Hot and Diffuse Clouds near the Galactic Center Probed by Metastable \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\t

Abstract

Using an absorption line from the metastable (J ; K) ¼ (3; 3) level of H þ 3 together with other lines of H þ 3 and CO observed along several sight lines, we have discovered a vast amount of high-temperature (T $ 250 K) and lowdensity (n $ 100 cm À3 ) gas with a large velocity dispersion in the central molecular zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately three-fourths of the H þ 3 along the line of sight to the brightest source we observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the remaining H , is probably closer to the center. CO is not very abundant in these clouds. Hot and diffuse gas in which the (3, 3) level is populated was not detected toward several dense clouds and diffuse clouds in the Galactic disk where large column densities of colder H þ 3 have been reported previously. Thus, the newly discovered environment appears to be unique to the CMZ. The large observed H þ 3 column densities in the CMZ suggest an ionization rate much higher than in the diffuse interstellar medium in the Galactic disk. Our finding that the H þ 3 in the CMZ is almost entirely in diffuse clouds indicates that the reported volume filling factor ( f ! 0:1) for n ! 10 4 cm À3 clouds in the CMZ is an overestimate by at least an order of magnitude.

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

“…The CMZ consists of non-axisymmetric clouds with complicated structure (Oka et al 2005;Kruijssen, Dale & Longmore 2015). Our simulation implies that such nonaxisymmetric clouds are a natural outcome of magnetic activity in the Galactic center.…”

“…Observations of the atomic and molecular interstellar medium in the inner Milky Way exhibit large noncircular motion of the gas (Rougoor & Oort 1960;Scoville 1972;Liszt & Burton 1978;Bally et al 1987;Oka et al 1998;Tsuboi, Handa & Ukita 1999;Sawada et al 2004;Oka et al 2005;Takeuchi et al 2010). Among various possible explanations for the noncircular motion, de Vaucouleurs (1964) raised a possibility that the gas responds to a stellar bar potential of the Milky Way.…”

On the origin of the 6.4keV line in the Galactic Center region

“…The density of these CRs in the GC can be derived from measurements of the absorption line of the ionised molecular hydrogen (H + 3 ). Thus, Oka et al (2005) and Goto et al (2008Goto et al ( , 2011 found an unusually high ionization rate in the GC, which is not observed in other parts of the Galactic Disk. The ionization rate, ζ, is almost uniform throughout of the GC on scales about 200 pc, ζ ∼ (1 − 3) × 10 −15 s −1 .…”

“…Yusef-Zadeh et al (2013a) assumed that these electrons ionize diffuse hydrogen gas and generate also the 6.4 keV line. As follows from Oka et al (2005) the rate of ionization is almost constant throughout the GC region; this means an almost uniform distribution of the electrons there. Yusef-Zadeh et al (2013a) derived parameters of these electrons from the observed nonthermal radio flux from the GC region 2 • × 0.85 • .…”

“…The flux is about Φ ν ≃ 2450 Jy at 325 MHz and the radio spectrum is ν −0.25 at frequencies ν < 3.3 GHz. They assumed that the spectrum of radioemitting electrons could be extrapolated into the region 100 keV -1 GeV, and just the electrons with E < 1 GeV ionized the GC molecular gas with the rate ζ ∼ (1−3)×10 −15 s −1 ; this about the value derived by (see Oka et al, 2005). Then the question is whether these electrons can provide the diffuse 6.4 keV emission in the GC as observed by Uchiyama et al (2012).…”