@article {292, title = {{Unveiling the radio counterparts of two binary AGN candidates: J1108+0659 and J1131-0204}}, journal = {\aap}, volume = {588}, year = {2016}, pages = {A102}, keywords = {galaxies: active, galaxies: interactions, galaxies: nuclei, radio continuum: galaxies, techniques: interferometric}, doi = {10.1051/0004-6361/201528021}, author = {Bondi, M. and Perez-Torres, M.~A. and Piconcelli, E. and Fu, H.} } @article {2015ApJ...799...11X, title = {{ALMA Observations of Warm Dense Gas in NGC 1614 - Breaking of the Star Formation Law in the Central Kiloparsec}}, journal = {The Astrophysical Journal}, volume = {799}, year = {2015}, month = {jan}, pages = {11}, abstract = {We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 {$μ$}m dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1$\{$$^{\prime \prime }$$\}$= 329 pc). The CO emission is well resolved by the ALMA beam (0.{\textquoteright}{\textquoteright}26 {\times} 0.{\textquoteright}{\textquoteright}20) into a circumnuclear ring, with an integrated flux of f $_{ CO(6-5)}$ = 898 ({\plusmn} 153) Jy km s$^{-1}$, which is 63({\plusmn} 12)\% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc {\l}t} r {\l}t} 350 pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of \~{}40 km s$^{-1}$. These knots are associated with strong star formation regions with {$Σ$}$_{SFR}$ \~{} 100 M $_{\&sun;}$ yr$^{-1}$ kpc$^{-2}$ and {$Σ$} $_{Gas}${\tilde} 10$^{4}$ $\{$M$\}$\_{\sun} pc$^{-2}$. The non-detections of the nucleus in both the CO (6-5) line emission and the 435 {$μ$}m continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between {$Σ$}$_{Gas}$ and {$Σ$}$_{SFR}$, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of \~{}100 pc. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.}, keywords = {galaxies: active, galaxies: evolution, galaxies: general, galaxies: interactions, galaxies: ISM, galaxies: magnetic fields, galaxies: nuclei, galaxies: starburst, submillimeter: galaxies}, doi = {10.1088/0004-637X/799/1/11}, url = {http://adsabs.harvard.edu/abs/2015ApJ...799...11X}, author = {Xu, C.~K. and Cao, C. and Lu, N. and Gao, Y. and Diaz-Santos, T. and R. Herrero-Illana and Meijerink, R. and Privon, G. and Zhao, Y.-H. and Evans, A.~S. and K{\"o}nig, S. and Mazzarella, J.~M. and Aalto, S. and Appleton, P. and Armus, L. and Charmandaris, V. and Chu, J. and Haan, S. and Inami, H. and Murphy, E.~J. and Sanders, D.~B. and Schulz, B. and van der Werf, P.} } @article {213, title = {{High-resolution imaging of the molecular outflows in two mergers: IRAS 17208-0014 and NGC 1614}}, journal = {Astronomy \& Astrophysics}, volume = {580}, year = {2015}, pages = {A35}, keywords = {galaxies: individual: IRAS 17208-0014, galaxies: individual: NGC1614, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: nuclei, galaxies: starburst}, doi = {10.1051/0004-6361/201526133}, author = {Garcia-Burillo, S. and Combes, F. and Usero, A. and Aalto, S. and Colina, L. and Alonso-Herrero, A. and Hunt, L.~K. and Arribas, S. and Costagliola, F. and Labiano, A. and Neri, R. and Pereira-Santaella, M. and Tacconi, L.~J. and van der Werf, P.~P.} } @article {2015A\&A...574A..65B, title = {{Molecular gas and nuclear activity in early-type galaxies: any link with radio loudness?}}, journal = {Astronomy and Astrophysics}, volume = {574}, year = {2015}, month = {feb}, pages = {A65}, abstract = {
Aims: We want to study the amount of molecular gas in a sample of nearby early-type galaxies (ETGs) that host low-luminosity active galactic nuclei (AGN). We look for possible differences between the radio-loud (RL) and radio-quiet (RQ) AGN.
Methods: We observed the CO(1-0) and CO(2-1) spectral lines with the IRAM 30 m and NRO 45 m telescopes for eight galaxies. They belong to a large sample of 37 local ETGs that host both RQ and RL AGN. We gather data from the literature for the entire sample.
Results: We report the new detection of CO(1-0) emission in four galaxies (UGC 0968, UGC 5617, UGC 6946, and UGC 8355) and CO(2-1) emission in two of them (UGC 0968 and UGC 5617). The CO(2-1)/CO(1-0) ratio in these sources is \~{} 0.7 {\plusmn} 0.2. Considering both the new observations and the literature, the detection rate of CO in our sample is 55{\plusmn} 9\%, with no statistically significant difference between the hosts of RL and RQ AGNs. For all the detected galaxies we converted the CO luminosities into the molecular masses, M$_{H2}$, which range from 10$^{6.5}$ to 10$^{8.5}$ M$_{\&sun;}$, without any statistically significant differences between RL and RQ galaxies. This suggests that the amount of molecular gas does not likely set the radio loudness of the AGN. Furthermore, despite the low statistical significance, the presence of a weak trend between the H$_{2}$ mass with various tracers of nuclear activity (mainly [O III] emission line nuclear power) cannot be excluded. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).}, keywords = {cD, galaxies: active, galaxies: elliptical and lenticular, galaxies: ISM, galaxies: nuclei, ISM: molecules}, doi = {10.1051/0004-6361/201425131}, url = {http://adsabs.harvard.edu/abs/2015A\%26A...574A..65B}, author = {Baldi, R.~D. and Giroletti, M. and Capetti, A. and Giovannini, G. and Casasola, V. and M. A. P{\'e}rez-Torres and Kuno, N.} } @article {2014A\&A...567A.125G, title = {{Molecular line emission in NGC 1068 imaged with ALMA. I. An AGN-driven outflow in the dense molecular gas}}, journal = {Astronomy and Astrophysics}, volume = {567}, year = {2014}, month = {jul}, pages = {A125}, abstract = {
Aims: We investigate the fueling and the feedback of star formation and nuclear activity in NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy, by analyzing the distribution and kinematics of the molecular gas in the disk. We aim to understand if and how gas accretion can self-regulate.
Methods: We have used the Atacama Large Millimeter Array (ALMA) to map the emission of a set of dense molecular gas (n(H$_{2}$) {\sime} 10$^{5 - 6}$ cm$^{-3}$) tracers (CO(3-2), CO(6-5), HCN(4-3), HCO$^{+}$(4-3), and CS(7-6)) and their underlying continuum emission in the central r \~{} 2 kpc of NGC 1068 with spatial resolutions \~{}0.3{\Prime} - 0.5{\Prime} (\~{}20-35 pc for the assumed distance of D = 14 Mpc).
Results: The sensitivity and spatial resolution of ALMA give an unprecedented detailed view of the distribution and kinematics of the dense molecular gas (n(H$_{2}$) {\ge} 10$^{5 - 6}$cm$^{-3}$) in NGC 1068. Molecular line and dust continuum emissions are detected from a r \~{} 200 pc off-centered circumnuclear disk (CND), from the 2.6 kpc-diameter bar region, and from the r \~{} 1.3 kpc starburst (SB) ring. Most of the emission in HCO$^{+}$, HCN, and CS stems from the CND. Molecular line ratios show dramatic order-of-magnitude changes inside the CND that are correlated with the UV/X-ray illumination by the active galactic nucleus (AGN), betraying ongoing feedback. We used the dust continuum fluxes measured by ALMA together with NIR/MIR data to constrain the properties of the putative torus using CLUMPY models and found a torus radius of 20$^{+6}$$_{-10}$pc. The Fourier decomposition of the gas velocity field indicates that rotation is perturbed by an inward radial flow in the SB ring and the bar region. However, the gas kinematics from r \~{} 50 pc out to r \~{} 400 pc reveal a massive (M$_{mol}$\~{} 2.7$^{+0.9}$$_{-1.2}$ {\times} 10$^{7}$ M$_{\&sun;}$) outflow in all molecular tracers. The tight correlation between the ionized gas outflow, the radio jet, and the occurrence of outward motions in the disk suggests that the outflow is AGN driven.
Conclusions: The molecular outflow is likely launched when the ionization cone of the narrow line region sweeps the nuclear disk. The outflow rate estimated in the CND, dM/dt\~{} 63$^{+21}$$_{-37}$ M$_{\&sun;}$ yr$^{-1}$, is an order of magnitude higher than the star formation rate at these radii, confirming that the outflow is AGN driven. The power of the AGN is able to account for the estimated momentum and kinetic luminosity of the outflow. The CND mass load rate of the CND outflow implies a very short gas depletion timescale of {\l}e}1 Myr. The CND gas reservoir is likely replenished on longer timescales by efficient gas inflow from the outer disk. Based on observations carried out with ALMA in Cycle 0.}, keywords = {galaxies: individual: NGC 1068, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: nuclei, galaxies: Seyfert, radio lines: galaxies}, doi = {10.1051/0004-6361/201423843}, url = {http://adsabs.harvard.edu/abs/2014A\%26A...567A.125G}, author = {S. Garc{\'\i}a-Burillo and Combes, F. and Usero, A. and Aalto, S. and Krips, M. and Viti, S. and Alonso-Herrero, A. and Hunt, L.~K. and Schinnerer, E. and Baker, A.~J. and Boone, F. and Casasola, V. and Colina, L. and F. Costagliola and Eckart, A. and Fuente, A. and Henkel, C. and Labiano, A. and Mart{\'\i}n, S. and Marquez, I. and Muller, S. and Planesas, P. and Ramos Almeida, C. and Spaans, M. and Tacconi, L.~J. and van der Werf, P.~P.} } @article {218, title = {{Molecular line emission in NGC 1068 imaged with ALMA. I. An AGN-driven outflow in the dense molecular gas}}, journal = {\aap}, volume = {567}, year = {2014}, pages = {A125}, keywords = {galaxies: individual: NGC 1068, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: nuclei, galaxies: Seyfert, radio lines: galaxies}, doi = {10.1051/0004-6361/201423843}, author = {Garcia-Burillo, S. and Combes, F. and Usero, A. and Aalto, S. and Krips, M. and Viti, S. and Alonso-Herrero, A. and Hunt, L.~K. and Schinnerer, E. and Baker, A.~J. and Boone, F. and Casasola, V. and Colina, L. and Costagliola, F. and Eckart, A. and Fuente, A. and Henkel, C. and Labiano, A. and Mart{\'\i}n, S. and Marquez, I. and Muller, S. and Planesas, P. and Ramos Almeida, C. and Spaans, M. and Tacconi, L.~J. and van der Werf, P.~P.} } @article {217, title = {{Molecular line emission in NGC 1068 imaged with ALMA. II. The chemistry of the dense molecular gas}}, journal = {\aap}, volume = {570}, year = {2014}, pages = {A28}, keywords = {galaxies: active, galaxies: individual: NGC 1068, galaxies: ISM, galaxies: nuclei, molecular processes, radio lines: galaxies}, doi = {10.1051/0004-6361/201424116}, author = {Viti, S. and Garcia-Burillo, S. and Fuente, A. and Hunt, L.~K. and Usero, A. and Henkel, C. and Eckart, A. and Mart{\'\i}n, S. and Spaans, M. and Muller, S. and Combes, F. and Krips, M. and Schinnerer, E. and Casasola, V. and Costagliola, F. and Marquez, I. and Planesas, P. and van der Werf, P.~P. and Aalto, S. and Baker, A.~J. and Boone, F. and Tacconi, L.~J.} } @article {2014A\&A...570A..28V, title = {{Molecular line emission in NGC 1068 imaged with ALMA. II. The chemistry of the dense molecular gas}}, journal = {Astronomy and Astrophysics}, volume = {570}, year = {2014}, month = {oct}, pages = {A28}, abstract = {
Aims: We present a detailed analysis of Atacama Large Millimeter/submillimeter Array (ALMA) Bands 7 and 9 data of CO, HCO$^{+}$, HCN, and CS, augmented with Plateau de Bure Interferometer (PdBI) data of the \~{}200 pc circumnuclear disc (CND) and the \~{}1.3 kpc starburst ring (SB ring) of NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy. We aim to determine the physical characteristics of the dense gas present in the CND, and to establish whether the different line intensity ratios we find within the CND, as well as between the CND and the SB ring, are due to excitation effects (gas density and temperature differences) or to a different chemistry.
Methods: We estimate the column densities of each species in local thermodynamic equilibrium (LTE). We then compute large one-dimensional, non-LTE radiative transfer grids (using RADEX) by using only the CO transitions first, and then all the available molecules to constrain the densities, temperatures, and column densities within the CND. We finally present a preliminary set of chemical models to determine the origin of the gas.
Results: We find that, in general, the gas in the CND is very dense ({\gt}10$^{5}$ cm$^{-3}$) and hot (T{\gt} 150 K), with differences especially in the temperature across the CND. The AGN position has the lowest CO/HCO$^{+}$, CO/HCN, and CO/CS column density ratios. The RADEX analyses seem to indicate that there is chemical differentiation across the CND. We also find differences between the chemistry of the SB ring and some regions of the CND; the SB ring is also much colder and less dense than the CND. Chemical modelling does not succeed in reproducing all the molecular ratios with one model per region, suggesting the presence of multi-gas phase components.
Conclusions: The LTE, RADEX, and chemical analyses all indicate that more than one gas-phase component is necessary to uniquely fit all the available molecular ratios within the CND. A higher number of molecular transitions at the ALMA resolution is necessary to determine quantitatively the physical and chemical characteristics of these components. Tables 5-11 are available in electronic form at http://www.aanda.org}, keywords = {galaxies: active, galaxies: individual: NGC 1068, galaxies: ISM, galaxies: nuclei, molecular processes, radio lines: galaxies}, doi = {10.1051/0004-6361/201424116}, url = {http://adsabs.harvard.edu/abs/2014A\%26A...570A..28V}, author = {Viti, S. and S. Garc{\'\i}a-Burillo and Fuente, A. and Hunt, L.~K. and Usero, A. and Henkel, C. and Eckart, A. and Mart{\'\i}n, S. and Spaans, M. and Muller, S. and Combes, F. and Krips, M. and Schinnerer, E. and Casasola, V. and F. Costagliola and Marquez, I. and Planesas, P. and van der Werf, P.~P. and Aalto, S. and Baker, A.~J. and Boone, F. and Tacconi, L.~J.} } @article {2014ApJ...786..156H, title = {{A Multi-wavelength View of the Central Kiloparsec Region in the Luminous Infrared Galaxy NGC 1614}}, journal = {The Astrophysical Journal}, volume = {786}, year = {2014}, month = {may}, pages = {156}, abstract = {The Luminous Infrared Galaxy NGC 1614 hosts a prominent circumnuclear ring of star formation. However, the nature of the dominant emitting mechanism in its central \~{}100 pc is still under debate. We present sub-arcsecond angular resolution radio, mid-infrared, Pa{$\alpha$}, optical, and X-ray observations of NGC 1614, aimed at studying in detail both the circumnuclear ring and the nuclear region. The 8.4 GHz continuum emission traced by the Very Large Array and the Gemini/T-ReCS 8.7 {$μ$}m emission, as well as the Pa{$\alpha$} line emission, show remarkable morphological similarities within the star-forming ring, suggesting that the underlying emission mechanisms are tightly related. We used a Hubble Space Telescope/NICMOS Pa{$\alpha$} map of similar resolution to our radio maps to disentangle the thermal free-free and non-thermal synchrotron radio emission, from which we obtained the intrinsic synchrotron power law for each individual region within the central kiloparsec of NGC 1614. The radio ring surrounds a relatively faint, steep-spectrum source at the very center of the galaxy, suggesting that the central source is not powered by an active galactic nucleus (AGN), but rather by a compact (r {\l}t}\~{} 90 pc) starburst (SB). Chandra X-ray data also show that the central kiloparsec region is dominated by SB activity, without requiring the existence of an AGN. We also used publicly available infrared data to model-fit the spectral energy distribution of both the SB ring and a putative AGN in NGC 1614. In summary, we conclude that there is no need to invoke an AGN to explain the observed bolometric properties of the galaxy.}, keywords = {galaxies: individual: NGC 1614, galaxies: nuclei, galaxies: starburst, infrared: galaxies, radio continuum: galaxies, supernovae: general}, doi = {10.1088/0004-637X/786/2/156}, url = {http://adsabs.harvard.edu/abs/2014ApJ...786..156H}, author = {R. Herrero-Illana and M. A. P{\'e}rez-Torres and Alonso-Herrero, A. and Alberdi, A. and Colina, L. and Efstathiou, A. and Hern{\'a}ndez-Garc{\'\i}a, L. and Miralles-Caballero, D. and V{\"a}is{\"a}nen, P. and Packham, C.~C. and Rajpaul, V. and Zijlstra, A.~A.} } @article {2012ApJ...746..151A, title = {{The 2010 Very High Energy {$\gamma$}-Ray Flare and 10 Years of Multi-wavelength Observations of M 87}}, journal = {The Astrophysical Journal}, volume = {746}, year = {2012}, month = {feb}, pages = {151}, abstract = {The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3 - 6) {\times} 10$^{9}$ M $_{\&sun;}$) provides a unique opportunity to investigate the origin of very high energy (VHE; E {\gt} 100 GeV) {$\gamma$}-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE {$\gamma$}-ray emitter since 2006. The VHE {$\gamma$}-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE {$\gamma$}-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of {$\tau$}$^{rise}$ $_{d}$ = (1.69 {\plusmn} 0.30) days and {$\tau$}$^{decay}$ $_{d}$ = (0.611 {\plusmn} 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (\~{}day), peak fluxes ({$\Phi$}$_{>0.35 TeV}$ \~{}= (1-3) {\times} 10$^{-11}$ photons cm$^{-2}$ s$^{-1}$), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken \~{}3 days after the peak of the VHE {$\gamma$}-ray emission reveal an enhanced flux from the core (flux increased by factor \~{}2; variability timescale {\l}t}2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE {$\gamma$}-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002-2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE {$\gamma$}-ray emission from M 87 are reviewed in the light of the new data.}, keywords = {galaxies: active, galaxies: individual: M 87, galaxies: jets, galaxies: nuclei, gamma rays: galaxies, radiation mechanisms: non-thermal}, doi = {10.1088/0004-637X/746/2/151}, url = {http://adsabs.harvard.edu/abs/2012ApJ...746..151A}, author = {Abramowski, A. and Acero, F. and Aharonian, F. and Akhperjanian, A.~G. and Anton, G. and Balzer, A. and Barnacka, A. and Barres de Almeida, U. and Becherini, Y. and Becker, J. and Behera, B. and Bernl{\"o}hr, K. and Birsin, E. and Biteau, J. and Bochow, A. and Boisson, C. and Bolmont, J. and Bordas, P. and Brucker, J. and Brun, F. and Brun, P. and Bulik, T. and B{\"u}sching, I. and Carrigan, S. and Casanova, S. and Cerruti, M. and Chadwick, P.~M. and Charbonnier, A. and Chaves, R.~C.~G. and Cheesebrough, A. and Clapson, A.~C. and Coignet, G. and Cologna, G. and Conrad, J. and Dalton, M. and Daniel, M.~K. and Davids, I.~D. and Degrange, B. and Deil, C. and Dickinson, H.~J. and Djannati-Ata{\"\i}, A. and Domainko, W. and Drury, L.~O. and Dubus, G. and Dutson, K. and Dyks, J. and Dyrda, M. and Egberts, K. and Eger, P. and Espigat, P. and Fallon, L. and Farnier, C. and Fegan, S. and Feinstein, F. and Fernandes, M.~V. and Fiasson, A. and Fontaine, G. and F{\"o}rster, A. and F{\"u}{\ss}ling, M. and Gallant, Y.~A. and Gast, H. and G{\'e}rard, L. and Gerbig, D. and Giebels, B. and Glicenstein, J.~F. and Gl{\"u}ck, B. and Goret, P. and G{\"o}ring, D. and H{\"a}ffner, S. and Hague, J.~D. and Hampf, D. and Hauser, M. and Heinz, S. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, J.~A. and Hoffmann, A. and Hofmann, W. and Hofverberg, P. and Holler, M. and Horns, D. and Jacholkowska, A. and de Jager, O.~C. and Jahn, C. and Jamrozy, M. and Jung, I. and Kastendieck, M.~A. and Katarzy{\'n}ski, K. and Katz, U. and Kaufmann, S. and Keogh, D. and Khangulyan, D. and Kh{\'e}lifi, B. and Klochkov, D. and Klu{\'z}niak, W. and Kneiske, T. and Komin, N. and Kosack, K. and Kossakowski, R. and Laffon, H. and Lamanna, G. and Lennarz, D. and Lohse, T. and Lopatin, A. and Lu, C.-C. and Marandon, V. and Marcowith, A. and Masbou, J. and Maurin, D. and Maxted, N. and Mayer, M. and McComb, T.~J.~L. and Medina, M.~C. and M{\'e}hault, J. and Moderski, R. and Moulin, E. and Naumann, C.~L. and Naumann-Godo, M. and de Naurois, M. and Nedbal, D. and Nekrassov, D. and Nguyen, N. and Nicholas, B. and Niemiec, J. and Nolan, S.~J. and Ohm, S. and de O{\~n}a Wilhelmi, E. and Opitz, B. and Ostrowski, M. and Oya, I. and Panter, M. and Paz Arribas, M. and Pedaletti, G. and Pelletier, G. and Petrucci, P.-O. and Pita, S. and P{\"u}hlhofer, G. and Punch, M. and Quirrenbach, A. and Raue, M. and Rayner, S.~M. and Reimer, A. and Reimer, O. and Renaud, M. and de los Reyes, R. and Rieger, F. and Ripken, J. and Rob, L. and Rosier-Lees, S. and Rowell, G. and Rudak, B. and Rulten, C.~B. and Ruppel, J. and Sahakian, V. and Sanchez, D.~A. and Santangelo, A. and Schlickeiser, R. and Sch{\"o}ck, F.~M. and Schulz, A. and Schwanke, U. and Schwarzburg, S. and Schwemmer, S. and Sheidaei, F. and Skilton, J.~L. and Sol, H. and Spengler, G. and Stawarz, {\L}. and Steenkamp, R. and Stegmann, C. and Stinzing, F. and Stycz, K. and Sushch, I. and Szostek, A. and Tavernet, J.-P. and Terrier, R. and Tluczykont, M. and Valerius, K. and van Eldik, C. and Vasileiadis, G. and Venter, C. and Vialle, J.~P. and Viana, A. and Vincent, P. and V{\"o}lk, H.~J. and Volpe, F. and Vorobiov, S. and Vorster, M. and Wagner, S.~J. and Ward, M. and White, R. and Wierzcholska, A. and Zacharias, M. and Zajczyk, A. and Zdziarski, A.~A. and Zech, A. and Zechlin, H.-S. and H.E.S.S.~Collaboration and Aleksi{\'c}, J. and Antonelli, L.~A. and Antoranz, P. and Backes, M. and Barrio, J.~A. and Bastieri, D. and Becerra Gonz{\'a}lez, J. and Bednarek, W. and Berdyugin, A. and Berger, K. and Bernardini, E. and Biland, A. and Blanch, O. and Bock, R.~K. and Boller, A. and Bonnoli, G. and Borla Tridon, D. and Braun, I. and Bretz, T. and Ca{\~n}ellas, A. and Carmona, E. and Carosi, A. and Colin, P. and Colombo, E. and Contreras, J.~L. and Cortina, J. and Cossio, L. and Covino, S. and Dazzi, F. and De Angelis, A. and De Cea del Pozo, E. and De Lotto, B. and Delgado Mendez, C. and Diago Ortega, A. and Doert, M. and Dom{\'\i}nguez, A. and Dominis Prester, D. and Dorner, D. and Doro, M. and Elsaesser, D. and Ferenc, D. and Fonseca, M.~V. and Font, L. and Fruck, C. and Garc{\'\i}a L{\'o}pez, R.~J. and Garczarczyk, M. and Garrido, D. and Giavitto, G. and Godinovi{\'c}, N. and Hadasch, D. and H{\"a}fner, D. and Herrero, A. and Hildebrand, D. and H{\"o}hne-M{\"o}nch, D. and Hose, J. and Hrupec, D. and Huber, B. and Jogler, T. and Klepser, S. and Kr{\"a}henb{\"u}hl, T. and Krause, J. and La Barbera, A. and Lelas, D. and Leonardo, E. and Lindfors, E. and Lombardi, S. and L{\'o}pez, M. and Lorenz, E. and Makariev, M. and Maneva, G. and Mankuzhiyil, N. and Mannheim, K. and Maraschi, L. and Mariotti, M. and Mart{\'\i}nez, M. and Mazin, D. and Meucci, M. and Miranda, J.~M. and Mirzoyan, R. and Miyamoto, H. and Mold{\'o}n, J. and Moralejo, A. and Munar, P. and Nieto, D. and Nilsson, K. and Orito, R. and Oya, I. and Paneque, D. and Paoletti, R. and Pardo, S. and Paredes, J.~M. and Partini, S. and Pasanen, M. and Pauss, F. and M. A. 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The nearby spiral galaxy M 81 harbours in its core a low-luminosity active galactic nucleus (LLAGN), and appears to be closely related to the more distant and powerful active galactic nuclei (AGNs) seen in quasars and radio galaxies. The intrinsic size of this object is unknown because of too much scattering, and it has shown a core-jet morphology with weak extended emission rotating with wavelength.
Aims: The proximity of M 81 (D = 3.63 Mpc) allows for a detailed investigation of its nucleus. The nucleus is four orders of magnitude more luminous than the Galactic centre, and is therefore considered to be a link between Sgr A$^{*}$ and the more powerful nuclei of radio galaxies and quasars. Our main goal was to determine the size of M 81{\l}owast} at a shorter wavelength to directly test whether the frequency-size dependent law {$\Theta$} {\prop} {$ν$}$^{-0.8}$ is still valid for wavelengths shorter than 1 cm. In addition, we also aimed to confirm the rotation of the source as a function of frequency.
Methods: We observed the continuum 7 mm radio emission of M 81{\l}owast} with the Very Long Baseline Array on Sep. 13, 2002, using nearby calibrators to apply their interferometric observables to the target source to increase the chances of detection. The source was detected on all baselines and hybrid mapping was possible.
Results: We present the first 7 mm VLBI image of the core of M 81{\l}owast}, which is the highest resolution image ever of this source. Modelling the interferometric visibilities with two Gaussian functions sets constraints on the angular size of its core down to 38 microarcseconds, corresponding to a maximum (projected) linear size of 138 AU, and shows extended emission towards the NE with a position angle of \~{}50{\deg}. A fit of a one Gaussian elliptical function yields a position angle of 28 {\plusmn} 8 degrees for its elongated, compact structure. Combining the 7 mm size with earlier measurements at other frequencies, we determine a frequency-size dependence of {$\Theta$} {\prop} {$ν$}$^{(-0.88 {\textpm} 0.04)}$.
Conclusions: Our VLBI imaging of M 81{\l}owast} has clearly detected its core-jet structure, and has allowed us to estimate a size for its core, with a minimum size of 138 AU ({\ap}100 Schwarzschild radii). Our work opens the way for future observations of M 81{\l}owast} at high-angular resolution, including the monitoring of its structure, given that much higher bandwidths are currently available on the interferometric networks. In particular, this would allow one to test for possible proper motions of the core or of its components in the inner jet of M 81{\l}owast}, and for the speed of the detected jet components.}, keywords = {galaxies: active, galaxies: individual: M 81, galaxies: nuclei, instrumentation: interferometers, radio continuum: galaxies}, doi = {10.1051/0004-6361/201118399}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...537A..93R}, author = {Ros, E. and M. A. P{\'e}rez-Torres} }