We present the results of new radio observations carried out with the Karl G. Jansky Very Large Array C-configuration at 5.5GHz for a sample of southern narrow-line Seyfert 1 galaxies (NLS1s). This work increases the number of known radio-detected NLS1s in the southern hemisphere, and confirms that the radio emission of NLS1s is mainly concentrated in a central region at kpc-scale and only a few sources show diffuse emission. In radio-quiet NLS1s, the radio luminosity tends to be higher in steep-spectrum sources and be lower in flat-spectrum sources, which is opposite to radio-loud NLS1s. This may be because the radio emission of steep NLS1s is dominated by misaligned jets, AGN-driven outflows, or star formation superposing on a compact core. Instead the radio emission of flat NLS1s may be produced by a central core which has not yet developed radio jets and outflows. We discover new NLS1s harboring kpc-scale radio jets and confirm that a powerful jet does not require a large-mass black hole to be generated. We also find sources dominated by star formation. These NLS1s could be new candidates in investigating the radio emission of different mechanisms.
We have conducted a search for ionized gas at 3.6cm, using the Very Large Array, toward 31 Galactic intermediate- and high-mass clumps detected in previous millimeter continuum observations. In the 10 observed fields, 35 HII regions are identified, of which 20 are newly discovered. Many of the HII regions are multiply peaked indicating the presence of a cluster of massive stars. We find that the ionized gas tends to be associated toward the millimeter clumps; of the 31 millimeter clumps observed, nine of these appear to be physically related to ionized gas, and a further six have ionized gas emission within 1'. For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7%+/-8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power-law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars.
We present new observations of the C-band continuum emission and masers to assess high-mass (>8M_{sun}_) star formation at early evolutionary phases in the inner 200pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuum observation is complete to free-free emission from stars above 10-11M_{sun}_ in 91% of the covered area. We identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact HII regions, 12 are candidates of ultracompact HII regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. We detect class II CH_3_OH masers at 23 positions, among which six are new detections. We confirm six known H_2_CO masers in two high-mass star-forming regions and detect two new H_2_CO masers toward the Sgr C cloud, making it the ninth region in the Galaxy that contains masers of this type. In spite of these detections, we find that current high-mass star formation in the inner CMZ is only taking place in seven isolated clouds. The results suggest that star formation at early evolutionary phases in the CMZ is about 10 times less efficient than expected from the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. This means that if there will be any impending, next burst of star formation in the CMZ, it has not yet begun.
We present new results based on high-resolution observations of Sgr A West at the Galactic center with the Very Large Array (VLA) at 1.3cm. By combining recent observations with those made at earlier epochs with the VLA at wavelengths of 1.3 and 3.6cm, we measured proper motions for 71 compact HII components in the central 80" (3pc, assuming D=8pc). Using VLA archival data for the H92{alpha} radio recombination line, we also investigated radial velocities in the LSR velocity range from +200 to -415km/s. Combining proper motion and radial velocity measurements, we have determined the three-dimensional velocity distribution in Sgr A West.
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.
The source G25.65+1.05 (RAFGL7009S, IRAS 18316-0602) is the least studied of the three regions of massive star formation known to show exceptionally powerful H_2_O maser bursts. We report spectral line observations of the H_2_O maser at 22GHz, the methanol maser transitions at 6.7, 12.2, and 44GHz, and the continuum in these same frequency bands with The Karl G. Jansky Very Large Array at the post-burst epoch of 2017. For the first time, maps of 22GHz H_2_O and 44GHz CH_3_OH maser spots are obtained and the absolute position of the 22GHz H_2_O bursting feature is determined with milliarcsecond precision. We detected four continuum components, three of which are closely spaced in a linear orientation, suggesting a physical link between them.
This table contains a deep centimeter-wavelength catalog of the Orion Nebula Cluster (ONC), based on a 30-hr single-pointing observation with the Karl G. Jansky Very Large Array (JVLA) in its high-resolution A configuration using two 1-GHz bands centered on 4.7 and 7.3 GHz. A total of 556 compact sources were detected in a map with a nominal rms noise of 3 µJy/beam, limited by complex source structure and the primary beam response. Compared to previous catalogs, these detections increase the sample of known compact radio sources in the ONC by more than a factor of seven. The new data show complex emission on a wide range of spatial scales. Following a preliminary correction for the wideband primary-beam response, the authors determine radio spectral indices for 170 sources whose index uncertainties are less than +/-0.5. They compare the radio to the X-ray and near-infrared point-source populations, noting similarities and differences. The observations were carried out with the JVLA of the National Radio Astronomy Observatory on 2012 September 30 and October 2-5 under the auspices of the project code SD630. Data were taken using the VLA's C-band (4-8 GHz) receivers in full polarization mode, with two 1-GHz basebands centered at 4.736 and 7.336 GHz to provide a good baseline for source spectral index determination. Apart from the first epoch, the field was simultaneously observed with the Chandra X-Ray Observatory. Mostly of interest for variability information, these data will be presented as part of a follow-up paper. This table was created by the HEASARC in September 2016 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/822/93">CDS Catalog J/ApJ/822/93</a> file table1.dat (the compact source catalog). Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018. This is a service provided by NASA HEASARC .
We have used the Very Large Array (VLA) to conduct a survey for radio continuum emission in the sample of 52 Seyfert nuclei selected from the optical spectroscopic galaxy catalog of Ho, Filippenko, & Sargent (1995, Cat. <J/ApJS/98/477>. This Seyfert sample is the most complete and least biased available, and, as such, it will be useful for a variety of statistical analyses. Here we present the observations, measurements, and an atlas of radio maps. The observations were made at 6 cm in the B array and at 20 cm in the A array, yielding matched angular resolutions of ~1". We detected 44 objects (85%) at 6 cm and 37 objects (71%) at 20 cm above a 3{sigma} threshold of 0.12mJy/beam. The sources have a wide range of radio powers (P~10^19^-10^25^W/Hz), spectral indices ({alpha}^20^_6_~+0.5 to 1), and linear sizes (L~few tens pc - 15kpc). The morphology of the radio emission is predominantly that of a compact core, either unresolved or slightly resolved, occasionally accompanied by elongated, jetlike features. Linearly polarized emission was detected at 6 cm in 12 sources, nine of which were also detected at 20 cm.
We have determined 194 Faraday rotation measures (RMs) of polarized extragalactic radio sources using new, multi-channel polarization observations at frequencies around 1.4GHz from the Very Large Array in the Galactic plane at 17{deg}<=l<=63{deg} and 205{deg}<=l<=253{deg}. This catalog fills in gaps in the RM coverage of the Galactic plane between the Canadian Galactic Plane Survey (CGPS; Taylor et al. 2003, Cat. VI/128; Brown et al. 2003, Cat. J/ApJS/145/213) and Southern Galactic Plane Survey (SGPS; Haverkorn et al. 2006ApJS..167..230H; Brown et al. 2007, Cat. J/ApJ/663/258).
This table contains results from a high-resolution radio survey of the Sloan Digital Sky Survey (SDSS) Southern Equatorial Stripe, also known as Stripe 82. This 1.4-GHz survey was conducted with the Very Large Array (VLA) primarily in the A configuration, with supplemental B configuration data to increase sensitivity to extended structure. The survey has an angular resolution of 1.8 arcseconds and achieves a median rms noise of 52 µJy/beam (µJy/beam) over 92 deg<sup>2</sup>. This is the deepest 1.4-GHz survey to achieve this large of an area, filling a gap in the phase space between small, deep and large, shallow surveys. It also serves as a pilot project for a larger high-resolution survey with the Expanded Very Large Array (EVLA). The authors discuss the technical design of the survey and details of the observations, and outline their method for data reduction, in the reference paper. They present a catalog of 17,969 isolated radio components, for an overall source density of ~195 sources deg<sup>-2</sup>. The astrometric accuracy of the data is excellent, with an internal check utilizing multiply observed sources yielding an rms scatter of 0.19 arcseconds in both Right Ascension and Declination. A comparison to the SDSS DR7 Quasar Catalog further confirms that the astrometry is well-tied to the optical reference frame, with mean offsets of 0.02" +/- 0.01" in Right Ascension, and 0.01" +/- 0.02" in Declination. A check of their photometry reveals a small, negative CLEAN-like bias on the level of 35 uJy. The authors report on the catalog completeness, finding that 97% of FIRST-detected quasars are recovered in the new Stripe 82 radio catalog, while faint, extended sources are more likely to be resolved out by the resolution bias. In their paper, they conclude with a discussion of the optical counterparts to the catalog sources, including 76 newly detected radio quasars. The full catalog as well as a search page and cutout server are available online at <a href="http://third.ucllnl.org/cgi-bin/stripe82cutout">http://third.ucllnl.org/cgi-bin/stripe82cutout</a>. The SDSS Stripe 82 observations were made with the National Radio Astronomy Observatory's (NRAO's) VLA. The data were collected over two VLA cycles, 2007-2008 and 2008-2009. The majority of the observations were taken in the A configuration, but the authors also obtained B-configuration coverage of the area in order to improve the sampling of the Fourier (U-V) plane and to increase sensitivity to the extended structure. Area 1 (delineated in black in Figure 1(a) of the paper) was covered in the A and B configurations in 2007-2008, and Area 2 (delineated in purple in Figure 1(a) of the paper) in the A and B configurations in 2008-2009. Area 1 is made up of 275 pointings, and Area 2 has 374, coming to 649 fields, and 92 deg<sup>2</sup> covered in total. This table was created by the HEASARC in August 2013 based on a complete machine-readable version of Table 1 from the reference paper which was kindly provided by the first author. This is a service provided by NASA HEASARC .
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