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23041. Ultra-compact dwarf candidates in Abell S0740
ID:
ivo://CDS.VizieR/J/AJ/136/2295
Title:
Ultra-compact dwarf candidates in Abell S0740
Short Name:
J/AJ/136/2295
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze three-band imaging data of the giant elliptical galaxy ESO 325-G004 from the Hubble Space Telescope Advanced Camera for Surveys (ACS). This is the nearest known strongly lensing galaxy, and it resides in the center of the poor cluster Abell S0740 at redshift z=0.034. Based on magnitude, color, and size selection criteria, we identify a sample of 15 ultra-compact dwarf (UCD) galaxy candidates within the ACS field.
23042. Ultra compact dwarf galaxies catalog
ID:
ivo://CDS.VizieR/J/A+A/625/A50
Title:
Ultra compact dwarf galaxies catalog
Short Name:
J/A+A/625/A50
Date:
21 Oct 2021
Publisher:
CDS
Description:
Photometric surveys of galaxy clusters have revealed a large number of ultra compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their origin is still debated as some UCDs are considered to be the remnant nuclei of stripped dwarf galaxies while others seem to mark the high-mass end of the star cluster population. We aim to characterize the properties of a UCD found at very close projected distance (r_wproj_=1.1kpc) from the centre of the low-mass (M~10^10^M_{sun}_) early-type galaxy FCC 47. This is a serendipitous discovery from MUSE adaptive optics science verification data. We explore the potential origin of this UCD as either a massive cluster or the remnant nucleus of a dissolved galaxy. We used archival Hubble Space Telescope data to study the photometric and structural properties of FCC 47-UCD1. In the MUSE data, the UCD is unresolved, but we used its spectrum to determine the radial velocity and metallicity. The surface brightness of FCC 47-UCD1 is best described by a single King profile with low concentration C=Rt/Rc~10 and large effective radius (r_eff_=24pc). Its integrated magnitude and blue colour (Mg=-10.55mag, (g-z)=1.46mag) combined with a metallicity of [M/H]=-1.12+/-0.10dex and an age >8Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar population mass of M*=4.87x10^6^M_{sun}_. The low S/N of the MUSE spectrum prevents detailed stellar population analysis. Due to the limited spectral resolution of MUSE, we can only give an upper limit on the velocity dispersion ({sigma}<17km/s), and consequently on its dynamical mass (M_dyn_<1.3x10^7^M_{sun}_). The origin of the UCD cannot be constrained with certainty. The low metallicity, old age, and magnitude are consistent with a star cluster origin, whereas the extended size is consistent with an origin as the stripped nucleus of a dwarf galaxy with a initial stellar mass of a few 10^8^M_{sun}_.
23043. Ultracompact dwarf galaxies in Perseus
ID:
ivo://CDS.VizieR/J/MNRAS/422/885
Title:
Ultracompact dwarf galaxies in Perseus
Short Name:
J/MNRAS/422/885
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of the first search for ultracompact dwarfs (UCDs) in the Perseus cluster core, including the region of the cluster around the unusual brightest cluster galaxy NGC 1275. Utilizing Hubble Space Telescope Advanced Camera for Surveys imaging, we identify a sample of 84 UCD candidates with half-light radii 10<r_e_<57pc out to a distance of 250kpc from the cluster centre, covering a total survey area of ~70arcmin^2^.
23044. Ultra compact dwarfs and globulars in Hya I
ID:
ivo://CDS.VizieR/J/A+A/531/A4
Title:
Ultra compact dwarfs and globulars in Hya I
Short Name:
J/A+A/531/A4
Date:
21 Oct 2021
Publisher:
CDS
Description:
We performed a large spectroscopic survey of compact, unresolved objects in the core of the Hydra I galaxy cluster (Abell 1060), with the aim of identifying ultra-compact dwarf galaxies (UCDs) and investigating the properties of the globular cluster (GC) system around the central cD galaxy NGC 3311. We obtained VIMOS medium-resolution spectra of about 1200 candidate objects with apparent magnitudes 18.5<V<24.0mag, covering both the bright end of the GC luminosity function and the luminosity range of all known UCDs.
23045. Ultracompact extragalactic radio sources at 86GHz
ID:
ivo://CDS.VizieR/J/A+A/622/A92
Title:
Ultracompact extragalactic radio sources at 86GHz
Short Name:
J/A+A/622/A92
Date:
21 Oct 2021
Publisher:
CDS
Description:
Very long baseline interferometry (VLBI) observations at 86 GHz (wavelength, {lambda}=3mm) reach a resolution of about 50{mu}as, probing the collimation and acceleration regions of relativistic outflows in active galactic nuclei (AGN). The physical conditions in these regions can be studied by performing 86GHz VLBI surveys of representative samples of compact extragalactic radio sources. To extend the statistical studies of compact extragalactic jets, a large global 86GHz VLBI survey of 162 compact radio sources was conducted in 2010-2011 using the Global Millimeter VLBI Array (GMVA). The survey observations were made in a snapshot mode, with up to five scans per target spread over a range of hour angles in order to optimize the visibility coverage. The survey data attained a typical baseline sensitivity of 0.1Jy and a typical image sensitivity of 5mJy/beam, providing successful detections and images for all of the survey targets. For 138 objects, the survey provides the first ever VLBI images made at 86GHz. Gaussian model fitting of the visibility data was applied to represent the structure of the observed sources and to estimate the flux densities and sizes of distinct emitting regions (components) in their jets. These estimates were used for calculating the brightness temperature (Tb) at the jet base (core) and in one or more moving regions (jet components) downstream from the core. These model-fit-based estimates of Tb were compared to the estimates of brightness temperature limits made directly from the visibility data, demonstrating a good agreement between the two methods. The apparent brightness temperature estimates for the jet cores in our sample range from 2.5x10^9^K to 1.3x10^12^K, with the mean value of 1.8x10^11^K. The apparent brightness temperature estimates for the inner jet components in our sample range from 7.0x10^7^K to 4.0x10^11^K. A simple population model with a single intrinsic value of brightness temperature, T0, is applied to reproduce the observed distribution. It yields T0=(3.77^+0.10^_0.14_)10^11^K for the jet cores, implying that the inverse Compton losses dominate the emission. In the nearest jet components, T0=(1.42^+0.16^_0.19_)10^11^K is found, which is slightly higher than the equipartition limit of 5x10^10^K expected for these jet regions. For objects with sufficient structural detail detected, the adiabatic energy losses are shown to dominate the observed changes of brightness temperature along the jet.
23046. Ultra-compact high velocity clouds from ALFALFA
ID:
ivo://CDS.VizieR/J/ApJ/768/77
Title:
Ultra-compact high velocity clouds from ALFALFA
Short Name:
J/ApJ/768/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34Jy.km/s, median angular diameters of 10', and median velocity widths of 23km/s. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ~1Mpc, the UCHVCs have neutral hydrogen (HI) masses of ~10^5^-10^6^M_{sun}_, HI diameters of ~2-3kpc, and indicative dynamical masses within the HI extent of ~10^7^-10^8^M_{sun}_, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.
23047. Ultra-compact HII regions & methanol masers. I.
ID:
ivo://CDS.VizieR/J/ApJ/833/18
Title:
Ultra-compact HII regions & methanol masers. I.
Short Name:
J/ApJ/833/18
Date:
21 Oct 2021
Publisher:
CDS
Description:
We conducted Very Large Array C-configuration observations to measure positions and luminosities of Galactic Class II 6.7GHz methanol masers and their associated ultra-compact HII regions. The spectral resolution was 3.90625kHz and the continuum sensitivity reached 45{mu}Jy/beam. We mapped 372 methanol masers with peak flux densities of more than 2Jy selected from the literature. Absolute positions have nominal uncertainties of 0.3". In this first paper on the data analysis, we present three catalogs; the first gives information on the strongest feature of 367 methanol maser sources, and the second provides information on all detected maser spots. The third catalog presents derived data of the 127 radio continuum counterparts associated with maser sources. Our detection rate of radio continuum counterparts toward methanol masers is approximately one-third. Our catalogs list properties including distance, flux density, luminosity, and the distribution in the Galactic plane. We found no significant relationship between luminosities of masers and their associated radio continuum counterparts, however, the detection rate of radio continuum emission toward maser sources increases statistically with the maser luminosities.
23048. Ultracompact HII regions radio images
ID:
ivo://CDS.VizieR/J/ApJS/91/659
Title:
Ultracompact HII regions radio images
Short Name:
J/ApJS/91/659
Date:
21 Oct 2021
Publisher:
CDS
Description:
Radio continuum observations were made of 59 IRAS sources that have 100{mu}m flux densities >=1000Jy and far-infrared colors identified with ultracompact (UC) HII regions. Eighty percent were found to have associated compact radio sources. Seventy-five sources were detected at <~1" resolution at 3.6 and 2cm wavelengths, for which we provide contour plots and flux density distributions ranging from the radio to the near-infrared. Over half are unresolved and their morphologies undetermined. The remaining sources can be described by only five morphological classes, whose frequency of occurrence is consistent with that of the Wood and Churchwell survey (1989ApJS...69..831W). We calculate physical properties of the nebulae and show that they are consistent with UC photoionized regions. Alternative explanations are explored and found to be unlikely. The correlation of UC HII region positions with proposed spiral arms is examined and found to be well correlated only for the local spiral arm or "spur". No obvious enhancement of UC HII regions is apparent along the proposed Sagittarius and Scutum arms, probably because of inaccuracies in the kinematic distances. We find the latitude distribution of UC HII regions to lie in the range 0.5deg<[b_FWHM_]<=0.8deg. No correlation between size and density of cometary and core-halo UC HII regions is found, consistent with the bow shock interpretation of these morphologies. Spherical and unresolved UC HII regions, however, appear to show a trend toward lower densities with increasing size, as expected for expanding HII regions. The observed ratios of far-infrared to radio flux densities of UC HII regions lie in the range 10^3^ to >=10^5^. By applying the results of model atmospheres, it is shown that this ratio depends on spectral type, ranging from ~10^3^ for an O4 star to >=10^5^ for a B3 star. We find that many of the UC HII regions in our sample must be excited by a cluster of stars, and most probably contain significant amounts of dust.
23049. Ultracompact H II regions studies. II.
ID:
ivo://CDS.VizieR/J/MNRAS/301/640
Title:
Ultracompact H II regions studies. II.
Short Name:
J/MNRAS/301/640
Date:
21 Oct 2021
Publisher:
CDS
Description:
High spatial resolution radio continuum and 6.67-GHz methanol spectral line data are presented for methanol masers previously detected by Walsh et al. (1997, Cat. <J/MNRAS/291/261>). Methanol maser and/or radio continuum emission is found in 364 cases towards IRAS-selected regions. For those sources with methanol maser emission, relative positions have been obtained to an accuracy of typically 0.05arcsec, with absolute positions accurate to around 1arcsec. Maps of selected sources are provided. The intensity of the maser emission does not seem to depend on the presence of a continuum source. The coincidence of water and methanol maser positions in some regions suggests there is overlap in the requirements for methanol and water maser emission to be observable. However, there is a striking difference between the general proximity of methanol and water masers to both cometary and irregularly shaped ultracompact (UC) HII regions, indicating that, in other cases, there must be differing environments conductive to stimulating their emission. We show that the methanol maser is most likely present before an observable UC HII region is formed around a massive star and is quickly destroyed as the UC HII region evolves. There are 36 out of 97 maser sites that are linearly extended. The hypothesis that the maser emission is found in a circumstellar disc is not inconsistent with these 36 maser sites, but is unlikely. It cannot, however, account for all other maser sites. An alternative model which uses shocks to create the masing spots can more readily reproduce the maser spot distributions.
23050. Ultracool Dwarf Companion Catalogue UCDC
ID:
ivo://org.gavo.dc/ucdc/q/cone
Title:
Ultracool Dwarf Companion Catalogue UCDC
Short Name:
UCDC cone
Date:
27 Dec 2024 08:31:03
Publisher:
The GAVO DC team
Description:
The Ultracool Dwarf Companion Catalogue consists of 278 multiple systems, 32 of which are newly discovered, each with at least one spectroscopically confirmed Ultracool Dwarf, within a 100 pc volume-limited sample. This catalogue is compiled using the Gaia Catalogue of Nearby Stars for stellar primaries and the Gaia Ultracool Dwarf Sample for low-mass companions and includes 241 doubles, 33 triples, and 4 higher-order systems established from positional, proper motion, and parallax constraints.

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