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Systematic studies 1-4 have revealed hundreds of ultra-compact dwarf galaxies (UCDs 5 ) in the nearby Universe. With half-light radii r h of approximately 10-100 parsecs and stellar masses M *  ≈ 10 6 -10 8  solar masses, UCDs are among the densest known stellar systems 6 . Although similar in appearance to massive globular clusters 7 , the detection of extended stellar envelopes 4,8,9 , complex star formation histories 10 , elevated mass-to-light ratio 11,12 and supermassive black holes 13-16 suggest that some UCDs are remnant nuclear star clusters 17 of tidally stripped dwarf galaxies 18,19 , or even ancient compact galaxies 20 . However, only a few objects have been found in the transient stage of tidal stripping 21,22 , and this assumed evolutionary path 19 has never been fully traced by observations. Here we show that 106 galaxies in the Virgo cluster have morphologies that are intermediate between normal, nucleated dwarf galaxies and single-component UCDs, revealing a continuum that fully maps this morphological transition and fills the 'size gap' between star clusters and galaxies. Their spatial distribution and redder colour are also consistent with stripped satellite galaxies on their first few pericentric passages around massive galaxies 23 . The 'ultra-diffuse' tidal features around several of these galaxies directly show how UCDs are forming through tidal stripping and that this evolutionary path can include an early phase as a nucleated ultra-diffuse galaxy 24,25 . These UCDs represent substantial visible fossil remnants of ancient dwarf galaxies in galaxy clusters, and more low-mass remnants probably remain to be found., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The observed scaling relations between supermassive black hole masses and their host galaxy properties indicate that supermassive black holes influence the evolution of galaxies. However, the scaling relations may be affected by selection biases. We propose to measure black hole masses in a mass-limited galaxy sample including all non-detections to inprove constraints on galaxy mass – black hole mass scaling relations and test for selection bias. We use high-spatial resolution spectroscopy from the Keck and Gemini telescopes, and the Jeans Anisotropic Modelling method to measure black hole masses in early-type galaxies from the Virgo Cluster. We present four new black hole masses and one upper limit in our mass-selected sample of galaxies of galaxy mass (1.0–3.2)  |$\times 10^{10} \, \mathrm{M}_\odot$|⁠. This brings the total measured to 11 galaxies out of a full sample of 18 galaxies, allowing us to constrain scaling relations. We calculate a lower limit for the average black hole mass in our sample of |$3.7 \times 10^{7} \, \mathrm{M}_\odot$|⁠. This is at an average galaxy stellar mass of |$(1.81 \pm 0.14)\times 10^{10} \, \mathrm{M}_\odot$| and an average bulge mass of |$(1.31 \pm 0.15) \times 10^{10} \, \mathrm{M}_\odot$|⁠. This lower limit shows that black hole masses in early-type galaxies are not strongly affected by selection biases. [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 the hydrodynamical EAGLE simulation to predict the numbers, masses, and radial distributions of tidally stripped galaxy nuclei in massive galaxy clusters, and compare these results to observations of ultracompact dwarf galaxies (UCDs) in the Virgo cluster. We trace the merger trees of galaxies in massive galaxy clusters back in time and determine the numbers and masses of stripped nuclei from galaxies disrupted in mergers. The spatial distribution of stripped nuclei in the simulations is consistent with those of UCDs surrounding massive galaxies in the Virgo cluster. Additionally, the numbers of stripped nuclei are consistent with the numbers of M > 107 M⊙ UCDs around individual galaxies and in the Virgo cluster as a whole. The mass distributions in this mass range are also consistent. We find that the numbers of stripped nuclei surrounding individual galaxies correlate better with the stellar or halo mass of individual galaxies than the total cluster mass. We conclude that most high mass (M > 107 M⊙) UCDs are likely stripped nuclei. It is difficult to draw reliable conclusions about low mass (M < 107 M⊙) UCDs because of observational selection effects. We additionally predict that a few hundred stripped nuclei below a mass of 2 × 106 M⊙ should exist in massive galaxies that will overlap in mass with the globular cluster population. Approximately 1–3 stripped nuclei in the process of forming also exist per massive galaxy. [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]

We have used Chandra observations of eight bulgeless disk galaxies to identify new ultraluminous X-ray source (ULX) candidates, study their high-mass X-ray binary (HMXB) population, and search for low-luminosity active galactic nuclei (AGNs). We report the discovery of 16 new ULX candidates in our sample of galaxies. Eight of these are found in the star forming galaxy NGC 337, none of which are expected to be background contaminants. The HMXB luminosity function of NGC 337 implies a star formation rate (SFR) of 6.8 M☼ yr–1, consistent at 1.5σ with a recent state of the art SFR determination. We also report the discovery of a bright ULX candidate (X-1) in ESO 501-23. X-1's spectrum is well fit by an absorbed power law with and NH = 1.13 cm–2, implying a 0.3-8 keV flux of erg s–1 cm–2. Its X-ray luminosity (LX) is poorly constrained due to uncertainties in the host galaxy's distance, but we argue that its spectrum implies LX > 1040 erg s–1. An optical counterpart to this object may be present in an Hubble Space Telescope image. We also identify ULX candidates in IC 1291, PGC 3853, NGC 5964, and NGC 2805. We find no evidence of nuclear activity in the galaxies in our sample, placing a flux upper limit of 4 × 10–15 erg s–1 cm–2 on putative AGN. Additionally, the Type II-P supernova SN 2011DQ in NGC 337, which exploded two months before our X-ray observation, is undetected. [ABSTRACT FROM AUTHOR]

We combine new Wide Field Camera 3 IR Channel (WFC3/IR) F160W (H160) imaging data for NGC 1399, the central galaxy in the Fornax cluster, with archival F475W (g475), F606W (V606), F814W (I814), and F850LP (z850) optical data from the Advanced Camera for Surveys (ACS). The purely optical g475-I814, V606-I814, and g475-z850 colors of NGC 1399's rich globular cluster (GC) system exhibit clear bimodality, at least for magnitudes I814 > 21.5. The optical--IR I814--H160 color distribution appears unimodal, and this impression is confirmed by mixture modeling analysis. The V606-H160 colors show marginal evidence for bimodality, consistent with bimodality in V606-I814 and unimodality in I814-H160. If bimodality is imposed for I814-H160 with a double Gaussian model, the preferred blue/red split differs from that for optical colors; these "differing bimodalities" mean that the optical and optical--IR colors cannot both be linearly proportional to metallicity. Consistent with the differing color distributions, the dependence of I814-H160 on g475-I814 for the matched GC sample is significantly nonlinear, with an inflection point near the trough in the g475-I814 color distribution; the result is similar for the I814-H160 dependence on g475-z850 colors taken from the ACS Fornax Cluster Survey. These g475-z850 colors have been calibrated empirically against metallicity; applying this calibration yields a continuous, skewed, but single-peaked metallicity distribution. Taken together, these results indicate that nonlinear color-metallicity relations play an important role in shaping the observed bimodal distributions of optical colors in extragalactic GC systems. [ABSTRACT FROM AUTHOR]

We present a new non-parametric deprojection algorithm, DOPING (Deprojection of Observed Photometry using an INverse Gambit), which is designed to extract the three-dimensional luminosity density distribution ρ, from the observed surface brightness profile of an astrophysical system such as a galaxy or a galaxy cluster, in a generalised geometry, while taking into account changes in the intrinsic shape of the system. The observable is the 2D surface brightness distribution of the system. While the deprojection schemes presented hitherto have always worked within the limits of an assumed intrinsic geometry, in DOPING, geometry and inclination can be provided as inputs. The ρ that is most likely to project to the observed brightness data is sought; the maximisation of the likelihood is performed with the Metropolis algorithm. Unless the likelihood function is maximised, ρ is tweaked in shape and amplitude, while maintaining positivity, but otherwise the luminosity distribution is allowed to be completely free-form. Tests and applications of the algorithm are discussed. [ABSTRACT FROM AUTHOR]

This review discusses the current status of supermassive black hole research, as seen from a purely observational standpoint. Since the early ‘90s, rapid technological advances, most notably the launch of the Hubble Space Telescope, the commissioning of the VLBA and improvements in near-infrared speckle imaging techniques, have not only given us incontrovertible proof of the existence of supermassive black holes, but have unveiled fundamental connections between the mass of the central singularity and the global properties of the host galaxy. It is thanks to these observations that we are now, for the first time, in a position to understand the origin, evolution and cosmic relevance of these fascinating objects. [ABSTRACT FROM AUTHOR]

We present evidence for the presence of a transition in the accretion properties of radio-loud sources. For a sample of radio galaxies and radio-loud quasars, selected based on their extended radio properties, the accretion rate is estimated from the black hole mass and nuclear luminosity. The inferred distribution is bimodal, with a paucity of sources at accretion rates, in Eddington units, of the order of ∼10−2– assuming a radiative efficiency of 10 per cent – and possibly spanning 1–2 orders of magnitude. Selection biases are unlikely to be responsible for such behaviour. We discuss possible physical explanations, including a fast transition to low accretion rates, a change in the accretion mode/actual accretion rate/radiative efficiency, the lack of stable disc solutions at intermediate accretion rates or the inefficiency of the jet formation processes in geometrically thin flows. This transition might be analogous to spectral states (and jet) transitions in black hole binary systems. [ABSTRACT FROM AUTHOR]

Examines the black hole demographics from the M[sub bulge] - sigma relation. Calculation of the mass of the central black hole for each galaxy; Estimation of the total mass density in black holes in the local Universe; Utilization of the tight empirical correlation between Mxx and the bulge stellar velocity dispersion.

Presents research on the distance to the galaxy NGC4258 from observation of Cepheid variable stars. How the pulsation of the variable stars make them useful as standards for determining distances to galaxies; Implications for the expansion age of the Universe.

Reports on a Cepheid distance of 18.6 +/- 1.9 +/- Mpc for the galaxy NGC1365 in Fornax, a cluster of galaxies in the Southern Hemisphere. How both galaxy distances and velocities are required in order to determine the expansion rate of the universe; Estimates; Findings.

Examines nucleus of galaxy called M33 using the Space Telescope Imaging Spectrograph at a resolution at least a factor of 10 higher than previously obtained. Decrease of random stellar velocities within a parsec of the center of the galaxy; Implied upper limit on the mass of the central black hole; Presence of a supermassive black hole.

We present a revised measurement of the mass of the central black hole (MBH ) in the Seyfert 1 galaxy NGC 4151. The new stellar dynamical mass measurement is derived by applying an axisymmetric orbit-superposition code to near-infrared integral field data obtained using adaptive optics with the Gemini Near-infrared Integral Field Spectrograph (NIFS). When our models attempt to fit both the NIFS kinematics and additional low spatial resolution kinematics, our results depend sensitively on how χ2 is computed—probably a consequence of complex bar kinematics that manifest immediately outside the nuclear region. The most robust results are obtained when only the high spatial resolution kinematic constraints in the nuclear region are included in the fit. Our best estimates for the black hole mass and H-band mass-to-light ratio are MBH ∼ 3.76 ± 1.15 × 107M☼ (1σ error) and ϒH ∼ 0.34 ± 0.03 M☼/L☼ (3σ error), respectively (the quoted errors reflect the model uncertainties). Our black hole mass measurement is consistent with estimates from both reverberation mapping () and gas kinematics (; 1σ errors), and our best-fit mass-to-light ratio is consistent with the photometric estimate of ϒH = 0.4 ± 0.2 M☼/L☼. The NIFS kinematics give a central bulge velocity dispersion σc = 116 ± 3 km s–1, bringing this object slightly closer to the MBH-σ relation for quiescent galaxies. Although NGC 4151 is one of only a few Seyfert 1 galaxies in which it is possible to obtain a direct dynamical black hole mass measurement—and thus, an independent calibration of the reverberation mapping mass scale—the complex bar kinematics makes it less than ideally suited for this purpose. [ABSTRACT FROM AUTHOR]