Observatorio Astronomico Nacional OAN

Las Rozas de Madrid, Spain

Observatorio Astronomico Nacional OAN

Las Rozas de Madrid, Spain

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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.


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..


Schinnerer E.,MPI for Astronomy | Meidt S.E.,MPI for Astronomy | Pety J.,Institute Of Radioastronomie Millimetrique | Pety J.,Paris Observatory | And 10 more authors.
Astrophysical Journal | Year: 2013

The Plateau de Bure Interferometer Arcsecond Whirlpool Survey has mapped the molecular gas in the central ∼9 kpc of M51 in its 12CO(1-0) line emission at a cloud-scale resolution of ∼40 pc using both IRAM telescopes. We utilize this data set to quantitatively characterize the relation of molecular gas (or CO emission) to other tracers of the interstellar medium, star formation, and stellar populations of varying ages. Using two-dimensional maps, a polar cross-correlation technique and pixel-by-pixel diagrams, we find: (1) that (as expected) the distribution of the molecular gas can be linked to different components of the gravitational potential; (2) evidence for a physical link between CO line emission and radio continuum that seems not to be caused by massive stars, but rather depends on the gas density; (3) a close spatial relation between polycyclic aromatic hydrocarbon (PAH) and molecular gas emission, but no predictive power of PAH emission for the molecular gas mass; (4) that the I-H color map is an excellent predictor of the distribution (and to a lesser degree, the brightness) of CO emission; and (5) that the impact of massive (UV-intense) young star-forming regions on the bulk of the molecular gas in central ∼9 kpc cannot be significant due to a complex spatial relation between molecular gas and star-forming regions that ranges from cospatial to spatially offset to absent. The last point, in particular, highlights the importance of galactic environment - and thus the underlying gravitational potential - for the distribution of molecular gas and star formation. © 2013. The American Astronomical Society. All rights reserved..


Meidt S.E.,Max Planck Institute for Astronomy | Schinnerer E.,Max Planck Institute for Astronomy | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN | Hughes A.,Max Planck Institute for Astronomy | And 9 more authors.
Astrophysical Journal | Year: 2013

We use the high spatial and spectral resolution of the PAWS CO(1-0) survey of the inner 9 kpc of the iconic spiral galaxy M51 to examine the effects of gas streaming motions on the star-forming properties of individual giant molecular clouds (GMCs). We compare our view of gas flows in M51 - which arise due to departures from axisymmetry in the gravitational potential (i.e., the nuclear bar and spiral arms) - with the global pattern of star formation as traced by Hα and 24 μm emission. We find that the dynamical environment of GMCs strongly affects their ability to form stars, in the sense that GMCs situated in regions with large streaming motions can be stabilized, while similarly massive GMCs in regions without streaming go on to efficiently form stars. We argue that this is the result of reduced surface pressure felt by clouds embedded in an ambient medium undergoing large streaming motions, which prevent collapse. Indeed, the variation in gas depletion time expected based on the observed streaming motions throughout the disk of M51 quantitatively agrees with the variation in the observed gas depletion time scale. The example of M51 shows that streaming motions, triggered by gravitational instabilities in the form of bars and spiral arms, can alter the star formation law; this can explain the variation in gas depletion time among galaxies with different masses and morphologies. In particular, we can explain the long gas depletion times in spiral galaxies compared with dwarf galaxies and starbursts. We suggest that adding a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies across cosmic time. © 2013. 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..


Cicone C.,University of Cambridge | Maiolino R.,University of Cambridge | Sturm E.,Max Planck Institute for Extraterrestrial Physics | Gracia-Carpio J.,Max Planck Institute for Extraterrestrial Physics | And 11 more authors.
Astronomy and Astrophysics | Year: 2014

We study the properties of massive, galactic-scale outflows of molecular gas and investigate their impact on galaxy evolution. We present new IRAM PdBI CO(1-0) observations of local ultra-luminous infrared galaxies (ULIRGs) and quasar-hosts: a clear signature of massive and energetic molecular outflows, extending on kpc scales, is found in the CO(1-0) kinematics of four out of seven sources, with measured outflow rates of several 100 M yr-1. We combine these new observations with data from the literature, and explore the nature and origin of massive molecular outflows within an extended sample of 19 local galaxies. We find that starburst-dominated galaxies have an outflow rate comparable to their star formation rate (SFR), or even higher by a factor of ~2-4, implying that starbursts can indeed be effective in removing cold gas from galaxies. Nevertheless, our results suggest that the presence of an active galactic nucleus (AGN) can boost the outflow rate by a large factor, which is found to increase with the LAGN/Lbol ratio. The gas depletion time scales due to molecular outflows are anti-correlated with the presence and luminosity of an AGN in these galaxies, and range from a few hundred million years in starburst galaxies down to just a few million years in galaxies hosting powerful AGNs. In quasar hosts, the depletion time scales due to the outflow are much shorter than the depletion time scales due to star formation. We estimate the outflow kinetic power and find that, for galaxies hosting powerful AGNs, it corresponds to about 5% of the AGN luminosity, as expected by models of AGN feedback. Moreover, we find that momentum rates of about 20 LAGN/c are common among the AGN-dominated sources in our sample. For "pure" starburst galaxies, our data tentatively support models in which outflows are mostly momentum-driven by the radiation pressure from young stars onto dusty clouds. Overall, our results indicate that, although starbursts are effective in powering massive molecular outflows, the presence of an AGN may strongly enhance such outflows, and therefore have a profound feedback effect on the evolution of galaxies by efficiently removing fuel for star formation, hence quenching star formation. © ESO, 2014.


Vastel C.,Toulouse 1 University Capitole | Vastel C.,Hoffmann-La Roche | 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.


Tacconi L.J.,Max Planck Institute for Extraterrestrial Physics | Genzel R.,Max Planck Institute for Extraterrestrial Physics | Genzel R.,University of California at Berkeley | Neri R.,IRAM | And 19 more authors.
Nature | Year: 2010

Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts >z< of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in todayĝ€™s massive spiral galaxies. The slow decrease between ≈z 2 and ≈z 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies. © 2010 Macmillan Publishers Limited. 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.


Garcia-Burillo S.,Observatorio Astronomico Nacional OAN | Usero A.,Observatorio Astronomico Nacional OAN | Alonso-Herrero A.,CSIC - National Institute of Aerospace Technology | Alonso-Herrero A.,Institute Fisica Of Cantabria | And 6 more authors.
Astronomy and Astrophysics | Year: 2012

Context. The observational study of star-formation relations in galaxies is central for unraveling the related physical processes that are at work on local and global scales. It is still debated whether star formation can be described by a universal law that remains valid in different populations of galaxies. Aims. We aim to expand the sample of extreme starbursts, represented by local luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs), with high-quality observations in the 1-0 line of HCN, which is taken as a proxy for the dense molecular gas content. The new data presented in this work allow us to enlarge in particular the number of LIRGs studied in HCN by a factor 3 compared to previous works. The chosen LIRG sample has a range of HCN luminosities that partly overlaps with that of the normal galaxy population. We study if a universal law can account for the star-formation relations observed for the dense molecular gas in normal star-forming galaxies and extreme starbursts and explore the validity of different theoretical prescriptions of the star-formation law. Methods. We have used the IRAM 30 m telescope to observe a sample of 19 LIRGs in the 1-0 lines of CO, HCN and HCO+. The galaxies were extracted from a sample of local LIRGs with available high-quality and high-resolution images obtained at optical, near and mid IR wavelengths, which probe the star-formation activity. We therefore derived the star-formation rates using different tracers and determined the sizes of the star-forming regions of all targets. Results. The analysis of the new data proves that the efficiency of star formation in the dense molecular gas (SFEdense) of extreme starbursts is a factor 3-4 higher compared to normal galaxies. Kennicutt-Schmidt (KS) power laws were also derived. We find a duality in KS laws that is further reinforced if we account for the likely different conversion factor for HCN (αHCN) in extreme starbursts and for the unobscured star-formation rate in normal galaxies. This result extends the more extreme bimodal behavior of star-formation laws that was derived from CO molecular lines by two recent surveys to the higher molecular densities probed by HCN lines. Conclusions. We compared our observations with the predictions of theoretical models in which the efficiency of star formation is determined by the ratio of a constant star-formation rate per free-fall time (SFRff) to the local free-fall time (tff). We find that it is possible to fit the observed differences in the SFEdense between normal galaxies and LIRGs/ULIRGs using a common constant SFRff and a set of physically acceptable HCN densities, but only if SFRff ∼ 0.005-0.01 and/or if αHCN is a factor of ∼a few lower than our favored values. Star-formation recipes that explicitly depend on the galaxy global dynamical time scales do not significantly improve the fit to the new HCN data presented in this work. © 2012 ESO.

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