Scientific Results in Press

Molecular outflows in intermediate-mass star forming regions: the case of CB3

C. Codella(^1,2) and R. Bachiller(¹)
(¹) Observatorio Astronomico Nacional (IGN), Apartado 1143, E-28800 Alcalá de Henares (Madrid), Spain, (²) Istituto di Fisica dello Spazio Interplanetario, CNR, Area di Ricerca Tor Vergata, Via Fosso del Cavaliere, 00133 Roma, Italy

Abstract:

The intermediate-mass star forming region in the Bok globule CB3 has been investigated through a multiline survey at mm-wavelengths. We have detected a chemically rich bipolar outflow, driven by a probably Class 0 submillimetre source, which reveals different clumps along the main axis, indicating episodic increases of the mass loss process. The outflow is quite massive (4 $M_{\rm\odot}$) and very powerful, since the kinetic energy is 5.5 10⁴⁵ ergs and the mechanical luminosity is 5.6 $L_{\rm\odot}$. The outflow motion is able to affect the structure of the globule and to clear a significant amount of the high-density gas hosting the star forming process. The dynamical flow parameters, as well as the analysis of the CO velocity profiles, place the CB3 outflow close to the HH7-11 and NGC2071 ones. The CS maps reveal the molecular clump around the driving source, while the CS line profiles show a self-absorption feature consistent with the presence of infall motions. The CH₃OH and SiO molecules are present only along the main outflow axis, confirming their close association with outflows, and their emission allows to detect the jet-like outflow structure and to point out four clumps with size less than 0.1 pc. We have detected two episodic mass losses, with ages of about 10⁴ and 10⁵ yr, indicating that the CB3 outflow is in a quite evolved evolutionary stage. Moreover, also the emission of S-bearing molecules such as SO, SO₂, H₂S and OCS is definitely enhanced towards the outflow. We have derived quite high densities, close to 10⁵-10⁶ cm^-3, and the indication that SiO is tracing gas at higher density with respect to SO and CH₃OH. The SiO molecule traces the highest velocity jet-like structure, while SO and CH₃OH play an intermediate role between SiO and CO, being associated with more extended regions produced by interaction of the mass loss with the surrounding gas. We have found SO/H₂S $\sim$ SO₂/H₂S $\ge$ 1, SO/SO₂ $\simeq$ 1, OCS/H₂S $\ge$ 1 and SO/SiO $\gg$1. These column density ratios, used as crude chemical clocks, indicate that the CB3 outflow in a relatively evolved evolutionary stage, in agreement with the age estimations based on its dynamics.

Accepted for publication in A&A
Preprints available at http://www.ifsi.rm.cnr.it or http://www.oan.es/preprints/lista.html
E-mail contact: codella@ifsi.rm.cnr.it

Interferometric mapping of a $\sim 600$pc SiO/H¹³CO⁺circumnuclear disk in the starburst galaxy NGC253

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

Abstract:

This paper presents the first high-resolution SiO map made in an external galaxy (Fig. 2). The nucleus of the nearby barred spiral NGC253 has been observed simultaneously in the v=0, J=2-1 line of SiO and in the J=1-0 line of H¹³CO⁺ with the IRAM interferometer, with a resolution of 7.5 $\mbox{$''$ }\times$2.6 $\mbox{$''$ }$. Emission from SiO and H¹³CO⁺ is extended in the nucleus of NGC253. The bulk of the SiO/ H¹³CO⁺ emission arises from a 600pc$\times$250pc circumnuclear disk (CND) with a double ringed structure. The inner ring (I), of radius r=60pc, viewed edge-on along PA=51$^\circ$, hosts the nuclear starburst; the outer pseudo-ring (II) opens out as a spiral-like arc up to r=300pc. The kinematics of the gaseous disk, characterized by strong non-circular motions, is interpreted in terms of the resonant response of the gas to the barred potential. The inner ring would correspond to the inner Inner Lindblad Resonance(iILR), whereas the outer region is linked to the onset of a trailing spiral wave across the outer ILR (oILR). Most notably, we report the detection of a molecular gas counterpart of the giant outflow of hot gas, previously seen in X-ray and optical lines, and tentatively identified as a dust chimney in the the 450$\mu$continuum band.

The SiO shows a high average fractional abundance in the CND of X(SiO)=1.5$\times$10^-10. This is more than an order of magnitude above the predicted value of a PDR. Moreover, X(SiO) varies at least by an order of magnitude between the inner starburst region, which dominates the global emission, where we derive X(SiO)= 1-2$\times$10^-10, and the outer region, where X(SiO) reaches a few 10^-9. SiO abundance is also significantly enhanced in the outflow (X(SiO)=3-5$\times$10^-10). Different mechanisms are explored to explain the unlike chemical processing of molecular gas within the nucleus.

  

Figure: (a,top): Emission contours of the 3mm (86.7GHz) continuum source at the center of NGC253. x and y are offsets (in arcsec) with respect to the dynamical center derived in this work, at $\alpha _{J2000}$= 00^h47^m33.18^s, $\delta _{J2000}$=- $25^{\circ }17'17.2''$; x and y axes are parallel to the major and minor axes of the stellar bar, respectively (x runs parallel to PA_bar=68$^\circ$). Contours are -1.5, 1.5, 2.5, 4, 5.5, 8 and 13 to 64 mJybeam^-1 by steps of 9 mJybeam^-1. 1$\sigma$-noise level is 0.44 mJybeam^-1. (b,middle): SiO(v=0,J=2-1) integrated intensity contours towards the center of NGC253. Contours are -0.2, 0.2 to 2.2 Jy.kms^-1beam^-1 by steps of 0.25 Jy.kms^-1beam^-1. 1$\sigma$-noise level in the integrated intensity is 0.07 Jy.km s^-1beam^-1. Orientation as in Figure 1a. Rings I and II are highlighted (see text). (c,bottom): same as (b) but for the J=1-0 line of H¹³CO⁺, with same contours, noise level and orientation.

To appear in A&A
Preprints can be obtained from
http://iram.fr/papers/papers.html

Gas-rich galaxy pair unveiled in the lensed quasar 0957+561

P.Planesas(¹), J.Martín-Pintado(¹), R.Neri(²), L.Colina(³)
(¹) OAN (IGN), Apartado 1143, E-28800 Alcalá de Henares, Madrid, Spain, (²) IRAM, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France, (³) CSIC-UC, Facultad de Ciencias, E-39005 Santander, Spain

Abstract:

Molecular gas in the host galaxy of the lensed quasar 0957+561 at the redshift of 1.41 has been detected in the carbon monoxide line. This detection shows the extended nature of the molecular gas distribution in the host galaxy and the pronounced lensing effects due to the differentially magnified CO luminosity at different velocities. The estimated mass of molecular gas is about $4\,10^9$M$_\odot$, a molecular gas mass typical of a spiral galaxy like the Milky Way. A second, weaker component of CO is interpreted as arising from a close companion galaxy that is rich in molecular gas and has remained undetected so far. Its estimated molecular gas mass is 1.4$\,10^9$solar masses, and its velocity relative to the main galaxy is 660km.s^-1. The ability to probe the molecular gas distribution and kinematics of galaxies associated with high-redshift lensed quasars can be used to improve the determination of the Hubble constant H₀.

Appeared in Science, 1999, 286, 2493

Gas-rich galaxy pair unveiled in the lensed quasar 0957+561

A.Natta(¹), T.Prusti(²), R.Neri(³), W.F.Thi(⁴), V.P.Grinin(⁵), V.Mannings(⁶)
(¹)OA-Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy, (²)SSD-ESA, Villafranca del Castillo, E-28020 Madrid, Spain, (³)IRAM, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France, (⁴)Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands, (⁵)Crimean Astrophysical Observatory, 334413 Nauchny, Ukraine, (⁶)CalTec, MS 169-327, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Abstract:

This paper presents new observations of UX Ori obtained with the millimeter interferometer of Plateau de Bure and with ISO. UX Ori is the prototype of a group of pre-main-sequence, intermediate-mass stars, often indicated as precursors of beta Pic. The interferometry observations at 1.2 and 2.6mm show that UX Ori has a circumstellar disk, with outer radius $\le 100\,$AU. We determine the spectral index between these two wavelengths to be 2.1$\pm$0.2, consistent with the disk being optically thick at mm wavelengths. Alternatively, the disk solid matter can be in the form of ``pebbles" (radius $\sim 10\,$cm). In both cases most of the disk mass must be in gas form, and small grains must be present, at least in the disk atmosphere. In both cases also, the disk must be rather massive ( $\ge 0.1\,$M$_\odot$). The existence of a circumstellar disk supports the model of the UXOR phenomenon in terms of a star+disk system. Self-consistent models of almost edge-on disks account well for the observed emission at all wavelengths longer than about 8$\,\mu$m, if we include the emission of the optically thin, superheated layers that enshroud the disk. These rather simple disk models fail to account for the strong emission observed in the near-IR (i.e., between $\sim 2$ and $7\,\mu$m), and we suggest a number of possible explanations.

Appeared in A&A, 1999, 350, 541

Carbon dioxide-methanol intermolecular complexes in interstellar grain mantles

E. Dartois(^1,2), K. Demyk (²), L. d'Hendecourt(²), P. Ehrenfreund,(³)
(¹)Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères,France, (²) Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, 91405 Orsay Cedex, France, (³) Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands

Abstract:

We present new laboratory data to interpret the Infrared Space Observatory (ISO) spectra of protostellar objects, and particularly RAFGL7009S. Our experimental results show that solid methanol and carbon dioxide exhibit specific intermolecular interactions.

  

Figure 3: Upper panel: schematic representation of the possible complex geometry between the CO₂ and CH₃OH interstellar ices. Lower panel: CO₂ bending mode band shape following the complex formation as measured in the laboratory in different mixtures (dashed and dotted line) as compared to ISO Short Wavelength Spectrometer data for RAFGL7009S and S140 protostellar objects.

We propose the formation of a Lewis acid-base complex between carbon dioxide and methanol molecules to explain specific substructure of the 15.2$\mu$m CO₂ bending mode observed in different objects. The various CO₂ bending mode patterns (Fig. 3) observed in many lines of sight can be interpreted as a combination of both this complex formation and the temperature evolution of the ices. The temperature induced segregation of ice mantles containing CO₂ can be monitored by the ¹³CO₂ stretching mode shift toward the pure CO₂ ice position. The large width observed for this mode towards interstellar sources partly results from the different temperatures sampled along the line of sight. Given the amount of methanol involved in RAFGL7009S, on the basis of ground based observations, we derive that about half of the so called ``6.85$\mu$m'' band and a quarter of the 4.9$\mu$m bands can be accounted for by the deformation modes and 2$\nu_8$ transitions of CH₃OH. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Appeared in A&A 1999, 351, 1066

CO detection of the extremely red galaxy HR10

Paola Andreani(¹),Andrea Cimatti(²),Laurent Loinard(³), Huub Röttgering(⁴)
(¹)Osservatorio Astronomico di Padova vicolo dell'Osservatorio 5, I-35122 Padova, Italy, Present-address: Max-Planck I. f. extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany, (²)Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy, (³)Institut de Radioastronomie Millimétrique, 300, rue de la Piscine, St. Martin d'Hères, France, (⁴)Sterrewacht Leiden, Sterrewacht, Postbus 9513, Leiden 2300 RA the Netherlands

Abstract:

CO J = 5 - 4 and J = 2 - 1 emission lines were detected towards the extremely red galaxy (ERG) HR10 (J164502+4626.4) at z=1.44. The CO intensities imply a molecular gas mass M(H$_{\rm 2}$) of $1.6 \times 10^{11}$ h $^{-2}_{\rm 50}$ M$_\odot$, and, combined with the intensity of the dust continuum, a gas-to-dust mass ratio around 200-400 (assuming galactic values for the conversion factors). The peak of the CO lines are at the same redshift as the [OII]3727 line, but blue-shifted by 430 km s^-1 from the H$\alpha$ line. These CO detections confirm the previous results that HR10 is a highly obscured object with a large thermal far-infrared luminosity and a high star-formation rate. The overall properties of HR10 (CO detection, L $_{\rm FIR}$ to L $^\prime_{\rm CO}$ ratio, and FIR to radio flux ratio) clearly favour the hypothesis that its extreme characteristics are related to star-formation processes rather than to a hidden AGN.

Accepted for publiction in A&A Letters

The Structure and Stability of Interstellar Molecular Absorption Line Profiles at Radio Frequencies

H. Liszt(¹) and R. Lucas(²)
(¹)NRAO, 520 Edgemont Road, Charlottesville, VA, USA 22903-2475, (²)IRAM, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France

Abstract:

We have taken new, broader-band and higher-resolution profiles of Galactic 1667 MHz OH and 89.2 GHz HCO⁺ absorption toward several compact, extragalactic mm-wave continuum sources. The profiles are generally stable - quite similar between epochs and between the two species - but with occasional time-variations and differences. Typical linewidths are 1.0 kms^-1 (FWHM) in either OH or HCO⁺ and there are no differences in mean velocity. Profiles are compound but do not show broad wings, multiplicity, assymmetry, or other phenomena strikingly indicative of formation under extraordinary circumstances, consistent with the low ambient thermal pressures reflected in the weak rotational excitation of CO and HCO⁺.

However, we have also discovered the existence of a low-lying, broad component of HCO⁺ absorption covering just those portions of the spectrum where $\tau_{\rm HI} \geq 0.1-0.2~{\rm at}~\lambda 21$ cm. Toward B0355+508 at b = -1.6 , HCO⁺ absorption extends continuously over more than 40 kms^-1. The broadly-distributed HCO⁺ absorption can be understood in terms of the known molecular fraction of local gas, as long as HCO⁺ is generally present at about its typical abundance n(HCO⁺)/n( $\mbox{H$_2$ }$) = $2 \times 10^{-9}$. The fact that CO forms rapidly from HCO⁺ in diffuse gas then suffices to account for the abundance of CO in diffuse/translucent material over the entire range $10^{12} \leq N({\rm CO}) \leq 10^{16}~\mbox{cm$^{-2}$ }$, $10^{19} \leq \mbox{H$_2$ }\leq 10^{21}~\mbox{cm$^{-2}$ }$, using otherwise standard cloud models.

Using models of molecular formation and excitation and the H- $\mbox{H$_2$ }$, C⁺-CO transition in diffuse gas, and noting the absence of HCO⁺ emission at levels of 0.02-0.05 K, we show very directly that the line profile variations are not the result of AU-sized inclusions of high hydrogen volume density, in the manner usually inferred. Instead, it is necessary to account for small-scale chemical and other inhomogeneities.

Accepted for publiction in A&A

SiO in Diffuse, Translucent And `Spiral-Arm' Clouds

R. Lucas(¹) and H. S. Liszt(²)
(¹)IRAM, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France, (²)NRAO, 520 Edgemont Road, Charlottesville, VA, USA 22903-2475

Abstract:

Using the Plateau de Bure interferometer, we searched for thermal SiO J=1-2 absorption at 86 GHz from the diffuse and translucent clouds which lie toward our sample of extragalactic continuum sources. SiO is present at a level N(SiO)/N(HCO⁺) $\approx 0.01 - 0.1$, or N(SiO)/N( $\mbox{H$_2$ }$) $\approx 2 \times 10^{-11} - 2\times 10^{-10}$. N(SiO) declines with increasing N(HCO⁺) and with increasing thermal pressure measured in the J=1-0 lines of CO. SiO is grossly underabundant, even compared to the known gas-phase depletion of Si in diffuse clouds.

To pursue the subject further, we mapped the H¹³CO⁺ J=1-0 and SiO J=2-1 lines toward the core of W49A: SiO and many other molecular absorption lines have been studied in spiral-arm' clouds seen along the galactic plane at v = 40 and 60 kms^-1 using single dishes. H¹³CO⁺ absorbs quite strongly at these velocities, with column densities at least 3-4 times larger than in any of the clouds we have studied toward extragalactic sources. But SiO absorption is absent at 40 kms^-1 and perhaps at 60 kms^-1 as well since the latter is overlaid by a series of dimethyl ether lines originating in the dense core of the W49A molecular gas: the dimethyl ether was not recognized as such in singledish absorption profiles. Our upper limit for SiO in the `spiral-arm' cloud at 40 kms^-1 is consistent with the trends seen in the more diffuse gas at higher galactic latitudes toward the extragalactic sources.

Accepted for publiction in A&A

Detection of CO in the inner part of M31's bulge

A.-L. Melchior(¹), F. Viallefond(²), M. Guélin(³), N. Neininger(⁴)
(¹)Astronomy Unit, Queen Mary and Westfield College, Mile End Road, London E14NS, UK, (²)DEMIRM, Observatoire de Paris, UMR8540, 61 Avenue de l'Observatoire, 75014 Paris Cédex, France, (³)IRAM, 300 rue de la Piscine, F-38406 St.Martin d'Hères, France, (⁴)Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Abstract:

  

Figure 4: ¹²CO(1-0) and ¹²CO(2-1) spectra obtained for the complex D395A/393/384 in the bulge of M31.

We report the first detection of CO in M31's bulge. The ¹²CO (1-0) and (2-1) lines are both detected in the dust complex D395A/393/384, at 1 $\hbox{$.\mkern-4mu^\prime$ }$3 ($\sim 0.35$ kpc) from the centre (Fig. 4). From these data and from visual extinction data we derive a CO-luminosity to reddening ratio (and a CO-luminosity to H₂ column density ratio) quite similar to that observed in the local Galactic clouds. The (2-1) to (1-0) line intensity ratio points to a CO rotational temperature and a gas kinetic temperature > 10 K. The molecular mass of the complex, inside a diameter of 25'' (100 pc), is 1.5 10⁴ $M_\odot$.

MNRAS, in press

Formation of molecular gas in the debris of violent galaxy interaction

J. Braine(¹), U. Lisenfeld(²), P.-A. Duc(³), S. Léon(⁴)
(¹)Observatoire de Bordeaux, UMR 5804, CNRS/INSU, B.P. 89, F-33270 Floirac, France, (²)IRAM, Avenida Divina Pastora 7 NC, 18012 Granada, Spain, (³)Institute of Astronomy, Madingley Rd. Cambridge, CB3OHA, UK, and CNRS and CEA/DSM/DAPNIA Service d'Astrophysique, Saclay, 91191 Gif sur Yvette Cedex, France, (⁴)ASIAA, Academica Sinica, P.O. Box 1-87, Nanking, Taipei 115, Taiwan

Abstract:

In many gravitational interactions between galaxies, gas and stars that have been torn from either or both of the precursor galaxies can collect in 'tidal tails'. Star formation begins anew in these regions to produce 'tidal dwarf galaxies' (TDGs), giving insight into the process of galaxy formation through the well-defined timescale of the interaction. But tracking the star formation process has proved to be difficult: the TDGs with stars showed no evidence of molecular gas out of which new stars form. Here we report the first discovery of molecular gas (CO emission) in two TDGs (Arp 105 and Arp 245) with the IRAM 30m telescope. In both cases, the molecular gas peaks at the same location as the maximum in HI density, unlike most gas-rich galaxies. We infer from this that the molecular gas formed from the HI, rather than being torn in molecular form from the interacting galaxies. Star formation in the tidal dwarfs therefore appears to mimic that process in normal spiral galaxies like our own.

Nature, in press