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Scientific Results in Press

Coupling the dynamics and the molecular chemistry in the Galactic center

N.J. Rodriguez-Fernandez$(^{1,2})$, F. Combes $(^{3})$, J. Martin-Pintado$(^{4})$, T. L. Wilson$(^{5})$ and A. Apponi$(^{6})$
$(^{1})$Observatoire de Bordeaux, L3AB (UMR 5804)/OASU, CNRS/Université Bordeaux 1, BP 89, 2 rue de l'Observatoire, 33270 Floirac, France, $(^{2})$Université Denis Diderot (Paris VII) & Observatoire de Paris, 61 Av de l'Observatoire, 75014 Paris, France, $(^{3})$LERMA, Observatoire de Paris, 61 Av de l'Observatoire, 75014 Paris, France, $(^{4})$DAMIR, IEM, CSIC, Serrano 121, Madrid, Spain, $(^{5})$ESO, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany, $(^{6})$Steward Observatory, University of Arizona, Tucson, AZ 85721, USA

Most of the Galactic center (GC) gas moves in nearly circular orbits in a nuclear ring (hereafter the Galactic center ring, GCR). This is the case of cloud complexes such as Sgr A or Sgr B, where the gas is dense, warm and exhibits a rich molecular chemistry. The origin of these properties is thought to be shocks, in particular due to the large scale dynamics of the Galaxy. In addition, there are gas clouds moving in highly non-circular orbits known from observations of low density tracers such as CO(1-0). The physical conditions of the clouds moving with non-circular velocities are not well known.

We have studied the physical conditions of the gas in non-circular orbits to better understand the origin of the unusual physical conditions of the GC molecular gas and the possible effect of the large scale dynamics on these physical conditions.

Using published CO(1-0) data, we have selected a set of clouds belonging to all the kinematical components seen in the longitude-velocity diagram of the GC. We have carried out a survey of dense gas in all the components using the $J=2-1$ lines of CS and SiO as tracers of high density gas and shock chemistry.

We have detected CS and SiO emission in all the kinematical components. The gas density and the SiO abundance of the clouds in non-circular orbits are similar to those in the GCR. Therefore, in all the kinematical components there are dense clouds that can withstand the tidal shear. However, there is no evidence of star formation outside the GCR. The high relative velocity and shear expected in the dust lanes along the bar major axis could inhibit the star formation process, as observed in other galaxies. The high SiO abundances derived in the non-circular velocity clouds are likely due to the large-scale shocks that created the dust lanes.

Appeared in: A&A 455, 963-969

NGC 2146's starburst region and extended structure

A. Greve$(^{1})$, N. Neininger$(^{2})$, A. Sievers$(^{3})$, A. Tarchi$(^{4,5})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{2})$Astronomisches Institut der Universität Bonn, 71 Auf dem Hügel, 53121 Bonn, Germany, $(^{3})$IRAM, Nucleo Central, 7 Avenida Divina Pastora, 18012 Granada, Spain, $(^{4})$INAF - Instituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy, $(^{5})$INAF - Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy

We present mm-wavelength and optical observations of the starburst region in NGC 2146. This region of $\sim 4$ kpc diameter contains a well-ordered distribution of stars, gas, and dust, and a well-ordered rotation. The possible anomalies found in our observations are a warped CO distribution and an increase in the CO line width at the NW edge of the starburst region. The investigation of a possible encounter or merger origin of the starburst may therefore have to concentrate on the distorted outer structure of the galaxy.

There are three large-scale features of $\sim 20$ kpc extent, two of which give the impression of being stellar sub-systems. The third feature is an imcomplete and expanding ring of H II regions and stars, apparently indicating an event that occurred some 300 Myrs ago.

Appeared in: A&A 459, 441

Adapting and expanding the Plateau de Bure interferometer

Karastergiou A.$(^{1})$, Neri R.$(^{1})$
$(^{1})$IRAM, 300 rue de la Piscine, Domaine Universitaire, Saint Martin d'Hères, France

We were recently faced with the following problem: The T-shaped Plateau de Bure Interferometer is expanding its tracks to achieve higher spatial resolution in astronomical images at mm wavelengths. Two more stations for positioning the antennas during observations are being built at the ends of the extended tracks. Which of the given stations should the remaining four antennas occupy to accommodate the new stations? What is the optimal set of antenna configurations, given the new extended one, to achieve necessary coverage of the uv-plane at a variety of spatial resolutions? We present in this paper the solutions to the above questions, resulting from a novel method we have recently developed. The method is based on identifying which placement of elements provides the most appropriate uv-plane sampling.

Appeared in: AIPC 848, 857

A Keplerian Gaseous Disk around the B0 Star R Monocerotis

Fuente A.$(^{1})$, Alonso-Albi T.$(^{1})$, Bachiller R.$(^{1})$, Natta A.$(^{2})$, Testi L.$(^{2})$, Neri R.$(^{3})$, Planesas P.$(^{1})$
$(^{1})$Observatorio Astronómico Nacional (OAN), Apartado 112, E-28803 Alcalá de Henares, Madrid, Spain, $(^{2})$INAF-Osservatorio Astrofisico de Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy, $(^{3})$Institute de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères Cedex, France

We present high angular resolution observations of the circumstellar disk around the massive Herbig Be star R Mon (M $_* \sim 8 \mbox{M$_\odot$}$) in the continuum at 2.7 and 1.3 mm and the $^{12}$CO 1-0 and 2-1 rotational lines. On the basis of the new 1.3 mm continuum image, we estimate a disk mass (gas+dust) of $0.007 \mbox{M$_\odot$}$ and an outer radius of $< 150$ AU. Our CO images are consistent with the existence of a Keplerian rotating gaseous disk around this star. Up to our knowledge, this is the most clear evidence for the existence of Keplerian disks around massive stars reported thus far. The mass and physical characteristics of this disk are similar to those of the more evolved T Tauri stars and indicate a shorter timescale for the evolution and dispersal of circumstellar disks around massive stars which lose most of their mass before the star becomes visible.

Appeared in: ApJ 649, L119

Atomic Carbon in APM 08279+5255 at z = 3.91

Wagg J.$(^{1,2})$, Wilner D.J.$(^{1})$, Neri R.$(^{3})$, Downes D.$(^{3})$, Wiklind, T.$(^{4})$
$(^{1})$Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, $(^{2})$Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Apartudo Postal 51 y 216, Puebla, Mexico, $(^{3})$Institut de Radio Astronomie Millimétrique, St. Martin d'Hères, F-38406, France, $(^{4})$ESA Space Telescope Division, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218

We present a detection of [C I] $^3P_1 - ^3P_0$ emission in the lensed quasar APM 08279+5255 at z=3.91 using the IRAM Plateau de Bure interferometer. The [C I] line velocity and width are similar to the values of previously detected high-J CO and HCN lines in this source, suggesting that the emission from all of these species arises from the same region. The apparent luminosity of the [C I] line is $L'_{C\: I}=(3.1 \pm 0.4)\times 10^{10}$ K km s$^{-1}$ pc$^2$, which implies a neutral carbon mass M $_{C\: I}=(4.4 \pm0.6) $m $^{-1} \times 10^7 \mbox{M$_\odot$}$, where m is the lensing magnification factor. The [C I] line luminosity is consistent with the large molecular gas mass inferred from the nuclear CO line luminosity ($\sim 10^{11}$m $^{-1}\mbox{M$_\odot$}$). We also present an upper limit on the H$_2$O $1_{10}-1_{01}$ line luminosity in APM 08279+5255 of $L'_{H_2O} < 1.8 \times 10^{10}$ K km s$^{-1}$ pc$^2$ ($3 \sigma$).

Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Appeared in: ApJ 651, 46

Interferometric CO J = 2-1 Emission Mapping of the Protoplanetary Nebula IRAS 19475+3119

Sánchez Contreras C.$(^{1,2})$, Bujarrabal V.$(^{3})$, Castro-Carrizo A.$(^{4})$, Alcolea J.$(^{5})$, Sargent A.$(^{1})$
$(^{1})$Division of Physics, Mathematics, and Astronomy, Mail Stop 105-24, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, $(^{2})$Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain, $(^{3})$Observatorio Astronómico Nacional, Apdo. 112, Alcalá de Henares, 28803 Madrid, Spain, $(^{4})$Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France, $(^{5})$Observatorio Astronómico Nacional, C/Alfonso XII, 3, 28014 Madrid, Spain

We present $\sim2\hbox{$^{\prime\prime}$}$ resolution interferometric maps of the $^{12}$CO J=2-1 emission in the PPN IRAS 19475+3119 obtained with OVRO. These data probe two distinct molecular components, namely, a slowly expanding shell and a fast bipolar outflow.We have used a spatiokinematic model of the 12CO J=2-1 emission to constrain the properties of these two components. The shell has inner and outer radii of $R_{in}\sim 6.5 \times 10^{16}$ cm and $R_{out} \sim 2\times10^{17}$ cm and expands at $V_{exp}\sim 11$ km s$^{-1}$. The $^{12}$CO $J=2-1$ line wing emission arises in a bipolar structure that emerges from two diametrically opposite holes in the slow shell. The bipolar outflow is aligned with one of the two lobe pairs of the quadrupolar optical nebula (at P.A.$\sim 80^\circ$). Both the holes and the bipolar outflow are most likely the result of the interaction of fast, collimated post-AGB winds with the shell. The quadrupolar morphology of the optical nebula indicates two distinct bipolar post-AGB winds ejected in two different directions. The elongation of the optical counterpart of the shell (at P.A. $\sim -45^\circ$) and two similarly aligned CO clumps suggest that the slow shell has also been affected by the wind interaction. The expansion velocity in the bipolar outflow increases linearly with the distance from the nebula center and reaches $V_{exp}=30$ km s$^{-1}$ (projected) at the tips of the lobes. This velocity gradient yields a relatively long kinematical age of $\sim 1900$ yr, assuming an outflow inclination of $i=30^\circ$ with respect to the plane of the sky; this age is comparable with the post-AGB lifetime estimated from the shell expansion velocity and inner radius. We derive a mean kinetic temperature of $\sim 14$ K and a total mass of $\sim 0.4 \mbox{M$_\odot$}$. The collimation and linear momentum ( $P\sim 4\times 10^{38}$ g cm s$^{-1}$) of the outflow are unlikely to result from radiation pressure on dust grains.

Appeared in: ApJ 643, 945

Spectral line confusion at $z=3.9$: detection of HNC and tentative detection of CN in APM 08279+5255

M. Guélin$(^{1})$, P. Salomé$(^{1})$, R. Neri$(^{1})$, S. García-Burillo$(^{2})$, J. Graciá-Carpio$(^{2})$, J. Cernicharo$(^{3})$, P. Cox$(^{1})$, P. Planesas$(^{2})$, P.M. Solomon$(^{4})$, L.J. Tacconi$(^{5})$ and P. Vanden Bout$(^{6})$
$(^{1})$IRAM, Domaine Universitaire, 300 rue de la Piscine, St Martin d'Hères F-38400, France, $(^{2})$Observatorio Astronómico Nacional, Calle Alfonso XII 3, E-28014 Madrid, Spain, $(^{3})$IEM-DAMIR, CSIC, Serrano 121, E28006, Spain, $(^{4})$Dept. of Physics and Astronomy, State Univ. of N.Y., Stony Brook, NY 11974, USA, $(^{5})$Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany, $(^{6})$NRAO, 520 Edgemont road, Charlottesville, VA 22903, USA.

The presence of large reservoirs of molecular gas in the early Universe has been demonstrated through the detection of rotational transitions of CO in high redshift ultraluminous galaxies and quasars. The derived masses are in excess of $\rm 10^{10} \, M_\odot$ and the gas is found to be warm and dense. Obviously, a prodigious star formation activity is taking place in some of those objects, as attested by the huge far-infrared luminosities. These considerations have triggered searches for molecular species having higher dipole moments than CO and that are better probes of the very dense gas associated with star formation. Two such molecules were detected so far in high-$z$ sources: HCN and HCO$^+$.

We report in this Letter the detection with the Plateau de Bure interferometer of a broad spectral line with a center frequency of 92294 MHz (relative to the LSR) in the quasar APM 08279+5255 ($z=3.91$) . We identify this line as a blend of the J = 5-4 transition of HNC and of the N= 4-3 transition of CN. Although the two transitions are well separated in frequency (336 MHz between HNC and the upper fine-structure component of CN), the large redshift of the quasar reduces the splitting to 68 MHz, so that the broad (FWHP 400 kms$^{-1}$) HNC and CN lines arising in the nuclear region of the quasar are blended.

HNC and CN are the 4$^{\rm th}$ and 5$^{\rm th}$ molecular species detected at redshift $z>1$. The derived HNC and CN line intensities are 0.6 and 0.4 times that of HCN J= 5-4. If HNC and HCN are co-spatial and if their J= 5-4 lines are collisionally excited, the [HNC]/[HCN] abundance ratio must be equal to 0.6 within a factor of 2, similar to its value in the cold Galactic clouds and much larger than in the hot molecular gas associated with Galactic HII regions. It is possible, however, that fluorescent infrared radiation plays an important role in the excitation of HNC and HCN.

Figure 5: Spectrum of the HNC(5-4) and CN (4-3) emissions from APM 08279+5255, The velocity scale is relative to the HNC frequency redshifted by $z=3.9118$. The velocity resolution is 97 km s$^{-1}$, the r.m.s. noise 0.5 mJy. The thick line represents the best fit synthetic spectrum and the dotted and dashed lines the contributions from CN and HNC to this spectrum. The CN contribution is the blend of 2 fine-structure components.

Dissipative structures of diffuse molecular gas: II - The translucent environment of a dense core

P. Hily-Blant$(^{1,2})$ and E. Falgarone$(^{1})$
$(^{1})$LRA-LERMA, 24 rue Lhomond, École normale supérieure (Observatoire de Paris), 75231 Paris Cedex 05, France, $(^{2})$IRAM, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France

Aims. This paper belongs to a series of four, dedicated to the analysis of the dynamical, thermal and chemical properties of translucent molecular gas, with the perspective of characterizing the processes driving the dissipation of supersonic turbulence, an anticipated prerequisite of dense core formation.

Methods. We analyze the small scale morphology and velocity structure of the parsec-scale environment of a low mass dense core (1M$_\odot$). Our work is based on large maps made with the IRAM-30m telescope in the two lowest rotational transitions of $^{12}$CO and $^{13}$CO with high angular (20 $^{\prime\prime}$ or 0.015 pc at 115 GHz) and spectral (0.055kms$^{-1}$) resolutions. The field is translucent, hence providing strong constraints on the column density and physical conditions in the gas.

Results.More than one third of the field mass (6.5 M$_\odot$) lies in an elongated tail of dense and cold gas, possibly extending beyond the edge of the map and connected to the core in space and velocity. This core tail is highly turbulent and sub-structured into narrow filaments of aspect ratio up to 20. These are pure velocity structures with velocity shears in the range $2-10$ km s$^{-1}$pc$^{-1}$. Another third of the mass, according to the weak extinction of the field, lies in more dilute molecular and atomic gas. Its molecular fraction, largely traced by optically thick $^{12}$CO lines, is even more turbulent than the dense core tail. The gas emitting in the broad wings of the $^{12}$CO lines is organized into a conspicuous network of narrow criss-crossed filaments, whose pattern at the parsec scale is seen for the first time. The gas there is optically thin in the $^{12}$CO $(1-0)$ line ($\tau_{12}<0.2$), warmer than 25 K and more dilute than 1000 cm$^{-3}$. These optically thin $^{12}$CO-filaments, though contributing to about 10% of the mass of the environment, have a CO cooling rate a few times larger than that of the whole field on average. Whether dense or dilute, all the filamentary structures in the field (with transverse sizes $0.015-0.03$ pc), are preferentially oriented along the direction of the magnetic fields, as measured a few parsecs away. Using the Chandrasekhar-Fermi method, we estimate the intensity of the magnetic fields intensity in the dilute molecular gas to be $B_{pos}=15$ $\mu$G. We infer that the turbulent motions in the dilute gas are in the trans-Alfvénic range.

Conclusions. The 1 M$_\odot$dense core is surrounded by a translucent and highly turbulent environment whose gas dynamics are not super-Alfvénic. The low mass dense core is not isolated but still connected to a massive reservoir of dense gas. Filaments of optically thin $^{12}$CO are found to radiate more efficiently in the CO lines than the whole field on average. These are the structures that we tentatively identify with the locus of intermittent dissipation of turbulence, and for which there is no observational evidence that they are shocks.

Accepted for publication in A&A

Resolving the inner dust disks surrounding LkCa 15 and MWC 480 at mm wavelengths

V. Pietu$(^{1})$, A. Dutrey$(^{2})$, S. Guilloteau$(^{2})$, E. Chapillon$(^{2})$, J. Pety$(^{1})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{2})$L3AB, CNRS UMR5804, OASU, 2 rue de l'Observatoire, BP 89, 3327 Floriac, France

We performed sub-arcsecond high-sensitivity interferometric observations of the thermal dust emission at 1.4 mm and 2.8 mm in the disks surrounding LkCa 15 and MWC 480, with the new 750 m baselines of the IRAM PdBI array. This provides a linear resolution of about 60 AU at the Taurus distance.

We report the existence of a cavity of about 50 AU radius in the inner disk of LkCa 15. Whereas LkCa 15 emission is optically thin, the optically thick core of MWC 480 is resolved at 1.4 mm with a radius of about 35 AU, constraining the dust temperature. In MWC 480, the dust emission is coming from a colder layer than the CO emission, most likely the disk mid-plane.

These observations provide direct evidence of an inner cavity around LkCa 15. Such a cavity most probably results from the tidal disturbance created by a low mass companion or large planet at about 30 AU from the star. These results suggest that planetary system formation is already at work in LkCa 15. They also indicate that the classical steady-state viscous disk model is a too simplistic description of the inner 50 AU of ''proto-planetary'' disks, and that the disk evolution is coupled to the planet formation process. The MWC 480 results indicate that a proper estimate of the dust temperature and size of the optically thick core are essential to determine the dust emissivity index.

Appeared in: A&A 2006, 460, L43-L47

A complete 12CO 2-1 map of M 51 with HERA. I. Radial averages of CO, HI, and radio continuum

Schuster K. F.$(^{1})$, Kramer C.$(^{2})$, Hitschfeld M.$(^{2})$, Garcia-Burillo S.$(^{3})$ Mookerjea B.$(^{2,4})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{2})$KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany, $(^{3})$Centro Astronomico de Yebes, IGN, 19080 Guadalajara, Spain, $(^{4})$Department of Astronomy, University of Maryland, College Park, MD 20742, USA

The mechanisms governing the star formation rate in spiral galaxies are not yet clear. The nearby, almost face-on, and interacting galaxy M 51 offers an excellent opportunity to study at high spatial resolutions the local star formation laws.

In this first paper, we investigate the correlation of H$_2$, H I, and total gas surface densities with the star forming activity, derived from the radio continuum (RC), along radial averages out to radii of 12 kpc.

We have created a complete map of M 51 in $^{12}$CO 2-1 at a resolution of 450 pc using HERA at the IRAM-30 m telescope. These data are combined with maps of H I and the radio-continuum at 20 cm wavelength. The latter is used to estimate the star formation rate (SFR), thus allowing to study the star formation efficiency and the local Schmidt law $\Sigma_{SFR} \propto \Sigma_{gas}^n$. The velocity dispersion from CO is used to study the critical surface density and the gravitational stability of the disk. Results: . The total mass of molecular material derived from the integrated $^{12}$CO 2-1 intensities is $2\times 10^9 \mbox{M$_\odot$}$. The $3 \sigma$ detection limit corresponds to a mass of $1.7\times 10^5 \mbox{M$_\odot$}$. The global star formation rate is $2.56 \mbox{M$_\odot$}$ yr$^{-1}$ and the global gas depletion time is 0.8 Gyr. H I and RC emission are found to peak on the concave, downstream side of the outer south-western CO arm, outside the corotation radius. The total gas surface density $\Sigma_{gas}$ drops by a factor of $\sim 20$ from $70 \mbox{M$_\odot$}$ pc$^{-2}$ at the center to $3
\mbox{M$_\odot$}$ pc$^{-2}$ in the outskirts at radii of 12 kpc. The fraction of atomic gas gradually increases with radius. The ratio of H I over H$_2$ surface densities, $\Sigma_{HI}/\Sigma_{H2}$, increases from $\sim 0.1$ near the center to $\sim 20$ in the outskirts without following a simple power-law. $\Sigma_{HI}$ starts to exceed $\Sigma_{H2}$ at a radius of $\sim 4$ kpc. The star formation rate per unit area drops from $\sim 400 \mbox{M$_\odot$}pc^{-2} Gyr^{-1}$ in the starburst center to $\sim 2 \mbox{M$_\odot$}pc^{-2} Gyr^{-1}$ in the outskirts. The gas depletion time varies between 0.1 Gyr in the center and 1 Gyr in the outskirts, and is shorter than in other non-interacting normal galaxies. Neither the H I surface densities nor the $H_2$ surface densities show a simple power-law dependence on the star formation rate per unit area. In contrast, $\Sigma_{gas}$ and $\Sigma_{SFR}$ are well characterized by a local Schmidt law with a power-law index of $n=1.4\pm0.6$. The index equals the global Schmidt law derived from disk-averaged values of $\Sigma_{gas}$ and $\Sigma_{SFR}$ of large samples of normal and starburst galaxies. The critical gas velocity dispersions needed to stabilize the gas against gravitational collapse in the differentially rotating disk of M 51 using the Toomre criterion, vary with radius between 1.7 and 6.8 km s$^{-1}$. Observed radially averaged dispersions derived from the CO data vary between 28 km s$^{-1}$ in the center and $\sim 8$ km s$^{-1}$ at radii of 7 to 9 kpc. They exceed the critical dispersions by factors $Q_{gas}$ of 1 to 5. We speculate that the gravitational potential of stars leads to a critically stable disk.

Appeared in: A&A 461, 143

The interstellar medium of the Antennae Galaxies

Schulz A.$(^{1,3})$, Henkel C.$(^{2})$, Muders D.$(^{})$2, Mao R. Q.$(^{4})$, Roellig M.$(^{3,5})$, Mauersberger R.$(^{6})$
$(^{1})$Institut für Physik und ihre Didaktik, Universität zu Köln, Groenewaldstr. 2, D-50931 Köln, Germany, $(^{2})$MPIfR, Auf dem Hügel 69, D-53121 Bonn, Germany, $(^{3})$Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany, $(^{4})$Purple Montain Observatory, Chinese Academy of Sciences, 210008 Nanjing, P.R. China, $(^{5})$I. Physikalisches Institut, Universität zu Köln, Universitätsstr. 17, D-50937 Köln, Germany, $(^{6})$Instituto de Radio Astronomía Milimétrica (IRAM) Avenida Divina Pastora 7, Local 20, E-18012 Granada, Spain

To study the properties of the interstellar medium in the prototypical merging system of the Antennae galaxies (NGC 4038 and NGC 4039), we have obtained $^{12}$CO (1-0), (2-1) and (3-2) line maps, as well as a map of the $870\mu$m continuum emission. Our results are analysed in conjunction with data from X-ray to radio wavelengths. In order to distinguish between exact coincidence and merely close correspondence of emission features, we compare the morphological structure of the different emission components at the highest available angular resolution. To constrain the physical state of the molecular gas, we apply models of photon dominated regions (PDRs) that allow us to fit CO and [CII] data, as well as other indicators of widespread PDRs in the Antennae system, particularly within the super giant molecular cloud (SGMC) complexes of the interaction region (IAR) between the two galaxies. The modeled clouds have cores with moderately high gas densities up to $4\times 10^4$ cm$^{-3}$ and rather low kinetic temperatures $\leq$ 25K). At present, all these clouds, including those near the galactic nuclei, show no signs of intense starburst activity. Thermal radio or mid-infrared emission are all observed to peak slightly offset from the molecular peaks. The total molecular gas mass of the Antennae system adds up to $\sim 10^{10} \mbox{M$_\odot$}$. In the vicinity of each galactic nucleus, the moleculargas mass, $1-2\times10^9 \mbox{M$_\odot$}$, exceeds that of the Galactic centre region by a factor of almost 100. Furthermore, the gas does not seem to deviate much from the $N_{H_2}/I_{CO}$ ratio typical of the disk of our Galaxy rather than our Galactic centre.

Accepted for publication in A&A

A global 86 GHz VLBI survey of compact radio sources

Lee S., Lobanov A. P., Krichbaum T. P., Witzel A., Zensus J. A., Bremer M., Greve A., Grewing M.
$(^{1})$MPIfR, Auf dem Hügel 69, D-53121 Bonn, Germany, $(^{2})$IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France

We present results from a large global VLBI(Very Long Baseline Interferometry) survey of compact radio sources at 86 GHz which started in October 2001. The main goal of the survey is to increase the total number of objects accessible for future 3mm-VLBI imaging by factors of 3-5. The survey data reach the baseline sensitivity of 0.1 Jy, and image sensitivity of better than 10 mJy/beam. To date, a total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, and only 6 sources have not been detected. Flux densities and sizes of core and jet components of all detected sources have been measured using Gaussian model fitting. From these measurements, brightness temperatures have been estimated, taking into account resolution limits of the data. Here, we compare the brightness temperatures of the cores and secondary jet components with similar estimates obtained from surveys at longer wavelengths (e.g. 15 GHz). This approach can be used to study questions related to mechanisms of initial jet acceleration (accelerating or decelerating sub-pc jets?) and jet composition (electron-positron or electron-proton plasma?).

To appear in: Proc. of the 8th EVN Symposium held in Torun Poland, Sep. 26-29 2006

Characteristics and Performance of the North American ALMA Prototype Antenna

Mangum J. G., Baars J.W.M., Greve A., Lucas R., Snel R., Wallace P.

The submillimeter antennas of the Atacama Large Millimeter Array (ALMA) have specifications that are beyond the current state of the art in accurate reflector antenna technology. Considering that as many as 64 of these antennas will eventually be needed, the ALMA partners AUI/NRAO and ESO each agreed to acquire a prototype antenna, and subject these to an extensive evaluation program. In this paper we summarize the performance of the ALMA North American prototype antenna.

Appeared in: Revealing the Molecular Universe: One Antenna is Never Enough, ASP Conf. Series 2006, 356, 253. Eds. D.C. Backer, J.W. Moran, and J.L. Turner

Multi-wavelength afterglow observations of the high redshift GRB 050730

Pandey S.B.$(^{1})$ et al. (and 24 co-authors)
$(^{1})$Instituto de Astrofísica de Andalucía, PO Box 03004, 18080 Granada, Spain

Context: GRB 050730 is a long duration high-redshift burst ($z=3.967$) that was discovered by Swift. The afterglow shows variability and was well monitored over a wide wavelength range. We present comprehensive temporal and spectral analysis of the afterglow of GRB 050730 including observations covering the wavelength range from the millimeter to X-rays.

Aims: We use multi-wavelength afterglow data to understand the complex temporal and spectral decay properties of this high redshift burst.

Methods: Five telescopes were used to study the decaying afterglow of GRB 050730 in the B, V, r', R, i', I, J and K photometric pass bands. A spectral energy distribution was constructed at 2.9 h post-burst in the B, V, R, I, J and K bands. X-ray data from the satellites Swift and XMM-Newton were used to study the afterglow evolution at higher energies.

Results: The early afterglow shows variability at early times and the slope steepens at 0.1 days (8.6 ks) in the B, V, r', R, i', I, J and K passbands. The early afterglow light curve decayed with a powerlaw slope index $\alpha_1 = -0.60\pm 0.07$ and subsequently steepened to $\alpha_2
= -1.71\pm 0.06$ based on the R and I band data. A millimeter detection of the afterglow around 3 days after the burst shows an excess in comparison to theoretical predictions. The early X-ray light curve observed by Swift is complex and contains flares. At late times the X-ray light curve can be fit by a powerlaw decay with $\alpha_x =
-2.5\pm 0.15$ which is steeper than the optical light curve. A spectral energy distribution (SED) was constructed at $\sim 2.9$ h after the burst. An electron energy index, p, of $\sim2.3$ was calculated using the SED and the photon index from the X-ray afterglow spectra and implies that the synchrotron cooling frequency $\nu_c$ is above the X-ray band.

Appeared in: A&A 460, 415

Extensive multiband study of the X-ray rich GRB 050408. A likely off-axis event with an intense energy injection

de Ugarte Postigo, A.$(^{1})$ et al. (and 42 co-authors)
$(^{1})$Instituto de Astrofísica de Andalucía (IAA-CSIC), Apartado de Correos 3004, 18080 Granada, Spain

Aims: Understand the shape and implications of the multiband light curve of GRB 050408, an X-ray rich (XRR) burst.

Methods: We present a multiband optical light curve, covering the time from the onset of the $\gamma$-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date.

Results: The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.

Based on observations collected at SAO, La Silla, Roque de los Muchachos, Haleakala, Kitt Peak, Cerro Tololo, TÜBITAK, Kiso, Observatorio de Sierra Nevada, Plateau du Bure, GMRT and RATAN-600. Appendices A and B are only available in electronic form at

Appeared in: A&A 462, 57

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