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Start Over Subject radio astronomy Content Level Research
511. First Caltech-Jodrell Bank VLBI Survey. II.
ID:
ivo://CDS.VizieR/J/ApJS/98/33
Title:
First Caltech-Jodrell Bank VLBI Survey. II.
Short Name:
J/ApJS/98/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report lambda-18 cm VLBI observations made in 1991 September of a further 25 objects from the first Caltech-Jodrell Bank VLBI Survey (the CJ1 survey). The CJ1 sample is a complete, flux-density limited sample of 135 radio sources with total flux density at lambda-6cm between 0.7 and 1.3Jy. These observations complete the lambda-18cm part of the survey. Together with the results of Paper I (Polatidis et al., <J/ApJS/98/1>), we have now observed 81 CJ1 sources at lambda-18cm. Later papers in the series will present lambda-6cm observations and the analysis and interpretation of the results.
512. First detection of HCOOH in TW Hya disk with ALMA
ID:
ivo://CDS.VizieR/J/ApJ/862/L2
Title:
First detection of HCOOH in TW Hya disk with ALMA
Short Name:
J/ApJ/862/L2
Date:
21 Oct 2021
Publisher:
CDS
Description:
The formation of asteroids, comets, and planets occurs in the interior of protoplanetary disks during the early phase of star formation. Consequently, the chemical composition of the disk might shape the properties of the emerging planetary system. In this context, it is crucial to understand whether and what organic molecules are synthesized in the disk. In this Letter, we report the first detection of formic acid (HCOOH) toward the TW Hydrae protoplanetary disk. The observations of the trans-HCOOH 6_(1,6)-5(1,5)_ transition were carried out at 129GHz with Atacama Large Millimeter/Submillimeter Array (ALMA). We measured a disk-averaged gas-phase t-HCOOH column density of ~(2-4)x10^12^cm^-2^, namely as large as that of methanol. HCOOH is the first organic molecule containing two oxygen atoms detected in a protoplanetary disk, a proof that organic chemistry is very active, albeit difficult to observe, in these objects. Specifically, this simplest acid stands as the basis for synthesis of more complex carboxylic acids used by life on Earth.
513. First list of the Karachentsev catalog
ID:
ivo://CDS.VizieR/J/A+AS/141/469
Title:
First list of the Karachentsev catalog
Short Name:
J/A+AS/141/469
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present HI observations of the galaxies in the first list of the Karachentsev catalog of previously unknown nearby dwarf galaxies (Karachentseva & Karachentsev, 1998, Cat. <J/A+AS/127/409>). This survey covers all known nearby galaxy groups within the Local Volume (i.e. within 10Mpc) and their environment, that is about 25% of the total sky. A total of 257 galaxies have been observed with a detection rate of 60%. We searched a frequency band corresponding to heliocentric radial velocities from -470km/s to ~+4000km/s. Non-detections are either due to limited coverage in radial velocity, confusion with Local HI (mainly in the velocity range -140km/s to +20km/s), or lack of sensitivity for very weak emission. 25% of the detected galaxies are located within the Local Volume. Those galaxies are dwarf galaxies judged by their optical linear diameter (1.4+/-0.2kpc on the average), their mean total HI mass (4.6x10^7^M_{sun}_), and their observed linewidths (39km/s).
514. FIRST-2MASS dust-reddened QSO spectra
ID:
ivo://CDS.VizieR/J/ApJ/757/51
Title:
FIRST-2MASS dust-reddened QSO spectra
Short Name:
J/ApJ/757/51
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a sample of 120 dust-reddened quasars identified by matching radio sources detected at 1.4GHz in the Faint Images of the Radio Sky at Twenty Centimeters survey (FIRST) with the near-infrared Two Micron All Sky Survey catalog (2MASS) and color-selecting red sources. Optical and/or near-infrared spectroscopy provide broad wavelength sampling of their spectral energy distributions that we use to determine their reddening, characterized by E(B-V). We demonstrate that the reddening in these quasars is best described by Small-Magellanic-Cloud-like dust. This sample spans a wide range in redshift and reddening (0.1<~z<~3, 0.1<~E(B-V)<~1.5), which we use to investigate the possible correlation of luminosity with reddening. At every redshift, dust-reddened quasars are intrinsically the most luminous quasars. We interpret this result in the context of merger-driven quasar/galaxy co-evolution where these reddened quasars are revealing an emergent phase during which the heavily obscured quasar is shedding its cocoon of dust prior to becoming a "normal" blue quasar. When correcting for extinction, we find that, depending on how the parent population is defined, these red quasars make up <~15%-20% of the luminous quasar population. We estimate, based on the fraction of objects in this phase, that its duration is 15%-20% as long as the unobscured, blue quasar phase.
515. FIRST-2MASS faint sources
ID:
ivo://CDS.VizieR/J/ApJ/607/60
Title:
FIRST-2MASS faint sources
Short Name:
J/ApJ/607/60
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have constructed a sample of bright near-infrared sources that are detected at radio wavelengths but undetected on the first-generation Palomar Observatory Sky Survey (POSSI) plates in order to search for a population of dust-obscured quasars. Optical and infrared spectroscopic follow-up of the sample has led to the discovery of 17 heavily reddened quasars (B-K>6.5), 14 of which are reported here for the first time. This has allowed us to define a region in the R-K, J-K color plane in which 50% of the radio-selected objects are highly reddened quasars. We compare the surface density of this previously overlooked population to that of ultraviolet-excess radio-selected quasars, finding that they make up ~20% of the total quasar population for K<~15.5.
516. FIRST-2MASS red quasar survey
ID:
ivo://CDS.VizieR/J/ApJ/667/673
Title:
FIRST-2MASS red quasar survey
Short Name:
J/ApJ/667/673
Date:
21 Oct 2021
Publisher:
CDS
Description:
Combining radio observations with optical and infrared color selection, demonstrated in our pilot study to be an efficient selection algorithm for finding red quasars, we have obtained optical and infrared spectroscopy for 120 objects in a complete sample of 156 candidates from a sky area of 2716deg^2^.
517. FIRST-Optical-VLA survey for lensed radio lobes
ID:
ivo://CDS.VizieR/J/AJ/130/1977
Title:
FIRST-Optical-VLA survey for lensed radio lobes
Short Name:
J/AJ/130/1977
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from a survey for gravitationally lensed radio lobes. Lensed lobes are a potentially richer source of information about galaxy mass distributions than lensed point sources, which have been the exclusive focus of other recent surveys. Our approach is to identify radio lobes in the Faint Images of the Radio Sky at Twenty cm (FIRST, Cat. <VIII/71>) catalog and then search optical catalogs for coincident foreground galaxies, which are candidate lensing galaxies. We then obtain higher resolution images of these targets at both optical and radio wavelengths and obtain optical spectra for the most promising candidates. We present maps of several radio lobes that are nearly coincident with galaxies. We have not found any new and unambiguous cases of gravitational lensing. One radio lobe in particular, FOV J0743+1553, has two hot spots that could be multiple images produced by a z=0.19 spiral galaxy, but the lensing interpretation is problematic.
518. First quadrant IRDCs in CS(2-1) with Mopra
ID:
ivo://CDS.VizieR/J/ApJ/764/102
Title:
First quadrant IRDCs in CS(2-1) with Mopra
Short Name:
J/ApJ/764/102
Date:
21 Oct 2021
Publisher:
CDS
Description:
Infrared dark clouds (IRDCs) are believed to host the earliest stages of high-mass star and cluster formation. Because O stars typically travel short distances over their lifetimes, if IRDCs host the earliest stages of high-mass star formation then these cold, dense molecular clouds should be located in or near the spiral arms in the Galaxy. The Galactic distribution of a large sample of IRDCs should therefore provide information on Galactic structure. Moreover, determination of distances enables mass and luminosity calculations. We have observed a large sample of IRDC candidates in the first Galactic quadrant in the dense gas tracer CS(2-1) using the Mopra telescope in order to determine kinematic distances from the molecular line velocities. We find that the IRDCs are concentrated around a Galactocentric distance of ~4.5kpc, agreeing with the results of Simon et al. (2006, J/ApJ/653/1325). This distribution is consistent with the location of the Scutum-Centaurus spiral arm. The group of IRDCs near the Sun in the first quadrant detected in ^13^CO(1-0) in Simon et al. is not detected in the CS data. This discrepancy arises from the differences in the critical densities between the ^13^CO(1-0) and CS(2-1) lines. We determine that the Midcourse Space Experiment selected IRDCs are not a homogeneous population, and ^13^CO(1-0) traces a population of IRDCs with lower column densities and lower 1.1 mm flux densities in addition to more dense IRDCs detected in CS. Masses of the first quadrant IRDCs are calculated from ^13^CO(1-0) maps. We find a strong peak in the Galactocentric IRDC mass surface density distribution at R_Gal_~4.5kpc.
519. Flat-spectrum radio sources at 0.97-21.7GHz
ID:
ivo://CDS.VizieR/J/AZh/77/407
Title:
Flat-spectrum radio sources at 0.97-21.7GHz
Short Name:
J/AZh/77/407
Date:
21 Oct 2021
Publisher:
CDS
Description:
The results of observations of a complete sample of flat-spectrum radio sources with spectral indices {alpha}>-0.5 are presented. The sample was selected from the Zelenchuk Survey at 3.9GHz (See Cat. <VIII/49>) and contains all sources with declinations 4-6 degrees, galactic latitudes |b|>10 degrees, and 3.9-GHz fluxes >200mJy. Spectra at 0.97-21.7 GHz were obtained for all 69 sample sources. The spectra were classified and a correlation between variability amplitude and spectrum shape was found.
520. Flat-spectrum radio sources at 327 MHz
ID:
ivo://CDS.VizieR/J/A+AS/106/29
Title:
Flat-spectrum radio sources at 327 MHz
Short Name:
J/A+AS/106/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)