Scientific Results in Press

M82's stellar bar

A. Greve (¹), K.A. Wills (²), N. Neininger (³), A. Pedlar (⁴),(⁵)
(¹)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d`Hères, France, (²)Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S37RH, UK, (³)Astronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany, (⁴)University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK119DL, UK (⁵)Onsala Space Observatory, S-43992 Onsala, Sweden

Abstract:
The fueling of the starburst in M82 may be related to a stellar bar which pushes gas towards the center where it forms stars. The observation by McKeith et al. (1993) of the near-IR CaII photospheric absorption line allows a direct velocity measurement of the stars in M82, and provides by this a confirmation of the predicted x₁ and x₂-orbits of the bar in M82. From this and other observations we find that the mass of the x₂-orbit stars is $\sim$15$\%$ of the mass of the bar, and that the mass of the bar of $2\times 10^{9} \,\mbox{M$_\odot$ }$ is 20-40% of M82's mass. This mass concentration of $\sim \,1\,$kpc extent at the center of M82 underlines the dynamic importance of the bar.

A&A, in print

Radio-millimetre investigation of galactic infrared dark clouds

D. Teyssier (¹), P. Hennebelle (¹) - M. Pérault (¹)
(¹)Laboratoire de radioastronomie millimétrique, URA 336 du CNRS, École normale supérieure and Observatoire de Paris, 24 rue Lhomond, 75231 Paris cedex 05, France

Abstract:
We present follow-up observations of the mid-Infrared dark clouds selected from the ISOGAL inner Galaxy sample. On-the-fly maps of ¹³CO, C¹⁸O and the 1.2 mm continuum emission were conducted at the IRAM 30-m telescope, showing spectacular correlation with the mid-IR absorption. The dark clouds are distributed as far as the prominent molecular ring at a distance of 3 to 7 kpc from the Sun. The clouds exhibit shapes ranging from globules to thin filaments down to $\leq$1 pc in size. The on-the-fly images obtained in ¹³CO and C¹⁸O confirmed that the cores are dense, compact molecular emitters, significantly more massive than local dark clouds (more than 1000 $\rm M_\odot$) and lie within low activity Giant Molecular Clouds (GMC's). Ratios of the emission in the J=(2-1) and (1-0) transitions of ¹³CO and C¹⁸O show a remarkable uniformity within each cloud, with a significant portion of the sample represented well by a ratio of 0.67$\pm0.12$. Preliminary analysis of temperature and density measurements reveals that most of the cores have densities above 10⁵cm^-3 and temperatures between 8 and 25 K, these latter clouds being associated with young embedded stars. Despite the high extinction inferred from mid-IR ( $A_{\rm v} > 50$), the molecular lines are surprisingly weak, indicating likely depletion onto cold grains.

Accepted for publication in A&A

SO and SiO emission around the young cluster in the CB34 globule

C. Codella (¹), F. Scappini (²), R. Bachiller (³) and M. Benedettini(¹)
(¹)Istituto di Fisica dello Spazio Interplanetario, CNR, Area di Ricerca Tor Vergata, Via Fosso del Cavaliere 100, 00133 Roma, Italy (²)Istituto di Spettroscopia Molecolare, CNR, Via P. Gobetti 101, 40129 Bologna, Italy (³)Observatorio Astronómico Nacional (IGN), Apartado 1143, E-28800, Alcalá de Henares (Madrid), Spain

Abstract:
The globule CB34, which harbors a cluster of Class 0 YSOs protostars, has been investigated through a multiline SO and SiO survey at mm-wavelengths. The SO data reveal that the globule consists of three quiescent high-density ($\sim$ 10⁵ cm^-3) clumps, labeled A, B, and C, with sizes of $\sim$ 0.2-0.3 pc. The SiO data provide evidence for high-velocity gas across the globule. Most likely, the high-velocity gas is distributed in three distinct high-velocity outflows associated with the YSOs in each of the three clumps. High-velocity SO features have been detected only towards the two brightest SiO outflows. These broad SO components exhibit spatial and spectral distributions which are consistent with those of the SiO emission, so they can also be used as tracers of the outflows.

The comparison between the spatial and spectral properties of the SO and SiO emissions in the three clumps suggests different evolutionary stages for the relative embedded YSOs. In particular, the YSO associated with clump C exhibits some peculiarities, namely: smaller SiO linewidths, lower SiO column densities, lack of extended SiO structure and of SO wings, and presence of a SO spatial distribution which is displaced with respect to the location of the YSO. This behaviour is well explained if the SiO and SO molecules which were produced at high-velocities in the shocked region have been destroyed or slowed down because of the interaction with the ambient medium and the chemistry is dominated again by low-temperature reactions. Thus, our observations strongly suggest that the YSO in clump C is in a more evolved phase than the other members of the cluster.

Accepted for publication in MNRAS.
E-mail contact: codella@ifsi.rm.cnr.it

(Sub)millimetre emission from NGC 1569: an abundance of very small grains

U. Lisenfeld (¹), F.P. Israel (²), J.M. Stil (^2,3) and A. Sievers (¹)
(¹)IRAM, Avendida Divina Pastora 7, N.C., 18012 Granada, Spain, (²)Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands, (³)Physics Department, Queen's University, Kingston ON K7L 4P1, Canada

Abstract:
We present new data of the dwarf galaxy NGC 1569 at 450 $\mu$m, 850 $\mu$m and 1200$\mu$m taken with SCUBA at the JCMT and the bolometer array at the IRAM 30m telescope. After including data from IRAS at 12, 25, 60 and 100 $\mu$m, we have successfully fitted the dust grain population model of Désert et al. (1990) to the observed midinfrared-to-millimeter spectrum. The fit requires a combination of both large and very small grains exposed to a strong radiation field as well as an enhancement of the number of very small grains relative to the number of large grains. We interpret this as the consequence of large grain destruction due to shocks in the turbulent interstellar medium of NGC 1569. The contribution of polyaromatic hydrocarbons (PAH's) is found to be negligible. Comparison of the dust emission maps with an HI map of similar resolution shows that both dust and molecular gas distributions peak close to the radio continuum maximum and at a minimum in the HI distribution. From a comparison of these three maps and assuming that the gas-to-dust mass ratio is the same everywhere, we estimate the ratio of molecular hydrogen column density to integrated CO intensity to be about 25 - 30 times the local Galactic value. The gas-to-dust ratio is 1500 - 2900, about an order of magnitude higher than in the Solar Neighbourhood.

Accepted for publication in A&A

A CO Survey of Gravitationally Lensed Quasars with the IRAM Interferometer

R. Barvainis(¹), D. Alloin(²) and M. Bremer(³)
(¹)National Science Foundation, 4201 Wilson Boulevard, Arlington VA 22230, USA, (²)European Southern Observatory, Casilla 19001, Santiago 19, Chile, (³)IRAM, 300 Rue de la Piscine, 38406 St Martin d'Hères, France

Abstract:
We present the results of a CO survey of gravitationally lensed quasars, conducted with the Plateau de Bure Interferometer over the last three years. Among the 18 objects surveyed, one was detected in CO line emission, while six were detected in the continuum at 3mm and three in the continuum at 1mm. The low CO detection rate may at least in part be due to uncertainties in the redshifts derived from quasar broad emission lines. The detected CO source, the z=3.2 radio quiet quasar MG0751+2716, is quite strong in the CO(4-3) line and in the millimeter/submillimeter continuum, the latter being emission from cool dust. The integrated CO line flux is $5.96\pm 0.45$ Jy$\cdot$kms^-1, and the total molecular gas mass is estimated to be in the range $M_{\rm H_2} = 1.6-3.1\times 10^9 \mbox{M$_\odot$ }$.

Accepted for publication in A&A

A Multiwavelength Study of the S106 Region
I. Structure and dynamics of the molecular gas

N. Schneider  (^1,2,3), R. Simon (^1,4), C. Kramer (^1,2), J. Stutzki (¹)and S. Bontemps (³)
(¹) I.Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany , (²) IRAM, BP 53, 38406 Saint Martin d'Hères, France, (³) Observatoire de Bordeaux, BP 89, 33270 Floirac, France, (⁴) Institute for Astrophysical Research, Boston University, MA 02215, USA

Abstract:
The molecular cloud associated with Sharpless 106 has been studied in a variety of (sub)millimeter CO rotational lines on angular resolution scales from 11'' to 80''. We used the KOSMA 3m telescope to obtain an extended ¹²CO J=3$\to$2 map, from which we calculate a total mass of 2000 M$_\odot$ and an average density of $1.4\times10^3$ cm^-3 for the molecular cloud. The peak intensity region around the massive young star S106 IR was observed in ¹³CO J=6$\to$5 and 3$\to$2 with KOSMA and in isotopomeric low-J CO lines with the IRAM 30m telescope. A clump decomposition made for several lines yields a common clump-mass spectral index of $\alpha$=1.7, illustrating the self-similarity of the detected structures for length-scales from 0.06 to 0.9 parsec.
All ¹²CO and ¹³CO line profiles within approximately 2'around S106 IR show blue wing emission and less prominent red wing emission, partly affected by self-absorption in colder foreground material. We attribute this high-velocity emission to the ionized wind of S106 IR driving a shock into the inhomogeneous molecular cloud. We do not find evidence for a smooth or fragmented disk around S106 IR and/or an expanding ring in the observed CO emission distribution.
The excitation conditions along a cut through the molecular cloud/HII region are studied with an LTE analysis (and an Escape Probability model at the position of S106 IR), using the observed CO line intensities and ratios. The kinetic gas temperature is typically 40 K, the average density of the cloud in the core region is $9\times10^3$ cm^-3, and the local density within the clumps is $9\times10^4$ cm^-3. The ¹³CO/C¹⁸O line and column density ratios away from S106 IR reflect the natural isotopic abundance but towards the optical lobes and the cavity walls, we see enhanced ¹³CO emission and abundance with respect to C¹⁸O. This shows that selective photo-dissociation is only important close to S106 IR and in a thin layer of the cavity walls. In combination with the results from the excitation analysis we conclude that the molecular line emission arises from two different gas phases: (i) rather homogeneous, low- to medium-density, spatially extended clumps and (ii) embedded, small ($\ll$0.2 pc), high-density clumps with a low volume filling factor.

Accepted by A&A. Preprints are available available at:
http://www.observ.u-bordeaux.fr/public/aeronomie/pages_web_aero/web_schneider/publications.html

Mass, linear momentum and kinetic energy of bipolar flows in protoplanetary nebulae.

V. Bujarrabal (¹), A. Castro-Carrizo (¹), J. Alcolea (¹)and C. Sánchez Contreras (^1,2)
(¹)Observatorio Astronómico Nacional, Apartado 1143, E-28800 Alcalá de Henares, Spain, (²)Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena CA 91109, USA

Abstract:
We have studied the CO emission from protoplanetary nebulae (PPNe). Our sample is composed of 37 objects and includes, we think, all well identified PPNe detected in CO, together with the two yellow hypergiants emitting in CO and one young PN. We present a summary of the existing CO data, including accurate new observations of the ¹²CO and ¹³CO J=1-0 and J=2-1 lines in 16 objects. We identify in the nebulae a slowly expanding shell (represented in the spectra by a central core) and a fast outflow (corresponding to the line wings), that in the well studied PPNe is known to be bipolar. Excluding poor data, we end up with a sample of 32 sources (including the 16 observed by us); fast flows are detected in 28 of these nebulae, being absent in only 4. We present a method to estimate from these data the mass, `scalar' momentum and kinetic energy of the different components of the molecular outflows. We argue that the uncertainties of our method can hardly lead to significant overestimates of these parameters, although underestimates may be present in not well studied objects. The total nebular mass is often as high as $\sim$1 $M_{\odot}$

SiO Chimneys and Supershells in M82

García-Burillo,S. (¹), Martín-Pintado,J. (¹), Fuente,A. (¹) and Neri,R. (²)
(¹)OAN, Apartado 1143, Alcalá de Henares, E-28800 Madrid, Spain, (²)IRAM, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France

Abstract:
In this Letter we present the first images of the emission of SiO and H¹³CO+ in the nucleus of the starburst galaxy M82. Contrary to other molecular species that mainly trace the distribution of the star-forming molecular gas within the disk, the SiO emission extends noticeably out of the galaxy plane. The bulk of the SiO emission is restricted to two major features. The first feature, referred to as the SiO supershell, is an open shell of 150pc diameter, located 120pc west from the galaxy center. The SiO supershell represents the inner front of a molecular shell expanding at $\sim 40$km s^-1, produced by mass ejection around a supercluster of young stars containing supernova remnant SNR41.95+57.5. The second feature is a vertical filament, referred to as the SiO chimney, emanating from the disk at 200pc east from the galaxy center. The SiO chimney reaches a 500pc vertical height, and it is associated with the most prominent chimney identified in radio continuum maps. The kinematics, morphology, and fractional abundances of the SiO gas features in M82 can be explained in the framework of shocked chemistry driven by local episodes of gas ejection from the starburst disk. The SiO emission stands out as a privileged tracer of the disk-halo interface in M82. We speculate that the chimney and the supershell, each injecting $\sim 10^7\,M_\odot$ of molecular gas, are two different evolutionary stages in the outflow phenomenon building up the gaseous halo.

Appeared in ApJ 563, 27