- ID:
- ivo://CDS.VizieR/J/MNRAS/426/833
- Title:
- Faint reddened AGNs in VLA-FIRST
- Short Name:
- J/MNRAS/426/833
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- More than half of the sources identified by recent radio sky surveys have not been detected by wide-field optical surveys. We present a study, based on our co-added image stacking technique, in which our aim is to detect the optical emission from unresolved, isolated radio sources of the Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-cm (FIRST) survey that have no identified optical counterparts in the Sloan Digital Sky Survey (SDSS) Stripe 82 co-added data set. From the FIRST catalogue, 2116 such radio point sources were selected, and cut-out images, centred on the FIRST coordinates, were generated from the Stripe 82 images. The already co-added cut-outs were stacked once again to obtain images of high signal-to-noise ratio, in the hope that optical emission from the radio sources would become detectable. Multiple stacks were generated, based on the radio luminosity of the point sources. The resulting stacked images show central peaks similar to point sources. The peaks have very red colours with steep optical spectral energy distributions.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/654/A5
- Title:
- Faraday cubes Fields A B and C
- Short Name:
- J/A+A/654/A5
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Faraday tomography of a field centred on the extragalactic point source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an intertwined structure of diffuse polarised emission with straight depolarisation canals and tracers of the magnetized and multi-phase interstellar medium (ISM), such as dust and line emission from atomic hydrogen (HI). This study aims at extending the multi-tracer analysis of LOFAR data to three additional fields in the surroundings of the 3C 196 field. For the first time, we study the three-dimensional structure of the LOFAR emission by determining the distance to the depolarisation canals. We use the Rolling Hough Transform to compare the orientation of the depolarisation canals with that of the filamentary structure seen in HI and, based on starlight and dust polarisation data, with that of the plane-of-the-sky magnetic field. Stellar parallaxes from Gaia complement the starlight polarisation with the corresponding distances. Faraday tomography of the three fields shows a rich network of diffuse polarised emission at Faraday depths between -10rad/m^2^ and +15rad/m^2^. A complex system of straight depolarisation canals resembles that of the 3C 196 field. The depolarisation canals align both with the HI filaments and with the magnetic field probed by dust. The observed alignment suggests that an ordered magnetic field organises the multiphase ISM over a large area (~20{deg}). In one field, two groups of stars at distances below and above 200pc, respectively, show distinct magnetic-field orientations. These are both comparable with the orientations of the depolarisation canals in the same field. We conclude that the depolarisation canals likely trace the same change of the magnetic field as probed by the stars, which corresponds to the edge of the Local Bubble.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/1170
- Title:
- Faraday rotation at high Galactic latitude
- Short Name:
- J/ApJ/714/1170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the vertical magnetic field of the Milky Way toward the Galactic poles, determined from observations of Faraday rotation toward more than 1000 polarized extragalactic radio sources at Galactic latitudes |b|>=77{deg}, using the Westerbork Radio Synthesis Telescope and the Australia Telescope Compact Array. We find median rotation measures (RMs) of 0.0+/-0.5rad/m^2^ and +6.3+/-0.7rad/m^2^ toward the north and south Galactic poles, respectively, demonstrating that there is no coherent vertical magnetic field in the Milky Way at the Sun's position. If this is a global property of the Milky Way's magnetism, then the lack of symmetry across the disk rules out pure dipole or quadrupole geometries for the Galactic magnetic field. The angular fluctuations in RM seen in our data show no preferred scale within the range ~0.1{deg} to ~25{deg}. The observed standard deviation in RM of ~9rad/m^2^ then implies an upper limit of ~1uG on the strength of the random magnetic field in the warm ionized medium at high Galactic latitudes.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/114
- Title:
- Faraday rotation in Cen A
- Short Name:
- J/ApJ/707/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an Australia Telescope Compact Array 1.4GHz spectropolarimetric aperture synthesis survey of 34deg^2^ centered on Centaurus A-NGC 5128. A catalog of 1005 extragalactic compact radio sources in the field to a continuum flux density of 3mJy/beam is provided along with a table of Faraday rotation measures (RMs) and linear polarized intensities for the 28% of sources with high signal to noise in linear polarization. We use the ensemble of 281 background polarized sources as line-of-sight probes of the structure of the giant radio lobes of Centaurus A. This is the first time such a method has been applied to radio galaxy lobes and we explain how it differs from the conventional methods that are often complicated by depth and beam depolarization effects. Assuming a magnetic field strength in the lobes of 1.3B1uG, where B1=1 is implied by equipartition between magnetic fields and relativistic particles, the upper limit we derive on the maximum possible difference between the average RM of 121 sources behind Centaurus A and the average RM of the 160 sources along sightlines outside Centaurus A implies an upper limit on the volume-averaged thermal plasma density in the giant radio lobes of <ne><5x10^-5^B1^-1^cm^-3^. We use an RM structure function analysis and report the detection of a turbulent RM signal, with rms=17rad/m^2^ and scale size 0.3deg, associated with the southern giant lobe. We cannot verify whether this signal arises from turbulent structure throughout the lobe or only in a thin skin (or sheath) around the edge, although we favor the latter. The RM signal is modeled as possibly arising from a thin skin with a thermal plasma density equivalent to the Centaurus intragroup medium density and a coherent magnetic field that reverses its sign on a spatial scale of 20kpc. For a thermal density of n1 10^-3^cm^-3^, the skin magnetic field strength is 0.8n1^-1^uG.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/L7
- Title:
- Faraday rotation of radio sources from THOR
- Short Name:
- J/ApJ/887/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results for Faraday rotation of compact polarized sources (1-2GHz continuum) in The HI/OH/Recombination line (THOR) survey of the inner Galaxy. In the Galactic longitude range 39{deg}<l<52{deg}, we find rotation measures (RMs) in the range -310rad/m^2^<=RM<=+4219rad/m^2^, with the highest values concentrated within a degree of l=48{deg} at the Sagittarius arm tangent. Most of the high RMs arise in diffuse plasma, along lines of sight that do not intersect HII regions. For l>49{deg}, RM drops off rapidly, while at l<47{deg}, the mean RM is higher with a larger standard deviation than at l>49{deg}. We attribute the RM structure to the compressed diffuse warm ionized medium in the spiral arm, upstream of the major star formation regions. The Sagittarius arm acts as a significant Faraday screen inside the Galaxy. This has implications for models of the Galactic magnetic field and the expected amount of Faraday rotation of fast radio bursts from their host galaxies. We emphasize the importance of sensitivity to high Faraday depth in future polarization surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/888/40
- Title:
- Fast radio bursts with AstroSat/CZTI
- Short Name:
- J/ApJ/888/40
- Date:
- 07 Dec 2021
- Publisher:
- CDS
- Description:
- Fast radio bursts (FRBs) are short-lived (~ms), energetic transients (having a peak flux density of ~Jy) with no known prompt emission in other energy bands. We present results of a search for prompt X-ray emissions from 41 FRBs using the Cadmium Zinc Telluride Imager (CZTI) on AstroSat, which continuously monitors ~70% of the sky. Our searches on various timescales in the 20-200keV range, did not yield any counterparts in this hard X-ray band. We calculate upper limits on hard X-ray flux, in the same energy range and convert them to upper bounds for {eta}: the ratio of X-ray to radio fluence of FRBs. We find {eta}<=10^8-10^ for hard X-ray emission. Our results will help constrain the theoretical models of FRBs as the models become more quantitative and nearer, brighter FRBs are discovered.
- ID:
- ivo://CDS.VizieR/J/ApJ/551/852
- Title:
- FCRAO CO survey of the outer Galaxy
- Short Name:
- J/ApJ/551/852
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A summary of global properties and an evaluation of the equilibrium state of molecular regions in the outer Galaxy are presented from the decomposition of the Five College Radio Astronomy Observatory (FCRAO, see 1998ApJS..115..241H) Outer Galaxy Survey and targeted ^12^CO and ^13^CO observations (at 115GHz) of four giant molecular cloud complexes. The ensemble of identified objects includes both small, isolated clouds and clumps within larger cloud complexes.
- ID:
- ivo://CDS.VizieR/J/A+A/656/A45
- Title:
- Feeding and feedback in Fornax A
- Short Name:
- J/A+A/656/A45
- Date:
- 14 Mar 2022 07:47:57
- Publisher:
- CDS
- Description:
- We present a multi-wavelength study of the gaseous medium surrounding the nearby active galactic nucleus (AGN), Fornax A. Using MeerKAT, ALMA, and MUSE observations, we reveal a complex distribution of the atomic (HI), molecular (CO 1-0), and ionised gas in its centre and along the radio jets. By studying the multi-scale kinematics of the multi-phase gas, we reveal the presence of concurrent AGN feeding and feedback phenomena. Several clouds and an extended 3kpc filament - perpendicular to the radio jets and the inner disc (r<4.5kpc) - show highly-turbulent kinematics, which likely induces non-linear condensation and subsequent chaotic cold accretion (CCA) onto the AGN. In the wake of the radio jets and in an external (r>4.5kpc) ring, we identify an entrained massive (~10^7^M_{sun}_) multi-phase outflow (v_OUT_~2000km/s^). The rapid flickering of the nuclear activity of Fornax A (~3Myr) and the gas experiencing turbulent condensation raining onto the AGN provide quantitative evidence that a recurrent, tight feeding and feedback cycle may be self-regulating the activity of FORN, in agreement with CCA simulations. To date, this is one of the most in-depth probes of such a mechanism, paving the way to apply these precise diagnostics to a larger sample of nearby AGN hosts and their multi-phase Interstellar Medium.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/L38
- Title:
- Fermi blazars with Doppler factors
- Short Name:
- J/ApJ/835/L38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between {gamma}-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic {gamma}-ray luminosity is strongly correlated with other intrinsic luminosities.
490. Fermi bright blazars
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/1899
- Title:
- Fermi bright blazars
- Short Name:
- J/MNRAS/441/1899
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The exact location of the {gamma}-ray emitting region in blazars is still controversial. In order to attack this problem we present first results of a cross-correlation analysis between radio (11cm to 0.8mm wavelength, F-GAMMA programme) and {gamma}-ray (0.1-300GeV) ~3.5yr light curves of 54 Fermi-bright blazars. We perform a source stacking analysis and estimate significances and chance correlations using mixed source correlations.
