- ID:
- ivo://CDS.VizieR/J/ApJ/698/740
- Title:
- VLA survey of CDF-S. III.
- Short Name:
- J/ApJ/698/740
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the X-ray properties of the radio sources detected in a deep 1.4 and 5GHz VLA Radio survey of the Extended Chandra Deep Field-South (E-CDFS). Among the 266 radio sources detected, we find 89 sources (1/3 of the total) with X-ray counterparts in the catalog of the 1Ms exposure of the central 0.08deg^2^ or in the catalog of the 250ks exposure of the 0.3deg^2^ E-CDFS field. For 76 (85%) of these sources, we have spectroscopic or photometric redshifts, and therefore we are able to derive their intrinsic properties from X-ray spectral analysis, namely intrinsic absorption and total X-ray luminosities. We find that the population of submillijansky radio sources with X-ray counterparts is composed of a mix of roughly 1/3 star-forming galaxies and 2/3 active galactic nuclei (AGNs).
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/151/74
- Title:
- VLA/VLBA obscured radio-loud active galactic nuclei
- Short Name:
- J/AJ/151/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper directed toward finding new highly redshifted atomic and molecular absorption lines at radio frequencies. To this end, we selected a sample of 80 candidates for obscured radio-loud active galactic nuclei (AGNs) and presented their basic optical/near-infrared (NIR) properties in Yan et al. 2012AJ....144..124Y. In this paper, we present both high-resolution radio continuum images for all of these sources and H I 21 cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz Very Large Array continuum observations find that 52 sources are compact or have substantial compact components with size <0.5" and flux densities >0.1 Jy at 4.9 GHz. The 36 most compact sources were then observed with the Very Long Baseline Array at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, which is a detection rate of CSOs ~three times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty-seven sources were observed for H I 21 cm absorption at their photometric or spectroscopic redshifts with only six detections (five definite and one tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra (i.e., any AGN emission is obscured) and for which accurate spectroscopic redshifts place the redshifted 21 cm line in a radio frequency intereference (RFI)-free spectral "window" (i.e., the percentage of H I 21 cm absorption-line detections could be as high as ~90% in this sample). It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude H I detections in similar sources (only 1 detection out of the remaining 22 sources observed, 13 of which have only photometric redshifts); that is, H I absorption may well be present but is masked by the RFI. Future searches for highly redshifted H I and molecular absorption can easily find more distant CSOs among bright, "blank field" radio sources, but will be severely hampered by an inability to determine accurate spectroscopic redshifts due to their lack of rest-frame UV continuum.
- ID:
- ivo://CDS.VizieR/J/ApJ/808/162
- Title:
- VLBA 15 and 43GHz obs. of 3C 120
- Short Name:
- J/ApJ/808/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of the radio jet evolution of the radio galaxy 3C 120 during a period of prolonged {gamma}-ray activity detected by the Fermi satellite between 2012 December and 2014 October. We find a clear connection between the {gamma}-ray and radio emission, such that every period of {gamma}-ray activity is accompanied by the flaring of the millimeter very long baseline interferometry (VLBI) core and subsequent ejection of a new superluminal component. However, not all ejections of components are associated with {gamma}-ray events detectable by Fermi. Clear {gamma}-ray detections are obtained only when components are moving in a direction closer to our line of sight. This suggests that the observed {gamma}-ray emission depends not only on the interaction of moving components with the millimeter VLBI core, but also on their orientation with respect to the observer. Timing of the {gamma}-ray detections and ejection of superluminal components locate the {gamma}-ray production to within ~0.13pc from the millimeter VLBI core, which was previously estimated to lie about 0.24pc from the central black hole. This corresponds to about twice the estimated extension of the broad line region, limiting the external photon field and therefore suggesting synchrotron self Compton as the most probable mechanism for the production of the {gamma}-ray emission. Alternatively, the interaction of components with the jet sheath can provide the necessary photon field to produced the observed {gamma}-rays by Compton scattering.
- ID:
- ivo://CDS.VizieR/J/ApJ/744/177
- Title:
- VLBA 5GHz observations of Fermi/LAT AGNs
- Short Name:
- J/ApJ/744/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. In particular, we see that {gamma}-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5GHz correlates strongly with {gamma}-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.
- ID:
- ivo://CDS.VizieR/J/A+A/450/959
- Title:
- VLBA images of High Frequency Peakers
- Short Name:
- J/A+A/450/959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We propose a morphological classification based on the parsec scale structure of fifty-one High Frequency Peakers (HFPs) from the "bright" HFP sample. VLBA images at two adjacent frequencies (chosen among 8.4, 15.3, 22.2 and 43.2GHz) have been used to investigate the morphological properties of the HFPs in the optically thin part of their spectrum. We confirm that there is quite a clear distinction between the pc-scale radio structure of galaxies and quasars: the 78% of the galaxies show a "Double/Triple" morphology, typical of Compact Symmetric Objects (CSOs), while the 87% of the quasars are characterised by Core-Jet or unresolved structure. This suggests that most HFP candidates identified with quasars are likely blazar objects in which a flaring self-absorbed component at the jet base was outshining the remainder of the source at the time of the selection based on the spectral shape. Among the sources classified as CSOs or candidates it is possible to find extremely young radio sources with ages of about 100 years or even less.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/141
- Title:
- VLBA observations of the AGN TXS 0128+554
- Short Name:
- J/ApJ/899/141
- Date:
- 14 Mar 2022 07:07:50
- Publisher:
- CDS
- Description:
- We have carried out a Chandra X-ray and multifrequency radio Very Long Baseline Array study of the active galactic nucleus (AGN) TXS0128+554, which is associated with the Fermi {gamma}-ray source 4FGLJ0131.2+5547. The AGN is unresolved in a target 19.3ks Chandra image, and its spectrum is well fit by a simple absorbed power-law model, with no distinguishable spectral features. Its relatively soft X-ray spectrum compared to other compact symmetric objects (CSOs) may be indicative of a thermal emission component, for which we were able to obtain an upper temperature limit of kT=0.08keV. The compact radio morphology and measured advance speed of 0.32c{+/-}0.07c indicate a kinematic age of only 82yr{+/-}17yr, placing TXS0128+554 among the youngest members of the CSO class. The lack of compact, inverted spectrum hotspots and an emission gap between the bright inner jet and outer radio lobe structure indicate that the jets have undergone episodic activity, and were relaunched a decade ago. The predicted {gamma}-ray emission from the lobes, based on an inverse Compton-emitting cocoon model, is three orders of magnitude below the observed Fermi-LAT flux. A comparison to other Fermi-detected and non-Fermi-detected CSOs with redshift z<0.1 indicates that the {gamma}-ray emission likely originates in the inner jet/core region, and that nearby, recently launched AGN jets are primary candidates for detection by the Fermi-LAT instrument.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A132
- Title:
- VLBA observations of the COSMOS field
- Short Name:
- J/A+A/607/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a project using wide-field Very Long Baseline Interferometry (VLBI) observations at 1.4GHz of 2865 known radio sources in the Cosmic Evolution Survey (COSMOS) field, whose main objective is to determine where Active Galactic Nuclei (AGN) are present. The combination of number of sources, sensitivity, angular resolution and area covered by this project are unprecedented. A catalogue which contains the VLBI detected sources is presented, the main purpose of which is to be used as an AGN catalogue. A catalogue containing complementary multiwavelength information of the VLBI detected sources is also presented.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A113
- Title:
- VLBI detection of 398 extragalactic radio sources
- Short Name:
- J/A+A/520/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The European space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames with the highest possible accuracy. It has been found that only 70 (10%) of the sources from the International Celestial Reference Frame (ICRF) are suitable for establishing this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of 447 optically- bright (magnitude <=18) extragalactic radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating an optical quasar catalog with the NRAO VLA Sky Survey (NVSS, Cat. VIII/65). This paper presents the observing strategy to detect, image, and measure accurate radio positions for these sources. It also provides results on the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, a high detection rate of 89% is found, which is promising for the continuation of this project. This high VLBI detection rate for sources from the NVSS catalog is probably due to the selection process, suggesting that optically-bright quasars have compact radio structures.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A102
- Title:
- VLBI images of 2 binary AGN candidates
- Short Name:
- J/A+A/588/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The sources SDSS J113126.08-020459.2 and SDSS J110851.04+065901.4 are two double-peaked [OIII] emitting AGN, identified as candidate binary AGNs by optical and near infrared (NIR) observations. We observed the two sources with high resolution Very Long Baseline Interferometry (VLBI) using the European VLBI Network at 5GHz, reduced VLA observations at three frequencies available for one of the sources, and used archival HST observations. For the source SDSS J113126.08-020459.2, the VLBI observations detected only one single compact component associated with the eastern NIR nucleus. In SDSS J110851.04+065901.4, the VLBI observations did not detect any compact components, but the VLA observations allowed us to identify a possible compact core in the region of the north-western optical/NIR nucleus. In this source we find kpc-scale extended radio emission that is spatially coincident to the ultraviolet continuum and to the extended emission narrow line region. The UV continuum is significantly obscured since the amount of extended radio emission yields a star formation rate of about 110M_{sun}_/yr, which is an order of magnitude larger than implied by the observed ultraviolet emission. Our analysis confirms the presence of only one AGN in the two candidate binary AGNs.
- ID:
- ivo://CDS.VizieR/J/A+A/526/A102
- Title:
- VLBI imaging of 105 extragalactic radio sources
- Short Name:
- J/A+A/526/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The European space astrometry mission Gaia, to be launched by 2012, will construct a dense optical QSO-based celestial reference frame which will need to be linked to the International Celestial Reference Frame (ICRF; the IAU fundamental frame), with the highest accuracy. However, it has been found that only 10% of the ICRF sources (70 sources) are suitable to establish this link. The remaining sources are not useful either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the accuracy of this alignment, we have developed a program of VLBI observations based on three steps to detect, image and measure astrometric positions of weak extragalactic radio sources, with bright optical counterparts, from a sample of 447 candidate sources. The experiments devoted to VLBI detection, carried out with the European VLBI Network (EVN) in June and October 2007, were very successful, with 398 sources detected at both S- and X-bands. From these, 105 sources were observed in March 2008 with a global VLBI array (EVN and VLBA; Very Long Baseline Array) for imaging their VLBI structures. All sources were successfully imaged in both bands and about 50% (47 sources) were found to be point-like on VLBI scales. These images are available at http://www.obs.u-bordeaux1.fr/BVID/GC030/. VLBI positions of these sources will be measured accurately in future astrometric experiments.
