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Davies J.I.,University of Cardiff | Baes M.,Ghent University | Bianchi S.,National institute for astrophysics | Jones A.,French National Center for Scientific Research | And 21 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2017

The European Space Agency has invested heavily in two cornerstones missions: Herschel and Planck. The legacy data from these missions provides an unprecedented opportunity to study cosmic dust in galaxies so that we can, for example, answer fundamental questions about the origin of the chemical elements, physical processes in the interstellar medium (ISM), its effect on stellar radiation, its relation to star formation and how this relates to the cosmic far-infrared background. In this paper we describe the DustPedia project, which enables us to develop tools and computer models that will help us relate observed cosmic dust emission to its physical properties (chemical composition, size distribution, and temperature), its origins (evolved stars, supernovae, and growth in the ISM), and the processes that destroy it (high-energy collisions and shock heated gas). To carry out this research, we combine the Herschel/Planck data with that from other sources of data, and provide observations at numerous wavelengths (≤41) across the spectral energy distribution, thus creating the DustPedia database. To maximize our spatial resolution and sensitivity to cosmic dust, we limit our analysis to 4231 local galaxies (v < 3000 km s-1) selected via their near-infrared luminosity (stellar mass). To help us interpret this data, we developed a new physical model for dust (THEMIS), a new Bayesian method of fitting and interpreting spectral energy distributions (HerBIE) and a state-of-the-art Monte Carlo photon-tracing radiative transfer model (SKIRT). In this, the first of the DustPedia papers, we describe the project objectives, data sets used, and provide an insight into the new scientific methods we plan to implement. © 2017. The Astronomical Society of the Pacific. All rights reserved.

Fuller L.,University of Texas at San Antonio | Lopez-Rodriguez E.,University of Texas at Austin | Packham C.,University of Texas at San Antonio | Packham C.,Japan National Astronomical Observatory | And 13 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present 31.5 μm imaging photometry of 11 nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We tentatively detect extended 31 μm emission for the first time in our sample. In combination with this new data set, subarcsecond resolution 1-18 μm imaging and 7.5-13 μm spectroscopic observations were used to compute the nuclear spectral energy distribution (SED) of each galaxy. We found that the turnover of the torus emission does not occur at wavelengths ≤31.5 μm, which we interpret as a lower-limit for the wavelength of peak emission. We used CLUMPY torus models to fit the nuclear infrared (IR) SED and infer trends in the physical parameters of the AGN torus for the galaxies in the sample. Including the 31.5 μm nuclear flux in the SED (1) reduces the number of clumpy torus models compatible with the data, and (2) modifies the model output for the outer radial extent of the torus for 10 of the 11 objects. Specifically, six (60 per cent) objects show a decrease in radial extent while four (40 per cent) show an increase. We find torus outer radii ranging from <1 to 8.4 pc. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Gonzalez-Martin O.,Institute Radioastronomia y Astrofisica IRyA UNAM | Hernandez-Garcia L.,Institute Astrofisica Of Andalucia | Masegosa J.,Institute Astrofisica Of Andalucia | Marquez I.,Institute Astrofisica Of Andalucia | And 8 more authors.
Astronomy and Astrophysics | Year: 2016

Context. Obscured active galactic nuclei (AGNs) are thought to be very common in the Universe. Observations and surveys have shown that the number of sources increases for near galaxies and at the low-luminosity regime (the so-called LLAGNs). Furthermore, many AGNs show changes in their obscuration properties at X-rays that may suggest a configuration of clouds very close to the accretion disk. However, these variations could also be due to changes in the intrinsic continuum of the source. It is therefore important to study nearby AGN to better understand the locus and distribution of clouds in the neighbourhood of the nucleus. Aims. We aim to study the nuclear obscuration of LLAGN NGC 835 and its extended emission using mid-infrared observations. Methods. We present sub-arcsecond-resolution mid-infrared 11.5 μm imaging of the LLAGN galaxy NGC 835 obtained with the instrument CanariCam in the Gran Telescopio CANARIAS (GTC), archival Spitzer/IRS spectroscopy, and archival Chandra data observed in 2000, 2008, and 2013. Results. The GTC/CanariCam 11.5 μm image reveals faint extended emission out to ~6 arcsec. We obtained a nuclear flux of F(11.5 μm) ~ 18 mJy, whereas the extended emission accounts for 90% of the total flux within the 6 arcsec. This means that the low angular resolution (~4 arcsec) IRS spectrum is dominated by this extended emission and not by the AGN. This is clearly seen in the Spitzer/IRS spectrum, which resembles that of star-forming galaxies. Although the extended soft X-ray emission shows some resemblance with that of the mid-infrared, the knots seen at X-rays are mostly located in the inner side of this mid-infrared emission. The nuclear X-ray spectrum of the source has undergone a spectral change between 2000/2008 and 2013. We argue that this variation is most probably due to changes in the hydrogen column density from ~8 × 1023 cm-2 to ~3 × 1023 cm-2. NGC 835 therefore is one of the few LLAGN, together with NGC 1052, in which changes in the absorber can be claimed. © 2016 ESO.

Hull C.L.H.,Harvard - Smithsonian Center for Astrophysics | Girart J.M.,Harvard - Smithsonian Center for Astrophysics | Girart J.M.,Institute Of Ciencies Of Lespai | Kristensen L.E.,Harvard - Smithsonian Center for Astrophysics | And 8 more authors.
Astrophysical Journal Letters | Year: 2016

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of a one-sided, high-velocity (∼80 km s-1) CO(J = ) jet powered by the intermediate-mass protostellar source Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle cavity; the walls of the cavity can be seen in both 4 cm free-free emission detected by the Very Large Array and 1.3 mm thermal dust emission detected by ALMA. This is the first time that ionization of an outflow cavity has been directly detected via free-free emission in a very young, embedded Class 0 protostellar source that is still powering a molecular jet. The cavity walls are ionized either by UV photons escaping from the accreting protostellar source or by the precessing molecular jet impacting the walls. These observations suggest that ionized outflow cavities may be common in Class 0 protostellar sources, shedding further light on the radiation, outflow, and jet environments in the youngest, most embedded forming stars. © 2016. The American Astronomical Society. All rights reserved.

Hernandez-Garcia L.,Institute Astrofisica Of Andalucia | Masegosa J.,Institute Astrofisica Of Andalucia | Gonzalez-Martin O.,Institute Radioastronomia y Astrofisica IRyA UNAM | Marquez I.,Institute Astrofisica Of Andalucia | Perea J.,Institute Astrofisica Of Andalucia
Astrophysical Journal | Year: 2016

X-ray variability is very common in active galactic nuclei (AGNs), but these variations may not occur similarly in different families of AGNs. We aim to disentangle the structure of low-ionization nuclear emission-line regions (LINERs) compared to Seyfert 2s by the study of their spectral properties and X-ray variations. We assembled the X-ray spectral parameters and variability patterns, which were obtained from simultaneous spectral fittings. Major differences are observed in the X-ray luminosities and the Eddington ratios, which are higher in Seyfert 2s. Short-term X-ray variations were not detected, while long-term changes are common in LINERs and Seyfert 2s. Compton-thick sources generally do not show variations, most probably because the AGN is not accesible in the 0.5-10 keV energy band. The changes are mostly related to variations in the nuclear continuum, but other patterns of variability show that variations in the absorbers and at soft energies can be present in a few cases. We conclude that the X-ray variations may occur similarly in LINERs and Seyfert 2s, i.e., they are related to the nuclear continuum, although they might have different accretion mechanisms. Variations at UV frequencies are detected in LINER nuclei but not in Seyfert 2s. This is suggestive of at least some LINERs having an unobstructed view of the inner disk where the UV emission might take place, with UV variations being common in them. This result might be compatible with the disappeareance of the torus and/or the broad-line region in at least some LINERs. © 2016. The American Astronomical Society. All rights reserved..

Rodriguez-Kamenetzky A.,Institute Astronomia Teorica y Experimental | Rodriguez-Kamenetzky A.,Institute Radioastronomia y Astrofisica IRyA UNAM | Carrasco-Gonzalez C.,Institute Radioastronomia y Astrofisica IRyA UNAM | Araudo A.,University of Oxford | And 5 more authors.
Astrophysical Journal | Year: 2016

While most protostellar jets present free-free emission at radio wavelengths, synchrotron emission has also been proposed to be present in a handful of these objects. The presence of nonthermal emission has been inferred by negative spectral indices at centimeter wavelengths. In one case (the HH 80-81 jet arising from a massive protostar), its synchrotron nature was confirmed by the detection of linearly polarized radio emission. One of the main consequences of these results is that synchrotron emission implies the presence of relativistic particles among the nonrelativistic material of these jets. Therefore, an acceleration mechanism should be taking place. The most probable scenario is that particles are accelerated when the jets strongly impact against the dense envelope surrounding the protostar. Here we present an analysis of radio observations obtained with the Very Large Array of the triple radio source in the Serpens star-forming region. This object is known to be a radio jet arising from an intermediate-mass protostar. It is also one of the first protostellar jets where the presence of nonthermal emission was proposed. We analyze the dynamics of the jet and the nature of the emission and discuss these issues in the context of the physical parameters of the jet and the particle acceleration phenomenon. © 2016. The American Astronomical Society. All rights reserved.

Pasetto A.,Max Planck Institute for Radio Astronomy | Kraus A.,Max Planck Institute for Radio Astronomy | Mack K.-H.,National institute for astrophysics | Bruni G.,Max Planck Institute for Radio Astronomy | And 2 more authors.
Astronomy and Astrophysics | Year: 2016

Context. We characterised and studied, in the radio band, a sample of candidates for high rotation measure (RM). These point-like objects show a strong depolarisation at 21 cm. This feature suggests the presence of a very dense medium surrounding them combined with a strong magnetic field. Aims. This work aims at selecting and studying a sample of radio sources with high RM, thus studying their physical conditions and their status with respect to their surrounding medium. We want to understand whether any connection is present between the AGN-hosting galaxy medium with some evolutionary track and/or some restarting phase of the AGN itself. Methods. Multifrequency single-dish observations were performed with the 100-m Effelsberg telescope to define the initial sample, to characterise the spectral energy distribution (SED) of the final sample (30 targets), and to determine their RM in the 11 to 2 cm wavelength range. Results. From the observations, the SED and the polarisation information, i.e. the fractional polarisation and the polarisation angle, have been determined. Three different object types were revealed from the SED analysis: older, GPS-like, and mixed. For each of the targets, the rotation measure was found and the depolarisation modelled. No significant correlation is found between the depolarisation behaviours and the SEDs, while a correlation is found between sources with mixed SED (with an old component at low frequency and compact components at high frequencies) and high values of the rotation measure (with values in the rest frame greater than 1000 rad/m2). Conclusions. This work helps us to define and identify a sample of sources with high RM. From the analysis we can conclude that the sources showing a restarting phase at high frequency (with a mixed SED) are characterised by a really dense and/or a magnetised medium that strongly rotates the polarisation angle at the different frequencies, leading to a high RM. © 2016 ESO.

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