- ID:
- ivo://CDS.VizieR/J/A+A/641/A62
- Title:
- Multi-wavelength census of blazars
- Short Name:
- J/A+A/641/A62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Blazars are the rarest and most powerful active galactic nuclei, playing a crucial and growing role in today multi-frequency and multi-messenger astrophysics. They dominate the high-energy extragalactic sky and recently have been associated to high-energy astrophysical neutrinos, and they may be among the accelerators of the ultra-high energy cosmic rays. Current blazar catalogs, however, are incomplete and particularly depleted at low Galactic latitudes. We aim at augmenting the current blazar census starting from a sample of ALMA calibrators that provides more homogeneous sky coverage, especially at low Galactic latitudes, to build a catalog of blazar candidates that can provide candidate counterparts to unassociated gamma-ray sources and to sources of high-energy neutrino emission or ultra-high energy cosmic rays. Starting from the ALMA Calibrator Catalog we built a catalog of 1580 blazar candidates (ALMA Blazar Candidates) for which we collect multi-wavelength information, including Gaia photometric, parallax and proper motion data, SDSS and LAMOST photometric and spectral data, WISE photometric data, X-ray (Swift-XRT, Chandra-ACIS and XMM-Newton-EPIC) count-rates and spectra, and Fermi-LAT fluxes and spectral slopes. We also compared our ALMA Blazar Candidates with existing blazar catalogs, like 4FGL, 3HSP, WIBRaLS2 and the KDEBLLACS. The ALMA Blazar Candidates catalogue fills the lack of low Galactic latitude sources in current blazar catalogues. Cross-matching this catalog with Gaia DR2, SDSS DR12, LAMOST DR5, AllWISE and 4FGL catalogues we obtained 805, 295, 31, 1311 and 259 matches, respectively. ALMA Blazar Candidates are significantly dimmer than known blazars in Gaia g band, while the difference in the Gaia b-r colour between the two populations is less pronounced. Also, ALMA Blazar Candidates sources appear bluer in SDSS than known blazars, although with low statistical significance. Most ALMA Blazar Candidates classified as QSO and BL Lac fall into the SDSS colour regions of low redshift quasars, with some QSOs entering the regions of higher redshift quasars. We collected 110 optical spectra in SDSS DR12 and LAMOST DR5, which mostly classify the corresponding sources as QSO (98), while 12 sources resulted galactic objects. Regarding WISE colours, we found that ABC sources are significantly bluer than known blazars in the w2-w3 and w3-w4 colours. In X-rays we detected 173 ALMA Blazar Candidates, and we were able to extract a X-ray spectra for 92 of them. Our sources are on average similar in X-rays to known blazar in terms of count-rates and spectral slopes, implying that our sample is covering the same region of the blazar parameter space in this band. A comparison of gamma-ray properties shown that ALMA Blazar Candidates are on average dimmer, and their gamma-ray spectra are softer than known blazars, indicating a significant contribution of FSRQ sources. Making use of WISE colours, we classified 715 ALMA Blazar Candidates as candidate gamma-ray blazar of different classes. We built a new catalogue of 1580 candidate blazars with a rich multi-wavelength data-set, filling the lack of low Galactic latitude sources in current blazar catalogues. This will be particularly important to identify the source population of high energy neutrinos or ultra-high energy cosmic rays, or to verify the Gaia optical reference frame. In addition, ALMA Blazar Candidates can be investigated both through optical spectroscopic observation campaigns or through repeated photometric observations for variability studies. In this context, the data collected by the upcoming LSST surveys will provide a key tool to investigate the possible blazar nature of these sources.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/573/A50
- Title:
- Multiwavelength observations of Mrk 501 in 2008
- Short Name:
- J/A+A/573/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the {gamma}-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available {gamma}-ray instrumentation was easier to perform. Our goal is to characterize in detail the source {gamma}-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE {gamma}-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopesMAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/53
- Title:
- Multiwavelength obs. of BL Lac in 2012-2013
- Short Name:
- J/ApJ/816/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012-2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse Compton emission from nonthermal seed photons originating from within the jet. The passage of four new superluminal very long baseline interferometry knots through the core and two stationary knots about 4 pc downstream accompanied the high flaring in 2012-2013. The seed photons for inverse Compton scattering may arise from the stationary knots and from a Mach disk near the core where relatively slow-moving plasma generates intense nonthermal radiation. The 95 spectral energy distributions obtained on consecutive days form the most densely sampled, broad wavelength coverage for any blazar. The observed spectral energy distributions and multi-waveband light curves are similar to simulated spectral energy distributions and light curves generated with a model in which turbulent plasma crosses a conical shock with a Mach disk.
- ID:
- ivo://CDS.VizieR/J/MNRAS/425/1215
- Title:
- Multiwavelength survey of AGNs
- Short Name:
- J/MNRAS/425/1215
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to study the effect of environment on the presence and fuelling of active galactic nuclei (AGNs) in massive galaxy clusters. We explore the use of different AGN detection techniques with the goal of selecting AGN across a broad range of luminosities, AGN/host galaxy flux ratios and obscuration levels. From a sample of 12 galaxy clusters at redshifts 0.5<z<0.9, we identify AGN candidates using optical variability from multi-epoch Hubble Space Telescope imaging, X-ray point sources in Chandra images and mid-infrared (IR) spectral energy distribution power-law fits through the Spitzer Infrared Array Camera channels. We find 178 optical variables, 74 X-ray point sources and 64 IR power-law sources, resulting in an average of ~25 AGN per cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A83
- Title:
- MURALES survey. I. 3C 459 data cube.
- Short Name:
- J/A+A/619/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed the FR II radio galaxy 3C 459 (z=0.22) with the MUSE spectrograph at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a filamentary ionized gas structure forming a one-sided, triangular-shaped region extending out to ~80kpc. The central emission line region is dominated by two compact knots of similar flux: the first (N1) cospatial with the radio core and the (N2) second located 1.2" (5.3kpc) to the SE. The two regions differ dramatically from the point of view of velocity (with an offset of ~400km/s), line widths, and line ratios. This suggests that we are observing a dual AGN system formed by a radio loud AGN and type 2 QSO companion, which is the result of the recent merger that also produced its disturbed host morphology. The alternative possibility that N2 is just a bright emission line knot resulting from, for example, a jet-cloud interaction, is disfavored because of 1) the presence of a high ionization bicone whose apex is located at N2; 2) the observed narrow line widths; 3) its line luminosity (~10^42^erg/s) typical of luminous QSOs; and 4) its location, which is offset from the jet path. The putative secondary AGN must be highly obscured, since we do not detect any emission in the Chandra and infrared Hubble Space Telescope images.
- ID:
- ivo://CDS.VizieR/J/A+A/424/519
- Title:
- Naked active galactic nuclei
- Short Name:
- J/A+A/424/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we report the discovery of a new class of active galactic nucleus in which although the nucleus is viewed directly, no broad emission lines are present. The results are based on a survey for AGN in which a sample of about 800 quasars and emission line galaxies were monitored yearly for 25 years. Among the emission line galaxies was the expected population of Seyfert 2 galaxies with only narrow forbidden lines in emission, and no broad lines. However, from the long term monitoring programme it was clear that some 10% of these were strongly variable with strong continuum emission. It is argued that these objects can only be Seyfert 1 galaxies in which the nucleus is viewed directly, but in which broad emission lines are completely absent. We compare these observations with other cases from the literature where the broad line region is reported to be weak or variable, and investigate the possibility that the absence of the broad line component is due to reddening. We conclude that this does not account for the observations, and that in these AGN the broad line region is absent. We also tentatively identify more luminous quasars from our sample where the broad emission lines also appear to be absent. The consequences of this for AGN models are discussed, and a case is made that we are seeing AGN in a transition stage between the fuel supply from a surrounding star cluster being cut off, and the nucleus becoming dormant.
- ID:
- ivo://CDS.VizieR/J/A+A/456/953
- Title:
- Narrow-band imaging of 6 Seyfert-2 galaxies
- Short Name:
- J/A+A/456/953
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While [OIII] narrow-band imaging is commonly used to measure the size of the narrow-line regions (NLRs) in active galactic nuclei (AGNs), it can be contaminated by emission from surrounding starbursts. Recently, we have shown that long-slit spectroscopy provides a valuable alternative approach to probe the size in terms of AGN photoionisation. Moreover, several parameters of the NLR can be directly accessed. We here apply the same methods developed and described for the Seyfert-2 galaxy NGC1386 to study the NLR of five other Seyfert-2 galaxies by using high-sensitivity spatially-resolved optical spectroscopy obtained at the VLT and the NTT. We probe the AGN-photoionisation of the NLR and thus, its "real" size using diagnostic line-ratio diagrams. We derive physical properties of the NLR such as reddening, ionisation parameter, electron density, and velocity as a function of distance from the nucleus. For NGC5643, the diagnostic diagrams unveil a similar transition between line ratios falling in the AGN regime and those typical for HII regions as found for NGC1386, thus determining the size of the NLR. For the other four objects, all measured line ratios fall in the AGN regime. In almost all cases, both electron density and ionisation parameter decrease with radius. Deviations from this general behaviour (such as a secondary peak) seen in both the ionisation parameter and electron density can be interpreted as signs of shocks from the interaction of a radio jet and the NLR gas. In several objects, the gaseous velocity distribution is characteristic for rotational motion in an (inclined) emission-line disk in the centre. We compare our results to those of NGC1386 and show that the latter can be considered as prototypical also for this larger sample. We discuss our findings in detail for each object.
- ID:
- ivo://CDS.VizieR/J/A+A/459/55
- Title:
- Narrow-band imaging of 5 Seyfert-1 galaxies
- Short Name:
- J/A+A/459/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spatially resolved emission-line spectroscopy is a powerful tool to determine the physical conditions in the narrow-line region (NLR) of active galactic nuclei (AGNs). We recently used optical long-slit spectroscopy to study the NLRs of a sample of six Seyfert-2 galaxies. We have shown that such an approach, in comparison to the commonly used [OIII] narrow-band imaging alone, allows us to probe the size of the NLR in terms of AGN photoionisation. Moreover, several physical parameters of the NLR can be directly accessed. We here apply the same methods to study the NLR of six Seyfert-1 galaxies and compare our results to those of Seyfert-2 galaxies. We employ diagnostically valuable emission-line ratios to determine the physical properties of the NLR, including the core values and radial dependencies of density, ionisation parameter, and reddening. Tracking the radial change of emission-line ratios in diagnostic diagrams allows us to measure the transition between AGN-like and HII-like line excitation, and thus we are able to measure the size of the NLR. In the diagnostic diagrams, we find a transition between line ratios falling in the AGN regime and those typical for HII regions in two Seyfert-1 galaxies, thus determining the size of the NLR. The central electron temperature and ionisation parameter are in general higher in type-1 Seyferts than in type 2s. In almost all cases, both electron density and ionisation parameter decrease with radius. In general, the decrease is faster in Seyfert-1 galaxies than in type 2s. In several objects, the gaseous velocity distribution is characteristic for rotational motion in an (inclined) emission-line disk in the centre. We give estimates of the black hole masses. We discuss our findings in detail for each object.
- ID:
- ivo://CDS.VizieR/J/ApJ/618/L83
- Title:
- Narrow iron K{alpha} lines in AGN
- Short Name:
- J/ApJ/618/L83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assemble a sample consisting of 66 active galactic nuclei (AGNs) from the literature (Page et al., 2004MNRAS.347..316P) and from the XMM-Newton archive in order to investigate the origin of the 6.4keV narrow iron K{alpha} line (NIKAL). The X-ray Baldwin effect of the NIKAL is confirmed in this sample.
- ID:
- ivo://CDS.VizieR/J/ApJS/229/39
- Title:
- Narrow line Seyfert 1 galaxies from SDSS-DR12
- Short Name:
- J/ApJS/229/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of narrow-line Seyfert 1 (NLSy1) galaxies from the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). This was obtained by a systematic analysis through modeling of the continuum and emission lines of the spectra of all the 68859 SDSS-DR12 objects that are classified as "QSO" by the SDSS spectroscopic pipeline with z<0.8 and a median signal-to-noise ratio (S/N)>2/pixel. This catalog contains a total of 11101 objects, which is about 5 times larger than the previously known NLSy1 galaxies. Their monochromatic continuum luminosity at 5100{AA} is found to be strongly correlated with H{beta}, H{alpha}, and [OIII] emission line luminosities. The optical FeII strength in NLSy1 galaxies is about two times larger than the broad-line Seyfert 1 (BLSy1) galaxies. About 5% of the catalog sources are detected in the FIRST survey. The Eddington ratio ({xi}_Edd_) of NLSy1 galaxies has an average of log({xi}_Edd_) of -0.34, much higher than -1.03 found for BLSy1 galaxies. Their black hole masses (M_BH_) have an average of log(M_BH_) of 6.9M_{sun}_, which is less than BLSy1 galaxies, which have an average of log(M_BH_) of 8.0M_{sun}_. The M_BH_ of NLSy1 galaxies is found to be correlated with their host galaxy velocity dispersion. Our analysis suggests that geometrical effects playing an important role in defining NLSy1 galaxies and their M_BH_ deficit is perhaps due to their lower inclination compared to BLSy1 galaxies.
