- ID:
- ivo://CDS.VizieR/J/MNRAS/441/3570
- Title:
- Nuclear star clusters in 228 spiral galaxies
- Short Name:
- J/MNRAS/441/3570
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of photometric and structural properties of 228 nuclear star clusters (NSCs) in nearby late-type disc galaxies. These new measurements are derived from a homogeneous analysis of all suitable Wide Field Planetary Camera 2 (WFPC2) images in the Hubble Space Telescope (HST) archive. The luminosity and size of each NSC are derived from an iterative point spread function (PSF) fitting technique, which adapts the fitting area to the effective radius (r_eff_) of the NSC and uses a WFPC2-specific PSF model tailored to the position of each NSC on the detector. The luminosities of NSCs are <=10^8^L_V,{sun}_, and their integrated optical colours suggest a wide spread in age. We confirm that most NSCs have sizes similar to globular clusters (GCs), but find that the largest and brightest NSCs occupy the regime between ultra-compact dwarf (UCD) and the nuclei of early-type galaxies in the size-luminosity plane. The overlap in size, mass, and colour between the different incarnations of compact stellar systems provides a support for the notion that at least some UCDs and the most massive Galactic GCs may be remnant nuclei of disrupted disc galaxies. We find tentative evidence for the NSCs' r_eff_ to be smaller when measured in bluer filters and discuss possible implications of this result. We also highlight a few examples of complex nuclear morphologies, including double nuclei, extended stellar structures, and nuclear F606W excess from either recent (circum-)nuclear star formation and/or a weak active galactic nucleus. Such examples may serve as case studies for ongoing NSC evolution via the two main suggested mechanisms, namely cluster merging and in situ star formation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/886/61
- Title:
- OGLE-III, MCPS and HST VI obs. of LMC & SMC
- Short Name:
- J/ApJ/886/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a calibration of the tip of the red giant branch (TRGB) in the Large Magellanic Cloud (LMC) on the Hubble Space Telescope (HST)/ACS F814W system. We use archival HST observations to derive blending corrections and photometric transformations for two ground-based wide-area imaging surveys of the Magellanic Clouds. We show that these surveys are biased bright by up to ~0.1mag in the optical due to blending, and that the bias is a function of local stellar density. We correct the LMC TRGB magnitudes from Jang & Lee (2017ApJ...835...28J) and use the geometric distance from Pietrzynski+ (2019Natur.567..200P) to obtain an absolute TRGB magnitude of M_F814W_=-3.97+/-0.046mag. Applying this calibration to the TRGB magnitudes from Freedman+ (2019ApJ...882...34F) in SN Ia hosts yields a value for the Hubble constant of H_0_=72.4+/-2.0km/s/Mpc for their TRGB+SNe Ia distance ladder. The difference in the TRGB calibration and the value of H_0_ derived here and by Freedman+ primarily results from their overestimate of the LMC extinction, caused by inconsistencies in their different sources of TRGB photometry for the Magellanic Clouds. Using the same source of photometry (OGLE) for both Clouds and applying the aforementioned corrections yields a value for the LMC I-band TRGB extinction that is lower by 0.06mag, consistent with independent OGLE reddening maps used by us and by Jang & Lee to calibrate TRGB and determine H0.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/160
- Title:
- Old star clusters in M101 from HST
- Short Name:
- J/ApJ/805/160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new photometric catalog of 326 candidate globular clusters (GCs) in the nearby spiral galaxy M101, selected from B, V, and I Hubble Space Telescope Advanced Camera for Surveys images. The luminosity function (LF) of these clusters has an unusually large number of faint sources compared with GCLFs in many other spiral galaxies. Accordingly, we separate and compare the properties of "bright" (M_v_<-6.5) versus "faint" (M_v_>-6.5; one magnitude fainter than the expected GC peak) clusters within our sample. The LF of the bright clusters is well fit by a peaked distribution similar to those observed in the Milky Way (MW) and other galaxies. These bright clusters also have similar size (r_eff_) and spatial distributions as MW GCs. The LF of the faint clusters, on the other hand, is well described by a power law, dN(L_v_)/dL_v_{propto}L_v_^{alpha}^ with {alpha}=2.6+/-0.3, similar to those observed for young and intermediate-age cluster systems in star forming galaxies. We find that the faint clusters have larger typical r_eff_ than the bright clusters, and have a flatter surface density profile, being more evenly distributed, as we would expect for clusters associated with the disk. We use the shape of the LF and predictions for mass-loss driven by two-body relaxation to constrain the ages of the faint clusters. Our results are consistent with two populations of old star clusters in M101: a bright population of halo clusters and a fainter, possibly younger, population of old disk clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/143/52
- Title:
- Old star clusters in NGC 4449 from HST imaging
- Short Name:
- J/AJ/143/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 (=UGC 7592) has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color-magnitude diagrams provide evidence that some of these clusters are old globular clusters (GCs). Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H]~-1) and subsolar Mg enhancement ([Mg/Fe]~-0.1 to -0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the other is very massive (~3*10^6^M_{sun}_). We have also identified a population of remote halo GCs. NGC 4449 is consistent with an emerging picture of the ubiquity of stellar halos among dwarf galaxies, and study of its GCs may help distinguish between accretion and in situ scenarios for such halos.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/14
- Title:
- Optical & FeII sources in Supernova remnant with HST
- Short Name:
- J/ApJ/899/14
- Date:
- 14 Mar 2022 07:07:21
- Publisher:
- CDS
- Description:
- NGC6946 is a high-star-formation-rate, face-on, spiral galaxy that has hosted 10 supernovae since 1917. Not surprisingly, a large number of supernova remnants and candidates have been identified either as optical nebulae with high [SII]:H{alpha} line ratios (147) or as compact non-thermal radio sources (35). However, there are only seven overlaps between these two samples. Here, we apply [FeII] 1.644{mu}m emission as a new diagnostic to search for supernova remnants in an attempt to resolve this discrepancy. [FeII] is expected to be relatively strong in the radiative shocks of supernova remnants and almost absent in HII regions. It is less susceptible to the effects of absorption along the line of sight than the optical lines normally used to identify remnants. Using data from the WFC3 camera on Hubble Space Telescope (HST), we identify 132 [FeII] emission nebulae in NGC6946 as likely supernova remnants. Of these, 54 align with previously known optical supernova remnants. The remaining 78 objects are new; of these 44 are visible in new HST imagery in H{alpha} and [SII]. This brings the total number of supernova remnant candidates (from optical and/or IR data) in NGC6946 to 225. A total of 14 coincidences with radio supernova remnant candidates (out of 30 in our search area) are found in this expanded list. The identification of so many new remnant candidates validates the use of [FeII] imagery for finding remnants, and suggests that previous remnant searches in other galaxies may be far from complete.
- ID:
- ivo://CDS.VizieR/J/ApJS/216/6
- Title:
- Opt-NIR HST photometry of cluster candidates in M82
- Short Name:
- J/ApJS/216/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using high-resolution, multiple-passband Hubble Space Telescope images spanning the entire optical/near-infrared wavelength range, we obtained a statistically complete U-band-selected sample of 846 extended star clusters across the disk of the nearby starburst galaxy M82 (NGC3034). Based on a careful analysis of the clusters' spectral energy distributions, we determined their galaxy-wide age and mass distributions. The M82 clusters exhibit three clear peaks in their age distribution, thus defining relatively young, log(t/yr)<=7.5, intermediate-age, log(t/yr){isin}[7.5,8.5], and old samples, log(t/yr)>=8.5. Comparison of the completeness-corrected mass distributions offers a firm handle on the galaxy's star cluster disruption history. The most massive star clusters in the young and old samples are (almost) all concentrated in the most densely populated central region, while the intermediate-age sample's most massive clusters are more spatially dispersed, which may reflect the distribution of the highest-density gas throughout the galaxy's evolutionary history, combined with the solid-body nature of the galaxy's central region.
- ID:
- ivo://CDS.VizieR/J/AJ/159/272
- Title:
- Orion Nebula Cluster PMs with HST Treasury Program
- Short Name:
- J/AJ/159/272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of high-precision proper motions in the Orion Nebula Cluster (ONC), based on Treasury Program observations with the Hubble Space Telescope's (HST) ACS/WFC camera. Our catalog contains 2454 objects in the magnitude range of 14.2<m_F775W_<24.7, thus probing the stellar masses of the ONC from ~0.4M{sun} down to ~0.02M{sun} over an area of ~550arcmin^2^. We provide a number of internal velocity dispersion estimates for the ONC that indicate a weak dependence on stellar location and mass. There is good agreement with the published velocity dispersion estimates, although nearly all of them (including ours at {sigma }_{v,x}_=0.94 and {sigma}_{v,y}_=1.25mas/yr) might be biased by the overlapping young stellar populations of Orion A. We identified four new ONC candidate runaways based on HST and the Gaia DR 2 data, all with masses less than ~1M{sun}. The total census of known candidate runaway sources is 10-one of the largest samples ever found in any Milky Way open star cluster. Surprisingly, none of them have tangential velocities exceeding 20km/s. If most of them indeed originated in the ONC, it may compel the re-examination of dynamical processes in very young star clusters. It appears that the mass function of the ONC is not significantly affected by the lost runaways.
- ID:
- ivo://CDS.VizieR/J/ApJ/772/27
- Title:
- Pa{alpha} (1.87um) LF of HII regions in 12 galaxies
- Short Name:
- J/ApJ/772/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H II region luminosity function (LF) is an important tool for deriving the birthrates and mass distribution of OB associations and is an excellent tracer of the newly formed massive stars and associations. To date, extensive work (predominantly in H{alpha}) has been done from the ground, which is hindered by dust extinction and the severe blending of adjacent (spatially or in projection) H II regions. Reliably measuring the properties of H II regions requires a linear resolution <40pc, but analyses satisfying this requirement have been done only in a handful of galaxies, so far. As the first space-based work using a galaxy sample, we have selected 12 galaxies from our HST/NICMOS Pa{alpha} survey and studied the LF and size distribution of H II regions both in individual galaxies and cumulatively, using a virtually extinction-free tracer of the ionizing photon rate. The high angular resolution and low sensitivity to diffuse emission of NICMOS also offer an advantage over ground-based imaging by enabling a higher degree of de-blending of the H II regions. We do not confirm the broken power-law LFs found in ground-based studies. Instead, we find that the LFs, both individual and co-added, follow a single power law dN(L)/dlnL{propto}L^-1^, are consistent with the mass function of star clusters in nearby galaxies, and are in agreement with the results of the existing analyses with Hubble Space Telescope (HST) data. The individual and co-added size distributions of H II regions are both roughly consistent with dN(D)/dlnD{propto}D^-3^, but the power-law scaling is probably contaminated by blended regions or complexes.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/107
- Title:
- Parameters of NGC 5139 SGBs stars
- Short Name:
- J/ApJ/791/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- {omega} Centauri is a peculiar globular cluster formed by a complex stellar population. To investigate it, we studied 172 stars belonging to the five SGBs that we can identify in our photometry, in order to measure their [Fe/H] content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs have a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several subpopulations. We were able to identify at least six of them based on their mean [Fe/H] content. These metallicity-based subpopulations are seen to varying extents in each of the five SGBs. Taking advantage of the age sensitivity of the SGB, we showed that, first of all, at least half of the subpopulations have an age spread of at least 2 Gyr. Then, we obtained an age-metallicity relation that is the most complete to date for this cluster. Interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations with different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they can be assumed to be two independent primordial objects, or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.
- ID:
- ivo://CDS.VizieR/J/ApJ/802/127
- Title:
- PHAT stellar cluster survey. II. AP catalog
- Short Name:
- J/ApJ/802/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a stellar cluster catalog for the Panchromatic Hubble Andromeda Treasury (PHAT) survey using image classifications collected from the Andromeda Project (AP) citizen science website. We identify 2753 clusters and 2270 background galaxies within ~0.5deg^2^ of PHAT imaging searched, or ~400kpc^2^ in deprojected area at the distance of the Andromeda Galaxy (M31). These identifications result from 1.82million classifications of ~20000 individual images (totaling ~7gigapixels) by tens of thousands of volunteers. We show that our crowd-sourced approach, which collects >80 classifications per image, provides a robust, repeatable method of cluster identification. The high spatial resolution Hubble Space Telescope images resolve individual stars in each cluster and are instrumental in the factor of ~6 increase in the number of clusters known within the survey footprint. We measure integrated photometry in six filter passbands, ranging from the near-UV to the near-IR. PHAT clusters span a range of ~8 magnitudes in F475W (g-band) luminosity, equivalent to ~4 decades in cluster mass. We perform catalog completeness analysis using >3000 synthetic cluster simulations to determine robust detection limits and demonstrate that the catalog is 50% complete down to ~500M_{sun}_ for ages <100Myr. We include catalogs of clusters, background galaxies, remaining unselected candidates, and synthetic cluster simulations, making all information publicly available to the community. The catalog published here serves as the definitive base data product for PHAT cluster science, providing a census of star clusters in an L^*^ spiral galaxy with unmatched sensitivity and quality.
