Particle Accelerators in the Hot Spots of the Radio Galaxy 3C445 Imaged With the VLT

Hot spots (HSs) are regions of enhanced radio emission produced by supersonic jets at the tip of the radio lobes of powerful radiosources. Obtained with the Very Large Telescope (VLT), images of the HSs in the radio galaxy 3C445 show bright knots embedded in diffuse optical emission distributed along the post shock region created by the impact of the jet into the intergalactic medium. The observations reported here confirm that relativistic electrons are accelerated by Fermi-I acceleration processes in HSs. Furthermore, both the diffuse emission tracing the rims of the front shock and the multiple knots demonstrate the presence of additional continuous re-acceleration processes of electrons (Fermi-II).Comment: 7 pages (latex format), 3 ps figures. Full text and PDF available at Science web site: http://www.sciencemag.org/cgi/content/full/298/5591/19

The X-ray properties of young radio-loud AGN

We present XMM-Newton observations of a complete sample of five archetypal young radio-loud AGN, also known Gigahertz Peaked Spectrum (GPS) sources. They are among the brightest and best studied GPS/CSO sources in the sky, with radio powers in the range L_{5GHz}=10^{43-44} erg/s and with 4 sources having measured kinematic ages of 570 to 3000 yrs. All sources are detected, and have 2-10 keV luminosities from 0.5 to 4.8x10^{44} erg/s. In comparison with the general population of radio galaxies, we find that: 1) GPS galaxies show a a range in absorption column densities similar to other radio galaxies. We therefore find no evidence that GPS galaxies reside in significantly more dense circumnuclear environment, such that they could be hampered in their expansion. 2) The ratio of radio to X-ray luminosity is significantly higher than for classical radio sources. This is consistent with an evolution scenario in which young radio sources are more efficient radio emitters than large extended objects at a constant accretion power. 3) Taking the X-ray luminosity of radio sources as a measure of ionisation power, we find that GPS galaxies are significantly underluminous in their [OIII]_{5007 Angstrom}, including a weak trend with age. This is consistent with the fact that the Stroemgren sphere should still be expanding in these young objects. This would mean that here we are witnessing the birth of the narrow line region of radio-loud AGN.Comment: 11 pages, 6 figures. Accepted for publication by the MNRA

A search for distant radio-loud quasars in the CLASS survey: three new radio-selected quasars at z>4

We report on the search for distant radio-loud quasars in the Cosmic Lens All Sky Survey (CLASS) of flat spectrum radio sources with S_5GHz>30 mJy. Unresolved optical counterparts were selected from APM scans of POSS-I plates, with e2.0 colours, in an effective area of ~6400 deg^2. Four sources were found to be quasars with z>4, of which one was previously known. This sample bridges the gap between the strong radio surveys with S_5GHz>200 mJy and the samples of radio-weak quasars that can be generated via radio observations of optically selected quasars. In addition, 4 new quasars at z>3 have been found. The selection criteria result in a success-rate of ~1:7 for radio-loud quasars at z>4, which is a significant improvement over previous studies. This search yields a surface density of 1 per 1600 deg^2, which is about a factor of ~15 lower than that found in a similar search for radio-quiet quasars at z>4. The study presented here is strongly biased against quasars beyond z>4.5, since the e-passband of the POSS-I only samples the spectra shortward of 1200 Angstrom at these redshifts.Comment: LaTeX, 7 pages, 5 Figs: to be published in MNRA

Signatures in a Giant Radio Galaxy of a Cosmological Shock Wave at Intersecting Filaments of Galaxies

Sensitive images of low-level, Mpc-sized radio cocoons offer new opportunities to probe large scale intergalactic gas flows outside clusters of galaxies. New radio images of high surface brightness sensitivity at strategically chosen wavelengths of the giant radio galaxy NGC 315 (Mack et al. 1997,1998) reveal significant asymmetries and particularities in the morphology, radio spectrum and polarization of the ejected radio plasma. We argue that the combination of these signatures provides a sensitive probe of an environmental shock wave. Analysis of optical redshifts in NGC 315 vicinity confirms its location to be near, or at a site of large-scale flow collisions in the 100 Mpc sized Pisces-Perseus Supercluster region. NGC 315 resides at the intersection of several galaxy filaments, and its radio plasma serves there as a `weather station' (Burns 1998) probing the flow of the elusive and previously invisible IGM gas. If our interpretation is correct, this is the first indication for a shock wave in flows caused by the cosmological large scale structure formation, which is located in a filament of galaxies. The possibility that the putative shock wave is a source of gamma-rays and ultra high energy cosmic rays is briefly discussed.Comment: accepted by Astrophysical Journal Letters, 4 pages, 3 figures (incl. 2 color), uses emulateapj5.sty (included), aastex.sty (included) and psfig.st

Probing the Large Faraday Rotation Measure Environment of Compact Active Galactic Nuclei

Knowing how the ambient medium in the vicinity of active galactic nuclei (AGNs) is shaped is crucial to understanding generally the evolution of such cosmic giants as well as AGN jet formation and launching. Thanks to the new broadband capability now available at the Jansky Very Large Array (JVLA), we can study changes in polarization properties, fractional polarization, and polarization angles, together with the total intensity spectra of a sample of 14 AGNs, within a frequency range from 1 to 12 GHz. Depolarization modeling has been performed by means of so-called "qu-fitting" to the polarized data, and a synchrotron self absorption model has been used for fitting to the total intensity data. We found complex behavior both in the polarization spectra and in the total intensity spectra, and several Faraday components with a large rotation measure (RM) and several synchrotron components were needed to represent these spectra. Here, results for three targets are shown. This new method of analyzing broadband polarization data through qu-fitting successfully maps the complex surroundings of unresolved objects

Compact radio-loud broad absorption line quasars

For a long time, radio-loud Broad Absorption Line Quasars (BAL QSOs) were thought to be extremely rare objects. The absorbing troughs seen in their optical spectra are due to strong winds which probably have their origin within the inner region of the AGN, as a result of the accretion processes. Their radio emission constitutes an additional diagnostic tool which is successfully contributing new perspectives and raise new questions, with the aim to enrich our understanding of the BAL phenomenon. In this contribution, we introduce a first characterisation of the radio-loud BAL QSO population. Radio continuum spectra have been collected for a sample of 15 objects, which we present together with their radio polarisation properties. VLA maps in A configuration confirm the compactness of these objects at di erent frequencies up to 43 GHz, yielding projected linear sizes below 1 kpc. We note that many of their radio properties are common to the population of young radio-sources, like Compact Steep Spectrum (CSS) or Gigahertz- Peaked Spectrum (GPS) sources

Divalent Cations and Redox Conditions Regulate the Molecular Structure and Function of Visinin-Like Protein-1

The NCS protein Visinin-like Protein 1 (VILIP-1) transduces calcium signals in the brain and serves as an effector of the non-retinal receptor guanylyl cyclases (GCs) GC-A and GC-B, and nicotinic acetyl choline receptors (nAchR). Analysis of the quaternary structure of VILIP-1 in solution reveals the existence of monomeric and dimeric species, the relative contents of which are affected but not exclusively regulated by divalent metal ions and Redox conditions. Using small-angle X-ray scattering, we have investigated the low resolution structure of the calcium-bound VILIP-1 dimer under reducing conditions. Scattering profiles for samples with high monomeric and dimeric contents have been obtained. The dimerization interface involves residues from EF-hand regions EF3 and EF4

Dish Washer: a Software Tool for RFI Mitigation in Single-dish Radio Astronomical Observations

Radio Frequency Interference is one of the most pressing problems in cm-wavelength world-wide radio astronomy, in particular for single-dish telescope observations. Due to both the increasing abundance of man-made interfering signals and the improved performance of the telescope instrumentation, the impact of RFI at the Italian radio telescope sites is now a major concern, thus strategies for its mitigation are to be applied. Dish Washer is a new software tool for the detection and flagging of RFI in signals collected by single-dish radio telescopes. It implements both interactive flagging and some level of automatic detection of RFI through dedicated algorithms. Its first public release is foreseen as free software under the GNU General Public License

Investigating the radio-loud phase of broad absorption line quasars

Context. Broad absorption lines (BALs) are present in the spectra of ~20% of quasars (QSOs); this indicates fast outflows (up to 0.2c) that intercept the observer’s line of sight. These QSOs can be distinguished again into radio-loud (RL) BAL QSOs and radio-quiet (RQ) BAL QSOs. The first are very rare, even four times less common than RQ BAL QSOs. The reason for this is still unclear and leaves open questions about the nature of the BAL-producing outflows and their connection with the radio jet. Aims. We explored the spectroscopic characteristics of RL and RQ BAL QSOs with the aim to find a possible explanation for the rarity of RL BAL QSOs. Methods. We identified two samples of genuine BAL QSOs from SDSS optical spectra, one RL and one RQ, in a suitable redshift interval (2.5 < z < 3.5) that allowed us to observe the Mg?ii and Hß emission lines in the adjacent near-infrared (NIR) band. We collected NIR spectra of the two samples using the Telescopio Nazionale Galileo (TNG, Canary Islands). By using relations known in the literature, we estimated the black-hole mass, the broad-line region radius, and the Eddington ratio of our objects and compared the two samples. Results. We found no statistically significant differences from comparing the distributions of the cited physical quantities. This indicates that they have similar geometries, accretion rates, and central black-hole masses, regardless of whether the radio-emitting jet is present or not. Conclusions. These results show that the central engine of BAL QSOs has the same physical properties with and without a radio jet. The reasons for the rarity of RL BAL QSOs must reside in different environmental or evolutionary variables.Acknowledgements. The authors acknowledge financial support from the Spanish Ministerio de Ciencia e Innovación under projects AYA2008-06311-C02-02 and AYA2011-29517-C03-02. Part of this work was supported by the COST Action MP0905 “Black Holes in a Violent Universe”. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) oper-ated on the island of La Palma by the Fundación Galileo Galilei of the INAF