- ID:
- ivo://CDS.VizieR/J/ApJ/795/63
- Title:
- Faraday rotation from magnesium II absorbers
- Short Name:
- J/ApJ/795/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Strong singly ionized magnesium (Mg II) absorption lines in quasar spectra typically serve as a proxy for intervening galaxies along the line of sight. Previous studies have found a correlation between the number of these Mg II absorbers and the Faraday rotation measure (RM) at ~5 GHz. We cross-match a sample of 35752 optically identified non-intrinsic Mg II absorption systems with 25649 polarized background radio sources for which we have measurements of both the spectral index and RM at 1.4 GHz. We use the spectral index to split the resulting sample of 599 sources into flat-spectrum and steep-spectrum subsamples. We find that our flat-spectrum sample shows significant (~3.5{sigma}) evidence for a correlation between Mg II absorption and RM at 1.4 GHz, while our steep-spectrum sample shows no such correlation. We argue that such an effect cannot be explained by either luminosity or other observational effects, by evolution in another confounding variable, by wavelength-dependent polarization structure in an active galactic nucleus, by the Galactic foreground, by cosmological expansion, or by partial coverage models. We conclude that our data are most consistent with intervenors directly contributing to the Faraday rotation along the line of sight, and that the intervening systems must therefore have coherent magnetic fields of substantial strength (B{bar}=1.8+/-0.4{mu}G). Nevertheless, the weak nature of the correlation will require future high-resolution and broadband radio observations in order to place it on a much firmer statistical footing.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/Ap/42.1
- Title:
- FBS blue stellar objects
- Short Name:
- J/other/Ap/42.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second part of the First Byurakan Survey is aimed at detecting all bright (B<16.5) UV-excess starlike objects in a large area of the sky. By comparison with other major surveys such as the ROSAT All Sky Survey (Cat. <IX/10>, the ROSAT WGACAT (Cat. <IX/12>) catalogue of point sources, the IRAS (Cat. <II/125>) survey, the 6cm Green Bank (Cat. <VIII/52>, the 1.4GHz NRAO VLA (Cat. <J/AJ/115/1693>, and the 92cm Westerbork Northern sky surveys (Cat. <VIII/62>) and with the catalogue of mean UBV data on stars, we estimate the number of AGNs present in the FBS survey and its completeness. We have made spectroscopic observations of nine of the most promising FBS candidates. We have found six new QSOs, bringing the total number of known QSOs in this survey to 42. By comparison with the Bright Quasar Survey, we found that the completeness of this last survey is of the order of 70% rather than 30-50% as suggested by several authors.
- ID:
- ivo://CDS.VizieR/J/ApJ/687/78
- Title:
- FeII emission in quasars
- Short Name:
- J/ApJ/687/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Broad FeII emission is a prominent feature of the optical and ultraviolet spectra of quasars. We report on a systematical investigation of optical FeII emission in a large sample of 4037 z<0.8 quasars selected from the SDSS-DR5 quasar catalog (Cat. VII/252). We have developed and tested a detailed line-fitting technique, taking into account the complex continuum and narrow and broad emission-line spectra. Our primary goal is to quantify the velocity broadening and velocity shift of the FeII spectrum in order to constrain the location of the FeII-emitting region and its relation to the broad-line region. We find that the majority of quasars show FeII emission that is redshifted, typically by ~400km/s, but up to 2000km/s, with respect to the systemic velocity of the narrow-line region or of the conventional broad-line region as traced by the H{beta} line. Moreover, the line width of FeII is significantly narrower than that of the broad component of H{beta}. We show that the magnitude of the FeII redshift correlates inversely with the Eddington ratio, and that there is a tendency for sources with redshifted FeII emission to show red asymmetry in the H{beta} line. These characteristics strongly suggest that FeII originates from a location different from, and most likely exterior to, the region that produces most of H{beta}. The FeII-emitting zone traces a portion of the broad-line region of intermediate velocities whose dynamics may be dominated by infall.
- 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.
245. 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/4193
- Title:
- Fermi/non-Fermi blazars jet power and accretion
- Short Name:
- J/MNRAS/451/4193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the relationship between jet power and accretion for Fermi and non-Fermi blazars. We also compare the relevant parameter. Our main results are: (i) Fermi and non-Fermi blazars have significant differences in red shift, black hole mass and broad line luminosity. (ii) Fermi blazars have a higher average core-dominance parameter than non-Fermi blazars, which suggests that Fermi blazars have a strong beaming effect. (iii) We find a significant correlation between broad line emission and jet power for Fermi and non-Fermi blazars, which suggests a direct tight connection between jet and accretion. (iv) The accretion and black hole mass may have a different contribution to jet power for Fermi and non-Fermi blazars.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A60
- Title:
- F-GAMMA 2.64-43GHz radio data over 2007-2015
- Short Name:
- J/A+A/626/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The advent of the Fermi gamma-ray space telescope with its superb sensitivity, energy range, and unprecedented capability to monitor the entire 4{pi} sky within less than 2-3 h, introduced a new standard in time domain gamma-ray astronomy. Among several breakthroughs, Fermi has - for the first time - made it possible to investigate, with high cadence, the variability of the broadband spectral energy distribution (SED), especially for active galactic nuclei (AGN). This is necessary for understanding the emission and variability mechanisms in such systems. To explore this new avenue of extragalactic physics the Fermi-GST AGN Multi-frequency Monitoring Alliance (F-GAMMA) programme undertook the task of conducting nearly monthly, broadband radio monitoring of selected blazars, which is the dominant population of the extragalactic gamma-ray sky, from January 2007 to January 2015. In this work we release all the multi-frequency light curves from 2.64 to 43 GHz and first order derivative data products after all necessary post-measurement corrections and quality checks. Along with the demanding task to provide the radio part of the broadband SED in monthly intervals, the F-GAMMA programme was also driven by a series of well-defined fundamental questions immediately relevant to blazar physics. On the basis of the monthly sampled radio SEDs, the F-GAMMA aimed at quantifying and understanding the possible multiband correlation and multi-frequency radio variability, spectral evolution and the associated emission, absorption and variability mechanisms. The location of the gamma-ray production site and the correspondence of structural evolution to radio variability have been among the fundamental aims of the programme. Finally, the programme sought to explore the characteristics and dynamics of the multi-frequency radio linear and circular polarisation. The F-GAMMA ran two main and tightly coordinated observing programmes. The Effelsberg 100 m telescope programme monitoring 2.64, 4.85, 8.35, 10.45, 14.6, 23.05, 32, and 43 GHz, and the IRAM 30 m telescope programme observing at 86.2, 142.3, and 228.9 GHz. The nominal cadence was one month for a total of roughly 60 blazars and targets of opportunity. In a less regular manner the F-GAMMA programme also ran an occasional monitoring with the APEX 12 m telescope at 345 GHz. We only present the Effelsberg dataset in this paper. The higher frequencies data are released elsewhere. The current release includes 155 sources that have been observed at least once by the F-GAMMA programme. That is, the initial sample, the revised sample after the first Fermi release, targets of opportunity, and sources observed in collaboration with a monitoring programme following up on Planck satellite observations. For all these sources we release all the quality-checked Effelsberg multi-frequency light curves. The suite of post-measurement corrections and flagging and a thorough system diagnostic study and error analysis is discussed as an assessment of the data reliability. We also release data products such as flux density moments and spectral indices. The effective cadence after the quality flagging is around one radio SED every 1.3 months. The coherence of each radio SED is around 40 min. The released dataset includes more than 3x104 measurements for some 155 sources over a broad range of frequencies from 2.64 GHz to 43 GHz obtained between 2007 and 2015. The median fractional error at the lowest frequencies (2.64-10.45 GHz) is below 2%. At the highest frequencies (14.6-43 GHz) with limiting factor of the atmospheric conditions, the errors range from 3% to 9%, respectively.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/3180
- Title:
- 3FGL Blazar of Unknown Type classification
- Short Name:
- J/MNRAS/462/3180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fermi-Large Area Telescope (LAT) is currently the most important facility for investigating the GeV {gamma}-ray sky. With Fermi-LAT, more than three thousand {gamma}-ray sources have been discovered so far. 1144 (~40 per cent) of the sources are active galaxies of the blazar class, and 573 (~20 per cent) are listed as blazar candidate of uncertain type (BCU), or sources without a conclusive classification. We use the empirical cumulative distribution functions and the artificial neural networks for a fast method of screening and classification for BCUs based on data collected at {gamma}-ray energies only, when rigorous multiwavelength analysis is not available. Based on our method, we classify 342 BCUs as BL Lacs and 154 as flat-spectrum radio quasars, while 77 objects remain uncertain. Moreover, radio analysis and direct observations in ground-based optical observatories are used as counterparts to the statistical classifications to validate the method. This approach is of interest because of the increasing number of unclassified sources in Fermi catalogues and because blazars and in particular their subclass high synchrotron peak objects are the main targets of atmospheric Cherenkov telescopes.
- ID:
- ivo://CDS.VizieR/J/AJ/130/2473
- Title:
- Fine-scale structure in 250 sources at 15GHz
- Short Name:
- J/AJ/130/2473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have examined the compact structure in 250 flat-spectrum extragalactic radio sources using interferometric fringe visibilities obtained with the Very Long Baseline Array (VLBA) at 15GHz. With projected baselines out to 440M{lambda}, we are able to investigate source structure on typical angular scales as small as 0.05mas.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/13
- Title:
- FIR properties of SDSS type 1 quasars
- Short Name:
- J/ApJ/768/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Spitzer Space Telescope Enhanced Imaging Products and the Spitzer Archival Far-InfraRed Extragalactic Survey to study the spectral energy distributions (SEDs) of spectroscopically confirmed type 1 quasars selected from the Sloan Digital Sky Survey (SDSS). By combining the Spitzer and SDSS data with the Two Micron All Sky Survey, we are able to construct a statistically robust rest-frame 0.1-100{mu}m type 1 quasar template. We find that the quasar population is well-described by a single power-law SED at wavelengths less than 20{mu}m, in good agreement with previous work. However, at longer wavelengths, we find a significant excess in infrared luminosity above an extrapolated power-law, along with significant object-to-object dispersion in the SED. The mean excess reaches a maximum of 0.8dex at rest-frame wavelengths near 100{mu}m.
