======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews ======================================================================== Vol. 29, No. 5 Mar 12, 2009 Recently submitted papers: -------------------------- 1) Suzaku Observation Adjacent to the South End of the Radio Arc (Fukuoka et al., PASJ) 2) The nuclear star cluster of the Milky Way: Proper motions and mass (Schoedel et al., A&A) 3) Interstellar Extinction Law toward the Galactic Center III : J, H, K_S bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 micron in the Spitzer/IRAC system (Nishiyama et al., ApJ) ------------------------------------------------------------------------ Email : fukuoka@cr.scphys.kyoto-u.ac.jp Title : Suzaku Observation Adjacent to the South End of the Radio Arc Author(s): Ryosuke Fukuoka, Katsuji Koyama, Syukyo G. Ryu, and Takeshi Go Tsuru Institute: (1) Department of Physics, Graduate School of Science, Kyoto University, Kita-shirakawa Oiwake-cho, Sakyo, Kyoto 606-8502 Paper : PASJ, Mar 2009, inpress Abstract: Suzaku observed the Galactic center region near the Radio Arc at 20' southeast of Sagittarius A*. In the 18'*18' field of view, we found four distinct X-ray sources: a bright star and a diffuse source associated with the star clusters in the soft band (0.5-2.0 keV), a small clump in a higher energy band (4-6 keV), and a peculiar clump in the 6.4 keV line band. The latter two clumps are located at the south end of the Radio Arc. This paper reports on the results, and discusses the origin of these X-ray sources, with a particular emphasis on small clumps. ------------------------------------------------------------------------ Email : rainer@iaa.es Title : The nuclear star cluster of the Milky Way: Proper motions and mass Author(s): R. Schoedel (1) and D. Merritt(2) and A. Eckart(3) Institute: (1) Instituto de Astrofisica de Andalucia (IAA) - CSIC, Camino Bajo de Huetor 50, E-18008 Granada, Spain (2) Department of Physics and Center for Computational Relativity and Gravitation, Rochester Institute of Technology, Rochester, NY 14623, USA (3) I.Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str.77, 50937 Koeln, Germany Paper : A&A, Mar 2009, in press EPrint : 0902.3892 Web : http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ Abstract: Nuclear star clusters (NSCs) are located at the photometric and dynamical centers of the majority of galaxies. They are among the densest star clusters in the Universe. The NSC in the Milky Way is the only object of this class that can be resolved into individual stars. The massive black hole Sagittarius A* is located at the dynamical center of the Milky Way NSC. In this work we examine the proper motions of stars out to distances of 1.0 pc from Sgr A*. The aim is to examine the velocity structure of the MW NSC and acquire a reliable estimate of the stellar mass in the central parsec of the MW NSC, in addition to the well-known black hole mass. We use multi-epoch adaptive optics assisted near-infrared observations of the central parsec of the Galaxy obtained with NACO/CONICA at the ESO VLT. Stellar positions are measured via PSF fitting in the individual images and transformed into a common reference frame via suitable sets of reference stars. We measured the proper motions of more than 6000 stars within 1.0 pc of Sagittarius A*. The full data set is provided in this work. We largely exclude the known early-type stars with their peculiar dynamical properties from the dynamical analysis. The cluster is found to rotate parallel to Galactic rotation, while the velocity dispersion appears isotropic (or anisotropy may be masked by the cluster rotation). The Keplerian fall-off of the velocity dispersion due to the point mass of Sgr A* is clearly detectable only at R<= 0.3 pc. Nonparametric isotropic and anisotropic Jeans models are applied to the data. They imply a best-fit black hole mass of 3.6^+0.2_-0.4*10^6 M_o. Although this value is slightly lower than the current canonical value of 4.0*10^6 M_o, this is the first time that a proper motion analysis provides a mass for Sagittarius A* that is consistent with the mass inferred from orbits of individual stars. The point mass of Sagittarius A* is not sufficient to explain the velocity data. In addition to the black hole, the models require the presence of an extended mass of 0.5-1.5* 10^6 M_o in the central parsec. This is the first time that the extended mass of the nuclear star cluster is unambiguously detected. The influence of the extended mass on the gravitational potential becomes notable at distances >= 0.4 pc from Sgr A*. Constraints on the distribution of this extended mass are weak. The extended mass can be explained well by the mass of the stars that make up the cluster. ------------------------------------------------------------------------ Email : shogo@kusastro.kyoto-u.ac.jp Title : Interstellar Extinction Law toward the Galactic Center III : J, H, K_S bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 micron in the Spitzer/IRAC system Author(s): Shogo Nishiyama(1), Motohide Tamura(2), Hirofumi Hatano(3), Daisuke Kato(4), Toshihiko Tanabe(5), Koji Sugitani(6), and Tetsuya Nagata(1) Institute: (1) Department of Astronomy, Kyoto University, Kyoto, 606-8502, Japan (2) National Astronomical Observatory of Japan, Mitaka, Tokyo, 181-8588, Japan (3) Department of Astrophysics, Nagoya University, Nagoya, 464-8602, Japan (4) Department of Astronomy, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan (5) Institute of Astronomy, Graduate School of Science, The University of Tokyo, Mitaka, Tokyo, 181-0015, Japan (6) Graduate School of Natural Sciences, Nagoya City University, Nagoya, 464-8602, Japan Paper : ApJ, accepted EPrint : 0902.3095 Web : http://www.kusastro.kyoto-u.ac.jp/~shogo/papers/09NishiyamaEx lawMIR.pdf Abstract: We have determined interstellar extinction law toward the Galactic center (GC) at the wavelength from 1.2 to 8.0 micron , using point sources detected in the IRSF/SIRIUS near-infrared survey and those in the 2MASS and Spitzer/IRAC/GLIMPSE II catalogs. The central region | l | < 3.^o0 and | b | < 1.^o0 has been surveyed in the J, H and K_S bands with the IRSF telescope and the SIRIUS camera whose filters are similar to the Mauna Kea Observatories (MKO) near-infrared photometric system. Combined with the GLIMPSE II point source catalog, we made K_S versus K_S - lambda color-magnitude diagrams where lambda = 3.6, 4.5, 5.8, and 8.0 micron . The K_S magnitudes of bulge red clump stars and the K_S - lambda colors of red giant branches are used as a tracer of the reddening vector in the color-magnitude diagrams. From these magnitudes and colors, we have obtained the ratios of total to selective extinction A_K_S/E_K_S- lambda for the four IRAC bands. Combined with A_ lambda /A_K_S for the J and H bands derived by Nishiyama et al., we obtain A_J : A_H : A_K_S : A_[3.6] : A_[4.5] : A_[5.8] : A_[8.0] = 3.02:1.73:1:0.50:0.39:0.36:0.43 for the line of sight toward the GC. This confirms the flattening of the extinction curve at lambda > 3 micron from a simple extrapolation of the power-law extinction at shorter wavelengths, in accordance with recent studies. The extinction law in the 2MASS JHK_S bands has also been calculated, and a good agreement with that in the MKO system is found. Thus, it is established that the extinction in the wavelength range of J, H, and K_S is well fitted by a power law of steep decrease A_ lambda \propto lambda ^-2.0 toward the GC. In nearby molecular clouds and diffuse interstellar medium, the lack of reliable measurements of the total to selective extinction ratios hampers unambiguous determination of the extinction law; however, observational results toward these lines of sight cannot be reconciled with a single extinction law. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Sera Markoff, Loránt Sjouwerman, Joseph Lazio, Cornelia Lang, Rainer Schödel, Masaaki Sakano, Feng Yuan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please follow the instructions which are at http://www.aoc.nrao.edu/~gcnews/home/submission.shtml ========================================================================