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Abstract We construct a catalog of star clusters from Hubble Space Telescope images of the inner disk of the Triangulum Galaxy (M33) using image classifications collected by the Local Group Cluster Search, a citizen science project hosted on the Zooniverse platform. We identify 1214 star clusters within the Hubble Space Telescope imaging footprint of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Comparing this catalog to existing compilations in the literature, 68% of the clusters are newly identified. The final catalog includes multiband aperture photometry and fits for cluster properties via integrated light spectral energy distribution fitting. The cluster catalog’s 50% completeness limit is ∼1500 M ☉ at an age of 100 Myr, as derived from comprehensive synthetic cluster tests.

Abstract The dense central regions of tidally disrupted galaxies can survive as ultracompact dwarfs (UCDs) that hide among the luminous globular clusters (GCs) in the halo of massive galaxies. An exciting confirmation of this model is the detection of overmassive black holes in the centers of some UCDs, which also lead to elevated dynamical mass-to-light ratios ( M / L dyn ). Here we present new high-resolution spectroscopic observations of 321 luminous GC candidates in the massive galaxy NGC 5128/Centaurus A. Using these data we confirm 27 new luminous GCs, and measure velocity dispersions for 57 luminous GCs (with g -band luminosities between 2.5 × 10 5 and 2.5 × 10 7 L ⊙ ), of which 48 are new measurements. Combining these data with size measurements from Gaia, we determine the M / L dyn for all 57 luminous GCs. We see a clear bimodality in the M / L dyn distribution, with a population of normal GCs with mean M / L dyn = 1.51 ± 0.31, and a second population of ∼20 GCs with elevated mean M / L dyn = 2.68 ± 0.22. We show that black holes with masses ∼4%–18% of the luminous GCs canmore »explain the elevated mass-to-light ratios. Hence, it is plausible that the NGC 5128 sources with elevated M / L dyn are mostly stripped galaxy nuclei that contain massive central black holes, though future high spatial resolution observations are necessary to confirm this hypothesis for individual sources. We also present a detailed discussion of an extreme outlier, VHH81-01 , one of the largest and most massive GC in NGC 5128, making it an exceptionally strong candidate to be a tidally stripped nucleus.« less

Abstract We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data reach ≳3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances, structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations (age ∼12 Gyr, [M/H] ≲ −1.5) and have sizes ( r h ∼ 110–3000 pc) and luminosities ( M V ∼ −7 to −12 mag) largely consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered beyond the Local Group. We also use archival H i data to place limits on the gas content of our discoveries. Deep imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity function and its scatter across a range of galaxy masses, morphologies,more »and environments in the decade to come.« less

We measure the star cluster mass function (CMF) for the Local Group galaxy M33. We use the catalog of stellar clusters selected from the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region survey. We analyze 711 clusters in M33 with$7.0<\log (\mathrm{Age}/\mathrm{yr})<8.5$, and log(M/M_⊙) > 3.0 as determined from color–magnitude diagram fits to individual stars. The M33 CMF is best described by a Schechter function with power-law slopeα= −${2.06}_{-0.13}^{+0.14}$, and truncation mass log(M_c/M_⊙)$={4.24}_{-0.13}^{+0.16}$. The data show strong evidence for a high-mass truncation, thus strongly favoring a Schechter function fit over a pure power law. M33's truncation mass is consistent with the previously identified linear trend betweenM_c, and star formation rate surface density, Σ_SFR. We also explore the effect that individual cluster mass uncertainties have on derived mass function parameters, and find evidence to suggest that large cluster mass uncertainties have the potential to bias the truncation mass of fitted mass functions at the 1σlevel.

ABSTRACT We estimate the mass of the intermediate-mass black hole at the heart of the dwarf elliptical galaxy NGC 404 using Atacama Large Millimetre/submillimetre Array (ALMA) observations of the molecular interstellar medium at an unprecedented linear resolution of ≈0.5 pc, in combination with existing stellar kinematic information. These ALMA observations reveal a central disc/torus of molecular gas clearly rotating around the black hole. This disc is surrounded by a morphologically and kinematically complex flocculent distribution of molecular clouds, that we resolve in detail. Continuum emission is detected from the central parts of NGC 404, likely arising from the Rayleigh–Jeans tail of emission from dust around the nucleus, and potentially from dusty massive star-forming clumps at discrete locations in the disc. Several dynamical measurements of the black hole mass in this system have been made in the past, but they do not agree. We show here that both the observed molecular gas and stellar kinematics independently require a ≈5 × 105 M⊙ black hole once we include the contribution of the molecular gas to the potential. Our best estimate comes from the high-resolution molecular gas kinematics, suggesting the black hole mass of this system is 5.5$^{+4.1}_{-3.8}\times 10^5$ M⊙ (at the 99 per cent confidence level), in good agreement with ourmore »revised stellar kinematic measurement and broadly consistent with extrapolations from the black hole mass–velocity dispersion and black hole mass–bulge mass relations. This highlights the need to accurately determine the mass and distribution of each dynamically important component around intermediate-mass black holes when attempting to estimate their masses.« less