- 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^.
Number of results to display per page
Search Results
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A170
- Title:
- Ultracool dwarf K2 light curves
- Short Name:
- J/A+A/641/A170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the discovery of a planetary system around the ultracool dwarf TRAPPIST-1, there has been a surge of interest in such stars as potential planet hosts. Planetary systems around ultracool dwarfs represent our best chance of characterising temperate rocky-planet atmospheres with the James Webb Space Telescope. However, TRAPPIST-1 remains the only known system of its kind and the occurrence rate of planets around ultracool dwarfs is still poorly constrained. We seek to perform a complete transit search on the ultracool dwarfs observed by NASA's K2 mission, and use the results to constrain the occurrence rate of planets around these stars. We filter and characterise the sample of ultracool dwarfs observed by K2 by fitting their spectral energy distributions and using parallaxes from Gaia. We build an automatic pipeline to perform photometry, detrend the light curves, and search for transit signals. Using extensive injection-recovery tests of our pipeline, we compute the detection sensitivity of our search, and thus the completeness of our sample. We infer the planetary occurrence rates within a hierarchical Bayesian model (HBM) to treat uncertain planetary parameters.With the occurrence rate parametrised by a step-wise function, we present a convenient way to directly marginalise over the second level of our HBM (the planetary parameters). Our method is applicable generally and can greatly speed up inference with larger catalogues of detected planets. We detect one planet in our sample of 702 ultracool dwarfs: a previously validated mini-Neptune. We thus infer a mini-Neptune (2-4R_{Earth}_) occurrence rate of {eta}=0.20^+0.16^_0.11_ within orbital periods of 1-20 days. For super-Earths (1-2R_{Earth}_) and ice or gas giants (4-6R_{Earth}_) within 1-20 days, we place 95% credible intervals of {eta}<1.14 and {eta}<0.29, respectively. If TRAPPIST-1-like systems were ubiquitous, we would have a 96% chance of finding at least one.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/3280
- Title:
- Ultra-cool dwarfs at low Galactic latitudes
- Short Name:
- J/MNRAS/427/3280
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an ultra-cool dwarf (UCD) catalogue compiled from low southern Galactic latitudes and mid-plane, from a cross-correlation of the Two Micron All-Sky Survey (2MASS) and the SuperCOSMOS survey. The catalogue contains 246 members identified from 5042deg^2^ within 220{deg}<=l<=360{deg} and 0{deg}<l<=30{deg}, for |b|<=15{deg}. Sixteen candidates are spectroscopically confirmed in the near-infrared as UCDs with spectral types from M7.5V to L9, the latest being the unusual blue L dwarf 2MASSJ11263991-5003550. Our catalogue selection method is presented enabling UCDs from ~M8V to the L-T transition to be selected down to a 2MASS limiting magnitude of Ks=~14.5mag (for S/N>=10).
