AKARI Near-Infrared Spectroscopy: Detection of H2O and CO2 Ices toward Young Stellar Objects in the Large Magellanic Cloud

We present the first results of AKARI Infrared Camera near-infrared spectroscopic survey of the Large Magellanic Cloud (LMC). We detected absorption features of the H2O ice 3.05 μm and the CO2 ice 4.27 μm stretching mode toward seven massive young stellar objects (YSOs). These samples are for the first time spectroscopically confirmed to be YSOs. We used a curve-of-growth method to evaluate the column densities of the ices and derived the CO2/H2O ratio to be 0.45 ± 0.17. This is clearly higher than that seen in Galactic massive YSOs (0.17 ± 0.03). We suggest that the strong ultraviolet radiation field and/or the high dust temperature in the LMC may be responsible for the observed high CO2 ice abundance.

[1]  Tokyo,et al.  AKARI IRC Survey of the Large Magellanic Cloud: Outline of the Survey and Initial Results , 2008, 0808.3022.

[2]  Linda J. Smith,et al.  SPITZER SAGE SURVEY OF THE LARGE MAGELLANIC CLOUD. III. STAR FORMATION AND ∼1000 NEW CANDIDATE YOUNG STELLAR OBJECTS , 2008 .

[3]  D. Padgett,et al.  The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. I. H2O and the 5-8 μm Bands , 2007, 0711.4616.

[4]  V. Pirronello,et al.  Laboratory Simulation of Competition between Hydrogenation and Photolysis in the Chemical Evolution of H2O-CO Ice Mixtures , 2007 .

[5]  Munetaka Ueno,et al.  Near-Infrared and Mid-Infrared Spectroscopy with the Infrared Camera (IRC) for AKARI , 2007, 0708.4290.

[6]  S. Oh,et al.  The infrared astronomical mission AKARI , 2007, 0708.1796.

[7]  D. Kato.  The IRSF Magellanic Clouds Point Source Catalog , 2007 .

[8]  N. Takeyama,et al.  The Infrared Camera (IRC) for AKARI–Design and Imaging Performance , 2007, 0705.4144.

[9]  E. Bergin,et al.  The Abundance of Carbon Dioxide Ice in the Quiescent Intracloud Medium , 2007 .

[10]  H. Fraser,et al.  Effects of CO2 on H2O band profiles and band strengths in mixed H2O:CO2 ices , 2006, astro-ph/0610751.

[11]  Linda J. Smith,et al.  SPITZER SURVEY OF THE LARGE MAGELLANIC CLOUD, SURVEYING THE AGENTS OF A GALAXY'S EVOLUTION (SAGE). IV. DUST PROPERTIES IN THE INTERSTELLAR MEDIUM , 2005, Proceedings of the International Astronomical Union.

[12]  H. Kaneda,et al.  The Properties of the Mid- to Far-Infrared Emission in the Large Magellanic Cloud , 2006 .

[13]  J. Blommaert,et al.  ESO–VLT and Spitzer spectroscopy of IRAS 05328−6827: a massive young stellar object in the Large Magellanic Cloud , 2005, astro-ph/0509695.

[14]  R. Indebetouw,et al.  Two-Dimensional Radiative Transfer in Protostellar Envelopes. III. Effects of Stellar Temperature , 2004 .

[15]  A. Tielens,et al.  Interstellar Ice: The Infrared Space Observatory Legacy , 2004 .

[16]  D. Alves,et al.  A review of the distance and structure of the Large Magellanic Cloud , 2003, astro-ph/0310673.

[17]  S. Meyer,et al.  The Spectrum of Integrated Millimeter Flux of the Magellanic Clouds and 30 Doradus from TopHat and DIRBE Data , 2003, astro-ph/0306425.

[18]  A. Tielens,et al.  Detection of strongly processed ice in the central starburst of NGC 4945 , 2003, astro-ph/0302568.

[19]  J. Chiar,et al.  Solid Carbon Dioxide in Regions of Low-Mass Star Formation , 2001 .

[20]  E. Herbst,et al.  New models of interstellar gas–grain chemistry – III. Solid CO2 , 2001 .

[21]  S. Sandford,et al.  H, C, N, and O Isotopic Substitution Studies of the 2165 Wavenumber (4.62 Micron) “XCN” Feature Produced by Ultraviolet Photolysis of Mixed Molecular Ices , 2000 .

[22]  Alexander G. G. M. Tielens,et al.  An Inventory of Interstellar Ices toward the Embedded Protostar W33A , 2000 .

[23]  P. Ehrenfreund,et al.  ISO observations of interstellar ices: Implications for the pristinity of comets , 2000 .

[24]  T. Prusti,et al.  Observations of Solid Carbon Dioxide in Molecular Clouds with the Infrared Space Observatory , 1999 .

[25]  E. Bergin,et al.  Formation of Interstellar Ices behind Shock Waves , 1998, astro-ph/9811228.

[26]  A. Tielens,et al.  Processing of Icy Mantles in Protostellar Envelopes , 1998, The Astrophysical journal.

[27]  W. Gieren,et al.  Magellanic Cloud Cepheids: Abundances , 1998 .

[28]  E. F. Dishoeck,et al.  Chemical evolution of star-forming regions. , 1998, Annual review of astronomy and astrophysics.

[29]  T. Graauw,et al.  Carbon Monoxide in the Magellanic Clouds , 1986 .