Joel Roediger

The Next Generation Virgo Cluster Survey (NGVS) is a deep, high-resolution imaging campaign that used the 1 deg ² MegaCam instrument on the Canada–France–Hawaii Telescope to carry out a comprehensive optical survey of the Virgo cluster, from its core to its virial radius. The NGVS covers a contiguous area of 104 deg ² (8.63 Mpc ² at the 16.5 Mpc distance of Virgo) in the u *, g , i , and z bands, with additional limited coverage in r . In this paper, we present the final catalog of Virgo galaxies across the entire NGVS area. The catalog includes 3680 galaxies considered to be bona fide members of the cluster, spanning a factor of 2.5 million in luminosity, from g = 8.42 mag to g = 24.41 mag ( M _g = −22.67 mag to M _g = −6.68 mag). With 2100 previously uncataloged galaxies, the NGVS catalog augments the number of known Virgo members by a factor of 2.3. The catalog is complete down to g = 18.6 mag ( M _g = −12.5 mag, corresponding to a stellar mass M _⋆ ∼ 1.6 × 10 ⁷ M _⊙ for an old stellar population) and 50% complete at g = 22.0 mag ( M _g = −9.1 mag, M _⋆ ∼ 6.2 × 10 ⁵ M _⊙ ), 3 mag deeper than the venerable Virgo Cluster Catalog (VCC), which for over 40 yr has served as the reference standard for Virgo. Photometric and structural parameters are derived for all NGVS galaxies and presented in a series of tables, alongside nuclear and morphological classification, as well as stellar masses and, when available, radial velocities.

We present the methods and data for a detailed structural analysis of over 600 ultracompact dwarf (UCD) galaxy candidates in the Virgo Cluster, based on deep ground-based imaging from the Next Generation Virgo Cluster Survey and archival Hubble Space Telescope (HST) Advanced Camera for Surveys imaging. Our goal is to test two main formation scenarios—whether UCDs are massive globular clusters (GCs) or the remnant nuclei of tidally stripped dwarf galaxies (nucleated dwarf elliptical galaxies, dEs)—by analyzing their morphologies and searching for extended stellar envelopes. We find that over 10% of Virgo UCD candidates exhibit two-component profiles with extended outer structures of R _e ∼ 30–300 pc that cannot be well fitted by standard King or Sérsic models, indicating the presence of diffuse envelopes (eUCDs). High-resolution HST imaging is essential for resolving compact eUCDs that are unresolved in ground-based data. We also present results of the Gemini/Gemini Multi-Object Spectrograph spectroscopy follow-up programs to confirm the Virgo Cluster membership for eUCD candidates. The full catalog consists of a near-complete spectroscopic sample of 68 Virgo eUCDs, as well as properties for 51 strongly nucleated dEs that resemble eUCDs. Together, this constitutes the largest and most comprehensive sample thus far of eUCDs and other possible nucleated dE–GC transition objects. This is a companion paper to K. Wang et al., which was based in large part on the data we present here. Future wide-field space-based surveys will offer unprecedented opportunities to identify eUCDs across a range of environments.

We present a study of morphologies, based on deep u * g ′ i ′ z ′ imaging of the Virgo Cluster from the Next Generation Virgo Cluster Survey, for 3689 Virgo cluster members spanning a mass range of ∼10 ¹¹ –10 ⁵ M _⊙ . Our analysis introduces a new, two-component visual classification scheme developed to capture the morphological diversity of galaxies over more than 6 orders of magnitude in stellar mass. Our morphological classifications use two parameters to describe the global structure and star formation activity of each galaxy. Structural subcodes denote features such as spiral arms, bars, disks, shells, and streams, while star formation subcodes indicate the form and location of the current star formation activity (e.g., in cores, clumps, filaments). These visual classifications rely on deep g ′ -band images, supplemented by u * g ′ i ′ ­ color images, as well as unsharp-masked images for a subset of objects. We compare our classifications to previous results for bright member galaxies that used more established schemes, finding good agreement. We also measure quantitative classification statistics (e.g., CASGM ₂₀ ) for a subset of the brighter galaxies, and present catalogs for some galaxy types of special interest, including structurally compact galaxies, ultradiffuse galaxies, candidate ultracompact dwarf transition objects, as well as candidate postmerger systems. These morphological classifications may be useful as a training set in the application of machine learning tools to the next generation of wide-field imaging surveys.

The integral-field unit mode of the Near-Infrared Spectrograph (NIRSpec+IFU) mounted on the James Webb Space Telescope has now enabled kinematic studies of smaller and less massive compact stellar systems in which to search for central massive black holes (BHs) than ever before. We present here the first such detection using NIRSpec+IFU in its highest resolution (R ∼ 2700) mode. We report the detection of a central BH with mass M BH = 2.1 ± 1.1 × 10⁶ M _⊙ (1σ uncertainties) in UCD736 orbiting within the Virgo galaxy cluster. Schwarzschild modeling of the 1D kinematic profile rules out a zero-mass central BH at the 3σ level; however, two other independent modeling approaches fail to rule out a zero-mass BH at >1σ significance. The presence of such a massive BH strongly argues against a globular cluster origin of this ultracompact dwarf galaxy (UCD), and rather suggests a tidally stripped formation route from a former ≳10⁹ M _⊙ dwarf galaxy host. This represents the detection of a BH in the most compact (r _h ≈ 15 pc) stellar system to date, with a M BH corresponding to ∼8% of the system’s stellar mass, roughly in line with previously reported UCD BH detections and comparable to the BH detected in the compact elliptical galaxy NGC4486B.

We analyze deep (M _* ≳ 10⁷ M _⊙) galaxy stellar mass functions (SMFs) of the Virgo cluster using stellar masses derived as part of the Next Generation Virgo Survey. The total SMF has a slope of α = − 1.3 5 − 0.02 + 0.02 , which is similar to or steeper than typical field values. Using deep Hα data from the Virgo Environmental Survey Tracing Ionised Gas Emission we separate out star-forming galaxies, quiescent galaxies with no ongoing star formation, and low star formation rate (SFR) galaxies that are intermediate between these two populations. For each of these populations, the shape of the SMF is found to be universal throughout the cluster, from the core to the outskirts. The star-forming and quiescent SMFs show stark differences with values seen in field galaxies. The relative fraction of quiescent galaxies is highest in the core of the cluster, with low-SFR and star-forming galaxies more significant in the outer regions of the cluster. At low stellar masses (M _* ≲ 10⁹ M _⊙), the quiescent fraction in the main cluster is significantly higher than that of the field and even satellites of massive groups. At high stellar masses, the quiescent fraction is similar to other studies of cluster galaxies. We model the quiescent population in the infall region of the cluster as a combination of backsplash and field quiescent galaxies, and find that the backsplash fractions needed to explain the observed population are unrealistically high. This suggests the existence of a third population of low-mass galaxies that are preprocessed outside the virial radius of the cluster, possibly in groups prior to infall.

CASTOR is a proposed wide-field (30′×30′=0.25 deg2), high-resolution (FWHM∼0.15″), 1-m-diameter space telescope that is under development by the Canadian Space Agency and the National Research Council of Canada. Optimized for UV/blue-optical wavelengths, the telescope uses dichroics to enable imaging in three channels (and up to five bands) that cover the 0.15 to 0.55 μm spectral region, simultaneously. CASTOR will also feature low- and low-medium-resolution spectroscopic capabilities through the use of a deployable grism for low-resolution (R≲420) slit-less spectroscopy in its UV and u channels, and low-medium-resolution R∼1400 multi-object spectroscopy in a parallel field using a digital micro-mirror device. High-speed, precision photometry will be possible using dedicated CMOS detectors in each of its three channels. We present an overview of the mission, including the optical design, instruments and detectors, payload layout, satellite bus, orbit, and ground segment. We describe the mission’s scientific capabilities and expected place within the astronomical landscape in the 2030s. The 5-year lifetime is baselined on a combination of legacy surveys, guest observer programs, and target-of-opportunity science. We summarize scientific plans for the mission in each of eight fields: cosmology, time domain and multi-messenger science, active galactic nuclei, galaxies, near-field cosmology, stellar astrophysics, exoplanets, and solar system studies. We conclude by describing ongoing development efforts, highlighting areas of particular relevance for NASA’s Habitable Worlds Observatory.

We present an analysis of the spatial distribution of globular cluster (GC) systems of 118 nearby early-type galaxies in the Next Generation Virgo Cluster Survey and Mass Assembly of early-Type GaLAxies with their fine Structures survey programs, which both used MegaCam on the Canada–France–Hawaii Telescope. We describe the procedure used to select GC candidates and fit the spatial distributions of GCs to a two-dimensional Sérsic function, which provides effective radii (half number radii) and Sérsic indices, and estimate background contamination by adding a constant term to the Sérsic function. In cases where a neighboring galaxy affects the estimation of the GC spatial distribution in the target galaxy, we fit two two-dimensional Sérsic functions, simultaneously. We also investigate the color distributions of GCs in our sample by using Gaussian mixture modeling. For GC systems with bimodal color distributions, we divide the GCs into blue and red subgroups and fit their respective spatial distributions with Sérsic functions. Finally, we measure the total number of GCs based on our fitted Sérsic function, and calculate the GC specific frequency.

We present an analysis of the spatial distribution of globular cluster (GC) systems of 118 nearby early-type galaxies in the Next Generation Virgo Cluster Survey (NGVS) and Mass Assembly of early-Type GaLAxies with their fine Structures (MATLAS) survey programs, which both used MegaCam on the Canada-France-Hawaii Telescope. We describe the procedure used to select GC candidates and fit the spatial distributions of GCs to a two-dimensional Sérsic function, which provides effective radii (half number radii) and Sérsic indices, and estimate background contamination by adding a constant term to the S'ersic function. In cases where a neighboring galaxy affects the estimation of the GC spatial distribution in the target galaxy, we fit two 2D Sérsic functions, simultaneously. We also investigate the color distributions of GCs in our sample by using Gaussian Mixture Modeling. For GC systems with bimodal color distributions, we divide the GCs into blue and red subgroups and fit their respective spatial distributions with Sérsic functions. Finally, we measure the total number of GCs based on our fitted Sérsic function, and calculate the GC specific frequency.