From martin@oan.es Mon Oct 14 10:13:47 1996 From: martin@oan.es To: gcnews@astro.umd.edu Cc: martin@oan.es Subject: Latex file of the SiO GC paper (NOT POSTSCIPT) Date: Mon, 14 Oct 96 16:18:22 +0200 X-Mts: smtp %%%%%%%%%%%%A+A%%%%%%%%%%%%%%%%%%% %%%%Articulo en formato A+A %%%%%%%%%%%%%% %\documentstyle{laa} % LaTeX A&A Standard Fonts %%%%Prepint en formato A+A %%%%%%%%%%%%%% %\documentstyle[]{/users3/martin/lib/aa/laa} %\documentstyle[referee]{/users3/martin/lib/aa/laa} %\pagestyle{plain} %%%%%%%%%%%%%%%%%%%%%%%%%%%% %\documentstyle[11pt,/users3/martin/lib/apj/aaspp4]{article} %\documentstyle[/users3/martin/lib/apj/aas2pp4]{article} %\received{} %\accepted{} %\journalid{}{} %\articleid{}{} \documentstyle[12pt,aasms4]{article} %%%%%%%%%%%%%%%%%%%%%%%% OWN DEFINITIONS %%%%%%%%%%%%%%%%%%%% %\input /users3/martin/lib/tex/aliasj.tex \def\kms{\ifmmode {{\rm \;km\;s^{-1}\;}} % km s-1 \else {\hbox{$\,${\rm km$\;$s$^{\rm -1}\;$}}}\fi} \def\solar {\ifmmode_{\mathord\odot\;} \else $_{\mathord\odot}\;$\fi} % _solar \def\mo {\ifmmode {\,{\it M}\solar\;} \else $\,M$\solar$\;$\fi} % M solar % cm-1, cm-2, cm-3, ... \def\cmm#1{\ifmmode {\,{\rm cm^{-#1}}\;} % cm-1, cm-2, cm-3, ... \else \hbox{$\,${\rm cm$^{\rm -#1}\;$}}\fi} \def\am {\ifmmode {^{\scriptscriptstyle\prime}} % arcmin \else $^{\scriptscriptstyle\prime}$\fi} \def\deg {\ifmmode^\circ\else$^\circ$\fi} % degree \def\x {\ifmmode\times\else$\times$\fi} % times (x) \def\E#1 {\ifmmode {\times 10^{#1}\;} \else \hbox{$\times 10^{#1}\;$}\fi} % x10^ \def\T#1 {\ifmmode \,10^{#1}\; \else {${\rm\,10^{#1}}\;$}\fi} % 10^ \def\half{\ifmmode \textstyle{1\over2} \else $\textstyle{1\over2}$\fi} % 1/2 \def\apro{$\sim$} %aproximado %aproximado \def\masmenos{\ifmmode {\pm} \else $\pm$ \fi} % mas menos \def\gsim {\ifmmode {\buildrel>\over\sim} % greater or similar \else {\lower.6ex\hbox{$\buildrel>\over\sim$}}\fi} \def\lsim {\ifmmode {\buildrel<\over\sim} % less or similar \else {\lower.6ex\hbox{$\buildrel<\over\sim$}}\fi} \def\lt{\ifmmode {<}\else{$<$}\fi} \def\gt{\ifmmode {>}\else{$>$}\fi} \def\tkin {$T_{\rm kin}$} \def\tastar {$T_{\rm A}^{*}$} \def\vlsr {\hbox{${v_{\rm LSR}}$}} \def\alcala{Observatorio Astron\'omico Nacional (IGN), Campus Universitario, Apartado 1143, E28800 Alcal\a de Henares, Spain} \chardef\isp="10 \def\i{\'\isp} \def\hdos {\hbox{${\rm H}_2$}} %H2 \def\nht {\hbox{${\rm NH}_{3}$}} %NH3 \def\chtcn{\hbox{${\rm CH}_3{\rm CN}$}} %CH3CN \def\uc{\rm J=$1\rightarrow0\;$} % J=1-0 \def\du{\rm J=$2\rightarrow1\;$} % J=2-1 \def\td{\rm J=$3\rightarrow2\;$} % J=3-2 \def\ct{\rm J=$4\rightarrow3\;$} % J=4-3 \def\cc{\rm J=$5\rightarrow4\;$} % J=5-4 \def\sc{\rm J=$6\rightarrow5\;$} % J=6-5 \def\ss{\rm J=$7\rightarrow6\;$} % J=7-6 \def\as {\ifmmode {^{\scriptscriptstyle\prime\prime}} % arcsec \else $^{\scriptscriptstyle\prime\prime}$\fi} \def\hcop {\hbox{${\rm HCO}^+$}} %HCO+ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \slugcomment{Manuscript draft: June 19, 1996} \lefthead{Mart{\i}n-Pintado \etal} \righthead{SiO in the Galactic center} \begin{document} %% %% Title page %% \title{SiO emission from the Galactic Center Molecular Clouds} \author{ J. Mart{\i}n-Pintado, P. de Vicente, A. Fuente, P. Planesas} \affil{Observatorio Astron\'omico Nacional (IGN), Campus Universitario, Apartado 1143, E-28800 Alcal\'a de Henares, Spain} %% %% Abstract %% \begin{abstract} We have mapped the {J=$1\rightarrow0$}\ line of SiO in a 1\deg$\times12^\prime$ (l$\times$b) region around the Galactic center (GC) with an angular resolution of 2$^\prime$\ ($\sim$ 4 pc). In contrast to the spatial distribution of other high dipole moment molecules like CS, whose emission is nearly uniform, the SiO emission is very fragmented and it is only associated with some molecular clouds. In particular, it is remarkable that the SiO emission closely follows the non-thermal radio arc in the GC. The SiO clouds are more extended than the beam with typical sizes between 4 and 20 pc. High angular resolution (26$^\prime$) mapping in the J=$2\rightarrow1$ line of SiO toward the molecular clouds in Sgr B2 and Sgr A shows that the SiO emission is relatively smooth with structures of typically 2 pc. From the line intensities of the J=$2\rightarrow1$, J=$3\rightarrow2$ and J=$5\rightarrow4$ transitions of SiO we derive ${\rm H}_2$ densities for these clouds of a few $10^4 {\rm cm}^{-3}$. The SiO fractional abundances are $\sim10^{-9}$ for the SiO clouds and $\la10^{-10}$ for the other molecular clouds in the GC. The characteristics (size and ${\rm H}_2$ densities) of the SiO emission in the GC are completely different from those observed in the Galactic disk, where the SiO emission arises from much smaller regions with larger ${\rm H}_2$ densities. We briefly discuss the implications of the SiO emission in the molecular clouds of the GC. We conclude that the particular chemistry in these clouds is probably related to large scale fast shocks occurring in the Galactic center region. \end{abstract} \keywords{Galaxy: center--- ISM: molecules --- ISM: clouds --- ISM: structure --- ISM: abundances--- radio lines: ISM} %% %% Main text %% %% \section{Introduction} The physical conditions of the molecular clouds in the Galactic center (GC) differ substantially from those of the molecular clouds in the Galactic disk (see e.g. G\"usten 1989). High gas kinetic temperatures (\tkin \gsim80 K) are found in these molecular clouds (G\"usten, Walmsley \& Pauls 1981; Morris et al. 1983; H\"uttermeister et al. 1993). The gas kinetic temperatures are clearly above the dust color temperatures, \apro30 K, derived from the FIR emission (Odenwald and Fazio 1984). To explain the high kinetic temperatures of the molecular gas, several heating mechanisms which act only on the gas have been discussed. In particular, the large linewidth (\gsim15 \kms) that the molecular lines exhibit in these molecular clouds and its possible correlation with the kinetic temperature suggest that dissipation of turbulence driven by differential Galactic rotation is an attractive heating mechanism for the GC molecular clouds (Wilson et al. 1982; G\"usten 1989). If supersonic turbulence is an efficient heating mechanism, it is expected to produce shocks which will heat the gas and also influence the chemical composition of the molecular clouds in the GC. % In fact, ionizing shocks have also been proposed as the origin of the ionization in the Galactic center (Morris 1989). % Molecular species which are formed by shock chemistry are then expected to be enhanced in these molecular clouds. Since the discovery of SiO emission in interstellar clouds, it is rather well established that SiO is an unambiguous tracer of high temperature and/or shock chemistry in interstellar clouds (Downes et al. 1982; Ziurys, Fribeg \& Irvine 1989; Mart{\i}n-Pintado, Bachiller \& Fuente 1992 ) In this letter we report the detection of widespread SiO emission toward some giant molecular clouds in the Galactic center. In contrast to the star-forming regions, the SiO maps reveal very extended emission which does not seem to be associated with recently formed stars, but most likely with large scale shocks in the Galactic center region. \section{Observations and Results} The large scale mapping of the molecular clouds in the \uc\ line of SiO was carried out with the 14-m telescope of the Centro Astron\'omico de Yebes (Spain). The Half Power Beamwidth (HPBW) of the telescope was 2\am. The receiver, equipped with a cooled Schottky mixer, had a double side band temperature of 75 K. The typical single side band system temperature was 250-300 K. The spectrometer was a 512 channel acusto-optic device with a resolution of 108 kHz (0.74 \kms). The calibration was made by using the standard chopper wheel method. The observations were made in position switching with the reference 15\am\ away from the Galactic plane. % In view of the unexpected large extent of the SiO emision, the most critical positions in our map have been checked for contamination with emission from the reference. % The typical noise in the map is 0.15 K. The SiO profiles show broad lines with typical widths to half power of 30-60 \kms, with most of their emission concentrated at radial velocities between $-$10 to 90 \kms. Fig. 1 shows the integrated intensity map of the \uc\ line of SiO for the velocity range between $-$10 to 90 \kms. The SiO emission shows a very fragmented distribution concentrating in 17 molecular clouds which are designated in Fig. 1 by their Galactic coordinates. The fragmented SiO emission is in contrast with the fairly uniform distribution of the CS emission (Bally et al. 1987) % obtained with the same angular resolution than the SiO data. % The SiO emission is also different from that of CS for negative radial velocities. While CS shows relatively strong emission for radial velocities from $-$50 to $-$10 \kms toward thermal arched filaments, SiO is not detected to our limit of 0.15 K. Along the Galactic plane, the SiO emission shows a similar spatial distribution to that of the hot gas observed in \nht\ emission (Morris et al. 1983). Both lines are not detected for Galactic longitudes between 0.3\deg\ and 0.4\deg. There are three major groups of SiO clouds. The first one, located south of Sgr A, surrounds the southern edge of the radio continuum emission from Sgr A East. The second one is found towards the Galactic center non-thermal radio arc at l\apro0.2\deg. It is remarkable that the SiO emission is not only restricted to the molecular cloud M0.20-0.03 (Bally et al. 1987; Serabyn \& G\"usten 1991; Lindqvist et al. 1995), but it shows the same morphology as the non-thermal radio arc over scales of several parsecs. The third SiO complex is found toward the star forming regions Sgr B1 and Sgr B2. The SiO emission does not show a clear correlation neither with the emission at 60$\mu$m nor with the radio continuum emission (Altenhoff et al. 1979) observed with similar angular resolution. This indicates that the bulk of the SiO clouds are not associated with newly formed OB stars. The SiO emission is more extended than the beam with typical sizes of 4-8\am\ (9-20pc). % High angular resolution (26\as) maps in the \du\ line of SiO of the two molecular clouds associated with Sgr A and Sgr B2 shows that the SiO emission is not highly clumply in the 2\am\ beam of the \uc\ line. % These observations were made with the IRAM 30-m telescope at Pico Veleta (Spain) and the observing procedure has been described by Mart{\i}n-Pintado et al (1992). Figs. 2a and 2b show the integrated intensity maps of the \du\ line of SiO towards the Sgr B2 and Sgr A molecular clouds respectively. These data will be analyzed in more detail elsewhere (Mart{\i}n-Pintado et al 1996). Simultaneously with the \du\ line we also observed the \td\ and \cc\ lines of SiO. % The HPBW of the telecopes for the \td\ and \cc\ lines were 17 and 13\as\ respectively. To derive the physical conditions, fully sampled maps (5\x5 point) in the \cc\ line were also made at selected positions. % Fig. 3 shows the typical line profiles of the SiO lines towards two positions in the Sgr B2 molecular cloud. The SiO profiles are very broad with linewidths to zero intensity up to 100 \kms. %The observations of the three transitions were made using SIS %receivers tuned in single side band (rejection of 6-10 dB) with %temperatures ranging from 130 to 180 K. As spectrometers, the two %1MHzx512 channel filter banks were used with one of the filter bank %split in two parts. This configuration provided a velocity resolution %of 3.5, 2.3 and 1.4 \kms for the \du, \td\ and \cc\ lines respectively. %The HPBW of the telescope at these wavelengths were 26, 17 and 14\as\ %respectively. We took the spectra in position switching mode with a %fixed reference position 15\am\ away in right ascension. The %calibration of the data were made by observing the sky, a cold and a %hot load. The line intensities are in units of \tastar. The SiO emission south of Sgr A (Fig. 2b) is elongated (8 pc\x16 pc) along the Galactic plane with two main clouds, M-0.13-0.08 (the 20 \kms cloud) and M-0.02-0.07 (the 50 \kms cloud) and a condensation close to Sgr A*. Like at large scale, the overall morphology of the SiO emission from these clouds is similar to that of the hot gas observed in the (3,3) line of \nht (G\"usten, Walmsley \& Pauls 1981; Ho et al. 1991). The SiO emission, however, does not show the prominent cold and dense FIR condensations observed at 1.3 mm (Mezger et al. 1989). The SiO emission toward Sgr B2 extends over a region of at least \apro24\x24 pc and presents a fragmented distribution. The typical size of the SiO condensations is \gsim1\am (\gsim2 pc). % The SiO lines show doubled peaked profiles. While the gas with low radial velocities, \apro0\kms, appears to the east of the star froming region, the high velocity gas, 60-80\kms, appears mainly to west. The very broad SiO lines and the systematic trend observed in radial velocities suggest that in the envelope of Sgr B2 very energetic events are taking place. Furthermore, from the integrated emission one can recognize several shell-like structures. The largest one, centered on Sgr B2M, surrounds the hot ring observed in \chtcn ( de Vicente et al. 1996) \section{Physical conditions in the SiO clouds} The main characteristic of the SiO lines in the GC clouds is that the intensity of the \cc\ line is typically 6-10 times weaker than that of the \du line, except for the star-forming regions Sgr B2M and Sgr B2N. % The line intensity ratios have been derived after smoothing the \cc and the \td lines to the the same resolution of the \du line. % The low intensity ratios in the GC clouds is in contrast with those found in star-forming regions in the Galactic disk where ratios of \apro1 are observed (Mart{\i}n-Pintado, Bachiller \& Fuente 1992). The low \cc/\du line intensity ratio in the GC suggests that the SiO emission in these clouds arises from material with moderate \hdos\ densities. Model calculations of the excitation of SiO using the Large Velocity Gradient Approximation (LVG) indicate that \hdos\ densities of a few \T{4} \cmm{3} can explain the observed line intensity ratios for the typical kinetic temperature, \gsim50 K, of the GC molecular clouds (G\"usten, Walmsley \& Pauls 1981; Morris et al. 1983; H\"uttermeister et al. 1993). The derived \hdos\ densities are basically independent of the kinetic temperatures for kinetic temperatures larger than 50 K. For the typical physical conditions of the GC molecular clouds (\hdos\ density of 5\T{4} \cmm{3} and a kinetic temperature of 80 K), the LVG analysis gives SiO column densities of 0.7-3\T{14} \cmm{2}. Asuming the same physical conditions for the clouds where the SiO emission is not detected, we derive upper limits to the SiO column density of \apro\T{13} \cmm{2}. For both types of clouds, the column densities estimated from LVG calculations for CS and \hcop\ are typically of 2-5\T{14} \cmm{2}, % similar to those derived from multitransition LVG analysis of CS towards some molecular clouds in the GC (Serabyn \& G\"usten 1987). The derived SiO column densities are similar to those of CS for the SiO clouds and a factor of, at least, 10 smaller for the other clouds. Since SiO and CS have similar dipole moments and energy level distributions, the derived column density ratio between these molecules is basically independent of the assumed physical conditions. Assuming the standard fractional abundance for CS and \hcop, we estimate the fractional abundance of SiO for the SiO clouds to be \apro\T{-9}. The fractional abundance of SiO is, at least, one order of magnitude smaller, \lsim\T{-10} , for the clouds where SiO emission has not been detected. Similar upper limits to the SiO abundances are derived for the molecular material with negative radial velocities associated with the thermal arched filaments in the GC. From the derived \hdos\ densities and the measured sizes, the SiO clouds have typical masses of a few\T{5} \mo. \section{Discussion} In the molecular clouds of the Galactic disk, the SiO emission is mainly associated with energetic mass outflows powered by young stars. This peculiar chemistry has led to the conclusion that Si is highly depleted in the molecular clouds and SiO appears only in very small regions where shock disruption of grains releases Si or SiO to the gas phase (Mart{\i}n-Pintado, Bachiller \& Fuente 1992). The variation of the SiO abundance in the GC molecular clouds also indicates a peculiar chemistry for this molecule in the GC region. However, the main characteristics (very widespread and moderate \hdos\ densities) of the SiO emission in the GC are substantially different from those observed in the Galactic disk. The GC SiO molecular clouds seem to be associated with warm gas, and high temperature chemistry (Ziurys, Fribeg \& Irvine 1989; Langer \& Glassgold 1990) could explain the SiO abundances if Si is less depleted in the GC clouds than in the clouds of the disk. Also, desorption of silicon bearing compounds from warm grains could explain the large SiO abundance in the GC clouds (Turner 1992a; MacKay 1995). However, chemistry schemes based only on high temperatures cannot explain the low SiO emission abundance found in the hot (\gsim80 K, Serabyn \& G\"usten 1987) material associated with the thermal arched filaments. The low SiO abundance in the thermal arched filaments is very likely related to the heating of these filaments. The main heating mechanism is thought to be the UV radiation from OB stars (Poglitsch et al. 1991). This will produce hot photodissociation regions but low SiO abundances. It has been proposed that the high temperatures in most of the GC clouds are related to cloud-cloud collisions which are expected to be more frequent in the GC region than in the disk (Wilson et al. 1982). Low velocity shocks associated with cloud-cloud collisions have also been claimed to explain the SiO abundances derived from absorption lines toward Sgr B2M (H\"uttemeister et al. 1995; Peng et al. 1996). The presence of low-velocity shocks were inferred from the narrow linewidths (\apro10 \kms) of the absorption lines. However, the absorption lines only sample a very particular line of sight of the envelope and the line width might not represent the complete kinematics of the envelope. Indeed, the SiO emission in the envelope of Sgr B2 (Fig. 2) shows much broader profiles than the absorption lines with radial velocities of up to \masmenos50 \kms. For shock velocities larger than 40 \kms grain destruction becomes important (Seab \& Shull 1983; Tielens et al. 1994) and Si and/or SiO can be released to gas phase. Therefore the SiO emission in the GC molecular clouds could be associated with relatively fast shocks. The fast shocks in the SiO molecular clouds are very likely of different origin for the different SiO complexes. For the molecular clouds south of Sgr A, there are several evidences suggesting that these molecular clouds are interacting with nearby supernova remnants (Ho et al. 1991; Mezger et al. 1989). In fact the broad lines and the large SiO abundances in the GC clouds resemble those observed in the molecular gas interacting with the supernova remnant IC443 (Turner et al. 1992b). The clouds SiO+0.17-0.01 and SiO+0.20-0.07 clearly follow at large scale the GC radio arc suggesting a physical association with this feature. The SiO emission probably traces the interaction of the molecular material with the non-thermal filaments. Strong shocks will occur either in the case that the relativistic particles present along the filaments impact on the molecular cloud or, conversely, that the relativistic particles originate in the molecular cloud by magnetic field reconnection between the magnetic fields in the molecular cloud and in the radio arc (Serabyn \& G\"usten 1991; Serabyn \& Morris 1994). The origin of strong shocks in the SiO clouds of the Sgr B complex could be due to large scale cloud collisions (Hasegawa et al 1994), expanding bubbles driven by supernovas or HII regions (Soufe 1990, de Vicente et al. 1996) and sources with strong stellar winds like Wolf Rayet stars (Mart{\i}n Pintado et al. 1996). Further high angular resolution observations of molecular and atomic lines are needed to establish the origin of the peculiar chemistry in the GC molecular clouds. \acknowledgments We would like to thank the staffs of the 14-m and 30-m telescopes for support during the observations and P. T. P. Ho for the critical reading of the manuscript. This work has been partially supported by the Spanish CICYT under grant number PB93-048. %% %% References %% \begin{thebibliography}{99} \bibitem{} Altenhoff, W.J., Downes, D., Pauls, T., Schraml, J. 1979, \aaps\ 35, 23 \bibitem{} Bally, J., Stark, A.A., Wilson, R.W. \& Henkel, C. 1987, \aap\ 136, 243 \bibitem{} de Vicente, P., Mart{\i}n-Pintado, J., Wilson, T.L., 1996, \aap, in press %\bibitem{} %Dickinson, D.F., and Rodriguez-Kuiper, E. 1981, \apj\ 247, 112 \bibitem{} Downes, D., Genzel, R., Hjalmarson, A., Nyman, L.A. \& Ronnang, B. 1982, \apjl, 252, L29 %\bibitem{} %Greaves, J. S., White, G. J., Ohishi, M., Hasegawa, T., \& %Sunada, K. 1992, \aap, 260, 381 \bibitem{} G\"usten, R., Walmsley, C.M. \& Pauls, T.A. 1981, \aap, 103, 197 %\bibitem{} %G\"usten, R., Walmsley, C. M., Ungerechts, H. \& Churchwell, E. %1985, \aap, 142, 381 \bibitem{} G\"usten, R., 1989, in IAU Symposium 136, The Galactic Center of the Galaxy, ed. M. Morris, Kluwer Academic Publisher, p. 89 \bibitem{} Hasegawa, T., Sato, F., Whiteoak, J.B., Miyawaki, R. 1994, \apj, 429, L77 \bibitem{} Ho, P. T. P., Ho, L. C., Szczepanski, J. C., Jackson, J. M. \& Armstrong, J. T. 1991, Nature 350, 309 \bibitem{} H\"uttemeister, S., Wilson, T. L., Mauersberger, R., Lemme, C., Dahmen, G. \& Henkel, C. 1995, \aap\, 294, 667 \bibitem{} H\"uttemeister, S., Wilson, T. L., Bania, T. M. \& Mart{\i}n-Pintado, J. 1993, \aap\ 280, 255 \bibitem{} Langer, W.D. \& Glassgold, A.E. 1990, \apj, 352, 121 \bibitem{} Lindqvist, M., Sandqvist, A., Winnberg, A., Johansson, L. E. B. \& Nyman, L. A. 1995, \aaps 113, 257 \bibitem{} Mackay, D.D.S. 1995, \mnras, 274, 694 \bibitem{} Mart{\i}n-Pintado, J., Bachiller, R. \& Fuente, A. 1992, \aap, 54, 315 \bibitem{} Mart{\i}n-Pintado, J., de Vicente, P., Wilson, T.L., Gaume, R., 1996, in ESO-IRAM-NFRA-Osala Workshop on "Science with Large Millimeter Arrays", in press \bibitem{} Mart{\i}n-Pintado, J., de Vicente, P., Fuente, A. 1996, \aap, in preparation \bibitem{} Mezger, P. G., Zylka, R., Chini, R., Salter, C. J. \& Wink, J. E. 1989, \aap, 209, 337 %\bibitem{} %Morris, M., Gilmore, W., Pakmer, P., Turner, B.E., and %Zuckerman, B. 1975, \apjl, 199, L47 \bibitem{} Morris, M., Polish, N., Zuckerman, B., Kaifu, N. 1983, \aj, 88, 1228 \bibitem{} Morris, M., 1989, in IAU Symposium 136, The Galactic Center of the Galaxy, ed. M. Morris, Kluwer Academic Publisher, p. 213 \bibitem{} Odenwald, S.F. \& Fazio, G.G. 1984, \apj, 283, 601 \bibitem{} Peng, Y., Vogel, S.N.\& Carlstrom, J.E. 1996, \apj, in press \bibitem{} Poglitsch, A., Stacey, G. J., Geis, N., Haggerty, M., Jackson, J.,Rumitz, M. Genzel, R. \& Townes, C. H. 1991, \apjl, 374, 33 \bibitem{} Seab, C. G. \& Shull, J. M. 1983, \apj 113, 257 \bibitem{} Serabyn, E. \& G\"usten, R. 1987, \aap\ 184, 133 \bibitem{} Serabyn, E. \& G\"usten, R. 1991, \aap,242, 376 \bibitem{} Serabyn, E. \& Morris, M., 1994, \apjl, 424, L91 \bibitem{} Soufe, Y. 1990, PASJ, 42, 827 \bibitem{} Tielens, A. G. G. M., McKee, C. F.,Seab, C. G. \& Hollenbach, D. J. 1994, \apj, 431, 321 \bibitem{} Turner, B.E. 1992a, \apj, 388, L35 \bibitem{} Turner, B. E., Chan, Kin-Wing, Green, S., Lubowich, D. A. 1992b, \apj, 399, 114 \bibitem{} Wilson, T.L., Ruf, K., Walmsley, C.M., Martin, R.N., Pauls, T.A. \& Batrla, W. 1982, \aap 115, 185 \bibitem{} Ziurys, L.M. \& Friberg, P. 1987, \apjl, 314, L49 %\bibitem{} %Ziurys, L.M. 1988, \apj, 324, L544 %\bibitem{} %Ziurys, L.M., Snell, R.L. \& Dickman, R.L. 1989a, \apj 341, 857 %\bibitem{} %Ziurys, L.M., Friberg, P. \& Irvine, W.M. 1989b, \apj, 343, 201 %\bibitem{} %Wright, M.C.H., Plambeck, R.L., Vogel, S.N., Ho, R.T.P., Welch, %W.J. 1983, \apjl, 267, L41 \end{thebibliography} \begin{plate} \figurenum{1} \caption{{} Fig. 1.-- Integrated line intensity ($-$10 to 90 \kms) map of the \uc\ SiO line toward the Galactic center. The beam size is shown as a open circle in the upper right corner. The dots show the positions where the spectra were taken. The contour levels are 7.3 (4$\sigma$) to 94.5 by 17.4 K \kms. Fig. 2 .-- a) Integrated line intensity map of the \du\ SiO line toward the Sgr B2 molecular cloud. The beam size is shown as a open circle in the lower right corner and the dots show the positions where the spectra were taken. The filled star shows the position of Sgr B2M. The dashed contours correspond to absorption lines observed toward the continuum sources Sgr B2M and Sgr B2N. The contour levels are: -2, 9.2 18.5, 27.7, 36.9 and 41.5 K \kms. b) Integrated line intensity map of the \du\ SiO line toward the Sgr A molecular clouds. The beam size is shown as an open circle in the lower left corner. The open star shows the location of Sgr ${\rm A^*}$ and the filled squares the FIR sources observed in the continuum emission at 1.3mm (Mezger et al. 1989). The dots show the positions where the spectra were taken. The contour levels are: 16 to 105 by 5 K \kms. The location of the two major clouds in the map is shown.} \end{plate} \begin{figure} \figurenum{3} \caption{{} Sample of the \du, \td\ and \cc SiO line profiles taken toward two positions in the Sgr B2 molecular cloud. The offsets in the upper right corner are in arcseconds and refer to the position of Sgr B2M. The line intensity is in units of antenna temperature.} \end{figure} \end{document} ----- End Included Message -----