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Title:CENTRAL 300 PC OF THE GALAXY PROBED BY THE INFRARED SPECTRA OF H3+ AND CO PART II. MORPHOLOGY AND DYNAMICS OF THE GAS
Author(s):Oka, Takeshi
Contributor(s):Indriolo, Nick; McCall, Benjamin J.; Usuda, Tomonori; Goto, Miwa; Geballe, Thomas R.
Subject(s):Astronomy
Abstract:Velocity-resolved spectra of infrared lines of H$_{3}^{+}$ at 3.7~$\mu$m and CO at 2.3~$\mu$m have been obtained toward $\sim$40 stars in the Central Molecular Zone (CMZ), a region of radius $\sim$150~pc centered on the Galactic center. Although the coverage of the region is limited by the available number of suitable stars for absorption spectroscopy, the rich Doppler profiles of the H$_{3}^{+}$ lines in warm ($T$$\sim$250~K) and diffuse ($n\leq$100~cm$^{-3}$) clouds\footnote{Oka, T., Geballe, T.R., Goto, M., Usuda, M., McCall, B.J., Indriolo, N. to be submitted (2018)} have allowed us to draw a longitude-velocity ($l$-$v$) plot to reach the following conclusions. (1) Based on the blue-shifted profiles of H$_{3}^{+}$ absorption lines, which are dominantly in the velocity range from -~200~km~s$^{-1}$ to 10~ km~s$^{-1}$, the warm diffuse gas is moving outward from the center. (2) Although limited in uniformity of longitudinal coverage, the observed ($l$-$v$) plot for H$_{3}^{+}$ suggests that the outer surface of the expanding gas forms a ring of radius of $\sim$140~pc and has a velocity of expansion of $\sim$140~km~s$^{-1}$. This finding revives the idea of the expanding molecule ring proposed by Kaifu et al.(1972)\footnote{Kaifu, N., Kato, T. Iguchi, T., 1972, Nature, 238, 105} and Scoville (1972)\footnote{Scoville, N.Z. 1972, ApJ, 175, L127} which contrasts with a more recent interpretation of the overall gas kinematics as due to a barred gravitational potential (Binney et al. 1991).\footnote{Binney, J., Gerhard, O.E., Stark, A.A., Bally J., Uchida, K.I. 1991, Mon. Not. R. astr. Soc. 252, 210} (3) The results revive the idea of an explosion or overall expulsion of gas from the center within the last few million years. Unlike the original proposals that the EMR is also rotating, the H$_{3}^{+}$ $l$-$v$ plot indicates purely expanding gas.
Issue Date:06/21/18
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:Conference Paper / Presentation
Type:Text
Language:English
URI:http://hdl.handle.net/2142/100816
DOI:10.15278/isms.2018.RL11
Other Identifier(s):RL11
Date Available in IDEALS:2018-08-17
2018-12-12


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