- ID:
- ivo://CDS.VizieR/J/ApJS/152/81
- Title:
- CO survey toward starless cores
- Short Name:
- J/ApJS/152/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A CO survey is undertaken toward about 80% of the starless cores in the Lee & Myers catalog that can be observed in the northern hemisphere to investigate their general observational properties such as line width and intensity, from which one can deduce their environmental physical conditions. The peak ^12^CO intensity implies a kinetic temperature close to 10K, as is already known, but for some of the cores the kinetic temperature is much higher than 10K, suggesting either that they are not really starless or that they are externally heated. We derive the ratios of peak intensities and line widths for the pairs of ^12^CO and ^13^CO lines and find a value of ~1.7 for both. The linear correlations between them are most likely to be due to clumpy structure. These data are also compared with data sets of CS 2-1 and N_2_H^+^ 1-0 lines tracing high-density regions. It is found that the peak intensity and line width of ^13^CO are roughly correlated with those of CS, suggesting that the outer envelope is kinematically related to the inner dense core. Confirming that the ^12^CO lines seldom exhibit deep self-reversal features, whereas this is not unusual for the CS lines, we propose a heuristic model where the outer part is clumpy, but the inner part has a rather smooth density profile, with a uniform temperature and mean density decreasing outward. We apply three-dimensional radiative transfer calculations to this simple model, demonstrating that the essential observational features of the starless cores are successfully reproduced.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/203/15
- Title:
- Counterparts to 1.4GHz sources in ECDF-S
- Short Name:
- J/ApJS/203/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study a sample of 883 sources detected in a deep Very Large Array survey at 1.4GHz in the Extended Chandra Deep Field South. This paper focuses on the identification of their optical and infrared (IR) counterparts. We use a likelihood-ratio technique that is particularly useful when dealing with deep optical images to minimize the number of spurious associations. We find a reliable counterpart for 95% of our radio sources. Most of the counterparts (74%) are detected at optical wavelengths, but there is a significant fraction (21%) that are only detectable in the IR. Combining newly acquired optical spectra with data from the literature, we are able to assign a redshift to 81% of the identified radio sources (37% spectroscopic). We also investigate the X-ray properties of the radio sources using the Chandra 4Ms and 250ks observations. In particular, we use a stacking technique to derive the average properties of radio objects undetected in the Chandra images. The results of our analysis are collected in a new catalog containing the position of the optical/IR counterpart, the redshift information, and the X-ray fluxes. It is the deepest multi-wavelength catalog of radio sources, which will be used for future study of this galaxy population.
- ID:
- ivo://CDS.VizieR/J/ApJ/405/498
- Title:
- Counts and spectral indices at 8.44GHz
- Short Name:
- J/ApJ/405/498
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the VLA to make deep images of two 7x7' fields at 8.44 GHz with 10" resolution. With an rms noise of 3.2 and 5.1 {micro}Jy, respectively, in the two fields, we compiled a catalog of 82 sources. The normalized differential 8.44 GHz counts are similar to those at 1.41 and 4.86 GHz. All show a similarly steep submillijansky slope, which is only somewhat flatter than that expected for a nonevolving Euclidean population ({gamma}=2.5). Microjansky radio sources at 4.86 GHz have been identified with faint blue galaxies (18<~V<~28 mag). We argue that their expected median redshift is about 0.5-0.75. Hence, cosmological evolution may be needed to explain the steep slope of the microjansky counts. The 8.44 GHz counts must converge with slope {gamma}<2.0 below S(8.44)~300 nJy, or they would exceed the available field galaxy counts down to V~28 mag, and they must permanently converge below S(8.44)~20 nJy, or their integrated sky brightness would distort the observed thermal cosmic background radiation spectrum at centimeter wavelengths. The estimated 31.5 GHz sky brightness from nanojansky to jansky levels is <36 {micro}K (3{sigma}). Even if weak radio sources cluster on scales of degrees as faint galaxies do, their anisotropic contribution to the COBE DMR experiment (with 7deg FWHM-beam) would not exceed ~1.2{micro}K.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A74
- Title:
- 4C +29.45 OVRO and KNV fluxes curve
- Short Name:
- J/A+A/651/A74
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present the results of multi-epoch, multifrequency monitoring of blazar 4C +29.45, which was regularly monitored as part of the Interferometric Monitoring of GAmma-ray Bright Active Galactic Nuclei (iMOGABA) program - a key science program of the Korean Very long baseline interferometry Network (KVN). Observations were conducted simultaneously at 22, 43, 86, and 129GHz over the 4 years from 5 December 2012 to 28 December 2016. We also used additional data from the 15GHz Owens Valley Radio Observatory (OVRO) monitoring program. From the 15GHz light curve, we estimated the variability timescales of the source during several radio flux enhancements. We found that the source experienced six radio flux enhancements with variability timescales of 9-187days during the observing period, yielding corresponding variability Doppler factors of 9-27. From the simultaneous multifrequency KVN observations, we were able to obtain accurate radio spectra of the source and hence to more precisely measure the turnover frequencies {nu}_r_, of synchrotron self-absorption (SSA) emission with a mean value of {nu}_r_=28.9GHz. Using jet geometry assumptions, we estimated the size of the emitting region at the turnover frequency. We found that the equipartition magnetic field strength is up to two orders of magnitude higher than the SSA magnetic field strength (0.001-0.1G). This is consistent with the source being particle dominated. We performed a careful analysis of the systematic errors related to the making of these estimations. From the results, we concluded that the equipartition region is located upstream from the SSA region.
- ID:
- ivo://CDS.VizieR/J/other/SciA/1.9
- Title:
- C/2014 Q2 (Lovejoy) spectra
- Short Name:
- J/other/SciA/1.9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of numerous complex organic molecules (COMs; defined as those containing 6 or more atoms) around protostars shows that star formation is accompanied by an increase of molecular complexity. These COMs may be part of the material from which planetesimals and ultimately planets formed. Comets sample some of the oldest and most primitive material in the solar system, including ices, and are thus our best window into the volatile composition of the solar proto-planetary disk. Molecules identified to be present in cometary ices include water, simple hydrocarbons, oxygen, sulfur and nitrogen-bearing species, as well as a few COMs, such as ethylene glycol and glycine. Here, we report the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first identification of ethyl alcohol (ethanol, C2H5OH) and the simplest monosaccharide sugar glycolaldehyde (CH2OHCHO) in a comet. The abundances of ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12 and 0.02% relative to water), are somewhat higher than values measured in solar-type protostars. Overall, the high abundance of COMs in cometary ices supports formation through grain-surface reactions in the solar system protoplanetary disk.
- ID:
- ivo://CDS.VizieR/J/MNRAS/410/2690
- Title:
- CRATES sources at 30 GHz
- Short Name:
- J/MNRAS/410/2690
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the population of radio sources in the range ~2-200GHz is important for understanding their effects on measurements of the cosmic microwave background power spectrum. We report measurements of the 30-GHz flux densities of 605 radio sources from the Combined Radio All-sky Targeted Eight-GHz Survey (CRATES), which have been made with the One Centimetre Receiver Array-prototype (OCRA-p) on the Torun 32-m telescope. The flux densities of sources that were also observed by Wilkinson Microwave Anisotropy Probe (WMAP) and previous OCRA surveys are in broad agreement with those reported here, however a number of sources display intrinsic variability. We find a good correlation between the 30GHz and Fermi gamma-ray flux densities for common sources. We examine the radio spectra of all observed sources and report a number of gigahertz-peaked and inverted spectrum sources. These measurements will be useful for comparison to those from the Low Frequency Instrument of the Planck satellite, which will make some of its most sensitive observations in the region covered here.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A67
- Title:
- CRL618, MWC922 and M2-9 RRL spectra
- Short Name:
- J/A+A/603/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results from a pilot search for radio recombination line (RRL) emission at millimeter wavelengths in a small sample of pre-planetary nebulae (pPNe) and young PNe (yPNe) with emerging central ionized regions. Observations of the H30{alpha}, H31{alpha}, H39{alpha}, H41{alpha}, H48{beta}, H49{beta}, H51{beta}, and H55{gamma} lines at ~1 and ~3mm have been performed with the IRAM 30m radio telescope. These lines are excellent probes of the dense inner (<~150 au) and heavily obscured regions of these objects, where the yet unknown agents for PN-shaping originate. We detected mm-RRLs in three objects: CRL 618, MWC922, and M2-9. For CRL 618, the only pPN with previous published detections of H41{alpha}, H35{alpha}, and H30{alpha} emission, we find significant changes in the line profiles indicating that current observations are probing regions of the ionized wind with larger expansion velocities and mass-loss rate than ~29 years ago. In the case of MWC922, we observe a drastic transition from single-peaked profiles at 3mm (H39{alpha} and H41{alpha}) to double-peaked profiles at 1mm (H31{alpha} and H30{alpha}), which is consistent with maser amplification of the highest frequency lines; the observed line profiles are compatible with rotation and expansion of the ionized gas, probably arranged in a disk+wind system around a ~5-10M_{sun}_ central mass. In M2-9, the mm-RRL emission appears to be tracing a recent mass outburst by one of the stars of the central binary system. We present the results from non-LTE line and continuum radiative transfer models, which enables us to constrain the structure, kinematics, and physical conditions (electron temperature and density) of the ionized cores of our sample. We find temperatures Te~6000-17000K, mean densities ne~10^5^-10^8^cm^-3^, radial density gradients ne{prop.to}r^-alpha_n_^ whit alpha_n_~2-3.5, and motions of velocities of ~10-30km/s in the ionized wind regions traced by these mm-wavelength observations. We deduce mass-loss rates of dM_pAGB_/dt~=10^-6^-10^-7^M_{sun}_/yr, which are significantly higher than the values adopted by stellar evolution models currently in use and would result in a transition from the asymptotic giant branch to the PN phase faster than hitherto assumed.
- ID:
- ivo://CDS.VizieR/J/PASP/97/932
- Title:
- 3CR Source Identifications
- Short Name:
- J/PASP/97/932
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog contains the third major update of new optical and radio data for the strong sources in the Revised Third Cambridge Catalogue (3CR). Positions, redshifts, magnitudes, and identifications are included, as well as some radio data for 298 3CR sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/373/1531
- Title:
- 6C** sample of steep-spectrum radio sources
- Short Name:
- J/MNRAS/373/1531
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present basic observational data on the 6C** sample. This is a new sample of radio sources drawn from the 151-MHz 6C survey, which was filtered with radio criteria chosen to optimize the chances of finding radio galaxies at z>4. The filtering criteria are a steep-spectral index and a small angular size. The final sample consists of 68 sources from a region of sky covering 0.421sr. We present Very Large Array radio maps, and the results of K-band imaging and optical spectroscopy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/375/1349
- Title:
- 6C** sample of steep-spectrum radio sources. II
- Short Name:
- J/MNRAS/375/1349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the 6C** sample to investigate the comoving space density of powerful, steep-spectrum radio sources. This sample, consisting of 68 objects, has virtually complete K-band photometry and spectroscopic redshifts for 32 per cent of the sources. In order to find its complete redshift distribution, we develop a method of redshift estimation based on the Kz diagram of the 3CRR, 6CE, 6C* and 7CRS radio galaxies. Based on this method, we derive redshift probability density functions for all the optically identified sources in the 6C** sample. Using a combination of spectroscopic and estimated redshifts, we select the most radio luminous sources in the sample. Their redshift distribution is then compared with the predictions of the radio luminosity function of Jarvis et al. (2001MNRAS.327..907J). We find that, within the uncertainties associated with the estimation method, the data are consistent with a constant comoving space density of steep-spectrum radio sources beyond z>2.5, and rule out a steep decline.
