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Scientific Results in Press

Arcsecond-resolution $^{12}$CO mapping of the yellow hypergiants IRC+10420 and AFGL2343

A. Castro-Carrizo$(^{1})$, G. Quintana-Lacaci$(^{2})$, V. Bujarrabal $(^{2})$, R. Neri$(^{1})$ and J. Alcolea$(^{3})$
$(^{1})$Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France, $(^{2})$Observatorio Astronómico Nacional (IGN), Apdo. 112, E-28803 Alcalá de Henares, Spain, $(^{3})$Observatorio Astronómico Nacional (IGN), c/ Alfonso XII n$^{\rm o}$13, E-28014 Madrid, Spain

IRC+10420 and AFGL2343 are the unique, known yellow hypergiants (YHGs) presenting a heavy circumstellar envelope (CSE). We aim to study the morphology, exceptional kinematics, and excitation conditions of their CSEs, and the implications for mass-loss processes. We have mapped the $^{12}$CO $J$=2$-$1 and 1$-$0 emission in these YHGs with the IRAM Plateau de Bure interferometer and the 30m telescope. We developed LVG models in order to analyze their circumstellar characteristics. The maps show that the overall shape of both CSEs is approximately spherical, although they also reveal several aspherical features. The CSE around IRC+10420 shows a rounded extended halo surrounding a bright inner region, with both components presenting aspherical characteristics. It presents a brightness minimum at the center. The envelope around AFGL2343 is a detached shell, showing spherical symmetry and clumpiness at a level of $\sim 15$% of the maximum brightness. The envelopes expand isotropically at $\sim 35$ kms$^{-1}$, about two or three times faster than typical CSEs around AGB stars. High temperatures ($\sim 200$ K) are derived for the innermost regions in IRC+10420, while denser and cooler ($\sim 30$ K) gas is found in AFGL2343. The mass-loss processes in these YHGs have been found to be similar. The deduced mass-loss rates ( $\sim 10^{-4} - 10^{-3}$ M$_\odot$yr$^{-1}$) are much higher than those obtained in AGB stars, and they present 5significant variations on time scales of $\sim 1000$ yr.

Appeared in: A&A 465, 457

Dust and Molecular Content of the Lensed Quasar, MG0751+2716, at $z=3.2$

Danielle Alloin$(^{1,2})$, Jean-Paul Kneib$(^{3})$, Stéphane Guilloteau$(^{4})$ and Michael Bremer$(^{5})$
$(^{1})$European Southern Observatory, Casilla 19001, Santiago 19, Chile, $(^{2})$AIM, CEA/DSM-CNRS-Université Paris 7, SAp, Bât.709, CE Saclay, l'Orme des Merisiers, 91191 Gif-sur-Yvette Cédex, France, $(^{3})$Laboratoire d'Astrophysique de Marseille, OAMP Traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France, $(^{4})$UMR5804 CNRS, OASU, Université Bordeaux 1, BP 89, 33270 Floirac, France, $(^{5})$Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France

Gravitational lenses offer unique opportunities to explore the molecular content around active galactic nuclei at high redshift, through the magnification and gain in angular resolution. We study here the molecular and dust content of the high redshift (z=3.2), gravitationally lensed quasar MG0751+2716. We used the IRAM Plateau de Bure interferometer to measure the CO J=3-2, J=4-3 and J=8-7 rotation lines and continuum flux between 1.1 mm and 3 mm in MG0751+2716. We use HST data and constraints from the high resolution MERLIN map at 6.2 cm to build an improved model of the lens. The position agreement between the CO emission and the millimeter continuum suggests that dust and molecules are closely related. A 500  $\mbox{km\,s$^{-1}$}$ velocity gradient is tentatively detected from the CO lines across the central $0{\farcs}5$. The continuum SED in the range 0.45 mm - 204 mm exhibits the signatures of two components: synchrotron emission from a core/jet system, and thermal emission related to warm dust. The CO line intensities are compatible with warm, dense molecular gas, suggesting a location in the close environment of the quasar. These observational constraints lead us to consider a source/quasar model made of a point-like core, a radio jet, and a molecular and dusty ring-like structure ($\sim$460 pc in radius) located in a plane perpendicular to the jet axis and seen almost edge-on. For this configuration, we derive a total magnification of 16 for the quasar radiation at rest frequency above 350 GHz and a magnification of 25 below 350 GHz. The dust mass (assuming a likely temperature $T=50$ K) is M $_{dust}=1.7 \times 10^8\mbox{M$_\odot$}$, the mass of molecular material is M$($H $_2) = 6 \times 10^{10}\mbox{M$_\odot$}$ and a lower limit to the dynamical mass is M $_{dyn} = 1.5 \times 10^{10}\mbox{M$_\odot$}$. Such values are comparable to those found in the small sample of CO detected sources at high redshifts.

Accepted for publication in A&A

A Detailed Study of Gas and Star Formation in a Highly Magnified Lyman Break Galaxy at z=3.07

Coppin K.E.K.$(^{1})$, Swinbank A.M.$(^{1})$, Neri R.$(^{2})$, Cox P.$(^{2})$, Smail Ian$(^{1})$, Ellis R.S.$(^{3})$, Geach J.E.$(^{1})$, Siana B.$(^{4})$, Teplitz H.$(^{4})$, Dye S.$(^{5})$, Kneib J.-P.$(^{6})$, Edge A.C.$(^{1})$, Richard, J.$(^{3})$
$(^{1})$Institute for Computational Cosmology, Durham University, South Road, Durham, DH1 3LE, UK, $(^{2})$IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Hères, France, $(^{3})$Caltech, MC 105-24, 1200 East California Blvd, Pasadena, California, CA91125, USA, $(^{4})$Spitzer Science Center, Caltech, MC 314-6, 1200 East California Blvd, Pasadena, California, CA91125, USA, $(^{5})$School of Physics and Astronomy, Cardiff University, 5, The Parade, Cardiff, Wales, CF24AA, UK, $(^{6})$Laboratoire d'Astrophysique de Marseille, Traverse du Siphon - B.P.8 13376, Marseille Cedec 12, France

We report the detection of CO(3-2) emission from a bright, gravitationally lensed Lyman Break Galaxy, LBG J213512.73-010143 (the ``Cosmic Eye''), at $z=3.07$ using the Plateau de Bure Interferometer. This is only the second detection of molecular gas emission from an LBG and yields an intrinsic molecular gas mass of $(2.4\pm 0.4)\times10^9$ M$_\odot$. The lens reconstruction of the UV morphology of the LBG indicates that it comprises two components separated by $\sim 2$ kpc. The CO emission is unresolved, $\Theta
\lower.5ex\hbox{$\; \buildrel < \over \sim \;$}2\hbox{$^{\prime\prime}$}$, and appears to be centered on the intrinsically fainter (and also less highly magnified) of the two UV components. The width of the CO line indicates a dynamical mass of $(8\pm
2)\times10^9$ $csc^2 i$ M$_\odot$within the central 2 kpc. Employing mid-infrared observations from Spitzer we derive a stellar mass of $\sim(6 \pm 2) \times 10^9$ M$_\odot$and a star-formation rate of $\sim 60$ M$_\odot$/yr, indicating that the molecular gas will be consumed in $\sim 40$ Myr. The gas fractions, star-formation efficiencies and line widths suggests that LBG J213512 is a high-redshift, gas-rich analog of a local luminous infrared galaxy. This galaxy has a similar gas-to-dynamical mass fraction as observed in the submillimeter-selected population, although the gas surface density and star-formation efficiency is a factor of $3 \times$ less, suggesting less vigorous activity. We discuss the uncertainties in our conclusions arising from adopting a CO-to-H$_2$ conversion factor appropriate for either the Milky Way or local luminous infrared galaxies. These observations demonstrate that current facilities, when aided by fortuitous gravitational magnification, can study 'ordinary' galaxies at high-redshift and so act as pathfinders for ALMA.

Accepted for publication in ApJ

Detection of emission from the CN radical in the Cloverleaf Quasar at z=2.56

Dominik A. Riechers$(^{1})$, Fabian Walter$(^{1})$, Pierre Cox$(^{2})$, Christopher L. Carilli$(^{3})$, Axel Weiß$(^{4})$, Frank Bertoldi$(^{5})$, and Roberto Neri$(^{2})$
$(^{1})$MPIA, Königstuhl 17, Heidelberg, D-69117, Germany, $(^{2})$IRAM, 300 Rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Hères, France, $(^{3})$NRAO, PO Box O, Socorro, NM 87801, USA, $(^{4})$MPIfR, Auf dem Hügel 69, Bonn, D-53121, Germany, $(^{5})$Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, Bonn, D-53121, Germany

We report the detection of CN $(N=3\rightarrow 2)$ emission towards the Cloverleaf quasar (z = 2.56) based on observations with the IRAM Plateau de Bure Interferometer. This is the first clear detection of emission from this radical at high redshift. CN emission is a tracer of dense molecular hydrogen gas $(n({\rm H}_2) > 10^4 {\rm cm}^{-3})$ within star-forming molecular clouds, in particular in regions where the clouds are affected by UV radiation. The HCN/CN intensity ratio can be used as a diagnostic for the relative importance of photodissociation regions (PDRs) in a source, and as a sensitive probe of optical depth, the radiation field, and photochemical processes. We derive a lensing-corrected CN $(N=3\rightarrow 2)$ line luminosity of L'CN(3-2) $ = (4.5 \pm 0.5) \times 10^9 {\rm K} {\rm km s}^{-1}{\rm pc}^2$. The ratio between CN luminosity and far-infrared luminosity falls within the scatter of the same relationship found for low-z (ultra-) luminous infrared galaxies. Combining our new results with CO $(J=3\rightarrow 2)$ and HCN $(J=1\rightarrow 0)$ measurements from the literature and assuming thermal excitation for all transitions, we find a CO/CN luminosity ratio of $9.3 \pm 1.9$ and a HCN/CN luminosity ratio of $0.95 \pm 0.15$. However, we find that the CN $(N=3\rightarrow 2)$ line is likely only subthermally excited, implying that those ratios may only provide upper limits for the intrinsic 1!0 line luminosity ratios. We conclude that, in combination with other molecular gas tracers like CO, HCN, and HCO$^+$, CN is an important probe of the physical conditions and chemical composition of dense molecular environments at high redshift.

Accepted for publication in ApJ

Astronomical detection of C$_4$H$^-$, the second interstellar anion

J. Cernicharo$(^{1})$, M. Guélin$(^{2})$, M. Agundez$(^{1})$, K. Kawaguchi$(^{3})$, M. McCarthy$(^{4})$ and P. Thaddeus $(^{4})$
$(^{1})$Dpt. Molecular and Infrared Astrophysics. Instituto de Estructura de la Materia, CSIC, Serrano 121, E28006, Spain, $(^{2})$IRAM, Domaine Universitaire, 300 rue de la Piscine, 38406 St Martin d'Hères, France, $(^{3})$Department of Chemistry, Faculty of Science, Okayama University, Tsushimanaka, Okayama 700-8530, Japan $(^{4})$Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

The presence of negative ions in the interstellar medium has been predicted many years ago on general grounds or on the basis of ion-molecule chemical models (see e.g. Herbst 1981). It was pointed out that a high electron affinity and a large number of vibrational states increase greatly the sticking coefficient of electrons, so that large, negatively charged carbon chains of the form C$_n$H$^-$ may be abundant. In particular, Millar et al. (2000) predicted an abundance of C$_8$H$^-$ as large as 1/4 of that of its neutral counterpart C$_8$H in the outer envelope of the C-star IRC +10216, a source known to be particularly rich in C-chain molecules. For a long time, however, negative ions escaped detection because of lack of accurate transition frequencies.
Figure 2: J=9-8, 11-10, 12-11, 14-13 and 15-14 lines of C$_4$H$^-$ toward IRC+10216. The spectral resolution is 1 MHz and the frequency scale (rest frequency) is relative to a systemic velocity of -26.5 km s$^{-1}$. The positions of the C$_4$H$^-$ lines are indicated by downward arrows. The lines of HCCC$^{13}$CCN correspond to its J=42-41, and 49-48 transitions. The corresponding transitions of HCC$^{13}$CCCN could be present in the same panels. However, within the S/N of the data these lines are not detected. Spectral intensities are in the antenna temperature scale, $T_A^*$.

Figure 3: Averaged spectrum of the J=9-8, 11-10, 12-11, 14-13 and 15-14 lines of C$_4$H$^-$ (histogram) and C$_4$H (thick continuous line). All lines blended with those of C$_4$H$^-$ have been fitted and removed. The C$_4$H averaged spectrum has been scaled by a factor 100.

Figure 4: Abundance profiles of C$_n$H and C$_n$H$^-$ given by chemical modelling of the envelope, using the model parameters of Agundez & Cernicharo (2006). Angular distance is given in the top axis for an assumed distance to the star of 150 pc. The model predicts that anions have a more extended distribution than their neutral counterparts, which is related to the increase of the electron abundance with radius.

Recently, McCarthy et al. (2006) have succeeded in studying the microwave spectrum of C$_6$H$^-$ in the laboratory and identified this species as the carrier of a series of lines observed in 1996 by Kawaguchi and co-workers in the C-rich circumstellar envelope IRC +10216. Pursuing their laboratory work, McCarthy and colleagues have measured the rotational spectra of two more polyacetylenic anions, C$_8$H$^-$ and C$_4$H$^-$ (Gupta et al. 2007). In this Letter, we report the astronomical detection of the latter species in IRC+10216.

We have observed five lines corresponding to the $J$= 9-8, 11-10, 12-11, 14-13 and 15-14 rotational transitions of C$_4$H$^-$ (Fig. 2). The C$_4$H$^-$ lines have a cusped shape, denoting that this ion is formed in the outer part of the envelope, like its neutral counterpart C$_4$H (Fig. 3). The abundance of C$_4$H$^-$ in IRC+10216 is 1/6 of the abundance of C$_6$H$^-$ and 1/4200 of that of C$_4$H. The detection of C$_4$H$^-$, after that of C$_6$H$^-$, confirms the theoretical prediction that C-chain anions are abundant in interstellar clouds (Fig. 4) and yields a first measurement of the electron radiative attachment rates.

The abundance decrement between the two ions, [C$_4$H$^-$]/[C$_6$H$^-$] = 1/6, is more than two orders of magnitude smaller than that between their neutral counterparts, [C$_4$H]/[C$_6$H] = 45. The two negative ions appear more abundant than their positive ion analogs which, so far, have not been identified.

The detection of C$_4$H$^-$ and C$_6$H$^-$ sustains the farsighted prediction of Herbst and co-workers that carbon-chain anions may be abundant in the interstellar medium. Other negative ions from the same family, such as CN$^-$, C$_3$N$^-$, CCH$^-$ and C$_8$H$^-$, are likely to be detectable, although, probably, at lower intensity levels. Some of these species have already been studied in the laboratory and their millimeter rotational frequencies are accurately known, awaiting only for deeper astronomical searches. The observed [C$_4$H$^-$]/[C$_6$H$^-$] abundance ratio differs significantly from that estimated from statistical calculations of radiative electron attachment. This shows that surprising results are likely in this matter.

Accepted for publication in A&A

NUclei of GAlaxies: V. Radio emission in 7 NUGA sources

M. Krips$(^{1,2})$, A. Eckart$(^{1})$, T.P. Krichbaum$(^{3})$, J.-U. Pott$(^{1,4})$, S. Leon$(^{5,6})$, R. Neri$(^{7})$, S. García-Burillo$(^{8})$, F.Combes$(^{9})$, F. Boone$(^{9})$, A.J. Baker$(^{10})$, L.J. Tacconi$(^{11})$, E. Schinnerer$(^{12})$, and L.K. Hunt$(^{13})$
$(^{1})$Universität zu Köln, I.Physikalisches Institut, Zülpicher Str. 77, 50937 Köln, Germany, $(^{2})$Harvard-Smithsonian Center for Astrophysics, SMA project, 645 North A`ohoku Place, Hilo, HI 96720, $(^{3})$MPIfR, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{4})$ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany, $(^{5})$Instituto de Astrofísica de Andalucía (CSIC), C/ Camino Bajo de Huétor,24, Apartado 3004, 18080 Granada, Spain, $(^{6})$IRAM, Avenida Divina Pastora, 7, Núcleo Central, 18012 Granada, Spain, $(^{7})$Institut de Radio-Astronomie Millimétrique (IRAM), 300, rue de la Piscine, 38406 St.Martin-d'Hères, France, $(^{8})$Observatorio Astronómico Nacional (OAN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain, $(^{9})$Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France, $(^{10})$Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019, United States, $(^{11})$Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany, $(^{12})$MPIA, Königstuhl 17, 69117 Heidelberg, Germany, $(^{13})$INAF-Istituto di Radioastronomia/Sezione Firenze, Largo E. Fermi, 5, 50125 Firenze, Italy

We present high angular resolution radio snap-shot observations of seven nearby low-luminosity active galaxies (LLAGN) from the NUclei of GAlaxies (NUGA) survey. The observations were conducted with MERLIN and EVN/VLBI at 18cm and 6cm. At all observed angular resolutions and frequencies, we find indications for extended emission in about $\sim 40$% of the sources, consistent with the decrease of flux with increasing angular resolution. The extended components resemble jet emission in a majority of cases, consistent with the optically thin synchrotron emission implied by their steep spectra. We consider the compact 6cm EVN/VLBI radio emission of our sources in the context of the ``fundamental plane'' that previous LLAGN studies identified within the three-dimensional parameter space of radio luminosity, X-ray luminosity, and black hole mass. We demonstrate, using NGC7217 and NGC1068 as particular examples, that high-resolution, multi-epoch radio observations offer useful information about the origin of offsets from the fundamental plane.

Appeared in A&A 464, 553

Detection of HNC and tentative detection of CN at z = 3.9

Guélin M.$(^{1})$, Salomé P.$(^{1})$, Neri R.$(^{1})$, García-Burillo S.$(^{2})$, Graciá-Carpio J.$(^{2})$, Cernicharo J.$(^{3})$, Cox P.$(^{1})$; Planesas P.$(^{2})$, Solomon P.M.$(^{4})$, Tacconi L.J.$(^{5})$, vanden Bout P.$(^{6})$
$(^{1})$IRAM, Domaine Universitaire, 300 rue de la Piscine, St Martin d'Hères, 38400, France $(^{2})$Observatorio Astronómico Nacional, Calle Alfonso XII 3, 28014 Madrid, Spain, $(^{3})$IEM-DAMIR, CSIC, Serrano 121, 28006, 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

Molecular line emission from high-redshift galaxies holds great promise for the study of galaxy formation and evolution. The weak signals can only be detected with the largest mm-wave telescopes, such as the IRAM interferometer. We report the detection of the $J = 5 - 4$ line of HNC and the tentative detection of the $N= 4 - 3$ line of CN in the quasar APM 08279+5255 at z=3.9. These are the 4th and 5th molecular species detected at such a high redshift. 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.

Appeared in: A&A 462, L45

The millimetre variability of M 81*. Multi-epoch dual frequency mm-observations of the nucleus of M 81

Schödel R.$(^{1})$, Krips M.$(^{2})$, Markoff S.$(^{3})$, Neri R.$(^{4})$, Eckart A.$(^{1})$
$(^{1})$I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany, $(^{2})$Harvard-Smithsonian Center for Astrophysics, SMA project, 645 North A'ohoku Place, Hilo, HI 96720, USA, $(^{3})$Sterrenkundig Instituut "Anton Pannekoek", Universiteit van Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands, $(^{4})$IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Hères

There are still many open questions as to the physical mechanisms at work in Low Luminosity AGN that accrete in the extreme sub-Eddington regime. Simultaneous multi-wavelength studies have been very successful in constraining the properties of Sgr A*, the extremely sub-Eddington black hole at the centre of our Milky Way. M 81*, the nucleus of the nearby spiral galaxy M 81, is an ideal source to extend the insights obtained on Sgr A* toward higher luminosity AGN. Here we present observations at 3 and 1 mm that were obtained within the framework of a coordinated, multi-wavelength campaign on M 81*. The continuum emission from M 81* was observed during three epochs with the IRAM Plateau de Bure Interferometer simultaneously at wavelengths of 3 and 1 mm. We present the first flux measurements of M 81* at wavelengths around 1 mm. We find that M 81* is a continuously variable source with the higher variability observed at the shorter wavelength. Also, the variability at 3 and 1 mm appears to be correlated. Like Sgr A*, M 81* appears to display the strongest flux density and variability in the mm-to-submm regime. There remains still some ambiguity concerning the exact location of the turnover frequency from optically thick to optically thin emission. The observed variability time scales point to an upper size limit of the emitting region of the order 25 Schwarzschild radii. The data show that M 81* is indeed a system with very similar physical properties to Sgr A* and an ideal bridge toward high luminosity AGN. The data obtained clearly demonstrate the usefulness and, above all, the necessity of simultaneous multi-wavelength observations of LLAGN.

Appeared in: A&A 463, 551

Highly-excited CO emission in APM08279+5255 at z=3.9

A. Weiß$(^{1})$, D. Downes$(^{2})$, R. Neri$(^{2})$, F. Walter$(^{3})$, C. Henkel$(^{1})$, D.J. Wilner$(^{4})$, J. Wagg$(^{4,5})$, and T. Wiklind$(^{6})$
$(^{1})$MPIfR, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{2})$IRAM, Domaine Universitaire, 38406 St-Martin-d'Hères, France, $(^{3})$MPIA, Königstuhl 17, 69117 Heidelberg, Germany, $(^{4})$Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, $(^{5})$Instituto Nacional de Astrofisica, Óptica y Electrónica (INAOE), Aptdo. Postal 51 y 216, Puebla, Mexico, $(^{6})$ESA-Space Telescope Division, STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA

We report the detection of the CO $4-3$, $6-5$, $9-8$, $10-9$, and $11-10$ lines in the Broad Absorption Line quasar APM08279+5255 at z=3.9 using the IRAM 30m telescope. We also present IRAM PdBI high spatial resolution observations of the CO $4-3$ and $9-8$ lines, and of the 1.4mm dust radiation as well as an improved spectrum of the HCN$(5-4)$ line. Unlike CO in other QSO host galaxies, the CO line SED of APM08279+5255 rises up to the CO$(10-9)$ transition. The line fluxes in the CO ladder and the dust continuum fluxes are best fit by a two component model, a ``cold'' component at $\sim65$K with a high density of $n(H_2)= 1\times 10^5$ cm$^{-3}$, and a ``warm'', $\sim 220$K component with a density of $1\times 10^4$ cm$^{-3}$. We show that IR pumping via the 14 micron bending mode of HCN is the most likely channel for the HCN excitation. From our models we find, that the CO(1-0) emission is dominated by the dense gas component which implies that the CO conversion factor is higher than usually assumed for high-z galaxies with $\alpha \simeq 5$ M$_\odot$/(K km/s pc$^2$)$^{-1}$. Using brightness temperature arguments, the results from our high-resolution mapping, and lens models from the literature, we argue that the molecular lines and the dust continuum emission arise from a very compact ( $r \sim 100-300$ pc), highly gravitationally magnified ($m= 60-110$) region surrounding the central AGN. Part of the difference relative to other high-$z$ QSOs may therefore be due to the configuration of the gravitational lens, which gives us a high-magnification zoom right into the central 200-pc radius of APM08279+5255 where IR pumping plays a significant role for the excitation of the molecular lines.

Accepted for publication in A&A

Large-scale molecular shocks in galaxies

Usero A., 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 review our on-going study of the shock-driven molecular gas chemistry in star-forming galaxies, based on observations with the IRAM Plateau de Bure Interferometer. We have obtained high-resolution ( $\sim 5\hbox{$^{\prime\prime}$}$) images of the emission of silicon monoxide (SiO) in the nuclei of the nearby galaxies NGC 253, IC 342 and M 82. From observations in the Galaxy and theoretical models, SiO is known to be a privileged tracer of molecular shock chemistry. The large SiO abundances, $<X(SiO)> \: \sim \:10^{-10} 10^{-9}$, found along several hundreds of pc imply that large-scale shock chemistry must be at play in the inner disks of the three surveyed galaxies. Noticeable differences in the morphology of the SiO emission call to different driving mechanisms, however. In NGC 253 and IC 342, the most plausible scenario is that of shocks arising in cloud cloud collisions, dynamically triggered along the bar potential. In the case of M 82, shocks arise in the disk halo interface, probably boosted by local episodes of mass ejection from the disk. These dissimilarities are explained in terms of the evolutionary stage of the starburst episodes. This work illustrates how high-resolution imaging of specific chemical tracers provide useful inputs to the understanding of galaxy evolution.

Appeared in: NewAR, 51, 75

Anatomy of HH 111 from CO Observations: A Bow-Shock-driven Molecular Outflow

Bertrand Lefloch$(^{1})$, José Cernicharo$(^{2})$, Bo Reipurth$(^{3})$, Juan Ramon Pardo$(^{2})$, Roberto Neri$(^{4})$
$(^{1})$Laboratoire d'Astrophysique de l'Observatoire de Grenoble, Grenoble, France, $(^{2})$Instituto de Estructura de la Materia, Departamento Física Molecular, Madrid, Spain, $(^{3})$Institute for Astronomy, University of Hawaii, Hilo, HI, $(^{4})$IRAM, Domaine Universitaire, St. Martin d'Hères, France

We present single-dish and interferometric millimeter line observations of the HH 111 outflow and its driving source. The physical conditions of the core have been determined from the emission of the millimeter line of CO and its isotopomers and CS with the IRAM 30 m telescope, and the CO $J=7\rightarrow 6$ line with the Caltech Submillimeter Observatory. The emission reveals a small condensation of cold (T$=20-25$ K) and dense gas [ $n(H_2)=3\times10^5$ cm$^{-3}$]. The outflow has been mapped with the IRAM Plateau de Bure interferometer (PdBI). The cold gas is distributed in a hollow cylinder surrounding the optical jet. The formation of this cavity and its kinematics are well accounted for in the frame of outflow gas entrainment by jet bow shocks. Evidence of gas acceleration is found along the cavity walls, correlated with the presence of optical bow shocks. The separation of the inner walls reaches $8\hbox{$^{\prime\prime}$}-10\hbox{$^{\prime\prime}$}$, which matches the transverse size of the wings in the bow shock. CSO observations of the $J=7\rightarrow 6$ line show evidence of a high-velocity and hot gas component ($T=300-1000$ K) with a low filling factor. This emission probably arises from shocked gas in the jet. Observations of the $^3P_2-^3P_1$ [C I] line are consistent with C-type nondissociative shocks. Mapping of the high-velocity molecular bullets B1-B3, located beyond the optical jet, reveals small structures of $3\hbox{$^{\prime\prime}$}\times 7\hbox{$^{\prime\prime}$}$ flattened perpendicular to the flow direction. They are made of cold ($T\sim 30$ K), moderate density gas [ $n(H_2)=(0.5-1.0)\times 10^4$ cm$^{-3}$], expanding into the low-density surrounding medium. Their properties are consistent with their being shocked gas knots resulting from past time-variable ejections in the jet.

Appeared in: ApJ 658, 498

Millimeter imaging of HD 163296: probing the disk structure and kinematics

Andrea Isella$(^{1,2})$, Leonardo Testi$(^{1})$, Antonella Natta$(^{1})$, Roberto Neri$(^{3})$, David Wilner$(^{4})$, and Chunhua Qi$(^{4})$
$(^{1})$Osservatorio Astrofisico di Arcetri, INAF, Largo E.Fermi 5, I-50125 Firenze, Italy, $(^{2})$Dipartimento di Fisica, Universitá di Milano, Via Celoria 16, 20133 Milano, Italy, $(^{3})$Institut de Radio Astronomie Millimétrique (IRAM), 300 Rue de la Piscine, Domaine Universitaire de Grenoble, St. Martin d'Hères F-38406, France, $(^{4})$ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA

We present new multi-wavelength millimeter interferometric observations of the Herbig Ae star HD 163296 obtained with the IRAM/PBI, SMA and VLA arrays both in continuum and in the $^{12}$CO, $^{13}$CO and C$^{18}$O emission lines. Gas and dust properties have been obtained comparing the observations with self-consistent disk models for the dust and CO emission. The circumstellar disk is resolved both in the continuum and in CO.We find strong evidence that the circumstellar material is in Keplerian rotation around a central star of 2.6 M$_\odot$. The disk inclination with respect to the line of sight is $46^\circ \pm 4^\circ$ with a position angle of $128^\circ
\pm 4^\circ$. The slope of the dust opacity measured between 0.87 and 7 mm ($\beta= 1$) confirms the presence of mm/cm-size grains in the disk midplane. The dust continuum emission is asymmetric and confined inside a radius of 200 AU while the CO emission extends up to 540 AU. The comparison between dust and CO temperature indicates that CO is present only in the disk interior. Finally, we obtain an increasing depletion of CO isotopomers from $^{12}$CO to $^{13}$CO and C$^{18}$O. We argue that these results support the idea that the disk of HD 163296 is strongly evolved. In particular, we suggest that there is a strong depletion of dust relative to gas outside 200 AU; this may be due to the inward migration of large bodies that form in the outer disk or to clearing of a large gap in the dust distribution by a low mass companion.

Accepted for publication in A&A

Chemistry in disks I. Deep search for N2H+ in the protoplanetary disks around LkCa 15, MWC 480, and DM Tauri

A. Dutrey$(^{1})$, T. Henning$(^{2})$, S. Guilloteau$(^{1})$, D. Semenov$(^{2})$, V. Piétu$(^{3})$, K. Schreyer$(^{4})$, A. Bacmann$(^{1})$, R. Launhardt$(^{2})$, J. Pety$(^{3})$, and F. Gueth$(^{3})$
$(^{1})$L3AB, Observatoire de Bordeaux, 2 rue de l'Observatoire, BP 89, 33270 Floirac, France, $(^{2})$Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany, $(^{3})$IRAM, 300 rue de la Piscine, 38406 Saint-Martin-d'Hères, France, $(^{4})$Astrophysikalisches Institut und Universitäts-Sternwarte, Schillergässchen 2-3, 07745 Jena, Germany

To constrain the ionization fraction in protoplanetary disks, we present new high-sensitivity interferometric observations of N$_2$H$^+$ in three disks surrounding DM Tau, LkCa 15, and MWC 480. We used the IRAM PdBI array to observe the N$_2$H$^+$ $J = 1-0$ line and applied a $\chi^2$-minimization technique to estimate corresponding column densities. These values are compared, together with HCO$^+$ column densities, to results of a steady-state disk model with a vertical temperature gradient coupled to gas-grain chemistry. Results. We report two N$_2$H$^+$ detections for LkCa 15 and DM Tau at the $5\sigma$ level and an upper limit for MWC 480. The column density derived from the data for LkCa 15 is much lower than previously reported. The [N$_2$H$^+$/HCO$^+$] ratio is on the order of $0.02-0.03$. So far, HCO$^+$ remains the most abundant observed molecular ion in disks. All the observed values generally agree with the modelled column densities of disks at an evolutionary stage of a few million years (within the uncertainty limits), but the radial distribution of the molecules is not reproduced well. The low inferred concentration of N$_2$H$^+$ in three disks around low-mass and intermediate-mass young stars implies that this ion is not a sensitive tracer of the overall disk ionization fraction.

Appeared in: A&A 464, 615

Sulfur chemistry in the Horsehead: An interferometric view of the Horsehead PDR

J.R. Goicoechea$(^{1})$, J. Pety$(^{1,2})$, M. Gerin$(^{1})$, D. Teyssier$(^{3})$, E. Roueff$(^{4})$, P. Hily-Blant$(^{2})$
$(^{1})$LERMA-LRA, UMR 8112, CNRS, Observatoire de Paris and Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris, France, $(^{2})$IRAM, 300 rue de la Piscine, 38406 Grenoble cedex, France, $(^{3})$European Space Astronomy Centre, Urb. Villafranca del Castillo, P.O. Box 50727, Madrid 28080, Spain, $(^{4})$LUTH UMR 8102, CNRS and Observatoire de Paris, Place J. Janssen 92195 Meudon cedex, France


Sulfur is an abundant element which remains undepleted in diffuse interstellar gas ($A_V < 1$) but it is traditionally assumed to deplete on dust grains at higher densities and larger AV. Photodissociation regions (PDRs) are an interesting intermediate medium between translucent and dark clouds where the chemistry and energetics are domi- nated by the illuminating FUV radiation field. Thus they can provide new insights about the sulfur depletion problem. However, physical and chemical gradients in PDRs take place at small angular scales ($\sim 1$ to $10\hbox{$^{\prime\prime}$}$). Aperture synthesis observations are therefore required to resolve such gradients. Besides, a complete understanding of molecular excitation is needed to correctly determine molecular abundances but also the preavailing physical conditions. Hence, multi-J observations at increasing frequencies are also required. Such high an- gular resolution and broad frequency coverage observa- tions will be provided by ALMA in the near future. In this work we present IRAM-PdBI observations of the CS $J=2-1$ line toward the Horsehead PDR comple- mented with IRAM-30m observations of several rota- tional lines of different sulfur bearing molecules (CS, HCS$^+$, SO, H$_2$S, etc.). Photochemical and nonlocal, non-LTE radiative transfer models adapted to the Horsehead geometry have been developed. The gas phase sulfur abundance has been inferred in the PDR.

To appear in: Astrophysics and Space Science, ``Science with ALMA: a new era for Astrophysics'' conf. proc., November 13-17 2006, ed. R. Bachiller

Deuterium fractionation in the Horsehead edge

J. Pety$(^{1,2})$, J. R. Goicoechea$(^{2})$, P. Hily-Blant$(^{1})$, M. Gerin$(^{2})$, and D. Teyssier$(^{3})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 Grenoble Cedex, France, $(^{2})$LERMA, UMR 8112, CNRS, Observatoire de Paris and École Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France, $(^{3})$European Space Astronomy Centre, Urb. Villafranca del Castillo, PO Box 50727, Madrid 28080, Spain

Deuterium fractionation is known to enhance the [DCO$^+$]/[HCO$^+$] abundance ratio over the $D/H \sim 10^{-5}$ elemental ratio in the cold and dense gas typically found in pre-stellar cores. We report the first detection and mapping of very bright DCO$^+$ $J = 3-2$ and $J=2-1$ lines (3 and 4K respectively) towards the Horsehead photodissociation region (PDR) observed with the IRAM-30m telescope. The DCO$^+$ emission peaks close to the illuminated warm edge of the nebula ( $<50\hbox{$^{\prime\prime}$}$ or $\lower.5ex\hbox{$\; \buildrel < \over \sim \;$}0.1$pc away). Detailed nonlocal, non-LTE excitation and radiative transfer analyses have been used to determine the prevailing physical conditions and to estimate the DCO$^+$ and H$^{13}$CO$^+$ abundances from their line intensities. A large [DCO$^+$]/[HCO+$^+$] abundance ratio ($\ge 0.02$) is inferred at the DCO$^+$ emission peak, a condensation shielded from the illuminating far-UV radiation field where the gas must be cold ($10-20$ K) and dense ($2 \times 10^5$ cm$^{-3}$). DCO$^+$ is not detected in the warmer photodissociation front, implying a lower [DCO$^+$]/[HCO$^+$] ratio ($<10^{-3}$). According to our gas phase chemical predictions, such a high deuterium fractionation of HCO$^+$ can only be explained if the gas temperature is below 20K, in good agreement with DCO$^+$ excitation calculations.

Appeared in: A&A 464, L41

Unveiling the Chemistry of Hot Protostellar Cores with ALMA

M. Guélin$(^{1})$, N. Brouillet$(^{2})$, J. Cernicharo$(^{3})$, F. Combes$(^{4})$ and A. Wooten$(^{5})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{2})$Observatoire de Bordeaux, France, $(^{3})$DAMIR/CSIC, Madrid, Spain, $(^{4})$Observatoire de Paris, France, $(^{5})$NRAO, Charlottesville, USA

High angular resolution mm-wave observations of the Orion-KL region, made with the IRAM Plateau de Bure interferometer (PdBI), reveal the presence of several hot cores (A,B, C, D) with distinct spectral signatures (Fig. 5) and different molecular content. The emission from complex molecules seems confined to these cores, the size of which is typically $10^3$ AU. As can be seen on the maps of Fig. 6, the bulk of the emission from ethyl cyanide (CH$_3$CH$_2$CN), vinyl cyanide (CH$_2$CHCN), ethanol (CH$_3$CH$_2$OH) and, to a lesser degree, methanol (CH$_3$OH) arise from such cores. Ethyl- and vinyl cyanide emission is observed in two small sources located few arcsec NE and W of IRC2 (triangle) and devoid of any visible ethanol or methanol emission. The alcohol emission actually peaks in another clump, S of IRC2, called the Orion ``Hot Core''.

Figure 5: Right: PdB interferometer spectra observed toward sources B and D. Left: maps of the emission in the 101 GHz lines of CH$_3$CH$_2$OH, and CH$_3$CH$_2$CN. The continuum emission was subtracted.

The absence of vinyl- and ethyl cyanide in the ``Hot Core'' has yet to be explained. It does not result from a lack of nitrogen as HCN, NH$_3$ and H$_2$CO are abundant in both the NE core and in the ``Hot Core'' (as a matter of fact, the NH$_3$ column density is a factor of 8 larger in the NE core). It is not a temperature effect, as both cores have teperatures $> 150$K, high enough for desorbing from grains most molecular species. The chemical differences may come from the warm-up time of the cores, a critical parameter according to models, which depends on the mass of the protostar.

The emission from each molecule covers only a small fraction (1/10 to 1/30) of the 30-m telescope beam, so that the column densities of the species in the cores are more than one order of magnitude larger than the beam-averaged column densities observed with the 30-m telescope or the JCMT. The abundance ratios between e.g. ethyl- or vinyl cyanide, on the one hand, and ethanol or methyl formate, on the other hand, also differ by large factors from those derived with single dish telescopes. Obviously, the predictions of hot core chemistry models must be compared only with high resolution interferometric observations.

Figure 6: Maps of the emission in the 101 GHz lines of CH$_3$OH, CH$_3$CH$_2$OH, CH$_2$CHCN and CH$_3$CH$_2$CN. The continuum emisssion has been subtracted. First contour and contour steps are 4 or 12 $\sigma $, as indicated. The triangle shows the position of IRC2. Axis are J2000 coordinates.

The PdBI observations were part of a search for interstellar glycine, also carried out with the IRAM 30-m telescope and the Green Bank Telescope. We derive a $3\sigma$ upper limit of $1 \cdot 10^{15}$ cm$^{-2}$ per $2\hbox{$^{\prime\prime}$}\times 3\hbox{$^{\prime\prime}$}$ beam in the Orion Hot Core and Compact Ridge - the lowest to date at this scale.

Accepted for publication in conf. proc: Science with ALMA: a new era for astrophysics, Springer 2007.

The initial conditions of star formation in the Ophiuchus main cloud: Kinematics of the protocluster condensations

Philippe André$(^{1,2})$, Arnaud Belloche$(^{1,3})$, Frédérique Motte$(^{1,2})$ and Nicolas Peretto$(^{1,4})$
$(^{1})$CEA/DSM/DAPNIA, Service d'Astrophysique, C.E. Saclay, Orme des Merisiers, F-91191 Gif-sur-Yvette, France, $(^{2})$Laboratoire AIM, Unité Mixte de Recherche CEA - CNRS - Université Paris Diderot, C.E. Saclay, France, $(^{3})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany, $(^{4})$Physics & Astronomy Department, University of Manchester, P.O. Box 88, Manchester M60 1QD, UK

The earliest phases of clustered star formation and the origin of the stellar initial mass function (IMF) are currently much debated. In one school of thought the IMF of embedded clusters is entirely determined by turbulent fragmentation at the prestellar stage of star formation, while in a major alternative view it results from dynamical interactions and competitive accretion at the protostellar stage. In an effort to discriminate between these two pictures for the origin of the IMF, we investigated the internal and relative motions of starless condensations and protostars previously detected by us in the dust continuum at 1.2 mm in the L1688 protocluster of the Ophiuchus molecular cloud complex. The starless condensations have a mass spectrum resembling the IMF and are therefore likely representative of the initial stages of star formation in the protocluster. We carried out detailed molecular line observations, including some N$_2$H$^+$(1-0) mapping, of the Ophiuchus protocluster condensations using the IRAM 30m telescope. We measured subsonic or at most transonic levels of internal turbulence within the condensations, implying virial masses which generally agree within a factor of $\sim 2$ with the masses derived from the 1.2 mm dust continuum. This supports the notion that most of the L1688 starless condensations are gravitationally bound and prestellar in nature. We detected the classical spectroscopic signature of infall motions in CS(2-1), CS(3-2), H$_2$CO( $2_{12} - 1_{11}$), and/or HCO$^+$(3-2) toward six condensations, and obtained tentative infall signatures toward 10 other condensations. In addition, we measured a global one-dimensional velocity dispersion of less than $0.4$ km s$^{-1}$ (or twice the sound speed) between condensations. The small relative velocity dispersion implies that, in general, the condensations do not have time to interact with one another before evolving into pre-main sequence objects.

Our observations support the view that the IMF is partly determined by cloud fragmentation at the prestellar stage. Competitive accretion is unlikely to be the dominant mechanism at the protostellar stage in the Ophiuchus protocluster, but it may possibly govern the growth of starless, self-gravitating condensations initially produced by gravoturbulent fragmentation toward an IMF, Salpeter-like mass spectrum.

Accepted for publication in A&A

Discovery of Interstellar Propylene (CH$_2$CHCH$_3$): Missing Links in Interstellar Gas-Phase Chemistry

N. Marcelino$(^{1,4})$, J. Cernicharo$(^{1})$, M. Agundez$(^{1})$, E. Roueff$(^{2})$, M. Gerin$(^{3})$, J. Martin-Pintado$(^{1})$, R. Mauersberger$(^{4})$, and C. Thum$(^{5})$
$(^{1})$DAMIR-IEM-CSIC, Spain, $(^{2})$LUTH, Obs. de Paris, France, $(^{3})$LERMA, Obs. de Paris and Ecole Normale Superieure, France, $(^{4})$IRAM, Spain, $(^{5})$IRAM, France

We report the discovery of propylene (also called propene, CH$_2$CHCH$_3$) with the IRAM 30-m radio telescope toward the dark cloud TMC-1. Propylene is the most saturated hydrocarbon ever detected in space through radio astronomical techniques. In spite of its weak dipole moment, 6 doublets (A and E species) plus another line from the A species have been observed with main beam temperatures above 20 mK. The derived total column density of propylene is $4 \times 10^{13}$ cm$^{-2}$, which corresponds to an abundance relative to H$_2$ of $4 \times 10^{-9}$, i.e., comparable to that of other well known and abundant hydrocarbons in this cloud, such as c-C$_3$H$_2$. Although this isomer of C$_3$H$_6$ could play an important role in interstellar chemistry, it has been ignored by previous chemical models of dark clouds as there seems to be no obvious formation pathway in gas phase. The discovery of this species in a dark cloud indicates that a thorough analysis of the completeness of gas phase chemistry has to be done.

Accepted for publication in ApJ Letters

Discovery of Phosphaethyne (HCP) in Space: Phosphorus Chemistry in Circumstellar Envelopes

Marcelino Agúndez$(^{1})$, José Cernicharo$(^{1})$ and Michel Guélin$(^{2})$
$(^{1})$Departamento de Astrofisica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, E-28006 Madrid, Spain, $(^{2})$Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France

We present the first detection in space of phosphaethyne, the phosphorus analogue of HCN. We have observed with the IRAM 30-m telescope four successive rotational transitions of HCP in the AGB star envelope IRC+10216. After PN and CP, HCP is the third phosphorus-bearing molecule identified in the interstellar medium. HCP forms under thermochemical equilibrium in the surroundings of the stellar photosphere, from which it is expelled into space. It locks 3 % of the phosphorus present in the expanding envelope, the remaining most likely being condensed on grains. We further discuss the chemistry of phosphorus in circumstellar envelopes in the light of our findings and speculate on other phosphorus compounds that may be detectable.

Appeared in: ApJ Letters, 662, L91

Particularly Efficient Star Formation in M33

E. Gardan$(^{1})$, J. Braine$(^{1})$, K.F. Schuster$(^{2})$, N. Brouillet$(^{1})$, A. Sievers$(^{2})$
$(^{1})$Université Bordeaux 1, CNRS, Laboratoire d'Astrophysique, Observatoire de Bordeaux, OASU, UMR 5804, Floirac, F-33270, $(^{2})$IRAM, 300 Rue de la Piscine, F-38406 St Martin d'Hères, France

The Star Formation (SF) rate in galaxies is an important parameter at all redshifts and evolutionary stages of galaxies. In order to understand the increased SF rates in intermediate redshift galaxies one possibility is to study star formation in local galaxies with properties frequently found at this earlier epoch like low metallicity and small size. We present sensitive observations of the molecular gas in M33, a small Local Group spiral at a distance of 840 kpc which shares many of the characteristics of the intermediate redshift galaxies. The observations were carried out in the CO$(2-1)$ line with the HERA heterodyne array on the IRAM 30m telescope. A $11^\prime \times 22^\prime$ region in the northern part of M33 was observed, reaching a detection threshold of a few $10^3$M$_\odot$. The correlation in this field between the CO emission and tracers of SF (8$\mu$m, 24$\mu$m, H$_{\alpha}$, FUV) is excellent and CO is detected very far North, showing that molecular gas forms far out in the disk even in a small spiral with a subsolar metallicity. One major molecular cloud was discovered in an interarm region with no HI peak and little if any signs of SF - without a complete survey this cloud would never have been found. The radial dependence of the CO emission has a scale length similar to the dust emission, less extended than the H or FUV. If, however, the $N(H_2)/I_{CO}$ ratio varies inversely with metallicity, then the scale length of the H$_2$ becomes similar to that of the H or FUV. Comparing the SF rate to the H$_2$ mass shows that M33, like the intermediate redshift galaxies it resembles, has a significantly higher SF eciency than large local universe spirals. The data presented here also provide an ideal test for theories of molecular cloud formation and cover a new region in parameter space, where $\sum_{stars} < \sum_{gas}$. We find that a simple pressure-based prescription for estimating the molecular to atomic gas fraction does not perform well for M33, at least in the outer parts. On the other hand, we show that the molecular gas fraction is influenced by (i) the total Hydrogen column density, dominated in M33 by the HI, and (ii) the galactocentric distance.

Accepted for publication in A&A

Imaging of thermal domains in ultra-thin NbN films for hot electron bolometers

D. Doenitz$(^{1})$, R. Keller$(^{1})$, D. Koelle$(^{1})$, T. Scherer$(^{2})$, K.F.Schuster$(^{2})$
$(^{1})$Physikalisches Institut-Experimentalphysik II, Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany, $(^{2})$Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St. Martin d'Hères, France

The authors present low-temperature scanning electron microscopy (LTSEM) investigations of superconducting microbridges made from ultrathin NbN films as used for hot electron bolometers. LTSEM probes the thermal structure within the microbridges under various dc bias conditions, either via electron-beam-induced generation of an unstable hot spot or via the beam-induced growth of a stable hot spot. Such measurements reveal inhomogeneities on a micron scale, which may be due to spatial variations in the NbN film or film-interface properties. Comparison with model calculations for the stable hot spot regime confirms the basic features of common hot spot models.

Accepted for publ. in: Applied Physics Letters 90, 1

Fabrication of sub-micrometer SIS Junctions for Radio Astronomy

N. Krebs$(^{1})$, A. Barbier$(^{1})$, D. Billon-Pierron$(^{1})$, S. Halleguen$(^{1})$, M. Schicke$(^{1})$ and K. F. Schuster$(^{1})$
$(^{1})$Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St. Martin d'Hères, France

We present a new fabrication scheme for high quality Nb-AlOx-Nb junctions as used for mm-wave mixers in radio astronomy. The key features of the fabrication process are high-resolution e-beam lithography for junction and contact definition as well as highly selective Niobium and SiO$_2$ inductively coupled plasma etching. Chemical-mechanical polishing, which is difficult to control for low volume production is not required. We further show that a new type of spin-on glass can be used as a reliable replacement for sputtered SiO$_2$. We present yield and parameter scattering of these devices.

Accepted for publ. in: IEEE Trans. Appl. Supercond.

Niobium SupraMEMS for Reconfigurable Millimeter Wave Filters

Matthias Schicke$(^{1})$, Alessandro Navarrini$(^{2})$, Philippe Ferrari$(^{3})$, Teresa Zöpfl$(^{4})$, Franz Wittmann$(^{4})$, Witek Bedyk$(^{4})$, Gabi Schrag$(^{4})$, and Karl-Friedrich Schuster$(^{1})$
$(^{1})$IRAM, 300, rue de la Piscine, Domaine Universitaire de Grenoble, 38406 St. Martin d'Hères Cedex, France, $(^{2})$Osservatorio Astronomico di Cagliari /INAF Loc. Poggio dei Pini, Strada 54 09012 Capoterra (CA) - Italy, $(^{3})$Institute for Microelectronics Electromagnetism and Photonics (IMEP) - INPG/Université Joseph Fourier, 23 rue de Martyrs, 38016 Grenoble, France, $(^{4})$Institute for Physics of Electrotechnology, Munich University of Technology, Arcisstraße 21, 80290 Munich, Germany

Reconfigurable passive superconducting devices for the mm-wave regime offer a large spectrum of novel applications in scientific and industrial remote sensing. Several groups have reported on cm-wave devices. We developed a surface mounted Niobium (Nb) MEMS technology that can be integrated with a wide range of cryogenic semiconductor and superconducting circuits. A first generation of circuits using our Niobium SupraMEMS has been optimized for radio astronomical applications. In this paper we present the micro-mechanical and electrical characterization of the devices. Mechanical modeling results in an improved understanding of the specific behavior of metallic cryogenic MEMS devices. The influence of the fabrication procedure on the mechanical properties of the devices and the resulting limitations are discussed. A particular design for improved tuning range has been investigated.

Accepted for publ. in in: IEEE Trans. Appl. Supercond.

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