Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black-hole masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star-formation activity in the X-shaped sample on the timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.Comment: 9 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

The XMM spectral catalog of SDSS optically selected Seyfert 2 galaxies

We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert 2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond the local universe, using good quality X-ray spectra in combination with high S/N optical spectra for their robust classification. We analyzed all available XMM-Newton archival observations of narrow emission line galaxies that meet the above criteria in the redshift range 0.05<z<0.35. We initially selected narrow line AGN using the SDSS optical spectra and the BPT classification diagram. We further modeled and removed the stellar continuum, and we analyzed the residual emission line spectrum to exclude any possible intermediate-type Seyferts. Our final catalog comprises 31 Sy2 galaxies with median redshift z~0.1. X-ray spectroscopy is performed using the available X-ray spectra from the 3XMM and the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick classification agrees with other commonly used diagnostics, such as the X-ray to mid-IR luminosity ratio and the X-ray to [OIII] luminosity ratio. Most importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the simplest unification model. Their accretion rates are significantly lower than the rest of our Sy2 sample, in agreement with previous studies that predict the absence of the broad line region below a certain Eddington ratio threshold.Comment: 12 pages, 6 figures, accepted for publication in A&

VLBI and Single Dish Monitoring of 3C84 in the Period of 2009-2011

The radio galaxy 3C 84 is a representative of gamma-ray-bright misaligned active galactic nuclei (AGNs) and one of the best laboratories to study the radio properties of the sub-pc jet in connection with the gamma-ray emission. In order to identify possible radio counterparts of the gamma-ray emissions in 3C 84, we study the change in structure within the central 1 pc and the light curve of sub-pc-size components C1, C2, and C3. We search for any correlation between changes in the radio components and the gamma-ray flares by making use of VLBI and single dish data. Throughout the radio monitoring spanning over two GeV gamma-ray flares detected by the {\it Fermi}-LAT and the MAGIC Cherenkov Telescope in the periods of 2009 April to May and 2010 June to August, total flux density in radio band increases on average. This flux increase mostly originates in C3. Although the gamma-ray flares span on the timescale of days to weeks, no clear correlation with the radio light curve on this timescale is found. Any new prominent components and change in morphology associated with the gamma-ray flares are not found on the VLBI images.Comment: 6 pages, 3 figures, accepted for publication in MNRAS lette

Correlation between Fermi/LAT gamma-ray and 37 GHz radio properties of northern AGN averaged over 11 months

Although the Fermi mission has increased our knowledge of gamma-ray AGN, many questions remain, such as the site of gamma-ray production, the emission mechanism, and the factors that govern the strength of the emission. Using data from a high radio band, 37 GHz, uncontaminated by other radiation components besides the jet emission, we study these questions with averaged flux densities over the the first year of Fermi operations. We look for possible correlations between the 100 MeV - 100 GeV band used by the Fermi satellite and 37 GHz radio band observed at the Aalto University Metsahovi Radio Telescope, as well as for differences between the gamma-ray emission of different AGN subsamples. We use data averaged over the 1FGL period. Our sample includes 249 northern AGN, including a complete sample of 68 northern AGN with a measured average flux density exceeding 1 Jy. We find significant correlation between both the flux densities and luminosities in gamma and radio bands. The Fermi luminosity is inversely correlated with the peak frequency of the synchrotron component of the AGN spectral energy distributions. We also calculate the gamma dominances, defined as the ratio between the gamma and radio flux densities, and find an indication that high-energy blazars are more gamma-dominated than low-energy blazars. After studying the distributions of gamma and radio luminosities, it is clear that BL Lacertae objects are different from quasars, with significantly lower luminosities. It is unclear whether this is an intrinsic difference, an effect of variable relativistic boosting across the synchrotron peak frequency range, or the result of Fermi being more sensitive to hard spectrum sources like BL Lacertae objects. Our results suggest that the gamma radiation is produced co-spatially with the 37 GHz emission, i.e., in the jet.Comment: 8+5 pages, 9 figures and 2 tables. To be published in A&

The connection between gamma-ray emission and millimeter flares in Fermi/LAT blazars

We compare the gamma-ray photon flux variability of northern blazars in the Fermi/LAT First Source Catalog with 37 GHz radio flux density curves from the Metsahovi quasar monitoring program. We find that the relationship between simultaneous millimeter (mm) flux density and gamma-ray photon flux is different for different types of blazars. The flux relation between the two bands is positively correlated for quasars and does not exist for BLLacs. Furthermore, we find that the levels of gamma-ray emission in high states depend on the phase of the high frequency radio flare, with the brightest gamma-ray events coinciding with the initial stages of a mm flare. The mean observed delay from the beginning of a mm flare to the peak of the gamma-ray emission is about 70 days, which places the average location of the gamma-ray production at or downstream of the radio core. We discuss alternative scenarios for the production of gamma-rays at distances of parsecs along the length the jet.Comment: 11 pages, 7 figures, accepted for publication in A&A, new version contains changes suggested by refere