Scientific Results in Press

Molecular line study of the very young protostar IRAM 04191 in Taurus: Infall, rotation, and outflow

A. Belloche(¹), P. André(¹), D. Despois(²), S. Blinder(^2,3)
(¹)Service d'Astrophysique, CEA/DSM/DAPNIA, C.E. Saclay, F-91191, Gif-sur-Yvette Cedex, France, (²)Observatoire de Bordeaux (INSU/CNRS), B.P. 89, F-33270 Floirac, France, (³)Division of Nuclear Medicine, Vancouver Hospital and Health Sciences Center, Vancouver, B.C., Canada

Abstract:
We present a detailed millimeter spectroscopic study of the circumstellar environment of the low-luminosity Class 0 protostar IRAM 04191 + 1522 in the Taurus molecular cloud. Molecular line observations with the IRAM 30m telescope demonstrate that the $\sim 14000$ AU radius protostellar envelope is undergoing both extended infall and fast, differential rotation. Radiative transfer modeling of multitransition CS and C³⁴S maps indicate an infall velocity $v_{\rm inf} \sim 0.15$ km s^-1 at $r \sim 1500$ AU and $v_{\rm inf} \sim 0.1$ km s^-1 up to $r \sim 11000$ AU, as well as a rotational angular velocity $\Omega \sim 3.9 \times 10^{-13}$  rad s^-1, strongly decreasing with radius beyond 3500 AU down to a value $\Omega \sim$ 1.5-3 $\times 10^{-14}$ rad s^-1 at $\sim$ 11000 AU. Two distinct regions, which differ in both their infall and their rotation properties, therefore seem to stand out: the inner part of the envelope ( $r \lower.5ex\hbox{$\; \buildrel < \over \sim \;$ }2000-4000$ AU) is rapidly collapsing and rotating, while the outer part undergoes only moderate infall/contraction and slower rotation. These contrasted features suggest that angular momentum is conserved in the collapsing inner region but efficiently dissipated due to magnetic braking in the slowly contracting outer region. We propose that the inner envelope is in the process of decoupling from the ambient cloud and corresponds to the effective mass reservoir ( $\sim 0.5\, M_\odot$) from which the central star is being built. Comparison with the rotational properties of other objects in Taurus suggests that IRAM 04191 is at a pivotal stage between a prestellar regime of constant angular velocity enforced by magnetic braking and a dynamical, protostellar regime of nearly conserved angular momentum. The rotation velocity profile we derive for the inner IRAM 04191 envelope should thus set some constraints on the distribution of angular momentum on the scale of the outer Solar system at the onset of protostar/disk formation.

Accepted for publication in A&A

¹²CO mapping of the low-metallicity BCD galaxy Mrk 86

A. Gil de Paz(^1,2), S. A. Silich(^3,4), B. F. Madore(^1,5), C. Sánchez Contreras(²), J. Zamorano(⁶), and J. Gallego(⁶)
(¹)NASA/IPAC Extragalactic Database, California Institute of Technology, MS 100-22, Pasadena, CA 91125, (²)Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, Pasadena, CA 91109, (³) Instituto Nacional de Astrofísica, Óptica y Electrónica, AP 51, Luis Enrique Erro 1, Tonantzintla 72000, Puebla, Mexico, (⁴) Main Astronomical Observatory, National Academy of Sciences of Ukraine, 03680 Kiyv-127, Golosiiv, Ukraine, (⁵) The Observatories, Carnegie Institution of Astronomy, 813 Santa Barbara Street, Pasadena, CA 91101, (⁶)Departamento de Astrofísica, Universidad Complutense de Madrid, Av. Complutense s/n. E-28040 Madrid, Spain

Abstract:
We have mapped the ¹²CO J=1-0 and J=2-1 line emission in Mrk 86, one of the most metal-deficient Blue Compact Dwarf galaxies so far detected in ¹²CO. The ¹²CO emission is distributed in a horseshoe-like structure that follows the locus of the most recent star formation regions. The minimum in molecular-line emission corresponds to the position of an older, massive nuclear starburst. The H₂ mass of the galaxy (in the range 0.4-5$\times$10⁷M$_\odot$) and its morphology have been compared with the predictions of hydrodynamic simulations of the evolution of the interstellar medium surrounding a nuclear starburst. These simulations suggest that the physical conditions in the gas swept out by the starburst could have led to the formation of the ring of molecular gas reported here. This result provides an attractive scenario for explaining the propagation (in a galactic scale) of the star formation in dwarf galaxies.

Accepted for publication in ApJ Letters

IRAS 05358+3543: Multiple outflows at the earliest stages of massive star formation

H. Beuther(¹), P. Schilke(¹),F. Gueth(^1,2), M. McCaughrean(³), M. Andersen(³), T.K. Sridharan(⁴) and K.M. Menten(¹)
(¹)Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, (²)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France, (³)Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany, (⁴)Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138, USA

Abstract:
We present a high-angular-resolution molecular line and millimeter continuum study of the massive star formation site IRAS 05358+3543. Observations with the Plateau de Bure Interferometer in CO 1-0, SiO 2-1 and H¹³CO⁺ 1-0 reveal at least three outflows which cannot be separated in single-dish data. Observations at millimeter and sub-millimeter wavelengths from the IRAM 30 m telescope and the CSO provide additional information on the region. The most remarkable feature is a highly collimated (collimation factor $\sim 10$) and massive (>10 M$_\odot$) bipolar outflow of $\sim1$ pc length, which is part of a quadrupolar outflow system. The three observed molecular outflows forming the IRAS 05358+3543 outflow system resemble, in structure and collimation, those typical of low-mass star-forming regions. They might therefore, just like low-mass outflows, be explained by shock entrainment models of jets. We estimate a mass accretion rate of $\sim 10^{-4}$ M$_\odot$/yr, sufficient to overcome the radiative pressure of the central object and to build up a massive star, lending further support to the hypothesis that massive star formation occurs similarly to low-mass star formation, only with higher accretion rates and energetics. In the millimeter continuum, we find three sources near the center of the quadrupolar outflow, each with a mass of 75-100 M$_\odot$. These cores are associated with a complex region of infrared reflection nebulosities and their embedded illuminating sources. The molecular line data show that SiO is found mostly in the outflows, whereas H¹³CO⁺traces core-like structures, though likely with varying relative abundances. Thermal CH₃OH comprises both features and can be disentangled into a core-tracing component at the line center, and wing emission following the outflows. A CO line-ratio study (using data of the $J=1-0, 2-1~\&~6-5$ transitions) reveals local temperature gradients.

Published in A&A 387, 931

The molecular environment of NGC3603
I. Spatial distribution and kinematic structure

Dieter E.A. Nürnberger(^1,2), Leonardo Bronfman(³), Harold W. Yorke(⁴) and Hans Zinnecker(⁵)
(¹)Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany, (²)Institut de Radio-Astronomie Millimétrique, 300 Rue de la Piscine DU, 38406 St. Martin-d'Hères, France, (³)Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile, (⁴)Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, U.S.A., (⁵)Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Abstract:
We present CS(2-1) and CS(3-2) observations of the molecular gas associated with the Galactic starburst template NGC3603, over an area of 5 $\hbox{$^{\prime}\!.\,$ }$8$\times$16 $\hbox{$^{\prime}\!.\,$ }$7, with the OB cluster at the center. Total velocity integrated maps and channel maps give insight into the spatial distribution and the kinematic structure of the dense gas in the giant molecular cloud from which the starburst cluster originated. We identify 13 molecular clumps with radii less than 0.8pc and derive upper limits for their virial masses as well as lower limits for their H₂ column densities: $\langle\cal M_{\rm vir}\rangle$ $\,\raise 0.3 ex\hbox{$\space < $ }\kern -0.8 em \lower 0.7 ex\hbox{$\sim$ }\,$(1.0$\pm$0.6)$\cdot$10³ $\cal M\hbox{$_{\odot}$ }$ and $\langle\cal N{\rm (H_2)}\rangle$ $\,\raise 0.3 ex\hbox{$\space > $ }\kern -0.8 em \lower 0.7 ex\hbox{$\sim$ }\,$(0.4$\pm$0.2)$\cdot$10²³cm^-2. One of the clumps, MM11, clearly stands out with a mass and column density 4 times higher than average. The CS(3-2)/CS(2-1) map shows higher intensity ratios to the south of the OB cluster than to the north (0.80$\pm$0.08 versus 0.32$\pm$0.11), which indicates a substantial difference in the physical conditions (either opacities or excitation temperatures) of the molecular gas. From the average of the line peak velocities, 14.2$\pm$1.6kms^-1, we deduce a kinematic distance of 7.7$\pm$0.2kpc for NGC3603. We estimate the star formation efficiency ( $\,\raise 0.3 ex\hbox{$\space > $ }\kern -0.8 em \lower 0.7 ex\hbox{$\sim$ }\,$30$\%$) of the central part of the NGC3603 H II region. If we assume the age of the OB cluster to be less than 3Myr and the star formation rate to be larger than 1.3$\cdot$10^-3 $\cal M\hbox{$_{\odot}$ }$yr^-1, the derived timescale for gas removal ($\tau$$\sim$6Myr) can explain why the starburst cluster itself is nearly void of interstellar material. The remnant clump MM1 appears to constitute the head of a prominent pillar which still becomes dispersed by ionizing radiation and stellar winds originating from the massive stars of the cluster. Because some of the molecular clumps are associated with near and mid infrared sources as well as OH, H₂O and CH₃OH maser sources we conclude that star formation is still going on within NGC3603.

A&A, in press

A search for radio supernovae and supernova remnants in the region of NGC1569's super star clusters

A. Greve(¹), A. Tarchi(^2,3), S. Hüttemeister(^4,5), R. de Grijs(⁶), J.M. van der Hulst(⁷),S.T. Garrington(⁸)and N. Neininger(²)
(¹)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d`Hères, France, (²)Astronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany, (³)Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany, (⁴)Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstr. 150, D-44780 Bochum, Germany, (⁵)Onsala Space Observatory, S-43920 Onsala, Sweden, (⁶)Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK, (⁷)Kapteyn Astronomical Instituut, Postbus 800, 9700 AV Groningen, The Netherlands, (⁸)Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield Cheshire SK11 9DL, UK

Abstract:
We have used MERLIN, at 1.4 and 5 GHz, to search for radio supernovae (RSNe) and supernova remnants (SNRs) in the unobscured irregular dwarf galaxy NGC1569, and in particular in the region of its super star clusters (SSCs) A and B. Throughout NGC1569 we find some 5 RSNe and SNRs but the SSCs and their immediate surroundings are largely devoid of non-thermal radio sources. Even though many massive stars in the SSCs are expected to have exploded already, when compared with M82 and its many SSCs the absence of RSNe and SNRs in and near A and B may seem plausible on statistical arguments. The absence of RSNe and SNRs in and near A and B may, however, also be due to a violent and turbulent outflow of stellar winds and supernova ejected material, which does not provide a quiescent environment for the development of SNRs within and near the SSCs.

Appeared in A&A 381, 825