mode RR Lyrae (RRL) stars in the Milky Way bulge by combining OGLE-IV photometric data and Gaia DR2 proper motions. We show that the longitudinal proper motions and the line-of-sight velocities can give similar results for the rotation in the Galactic central regions. The angular velocity of bulge RRLs is found to be around 35 km s−1 kpc−1, significantly smaller than that for the majority of bulge stars (50–60 km s−1 kpc−1); bulge RRLs have larger velocity dispersion (120–140 km s−1) than younger stars. The dependence of the kinematics of the bulge RRLs on their metallicities is shown by their rotation curves and spatial distributions. Metal-poor RRLs ([Fe/H]<−1) show a smaller bar angle than metal-rich ones. We also find clues suggesting that RRLs in the bulge are not dominated by halo stars. These results might explain some previous conflicting results over bulge RRLs and help understand the chemodynamical evolution of the Galactic bulge. [ABSTRACT FROM AUTHOR]

Three basic ingredients are required to generate a simple stellar population (SSP) library, i.e. an initial mass function (IMF), a stellar evolution model/isochrones, and an empirical/theoretical stellar spectral library. However, there are still some uncertainties to the determination and understanding of these ingredients. We perform the spectral fitting to test the relative parameter offsets between these uncertainties using two different stellar population models, two different empirical stellar libraries, two different isochrones, and the Salpeter and Chabrier IMFs. Based on these setups, we select five SSP libraries generated with the Galaxev/STELIB and Vazdekis/MILES models, and apply them to the pPXF full-spectrum fitting of both MaNGA and mock spectra. We find that: (1) Compared to the Galaxev/STELIB model, spectral fitting qualities with the Vazdekis/MILES model have significant improvements for those metal-rich (especially oversolar) spectra, which cause better reduced χ2 distributions and more precisely fitted absorption lines. This might due to the lack of metal-rich stars in the empirical STELIB library, or code improvement of the Vazdekis model. (2) When applying the Vazdekis/MILES model for spectral fitting, the IMF variation will lead to not only a systematic offset in M */ Lr, but also offsets in age and metallicity, and these offsets increase with increasing stellar population ages. However, the IMF variation caused metallicity offsets disappear in the case of Galaxev/STELIB based libraries. (3) The Padova2000 model provides a better match to the MaNGA galaxy spectra at [M/H] L < −1.0, while the BaSTI model match the local galaxy spectra better at [M/H] L > −1.0. Current tests suggest that spectral fitting with the Vazdekis/MILES + BaSTI combination would be a better choice for local galaxies. [ABSTRACT FROM AUTHOR]

We explore orbit properties of 35 prolate-triaxial galaxies selected from the Illustris cosmological hydrodynamic simulation. We present a detailed study of their orbit families, and also analyse relations between the relative abundance of the orbit families and the spin parameter, triaxiality, the ratio of the angular momentum, and the baryon fraction. We find that box orbits dominate the orbit structure for most prolate-triaxial galaxies, especially in the central region. The fraction of irregular orbits in the prolate-triaxial galaxies is small, and it increases with galaxy radius. Both the x -tube and z -tube orbits are important in prolate-triaxial galaxies, especially in the outer regions. The fraction of box orbits for prolate-triaxial galaxies (0.7 < T < 1) decreases with the triaxiality of the stars, while the fraction of x -tube orbits increases with the triaxiality for a given axis ratio. The fraction of box orbits increases and the fractions of x -tube and z -tube orbits weakly decrease with increasing baryon fraction. These results help to understand the structure of prolate-triaxial galaxies and provide cross-checks for constructing dynamical models of prolate-triaxial galaxies by using the Schwarzschild or the made-to-measure methods. [ABSTRACT FROM AUTHOR]

The MaNGA project has obtained integral field unit (IFU) data for several thousand nearby galaxies, including barred galaxies. With the two-dimensional spectral and kinematic information provided by IFUs, we can measure the pattern speed of a barred galaxy, which determines the bar dynamics. We apply the non-parametric method proposed by Tremaine & Weinberg to estimate the bar pattern speed for 53 barred galaxies, making this the largest sample studied so far in this way. Our sample is selected from the MaNGA first public data release as part of SDSS Data Release 13 according mainly to the axial ratio and position angle difference between the bar and disc, while kinematic data are from the later SDSS Data Release 14. We have used both the photometric position angle from the photometric image and the kinematic position angle from the stellar velocity map to derive the pattern speed. Combining three independent bar length measurements and the circular velocity from Jeans anisotropic modelling (JAM), we also determine the dimensionless ratio |$\cal {R}$| of the corotation radius to the bar length. We find that the galaxy's position angle is the main uncertainty in determining the bar pattern speed. The kinematic position angle leads to fewer ultrafast bars than the photometric position angle, and this could be due to the method of measuring the kinematic position angle. We study the dependence of |$\cal {R}$| values on galaxy properties such as the dark matter fraction from JAM modelling and the stellar age and metallicity from stellar population synthesis. A positive correlation between the bar length and bar strength is found: the longer the bar, the stronger the bar. However, no other significant correlations are found. This may result from errors in deriving the |$\cal {R}$| values or from the complex formation and slowdown processes of galactic bars. [ABSTRACT FROM AUTHOR]

Peculiar motion of galaxies probes the structure growth in the universe. In this study, we employ the galaxy stellar mass-binding energy (massE) relation with only two nuisance parameters to build the largest peculiar-velocity (PV) catalogue to date, consisting of 229 890 ellipticals from the main galaxy sample (MGS) of the Sloan Digital Sky Survey (SDSS). We quantify the distribution of the massE-based distances in individual narrow redshift bins (dz  = 0.005), and then estimate the PV of each galaxy based on its offset from the Gaussian mean of the distribution. As demonstrated with the Uchuu-SDSS mock data, the derived PV and momentum power spectra are insensitive to accurate calibration of the massE relation itself, enabling measurements out to a redshift of 0.2, well beyond the current limit of z  = 0.1 using other galaxy scaling laws. We then measure the momentum power spectrum and demonstrate that it remains almost unchanged if varying significantly the redshift bin size within which the distance is measured, as well as the intercept and slope of the massE relation, respectively. By fitting the spectra using the perturbation theory model with four free parameters, f σ8 is constrained to f σ8 = 0.459 |$^{+0.068}_{-0.069}$|  over Δ z  = 0.02–0.2, 0.416 |$^{+0.074}_{-0.076}$|  over Δ z  = 0.02–0.1, and 0.526 |$^{+0.133}_{-0.148}$|  over Δ z  = 0.1–0.2. The error of f σ8 is 2.1 times smaller than that by the redshift space distortion (RSD) of the same sample. A Fisher matrix forecast illustrates that the constraint on f σ8 from the massE-based PV can potentially exceed that from the stage-IV RSD in late universe (z <0.5). [ABSTRACT FROM AUTHOR]

We analyse the integral field spectroscopy data for the ≈10 000 galaxies in final data release of the MaNGA survey. We identify 188 galaxies for which the emission lines cannot be described by single Gaussian components. These galaxies can be classified into (1) 38 galaxies with broad |$\rm H\alpha$| and [O  iii ]  |$\rm \lambda$| 5007 lines, (2) 101 galaxies with broad |$\rm H\alpha$| lines but no broad [O  iii ]  |$\rm \lambda$| 5007 lines, and (3) 49 galaxies with double-peaked narrow emission lines. Most of the broad-line galaxies are classified as active galactic nuclei (AGNs) from their line ratios. The catalogue helps us further understand the AGN-galaxy coevolution through the stellar population of broad-line region host galaxies and the relation between broad lines' properties and the host galaxies' dynamical properties. The stellar population properties (including mass, age, and metallicity) of broad-line host galaxies suggest there is no significant difference between narrow-line Seyfert-2 galaxies and Type-1 AGNs with broad |$\rm H\alpha$| lines. We use the broad- |$\rm H\alpha$| line width and luminosity to estimate masses of black hole in these galaxies, and test the M BH–σe relation in Type-1 AGN host galaxies. Furthermore, we find three dual AGN candidates supported by radio images from the VLA FIRST survey. This sample may be useful for further studies on AGN activities and feedback processes. [ABSTRACT FROM AUTHOR]

Time delays in gravitational lenses can be used to determine the Hubble constant and the lens potential. In future surveys, many gravitational lenses can be discovered, and their time delays and image positions can in principle be measured. Using an elliptical power-law potential, we show that combinations of image positions and time delays for quadruple lenses yield simple analytical expressions that are connected with observable quantities. These relations can be used to obtain the approximate axis ratio q, the Einstein radius and the slope. We apply this method to RX J1131-1231, and show that our analytical results match the full numerical determinations approximately. Our approach can quickly determine rough values of lens parameters, which can then be used as initial guesses for further refinement through numerical modelling and may be useful for automated lens search in large surveys. [ABSTRACT FROM AUTHOR]

We demonstrate how the Syer and Tremaine made-to-measure method of stellar dynamical modelling can be adapted to model a rotating galactic bar. We validate our made-to-measure changes using observations constructed from the existing Shen et al. N-body model of the Milky Way bar, together with kinematic observations of the Milky Way bulge and bar taken by the Bulge Radial Velocity Assay. Our results for a combined determination of the bar angle and bar pattern speed (≈30° and ≈40 km s−1 kpc−1) are consistent with those determined by the N-body model. Whilst the made-to-measure techniques we have developed are applied using a particular N-body model and observational data set, they are in fact general and could be applied to other Milky Way modelling scenarios utilizing different N-body models and data sets. Additionally, we use the exercise as a vehicle for illustrating how N-body and made-to-measure methods might be combined into a more effective method. [ABSTRACT FROM AUTHOR]

ABSTRACT The masses of stars, including stellar remnants, are almost exclusively known from binary systems. In this paper, we study the gravitational microlensing of faint background galaxies caused by isolated neutron stars (pulsars). We show that the resulting distortions in the surface brightness can be used to determine the masses of neutron stars. Because of their different evolutionary histories, isolated neutron stars might have different masses from those in binary systems, which can thus provide a unique insight into their equation of states under extreme physical conditions. Having searched the existing pulsar catalogues, we have found one promising pair, consisting of a nearby pulsar and a background galaxy. This method will become more practical for the next-generation optical and radio surveys and telescopes. [ABSTRACT FROM AUTHOR]

ABSTRACT We identify a total of 120 early-type brightest cluster galaxies (BCGs) at 0.1 < z < 0.4 in two recent large cluster catalogues selected from the Sloan Digital Sky Survey (SDSS). They are selected with strong emission lines in their optical spectra, with both Hα and [O II]λ3727 line emission, which indicates significant ongoing star formation. They constitute about ∼0.5 per cent of the largest, optically selected, low-redshift BCG sample, and the fraction is a strong function of cluster richness. Their star formation history can be well described by a recent minor and short starburst superimposed on an old stellar component, with the recent episode of star formation contributing on average only less than 1 per cent of the total stellar mass. We show that the more massive star-forming BCGs in richer clusters tend to have higher star formation rate (SFR) and specific SFR (SFR per unit galaxy stellar mass). We also compare their statistical properties with a control sample selected from X-ray luminous clusters, and show that the fraction of star-forming BCGs in X-ray luminous clusters is almost one order of magnitude larger than that in optically selected clusters. BCGs with star formation in cooling flow clusters usually have very flat optical spectra and show the most active star formation, which may be connected with cooling flows. [ABSTRACT FROM AUTHOR]

ABSTRACT We study moderate gravitational lensing where a background galaxy is magnified substantially, but not multiply imaged, by an intervening galaxy. We focus on the case where both the lens and source are elliptical galaxies. The signatures of moderate lensing include isophotal distortions and systematic shifts in the Fundamental Plane and Kormendy relation, which can potentially be used to statistically determine the galaxy mass profiles. These effects are illustrated using Monte Carlo simulations of galaxy pairs where the foreground galaxy is modelled as a singular isothermal sphere model and observational parameters appropriate for the Large Synoptic Survey Telescope. The range in radius probed by moderate lensing will be larger than that by strong lensing, and is in the interesting regime where the density slope may be changing. [ABSTRACT FROM AUTHOR]

ABSTRACT The flux-ratio anomalies observed in multiply lensed quasar images are most plausibly explained as the result of perturbing structures superposed on the underlying smooth matter distribution of the primary lens. The cold dark matter cosmological model predicts that a large number of substructures should survive inside larger haloes but, surprisingly, this population alone has been shown to be insufficient to explain the observed distribution of the flux ratios of quasars' multiple images. Other haloes (and their subhaloes) projected along the line of sight to the primary lens have been considered as additional sources of perturbation. In this work, we use ray tracing through the Millennium II simulation to investigate the importance of projection effects due to haloes and subhaloes of mass m > 108 h−1 M⊙ and extend our analysis to lower masses, m≥ 106 h−1 M⊙, using Monte Carlo halo distributions. We find that the magnitude of the violation depends strongly on the density profile and concentration of the intervening haloes, but clustering plays only a minor role. For a typical lensing geometry (lens at a redshift of 0.6 and source at a redshift of 2), background haloes (behind the main lens) are more likely to cause a violation than foreground haloes. We conclude that line-of-sight structures can be as important as intrinsic substructures in causing flux-ratio anomalies. The combined effect of perturbing structures within the lens and along the line of sight in the Λ cold dark matter ( ΛCDM) universe results in a cusp-violation probability of 20-30 per cent. This alleviates the discrepancy between models and current data, but a larger observational sample is required for a stronger test of the theory. [ABSTRACT FROM AUTHOR]

ABSTRACT We take a sample of 24 elliptical and lenticular galaxies previously analysed by the SAURON project using three integral dynamical models created with Schwarzschild method, and re-analyse them using the made-to-measure (M2M) method of dynamical modelling. We obtain good agreement between the two methods in determining the dynamical mass-to-light ratios ( M/ L values) for the galaxies with over 80 per cent of ratios differing by <10 per cent and over 95 per cent differing by <20 per cent. We show that . For the global velocity dispersion anisotropy parameter δ, we find similar values but with fewer of the M2M models tangentially anisotropic by comparison with their SAURON Schwarzschild counterparts. Our investigation is the largest comparative application of the M2M method to date. [ABSTRACT FROM AUTHOR]

ABSTRACT Most galaxies host central supermassive black holes. As two galaxies merge, the black holes also merge. The final single black hole may suffer a kick due to asymmetric gravitational radiation and may not be at the centre of the galaxy; off-centre black holes may also be produced by other means such as sustained acceleration due to asymmetric jet power. We model the main galaxy as a singular isothermal sphere and the black hole as an off-centre point lens, and study the critical curves and caustics using complex notation. We identify the critical parameters that govern the transitions in the topology of critical curves, caustics and pseudo-caustics, and find that the number of images can be 2, 3, 4 and 5. We show examples of image configurations, including cases where three highly de-magnified images are found close to the centre. The perturbation on the image magnification due to the black hole scales linearly with its mass in the off-centre case, and quadratically when the black hole is at the centre. Such images are difficult to observe unless high-contrast and high-resolution imaging facilities (e.g. the Square Kilometre Array in the radio) become available. [ABSTRACT FROM AUTHOR]

ABSTRACT Recent observations indicate that many, if not all, galaxies host massive central black holes (BHs). In this paper, we explore the influence of supermassive binary black holes (SMBBHs) on their actions as gravitational lenses. When lenses are modelled as singular isothermal ellipsoids, binary BHs change the critical curves and caustics differently as a function of distance. Each BH can in principle create at least one additional image, which, if observed, provides evidence of BHs. By studying how SMBBHs affect the cumulative distribution of magnification for images created by BHs, we find that the cross-section for at least one such additional image to have a magnification larger than 10−5 is comparable to the cross-section for producing multiple images in singular isothermal lenses. Such additional images may be detectable with high-resolution and large dynamic range maps of multiply imaged systems from future facilities, such as the Square Kilometre Array. The probability of detecting at least one image (two images) with magnification above 10−3 is ∼0.2 fBH (∼0.05 fBH) in a multiply imaged lens system, where fBH is the fraction of galaxies housing binary BHs. We also study the effects of SMBBHs on the core images when galaxies have shallower central density profiles (modelled as non-singular isothermal ellipsoids). We find that the cross-section of the usually faint core images is further suppressed by SMBBHs. Thus, their presence should also be taken into account when one constrains the core radius from the lack of central images in gravitational lenses. [ABSTRACT FROM AUTHOR]

ABSTRACT The cold dark matter theory predicts triaxial dark matter haloes. The radial distribution of halo ellipticity depends on baryonic processes and the nature of dark matter particles (collisionless or collisional). Here we show that we can use lensing flexion ratios to measure the halo ellipticity as a function of radius. We introduce a weight function and study the relationship between the first- and second-order statistics of flexion ratios, both of which can be used to reduce the bias in the estimation of ellipticity. We perform numerical tests for our method, and demonstrate that it can reduce the bias and determine the halo ellipticity as a function of radius. We also point out that the minimum mean flexion ratio can be used to trace the centres of galaxy clusters. [ABSTRACT FROM AUTHOR]

ABSTRACT Starburst galaxies are primary feedback sources of mechanical energy and metals, which are generally measured from associated X-ray emission lines, assuming that they are from the thermal emission of the outflowing hot gas. Such line emission, however, can also arise from the charge-exchange X-ray emission (CXE) between highly ionized ions and neutral species. To understand the feedback of energy and metals, it is crucial to determine the origin of the X-ray emission lines and to distinguish the contributions from the CXE and the thermal emission. The origin of the lines can be diagnosed by the Kα triplets of He-like ions, because the CXE favours the intercombination and forbidden lines, while the thermal emission favours the resonance line. We analyse the triplets of O vii, Ne ix and Mg xi observed in the XMM-Newton reflection grating spectra of the starburst galaxy M82. The flux contribution of the CXE is 90, 50 and 30 per cent to the O vii, Ne ix and Mg xi triplets, respectively. Averaged over all the three triplets, the contribution of the CXE is ∼50 per cent of the total observed triplet flux. To correctly understand the hot outflow of starburst galaxies, it is necessary to include the CXE. Based on the measured CXE fluxes of the O vii, Ne ix and Mg xi triplets, we estimate the relative abundances of O, Ne and Mg of the outflow and find they are similar to the solar ratios. [ABSTRACT FROM AUTHOR]

A standard binary microlensing event light curve allows just two parameters of the lensing system to be measured: the mass ratio of the companion to its host and the projected separation of the components in units of the Einstein radius. However, other exotic effects can provide more information about the lensing system. Orbital motion in the lens is one such effect, which, if detected, can be used to constrain the physical properties of the lens. To determine the fraction of binary-lens light curves affected by orbital motion (the detection efficiency), we simulate light curves of orbiting binary star and star-planet (planetary) lenses and simulate the continuous, high-cadence photometric monitoring that will be conducted by the next generation of microlensing surveys that are beginning to enter operation. The effect of orbital motion is measured by fitting simulated light-curve data with standard static binary microlensing models; light curves that are poorly fitted by these models are considered to be detections of orbital motion. We correct for systematic false positive detections by also fitting the light curves of static binary lenses. For a continuous monitoring survey without intensive follow-up of high-magnification events, we find the orbital motion detection efficiency for planetary events with caustic crossings to be , consistent with observational results, and for events without caustic crossings (smooth events). Similarly, for stellar binaries, the orbital motion detection efficiency is for events with caustic crossings and is for smooth events. These result in combined (caustic-crossing and smooth) orbital motion detection efficiencies of for planetary lenses and for stellar binary lenses. We also investigate how various microlensing parameters affect the orbital motion detectability. We find that the orbital motion detection efficiency increases as the binary mass ratio and event time-scale increase, and as the impact parameter and lens distance decrease. For planetary caustic-crossing events, the detection efficiency is highest at relatively large values of semimajor axis 4 au, due to the large size of the resonant caustic at this orbital separation. Effects due to the orbital inclination are small and appear to significantly affect only smooth stellar binary events. We find that, as suggested by Gaudi, many of the events that show orbital motion can be classified into one of the following two classes. The first class, separational events, typically show large effects due to subtle changes in resonant caustics, caused by changes in the projected binary separation. The second class, rotational events, typically show much smaller effects, which are due to the magnification patterns of close lenses exhibiting large changes in angular orientation over the course of an event; these changes typically cause only subtle changes to the light curve. [ABSTRACT FROM AUTHOR]

Lensing flux-ratio anomalies have been frequently observed and taken as evidence for the presence of abundant dark matter substructures in lensing galaxies, as predicted by the cold dark matter (CDM) model of cosmogony. In previous work, we examined the cusp-caustic relations of the multiple images of background quasars lensed by galaxy-scale dark matter haloes, using a suite of high-resolution N-body simulations (the Aquarius simulations). In this work, we extend our previous calculations to incorporate both the baryonic and diffuse dark components in lensing haloes. We include in each lensing simulation: (1) a satellite galaxy population derived from a semi-analytic model applied to the Aquarius haloes; (2) an empirical Milky Way globular cluster population and (3) satellite streams (diffuse dark component) identified in the simulations. Accounting for these extra components, we confirm our earlier conclusion that the abundance of intrinsic substructures (dark or bright, bound or diffuse) is not sufficient to explain the observed frequency of cusp-caustic violations in the Cosmic Lens All-Sky Survey (CLASS). We conclude that the observed effect could be the result of the small number statistics of CLASS, or intergalactic haloes along the line of sight acting as additional sources of lensing flux anomalies. Another possibility is that this discrepancy signals a failure of the CDM model. [ABSTRACT FROM AUTHOR]

We use the high-resolution Aquarius simulations of the formation of Milky Way-sized haloes in the Λ cold dark matter cosmology to study the effects of dark matter substructures on gravitational lensing. Each halo is resolved with particles (at a mass resolution to ) within its virial radius. Subhaloes with masses are well resolved, an improvement of at least two orders of magnitude over previous lensing studies. We incorporate a baryonic component modelled as a Hernquist profile and account for the response of the dark matter via adiabatic contraction. We focus on the ‘anomalous’ flux ratio problem, in particular on the violation of the cusp–caustic relation due to substructures. We find that subhaloes with masses less than play an important role in causing flux anomalies; such low-mass subhaloes have been unresolved in previous studies. There is large scatter in the predicted flux ratios between different haloes and between different projections of the same halo. In some cases, the frequency of predicted anomalous flux ratios is comparable to that observed for the radio lenses, although in most cases it is not. The probability for the simulations to reproduce the observed violations of the cusp lenses is . We therefore conclude that the amount of substructure in the central regions of the Aquarius haloes is insufficient to explain the observed frequency of violations of the cusp–caustic relation. These conclusions are based purely on our dark matter simulations which ignore the effect of baryons on subhalo survivability. [ABSTRACT FROM AUTHOR]

We search for ongoing major dry mergers in a well-selected sample of local brightest cluster galaxies (BCGs) from the C4 cluster catalogue. 18 out of 515 early-type BCGs with redshift between 0.03 and 0.12 are found to be in major dry mergers, which are selected as pairs (or triples) with r-band magnitude difference and projected separation , and showing signatures of interaction in the form of significant asymmetry in residual images. We find that the fraction of BCGs in major dry mergers increases with the richness of the clusters, consistent with the fact that richer clusters usually have more massive (or luminous) BCGs. We estimate that present-day early-type BCGs may have experienced on average major dry mergers and through this process increases their luminosity (mass) by 15 per cent on average since , where tmerge is the merging time-scale and fmass is the mean mass fraction of companion galaxies added to the central ones. We also find that major dry mergers do not seem to elevate radio activities in BCGs. Our study shows that major dry mergers involving BCGs in clusters of galaxies are not rare in the local Universe, and they are an important channel for the formation and evolution of BCGs. [ABSTRACT FROM AUTHOR]

The photometry data base of the second phase of the OGLE microlensing experiment, OGLE-II, is a rich source of information about the kinematics and structure of the Galaxy. In this work, we use the OGLE-II proper motion catalogue to identify candidate stars which have high proper motions. 521 stars with proper motion μ > 50 mas yr−1 in the OGLE-II proper motion catalogue were cross-identified with stars in the MACHO high proper motion catalogue, and the DEep Near-Infrared Survey and Two-Micron All-Sky Survey infrared photometry catalogues. Photometric distances were computed for stars with colours consistent with G/K- and M-type stars. Six stars were newly identified as possible nearby (<50 pc) M dwarfs. [ABSTRACT FROM AUTHOR]

Red clump giant (RCG) stars can be used as distance indicators to trace the mass distribution of the Galactic bar. We use RCG stars from 44 bulge fields from the OGLE-II microlensing collaboration data base to constrain analytic triaxial models for the Galactic bar. We find the bar major-axis is oriented at an angle of 24°–27° to the Sun–Galactic Centre line-of-sight. The ratio of semimajor and semiminor bar axis scalelengths in the Galactic plane , and vertical bar scalelength z0, is , suggesting a slightly more prolate bar structure than the working model of Gerhard which gives the scalelength ratios as . [ABSTRACT FROM AUTHOR]

Red clump giants (RCGs) in the Galactic bulge are approximate standard candles and hence they can be used as distance indicators. We compute the proper motion dispersions of RCG stars in the Galactic bulge using the proper motion catalogue from the second phase of the Optical Gravitational Microlensing Experiment (OGLE-II) for 45 fields. The proper motion dispersions are measured to a few per cent accuracy due to the large number of stars in the fields. The observational sample comprises 577 736 stars. These observed data are compared to a state-of-the-art particle simulation of the Galactic bulge region. The predictions are in rough agreement with observations, but appear to be too anisotropic in the velocity ellipsoid. We note that there is significant field-to-field variation in the observed proper motion dispersions. This could either be a real feature, or due to some unknown systematic effect. [ABSTRACT FROM AUTHOR]

Gravitational lensing deflects light. A single lens deflector can only shear images, but cannot induce rotations. Multiple lens planes can induce rotations. Such rotations can be observed in quadruply imaged sources, and can be used to distinguish between two proposed solutions of the flux anomaly problem: substructures in lensing galaxies versus large-scale structure. We predict the expected amount of rotation due to large-scale structure in strong lensing systems, and show how this effect can be measured using ∼mas very long baseline interferometry astrometry of quadruple lenses with extended source structures. The magnitude of rotation is around 1°. The biggest theoretical uncertainty is the power spectrum of dark matter on very small scales. This procedure can potentially be turned around to measure the dark matter power spectrum on very small scales. We list the predicted rms rotation angles for several quadruple lenses with known lens and source redshifts. [ABSTRACT FROM AUTHOR]

Interferometers from the ground and space will be able to resolve the two images in a microlensing event. This will at least partially lift the inherent degeneracy between physical parameters in microlensing events. To increase the signal-to-noise ratio, intrinsically bright events with large magnifications will be preferentially selected as targets. These events may be influenced by finite source size effects both photometrically and astrometrically. Using observed finite source size events as examples, we show that the fringe visibility can be affected by ∼5–10 per cent, and the closure phase by a few degrees – readily detectable by ground and space interferometers. Such detections will offer unique information about the lens–source trajectory relative to the baseline of the interferometers. Combined with photometric finite source size effects, interferometry offers a way to measure the angular sizes of the source and the Einstein radius accurately. Limb-darkening changes the visibility by a small amount compared with a source with uniform surface brightness, marginally detectable with ground-based instruments. We discuss the implications of our results for the plans to make interferometric observations of future microlensing events. [ABSTRACT FROM AUTHOR]

We present microlensing calculations for a Galactic model based on that of Han & Gould, which is empirically normalized by star counts. We find good agreement between this model and data recently published by the MACHO and OGLE collaborations for the optical depth in various Galactic fields, and the trends thereof with Galactic longitude l and latitude b. We produce maps of optical depth and, by adopting simple kinematic models, of average event time-scales for microlensing towards the Galactic bulge. We also find that our model predictions are in reasonable agreement with the OGLE data for the expected time-scale distribution. We show that the fractions of events with very long and short time-scales owing to a lens of mass M are weighted by and , respectively, independent of the density and kinematics of the lenses. [ABSTRACT FROM AUTHOR]

RecentN-body simulations show that the formation of a present-day, galaxy-sized dark matter halo in the cold dark matter (CDM) cosmogony in general consists of an early fast-collapse phase, during which the potential associated with a halo is established, followed by a slow-accretion phase, during which mass is added gently in the outer region. In this paper, we consider the implication of such a halo assemble history for galaxy formation. We outline a scenario in which the fast-collapse phase is accompanied by the rapid formation of cold clouds and by starbursts that can eject a large amount of gas from the halo centre. The loss of orbital energy of the cold clouds to the dark matter and the ejection of gas from the halo centre by starbursts can significantly reduce the halo concentration. The outflow from the starburst can also heat the gas in the protogalaxy region. Subsequent formation of galaxies in the slow-accretion regime is therefore in haloes that have been pre-processed by these processes and may have properties different from that given byN-body simulations. This scenario can help to solve several outstanding problems in the standardΛCDM model of galaxy formation without compromising its success in allowing structure formation at high redshift. The predicted rotation curves can be significantly flatter than those based on the halo profiles obtained fromN-body simulations, alleviating the discrepancy of the Tully–Fisher relation predicted in the standardΛCDM model with observations. The flattened galaxy haloes allow accreted minihaloes to survive in their central regions for longer, a fact that may be helpful in producing the flux anomalies observed in some gravitational lensing systems. The preheating by the early starbursts effectively reduces the amount of gas that can be accreted into galaxy haloes, which may explain why the baryon fraction in a spiral galaxy is in general much lower than the universal baryon fraction,, in the standardΛCDM model. [ABSTRACT FROM AUTHOR]

ABSTRACT To generate the standard microlensing light curve, we assume that the relative motion of the source, the lens and the observer is linear. In reality, the relative motion is likely to be more complicated due to accelerations of the observer, the lens and the source. The simplest approximation beyond the linear-motion assumption is to add a constant acceleration. Microlensing light curves due to accelerations can be symmetric or asymmetric depending on the angle between the acceleration and the velocity. We show that it is possible that some of the previously reported shorter marginal parallax events can be reproduced with constant-acceleration models, while the longer, multi-year parallax events are ill-fitted by such models. We find that there is a generic degeneracy inherent in constant-acceleration microlensing models. We also find that there is an equivalent degeneracy in parallax models, which manifests itself in short-duration events. The importance of this new parallax degeneracy is illustrated with an example, using one of these marginal parallax events. Our new analysis suggests that another of these previously suspected parallax candidate events may be exhibiting some weak binary-source signatures. If this turns out to be true, spectroscopic observations of the source could determine some parameters in the model and may also constrain or even determine the lens mass. We also point out that symmetric light curves with constant accelerations can mimic blended light curves, producing misleading Einstein-radius crossing time-scales when fitted by the standard ‘blended’ microlensing model; this may have some effect on the estimation of optical depth. [ABSTRACT FROM AUTHOR]

Red clump giants in the Galactic bulge occupy a distinct region in the colour-magnitude diagram. They have a very small spread in intrinsic luminosities and their number counts have a well-defined peak. We show that these characteristics can be used to constrain the differences in the streaming motions of stars on the near side and those on the far side. We propose two methods to select two samples with one preferentially on the near side and the other on the far side. In the first method, we divide red clump giants into a bright sample and a faint one; stars in the bright sample will be on average more on the near side and vice versa. The second method relies on the fact that lensed bulge stars lie preferentially on the far side because of the enhanced lensing probability by the stars on the near side and in the disc. If the radial streaming motion is ≈50 km s[sup -1], we find the difference in the average radial velocity between the bright and faint samples can reach ≈33 kms[sup -1], while the corresponding difference is ≈10 km s[sup -1] between the lensed stars and all observed stars. The difference in the average proper motion between the bright and faint samples is ≈ 1.6 mas yr[sup -1] if there is a tangential streaming motion of 100 km s[sup -1]; the corresponding shift between the lensed stars and all observed stars is approximately ≈1 mas yr[sup -1]. To observe the shifts in the radial velocity and proper motion, roughly 100 microlensing events, and/or bright/faint red clump giants, need to be observed either spectroscopically or astrometrically. The spectroscopic observations can be performed efficiently using multi-object spectrographs already available. The proper motion signature of microlensed objects can be studied using ground-based telescopes and the Hubble Space Telescope. These observations will provide strong constraints on the Galactic bar parameters. [ABSTRACT FROM AUTHOR]

Describes the optical microlensing event, OGLE-1999-BUL-19. Einstein radius crossing time; Transverse velocity of the lens projected onto the observer plane; Nature of the majority of the I-band blending.

We outline a scenario of galaxy formation in which the gas in galaxy-forming regions was pre-heated to high entropy by vigorous energy feedback associated with the formation of stars in old ellipticals and bulges and with active galactic nuclei activity. Such pre-heating probably occurred at redshifts of z∼2–3 , and can produce the entropy excess observed today in low-mass clusters of galaxies without destroying the bulk of the Lyα forest. Subsequent galaxy formation is affected by the pre-heating, because the gas no longer follows the dark matter on galaxy scales. The hot gas around galaxy haloes has very shallow profiles and emits only weakly in the X-ray range. Cooling in a pre-heated halo is not inside–out, because the cooling efficiency does not change significantly with radius. Only part of the gas in a protogalaxy region can cool and be accreted into the final galaxy halo by the present time. The accreted gas is probably in diffuse clouds and so does not lose angular momentum to the dark matter. Cluster ellipticals are produced by mergers of stellar systems formed prior to the pre-heating, while large galaxy discs form in low-density environments where gas accretion can continue to the present time. [ABSTRACT FROM AUTHOR]

We present a systematic search for parallax microlensing events among a total of 512 microlensing candidates in the OGLE II data base for the 1997–1999 seasons. We fit each microlensing candidate with both the standard microlensing model and a parallax model that accounts for the Earth's motion around the Sun. We then search for the parallax signature by comparing the χ[sup 2] of the standard and parallax models. For the events which show a significant improvement, we further use the ‘duration’ of the event and the signal-to-noise ratio as criteria to separate true parallax events from other noisy microlensing events. We have discovered one convincing new candidate, sc33_4505, and seven other marginal cases. The convincing candidate (sc33_4505) is caused by a slow-moving, and likely low-mass, object, similar to other known parallax events. We found that irregular sampling and gaps between observing seasons hamper the recovery of parallax events. We have also searched for long-duration events that do not show parallax signatures. The lack of parallax effects in a microlensing event puts a lower limit on the Einstein radius projected on to the observer plane, which in turn imposes a lower limit on the lens mass divided by the relative lens–source parallax. Most of the constraints are however quite weak. [ABSTRACT FROM AUTHOR]

We describe the discovery of the longest microlensing event ever observed, OGLE-1999-BUL-32, also independently identified by the MACHO collaboration as MACHO-99-BLG-22. This unique event has an Einstein radius crossing time of 640 d. The high-quality data obtained with difference image analysis shows a small but significant parallax signature. This parallax effect allows one to determine the Einstein radius projected on to the observer plane as . The transverse velocity projected on to the observer plane is about 79 km s[sup -1]. We argue that the lens is likely to have a mass of at least a few solar masses, i.e. it could be a stellar black hole. The black hole hypothesis can be tested using the astrometric microlensing signature with the soon-to-be installed Advanced Camera for Surveys on board the Hubble Space Telescope. Deep X-ray and radio images may also be useful for revealing the nature of the object. [ABSTRACT FROM AUTHOR]

We test possible lensing scenarios of the JVAS system B2114+022, in which two galaxies at different redshifts (‘G1’ at z[sub 1]=0.3157 and ‘G2’ at z[sub 2]=0.5883) are found within 2 arcsec of quadruple radio sources. For our investigation, we use possible lensing constraints derived from a wealth of data on the radio sources obtained with VLA, MERLIN, VLBA and EVN as well as HST imaging data on the two galaxies, which were presented recently in Augusto et al. In the present study, we focus on reproducing the widest separated, observationally similar radio components A and D as lensed images. We first treat G2 (which is the more distant one from the geometric centre) as a shear term, and then consider two-plane lensing explicitly including G2's potential at the z[sub 2] plane as the first case of two-plane lens modelling. Our modelling results not only support the hypothesis that the system includes gravitationally lensed images of a higher-redshift extragalactic object, but they also show that the explicit inclusion of G2's potential at the second lens plane is necessary in order to fit the data with astrophysically plausible galaxy parameters. Finally, we illustrate a natural consequence of a two-plane lens system, namely the prediction of distortion as well as shift and stretching of G2's isophotes by G1's potential, which can in principle be measured by subtracting out G1's light distribution in an image of high signal-to-noise ratio and good angular resolution, especially a multicolour one. [ABSTRACT FROM AUTHOR]

Numerical simulations indicate that correlations exist between the velocity distributions of stars and dark matter (DM). We study the local DM velocity distribution based on these correlations. We select K giants from LAMOST DR8 cross-matched with Gaia DR3, which have robust measurements of velocity and metallicity, and separate them into the disk, halo substructure, and isotropic halo components in the chemodynamical space utilizing the Gaussian mixture model. The substructure component is highly radially anisotropic and possibly related to the Gaia–Enceladus–Sausage (GES) merger event, while the isotropic halo component is accreted from the earliest mergers following the Maxwell–Boltzmann distribution (standard halo model [SHM]). We find that the GES-like substructure contributes ∼85% of the local nondisk stars in the solar neighborhood, which is nearly invariant when applying different volume cuts or additional angular momentum constraints. Utilizing the metallicity–stellar mass relation and the stellar mass–halo mass relation, we find that ∼ 25 − 15 + 24 % of local DM is in the kinematic substructure. Combined with the stellar distributions of nondisk components, we modify the heliocentric velocity distribution of local DM. It shifts to a lower speed with a sharper peak compared to the SHM and updates the detection limits of DM direct detection experiments. We discuss extensively the degeneracies present in the GMM fitting and propose that more kinematic and chemical information such as α abundance could help to break the degeneracy in the future. Our work confirms that the local DM velocity distribution deviates significantly from the SHM and needs to be properly accounted for in the DM detection experiments. [ABSTRACT FROM AUTHOR]

We investigate how the stellar rotational support changes as a function of spatially resolved stellar population age (⁠|$D_n4000$|⁠) and relative central stellar surface density (⁠|$\Delta \Sigma _1$|⁠) for MaNGA isolated/central disc galaxies. We find that the galaxy rotational support indicator |$\lambda _{R_\mathrm{e}}$| varies smoothly as a function of |$\Delta \Sigma _1$| and |$D_n4000$|⁠. |$D_n4000$| versus |$\Delta \Sigma _1$| follows a 'J-shape', with |$\lambda _{R_\mathrm{e}}$| contributing to the scatters. In this 'J-shaped' pattern rotational support increases with central |$D_n4000$| when |$\Delta \Sigma _1$| is low but decreases with |$\Delta \Sigma _1$| when |$\Delta \Sigma _1$| is high. Restricting attention to low- |$\Delta \Sigma _1$| (i.e. large-radius) galaxies, we suggest that the trend of increasing rotational support with |$D_n4000$| for these objects is produced by a mix of two different processes, a primary trend characterized by growth in |$\lambda _{R_\mathrm{e}}$| along with mass through gas accretion, on top of which disturbance episodes are overlaid, which reduce rotational support and trigger increased star formation. An additional finding is that star-forming galaxies with low |$\Delta \Sigma _1$| have relatively larger radii than galaxies with higher |$\Delta \Sigma _1$| at fixed stellar mass. Assuming that these relative radii rankings are preserved while galaxies are star forming then implies clear evolutionary paths in central |$D_n4000$| versus |$\Delta \Sigma _1$|⁠. The paper closes with comments on the implications that these paths have for the evolution of pseudo-bulges versus classical bulges. The utility of using |$\rm D_n4000$| – |$\Delta \Sigma _1$| to study |$\lambda _{R_\mathrm{e}}$| reinforces the notion that galaxy kinematics correlate both with structure and with stellar-population state, and indicates the importance of a multidimensional description for understanding bulge and galaxy evolution. [ABSTRACT FROM AUTHOR]

ABSTRACT The number density and clustering properties of Lyman-break galaxies (LBGs) are consistent with them being the central galaxies of the most massive dark haloes present at z ∼ 3. This conclusion holds in all currently popular hierarchical models for structure formation, and is almost independent of the global cosmological parameters. We examine whether the sizes, luminosities, kinematics and star formation rates of LBGs are also consistent with this identification. Simple formation models tuned to give good fits to low-redshift galaxies can predict the distribution of these quantities in the LBG population. The LBGs should be small (with typical half-light radii of 0.6--2 h-1kpc), should inhabit haloes of moderately high circular velocity (180--290 km s-1) but have low stellar velocity dispersions (70--120 km s-1) and should have substantial star formation rates (15--100 M⊙ yr-1). The numbers here refer to the predicted median values in the LBG sample of Adelberger et al.; the first number assumes an ω0=1 universe and the second number a flat universe with ω0=0.3. For either cosmology these predictions are consistent with the current (rather limited) observational data. Following the work of Kennicutt, we assume stars to form more rapidly in gas of higher surface density. This predicts that LBG samples should preferentially contain objects with low angular momentum, and therefore small size, for their mass. In contrast, samples of damped Ly α systems (DLSs) should be biased towards objects with large angular momentum. Bright LBGs and DLSs may therefore form distinct populations, with very different sizes and star formation rates, LBGs being smaller and more metal-rich than DLSs of similar mass and redshift. [ABSTRACT FROM AUTHOR]

Distance-redshift diagrams probe expansion history of the Universe. We show that the stellar mass-binding energy (massE) relation of galaxies proposed in our previous study offers a new distance ruler at cosmic scales. By using elliptical galaxies in the main galaxy sample of the Sloan Digital Sky Survey Data Release 7, we construct a distance-redshift diagram over the redshift range from 0.05 to 0.2 with the massE ruler. The best-fit dark energy density is 0.675 ± 0.079  for flat Λ-cold dark matter (ΛCDM) model, consistent with those by other probes. At the median redshift of 0.11, the median distance is estimated to have a fractional error of 0.34 per cent, much lower than those by supernova (SN) Ia and baryonic acoustic oscillation (BAO) and even exceeding their future capability at this redshift. The above low- |$\mathit{ z}$| measurement is useful for probing dark energy that dominates at the late Universe. For a flat dark energy equation of state model (flat w CDM), the massE alone constrains w to an error that is only a factor of 2.2, 1.7, and 1.3 times larger than those by BAO, SN Ia, and cosmic microwave background (CMB), respectively. [ABSTRACT FROM AUTHOR]

Using the final Mapping Nearby Galaxies at Apache Point Observatory sample of 10K galaxies, we investigate the dark matter (DM) fraction f DM within one half-light radius R e for about 6K galaxies with good kinematics spanning a wide range of morphologies and stellar velocity dispersion. We employ two techniques to estimate f DM: (i) Jeans anisotropic modelling (JAM), which performs DM decomposition based on stellar kinematics and (ii) comparing the total dynamical mass-to-light ratios (M / L)JAM and (M */ L)SPS from stellar population synthesis (SPS). We find that both methods consistently show a significant trend of increasing f DM with decreasing σe and low f DM at larger σe. For 235 early-type galaxies with the best models, we explore the variation of stellar initial mass function (IMF) by comparing the stellar mass-to-light ratios from JAM and SPS. We confirm that the stellar mass excess factor αIMF increases with σe, consistent with previous studies that reported a transition from Chabrier-like to Salpeter IMF among galaxies. We show that the αIMF trend cannot be driven by M */ L or IMF gradients as it persists when allowing for radial gradients in our model. We find no evidence for the total M / L increasing toward the centre. We detect weak positive correlations between αIMF and age, but no correlations with metallicity. We stack galaxy spectra according to their αIMF to search for differences in IMF-sensitive spectral features (e.g. the |$\rm Na_{\rm I}$| doublet). We only find marginal evidence for such differences, which casts doubt on the validity of one or both methods to measure the IMF. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate that stellar masses of galaxies (M star) are universally correlated through a double power-law function with the product of the dynamical velocities (V e) and sizes to one-fourth power (⁠|$R_{\rm e}^{0.25}$|⁠) of galaxies, both measured at the effective radii. The product |$V_{\rm e}R_{\rm e}^{0.25}$| represents the fourth root of the total binding energies within effective radii of galaxies. This stellar mass-binding energy correlation has an observed scatter of 0.14 dex in log(⁠|$V_{\rm e}R_{\rm e}^{0.25}$|⁠) and 0.46 dex in log(M star). It holds for a variety of galaxy types over a stellar mass range of nine orders of magnitude, with little evolution over cosmic time. A toy model of self-regulation between binding energies and supernovae feedback is shown to be able to reproduce the observed slopes, but the underlying physical mechanisms are still unclear. The correlation can be a potential distance estimator with an uncertainty of 0.2 dex independent of the galaxy type. [ABSTRACT FROM AUTHOR]

There is a population of stars with velocities in excess of 500 km s−1 relative to the Galactic center. Many, perhaps most, of these hypervelocity stars (HVSs) are B stars similar to the disk and S stars in a nuclear cluster around a supermassive black hole (SMBH) near Sgr A⋆. In Paper I of this series, we showed that the eccentricity of the stars emerged from a hypothetical disk around the SMBH that can be rapidly excited by the secular perturbation of its intermediate-mass companion (IMC), and we suggested IRS 13E as a potential candidate for the IMC. Here we show that this process leads to an influx of stars on parabolic orbits to the proximity of Sgr A⋆ on a secular timescale of a few megayears. This timescale is much shorter than the diffusion timescale into the lost cone through either the classical or the resonant relaxation. Precession of the highly eccentric stars' longitude of periastron, relative to that of the IMC, brings them to its proximity within a few megayears. The IMC's gravitational perturbation scatters a fraction of the stars from nearly parabolic to hyperbolic orbits with respect to the SMBH. Their follow-up close encounters with the SMBH induce them to escape with hypervelocity. This scenario is a variant of the hypothesis proposed by Hills based on the anticipated breakup of some progenitor binary stars in the proximity of the SMBH, and its main objective is to account for the limited life span of the known HVSs. We generalize our previous numerical simulations of this process with a much wider range of orbital configurations. We demonstrate the robustness and evaluate the efficiency of this channel of HVS formation. From these numerical simulations, we infer observable kinematic properties for the HVSs. [ABSTRACT FROM AUTHOR]

We try to understand the trends in the mass density slopes as a function of galaxy properties. We use the results from the best Jeans Anisotropic Modelling (JAM) of the integral-field stellar kinematics for near 6000 galaxies from the MaNGA DynPop project, with stellar masses |$10^9\ {\rm {\rm M}_{\odot }}\lesssim M_*\lesssim 10^{12}\ {\rm {\rm M}_{\odot }}$|⁠ , including both early-type and late-type galaxies. We use the mass-weighted density slopes for the stellar |$\overline{\gamma }_*$|⁠ , dark |$\overline{\gamma }_{_{\rm DM}}$| and total |$\overline{\gamma }_{_{\rm T}}$| mass from the MaNGA DynPop project. As previously reported, |$\overline{\gamma }_{_{\rm T}}$| approaches a constant value of |$\overline{\gamma }_{_{\rm T}}\approx 2.2$| for high σe galaxies, and flattens for |$\lg (\sigma _{\rm e}/{\rm km\ s^{-1}})\lesssim 2.3$| galaxies, reaching |$\overline{\gamma }_{_{\rm T}}\approx 1.5$| for |$\lg (\sigma _{\rm e}/{\rm km\ s^{-1}})\approx 1.8$|⁠. We find that total and stellar slopes track each other tightly, with |$\overline{\gamma }_{_{\rm T}}\approx \overline{\gamma }_*-0.174$| over the full σe range. This confirms the dominance of stellar matter within R e. We also show that there is no perfect conspiracy between baryonic and dark matter, as |$\overline{\gamma }_*$| and |$\overline{\gamma }_{_{\rm DM}}$| do not vary inversely within the σe range. We find that the central galaxies from TNG50 and TNG100 simulations do not reproduce the observed galaxy mass distribution, which we attribute to the overestimated dark matter fraction, possibly due to a constant IMF and excessive adiabatic contraction effects in the simulations. Finally, we present the stacked dark matter density profiles and show that they are slightly steeper than the pure dark matter simulation prediction of |$\overline{\gamma }_{_{\rm DM}}\approx 1$|⁠ , suggesting moderate adiabatic contraction in the central region of galaxies. Our work demonstrates the power of stellar dynamics modelling for probing the interaction between stellar and dark matter and testing galaxy formation theories. [ABSTRACT FROM AUTHOR]

There is a dense group of OB and Wolf–Rayet stars within a fraction of a parsec from the supermassive black hole (SMBH) at the Galactic Center. These stars appear to be coeval and relatively massive. A subgroup of these stars orbits on the same plane. If they emerged with low- to modest-eccentricity orbits from a common gaseous disk around the central SMBH, their inferred life span would not be sufficiently long to account for the excitation of their high orbital eccentricity through dynamical relaxation. Here we analyze the secular perturbation of Galactic Center stars by an intermediate-mass companion (IMC) as a potential mechanism to account for these young disk stars' high eccentricity. This IMC may be either an intermediate-mass black hole or a compact cluster such as IRS 13E. If its orbital angular momentum vector is antiparallel to that of the disk stars, this perturbation would be effective in exciting the eccentricity of stars with orbital precession rates that resonate with the IMC's precession rate. If it orbits around the SMBH in the same direction as the disk stars, the eccentricity of the young stars can still be highly excited by the IMC during the depletion of their natal disk, possibly associated with the launch of the Fermi bubble. In this scenario, the IMC's precession rate decreases, and its secular resonance sweeps through the proximity of the young stars. We carry out numerical simulations with various inclination angles between the orbits of the IMC and the disk stars and show that this secular interaction is a robust mechanism to excite the eccentricity and inclination of some disk stars. [ABSTRACT FROM AUTHOR]