Scientific Results in Press

Mapping the cold molecular gas in a cooling flow cluster: Abell 1795

Philippe Salomé(¹) and Françoise Combes(¹)
(¹)LERMA, Observatoire de Paris, 61 av. de l'Observatoire, 75014 Paris, France

Abstract:
Cold molecular gas is found in several clusters of galaxies (Edge, 2001, Salomé & Combes, 2003): single dish telescope observations in CO(1-0) and CO(2-1) emission lines have revealed the existence of large amounts of cold gas (up to $\propto10^{11}$M$_\odot$

Molecular gas in NUclei of GAlaxies (NUGA). II. The ringed LINER NGC 7217

F. Combes(¹), S. García-Burillo(²), F. Boone(³), L.K. Hunt(⁴), A.J. Baker(⁵), A. Eckart(⁶), P. Englmaier(⁷), S. Leon(⁸), R. Neri(⁹), E. Schinnerer(¹⁰), L.J. Tacconi(¹¹)
(¹)Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France, (²)Observatorio Astronómico Nacional (OAN), Alfonso XII, 3, 28014 Madrid, Spain, (³)Bochum University, Universitätstrasse 150, 44780 Bochum, Germany, (⁴)Istituto di Radioastronomia/CNR, Largo Enrico Fermi 5, 50125 Firenze, Italy, (⁵)Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany, (⁶)I. Physikalisches Institut, Universität zu Köln, Zülpicherstrasse 77, 50937 Köln, Germany, (⁷)Astronomy, Universtät Basel, Venusstrasse 7, CH 4102 Binningen, Switzerland, (⁸)Instituto de Astrofísica de Andalucía (CSIC), Camino Bajo de Huétor, 24, 18008 Granada, Spain, (⁹)IRAM-Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, 38406 St. Martin d'Hères, France, (¹⁰)NRAO, PO Box 0, Socorro, NM-87801, USA, (¹¹)Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

Abstract:
We present CO(1-0) and CO(2-1) maps of the LINER galaxy NGC 7217, obtained with the IRAM interferometer, at $2.4 \hbox{$^{\prime\prime}$ }\times 1.9 \hbox{$^{\prime\prime}$ }$ and $1.2\hbox{$^{\prime\prime}$ }\times 0.8 \hbox{$^{\prime\prime}$ }$ resolution respectively. The nuclear ring (at $r=12\hbox{$^{\prime\prime}$ }=0.8$ kpc) dominates the CO maps, and has a remarkable sharp surface density gradient at its inner edge. The latter is the site of the stellar/H$\alpha$ ring, while the CO emission ring extends farther or is broader (500-600 pc). This means that the star formation has been more intense toward the inner edge of the CO ring, in a thin layer, just at the location of the high gas density gradient. The CO(2-1)/CO(1-0) ratio is close to 1, typical of warm optically thick gas with high density. The overall morphology of the ring is quite circular, with no evidence of non-circular velocities. In the CO(2-1) map, a central concentration might be associated with the circumnuclear ionized gas detected inside r=3 $^{\prime\prime}$ and interpreted as a polar ring in the literature. The CO(2-1) emission inside 3 $^{\prime\prime}$ coincides with a spiral dust lane, clearly seen in the HST V - I color image.

N-body simulations including gas dissipation and star formation are performed to better understand the nature of the nuclear ring observed. The observed rotation curve of NGC 7217 allows two possibilities, according to the adopted mass for the disk: (1) either the disk is massive, allowing a strong bar to develop, or (2) it is dominated in mass by an extended bulge/stellar halo, and supports only a mild oval distortion. The amount of gas also plays an important role in the disk stability, and therefore the initial gas fraction was varied, with star formation reducing the total gas fraction to the observed value.

The present observations support only the bulge-dominated model, which is able to account for the nuclear ring in CO and its position relative to the stellar and H$\alpha$ ring. In this model, the gas content was higher in the recent past (having been consumed via star formation), and the structures formed were more self-gravitating. Only a mild bar formed, which has now vanished, but the stars formed in the highest gas density peaks toward the inner edge of the nuclear ring, which corresponds to the observed thin stellar ring. We see no evidence for an ongoing fueling of the nucleus; instead, gas inside the ring is presently experiencing an outward flow. To account for the nuclear activity, some gas infall and fueling must have occured in the recent past (a few Myr ago), since some, albeit very small, CO emission is detected at the very center. These observations have been made in the context of the NUclei of GAlaxies (NUGA) project, aimed at the study of the different mechanisms for gas fueling of AGN. Based on observations carried out with the IRAM Plateau de Bure Interferometer and IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Appeared in: A& A, 414, 857-872 (2004)

IRAS 23385+6053: A candidate protostellar massive object

F. Fontani(¹), R. Cesaroni(²), L. Testi(²), C.M. Walmsley(²), S. Molinari(³) R. Neri(⁴); D. Shepherd(⁵), J. Brand(⁶), F. Palla(²) and Q. Zhang(⁷)
(¹)Dipartimento di Astronomia e Fisica dello spazio, Largo E. Fermi 2, 50125 Firenze, Italy, (²)INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy, (³)IFSI, CNR, via Fosso del Cavaliere, 00133 Roma, Italy, (⁴)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, (⁵)National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA, (⁶)Istituto di Radioastronomia, CNR, via Gobetti 101, 40129 Bologna, Italy, (⁷)Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Abstract:
We present the results of a multi-line and continuum study towards the source IRAS 23385+6053 performed with the IRAM-30 m telescope, the Plateau de Bure Interferometer, the Very Large Array Interferometer and the James Clerk Maxwell Telescope. We have obtained single-dish maps in the C¹⁸O (1-0), C¹⁷O (1-0) and (2-1) rotational lines, interferometric maps in the CH₃C₂H (13-12) line, NH₃(1,1) and (2,2) inversion transitions, and single-pointing observations of the CH₃C₂H(6-5), (8-7) and (13-12) rotational lines. The new results confirm our earlier findings, namely that IRAS 23385+6053 is a good candidate high-mass protostellar object, precursor of an ultracompact HII region.

The source is roughly composed of two regions: a molecular core $\approx 0.03 / 0.04$ pc in size, with a temperature of $\approx 40$ K and an H₂volume density of the order of 10⁷  cm^-3, and an extended halo of diameter $\approx 0.4$ pc, with an average kinetic temperature of $\approx 15$ K and H₂volume density of the order of 10⁵ cm^-3. The core temperature is much smaller than what is typically found in molecular cores of the same diameter surrounding massive ZAMS stars. From the continuum spectrum we deduce that the core luminosity is between 150 and $1.6 \times 10^4$ L$_\odot$

Non-Gaussian velocity shears in the environment of low mass dense cores

Jerôme Pety(¹) and Edith Falgarone(²)
(¹)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France, (²)LERMA/LRA, Observatoire de Paris & École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France

Abstract:
We report on a novel kind of small scale structure in molecular clouds found in IRAM-30m and CSO maps of ¹²CO and ¹³CO lines around low mass starless dense cores. These structures come to light as the locus of the extrema of velocity shears in the maps, computed as the increments at small scale ( $\approx 0.02$ pc) of the line velocity centroids. These extrema populate the non-Gaussian wings of the shear probability distribution function (shear-PDF) built for each map. They form elongated structures of variable thickness, ranging from less than 0.02 pc for those unresolved, up to 0.08 pc. They are essentially pure velocity structures. We propose that these small scale structures of velocity shear extrema trace the locations of enhanced dissipation in interstellar turbulence. In this picture, we find that a significant fraction of the turbulent energy present in the field would be dissipating in structures filling less than a few % of the cloud volume.

Appendices A, B and Figs. 5, 13-15, 17 and 18 are only available in electronic form at http://www.edpsciences.org

Appeared in: A&A 412, 417-430 (2003)

The association between masers and outflows in massive star forming regions

C. Codella(¹), A. Lorenzani(¹), A.T. Gallego(²), R. Cesaroni(³) and L. Moscadelli(⁴)
(¹)Istituto di Radioastronomia, CNR, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy, (²)IRAM, Avda Divina Pastora 7, Núcleo Central, 18012 Granada, Spain, (³)INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy, (⁴)INAF, Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, 09012 Capoterra (Cagliari), Italy

Abstract:
We report the results of a single-dish survey of molecular outflows towards a homogeneous sample of 136 ultracompact H II regions for which we had previously obtained observations in the methanol 6.7 GHz and water 22.2 GHz maser lines. The line profiles of the ¹³CO J = 1-0 and 2-1 transitions have been compared to those of the corresponding lines of the C¹⁸O isotopomer to reveal the occurrence of line wings and hence of molecular outflows. We found 53 outflows resulting in an overall detection rate of $\sim$39$\%$. The probability to have an outflow increases to about 50$\%$ in regions with maser emission, whereas it is about 25$\%$ in those without masers. If we consider just the outflow sources, the chance to find a maser is very high: 74$\%$, without a significant difference between H₂O and CH₃OH. These results strongly confirm from a statistical point of view that both types of masers are closely associated with the evolutionary phase when outflows occur.
The temperatures and optical depths of the molecular cloud hosting the ultracompact H II regions and the comparison between the detection rates suggest a tentative evolutionary scheme for massive star forming regions: the earliest phase is associated with maser emission and with an outflow not yet developed enough to be detected with single-dish observations; then maser emission disappears while the outflow is still present; and finally, only the ultracompact H II region without masers or outflows is present.

Accepted by A&A