- ID:
- ivo://CDS.VizieR/J/ApJ/856/67
- Title:
- VLA 3GHz radio source catalog in the Lockman Hole
- Short Name:
- J/ApJ/856/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We made two new sensitive (rms noise {sigma}_n_~1{mu}Jy/beam) high-resolution ({theta}=3.0" and {theta}=0.66" FWHM) S-band (2<{nu}<4GHz) images covering a single JVLA primary beam (FWHM~14') centered on RAJ2000=10:46,DEJ2000=+59:01 in the Lockman Hole. These images yielded a catalog of 792 radio sources, 97.7+/-0.8% of which have infrared counterparts stronger than S~2{mu}Jy at {lambda}=4.5{mu}m. About 91% of the radio sources found in our previously published, comparably sensitive low-resolution ({theta}=8" FWHM) image covering the same area were also detected at 0.66" resolution, so most radio sources with S(3GHz)>~5{mu}Jy have angular structure {phi}<~0.66". The ratios of peak brightness in the 0.66" and 3" images have a distribution indicating that most {mu}Jy radio sources are quite compact, with a median Gaussian angular diameter <{phi}>=0.3"+/-0.1" FWHM and an rms scatter {sigma}_{phi}_<~0.3" of individual sizes. Most of our {mu}Jy radio sources obey the tight far-infrared/radio correlation, indicating that they are powered by star formation. The median effective angular radius enclosing half the light emitted by an exponential disk is <{rho}_e_>~<{phi}>/2.43~0.12", so the median effective radius of star-forming galaxies at redshifts z~1 is <r_e_>~1.0kpc.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/896/18
- Title:
- VLA imaging of obscured WISE+NVSS QSOs
- Short Name:
- J/ApJ/896/18
- Date:
- 07 Mar 2022 07:27:35
- Publisher:
- CDS
- Description:
- We present new subarcsecond-resolution Karl G. Jansky Very Large Array (VLA) imaging at 10GHz of 155 ultraluminous (Lbol~10^11.7^-10^14.2^L_{sun}_) and heavily obscured quasars with redshifts z~0.4-3. The sample was selected to have extremely red mid-infrared-optical color ratios based on data from the Wide-Field Infrared Survey Explorer (WISE) along with a detection of bright, unresolved radio emission from the NRAO VLA Sky Survey (NVSS) or Faint Images of the Radio Sky at Twenty cm Survey. Our high-resolution VLA observations have revealed that the majority of the sources in our sample (93 out of 155) are compact on angular scales <0.2 (<=1.7kpc at z~2). The radio luminosities, linear extents, and lobe pressures of our sources are similar to young radio active galactic nuclei (e.g., gigahertz-peaked spectrum [GPS] and compact steep-spectrum [CSS] sources), but their space density is considerably lower. Application of a simple adiabatic lobe expansion model suggests relatively young dynamical ages (~10^4-7yr^), relatively high ambient ISM densities (~1-10^4^cm^-3^), and modest lobe expansion speeds (~30-10000km/s). Thus, we find our sources to be consistent with a population of newly triggered, young jets caught in a unique evolutionary stage in which they still reside within the dense gas reservoirs of their hosts. Based on their radio luminosity function and dynamical ages, we estimate that only ~20% of classical large-scale FR I/II radio galaxies could have evolved directly from these objects. We speculate that the WISE-NVSS sources might first become GPS or CSS sources, of which some might ultimately evolve into larger radio galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/461/197
- Title:
- VLA NH3 observations of 5 IRAS sources
- Short Name:
- J/A+A/461/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high angular resolution images with the Very Large Array (VLA) allow us to explore the general properties of protostellar cores in massive star forming regions at large distances. We observed the NH3 (J, K)=(1, 1) and (2, 2) lines toward five massive protostar candidates (IRAS 18196-1331, IRAS 18352-0148, IRAS 18361-0627, IRAS 18414-0339 and IRAS 19474+2637) with the VLA D configuration.
- ID:
- ivo://CDS.VizieR/J/A+A/336/339
- Title:
- VLA observations of ultracompact HII regions
- Short Name:
- J/A+A/336/339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Very Large Array (VLA) to search for radio continuum emission towards a sample of 67 IRAS sources selected from a previous study. All observed sources are associated with high density molecular gas, exhibit an infrared spectral energy distribution characteristic of very cold young stellar objects and many of them are associated with H_2_O masers. The observed sample is divided into two groups of sources: High, with IRAS spectral energy distributions resembling those of ultracompact HII regions, and Low, for which previously collected evidence suggests that they may contain a higher fraction of protostellar objects than the High group; such objects might not have started hydrogen burning yet. Radio continuum emission was detected towards 37 sources (55%), although only in 22 cases an association with the IRAS source is established. Of the latter, 9 (24%) objects belong to the Low type and 13 (43%) to the High type. Thus, we find that 76% of Low and 57% of High sources are not associated with a radio counterpart. Because the majority of the sources have luminosities above ~10^4^L_{sun}_, corresponding to central stars of spectral type between B2 and O7, the lack of radio emission is interpreted as being due to the action of accreting matter that chokes off the expansion of the ionised gas. We show that this require s only moderate mass accretion rates, below ~10^-4^M_{sun}_/yr. Alternatively, dust absorption can also effectively absorb UV photons and the gas column density implied by our observations indicates values in excess of 10^22^cm^-2^. The physical properties of IRAS sources with associated radio counterpa rt derived from the present observations do not distinguish between High and Low sources. These sources are likely to be ZAMS stars with variable amounts of dust within the ionised region which acts as UV field absorber. The large majority of detected sources (75%) have spherical or unresolved morphology, while 15% are irregular or multiply peaked and only 10% have a core-halo structure. These results agree with the known properties of ultracompact HII regions, even though the average luminosity of the present sample is an order of magnitude lower than that in previous studies.
- ID:
- ivo://CDS.VizieR/J/AJ/138/33
- Title:
- VLT JHKs imaging of RCW 38
- Short Name:
- J/AJ/138/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of high angular resolution adaptive optics (AO) near-infrared (JHKs) observations of the deeply embedded massive cluster RCW 38 using NACO on the Very Large Telescope. Narrowband AO observations centered at wavelengths of 1.28um, 2.12um, and 2.17um were also obtained. The area covered by these observations is about 0.5pc^2^, centered on the O-star RCW 38 IRS 2. We use the JHKs colors to identify young stars with infrared (IR) excess in this region.
- ID:
- ivo://CDS.VizieR/J/AJ/128/1254
- Title:
- VLT 3.8{mu}m Trapezium catalog
- Short Name:
- J/AJ/128/1254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep 3.8{mu}m L' imaging observations of the Trapezium cluster in Orion obtained with the ESO VLT. We use these observations to (1) search for infrared excess emission and evidence for protoplanetary disks associated with the faint, substellar population of this young cluster and (2) investigate the nature and extent of a recently discovered population of deeply embedded sources located in dense molecular gas behind the cluster. We detected 38 L' sources with substellar luminosities. In addition, we detected 24 L' sources that were spectroscopically classified as substellar objects in previous studies. Examining the infrared colors of all these sources, we determine an infrared excess fraction of 50%{+/-}20% from the J, H, K_s_ and L' colors for both the luminosity-selected and spectroscopically selected substellar samples.
- ID:
- ivo://CDS.VizieR/J/ApJ/898/L38
- Title:
- VLT/SPHERE Y-band images of MWC 758 at two epochs
- Short Name:
- J/ApJ/898/L38
- Date:
- 21 Mar 2022 09:24:26
- Publisher:
- CDS
- Description:
- More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses-companion-disk interaction and gravitational instability (GI)-predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ~5yr using the SPHERE instrument on the Very Large Telescope (VLT), we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is 0.22+/-0.03/yr, pointing to a driver at 172_-14_^+18^ au around a 1.9M_{sun}_ central star if it is on a circular orbit. In addition, we witness time-varying shadowing effects on a global scale that are likely originating from an inner disk.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A25
- Title:
- VLT/X-shooter observations of PHL293B
- Short Name:
- J/A+A/533/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present VLT/X-shooter spectroscopic observations in the wavelength range {lambda}{lambda}3000-23000{AA} of the extremely metal-deficient blue compact dwarf (BCD) galaxy PHL 293B containing a luminous blue variable (LBV) star and compare them with previous data. This BCD is one of the two lowest-metallicity galaxies where LBV stars were detected, allowing us to study the LBV phenomenon in the extremely low metallicity regime. We determine abundances of nitrogen, oxygen, neon, sulfur, argon, and iron by analyzing the fluxes of narrow components of the emission lines using empirical methods and study the properties of the LBV from the fluxes and widths of broad emission lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/31
- Title:
- VMC survey. XXIX. Star formation in the SMC
- Short Name:
- J/ApJ/858/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we report a clustering analysis of upper main-sequence stars in the Small Magellanic Cloud, using data from the VMC survey (the VISTA near-infrared YJKs survey of the Magellanic system). Young stellar structures are identified as surface overdensities on a range of significance levels. They are found to be organized in a hierarchical pattern, such that larger structures at lower significance levels contain smaller ones at higher significance levels. They have very irregular morphologies, with a perimeter-area dimension of 1.44+/-0.02 for their projected boundaries. They have a power-law mass-size relation, power-law size/mass distributions, and a log-normal surface density distribution. We derive a projected fractal dimension of 1.48+/-0.03 from the mass-size relation, or of 1.4+/-0.1 from the size distribution, reflecting significant lumpiness of the young stellar structures. These properties are remarkably similar to those of a turbulent interstellar medium, supporting a scenario of hierarchical star formation regulated by supersonic turbulence.
- ID:
- ivo://CDS.VizieR/J/A+A/636/A48
- Title:
- VMC Survey. XXXVII. MC AGB stars
- Short Name:
- J/A+A/636/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Variability is a key property of stars on the asymptotic giant branch (AGB). Selection criteria are derived based on colour-colour and colour-magnitude diagrams from the combination of VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC, and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a sample of 1299 candidate obscured AGB stars is selected. K-band LCs are constructed combining the epoch photometry available in the VMC survey with literature data, analysed for variability and fitted with a single period sine curve to derive mean magnitudes, amplitudes and periods. A subset of 254 stars are either new variables, or known variables where the period we find is better determined than the literature value, or longer than 1000 days. The spectral energy distributions (SEDs) of these stars are fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars (Be stars, Hii regions and young stellar objects [YSOs]) are also fitted to have templates of the most likely contaminants in the sample. A sample of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days although some of them have alternative shorter periods.
