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We present deep kpc- and pc-scale neutral atomic hydrogen (HI) absorption observations of a very young radio source (< 5000 yrs), 4C 31.04, using the WSRT and the Global VLBI array. Using $z=0.0598$, we detect a broad absorption feature centred at the systemic velocity, and narrow absorption redshifted by 220 km/s both previously observed. Additionally, we detect a new blueshifted, broad, shallow absorption wing. At pc scales, the broad absorption at the systemic velocity is detected across the entire radio source while the shallow wing is only seen against part of the eastern lobe. The velocity dispersion of the gas is overall high ($\geq$40 km/s), and is highest (>60 km/s) in the region including the outflow and the radio hot spot. While we detect a velocity gradient along the western lobe and parts of the eastern lobe, most of the gas along the rest of the eastern lobe exhibits no signs of rotation. We therefore conclude that the radio lobes of 4C 31.04 are expanding into a circumnuclear disc, partially disrupting it and making the gas highly turbulent. The distribution of gas is predominantly smooth at the spatial resolution of ~4 pc studied here. However, clumps of gas are also present, particularly along the eastern lobe. This lobe is strongly interacting with the clouds and driving an outflow ~35 pc from the radio core, with a mass-outflow rate of $0.3 \leq \dot{M} \leq 1.4$ M$_\odot$/yr. We compare our observations with a model on the survival of atomic gas clouds in radio-jet-driven outflows and find that the existence of a sub-kpc outflow implies high gas density and inefficient mixing of the cold gas with the hot medium, leading to shorter cooling times. Overall, this provides further evidence of the strong impact of young radio jets on cold ISM and supports the predictions of simulations regarding jet$-$ISM interactions and the nature of the gas into which the jets expand., Comment: 9 pages, 4 figures. Accepted for publication in Astronomy & Astrophysics

We present new JVLA and VLBA observations tracing the HI in the central region of 3C84 (Perseus A). This radio source is hosted by the bright cluster galaxy NGC 1275 in the centre of the iconic Perseus cluster. With the JVLA, we detected broad (FWHM~500 km/s) HI absorption at arcsecond resolution (~300 pc) centred at the systemic velocity of NGC 1275 against the bright radio continuum, suggesting that the detected gas is very close to the supermassive black hole (SMBH). However, we did not detect any absorption in the higher-resolution VLBA data against the parsec-scale radio core and jet. Based on a comparison of the properties of the HI absorption with those of the molecular circum-nuclear disc (CND) known to be present in NGC 1275, we argue that the HI seen in absorption arises from HI in this fast-rotating CND, and that neutral atomic hydrogen is present as close as ~20 pc from the SMBH. The radio continuum providing the background for absorption arises from non-thermal synchrotron emission from the star formation activity in the CND, whose presence has been reported by earlier VLBA studies. We did not detect any signature that the HI gas is affected by an interaction with the radio jet. Thus, at this stage of the evolution of the source, the impact of the radio jet on the gas in NGC 1275 mainly creates cavities on much larger galaxy scales. Overall, the properties of the CND in Perseus A present strong similarities with Mrk 231, suggesting that, unlike often assumed, HI absorption can arise against the radio emission from star formation in a CND. With the JVLA, we serendipitously detected a new, faint absorbing system that is redshifted by ~2660 km/s, in addition to the already known high-velocity absorption system that is redshifted 2850 km/s with respect to NGC 1275. We identify this new system as gas that is stripped from a foreground galaxy falling into the Perseus cluster., Comment: Accepted for publication in A&A, 12 pages, 10 figures

This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and provides suggestions towards upgrade paths for the European VLBI Network (EVN). The EVN is a distributed long-baseline radio interferometric array, that operates at the very forefront of astronomical research. Recent results, together with the new science possibilities outlined in this vision document, demonstrate the EVN's potential to generate new and exciting results that will transform our view of the cosmos. Together with e-MERLIN, the EVN provides a range of baseline lengths that permit unique studies of faint radio sources to be made over a wide range of spatial scales. The science cases are reviewed in six chapters that cover the following broad areas: cosmology, galaxy formation and evolution, innermost regions of active galactic nuclei, explosive phenomena and transients, stars and stellar masers in the Milky Way, celestial reference frames and space applications. The document concludes with identifying the synergies with other radio, as well as multi-band/multi-messenger instruments, and provide the recommendations for future improvements. The appendices briefly describe other radio VLBI arrays, the technological framework for EVN developments, and a selection of spectral lines of astrophysical interest below 100 GHz. The document includes a glossary for non-specialists, and a list of acronyms at the end., Comment: Editors: Tiziana Venturi, Zsolt Paragi, Michael Lindqvist. "EVN Vision Document (2020)", 7 chapters, 3 appendices, 191 pages, 64 figures. Chapter coordinators and all the contributors are listed in the document

Low-luminosity radio-loud active galactic nuclei (AGN) are of importance in studies concerning feedback from radio AGN since a dominant fraction of AGN belong to this class. We report high-resolution Very Large Array (VLA) and European VLBI Network (EVN) observations of HI-21cm absorption from a young, compact steep-spectrum radio source, B2 0258+35, nested in the early-type galaxy NGC 1167, which contains a 160 kpc HI disc. Our VLA and EVN HI absorption observations, modelling, and comparison with molecular gas data suggest that the cold gas in the centre of NGC 1167 is very turbulent (with a velocity dispersion of ~ 90 km/s) and that this turbulence is induced by the interaction of the jets with the interstellar medium (ISM). Furthermore, the ionised gas in the galaxy shows evidence of shock heating at a few kpc from the radio source. These findings support the results from numerical simulations of radio jets expanding into a clumpy gas disc, which predict that the radio jets in this case percolate through the gas disc and drive shocks into the ISM at distances much larger than their physical extent. These results expand the number of low-luminosity radio sources found to impact the surrounding medium, thereby highlighting the possible relevance of these AGN for feedback., Comment: 11 pages, 9 figures; Accepted for publication in Astronomy & Astrophysics

Radio jets can play multiple roles in the feedback loop by regulating the accretion of the gas, by enhancing gas turbulence, and by driving gas outflows. Numerical simulations are beginning to make detailed predictions about these processes. Using high resolution VLBI observations we test these predictions by studying how radio jets of different power and in different phases of evolution affect the properties and kinematics of the surrounding HI gas. Consistent with predictions, we find that young (or recently restarted) radio jets have stronger impact as shown by the presence of HI outflows. The outflowing medium is clumpy {with clouds of with sizes up to a few tens of pc and mass ~10^4 m_sun) already in the region close to the nucleus ($< 100$ pc), making the jet interact strongly and shock the surrounding gas. We present a case of a low-power jet where, as suggested by the simulations, the injection of energy may produce an increase in the turbulence of the medium instead of an outflow., Comment: To appear in proceedings of Focus Meeting 3: Radio Galaxies: Resolving the AGN phenomenon, XXXth IAU General Assembly, "Astronomy in Focus, Volume I," Volker Beckmann & Claudio Ricci, eds. 4 pages, 2 figures

Our view of the central regions of AGN has been enriched by the discovery of fast and massive outflows of HI and molecular gas. Here we present a brief summary of results obtained for young (and restarted) radio AGN. We find that HI outflows tend to be particularly common in this group of objects. This supports the idea that the jet, expanding in a clumpy medium, plays a major role in driving these outflows. The clumpiness of the medium is confirmed by VLBI and ALMA observations. The HI observations reveal that, at least part of the gas, is distributed in clouds with sizes up to a few tens of pc and mass ~10^4 Msun. A change of the conditions in the outflow, with an increasing fraction of diffuse components, as the radio jets grow, is suggested by the high resolution HI observations. The molecular gas completes the picture, showing that the radio plasma jet can couple well with the ISM, strongly affecting the kinematics, but also the physical conditions of the molecular gas. This is confirmed by numerical simulations reproducing, to first order, the kinematics of the gas., Comment: Proceedings of IAU-S342 -- Perseus in Sicily: from black hole to cluster outskirts -- K. Asada, E. de Gouveia dal Pino, H. Nagai, R. Nemmen, M. Giroletti, eds - 6 pages, 3 figures

Radio galaxies are relatively faint at $\gamma$-ray energies, where they make up only 1-2% of all AGN detected by Fermi-LAT. However, they offer a unique perspective to study the intrinsic properties of AGN jets. For this reason, the combination of $\gamma$-ray and multi-wavelength data with high-resolution VLBI monitoring is a powerful tool to tackle the basic unanswered questions about AGN jets. Here we present preliminary results from a sample study of radio galaxies in the Southern hemisphere observed by the TANAMI VLBI monitoring program. We obtain high-resolution maps at 8.4 and 22.3 GHz, and study the jet kinematics using multi-epoch data. We present a preliminary kinematic analysis for the peculiar $\gamma$-ray AGN PKS 0521$-$36., Comment: Submitted to the proceedings of the 13th EVN Symposium and Users Meeting held in St. Petersburg, Russia, 20-23 September 2016. Contributed talk: 6 pages, 1 figure

Simultaneous broadband spectral and temporal studies of blazars are an important tool for investigating active galactic nuclei (AGN) jet physics. We study the spectral evolution between quiescent and flaring periods of 22 radio-loud AGN through multi-epoch, quasi-simultaneous broadband spectra. For many of these sources these are the first broadband studies. We use a Bayesian block analysis of \Fermi/LAT light curves in order to determine time ranges of constant flux for constructing quasi-simultaneous SEDs. The shapes of the resulting 81 SEDs are described by two logarithmic parabolas and a blackbody spectrum where needed. For low states the peak frequencies and luminosities agree well with the blazar sequence, higher luminosity implying lower peak frequencies. This is not true for sources in a high state. The $\gamma$-ray photon index in Fermi/LAT correlates with the synchrotron peak frequency in low and intermediate states. No correlation is present in high states. The black hole mass cannot be determined from the SEDs. Surprisingly, the thermal excess often found in FSRQs at optical/UV wavelengths can be described by blackbody emission and not an accretion disk spectrum. The "harder-when-brighter" trend, typically seen in X-ray spectra of flaring blazars, is visible in the blazar sequence. Our results for low and intermediate states, as well as the Compton dominance, are in agreement with previous results. Black hole mass estimates using the parameters from Bonchi (2013) are in agreement with some of the more direct measurements. For two sources, estimates disagree by more than four orders of magnitude, possibly due to boosting effects. The shapes of the thermal excess seen predominantly in flat spectrum radio quasars are inconsistent with a direct accretion disk origin., Comment: accepted for publication in A&A

As part of the TANAMI multiwavelength progam, we discuss new X-ray observations of the $\gamma$-ray and radio-loud Narrow Line Seyfert galaxy ($\gamma$-NLS1) PKS 2004-447. The active galaxy is a member of a small sample of radio-loud NLS1s detected in $\gamma$-rays by the Fermi Large Area Telescope. It is the radio-loudest and only southern-hemisphere source in this sample. We present results from our X-ray monitoring program comprised of Swift snapshot observations from 2012 through 2014 and two new X-ray observations with XMM-Newton in 2012. We analyze the X-ray spectrum and variability of this peculiar source using supplementary archival data from 2004 and 2011. The (0.5-10) keV spectrum is well described by a flat power law, which can be interpreted as non-thermal emission from a relativistic jet. The source exhibits moderate flux variability on timescales of both months and years. Correlated brightness variations in the (0.5-2) keV and (2-10) keV bands are explained by a single variable spectral component, such as the jet. A possible soft excess seen in the data from 2004 cannot be confirmed by the new \xmm{} observations in 2012. Any contribution to the total flux in 2004 is less than $20\%$ of the power-law component. The (0.5-10) keV luminosities of PKS 2004-447 are in the range of (0.5--2.7)$\times10^{44}\,\mathrm{erg\,s}^{-1}$. A comparison of the X-ray properties among the known $\gamma$-NLS1 galaxies shows that X-ray spectrum is typically dominated by a flat power law without intrinsic absorption. These objects are moderately variable in their brightness, while spectral variability is observed in at least two sources. The major difference across the X-ray spectra of $\gamma$-NLS1s is the luminosity, which spans a range of almost two orders of magnitude, from $10^{44}\,\mathrm{erg\,s}^{-1}$ to $10^{46}\,\mathrm{erg\,s}^{-1}$ in the (0.5-10) keV band., Comment: 12 pages, 12 figures, accepted by Astronomy & Astrophysics on 02/10/15

The nearby active galaxy IC 310, located in the outskirts of the Perseus cluster of galaxies is a bright and variable multi-wavelength emitter from the radio regime up to very high gamma-ray energies above 100 GeV. Originally, the nucleus of IC 310 has been classified as a radio galaxy. However, studies of the multi-wavelength emission showed several properties similarly to those found from blazars as well as radio galaxies. In late 2012, we have organized the first contemporaneous multi-wavelength campaign including radio, optical, X-ray and gamma-ray instruments. During this campaign an exceptionally bright flare of IC 310 was detected with the MAGIC telescopes in November 2012 reaching an averaged flux level in the night of up to one Crab above 1 TeV with a hard spectrum over two decades in energy. The intra-night light curve showed a series of strong outbursts with flux-doubling time scales as fast as a few minutes. The fast variability constrains the size of the gamma-ray emission regime to be smaller than 20% of the gravitational radius of its central black hole. This challenges the shock acceleration models, commonly used to explain gamma-ray radiation from active galaxies. Here, we will present more details on the MAGIC data and discuss several possible alternative emission models., Comment: 8 pages, 5 figures, Proceedings of the 34th International Cosmic Ray Conference, 30 July - 6 August, 2015, The Hague, The Netherlands

Since the discovery of a neutrino flux in excess of the atmospheric background by the IceCube Collaboration, searches for the astrophysical sources have been ongoing. Due to the steeply falling background towards higher energies, the PeV events detected in three years of IceCube data are the most likely ones to be of extraterrestrial origin. Even excluding the PeV events detected so far, the neutrino flux is well above the atmospheric background, so it is likely that a number of sub-PeV events originate from the same astrophysical sources that produce the PeV events. We study the high-energy properties of AGN that are positionally coincident with the neutrino events from three years of IceCube data and show the results for event number 4. IC 4 is a event with a low angular error (7.1$^\circ$) and a large deposited energy of 165 TeV. We use multiwavelength data, including Fermi/LAT and X-ray data, to construct broadband spectra and present parametrizations of the broadband spectral energy distributions with logarithmic parabolas. Assuming the X-ray to {\gamma}-ray emission in blazars originates in the photoproduction of pions by accelerated protons, their predicted neutrino luminosity can be estimated. The measurements of the diffuse extragalactic background by Fermi/LAT gives us an estimate of the flux contributions from faint unresolved blazars. Their contribution increases the number of expected events by a factor of $\sim$2. We conclude that the detection of the IceCube neutrinos IC4, IC14, and IC20 can be explained by the integral emission of blazars, even though no individual source yields a sufficient energy output., Comment: 2014 Fermi Symposium proceedings - eConf C141020.1