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Vastel C.,Toulouse 1 University Capitole | Vastel C.,Roche Holding AG | Ceccarelli C.,University Grenoble alpes | Ceccarelli C.,French National Center for Scientific Research | And 3 more authors.
Astrophysical Journal Letters | Year: 2014

Complex organic molecules (COMs) have been detected in a variety of environments including cold prestellar cores. Given the low temperatures of these objects, these detections challenge existing models. We report here new observations toward the prestellar core L1544. They are based on an unbiased spectral survey of the 3 mm band at the IRAM 30 m telescope as part of the Large Program ASAI. The observations allow us to provide a full census of the oxygen-bearing COMs in this source. We detected tricarbon monoxide, methanol, acetaldehyde, formic acid, ketene, and propyne with abundances varying from 5 × 10-11 to 6 × 10-9. The non-LTE analysis of the methanol lines shows that they are likely emitted at the border of the core at a radius of ∼8000 AU, where T ∼ 10 K and nH2 ∼ 2 × 104 cm-3. Previous works have shown that water vapor is enhanced in the same region because of the photodesorption of water ices. We propose that a non-thermal desorption mechanism is also responsible for the observed emission of methanol and COMs from the same layer. The desorbed oxygen and a small amount of desorbed methanol and ethene are enough to reproduce the abundances of tricarbon monoxide, methanol, acetaldehyde, and ketene measured in L1544. These new findings open the possibility that COMs in prestellar cores originate in a similar outer layer rather than in the dense inner cores, as previously assumed, and that their formation is driven by the non-thermally desorbed species. © 2014. The American Astronomical Society. All rights reserved.

Aalto S.,Chalmers University of Technology | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN | Muller S.,Chalmers University of Technology | Winters J.M.,Institut Universitaire de France | And 5 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. Our goal is to study gas properties in large-scale molecular outflows and winds from active galactic nuclei (AGNs) and starburst galaxies. Methods. We obtained high-resolution (1′′.55 × 1′′.28) observations of HCN, HCO+, HNC 1-0 and HC3N 10-9 of the ultraluminous galaxy (ULIRG) Mrk 231 with the IRAM Plateau de Bure Interferometer. Results. We detect luminous emission from HCN, HCO+ and HNC 1-0 in the QSO ULIRG Mrk 231. All three lines show broad line wings-which are particularly prominent for HCN. Velocities are found to be similar (≈± 750 km s-1) to those found for CO 1-0. This is the first time bright HCN, HCO+ and HNC emission has been detected in a large-scale galactic outflow. We find that both the blue-and red-shifted line wings are spatially extended by at least 0′′.75 (>700 pc) in a north-south direction. The line wings are brighter (relative to the line center intensity) in HCN than in CO 1-0 and line ratios suggest that the molecular outflow consists of dense (n > 104 cm-3) and clumpy gas with a high HCN abundance X(HCN) > 10-8. These properties are consistent with the molecular gas being compressed and fragmented by shocks in the outflow. Alternatively, HCN is instead pumped by mid-IR continuum, but we propose that this effect is not strong for the spatially extended outflowing gas. In addition, we find that the rotation of the main disk, in east-west direction, is also evident in the HCN, HCO+ and HNC line emission. An unexpectedly bright HC3N 10-9 line is detected inside the central 400 pc of Mrk 231. This HC3N emission may emerge from a shielded, dust-enshrouded region within the inner 40-50 pc where the gas is heated to high temperatures (200-300 K) by the AGN. © 2012 ESO.

Colombo D.,Max Planck Institute for Astronomy | Hughes A.,Max Planck Institute for Astronomy | Schinnerer E.,Max Planck Institute for Astronomy | Meidt S.E.,Max Planck Institute for Astronomy | And 9 more authors.
Astrophysical Journal | Year: 2014

Using data from the PdBI Arcsecond Whirlpool Survey (PAWS), we have generated the largest extragalactic giant molecular cloud (GMC) catalog to date, containing 1507 individual objects. GMCs in the inner M51 disk account for only 54% of the total 12CO(1-0) luminosity of the survey, but on average they exhibit physical properties similar to Galactic GMCs. We do not find a strong correlation between the GMC size and velocity dispersion, and a simple virial analysis suggests that ∼30% of GMCs in M51 are unbound. We have analyzed the GMC properties within seven dynamically motivated galactic environments, finding that GMCs in the spiral arms and in the central region are brighter and have higher velocity dispersions than inter-arm clouds. Globally, the GMC mass distribution does not follow a simple power-law shape. Instead, we find that the shape of the mass distribution varies with galactic environment: the distribution is steeper in inter-arm region than in the spiral arms, and exhibits a sharp truncation at high masses for the nuclear bar region. We propose that the observed environmental variations in the GMC properties and mass distributions are a consequence of the combined action of large-scale dynamical processes and feedback from high-mass star formation. We describe some challenges of using existing GMC identification techniques for decomposing the 12CO(1-0) emission in molecule-rich environments, such as M51's inner disk. © 2014. The American Astronomical Society. All rights reserved.

Pety J.,Institute Of Radioastronomie Millimetrique | Pety J.,Paris Observatory | Schinnerer E.,Max Planck Institute for Astronomy | Leroy A.K.,U.S. National Radio Astronomy Observatory | And 9 more authors.
Astrophysical Journal | Year: 2013

We present the data of the Plateau de Bure Arcsecond Whirlpool Survey, a high spatial and spectral resolution 12CO (1-0) line survey of the inner ∼10 × 6 kpc of the M51 system, and the first wide-field imaging of molecular gas in a star-forming spiral galaxy with resolution matched to the typical size of giant molecular clouds (40 pc). We describe the observation, reduction, and combination of the Plateau de Bure Interferometer (PdBI) and IRAM-30 m "short spacing" data. The final data cube attains 1.″1 resolution over the ∼270″ × 170″ field of view, with sensitivity to all spatial scales from the combination of PdBI and IRAM-30 m data, and a brightness sensitivity of 0.4 K (1σ) in each 5 km s -1-wide channel map. We find a CO luminosity of 9 × 10 8 K km s-1 pc2, corresponding to a molecular gas mass of 4 × 109 M for a standard CO-to-H2 conversion factor. Unexpectedly, we find that a large fraction of this emission, (50 ± 10)%, arises mostly from spatial scales larger than 36″ ≃ 1.3 kpc. Through a series of tests, we demonstrate that this extended emission does not result from a processing artifact. We discuss its origin in light of the stellar component, the 12CO/13CO ratio, and the difference between the kinematics and structure of the PdBI-only and hybrid synthesis (PdBI + IRAM-30 m) images. The extended emission is consistent with a thick, diffuse disk of molecular gas with a typical scale height of ∼200 pc, substructured in unresolved filaments that fill ∼0.1% of the volume. © 2013. The American Astronomical Society. All rights reserved..

Van Kempen T.A.,Joint ALMA Offices | Van Kempen T.A.,Leiden University | Van Kempen T.A.,Harvard - Smithsonian Center for Astrophysics | Longmore S.N.,Harvard - Smithsonian Center for Astrophysics | And 5 more authors.
Astrophysical Journal | Year: 2012

Intermediate-mass (IM) protostars, the bridge between the very common solar-like protostars and the more massive, but rarer, O and B stars, can only be studied at high physical spatial resolutions in a handful of clouds. In this paper, we present and analyze the continuum results from an observing campaign at the Submillimeter Array (SMA) targeting two well-studied IM protostars in Orion, NGC2071 and L1641 S3 MMS 1. The extended SMA (eSMA) probes structure at angular resolutions up to 02, revealing protostellar disks on scales of 200AU. Continuum flux measurements on these scales indicate that a significant amount of mass, a few tens of M ⊙, is present. Envelope, stellar, and disk masses are derived using compact, extended, and eSMA configurations and compared against spectral energy distribution fitting models. We hypothesize that fragmentation into three components occurred within NGC2071 at an early time, when the envelopes were less than 10% of their current masses, e.g., <0.5 M ⊙. No fragmentation occurred for L1641 S3 MMS 1. For NGC2071, evidence is given that the bulk of the envelope material currently around each source was accreted after the initial fragmentation. In addition, about 30% of the total core mass is not yet associated to one of the three sources. A global accretion model is favored and a potential accretion history of NGC2071 is presented. It is shown that the relatively low level of fragmentation in NGC2071 was stifled compared to the expected fragmentation from a Jeans argument. Similarly, the lack of fragmentation in L1641 S3 MMS 1 is likely due to similar arguments. © 2012. The American Astronomical Society. All rights reserved..

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