------------------------------------------------------------------------ From: Pablo de Vicente vicente@oan.es To: gcnews@aoc.nrao.edu %http://www.oan.es/preprints/oan00-23.pdf %astro-ph/0011512 %\documentclass{aastex} %\documentclass[preprint]{aastex} \documentclass[preprint2]{aastex} %\def\lsim{\raisebox{-.4ex}{$\stackrel{<}{\scriptstyle \sim}$\,}} % less or similar to \def\c2h5oh {\hbox{${\rm C}_2{\rm H}_5{\rm OH}$}} %C2H5OH \def\tco {\hbox{$^{13}{\rm CO}$}} %13CO \def\cdo {\hbox{${\rm C}^{18}{\rm O}$}} %C18O \def\ct {\rm J$_{Ka,Kc}$=4$_{1,4}$\raw 3$_{0,3}$} \def\sc {\rm J$_{Ka,Kc}$=6$_{3,4}$\raw 5$_{2,3}$} \def\no {\rm J$_{Ka,Kc}$=9$_{0,9}$\raw 8$_{1,8}$} \def\as {\ifmmode {^{\scriptscriptstyle\prime\prime}} % arcsec \else $^{\scriptscriptstyle\prime\prime}$\fi} \def\asns {\ifmmode {^{\scriptscriptstyle\prime\prime};} %arcsec \else $^{\scriptscriptstyle\prime\prime};$\fi} \def\ta*{$T_{\rm A}^{*}$} \def\tex {$T_{\rm ex}$} \def\tkin {$T_{\rm kin}$} \chardef\isp="10 \def\i{\'\isp} \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\am {\ifmmode {^{\scriptscriptstyle\prime}} % arcmin \else $^{\scriptscriptstyle\prime}$\fi} \def\deg {\ifmmode^\circ\else$^\circ$\fi} % degree \def\eg{{\rm e.g.\/\ }} \def\raw {\ifmmode\rightarrow\else$\rightarrow$\fi} \def\uc{\rm J=1\raw0} \def\du{\rm J=2\raw1} % J=2-1 \def\td{\rm J=3\raw2} % J=3-2 \def \galpha {$\alpha $} % gr. alpha \def\hdos {\hbox{${\rm H}_2$}} %H2 \def\cmm#1{\ifmmode {\,{\rm cm^{-#1}}\;} % cm-1, cm-2, cm-3, ... \else \hbox{$\,${\rm cm$^{\rm -#1}\;$}}\fi} \def\menos{$-$} \def\masmenos{\ifmmode {\pm} \else $\pm$ \fi} % mas menos \def\kmsns{~km~s$^{-1}$} \def\kms{\ifmmode {{\rm \;km\;s^{-1}\;}} % km s-1 \else {\hbox{$\,${\rm km$\;$s$^{\rm -1}\;$}}}\fi} \def\ie {i.\,e.} \def\apro{$\sim$} %aproximado \def\gt{\ifmmode {>}\else{$>$}\fi} \def\c2h5oh{\hbox{${\rm C}_2{\rm H}_5{\rm OH}$}} %C2H5OH \def\E#1{\ifmmode \,10^{#1}\; \else {${\rm\,10^{#1}}\;$}\fi} %10^ \def\T#1{\ifmmode {$\times$10^{#1}\;} \else {\hbox{$$\times$10^{#1}\;$}\fi}} %\received{} %\accepted{} %\journalid{}{} %\articleid{}{} %\slugcomment{Manuscript draft September, 2000} \lefthead{} \righthead{} \begin{document} \title{Large scale grain mantle disruption in the Galactic Center } \author{J. Mart{\i}n-Pintado\altaffilmark{1}, J. R. Rizzo\altaffilmark{1}, P. de Vicente\altaffilmark{1}, N. J. Rodr{\i}guez-Fern\'andez\altaffilmark{1} and A. Fuente\altaffilmark{1}} \altaffiltext{1} {Observatorio Astron\'omico Nacional, Apartado 1143, E-28800 Alcal\'a de Henares, Spain} \begin{abstract} We present observations of \c2h5oh toward molecular clouds in Sgr A, Sgr B2 and associated with thermal and non-thermal features in the Galactic center. \c2h5oh emission in Sgr A and Sgr B2 is widespread, but not uniform. \c2h5oh emission is much weaker or it is not detected in some molecular clouds in both complexes, in particular those with radial velocities between 70 and 120 \kms. While most of the clouds associated with the thermal features do not show \c2h5oh emission, that associated with the Non-Thermal Radio Arc shows emission. % Comparison between the column densities of \tco, CS and \c2h5oh shows that %the \tco/CS abundance ratio is fairly constant in all molecular clouds and %that the %abundance of \c2h5oh must change by more than one order of magnitude. The fractional abundance of \c2h5oh in most of the clouds with radial velocities between 0 and 70 \kms in Sgr A and Sgr B2 is relatively high, of few \E{-8}. The \c2h5oh abundance decreases by more than one order of magnitude (\lsim \E{-9}) in the clouds associated with the thermal features. The large abundance of \c2h5oh in the gas-phase indicates that \c2h5oh has formed in grains and released to gas-phase by shocks in the last \apro \E{5} years. %This picture also explains the low \c2h5oh abundance in the thermal features %where heating is dominated by the UV radiation from massive evolved stars. %According with current chemical model, the of \c2h5oh in the Sgr A and Sgr %B2 clouds should have occurred nearly simultaneously and very recently, in %\lsim \T{5} years. The implications of this finding in the origin of the shocks in the GC is briefly discussed. %Two possible scenarios could account for the %time scale implied from the ethanol evaporation, large scale shocks related %to infall of matter toward the GC and/or shocks produced by evolved massive %stars formed in a starburst \apro\T{7} years ago. \end{abstract} \keywords{ Galaxy: center--ISM: abundance -- ISM: molecules-radio lines} \section{Introduction} Ethanol (\c2h5oh) was first detected by \citet{zuckerman75} towards the massive star forming region in the Galactic center (GC) Sgr B2. Subsequent observations of this molecule in the interstellar medium have shown that \c2h5oh is only present in the dense (\gsim\E{6}\cmm3) and hot (\gsim 100K) cores associated with newly formed massive stars \citep{irvine87,millar88,ohishi95,millar95,nummelin98}. In hot cores, the abundance of \c2h5oh in gas-phase ranges from \E{-8} to \E{-9}, and gas-phase chemistry cannot account even for the lowest fractional abundance of this molecule. Therefore, \c2h5oh emission is considered one of the best tracers of dust chemistry \citep{millar88,charnley92,charnley95}. %In the hot cores, c2h5oh %or its precursor in the gas-phase chemistry %was likely formed in grains during the colder previous stage. Furthermore, the transient nature of the alcohol chemistry in molecular clouds, makes the abundance of \c2h5oh an excellent clock to estimate when this molecule was injected to the gas-phase \citep{charnley95}. %Evaporation of the % of \c2h5oh or its precursor %icy mantles from warm grains heated by recently formed massive stars can %account for the abundance of gas-phase \c2h5oh in hot cores. The GC molecular clouds show high kinetic temperatures (\gsim 80 K) \citep{hutte93, rodriguez01} and widespread large abundance of refractory molecules like SiO \citep{martin97}. Shock waves have been invoked to explain the heating, the morphology and the relatively large abundance of SiO in the GC \citep{martin97}. Shocks are also expected to sputter molecules from the icy grain mantles increasing the gas-phase abundance of the molecules formed in grains. Evidences for the release of molecules from grain mantles in selected molecular clouds close to Sgr A comes from the detection of \c2h5oh and HOCO$^+$\ in this region \citep{minh92, charnley00}. In the scenario that shocks drive the chemistry in the GC clouds, it is expected that widespread \c2h5oh emission closely follows that of SiO. In this letter we present observations of \c2h5oh toward molecular clouds in Sgr A, Sgr B2 complexes and associated with the thermal features (Arched Filaments --hereafter TAF-- and the Sickle) and the Non Thermal Radio Arc (NTRA) in the GC \citep[for the nomenclature]{lang99}. We find that the \c2h5oh emission in the GC is widespread, but large variations in the abundance of this molecule are found between the different GC molecular clouds. The large \c2h5oh abundance and its variations are consistent with a scenario in which recent (\lsim \E{5} years) shocks dominate the chemistry in the GC by grain processing. \section {Observations and results} The observations of the \ct, \sc\ and \no\ lines of \c2h5oh towards the GC were carried out simultaneously with the IRAM 30-m telescope. To estimate the \hdos\ column density we also observed simultaneously the \uc\ line of \tco\ and \cdo, the \du\ line of \cdo\, and the \td\ line of CS. The half power beam width of the telescope was 24\as, 17\as\ and 12\as\ for the 3, 2 and 1.3 mm bands. The receivers, equipped with SIS mixers, were tuned to single side band with image rejections of \gsim 10 dB. The typical system temperatures were 300, 500 and 900 K for the 3, 2 and 1.3 mm lines respectively. We used two filter banks of 256$\times$1MHz and one of 512$\times$1MHz as spectrometers. The velocity resolution provided by the filter banks were 3, 2 and 1.3 \kms for the 3, 2 and 1.3 mm bands respectively. The calibration was achieved by observing hot and cold loads. The line intensities are given in units of \ta*. The observed molecular clouds were selected from the SiO maps of \cite{martin97} and their locations are shown in the upper panel of Fig. 1. The typical line profiles of \c2h5oh, \tco\ and CS towards selected clouds in SgrA (M-0.11-0.08), in Sgr B2 (M+0.76-0.05), and associated with the Sickle (M+0.20-0.03) and the NTRA (M+0.17+0.01) are shown in the lower panels of Fig. 1. Table 1 summarizes the results obtained for all molecular clouds. The emission in the \ct\ line of \c2h5oh is widespread in Sgr A and Sgr B2. However, the line profiles of \c2h5oh are different from those of CS, \tco, and \cdo. This is illustrated in Fig. 1 for M+0.76-0.06. The CS and the \tco\ emission appears from -20 \kms to 120 \kms. However, like the SiO emission in Sgr A and Sgr B2 \citep{martin00}, the \c2h5oh emission mainly appears for radial velocities between 10 and 70 \kms. This indicates variations in the abundance of \c2h5oh in the molecular clouds along the line of sight with different radial velocities. Column 4 in Table 1 gives the radial velocity of the peak intensity of the \ct\ \c2h5oh line and the velocity range where the \c2h5oh emission is detected. The morphology of the \c2h5oh emission in the GC is also different from those of CS, \tco, and \cdo. \c2h5oh emission is not detected towards M-0.08-0.06 in SgrA. Furthermore, the \c2h5oh emission shows different behavior towards the different kind of filaments in the GC. In general, the molecular clouds associated with the thermal features like the Sickle \citep[M+0.18-0.04 and M+0.20-0.03]{serabyn91} and the TAFs E1 and E2 \citep[M+0.13+0.02 and M+0.17+0.01]{serabyn87} do not show \c2h5oh emission. An interesting exception is the detection of \c2h5oh emission towards M+0.04+0.03, a molecular cloud located south of the TAF W1. However, the rather narrow radial velocity range of the \c2h5oh emission as compared with those of the CS and \tco \ emission \citep{serabyn87} suggests that the bulk of the molecular gas associated with thermal features does not show \c2h5oh emission. Mapping of the \c2h5oh emission in this region will tell the possible association of this velocity component with the thermal features. In contrast to the lack of \c2h5oh emission from the molecular clouds associated with the thermal features, weak \c2h5oh emission is detected towards M+0.17+0.01 in the NTRA. In summary, \c2h5oh emission in the GC molecular clouds is widespread, but it shows substantial differences between the different features in the GC. Furthermore, the \c2h5oh emission is mainly restricted to molecular clouds with radial velocities between 10 and 70 \kms. \section{Excitation and abundance of \c2h5oh in the GC} The lack of \c2h5oh emission towards some molecular clouds in the GC with CS emission cannot be due to excitation effects since the \ct\ line of \c2h5oh and the CS J=3-2 line have similar critical densities. The difference between CS and \c2h5oh emissions must be due to changes in the abundance of these molecules. The three \c2h5oh lines can be combined to estimate the \hdos\ densities and the \c2h5oh column densities. The excitation temperature, \tex, derived from the column densities of the \ct\ and \no\ lines are given in column 5 of Table 1. For the sources detected in both lines, the derived \tex\ ranges from 9 to 14 K. Considering a collisional cross section of \c2h5oh similar to that of CH$_3$OH, the \tex\ derived from the \c2h5oh lines indicates \hdos\ densities of few \E{4}cm$^{-3}$. These densitites are in good agreement with those obtained from SiO and CS for the GC clouds \citep{martin97,hutte98,serabyn87,serabyn91}. For the other sources, the upper limits are between 8 and 13 K. In the following we will assume a \tex\ of 7 K for these sources. The total \c2h5oh column densities have been derived by assuming optically thin emission, and using the three substates partition function given by \citet{pearson97} for the \tex\ in Table 1. Since the {\it $gauche+$} and {\it gauche--} torsional substates are not excited, only the {\it trans} substate has been considered. Since the \c2h5oh profiles are, in general, different from those of CS and \tco, in Table 1 we give two different column densities for \c2h5oh. The first one derived for the velocity range (column 4 in Table 1) where the \c2h5oh line has been detected ('yes' column), and the second one the upper limit derived for the velocity range with CS and \tco, but without \c2h5oh emission ('no' column). Table 1 also gives the column densities of \tco\ and CS derived for the two velocity ranges using the typical conditions in the GC, an \hdos\ density of 3 \E{4}\cmm3 and a kinetic temperature of \apro80 K. The ratio between CS and \tco\ column densities for all sources and the two velocity ranges is fairly constant with a value of \apro\E{-2}. This indicates that the CS abundance in the GC molecular clouds is roughly constant. For the typical \tco\ to \hdos\ abundance ratio in the GC of 5 \E{-6}, we derive a CS abundance of \apro 5 \E{-8}. For this CS abundance we derive a \c2h5oh abundance (see column 9 of Table 1) of 0.4-5$\times$\E{-8} for the clouds with \c2h5oh emission. For the other clouds such as those associated with the thermal features, the \c2h5oh abundance decreases by at least more than one order of magnitude. We conclude that large \c2h5oh abundance of a few \E{-8} is found in most of the GC molecular clouds in the Sgr A and Sgr B2 complexes with radial velocities between 10 and 70 \kms and the NTRA. However, the \c2h5oh abundance is not uniform and drops by more than one order of magnitude towards some molecular clouds in both complexes and the material associated with the thermal features in the GC. \section {Discussion} The widespread large abundance of \c2h5oh in most of the GC clouds is a clear signature that large scale grain mantle erosion is taking place in this region of the Galaxy. The abundance of \c2h5oh in the GC clouds is even larger than those measured in the hot cores in the galactic disk \citep{nummelin98}. In hot cores, the high \c2h5oh abundance is explained by grain surface chemistry and subsequent thermal evaporation from the grains when they are heated by recently formed massive stars \citep{millar91,charnley95}. In the GC clouds, most of the dust is cold with dust temperatures of 20-30 K \citep{martin99b,rodriguez00} which are too low to evaporate the icy mantle from the grains. %Thermal evaporation of \c2h5oh from the warm dust component %in the GC is very unlikely. For the column densities of warm dust, typically %three orders of magnitude smaller than those of the cold dust %\cite{martin99b}, the abundance of \c2h5oh would be few \E{-5}, %close to that of CO. Further support for the association of \c2h5oh with the cold dust comes from the low \c2h5oh abundance measured toward the thermal features such as the Sickle that show large column densities of warm dust \citep{simpson97}. This is likely due to the fact that the UV photons that heat the dust also photodissociate the thermal evaporated \c2h5oh. Thus, thermal evaporation of grain mantles in the GC clouds does not seem to account for the measured \c2h5oh abundance in the GC. Shock waves are thought to dominate the heating and the chemistry of refractory elements in the GC \citep{wilson82,martin97,hutte98}. \c2h5oh sputtered off the grain mantles by shock waves can explain the observed widespread large abundance of this molecule associated with the cold dust in the GC. C-shocks with moderate velocities of 30-40 \kms can produce substantial grain processing \citep{flower96,caselli97,charnley00} explaining the large abundance of SiO, \c2h5oh and HOCO$^+$ in the GC. The picture emerging from all the molecular data is that the chemistry in the GC is largely driven by widespread shocks with moderate velocities of \lsim 40 \kms. One interesting aspect of alcohol chemistry is its transient nature \citep{millar91,charnley95}. The typical time scale for ethanol destruction after the injection into gas-phase is \apro \E{4} years for the hot core conditions \citep{charnley95}. For the typical \hdos\ densities in the GC clouds, an order of magnitude smaller than those for the hot cores, the estimated time scale for destruction of \c2h5oh would be \apro \E{5} years. This indicates that the widespread shocks that drive the chemistry in the GC have occurred in the last \apro \E{5} years. Similar time scales for the shocks have been derived from the non-equilibrium \hdos\ ortho-to-para ratios in two GC clouds \citep{rodriguez00}. Several possibilities have been proposed for the origin of the widespread shocks in the GC: shocks due to cloud-cloud collisions associated with the large scale dynamics in the context of a bar potential \citep{wilson82,hasegawa94,hutte98} and shocks produced by wind-blown bubbles driven by evolved massive stars \citep{martin99a}. Both mechanisms seem to account for the time scales derived from the abundance of \c2h5oh. The time scale derived for the cloud-cloud collisions would be less than the galactic rotation period of \apro \E{6} years \citep{gusten89}. This scenario is supported by the large SiO abundances found at the outer inner Lindblad resonance in the Milky Way \citep{hutte98} and in NGC253 \citep{burillo00}. The wind-blown bubbles driven by evolved massive stars have typical dynamical ages of \apro \E{5} years, consistent with the life time derived from ethanol. Furthermore, evolved massive stars also explain the correlation between the large \c2h5oh and SiO abundance in the molecular clouds with radial velocities between 10 and 70 \kms and the Fe 6.4 keV lines \citep{martin00}. However, this scenario can only explain the widespread large \c2h5oh and SiO abundance if a burst of massive star formation has occurred in the GC \apro \E{7} years ago. Large scale mapping of the GC in molecular species dominated by different type of chemistry will help to establish the origin of the shocks. 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O., 1975 \apjl, 196, L99--L102 \end{thebibliography} \clearpage \figcaption[fig.eps]{ Upper panel) Location of the position observed in \c2h5oh, \tco, \cdo\ and CS shown by filled circles superposed on the spatial distribution of the SiO emission from \cite{martin97}. The contour levels from 7.3 to 94.5 by 17.4 K \kms. Lower panel) Profiles of the \tco\ \uc, CS \td, and the \ct\ and \no\ \c2h5oh (Ethanol 4--3, Ethanol 9--8) lines towards the selected position shown in the upper panel. \label{fig1}} \begin{deluxetable}{lccrrrrrrrrrrrrr} % \tablecolumns{16} \tablewidth{0pc} \tablecaption{Derived physical conditions} %\footnotesize %\scriptsize \rotate \tabletypesize{\footnotesize} % \tablehead{ \colhead{Source} & \colhead{$\alpha$} & \colhead{$\delta$} & \colhead{V$_0$ (V$_i$,V$_f$)\tablenotemark{a}} & \colhead{T$_{ex}$\tablenotemark{b}} & \multicolumn{2}{c}{N($^{13}$CO)} && \multicolumn{2}{c}{N(CS)} && \multicolumn{2}{c}{N(eth.)} && \multicolumn{2}{c}{[eth.]/[CS]}\\ \colhead{} & \colhead{17$^{\rm h}42^{\rm m}$} & \colhead{$-28\degr$} & \colhead{(km s$^{-1}$)} & \colhead{(K)} & \multicolumn{2}{c}{(10$^{16}$\,cm$^{-2}$)} && \multicolumn{2}{c}{(10$^{14}$\,cm$^{-2}$)} && \multicolumn{2}{c}{(10$^{14}$\,cm$^{-2}$)} && \multicolumn{2}{c}{$10^{-1}$}\\ \cline{6-7} \cline{9-10} \cline{12-13} \cline{15-16} \colhead{} & \multicolumn{2}{c}{(B1950)} & \multicolumn{2}{c}{} & \colhead{yes} & \colhead{no} && \colhead{yes} & \colhead{no} && \colhead{yes} & \colhead{no} && \colhead{yes} & \colhead{no} } % \startdata M-0.11-0.08 & 28.0 & 62.9 & 19.8\,(5,\,32) & 11 & 5& 3&& 15& 2&& 7& \lsim0.4&& 4.7& \lsim2.2 \\ M-0.08-0.06 & \phn30.0 & 61.0 & 29.7\,(19,\,42) & \lsim9 & 7& 5&& 6& 3&& 2& \lsim0.8&& 2.8& \lsim2.4 \\ M-0.04-0.03 & \phn29.1 & 58.1 & (-20,\,103) & \nodata & \nodata & 15&& \nodata & 15&& \nodata & \lsim0.4&& \nodata & \lsim0.3 \\ M-0.02-0.07 & \phn40.0 & 58.0 & 47.4\,(36,\,67) & 14 & 44& \nodata && 22& \nodata && 11& \nodata && 4.7 & \nodata \\ M+0.04+0.03 & \phn26.2 & 51.8 & -30.6\,(-38,\,-25) & $\approx$ 10 & 4& 12&& 4& 8&& 1& \lsim0.6&& 2.8 & \lsim0.7 \\ M+0.07-0.07 & \phn54.2 & 53.5 & 52.8\,(37,\,67) & 12 & 10& 7&& 12& 5&& 5& \lsim0.6&& 3.9 & \lsim1.1 \\ M+0.13+0.02 & \phn41.4 & 47.6 & (-39,\,95) & \nodata & \nodata & 17&& \nodata & 17&& \nodata & \lsim0.5&& \nodata & \lsim0.3 \\ M+0.17+0.01 & \phn50.0 & 45.8 & 59.8\,52,\,69) & $\approx$13 & 9& \nodata && 7& \nodata && 1& \nodata && 0.8 & \nodata \\ M+0.18-0.04 & \phn61.0 & 47.3 & (5,\,90)& \nodata & \nodata & 13&& \nodata & 10&& \nodata & \lsim0.3&& \nodata & \lsim0.3 \\ M+0.20-0.03 & \phn63.6 & 45.7 & (3,\,100) & \nodata & \nodata & 19&& \nodata & 13&& \nodata & \lsim0.2&& \nodata & \lsim0.2 \\ M+0.24+0.01 & \phn59.6 & 42.6 & 36.4\,(23,\,53) & 12 & 10& 8&& 10& 4&& 8& \lsim0.4&& 8.4 & \lsim1.1 \\ M+0.59-0.02 & 116.4 & 25.3& 73.5\,(50,\,94) & \lsim11 & 6& \nodata && 4& \nodata && 1& \nodata && 3.2 & \nodata \\ M+0.62-0.10 & 137.0 & 26.5& 56.5\,(42,\,72)& 10 & 6& 2&& 6& 1&& 3& \lsim0.3&& 5.9 & \lsim2.1 \\ M+0.64-0.08 & 137.5 & 24.5& 60.8\,(42,\,72) & \lsim9 & 5& 4&& 6& 4&& 2& \lsim0.5&& 3.3 & \lsim1.3 \\ M+0.67-0.06 & 137.0 & 22.5& 50.6\,(31,\,78)& $\approx$ 9 & 10& 3&& 14& 2&& 3& \lsim0.4&& 1.9 & \lsim1.9 \\ M+0.68-0.10 & 147.2 & 23.3& 22.1\,(0,\,40) & $\approx$ 9 & 10& 3&& 13& 1&& 5& \lsim0.5&& 3.7 & \lsim3.4 \\ M+0.70-0.01\tablenotemark{c} & 130.0 & 19.5& 62.2\,(52,\,74)& 13 & \nodata & \nodata && \nodata & \nodata && 3& \nodata && \nodata & \nodata \\ M+0.70-0.09 & 147.2 & 22.1& 43.0\,(29,\,62)& \lsim10 & 8& 8&& 5& 5&& 2& \lsim1.0&& 3.3& \lsim2.2 \\ M+0.71-0.13 & 158.4 & 22.4& 42.0\,(13,\,74) & \lsim9 & 13& 6&& 9& 4&& 2& \lsim1.2&& 2.7& \lsim3.1 \\ M+0.76-0.05 & 147.2 & 17.6& 32.4\,(14,\,59) & \lsim8 & 13& 10&& 13& 10&& 6& \lsim0.4&& 5.0 & \lsim0.4 \\ \enddata % \tablenotetext{a}{\ V$_0$ is the LSR velocity at the peak intensity of the \c2h5oh \ct line. When this line is detected, (V$_i$, V$_f$) is the velocity range where \c2h5oh emission is detected. When \c2h5oh is not detected, (V$_i$, V$_f$) represent the full velocity range of the CS and \tco\ emission.} \tablenotetext{b}{\ T$_{ex}$ is the excitation temperature derived from the \ct\ and the \no lines of \c2h5oh (see text).} % \end{deluxetable} % \end{document} ------------------------------------------------------- -- ________________________________________________________ Pablo de Vicente (vicente@oan.es), http://www.oan.es, OAN Spain