- 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.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/108/79
- Title:
- Ultra-steep spectrum radiosources
- Short Name:
- J/A+AS/108/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio sources with ultra-steep spectra (USS; spectral index <~ -1.0) have been found to be excellent tracers of galaxies at redshifts z>~2. The samples are selected from the set of catalogues referenced below, in a range of frequencies from 38 to 408MHz; they are are fainter by a factor of three than the previously well-studied samples of USS sources from 4C. Snapshot observations of sources from these samples have been made with the VLA at 1.5arcsec resolution and are presented in the printed paper. The list of the sources (Appendix A of the paper) includes positions, flux densities and radio structures for a total number of 605 sources derived from these observations.
- ID:
- ivo://CDS.VizieR/J/AJ/123/637
- Title:
- Ultra-steep-spectrum radio sources
- Short Name:
- J/AJ/123/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical and/or near-IR images of 128 ultra-steep-spectrum radio sources. Roughly half of the objects are identified in the optical images (R<~24), while in the near-IR images, more than 94% are detected at K<~22. The mean K magnitude is 19.26 within a 2" diameter aperture. The distribution of R-K colors indicates that at least one-third of the objects observed have very red colors (R-K>5). The major axes of the identifications in the K band are preferentially oriented along the radio axes, with half of them having compact morphologies. The 22 sources with spectroscopic redshifts and K-band magnitudes follow the K-z relation found from previous radio samples, but with a larger scatter.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/303
- Title:
- Ultra steep spectrum radio sources catalog
- Short Name:
- J/A+AS/143/303
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The three tables contain the 669 Ultra Steep Spectrum sources from the 3 samples WN (WENSS-NVSS), TN (TEXAS-NVSS) and MP (MRC-PMN) (tables A.1, A.2 and A.3). For each source, the radio fluxes from the surveys and from VLA or ATCA observations are given, as well as coordinates, radio structure, angular size and position angle determined from the radio map indicated in the last column.
- ID:
- ivo://CDS.VizieR/J/A+A/452/739
- Title:
- ULX sources and FIRST radio sources
- Short Name:
- J/A+A/452/739
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We search for ultra luminous X-ray source (ULXs) radio counterparts located in nearby galaxies in order to constrain their physical nature. Our work is based on a systematic cross-identification of the most recent and extensive available ULX catalogues and archival radio data. A catalogue of 70 positional coincidences is reported. Most of them are located within the galaxy nucleus. Among them, we find 11 new cases of non-nuclear ULX sources with possibly associated radio emission.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A11
- Title:
- 70um-1.2mm and N_2_H+ maps of IRDC18454 (W43)
- Short Name:
- J/A+A/538/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The earliest stages of high-mass star formation are still poorly characterized. Densities, temperatures and kinematics are crucial parameters for simulations of high-mass star formation. It is also unknown whether the initial conditions vary with environment. We want to investigate the youngest massive gas clumps in the environment of extremely active star formation. We selected the IRDC18454 complex, directly associated with the W43 Galactic mini-starburst, and observed it in the continuum emission between 70um and 1.2mm with Herschel, APEX and the 30m telescope, and in spectral line emission of N_2_H+ and ^13^CO with the Nobeyama 45m, the IRAM 30m and the Plateau de Bure Interferometer.
- ID:
- ivo://CDS.VizieR/J/ApJS/249/1
- Title:
- 500um risers with HerMES & SPIRE drop-outs with S2CLS
- Short Name:
- J/ApJS/249/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our systematic search for the reddest far-infrared (FIR) and submillimeter (sub-mm) galaxies using the data from the Herschel Multi-tiered Extragalactic Survey (HerMES) and the SCUBA2 Cosmological Legacy Survey (S2CLS). The red FIR galaxies are "500{mu}m risers," whose spectral energy distributions increase with wavelength across the three FIR passbands of the Spectral and Photometric Imaging REceiver (SPIRE) of Herschel. Within 106.5deg^2^ of the HerMES fields, we have selected 629 500{mu}m risers. The red sub-mm galaxies are "SPIRE drop-outs," which are prominent detections in the S2CLS 850{mu}m data but are extremely weak or invisible in the SPIRE bands. Within the 2.98deg^2^ common area of HerMES and S2CLS, we have selected 95 such objects. These very red sources could be dusty starbursts at high redshifts (z>~4-6) because the peak of their cold-dust emission heated by star formation is shifted to the reddest FIR/sub-mm bands. The surface density of 500{mu}m risers is ~8.2deg^-2^ at the >=20mJy level in 500{mu}m, while that of SPIRE drop-outs is ~19.3deg^-2^ at the >=5mJy level in 850{mu}m. Both types of objects could span a wide range of redshifts, however. Using deep radio data in these fields to further select the ones likely at the highest redshifts, we find that the surface density of z>6 candidates is 5.5deg^-2^ among 500{mu}m risers and is 0.8-13.6deg^-2^ among SPIRE drop-outs. If this is correct, the dust-embedded star formation processes in such objects could contribute comparably as Lyman-break galaxies to the global SFR density at z>6.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/1135
- Title:
- Unbiased sample of CSS and GPS
- Short Name:
- J/MNRAS/416/1135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compact Steep Spectrum (CSS) and Gigahertz Peaked Spectrum (GPS) sources are classes of compact, powerful, extragalactic objects. These sources are thought to be the earliest stages in the evolution of radio galaxies, capturing the ignition (or, in some cases, re-ignition) of the active galactic nucleus. As well as serving as probes of the early stages of large-scale radio sources, these sources are good, stable, amplitude calibrators for radio telescopes. We present an unbiased flux density limited (>1.5Jy at 2.7GHz) catalogue of these objects in the Southern hemisphere, including tabulated data, radio spectra, and where available, optical images and measurements. The catalogue contains 26 sources, consisting of two new candidates and 15 known CSS sources, and nine known GPS sources. We present new Australia Telescope Compact Array (ATCA) data on 10 of these 26 sources, and data on a further 42 sources which were excluded from our final sample. This bright sample will serve as a reference sample for comparison with subsequent faint (mJy level) samples of CSS and GPS candidates currently being compiled.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/4
- Title:
- Unidentified {gamma}-ray sources. III. Radio
- Short Name:
- J/ApJS/207/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- About one-third of the {gamma}-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) have no firmly established counterpart at lower energies and so are classified as unidentified {gamma}-ray sources (UGSs). Here, we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with the Westerbork Synthesis Radio Telescope in the northern hemisphere. First, we investigate the low-frequency radio properties of blazars, the largest known population of {gamma}-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS, Rengelink et al. 1997, Cat. J/A+AS/124/259; superseded by Cat. VIII/62) with those of the NRAO Very Large Array Sky Survey (NVSS, Condon et al. 1998, Cat. VIII/65). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in the literature to look for infrared and optical counterparts of the {gamma}-ray blazar candidates selected using the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research, we identify 23 new {gamma}-ray blazar candidates out of the 32 UGSs investigated. Comparison with previous results on the UGSs is also presented. Finally, we speculate on the advantages of using low-frequency radio observations to associate UGSs and to search for {gamma}-ray pulsar candidates.
- ID:
- ivo://CDS.VizieR/J/MNRAS/484/3691
- Title:
- UTMOST pulsar timing programme. I.
- Short Name:
- J/MNRAS/484/3691
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an overview and the first results from a large-scale pulsar timing programme that is part of the UTMOST project at the refurbished Molonglo Observatory Synthesis Radio Telescope (MOST) near Canberra, Australia. We currently observe more than 400 mainly bright southern radio pulsars with up to daily cadences. For 205 (8 in binaries, 4 millisecond pulsars), we publish updated timing models, together with their flux densities, flux density variability, and pulse widths at 843 MHz, derived from observations spanning between 1.4 and 3 yr. In comparison with the ATNF pulsar catalogue, we improve the precision of the rotational and astrometric parameters for 123 pulsars, for 47 by at least an order of magnitude. The time spans between our measurements and those in the literature are up to 48 yr, which allow us to investigate their long-term spin-down history and to estimate proper motions for 60 pulsars, of which 24 are newly determined and most are major improvements. The results are consistent with interferometric measurements from the literature. A model with two Gaussian components centred at 139 and 463km/s fits the transverse velocity distribution best. The pulse duty cycle distributions at 50 and 10 per cent maximum are best described by lognormal distributions with medians of 2.3 and 4.4 per cent, respectively. We discuss two pulsars that exhibit spin-down rate changes and drifting subpulses. Finally, we describe the autonomous observing system and the dynamic scheduler that has increased the observing efficiency by a factor of 2-3 in comparison with static scheduling.
