- ID:
- ivo://CDS.VizieR/J/A+A/648/A82
- Title:
- Quasar 3C 345 at 18 cm with RadioAstron
- Short Name:
- J/A+A/648/A82
- Date:
- 23 Mar 2022 16:32:52
- Publisher:
- CDS
- Description:
- Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron. We observed the flat spectrum radio quasar 3C 345 at 1.6GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode. Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300{mu}as as angular resolution, corresponding to a projected linear scale of about 2pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest uv-distances of 1.1x10^12^K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be >11 to explain the high brightness temperatures.
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Search Results
1302. Quasars from 7C survey
- ID:
- ivo://CDS.VizieR/J/MNRAS/307/293
- Title:
- Quasars from 7C survey
- Short Name:
- J/MNRAS/307/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the selection of candidate radio-loud quasars obtained by cross-matching radio source positions from the low-frequency (151-MHz) 7C survey with optical positions from five pairs of EO POSS-1 plates scanned with the Cambridge Automatic Plate-measuring Machine (APM). The sky region studied is centred at RA=10h28m, DE=+41{deg} and covers ~0.057sr. We present VLA observations of the quasar candidates, and tabulate various properties derived from the radio maps. We discuss the selection criteria of the resulting '7CQ' sample of radio-loud quasars. The 70 confirmed quasars, and some fraction of the 36 unconfirmed candidates, constitute a filtered sample with the following selection criteria: 151-MHz flux density S_151_>100mJy; POSS-I E-plate magnitude E~R<20; POSS-I colour (O-E)<1.8; the effective area of the survey drops significantly below S_151_~200mJy. We argue that the colour criterion excludes few if any quasars, but note, on the basis of recent work by Willott et al. (1998MNRAS.300..625W), that the E magnitude limit probably excludes more than 50 per cent of the radio-loud quasars.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/90
- Title:
- Radial profiles of 5 nearby galaxies
- Short Name:
- J/ApJ/858/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate (SFR), and local environment across the inner region of four local galaxies showing a wide range of molecular gas depletion times. We map HCN(1-0), HCO^+^(1-0), CS(2-1), ^13^CO(1-0), and C^18^O(1-0) across the inner few kiloparsecs of each target. We combine these data with short-spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel+ (2016ApJ...822L..26B) and Usero+ (2015AJ....150..115U). We test the degree to which changes in the dense gas fraction drive changes in the SFR. I_HCN_/I_CO_ (tracing the dense gas fraction) correlates strongly with I_CO_ (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, P_DE_ (Elmegreen 1989ApJ...338..178E). Therefore, I_HCN_/I_CO_ becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as I_HCN_/I_CO_~0.01 become common. The apparent ability of dense gas to form stars, {Sigma}_SFR_/{Sigma}_dense_ (where {Sigma}_dense_ is traced by the HCN intensity and the star formation rate is traced by a combination of H{alpha} and 24{mu}m emission), also depends on environment. {Sigma}_SFR_/{Sigma}_dense_ decreases in regions of high gas surface density, high stellar surface density, and high P_DE_. Statistically, these correlations between environment and both {Sigma}_SFR_/{Sigma}_dense_ and I_HCN_/I_CO_ are stronger than that between apparent dense gas fraction (I_HCN_/I_CO_) and the apparent molecular gas star formation efficiency {Sigma}_SFR_/{Sigma}_mol_. We show that these results are not specific to HCN.
- ID:
- ivo://CDS.VizieR/J/ApJ/746/156
- Title:
- Radio afterglow observations of GRBs
- Short Name:
- J/ApJ/746/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of radio afterglow observations of gamma-ray bursts (GRBs) over a 14 year period from 1997 to 2011. Our sample of 304 afterglows consists of 2995 flux density measurements (including upper limits) at frequencies between 0.6 GHz and 660 GHz, with the majority of data taken at 8.5 GHz frequency band (1539 measurements). We use this data set to carry out a statistical analysis of the radio-selected sample. The detection rate of radio afterglows has stayed unchanged almost at 31% before and after the launch of the Swift satellite. The canonical long-duration GRB radio light curve at 8.5 GHz peaks at three to six days in the source rest frame, with a median peak luminosity of 10^31^ erg/s/Hz. The peak radio luminosities for short-hard bursts, X-ray flashes, and the supernova-GRB classes are an order of magnitude or more fainter than this value. There are clear relationships between the detectability of a radio afterglow and the fluence or energy of a GRB, and the X-ray or optical brightness of the afterglow. However, we find few significant correlations between these same GRB and afterglow properties and the peak radio flux density. We also produce synthetic light curves at centimeter and millimeter bands using a range of blast wave and microphysics parameters derived from multiwavelength afterglow modeling, and we use them to compare to the radio sample. Finding agreement, we extrapolate this behavior to predict the centimeter and millimeter behavior of GRBs observed by the Expanded Very Large Array and the Atacama Large Millimeter Array.
- ID:
- ivo://CDS.VizieR/J/ApJS/237/27
- Title:
- Radio Ammonia Mid-plane Survey (RAMPS) pilot survey
- Short Name:
- J/ApJS/237/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Radio Ammonia Mid-Plane Survey (RAMPS) is a molecular line survey that aims to map a portion of the Galactic midplane in the first quadrant of the Galaxy (l=10{deg}-40{deg}, |b|<=0.4{deg}) using the Green Bank Telescope. We present results from the pilot survey, which has mapped approximately 6.5 square degrees in fields centered at l=10{deg}, 23{deg}, 24{deg}, 28{deg}, 29{deg}, 30{deg}, 31{deg}, 38{deg}, 45{deg}, and 47{deg}. RAMPS observes the NH3 inversion transitions NH_3_(1,1)-(5,5), the H_2_O 6_1,6_-5_2,3_ maser line at 22.235GHz, and several other molecular lines. We present a representative portion of the data from the pilot survey, including NH_3_(1,1) and NH_3_(2,2) integrated intensity maps, H_2_O maser positions, maps of NH_3_ velocity, NH_3_ line width, total NH_3_ column density, and NH_3_ rotational temperature.
- ID:
- ivo://CDS.VizieR/J/ApJ/581/844
- Title:
- Radio and Infrared observations of EROs
- Short Name:
- J/ApJ/581/844
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a sensitive multiwavelength analysis of the properties of extremely red objects (EROs). Our analysis employs deep RIzJHK photometry of an 8.5'x8.5' region to select a sample of 68 EROs with (R-K)>=5.3 and brighter than K=20.5 (5{sigma}). We combine this photometric data set with an extremely deep 1.4GHz radio map of the field obtained from the VLA. This map reaches a 1{sigma} limiting flux density of 3.5{mu}Jy , making it the deepest 1.4GHz map taken, and is sensitive enough to detect an active galaxy with L1.4>~10^23^W/Hz at z>1.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/285
- Title:
- Radio and IR counterparts of BLAST sources in CDFS
- Short Name:
- J/ApJ/703/285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified radio and/or mid-infrared counterparts to 198 out of 350 sources detected at >=5{sigma} over ~9deg^2^ centered on the Chandra Deep Field South by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) at 250, 350, and 500um. We have matched 114 of these counterparts to optical sources with previously derived photometric redshifts and fitted spectral energy distributions to the BLAST fluxes and fluxes at 70 and 160um acquired with the Spitzer Space Telescope. In this way, we have constrained dust temperatures, total far-infrared/submillimeter luminosities, and star formation rates for each source. Our findings show that, on average, the BLAST sources lie at significantly lower redshifts and have significantly lower rest-frame dust temperatures compared to submillimeter sources detected in surveys conducted at 850um. We demonstrate that an apparent increase in dust temperature with redshift in our sample arises as a result of selection effects. Finally, we provide the full multiwavelength catalog of >=5{sigma} BLAST sources contained within the complete ~9deg^2^ survey area.
- ID:
- ivo://CDS.VizieR/J/MNRAS/347/837
- Title:
- Radio and K-band obs. of Ultra-Steep sources
- Short Name:
- J/MNRAS/347/837
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 76 ultra-steep spectrum (USS) radio sources is defined from the 843-MHz Sydney University Molonglo Sky Survey (SUMSS) and 1.4-GHz NRAO VLA Sky Survey (NVSS) radio surveys with spectral index {alpha}<-1.3 and S(1.4GHz)>15mJy; 71 of these sources without bright optical or near-infrared counterparts at 1.385GHz were observed with the Australia Telescope Compact Array (ATCA), providing 5arcsec resolution images and subarcsec positional accuracy. To identify their host galaxies, near-infrared K-band images were obtained with IRIS2 at the AAT and SofI at the NTT; 92% of the USS sources could be identified down to K~20.5. 142 FITS files containing the radio maps and the K-band images are included in the fits subdirectory.
- ID:
- ivo://CDS.VizieR/J/AJ/141/182
- Title:
- Radio and optical properties of QSOs
- Short Name:
- J/AJ/141/182
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the largest homogeneous quasar sample with high-quality optical spectra and robust radio morphology classifications assembled to date, we investigate relationships between radio and optical properties with unprecedented statistical power. The sample consists of 4714 radio quasars from FIRST with S_20_>=2mJy and with spectra from the Sloan Digital Sky Survey (SDSS). Radio morphology classes include core-only (core), core-lobe (lobe), core-jet (jet), lobe-core-lobe (triple), and double-lobe.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/940
- Title:
- Radio and UV spectra of HVC toward the MC
- Short Name:
- J/ApJ/702/940
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the spectra of 139 early-type Large Magellanic Cloud (LMC) stars observed with Far Ultraviolet Spectroscopic Explorer and with deep radio Parkes HI 21cm observations along with those stars, we search for and analyze the absorption and emission from high-velocity gas at +90<={nu}_LSR_<=+175km/s. The HI column density of the high-velocity clouds (HVCs) along these sightlines ranges from <1018.4 to 1019.2cm^-2^. The incidence of the HVC metal absorption is 70%, significantly higher than the HI emission occurrence of 32%. We find that the mean metallicity of the HVC is [OI/HI]=-0.51+/-^0.12^_0.16_. This is the first example of a large (>10^6^M_{sun}_) HVC complex that is linked to stellar feedback occurring in a dwarf spiral galaxy.