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We analyze the dark matter (DM) halos of a sample of dwarf ellipticals (dEs) and discuss cosmological and evolutionary implications. Using orbit modeling, we recover their density slopes and, for the first time, halo flattening. We find that the "cusp-core" tension is mild; on average, dEs have central slopes slightly below the Navarro–Frenk–White predictions. However, the measured flattenings are still more spherical than cosmological simulations predict. Unlike brighter early-type galaxies, the total density slopes of dEs are shallower, and their average DM density does not follow their scaling relation with luminosity. Conversely, dE halos are denser and the densities steeper than in late-type galaxies. We find average DM density and slope are strongly correlated with the environment and moderately with the angular momentum. Central, nonrotating dEs have dense and cuspy halos, whereas rotating dEs in Virgo's outskirts are more cored and less dense. This can be explained by a delayed formation of the dEs in the cluster outskirts, or alternatively by the accumulated baryonic feedback that the dEs in the outskirts have experienced during their very different star formation history. Our results suggest halo profiles are not universal (they depend on assembly conditions) and they evolve only mildly due to internal feedback. We conclude dEs in the local Universe have assembled at a higher redshift than local spirals. In these extreme conditions, star formation and halo assembly, for example, were very different, suggesting no new dEs are formed at present. [ABSTRACT FROM AUTHOR]

We analyze the stellar structure of a sample of dwarf ellipticals (dEs) inhabiting various environments within the Virgo cluster. Integral-field observations with a high spectral resolution allow us to robustly determine their low-velocity dispersions (∼25 km s−1) and higher-order kinematic moments out to the half-light radius. We find the dEs exhibit a diversity in ages, with the younger dEs being less enhanced than the older, suggesting a complex star formation history for those dEs that recently entered Virgo, while others have been quenched shortly after reionization. Orbit-superposition modeling allowed us to recover viewing angles, stellar mass-to-light ratios (with gradients), as well as the intrinsic orbit structure. We find that the angular momentum of the dEs is strongly suppressed compared to ordinary early-type galaxies and correlates with the environment. Flattened dEs are so because of a suppressed kinetic energy perpendicular to their equatorial plane. Combining population and dynamical modeling results, we find an age-dependent stellar initial mass function or, alternatively, evidence for a more extended star formation history for those galaxies that have had higher initial mass and/or inhabited lower-density environments. dEs appear to have a spatially homogeneous stellar structure, but the state they were "frozen" in as they stopped forming stars varies dramatically according to their initial conditions. [ABSTRACT FROM AUTHOR]

RR Lyrae stars are standard candles with characteristic photometric variability and serve as powerful tracers of Galactic structure, substructure, accretion history, and dark matter content. Here we report the discovery of distant RR Lyrae stars, including some of the most distant stars known in the Milky Way halo, with Galactocentric distances of ∼300 kpc. We use time-series u * g ′ i ′ z ′ Canada–France–Hawaii Telescope/MegaCam photometry from the Next Generation Virgo Cluster Survey (NGVS). We use a template light-curve fitting method based on empirical Sloan Digital Sky Survey Stripe 82 RR Lyrae data to identify RR Lyrae candidates in the NGVS data set. We eliminate several hundred suspected quasars and identify 180 RR Lyrae candidates with heliocentric distances of ∼20–300 kpc. The halo stellar density distribution is consistent with an r −4.09±0.10 power-law radial profile over most of this distance range with no signs of a break. The distribution of ab-type RR Lyrae in a period–amplitude plot (Bailey diagram) suggests that the mean metallicity of the halo decreases outward. Compared to other recent RR Lyrae surveys, like Pan-STARRS1, the High Cadence Transient Survey, and the Dark Energy Survey, our NGVS study has better single-epoch photometric precision and a comparable number of epochs but smaller sky coverage. At large distances, our RR Lyrae sample appears to be relatively pure and complete, with well-measured periods and amplitudes. These newly discovered distant RR Lyrae stars are important additions to the few secure stellar tracers beyond 150 kpc in the Milky Way halo. [ABSTRACT FROM AUTHOR]

We study the size and structure of globular cluster (GC) systems of 118 early-type galaxies from the NGVS, MATLAS, and ACSVCS surveys. Fitting Sérsic profiles, we investigate the relationship between effective radii of GC systems (R e,gc) and galaxy properties. GC systems are 2–4 times more extended than host galaxies across the entire stellar mass range of our sample (108.3 M ⊙ < M * < 1011.6 M ⊙). The relationship between R e,gc and galaxy stellar mass exhibits a characteristic "knee" at a stellar mass of M p ≃ 1010.8, similar to the galaxy R e –stellar mass relationship. We present a new characterization of the traditional blue and red GC color subpopulations, describing them with respect to host galaxy (g ′ − i ′) color (Δgi): GCs with similar colors to their hosts have a "red" Δgi, and those significantly bluer GCs have a "blue" Δgi. The GC populations with red Δgi, even in dwarf galaxies, are twice as extended as the stars, suggesting that formation or survival mechanisms favor the outer regions. We find a tight correlation between R e,gc and the total number of GCs, with intrinsic scatter ≲0.1 dex spanning two and three orders of magnitude in size and number, respectively. This holds for both red and blue subpopulations, albeit with different slopes. Assuming that N GC,Total correlates with M 200, we find that the red GC systems have effective radii of roughly 1%–5% R 200, while the blue GC systems in massive galaxies can have sizes as large as ∼10% R 200. Environmental dependence on R e,gc is also found, with lower-density environments exhibiting more extended GC systems at fixed mass. [ABSTRACT FROM AUTHOR]

Galaxy interactions and mergers can enhance or reduce star formation, but a complete understanding of the involved processes is still lacking. The effect of dwarf galaxy mergers is even less clear than their massive counterpart. We present a study on a dwarf merger remnant in the Virgo cluster, VCC322, which might form a triple system with VCC334 and VCC319. We identify a prominent long and straight tail-like substructure that has a size comparable to its host galaxy VCC322. By comparing the color–color (g − r versus r − H) distribution with simple stellar population models, we infer that the metallicity and stellar age of this tail are Z ⋆ ∼ 0.02 Z ⊙ and t ⋆ ∼ 10 Gyr, respectively. In VCC319, we find a sign of isophotal twisting. This suggests that VCC319 may be subject to tidal interaction. An analysis of the Sloan Digital Sky Survey optical spectra of VCC322 indicates mass- and light-weighted ages of about 109.8 yr and 107.5 yr, respectively, indicating an ongoing star formation activity. However, the star formation in VCC322 seems suppressed when compared to other star-forming dwarfs of comparable stellar masses. Our finding of shock excitation of optical emission lines indicates that interaction-induced shock may contribute to the heating of cold gas and suppression of star formation. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/submillimeter Array data on the 3 mm continuum emission, CO isotopologues (12CO, 13CO, and C18O), and high-density molecular tracers (HCN, HCO+, HNC, HNCO, CS, CN, and CH3OH) in NGC 4526. These data enable a detailed study of the physical properties of the molecular gas in a longtime resident of the Virgo Cluster; comparisons to more commonly studied spiral galaxies offer intriguing hints into the processing of molecular gas in the cluster environment. Many molecular line ratios in NGC 4526, along with our inferred abundances and CO/H2 conversion factors, are similar to those found in nearby spirals. One striking exception is the very low observed 12CO/13CO(1âˆ'0) line ratio, 3.4 ± 0.3, which is unusually low for spirals though not for Virgo Cluster early-type galaxies. We carry out radiative transfer modeling of the CO isotopologues with some archival (2âˆ'1) data, and we use Bayesian analysis with Markov Chain Monte Carlo techniques to infer the physical properties of the CO-emitting gas. We find surprisingly low [12CO/13CO] abundance ratios of 7.8 âˆ' 1.5 + 2.7 and 6.5 âˆ' 1.3 + 3.0 at radii of 0.4 kpc and 1 kpc. The emission from the high-density tracers HCN, HCO+, HNC, CS, and CN is also relatively bright, and CN is unusually optically thick in the inner parts of NGC 4526. These features hint that processing in the cluster environment may have removed much of the galaxy’s relatively diffuse, optically thinner molecular gas along with its atomic gas. Angular momentum transfer to the surrounding intracluster medium may also have caused contraction of the disk, magnifying radial gradients such as we find in [13CO/C18O]. More detailed chemical evolution modeling would be interesting in order to explore whether the unusual [12CO/13CO] abundance ratio is entirely an environmental effect or whether it also reflects the relatively old stellar population in this early-type galaxy. [ABSTRACT FROM AUTHOR]

In this VERTICO early science paper we explore in detail how environmental mechanisms, identified in H i, affect the resolved properties of molecular gas reservoirs in cluster galaxies. The molecular gas is probed using ALMA ACA (+TP) observations of 12CO(2â€"1) in 51 spiral galaxies in the Virgo cluster (of which 49 are detected), all of which are included in the VIVA H i survey. The sample spans a stellar mass range of 9 ≤ log M ⋆ / M ⊙ ≤ 11. We study molecular gas radial profiles, isodensity radii, and surface densities as a function of galaxy H i deficiency and morphology. There is a weak correlation between global H i and H2 deficiencies, and resolved properties of molecular gas correlate with H i deficiency: galaxies that have large H i deficiencies have relatively steep and truncated molecular gas radial profiles, which is due to the removal of low-surface-density molecular gas on the outskirts. Therefore, while the environmental mechanisms observed in H i also affect molecular gas reservoirs, there is only a moderate reduction of the total amount of molecular gas. [ABSTRACT FROM AUTHOR]

Combining data from the ACS Virgo Cluster Survey and the Next Generation Virgo cluster Survey, we extend previous studies of color gradients of the globular cluster (GC) systems of the two most massive galaxies in the Virgo cluster, M87 and M49, to radii of ∼15 Re (∼200 kpc for M87 and ∼250 kpc for M49, where Re is the effective radius). We find significant negative color gradients, i.e., becoming bluer with increasing distance, out to these large radii. The gradients are driven mainly by the outward decrease in the ratio of red to blue GC numbers. The color gradients are also detected out to ∼15 Re in the red and blue subpopulations of GCs taken separately. In addition, we find a negative color gradient when we consider the satellite low-mass elliptical galaxies as a system, i.e., the satellite galaxies closer to the center of the host galaxy usually have redder color indices, for both their stars and their GCs. According to the "two phase" formation scenario of massive early-type galaxies, the host galaxy accretes stars and GCs from low-mass satellite galaxies in the second phase. So an accreted GC system naturally inherits the negative color gradient present in the satellite population. This can explain why the color gradient of the GC system can still be observed at large radii after multiple minor mergers. [ABSTRACT FROM AUTHOR]

We use deep Hubble Space Telescope imaging to derive a distance to the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch (TRGB) distance estimator. We detect 5023 stars within the galaxy, down to a 50% completeness limit of F814W ≈ 28.0, using counts in the surrounding field to correct for contamination due to background sources and Virgo intracluster stars. We derive an extinction-corrected F814W tip magnitude of , yielding a distance of Mpc. This places VCC 615 on the far side of the Virgo Cluster (dVirgo = 16.5 Mpc), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the main body of Virgo. Coupling this distance with the galaxy's observed radial velocity, we find that VCC 615 is on an outbound trajectory, having survived a recent passage through the inner parts of the cluster. Indeed, our orbit modeling gives a 50% chance the galaxy passed inside the Virgo core (r < 620 kpc) within the past gigayear, although very close passages directly through the cluster center (r < 200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by the Virgo cluster tides. Finally, we also describe the serendipitous discovery of a nearby Virgo dwarf galaxy projected 90″ (7.2 kpc) away from VCC 615. [ABSTRACT FROM AUTHOR]

Sharp spectral structures in the γ -ray band are an important dark matter (DM) signature. Previously, a tentative line feature at ∼43 GeV was reported in 16 nearby galaxy clusters (GCls) with 7.1 yr of Fermi Large Area Telescope (LAT) data, whose test statistic (TS) value is ∼16.7. In this work, we search for line signals and box-shaped structures using the stacked data from those 16 GCls with 11.4 yr of Fermi-LAT P8R3 data. There is still a hint at ∼42 GeV, dominated by the radiation of the Virgo and Ophiuchus clusters. Though the TS value was high up to 21.2 in 2016 October, currently it has dropped to 13.1. Moreover, the TS value at ∼42 GeV decreases to 2.4 when the EDISP2 data are excluded from the analysis. Consequently, we do not find any statistically significant line-like signal and then set up the 95% confidence level upper limits on the thermally averaged cross section of DM annihilating into double photons. The same line search has been carried out for an alternative GCl sample from the Two Micron All-Sky Survey, but no evidence has been found. We also search for box-shaped features in those 16 baseline GCls. No signal is found, and the corresponding upper limits on the annihilation cross section are given. [ABSTRACT FROM AUTHOR]

Intermediate-mass black holes (IMBHs) by definition have masses of MIMBH ∼ 102−5M⊙, a range with few observational constraints. Finding IMBHs in globular star clusters (GCs) would validate a formation channel for massive black-hole seeds in the early universe. Here, we simulate a 60 hr observation with the next-generation Very Large Array (ngVLA) of 728 GC candidates in the Virgo Cluster galaxy NGC 4472. Interpreting the radio detection thresholds as signatures of accretion onto IMBHs, we benchmark IMBH mass thresholds in three scenarios and find the following: (1) radio analogs of ESO 243-49 HLX-1, a strong IMBH candidate with in a star cluster, are easy to access in all 728 GC candidates. (2) For the 30 GC candidates with extant X-ray detections, the empirical fundamental-plane relation involving black-hole mass plus X-ray and radio luminosities suggests access to , with an uncertainty of 0.44 dex. (3) A fiducial Bondi accretion model was applied to all 728 GC candidates and to radio stacks of the GC candidates. This model suggests access to IMBH masses, with a statistical uncertainty of 0.39 dex, of for individual GC candidates, and for radio stacks of about 100–200 GC candidates. The fiducial Bondi model offers initial guidance, but is subject to additional systematic uncertainties and should be superseded by hydrodynamical simulations of gas flows in GCs. [ABSTRACT FROM AUTHOR]

We present the first results of an MMT/Hectospec campaign to measure the kinematics of globular clusters (GCs) around M49—the brightest galaxy in the Virgo galaxy cluster, which dominates the Virgo B subcluster. The data include kinematic tracers beyond 95 kpc (∼5.2 effective radii) for M49 for the first time, enabling us to achieve three key insights reported here. First, beyond ∼20′–30′ (∼100–150 kpc), the GC kinematics sampled along the minor photometric axis of M49 become increasingly hotter, indicating a transition from GCs related to M49 to those representing the Virgo B intra-cluster medium. Second, there is an anomaly in the line-of-sight radial velocity dispersion (σr,los) profile in an annulus ∼10–15′ (∼50–90 kpc) from M49 in which the kinematics cool by Δσr,los ≈ 150 km s−1 relative to those in- or outward. The kinematic fingerprint of a previous accretion event is hinted at in projected phase-space, and we isolate GCs that both give rise to this feature, and are spatially co-located with two prominent stellar shells in the halo of M49. Third, we find a subsample of GCs with velocities representative of the dwarf galaxy VCC 1249 that is currently interacting with M49. The spatial distribution of these GCs closely resembles the morphology of VCC 1249's isophotes, indicating that several of these GCs are likely in the act of being stripped from the dwarf during its passage through M49's halo. Taken together, these results point toward the opportunity of witnessing ongoing giant halo assembly in the depths of a cluster environment. [ABSTRACT FROM AUTHOR]

We investigate the cold-gas properties of massive Virgo galaxies (>109M⊙) at <3R200 (R200 is the radius where the mean interior density is 200 times the critical density) on the projected phase-space diagram with the largest archival data set to date to understand the environmental effects on galaxy evolution in the Virgo cluster. We find lower H i and H2 mass fractions and higher star formation efficiencies (SFEs) from H i and H2 in the Virgo galaxies than in the field galaxies for matched stellar masses; the Virgo galaxies generally follow the field relationships between the offset from the main sequence of the star-forming galaxies [Δ(MS)] and the gas fractions and SFEs, to the slight offset to lower gas fractions or higher SFEs compared to field galaxies at Δ(MS) < 0; lower gas fractions in galaxies with smaller clustocentric distance and velocity; and lower gas fractions in the galaxies in the W cloud, a substructure of the Virgo cluster. Our results suggest the cold-gas properties of some Virgo galaxies are affected by their environment at least at 3R200 maybe via strangulation and/or preprocesses, and H i and H2 in some galaxies are removed by ram pressure at <1.5R200. Our data cannot rule out the possibility of other processes such as strangulation and galaxy harassment accounting for gas reduction in some galaxies at <1.5R200. Future dedicated observations of a mass-limited complete sample are required for definitive conclusions. [ABSTRACT FROM AUTHOR]

Nearby massive compact elliptical galaxies (MCEGs) are strong candidates for relic galaxies (i.e., local analogs of red nuggets at high redshifts). It is expected that the globular cluster (GC) systems of relic galaxies are dominated by red (metal-rich) GCs. NGC 1277 is known as a unique example of such a galaxy in the previous study. In this study, we search for GCs in 12 nearby MCEGs at distances of ≲100 Mpc from the Hubble Space Telescope/Wide Field Camera 3 F814W(I814)/F160W(H160) archival images. We find that most of these MCEGs host a rich population of GCs with a color range of. The fractions of their red GCs range from fRGC = 0.2 to 0.7 with a mean of fRGC = 0.48 ± 0.14. We divide the MCEG sample into two groups: one in clusters and the other in groups/fields. The mean red GC fraction of the cluster MCEGs is 0.60 ± 0.06, which is 0.2 larger than the value of the group/field MCEGs, 0.40 ± 0.10. The value for the cluster MCEGs is ∼0.3 larger than the mean value of giant early-type galaxies with similar stellar mass in the Virgo Cluster (fRGC = 0.33 ± 0.13). Our results show that most of the MCEGs in our sample are indeed relic galaxies. This further implies that a majority of the red GCs in MCEGs are formed early in massive galaxies and that most MCEGs in the local universe have rarely undergone mergers after they became red nuggets about 10 Gyr ago. [ABSTRACT FROM AUTHOR]

We present a measurement of the Hubble constant H0 from surface brightness fluctuation (SBF) distances for 63 bright, mainly early-type galaxies out to 100 Mpc observed with the WFC3/IR on the Hubble Space Telescope (HST). The sample is drawn from several independent HST imaging programs using the F110W bandpass, with the majority of the galaxies being selected from the MASSIVE survey. The distances reach the Hubble flow with a median statistical uncertainty per measurement of 4%. We construct the Hubble diagram with these IR SBF distances and constrain H0 using four different treatments of the galaxy velocities. For the SBF zero-point calibration, we use both the existing tie to Cepheid variables, updated for consistency with the latest determination of the distance to the Large Magellanic Cloud from detached eclipsing binaries, and a new tie to the tip of the red giant branch (TRGB) calibrated from the maser distance to NGC 4258. These two SBF calibrations are consistent with each other and with theoretical predictions from stellar population models. From a weighted average of the Cepheid and TRGB calibrations, we derive H0 = 73.3 ± 0.7 ± 2.4 km s−1 Mpc−1, where the error bars reflect the statistical and systematic uncertainties. This result accords well with recent measurements of H0 from Type Ia supernovae, time delays in multiply lensed quasars, and water masers. The systematic uncertainty could be reduced to below 2% by calibrating the SBF method with precision TRGB distances for a statistical sample of massive early-type galaxies out to the Virgo cluster measured with the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

We present the properties of galaxies in filaments around the Virgo cluster with respect to their vertical distance from the filament spine using the NASA–Sloan Atlas catalog. The filaments are mainly composed of low-mass, blue dwarf galaxies. We observe that the g − r color of galaxies becomes blue and stellar mass decreases with increasing vertical filament distance. The galaxies were divided into higher-mass () and lower-mass () subsamples. We also examine the distributions of g − r color, stellar mass, Hα equivalent width (EW(Hα)), near-ultraviolet (NUV) − r color, and H i fraction of the two subsamples with the vertical distance. The lower-mass galaxies exhibit a negative g − r color gradient, whereas higher-mass galaxies have a flat g − r color distribution. We observe a negative EW(Hα) gradient for higher-mass galaxies, whereas lower-mass galaxies show no distinct EW(Hα) variation. In contrast, the NUV − r color distribution of higher-mass galaxies shows no strong trend, whereas the lower-mass galaxies show a negative NUV − r color gradient. We do not see clear gradients of H i fraction in either the higher- or lower-mass subsample. We propose that the negative color and stellar mass gradients of galaxies can be explained by mass assembly from past galaxy mergers at different vertical filament distances. In addition, galaxy interactions might be responsible for the contrasting features of EW(Hα) and NUV − r color distributions between the higher- and lower-mass subsamples. The distributions of H i fraction of the two subsamples suggest that the processes of ram pressure stripping and gas accretion may be ignored in the Virgo filaments. [ABSTRACT FROM AUTHOR]

Close binaries of double white dwarfs (DWDs) inspiral and merge by emitting gravitational waves (GWs). Orbital motion of some of these binaries is expected to be observed at a low-frequency band by space-borne laser interferometric detectors of GWs. The merger remnant may suffer thermonuclear runaway and explode as SNe Ia if they are massive enough. As GW sources, the remnants have so far been scarcely studied. Here we propose a new mechanism of GW emission from DWD merger remnants that may be observed by planned GW detectors in a decihertz frequency band. A remnant is temporarily expected to have a high degree of differential rotation as a consequence of the merger process. It is then unstable to oscillation modes whose azimuthal pattern speed coincides with the stellar rotation. We solve the eigenvalue problem of differentially rotating remnants and identify unstable eigenmodes, which may be categorized to inertial modes. The estimate of characteristic strain of GWs shows that they may be detectable within the distance of the Virgo cluster by planned gravitational wave observatories targeting the decihertz band. [ABSTRACT FROM AUTHOR]

An independent determination of H0 is crucial given the growing tension between the Hubble constant, H0, derived locally and that determined from the modeling of the cosmic microwave background (CMB) originating in the early universe. In this work, we present a new determination of H0 using velocities and tip of the red giant branch (TRGB) distances to 33 galaxies located between the Local Group and the Virgo cluster. We use a model of the infall pattern of the local Hubble flow modified by the Virgo mass, which is given as a function of the cosmological constants (H0, ΩΛ), the radius of the zero-velocity surface R0, and the intrinsic velocity dispersion, σv. Fitting velocities and TRGB distances of 33 galaxies to the model, we obtain H0 = 65.8 ± 3.5 (stat) ± 2.4 (sys) km s−1 Mpc−1 and R0 = 6.76 ± 0.35 Mpc. Our local H0 is consistent with the global H0 determined from CMB radiation, showing no tension. In addition, we present new TRGB distances to NGC 4437 and NGC 4592, which are located near the zero-velocity surface: D = 9.28 ± 0.39 Mpc and D = 9.07 ± 0.27 Mpc, respectively. Their spatial separation is 0.29 Mpc, suggesting that they form a physical pair. [ABSTRACT FROM AUTHOR]

High-resolution (1″ × 2″) Atacama Large Millimeter Array CO(2−1) observations of the ram pressure stripped galaxy NGC 4402 in the Virgo cluster show some of the clearest evidence yet for the impacts of ram pressure on the molecular interstellar medium (ISM) of a galaxy. The eastern side of the galaxy at r ∼ 4.5 kpc, upon which ram pressure is incident, has a large (width ∼1 kpc, height ∼1 kpc above the disk midplane) extraplanar plume of molecular gas and dust. Molecular gas in the plume region shows distinct noncircular motions in the direction of the ram pressure; the kinematic offset of up to 60 km s−1 is consistent with acceleration by ram pressure. We also detect a small amount of gas in clouds below the plume that are spatially and kinematically distinct from the surrounding medium, and appear to be decoupled from the stripped ISM. We propose that diffuse molecular gas is directly stripped but giant molecular cloud (GMC) density gas is not directly stripped, and so decouples from lower density stripped gas. However, GMCs become effectively stripped on short timescales. We also find morphological and kinematic signatures of ram pressure compression of molecular gas in a region of intense star formation on the leading side at r ∼ 3.5 kpc. We propose that the compressed and stripped zones represent different evolutionary stages of the ram pressure interaction, and that feedback from star formation in the compressed zone facilitates the effective stripping of GMCs by making the gas cycle rapidly to a lower density diffuse state. [ABSTRACT FROM AUTHOR]

We have carried out a search for substructure within the globular cluster (GC) systems of M84 (NGC 4374) and M86 (NGC 4406), two giant elliptical galaxies in the Virgo Cluster. We use wide-field (36′ × 36′), multicolor broadband imaging to identify GC candidates in these two galaxies, as well as several other nearby lower-mass galaxies. Our analysis of the spatial locations of the GC candidates reveals several substructures, including a peak in the projected number density of GCs in M86 that is offset from the system center and may be at least partly due to the presence of the dwarf elliptical galaxy NGC 4406B, a bridge that connects the M84 and M86 GC systems, and a boxy isodensity contour along the southeast side of the M86 GC system. We divide our sample into red (metal-rich) and blue (metal-poor) GC candidates to look for differences in the spatial distributions of the two populations and find that the blue cluster candidates are the dominant population in each of the substructures we identify. We also incorporate the measurements from two radial velocity surveys of the GCs in the region and find that the bridge substructure is populated by GCs with a mix of velocities that are consistent with either M86 and M84, possibly providing further evidence for interaction signatures between the two galaxies. [ABSTRACT FROM AUTHOR]

We present a study of ultra-diffuse galaxies (UDGs) in the Virgo Cluster based on deep imaging from the Next Generation Virgo Cluster Survey. Applying a new definition for the UDG class based on galaxy scaling relations, we define samples of 44 and 26 UDGs using expansive and restrictive selection criteria, respectively. Our UDG sample includes objects that are significantly fainter than previously known UDGs: i.e., more than half are fainter than mag arcsec−2. The UDGs in Virgo's core region show some evidence for being structurally distinct from "normal" dwarf galaxies, but this separation disappears when considering the full sample of galaxies throughout the cluster. UDGs are more centrally concentrated in their spatial distribution than other Virgo galaxies of similar luminosity, while their morphologies demonstrate that at least some UDGs owe their diffuse nature to physical processes—such as tidal interactions or low-mass mergers—that are at play within the cluster environment. The globular cluster (GC) systems of Virgo UDGs have a wide range in specific frequency (SN), with a higher mean SN than "normal" Virgo dwarfs, but a lower mean SN than Coma UDGs at fixed luminosity. Their GCs are predominantly blue, with a small contribution from red clusters in the more massive UDGs. The combined GC luminosity function is consistent with those observed in dwarf galaxies, showing no evidence of being anomalously luminous. The diversity in their morphologies and their GC properties suggests no single process has given rise to all objects within the UDG class. Based on the available evidence, we conclude that UDGs are simply those systems that occupy the extended tails of the galaxy size and surface brightness distributions. [ABSTRACT FROM AUTHOR]

The fraction of star-forming to quiescent dwarf galaxies varies from almost infinity in the field to zero in the centers of rich galaxy clusters. What is causing this pronounced morphology-density relation? What do quiescent dwarf galaxies look like when studied in detail, and what conclusions can be drawn about their formation mechanism? Here we study a nearly magnitude-complete sample (–19 < Mr < –16 mag) of 121 Virgo cluster early types with deep near-infrared images from the SMAKCED project. We fit two-dimensional models with optional inner and outer components, as well as bar and lens components (in ∼15% of the galaxies), to the galaxy images. While a single Sérsic function may approximate the overall galaxy structure, it does not entirely capture the light distribution of two-thirds of our galaxies, for which multicomponent models provide a better fit. This fraction of complex galaxies shows a strong dependence on luminosity, being larger for brighter objects. We analyze the global and component-specific photometric scaling relations of early-type dwarf galaxies and discuss similarities with bright early and late types. The dwarfs' global galaxy parameters show scaling relations that are similar to those of bright disk galaxies. The inner components are mostly fitted with Sérsic n values close to 1. At a given magnitude, they are systematically larger than the bulges of spirals, suggesting that they are not ordinary bulges. We argue that the multicomponent structures in early-type dwarfs are mostly a phenomenon inherent to the disks and may indeed stem from environmental processing. [ABSTRACT FROM AUTHOR]

We measured the tip of the red giant branch distances to nine galaxies in the direction to the Virgo cluster using the Advanced Camera for Surveys on the Hubble Space Telescope. These distances put seven galaxies (GR 34, UGC 7512, NGC 4517, IC 3583, NGC 4600, VCC 2037, and KDG 215) in front of Virgo and two galaxies (IC 3023 and KDG 177) likely inside the cluster. Distances and radial velocities of the galaxies situated between us and the Virgo core clearly exhibit the infall phenomenon toward the cluster. In the case of spherically symmetric radial infall, we estimate the radius of the “zero-velocity surface” to be (7.2 ± 0.7) Mpc, which yields a total mass of the Virgo cluster of (8.0 ± 2.3) × 1014M☼, in good agreement with its virial mass estimates. We conclude that the Virgo outskirts do not contain significant amounts of dark matter beyond their virial radius. [ABSTRACT FROM AUTHOR]

We revisit the color-magnitude relation of Virgo Cluster early-type galaxies in order to explore its alleged nonlinearity. To this aim, we reanalyze the relation already published from data obtained within the ACS Virgo Cluster Survey of the Hubble Space Telescope and perform our own photometry and analysis of the images of 100 early-type galaxies observed as part of this survey. In addition, we compare our results with those reported in the literature from data of the Sloan Digital Sky Survey. We have found that when the brightest galaxies and untypical systems are excluded from the sample, a linear relation arises in agreement with what is observed in other groups and clusters. The central regions of the brightest galaxies also follow this relation. In addition, we notice that Virgo contains at least four compact elliptical galaxies besides the well-known object VCC 1297 (NGC 4486B). Their locations in the {μeff}-luminosity diagram define a trend different from that followed by normal early-type dwarf galaxies, setting an upper limit in effective surface brightness and a lower limit in the effective radius for their luminosities. Based on the distribution of different galaxy sub-samples in the color-magnitude and {μeff}-luminosity diagrams, we draw some conclusions on their formation and the history of their evolution. [ABSTRACT FROM AUTHOR]

We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation (ϵ > 0.2) and intermediate to high luminosities (Mz < -19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, wealso find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and that the present-day major axis is an indicator of the preferred merging axis. [ABSTRACT FROM AUTHOR]

We present deep color–magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Over density (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g ≈ 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1+1.0 −1.1 Gyr, a median abundance of [Fe/H] = –0.70+0.15 –0.20 dex, and a heliocentric distance of 30.9 ± 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields (Λ⊙ ≈ 265◦, B⊙ ≈ 13◦) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ∼8.2 Gyr, and an abundance of [Fe/H]=–0.67+0.16 −0.12 dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0±1.5 Gyr). They also agree with the peak in the metallicity distribution of 2–3 Gyr old Mg iants, [Fe/H]≈ –0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law & Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at ∼9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42–53 kpc. At best there is only marginal evidence for the presence of these populations in our data. Our findings then suggest that while there are probably some Sgr debris stars present, the dominant stellar population in the VOD originates from a different halo structure that has an almost identical age and metallicity as some sections of the Sgr tidal stream. [ABSTRACT FROM AUTHOR]

We present a multi-wavelength study of the emission-line nebulae located ~38" (3 kpc in projection) southeast of the nucleus of M87, the central dominant galaxy of the Virgo Cluster. We report the detection of far-infrared (FIR) [Cii] line emission at 158μm from the nebulae using observations made with the Herschel Photodetector Array Camera and Spectrometer (PACS). The infrared line emission is extended and co-spatial with optical Hα+ [Nii], far-ultraviolet C iv lines, and soft X-ray emission. The filamentary nebulae evidently containmulti-phase material spanning a temperature range of at least five orders of magnitude, from ~100 K to ~107 K. This material has most likely been uplifted by the active galactic nucleus from the center of M87. The thermal pressure of the 104 K phase appears to be significantly lower than that of the surrounding hot intraclustermedium (ICM), indicating the presence of additional turbulent and magnetic pressure in the filaments. If the turbulence in the filaments is subsonic then themagnetic field strength required to balance the pressure of the surrounding ICM is B ~ 30-70 μG. The spectral properties of the soft X-ray emission from the filaments indicate that it is due to thermal plasma with kT ~ 0.5-1 keV, which is cooling by mixing with the cold gas and/or radiatively. Charge exchange can be ruled out as a significant source of soft X-rays. Both cooling and mixing scenarios predict gas with a range of temperatures. This is at first glance inconsistent with the apparent lack of X-ray emitting gas with κT < 0.5 keV. However, we show that the missing very soft X-ray emission could be absorbed by the cold gas in the filaments with an integrated hydrogen column density of NH ~ 1.6 ×1021 cm-2, providing a natural explanation for the apparent temperature floor to the X-ray emission at κT ~ 0.5 keV. The FIR through ultraviolet line emission is most likely primarily powered by the ICM particles penetrating the cold gas following a shearing induced mixing process. An additional source of energy may, in principle, be provided by X-ray photoionization from cooling X-ray emitting plasma. The relatively small line ratio of [O i]/[C ii] < 7.2 indicates a large optical depth in the FIR lines. The large optical depth in the FIR lines and the intrinsic absorption inferred from the X-ray and optical data imply significant reservoirs of cold atomic and molecular gas distributed in filaments with small volume filling fraction, but large area covering factor. [ABSTRACT FROM AUTHOR]

The final stages of mass assembly of present-day massive galaxies are expected to occur through the accretion of multiple satellites. Cosmological simulations thus predict a high frequency of stellar streams resulting from this mass accretion around the massive galaxies in the Local Volume. Such tidal streams are difficult to observe, especially in dense cluster environments, where they are readily destroyed. We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird telescope. Using the deeper, higher-resolution, and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low surface brightness features and investigate their origin. The likely progenitors of the structures were identified as either already cataloged Virgo Cluster Catalog dwarfs or newly discovered satellites caught in the act of being destroyed. They have the same g -- i color index and likely contain similar stellar populations. The alignment of three dwarfs along an apparently single stream is intriguing, and we cannot totally exclude that these are second-generation dwarf galaxies being born inside the filament from the debris of an original dwarf. The observed complex structures, including in particular a stream apparently emanating from a satellite of a satellite, point to a high rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster where NGC 4216 is located. We discuss the age of the interactions and whether they occurred in a group that is just falling into the cluster and shows signs of the so-called pre-processing before it gets affected by the cluster environment, or in a group which already ventured toward the central regions of Virgo Cluster. In any case, compared to the other spiral galaxies in the Virgo Cluster, but also to those located in lower density environments, NGC 4216 seems to suffer an unusually heavy bombardment. Further studies will be needed to determine whether, given the surface brightness limit of our survey, about 29 mag arcsec-2, the number of observed streams around that galaxy is as predicted by cosmological simulations or conversely, whether the possible lack of similar structures in other galaxies poses a challenge to the merger-based model of galaxy mass assembly. [ABSTRACT FROM AUTHOR]

We use deep Hubble Space Telescope Wide Field Camera 3 near-infrared imaging obtained of the GOODS- Southfield as part of the CANDELS survey to investigate a stellar mass-limited sample of quiescent galaxies at 1.5 < z < 2.5. We measure surface brightness profiles for these galaxies using a method that properly measures low surface brightness flux at large radii. We find that quiescent galaxies at z ~ 2 very closely follow Sérsic profiles, with nmedian = 3.7, and have no excess flux at large radii. Their effective radii are a factor of ~4 smaller than those of low-redshift quiescent galaxies of similar mass. However, there is a significant spread in sizes (σ ... = 0.24), with the largest z ~ 2 galaxies lying close to the z = 0 mass-size relation. We compare the stellar mass surface density profiles with those of massive elliptical galaxies in the Virgo Cluster and confirm that most of the mass growth which occurs between z ~ 2 and z = 0 must be due to accretion of material onto the outer regions of the galaxies. Additionally, we investigate the evolution in the size distribution of massive quiescent galaxies. We find that the minimum size growth required for z ~ 2 quiescent galaxies to fall within the z = 0 size distribution is a factor of ~2 smaller than the total median size growth between z ~ 2 and z = 0. [ABSTRACT FROM AUTHOR]

We complete our census of low-level nuclear activity in Virgo Cluster early-type galaxies by searching for obscured emission using Spitzer Space Telescope mid-infrared (MIR) imaging at 24 µm. Of a total sample of 95 early-type galaxies, 53 objects are detected, including 16 showing kiloparsec-scale dust in optical images. One-dimensional and two-dimensional surface photometry of the 37 detections without extended dust features reveals that the MIR light is more centrally concentrated than the optical light as traced by Hubble Space Telescope F850LP-band images. No such modeling was performed for the sources with dust detected in the optical images. We explore several possible sources of the MIR excess emission, including obscured nuclear emission. We find that radial metallicity gradients in the stellar population appear to be a natural and most likely explanation for the observed behavior in a majority of the sources. Alternatively, if the concentrated MIR emission were due to nuclear activity, it would imply a MIR-to-X luminosity ratio ~5-10 for the low-luminosity active galactic nucleus (AGN) detected in X-rays by our survey. This ratio is an order of magnitude larger than that of typical low-luminosity AGNs and would imply an unusual spectral energy distribution. We conclude that the black holes found by our survey in quiescent early-type galaxies in Virgo have low bolometric Eddington ratios arising from low accretion rates and/or highly radiatively inefficient accretion. [ABSTRACT FROM AUTHOR]

We present 3.6 and 4.5 μm Spitzer Infrared Array Camera (IRAC) imaging over 0.77 deg² at the Virgo cluster core for the purpose of understanding the formation mechanisms of the low surface brightness intracluster light (ICL) features. Instrumental and astrophysical backgrounds that are hundreds of times higher than the signal were carefully characterized and removed. We examine ICL plumes as well as the outer halo of the giant elliptical M87. For two ICL plumes, we use optical colors to constrain their ages to be greater than 3 and 5 Gyr, respectively. Upper limits on the IRAC fluxes constrain the upper limits to the masses, and optical detections constrain the lower limits to the masses. In this first measurement of mass of ICL plumes we find masses in the range of 5.5 × 108 – 4.5 × 109 and 2.1 × 108-1.5 × 109 M ☉ for the two plumes for which we have coverage. Given their expected short lifetimes, and a constant production rate for these types of streams, integrated over Virgo's lifetime, they can account for the total ICL content of the cluster, implying that we do not need to invoke ICL formation mechanisms other than gravitational mechanisms leading to bright plumes. We also examined the outer halo of the giant elliptical M87. The color profile from the inner to outer halo of M87 (160 kpc) is consistent with either a flat or optically blue gradient, where a blue gradient could be due to younger or lower metallicity stars at larger radii. The similarity of the age predicted by both the infrared and optical colors (> a few gigayears) indicates that the optical measurements are not strongly affected by dust extinction. [ABSTRACT FROM AUTHOR]

Screened modified gravity (SMG) is a unified theoretical framework that describes scalar–tensor gravity with a screening mechanism. Based on the gravitational-wave (GW) waveform derived in our previous work, in this article we investigate the potential constraints on SMG theory through GW observation by future spaceborne GW detectors, including the Laser Interferometer Space Antenna (LISA), TianQin, and Taiji. We find that, for the extreme-mass-ratio inspirals (EMRIs) consisting of a massive black hole and a neutron star, if the EMRIs are at the Virgo cluster, the GW signals can be detected by the detectors at quite high significance level, and the screened parameter ϵNS can be constrained at about , which is more than one order of magnitude tighter than the potential constraint given by a ground-based Einstein telescope. However, for the EMRIs consisting of a massive black hole and a white dwarf, it is more difficult to detect them than in the previous case. For the specific SMG models, including chameleon, symmetron, and dilaton, we find these constraints are complementary to that from the Cassini experiment, but weaker than those from lunar laser ranging observations and binary pulsars, due to the strong gravitational potentials on the surface of neutron stars. By analyzing the deviation of the GW waveform in SMG from that in general relativity, as anticipated, we find the dominant contribution of the SMG constraint comes from the correction terms in the GW phases, rather than the extra polarization modes or the correction terms in the GW amplitudes. [ABSTRACT FROM AUTHOR]

The Next Generation Virgo Cluster Survey (NGVS) was designed to provide a deep census of baryonic structures in the Virgo cluster. The survey covers the 104 deg2 area from the core of Virgo out to one virial radius, in the u*griz bandpasses, to a point-source depth of g ∼ 25.9 mag (10σ) and a single pixel surface brightness limit of μg ∼ 29 mag arcsec−2 (2σ above the sky). Here we present the final catalog of 404 Virgo galaxies located within a 3.71 deg2 (0.3 Mpc2) region centered on M87, Virgo’s dominant galaxy. Of these, 154 were previously uncataloged and span the range 17.8 mag < g < 23.7 mag (−13.4 mag < Mg < −7.4 mag at the 16.5 Mpc distance of Virgo). Extensive simulations show that the NGVS catalog is complete down to g = 18.6 mag (Mg = −12.5 mag, corresponding to a stellar mass for an old stellar population), and 50% complete at g = 22.0 mag (Mg = −9.1 mag, ). The NGVS 50% completeness limit is 3 mag deeper than that of the Virgo Cluster Catalog (VCC), which has served as Virgo’s reference standard for over a quarter century, and 2 mag deeper than the VCC detection limit. We discuss the procedure adopted for the identification of objects and the criteria used to assess cluster membership. For each of the 404 galaxies in the NGVS Virgo Cluster core catalog, we present photometric and structural parameters based on a nonparametric curve-of-growth and isophotal analysis, as well as parametric (Sérsic, double-Sérsic, and/or core-Sérsic) fits to the one-dimensional surface brightness profiles and two-dimensional light distributions. [ABSTRACT FROM AUTHOR]

A fraction of dwarf galaxies in the Virgo Cluster contain disk features like bars and spiral arms. Using N-body simulations, we investigate the effects of tidal forces on the formation of such disk features in disk dwarf galaxies resembling VCC 856. We consider eight cluster–galaxy models in which disk dwarf galaxies with differing pericenter distance and spin orientation experience the tidal gravitational force of a Virgo-like Navarro–Frenk–White halo, as well as an additional eight galaxy–galaxy models in which two dwarf galaxies undergo tidal interactions with different strength. We find that the cluster tidal effect is moderate owing to the small galaxy size, making the bars form earlier by ∼1–1.5 Gyr compared to the cases in isolation. While the galactic halos significantly lose their mass within the virial radius due to the cluster tidal force, the mass of the stellar disks is nearly unchanged, suggesting that the inner regions of a disk–halo system are secured from the tidal force. The tidal forcing from either the cluster potential or a companion galaxy triggers the formation of two-armed spirals at early time before a bar develops. The tidally driven arms decay and wind with time, suggesting that they are kinematic density waves. In terms of the strength and pitch angle, the faint arms in VCC 856 are best matched with the arms in a marginally unstable galaxy produced by a distant tidal encounter with its neighbor ∼0.85 Gyr ago. [ABSTRACT FROM AUTHOR]

The occurrence of planetary nebulae (PNe) in globular clusters (GCs) provides an excellent chance to study low-mass stellar evolution in a special (low-metallicity, high stellar density) environment. We report a systematic spectroscopic survey for the [O iii] 5007 Å emission line of PNe in 1469 Virgo GCs and 121 Virgo ultra-compact dwarfs (UCDs), mainly hosted in the giant elliptical galaxies M87, M49, M86, and M84. We detected zero PNe in our UCD sample and discovered one PN () associated with an M87 GC. We used the [O iii] detection limit for each GC to estimate the luminosity-specific frequency of PNe, α, and measured α in the Virgo cluster GCs to be . The value of α in the Virgo GCs is among the lowest reported in any environment, due in part to the large sample size, and it is 5–6 times lower than that for the Galactic GCs. We suggest that α decreases toward brighter and more massive clusters, sharing a similar trend as the binary fraction, and the discrepancy between the Virgo and Galactic GCs can be explained by the observational bias in extragalactic surveys toward brighter GCs. This low but nonzero efficiency in forming PNe may highlight the important role played by binary interactions in forming PNe in GCs. We argue that a future survey of less massive Virgo GCs will be able to determine whether PN production in the Virgo GCs is governed by an internal process (mass, density, binary fraction) or if it is largely regulated by the external environment. [ABSTRACT FROM AUTHOR]

Observations indicate that nearly all galaxies contain supermassive black holes at their centers. When galaxies merge, their component black holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays. We have searched the North American Nanohertz Observatory for Gravitational Waves 11 yr data set for GWs from individual SMBHBs in circular orbits. As we did not find strong evidence for GWs in our data, we placed 95% upper limits on the strength of GWs from such sources. At = 8 nHz, we placed a sky-averaged upper limit of h0 < 7.3(3) × 10−15. We also developed a technique to determine the significance of a particular signal in each pulsar using “dropout” parameters as a way of identifying spurious signals. From these upper limits, we ruled out SMBHBs emitting GWs with = 8 nHz within 120 Mpc for , and within 5.5 Gpc for at our most sensitive sky location. We also determined that there are no SMBHBs with emitting GWs with = 2.8–317.8 nHz in the Virgo Cluster. Finally, we compared our strain upper limits to simulated populations of SMBHBs, based on galaxies in the Two Micron All-Sky Survey and merger rates from the Illustris cosmological simulation project, and found that only 34 out of 75,000 realizations of the local universe contained a detectable source. [ABSTRACT FROM AUTHOR]

Cosmicflows-3 distances and inferred peculiar velocities of galaxies have permitted the reconstruction of the structure of overdensities and underdensities within the volume extending to 0.05c. This study focuses on the underdense regions, particularly the Local Void that lies largely in the zone of obscuration and consequently has received limited attention. Major overdense structures that bound the Local Void are the Perseus-Pisces and Norma-Pavo-Indus filaments separated by 8500 km s−1. The void network of the universe is interconnected and void passages are found from the Local Void to the adjacent very large Hercules and Sculptor voids. Minor filaments course through voids. A particularly interesting example connects the Virgo and Perseus clusters, with several substantial galaxies found along the chain in the depths of the Local Void. The Local Void has a substantial dynamical effect, causing a deviant motion of the Local Group of 200–250 km s−1. The combined perturbations due to repulsion from the Local Void and attraction toward the Virgo Cluster account for ∼50% of the motion of the Local Group in the rest frame given by the cosmic microwave background. [ABSTRACT FROM AUTHOR]

The presence of blue cores in some dwarf early-type galaxies (dEs) in galaxy clusters suggests the scenario of late-type galaxy infall and subsequent transformation into red, quiescent dEs. We present Gemini Multi-Object Spectrograph long-slit spectroscopy of two dEs with blue cores (dE(bc)s), EVCC 591 and EVCC 516, located at the core and outskirts of the Virgo cluster, respectively. We obtained their internal kinematics along the major axis out to at least ∼1 effective radius. The EVCC 591 shows evidence of a kinematically decoupled core (KDC) with a size of 2″ (160 pc), exhibiting an inverted pattern for velocity with respect to the main body of its host galaxy. The rotation curve of the stellar component in the inner region of EVCC 591 is steeper than that in the rest of the galaxy. On the other hand, the overall velocity profiles of the stellar and ionized gas components of EVCC 516 show no signature of significant rotation. The occurrence of a KDC and zero rotation in the internal kinematics along with the central star formation support the scenario of gas-rich dwarf–dwarf mergers in the formation of these two dE(bc)s. Furthermore, evolution of dE(bc)s in a cluster environment into ordinary dEs with KDCs is possible based on their structural properties. We suggest that at least some of the dE(bc)s in the Virgo cluster were formed through dwarf–dwarf mergers in lower-density environments before they subsequently fell into the cluster; they were then quenched by subsequent effects within the cluster environment. [ABSTRACT FROM AUTHOR]

Using deep, high-resolution optical imaging from the Next Generation Virgo Cluster Survey, we study the properties of nuclear star clusters (NSCs) in a sample of nearly 400 quiescent galaxies in the core of Virgo with stellar masses 105 ≲ / ≲ 1012. The nucleation fraction reaches a peak value fn ≈ 90% for ≈ 109 galaxies and declines for both higher and lower masses, but nuclei populate galaxies as small as ≈ 5 × 105 . Comparison with literature data for nearby groups and clusters shows that at the low-mass end nucleation is more frequent in denser environments. The NSC mass function peaks at MNSC ≈ 7 × 105 , a factor 3–4 times larger than the turnover mass for globular clusters (GCs). We find a nonlinear relation between the stellar masses of NSCs and those of their host galaxies, with a mean nucleus-to-galaxy mass ratio that drops to MNSC/M⋆ ≈ 3.6 × 10−3 for ≈ 5 × 109 galaxies. Nuclei in both more and less massive galaxies are much more prominent: at the low-mass end, where nuclei are nearly 50% as massive as their hosts. We measure an intrinsic scatter in NSC masses at a fixed galaxy stellar mass of 0.4 dex, which we interpret as evidence that the process of NSC growth is significantly stochastic. At low galaxy masses we find a close connection between NSCs and GC systems, including very similar occupation distributions and comparable total masses. We discuss these results in the context of current dissipative and dissipationless models of NSC formation. [ABSTRACT FROM AUTHOR]

Based on archival Chandra observations with a total exposure of 1.3 Ms, we study X-ray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intracluster X-ray source populations. We detect 1177 point sources out to a projected radius of ∼30 arcmin (∼180 kpc) from the cluster center and down to a limiting 0.5–8 keV luminosity of ∼3 × 1037 erg s−1. We construct the source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultra-compact dwarfs, and galactic nuclei. From this profile we statistically identify ∼183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at the ≳2σ level (with a maximum of 3.6σ) outside three effective radii of the central giant elliptical, NGC 1399. The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources (presumably low-mass X-ray binaries (LMXBs)), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC 1399 and/or the diffuse intracluster light, thus providing strong evidence for the presence of intracluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed. [ABSTRACT FROM AUTHOR]

The globular cluster (GC) specific frequency (SN), defined as the number of GCs per unit galactic luminosity, represents the efficiency of GC formation (and survival) compared to field stars. Despite the naive expectation that star cluster formation should scale directly with star formation, this efficiency varies widely across galaxies. To explore this variation, we measure the z-band GC specific frequency () for 43 early-type galaxies (ETGs) from the Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) Fornax Cluster Survey. Combined with the homogeneous measurements of in 100 ETGs from the HST/ACS Virgo Cluster Survey from Peng et al., we investigate the dependence of on mass and environment over a range of galaxy properties. We find that behaves similarly in the two galaxy clusters, despite the clusters’ order-of-magnitude difference in mass density. The is low in intermediate-mass ETGs (−20 < Mz < −23) and increases with galaxy luminosity. It is elevated at low masses, on average, but with a large scatter driven by galaxies in dense environments. The densest environments with the strongest tidal forces appear to strip the GC systems of low-mass galaxies. However, in low-mass galaxies that are not in strong tidal fields, denser environments correlate with enhanced GC formation efficiencies. Normalizing by inferred halo masses, the GC mass fraction, η = (3.36 ± 0.2) × 10−5, is constant for ETGs with stellar masses , in agreement with previous studies. The lack of correlation between the fraction of GCs and the nuclear light implies only a weak link between the infall of GCs and the formation of nuclei. [ABSTRACT FROM AUTHOR]

We characterize the incidence and intensity of low-level supermassive black hole activity within the Fornax cluster, through X-ray observations of the nuclei of 29 quiescent early-type galaxies. Using the Chandra X-ray Telescope, we target 17 galaxies from the Hubble Space Telescope Fornax Cluster Survey, down to a uniform (3σ) limiting X-ray luminosity threshold of 5 · 1038 erg s−1, which we combine with deeper, archival observations for an additional 12 galaxies. A nuclear X-ray point source is detected in 11 out of 29 targets. After accounting for the low-mass X-ray binary contamination to the nuclear X-ray signal, the X-ray active fraction is measured at 26.6% ± 9.6%. The results from this analysis are compared to similar investigations targeting quiescent early types in the Virgo cluster, as well as the field. After correcting for the different mass distributions, the measured Fornax active fraction is less than the field fraction, at more than 3σ, confirming that the funneling of gas to the nuclear regions of cluster members is inhibited compared to those galaxies in the field. At the same time, we find no statistically significant difference between Fornax and Virgo galaxies, with only marginal evidence for a lower active fraction in Fornax (1σ); if real, owing to Fornax's higher galaxy number density, this could indicate that galaxy–galaxy interactions are more effective at gas removal than galaxy-gas effects. [ABSTRACT FROM AUTHOR]

Intracluster (IC) populations are expected to be a natural result of the hierarchical assembly of clusters, yet their low space densities make them difficult to detect and study. We present the first definitive kinematic detection of an IC population of globular clusters (GCs) in the Virgo cluster, around the central galaxy M87. This study focuses on the Virgo core, for which the combination of Next Generation Virgo Cluster Survey photometry and follow-up spectroscopy allows us to reject foreground star contamination and explore GC kinematics over the full Virgo dynamical range. The GC kinematics changes gradually with galactocentric distance, decreasing in mean velocity and increasing in velocity dispersion, eventually becoming indistinguishable from the kinematics of Virgo dwarf galaxies at R > 320 kpc. By kinematically tagging M87 halo and intracluster GCs, we find that (1) the M87 halo has a smaller fraction (52 ± 3%) of blue clusters with respect to the IC counterpart (77 ± 10%), (2) the (g′−r′)0 versus (i′−z′)0 color–color diagrams reveal a galaxy population that is redder than the IC population, which may be due to a different composition in chemical abundance and progenitor mass, and (3) the ICGC distribution is shallower and more extended than the M87 GCs, yet still centrally concentrated. The ICGC specific frequency, SN,ICL = 10.2 ± 4.8, is consistent with what is observed for the population of quenched, low-mass galaxies within 1 Mpc from the cluster’s center. The IC population at Virgo’s center is thus consistent with being an accreted component from low-mass galaxies tidally stripped or disrupted through interactions, with a total mass of . [ABSTRACT FROM AUTHOR]

We present a study of X-ray source populations in M87, the cD galaxy of the Virgo cluster, using 12 archival Chandra observations with a total exposure of ∼680 ks spanning about a decade. A total of 346 point-like sources are detected down to a limiting 0.5–8 keV luminosity of 4 × 1037 erg s−1 and out to a galactocentric radius of ∼40 kpc. We cross-correlate the X-ray sources with published catalogs of globular clusters (GCs), derived from the ACS Virgo Cluster Survey and the Next Generation Virgo Cluster Survey. This results in 122 matches, making it one of the largest samples of GC-hosting X-ray sources in an external galaxy. These sources, most likely low-mass X-ray binaries (LMXBs), correspond to ∼5% of all known GCs within the Chandra field-of-view. Conversely, ∼50% of the detected X-ray sources are found in a GC. Moreover, red (metal-rich) GCs are ∼2.2 times more likely to host an X-ray source than blue (metal-poor) GCs. We also examine 76 currently known ultra-compact dwarf galaxies around M87 but find no significant X-ray counterparts. After statistically accounting for the cosmic X-ray background, we identify ∼110 field-LMXBs. The GC-LMXBs and field-LMXBs differ in their luminosity function and radial distribution, which indicates that the latter cannot be primarily originated from GCs. Using another set of deep Chandra observations toward ∼100 kpc northwest of the M87 center, we statistically constrain the abundance of field-LMXBs in the stellar halo, which is consistent with that found in the central region. We also identify 40 variable X-ray sources, among which one source is likely a black hole binary residing in a GC. [ABSTRACT FROM AUTHOR]

We present a vestige of the linear tidal influence on the spin orientations of the constituent galaxies of the WM sheet discovered in the vicinity of the Virgo Cluster and the Local Void. The WM sheet is chosen as an optimal target since it has a rectangular parallelepiped-like shape whose three sides are in parallel with the supergalactic Cartesian axes. Determining three probability density functions of the absolute values of the supergalactic Cartesian components of the spin vectors of the WM sheet galaxies, we investigate their alignments with the principal directions of the surrounding large-scale tidal field. When the WM sheet galaxies located in the central region within the distance of 2 h−1 Mpc are excluded, the spin vectors of the remaining WM sheet galaxies are found to be weakly aligned, strongly aligned, and strongly anti-aligned with the minor, intermediate, and major principal directions of the surrounding large-scale tidal field, respectively. To examine whether or not the origin of the observed alignment tendency from the WM sheet is the linear tidal effect, we infer the eigenvalues of the linear tidal tensor from the axial ratios of the WM sheet with the help of the Zeldovich approximation and conduct a full analytic evaluation of the prediction of the linear tidal torque model for the three probability density functions. A detailed comparison between the analytical and the observational results reveals a good quantitative agreement not only in the behaviors but also in the amplitudes of the three probability density functions. [ABSTRACT FROM AUTHOR]

Tip of the red giant branch distances are acquired from Hubble Space Telescope images for 16 galaxies to the foreground of the Virgo Cluster. The new distances with 5% accuracy, combined with archival measurements, tightly constrain the near-side location of the onset of infall into the Virgo Cluster to be 7.3 ± 0.3 Mpc from the cluster, reaching within 9 Mpc of the Milky Way. The mass within this turnaround radius about the cluster is (8.3 ± 0.9) × 1014M⊙. Color–magnitude diagrams are provided for galaxies in this study and there is a brief discussion of their group affiliations. [ABSTRACT FROM AUTHOR]

The jet breaks in the afterglow light curves of short gamma-ray bursts (SGRBs), rarely detected so far, are crucial for estimating the half-opening angles of the ejecta (θj) and hence the neutron star merger rate. In this work, we report the detection of jet decline behaviors in GRB 150424A and GRB 160821B, and find θj ∼ 0.1 rad. Together with five events reported before 2015 and three others “identified” recently (GRB 050709, GRB 060614, and GRB 140903A), we have a sample consisting of nine SGRBs and one long-short GRB with reasonably estimated θj. In particular, three Swift bursts in the sample have redshifts z ≤ 0.2, with which we estimate the local neutron star merger rate density to be or if the narrowly beamed GRB 061201 is excluded. Inspired by the typical θj ∼ 0.1 rad found currently, we further investigate whether the off-beam GRBs (in the uniform jet model) or the off-axis events (in the structured jet model) can significantly enhance the GRB/GW association. For the former, the enhancement is at most moderate, while for the latter the enhancement can be much greater and a high GRB/GW association probability of ∼10% is possible. We also show that the data of GRB 160821B may contain a macronova/kilonova emission component with a temperature of ∼3100 K at ∼3.6 days after the burst and more data are needed to ultimately clarify. [ABSTRACT FROM AUTHOR]

We describe a program to measure surface brightness fluctuation (SBF) distances to galaxies observed in the Next Generation Virgo Cluster Survey (NGVS), a photometric imaging survey covering 104 deg2 of the Virgo cluster in the u*, g, i, and z bandpasses with the Canada–France–Hawaii Telescope. We describe the selection of the sample galaxies, the procedures for measuring the apparent i-band SBF magnitude , and the calibration of the absolute Mibar as a function of observed stellar population properties. The multiband NGVS data set provides multiple options for calibrating the SBF distances, and we explore various calibrations involving individual color indices as well as combinations of two different colors. Within the color range of the present sample, the two-color calibrations do not significantly improve the scatter with respect to wide-baseline, single-color calibrations involving u*. We adopt the calibration as a reference for the present galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack good u* photometry, we use an alternative relation based on a combination of and colors, with only a slightly larger observed scatter of 0.12 mag. The agreement of our measurements with the best existing distance estimates provides confidence that our measurements are accurate. We present a preliminary catalog of distances for 89 galaxies brighter than BT ≈ 13.0 mag within the survey footprint, including members of the background M and W Clouds at roughly twice the distance of the main body of the Virgo cluster. The extension of the present work to fainter and bluer galaxies is in progress. [ABSTRACT FROM AUTHOR]