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Next: New Preprints Up: IRAM Newsletter 66 (June 2006) Previous: VLBI News


Scientific Results in Press

Radio wavelength molecular observations of comets C/1999 T1 (McNaught-Hartley), C/2001 A2 (LINEAR), C/2000 WM$_1$ (LINEAR) and 153P/Ikeya-Zhang

N. Biver$(^{1})$, D. Bockelée-Morvan$(^{1})$, J. Crovisier$(^{1})$, D.C. Lis$(^{2})$, R. Moreno$(^{1,3})$, P. Colom$(^{1})$, F. Henry$(^{1})$, F. Herpin$(^{4})$, G. Paubert$(^{5})$ and M. Womack$(^{6})$
$(^{1})$LESIA, CNRS UMR 8109, Observatoire de Paris, 5 pl. J. Janssen, F-92195 Meudon, $(^{2})$California Institute of Technology, MS 320-47, Pasadena, CA 91125, USA, $(^{3})$IRAM, 300, rue de la Piscine, F-38406 Saint Martin d'Hères, France, $(^{4})$Observatoire de Bordeaux, BP 89, F-33270 Floirac, France, $(^{5})$IRAM, Avd. Divina Pastora, 7, 18012 Granada, Spain, $(^{6})$St. Cloud State University, MS 324, St. Cloud, MN 56301-4498, USA

We present a comparative study of the relative abundances of CO, CH$_3$OH, H$_2$CO, HCN, HNC, CS, H$_2$S, CH$_3$CN, SO and HNCO in comets C/1999 T1 (McNaught-Hartley), C/2001 A2 (LINEAR), C/2000 WM$_1$(LINEAR) and 153P/Ikeya-Zhang, four of the brightest comets seen in 2001-2002. This investigation is based on millimetre/submillimetre observations made with the IRAM 30-m, SEST, CSO and Kitt Peak 12-m telescopes. Although these four comets are expected to originate from the Oort cloud, they present significant differences in molecular abundances, especially as regards to the most volatile species: CO and H$_2$S. In particular comet C/2000 WM$_1$ looks quite depleted in these volatiles, suggesting it may have a different origin that the others. Heliocentric variations of molecular relative abundance in the coma are also investigated. Significant increases in the CS/HCN and HNC/HCN production rate ratios with decreasing heliocentric distances are observed.

Appeared in: A&A 449, 1255

A Multi-Layered Thermal Model of Backup Structures for mm-Wavelength Radio Telescopes

A. Greve$(^{1})$, D.R. Smith$(^{2})$, M. Bremer$(^{1})$
$(^{1})$Institut de Radio Astronomie Millimétrique (IRAM), 300, rue de la Piscine, 38406 St. Martin d' Hères, France, $(^{2})$MERLAB, P.C., 357 S. Candler Street, Decatur, GA 30030-3746, USA

An unfavourable influence that degrades the performance of any millimeter wavelength radio telescope is the deformation of the reflector surface due to temperature differences in the supporting backup structure. To avoid, or at least reduce this in influence, the backup structures are typically protected by a rear side cladding, insulation at the panel inner side, and ventilation or climatization of the air inside the backup structure. During the design of a mm-wavelength telescope, the layout of a thermal protection system is made, based on experience gained on other telescopes, and on thermal model calculations of the complete backup structure. The available thermal programs allow today the construction of a multi-layered backup structure model, consisting of the backup structure tube network, without and with ventilation/climatization, the panels, insulation behind the panels, and the rear side cladding. We provide a guideline for the construction of such a multi-layered thermal model, and demonstrate that realistic temperature gradients across and through a backup structure can be calculated. These gradients can be used in a finite element model to calculate the reflector surface deformations, which can be used in a diffraction program to calculate the radio beam pattern.

Submitted to: SPIE conference proceedings ``Astronomical Telescopes and Instrumentation'', 24-31 May 2006, Orlando, Florida, USA

First evidence for molecular interfaces between outflows and ambient cloud in high-mass star forming regions?

C. Codella$(^{1})$, S. Viti$(^{2})$, D.A. Williams$(^{2})$ and R. Bachiller$(^{3})$
$(^{1})$INAF - Istituto di Radioastronomia, Sezione di Firenze, Largo E. Fermi 5, 50137 Firenze, Italy, $(^{2})$Department of Physics and Astronomy, University College London, Gower Street, London, WC1E6BT, $(^{3})$Observatorio Astronómico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain

We present new observations of the CepA-East region of massive star formation and describe an extended and dynamically distinct feature not previously recognised. This feature is present in emission from H$_2$CS, OCS, CH$_3$OH, and HDO at -5.5 km s$^{-1}$, but is not traced by conventional tracers of star forming regions H$_2$S, SO$_2$, SO, CS. The feature is extended up to at least 0.1 pc. We show that the feature is neither a hot core nor a shocked outflow. However, the chemistry of the feature is consistent with predictions of a model of an eroding interface between a fast wind and a dense core; mixing between the two media occurs in the interface on a timescale of 10-50 years. If these observations are confirmed by detailed maps and by detections in species also predicted to be abundant (e.g. HCO$^+$, H$_2$CO, and NH$_3$) this feature would be the first detection of such an interface in regions of massive star formation. An important implication of the model is that a significant reservoir of sulfur in grain mantles is required to be in the form of OCS.

ApJ Letters, in press

High-Resolution Millimeter Imaging of Submillimeter Galaxies

Tacconi L.J.$(^{1})$, Neri R.$(^{2})$, Chapman S.C.$(^{3})$, Genzel R.$(^{1})$, Smail I.$(^{4})$, Ivison R.J.$(^{5})$, Bertoldi F.$(^{6})$, Blain A.$(^{3})$, Cox P.$(^{2,7})$, Greve T.$(^{3})$, Omont A.$(^{8})$
$(^{1})$Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany, $(^{2})$Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, Domaine Universitaire de Grenoble, F-38406 St. Martin d'Hères, France, $(^{3})$Department of Astronomy, California Institute of Technology, MS 105-24, 1201 East California Boulevard, Pasadena, CA 91125, $(^{4})$Institute for Computational Cosmology, University of Durham, South Road, Durham DH1 3LE, UK, $(^{5})$Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK, $(^{6})$Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany, $(^{7})$Institute d'Astrophysique Spatiale, Université de Paris XI, F-91405 Orsay, France, $(^{8})$Institute d'Astrophysique de Paris, Centre National de la Recherche Scientifique, 98 bis Boulevard Arago, F-75014 Paris, France

We present $\sim 0\farcs 6$ resolution IRAM PdBI interferometry of eight submillimeter galaxies at $z\sim 2 - 3.4$, where we detect continuum at 1 mm and/or CO lines at 3 and 1 mm. The CO 3-2/4-3 line profiles in five of the sources are double-peaked, indicative of orbital motion either in a single rotating disk or of a merger of two galaxies. The millimeter line and continuum emission is compact; we marginally resolve the sources or obtain tight upper limits to their intrinsic sizes in all cases. The median FWHM diameter for these sources and the previously resolved sources, SMM J023952-0136 and SMM J140104+0252, is $\leq 0\farcs 5$ (4 kpc). The compactness of the sources does not support a scenario in which the far-IR/submillimeter emission comes from a cold (T$<30$ K), very extended dust distribution. These measurements clearly show that the submillimeter galaxies (SMGs) we have observed resemble scaled-up and more gas-rich versions of the local universe, ultraluminous galaxy population. Their central densities and potential well depths are much greater than those in other $z \sim 2 - 3$ galaxy samples studied so far. They are comparable to those of elliptical galaxies or massive bulges. The SMG properties fulfill the criteria of ``maximal'' starbursts, in which most of the available initial gas reservoir of $10^{10}-10^{11}\mbox{M$_\odot$}$ is converted to stars on a timescale $\sim
3^{-10} t_{dyn}$ $\sim$ a few times $10^8$ yr. Based on observations obtained at the IRAM Plateau de Bure Interferometer (PdBI). IRAM is funded by the Centre National de la Recherche Scientifique (France), the Max-Planck Gesellschaft (Germany), and the Instituto Geografico Nacional (Spain).

Appeared in: ApJ 640, 228

Large-scale molecular shocks in galaxies: the SiO interferometer map of IC 342

Usero A.$(^{1})$, García-Burillo S.$(^{1})$, Martín-Pintado J.$(^{2})$, Fuente A.$(^{1})$, Neri R.$(^{3})$
$(^{1})$Observatorio Astronómico Nacional (OAN) - Observatorio de Madrid, C/ Alfonso XII 3, 28014 Madrid, Spain, $(^{2})$Instituto de Estructura de la Materia, DAMIR-CSIC, C/ Serrano 121, 28006 Madrid, Spain, $(^{3})$IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 St. Martin d'Hères Cedex, France

We present the first high-resolution ( $5\farcs 6 \times 5\farcs 1$ ) images of the emission of silicon monoxide (SiO) in the nucleus of the nearby spiral IC 342, obtained with the IRAM Plateau de Bure Interferometer (PdBI). Using a two-field mosaic, we have simultaneously mapped the emission of the SiO(v=0, J=2-1) and H$^{13}$CO$^{+}$(J=1-0) lines in a region of 0.9 kpc $\times 1.3$ kpc (RA $\times$ Dec) centered around the nucleus of IC 342. The bulk of the emission in the two lines comes from a $\sim 290$ pc spiral arm located to the North and a central component that forms the southern ridge of a $r \sim 80$ pc nuclear ring that was identified in other interferometer maps of the galaxy. We detect continuum emission at 86.8 GHz in a $\sim 80-180$ pc central source. The continuum emission, dominated by thermal free-free bremsstrahlung, is mostly anticorrelated with the observed distribution of SiO clouds. The SiO-to-H$^{13}$CO$^+$ intensity ratio is seen to increase by an order of magnitude from the nuclear ring ( 0.3) to the spiral arm ( 3.3). Furthermore the gas kinematics show significant differences between SiO and H$^{13}$CO$^{+}$ over the spiral arm, where the linewidths of SiO are a factor of 2 larger than those of H$^{13}$CO$^+$. The average abundance of SiO in the inner $r\sim 320$ pc of IC 342 is X(SiO) $ \ga 2 \times 10^{-10}$. This shows that shock chemistry is at work in the inner molecular gas reservoir of IC 342. To shed light on the nature of shocks in IC 342, we have compared the emission of SiO with another tracer of molecular shocks: the emission of methanol (CH3OH). We find that the significant difference of the abundance of SiO measured between the spiral arm (X(SiO) a few $10^{-9}$) and the nuclear ring (X(SiO)$10^{-10}$) is not echoed by a comparable variation in the SiO-to-CH3OH intensity ratio. This implies that the typical shock velocities should be similar in the two regions. In contrast, the fraction of shocked molecular gas should be 5-7 times larger in the spiral arm (up to 10% of the available molecular gas mass over the arm region) compared to the nuclear ring. In the light of these results, we revise the validity of the various scenarios that have been proposed to explain the onset of shock chemistry in galaxies and study their applicability to the nucleus of IC 342. We conclude that the large-scale shocks revealed by the SiO map of IC 342 are mostly unrelated to star formation and arise instead in a pre-starburst phase. Shocks are driven by cloud-cloud collisions along the potential well of the IC 342 bar. The general implications for the current understanding of galaxy evolution are discussed.

Appeared in: A&A 448, 457

Full polarization study of SiO masers at 86 GHz

Herpin F.$(^{1})$, Baudry A.$(^{1})$, Thum C.$(^{2})$, Morris D.$(^{2})$, Wiesemeyer H.$(^{2})$
$(^{1})$Observatoire Aquitain des Sciences de l'Univers, Laboratoire d'Astrodynamique, d'Astrophysique et d'Aéronomie de Bordeaux, CNRS/INSU UMR N$^{\circ}$ 5804, BP 89, 33270 Floirac, France, $(^{2})$IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Hères, France


Aims. We study the polarization of the SiO maser emission in a representative sample of evolved stars in order to derive an estimate of the strength of the magnetic field, and thus determine the influence of this magnetic field on evolved stars.
Methods. We made simultaneous spectroscopic measurements of the 4 Stokes parameters, from which we derived the circular and linear polarization levels. The observations were made with the IF polarimeter installed at the IRAM 30 m telescope.
Results. A discussion of the existing SiO maser models is developed in the light of our observations. Under the Zeeman splitting hypothesis, we derive an estimate of the strength of the magnetic field. The averaged magnetic field varies between 0 and 20 Gauss, with a mean value of 3.5 Gauss, and follows a 1/r law throughout the circumstellar envelope. As a consequence, the magnetic field may play the role of a shaping, or perhaps collimating, agent of the circumstellar envelopes in evolved objects.

Appeared in: A&A 450, 667

Comparative chemistry of diffuse clouds. V. Ammonia and formaldehyde

Liszt H. S.$(^{1})$, Lucas R.$(^{2})$, Pety, J.$(^{2,3})$
$(^{1})$NRAO, 520 Edgemont Road, Charlottesville, VA, 22903-2475, USA, $(^{2})$IRAM, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France, $(^{3})$Obs. de Paris, 61 Av. de l'Observatoire, 75014 Paris, France

Using the VLA and NRAO 140' telescopes we observed the $\lambda
1.3$ cm (1, 1) and (2, 2) lines of NH$_3$ in absorption and emission toward the compact extragalactic continuum sources NRAO150 (B0355+508) and 3C 111 (B0415+379). These sources are occulted by some seven local diffuse and translucent clouds showing molecular absorption in OH, CO, HCO$^+$ and C$_2$H: for the four features having NH$_3$ absorption, we find rotational excitation temperatures 18-24 K, suggesting kinetic temperatures of at least 25-30 K. The abundance ratio N(NH$_3$)/N(HCO$^+$) is comparable to values quoted for the cyanopolyyne peak in TMC-1 (i.e., 2.5) in three of four cases where NH$_3$ was seen. For clouds with higher column density $N(HCO^+) \la
10^{12}$ cm$^{-2}$, the NH$_3$ column density N(NH$_3$) is well correlated only with N(CS) (<N(NH$_3$)/N(CS)> $\approx 1.0$) and N(H$_2$CO) (<N(NH$_3$)/N(H$_2$CO)>$ \approx 0.4$). N(H$_2$CO) is well correlated with N(NH$_3$) and N(CS) (<N(H$_2$CO)/N(CS)> $ \approx 2.3$) and the H$_2$CO abundance relative to other species is like TMC-1, with (<N(H$_2$CO)/N(HCO$^+$)> $ \approx 2.3$).

Appeared in A&A 448, 253

Deuterated molecules in DM Tauri: DCO$^+$, but no HDO

Guilloteau$(^{1})$ S., Piétu V.$(^{1})$, Dutrey A.$(^{1})$, Guélin, M.$(^{2})$
$(^{1})$L3AB, Observatoire de Bordeaux, 2 rue de l'Observatoire, BP 89, 33270 Floirac, France, $(^{2})$IRAM, 300 rue de la piscine, 38406 Saint Martin d'Hères Cedex, France

We report the detection of the J=2-1 line of DCO$^+$ in the proto-planetary disk of DM Tau and re-analyze the spectrum covering the 465 GHz transition of HDO in this source, recently published by Ceccarelli et al. (2005, ApJ, 631, L81). A modelling of the DCO$^+$ line profile with the source parameters derived from high resolution HCO$^+$ observations yields a DCO$^+$/HCO$^+$ abundance ratio of $\simeq 4\times
10^{-3}$, an order of magnitude smaller than that derived in the low mass cores. The re-analysis of the 465 GHz spectrum, using the proper continuum flux (0.5 Jy) and source systemic velocity (6.05 km s$^{-1}$), makes it clear that the absorption features attributed to HDO and C$_6$H are almost certainly unrelated to these species. We show that the line-to-continuum ratio of an absorption line in front of a Keplerian disk can hardly exceed the ratio of the turbulent velocity to the projected rotation velocity at the disk edge, unless the line is optically very thick ($\tau > 10^4$). This ratio is typically 0.1-0.3 in proto-planetary disks and is $\simeq 0.15$ in DM Tau, much smaller than that for the alleged absorption features. We also show that the detection of H2D$^+$ in DM Tau, previously reported by these authors, is only a 2-sigma detection when the proper velocity is adopted. So far, DCO$^+$ is thus the only deuterated molecule clearly detected in proto-planetary disks.

Appeared in: A&A 448, 5

A 2mm spectral line survey of the starburst galaxy NGC253

S. Martín$(^{1})$, R. Mauersberger$(^{1})$, J. Martín-Pintado$(^{2})$, C. Henkel$(^{3})$, S. García-Burillo$(^{4})$
$(^{1})$Instituto de Radioastronomía Milimétrica, Avda. Divina Pastora 7, Local 20, 18012 Granada, $(^{2})$Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain, $(^{3})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{4})$Observatorio Astronómico Nacional, Apdo. 112, E-28803 Alcalá de Henares, Spain

We present the first unbiased molecular line survey towards an extragalactic source, namely the nuclear region of the starburst galaxy NGC253. The scan covers the frequency band from 129.1 to 175.2GHz, i.e. most of the 2mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers $^{34}$SO and HC$^{18}$O$^+$. Tentative detections of two deuterated species, DNC and N$_2$D$^+$, are reported for the first time from a target beyond the Magellanic Clouds. Additionally, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC342 and NGC4945 to that of NGC253. On the other hand, the chemistries characterizing NGC253 and M82 are clearly different. We also present a comparison of the chemical composition of NGC253 with those observed in Galactic prototypical sources. The chemistry of NGC253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC253 is dominated by the same mechanism as that in the central region of the Milky Way.

Accepted for publitation in ApJ.

Methanol detection in M82

S. Martín$(^{1})$, J. Martín-Pintado$(^{2})$, R. Mauersberger$(^{1})$
$(^{1})$Instituto de Radioastronomía Milimétrica, Avda. Divina Pastora 7, Local 20, 18012 Granada, $(^{2})$Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain

The nuclear starburst region in M82 shows systematical low abundances of some complex molecules when compared with other starburst galaxies. This is likely related to a presumably photodissociation dominated environment. In particular, methanol is known to show relatively low abundance because it is easily photodissociated. We present a multilevel study of the emission of methanol, detected for the first time in this galaxy, and discuss the origin of its emission. Observations of three transitions of CH$_3$OH towards the center and two positions around the nucleus of M82 are presented. Two different components are found, one with high excitation ( $n(\rm H_2)\sim 106 cm^{-3}$, $T_{\rm rot}\sim 20$K) and a the other with low excitation ( $n(\rm H_2)\sim 104 cm^{-3}$, $T_{\rm rot}\sim 5$K). The high observed methanol abundance of a few $10^{-9}$ can only be explained if injection of methanol from dust grains is taken into account. While the overall [CH$_3$OH]/[NH$_3$] ratio is much larger than observed towards other starbursts, the dense high excitation component shows a similar value to that found in NGC253 and Maffei2. Our observations suggest the molecular material in M82 to be formed by dense warm cores, shielded from the UV radiation and similar to the molecular clouds in other starbursts, surrounded by a less dense photodissociated halo. The dense warm cores are likely the location of recent and future star formation within M82.

Appeared in: A&A 450, L13

Is HCN a True Tracer of Dense Molecular Gas in Luminous and Ultraluminous Infrared Galaxies?

Graciá-Carpio J.$(^{1})$, García-Burillo S.$(^{1})$, Planesas P.$(^{1})$, Colina L.$(^{2})$
$(^{1})$Observatorio Astronomico Nacional, Alfonso XII 3, 28014 Madrid, Spain,$(^{2})$Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid, Spain

We present the results of the first HCO$^+$ survey probing the dense molecular gas content of a sample of 16 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs). Previous work, based on HCN(1-0) observations, had shown that LIRGs and ULIRGs possess a significantly higher fraction of dense molecular gas compared to normal galaxies. While the picture issued from HCO$^+$ partly confirms this result, we have discovered an intriguing correlation between the HCN(1-0)/HCO$^+$(1-0) luminosity ratio and the IR luminosity of the galaxy (L$_{IR}$). This trend casts doubts on the use of HCN as an unbiased quantitative tracer of the dense molecular gas content in LIRGs and ULIRGs. A plausible scenario explaining the observed trend implies that X-rays coming from an embedded active galactic nucleus may play a dominant role in the chemistry of molecular gas at $L_{IR}\ge 10^{12}
\mbox{L$_\odot$}$. We discuss the implications of this result for the understanding of LIRGs, ULIRGs, and high-redshift gas-rich galaxies.

Appeared in: ApJ 640, L135

A New Probe of Dense Gas at High Redshift: Detection of HCO+(5-4) Line Emission in APM 08279+5255

S. García-Burillo$(^{1})$, J. Graciá-Carpio$(^{1})$, M. Guélin$(^{2})$, R. Neri$(^{2})$, P. Cox$(^{2})$, P. Planesas$(^{1})$, P. M. Solomon$(^{3})$, L. J. Tacconi$(^{4})$, P. A. Vanden Bout$(^{5})$
$(^{1})$OAN, C/ Alfonso XII 3, 28014 Madrid, Spain, $(^{2})$IRAM, 300 rue de la Piscine, 38406 St Martin d'Hères, France, $(^{3})$Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY 11974, USA, $(^{4})$MPI für extraterrestrische Physik, Postfac 1312, 85741 Garching, Germany, $(^{5})$NRAO, 520 Edgemont Road, Charlottesville, VA 22903

We report the detection of HCO$^+$(5-4) emission from the Broad Absorption Line (BAL) quasar APM 08279+5255 at $z=3.911$ based on observations conducted at the IRAM Plateau de Bure interferometer. This represents the first detection of this molecular ion at such a high redshift. The inferred line luminosity, uncorrected for lensing, is $L'(HCO^+)=(3.5\pm0.6)\times 10^{10}$K km s$^{-1}$pc$^{^2}$. The HCO$^+$ J=5-4 source position coincides within the errors with that reported from previous HCN J=5-4 and high-J CO line observations of this quasar. The HCO$^+$ line profile central velocity and width are consistent with those derived from HCN. This result suggests that HCO$^+$(5-4) emission comes roughly from the same circumnuclear region probed by HCN. However, the HCN(5-4)/HCO$^+$(5-4) intensity ratio measured in APM 08279+5255 is significantly larger than that predicted by simple radiative transfer models, which assume collisional excitation and equal molecular abundances. This could imply that the [HCN]/[HCO$^+$] abundance ratio is particularly large in this source, or that the J=5 rotational levels are predominantly excited by IR fluorescent radiation.

Accepted for publication in ApJ Letters

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Next: New Preprints Up: IRAM Newsletter 66 (June 2006) Previous: VLBI News