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Saint-Martin-d'Hères, France

Agudo I.,Institute Astrofisica Of Andalucia | Agudo I.,Boston University | Thum C.,Institute Of Radio Astronomie Millimetrique | Wiesemeyer H.,Max Planck Institute for Radio Astronomy | And 5 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Several millimeter and submillimeter facilities with linear polarization observing capabilities have started operating during the last years. These facilities, as well as other previous millimeter telescopes and interferometers, require bright and stable linear polarization calibrators to calibrate new instruments and to monitor their instrumental polarization. The current limited number of adequate calibrators implies difficulties in the acquisition of these calibration observations. Aims. Looking for additional linear polarization calibrators in the millimeter spectral range, we started monitoring 3C 286 in mid-2006. This source is a standard and highly stable polarization calibrator for radio observations. Methods. Here we present the 3 mm and 1 mm monitoring observations obtained between September 2006 and January 2012 with the XPOL polarimeter on the IRAM 30 m Millimeter Telescope. Results. Our observations show that 3C 286 is a bright source of constant total flux with 3 mm flux density S 3 mm = (0.91 ± 0.02) Jy. The 3 mm linear polarization degree (p 3 mm = [13.5 ± 0.3] %) and polarization angle (χ 3 mm = [37.3 ± 0.8] °, expressed in the equatorial coordinate system) were also constant during the time span of our observations. Although with poorer time sampling and signal-to-noise ratio, our 1 mm observations of 3C 286 are also reproduced by a constant source of 1 mm flux density (S 1 mm = [0.30 ± 0.03] Jy), polarization fraction (p 1 mm = [14.4 ± 1.8] %), and polarization angle (χ 1 mm = [33.1 ± 5.7]°). Conclusions. This, together with the previously known compact structure of 3C 286-extended by ∼3.5′′ in the sky-allow us to propose 3C 286 as a new calibrator for both single-dish and interferometric polarization observations at 3 mm, and possibly at shorter wavelengths. © 2012 ESO.

Dasyra K.M.,Paris Observatory | Combes F.,Paris Observatory | Novak G.S.,Paris Observatory | Bremer M.,Institute Of Radio Astronomie Millimetrique | And 4 more authors.
Astronomy and Astrophysics | Year: 2014

We present a comparison of the molecular gas properties in the outflow vs. in the ambient medium of the local prototype radio-loud and ultraluminous- infrared galaxy 4C12.50 (IRAS 13451+1232), using new data from the IRAM Plateau de Bure Interferometer and 30m telescope and from the Herschel space telescope. Previous H2 (0-0) S(1) and S(2) observations with the Spitzer space telescope had indicated that the warm (~400 K) molecular gas in 4C12.50 is made up of a 1.4(± 0.2) × 108M⊙ ambient reservoir and a 5.2(±1.7) × 107M⊙ outflow. The new CO(1-0) data cube indicates that the corresponding cold (25 K) H2 gas mass is 1.0(±0.1) × 1010M ⊙ for the ambient medium and < 1.3 × 108 M⊙ for the outflow, when using a CO-intensity-to-H 2-mass conversion factor α of 0.8 M⊙/(K kms-1 pc2). The combined mass outflow rate is high, 230-800 M⊙/yr, but the amount of gas that could escape the galaxy is low. A potential inflow of gas from a 3.3(±0.3) × 10 8M⊙ tidal tail could moderate any mass loss. The mass ratio of warm-to-cold molecular gas is ≳30 times higher in the outflow than in the ambient medium, indicating that a non-negligible fraction of the accelerated gas is heated to temperatures at which star formation is inefficient. This conclusion is robust against the use of different α factor values and/or different warm gas tracers (H2 vs. H2 plus CO). With the CO-probed gas mass at least 40 times lower at 400 K than at 25 K, the total warm-to-cold mass ratio is always lower in the ambient gas than in the entrained gas. Heating of the molecular gas could facilitate the detection of new outflows in distant galaxies by enhancing their emission in intermediate rotational number CO lines. © 2014 ESO.

Benedettini M.,National institute for astrophysics | Viti S.,University College London | Codella C.,National institute for astrophysics | Gueth F.,Institute Of Radio Astronomie Millimetrique | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present high spatial resolution (750 au at 250 pc) maps of the B1 shock in the blue lobe of the L1157 outflow in four lines: CS (3-2), CH3OH (3K-2K), HC3N (16-15) and p-H2CO (202-301). The combined analysis of the morphology and spectral profiles has shown that the highest velocity gas is confined in a few compact (≈5 arcsec) bullets, while the lowest velocity gas traces the wall of the gas cavity excavated by the shock expansion. A large velocity gradient model applied to the CS (3-2) and (2-1) lines provides an upper limit of 106 cm-3 to the averaged gas density in B1 and a range of 5 × 103 = nH2 = 5 × 105 cm-3 for the density of the high-velocity bullets. The origin of the bullets is still uncertain: they could be the result of local instabilities produced by the interaction of the jet with the ambient medium or could be clumps already present in the ambient medium that are excited and accelerated by the expanding outflows. The column densities of the observed species can be reproduced qualitatively by the presence in B1 of a C-type shock and only models where the gas reaches temperatures of at least 4000K can reproduce the observed HC3N column density. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Jimenez-Serra I.,Harvard - Smithsonian Center for Astrophysics | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | Baez-Rubio A.,CSIC - National Institute of Aerospace Technology | Patel N.,Harvard - Smithsonian Center for Astrophysics | Thum C.,Institute Of Radio Astronomie Millimetrique
Astrophysical Journal Letters | Year: 2011

We present the first detection of the H40α, H34α, and H31α radio recombination lines (RRLs) at millimeter wavelengths toward the high-velocity ionized jet in the Cepheus A HW2 star-forming region. From our single-dish and interferometric observations, we find that the measured RRLs show extremely broad asymmetric line profiles with zero-intensity line widths of ∼1100 kms-1. From the line widths, we estimate a terminal velocity for the ionized gas in the jet of ≥500 km s-1, consistent with that obtained from the proper motions of the HW2 radio jet. The total integrated line-to-continuum flux ratios of the H40α, H34α, and H31α lines are 43, 229, and 280 km s-1, clearly deviating from LTE predictions. These ratios are very similar to those observed for the RRL masers toward MWC349A, suggesting that the intensities of the RRLs toward HW2 are affected by maser emission. Our radiative transfer modeling of the RRLs shows that their asymmetric profiles could be explained by maser emission arising from a bi-conical radio jet with a semi-opening angle of 18°, electron density distribution varying as r-2.11, and turbulent and expanding wind velocities of 60 and 500 km s-1. © 2011. The American Astronomical Society. All rights reserved.

Agudo I.,Institute Astrofisica Of Andalucia Csic | Agudo I.,Boston University | Thum C.,Institute Of Radio Astronomie Millimetrique | Wiesemeyer H.,Institute Radio Astronomia Milimetrica | Krichbaum T.P.,Max Planck Institute for Radio Astronomy
Astrophysical Journal, Supplement Series | Year: 2010

We present the results from the first large (>100 sources) 3.5mm polarimetric survey of radio-loud active galactic nuclei (AGNs). This wavelength is favorable within the radio-millimeter range for measuring the intrinsic linearly polarized emission from AGNs, since in general it is only marginally affected by Faraday rotation of the electric vector position angle and depolarization. The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30m Telescope on different observing epochs from 2005 July (when most of the measurements were made) to 2009 October. Our sample consists of 145 flat-radio-spectrum AGNs with declination >-30°(J2000.0) and flux density ≳1Jy at ∼ 86GHz, as measured at the IRAM 30m Telescope from 1978 to 1994. This constraint on the radio spectrum causes our sample to be dominated by blazars, which allows us to conduct new statistical studies on this class of high-luminosity, relativistically beamed emitters. We detect linear and circular polarization (above minimum 3σ levels of ∼ 1.5% and ∼ 0.3%) for 76% and 6% of the sample, respectively. We find a clear excess in degree of linear polarization detected at 86GHz with regard to that at 15GHz by a factor of 2. Over our entire source sample, the luminosity of the jets is anticorrelated with the degree of linear polarization. Consistent with previous findings claiming larger Doppler factors for brighter γ-ray blazars, quasars listed in our sample, and in the Fermi Large Area Telescope Bright Source Catalog (LBAS), show larger luminosities than non-LBAS ones, but our data do not allow us to confirm the same for BL Lac objects. We do not find a clear relation between the linear polarization angle and the jet structural position angle for any source class in our sample. We interpret this as the consequence of a markedly non-axisymmetric character of the 3mm emitting region in the jets. We find that intrinsic circular polarization is the most likely mechanism for generation of the circular polarization detected in our observations. Our new data can be used to estimate the 3.5mm AGN contribution to measurements of the linear polarization of the cosmic microwave background, such as those performed by the Planck satellite. © 2010 The American Astronomical Society.

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