From colgan@cygnus.arc.nasa.gov Wed Apr 24 14:51:12 1996
Date: Wed, 24 Apr 1996 11:50:06 -0700
From: "Sean W. J. Colgan" <colgan@cygnus.arc.nasa.gov>
To: gcnews@astro.umd.edu
Subject: submit Filaments ApJ accepted

\title{Excitation of the \lq\lq Arched\rq\rq\  Filaments 
near the Galactic Center }
\vskip0.7in
\author{Sean W. J. Colgan$^{1,2}$, Edwin F. Erickson$^{2}$, 
Janet P. Simpson$^{1,2}$, }
\author{
Michael R. Haas$^{2}$,
and Mark Morris$^{3}$}
\vskip.6in\noindent
\institute{$^{1}$The SETI Institute
\vskip.02in\noindent
$^{2}$NASA/Ames Research Center, MS 245-6, Moffett Field
      CA 94035-1000
\vskip.02in\noindent
$^{3}$UCLA, Dept. of Astronomy, 8979 Math-Sciences Bldg., Los Angeles, CA 90024
}\vskip2.in
\noindent Submitted to  {\it The Astrophysical Journal }:  October 9, 1995

\abstract

We present measurements of 
the far-infrared (FIR) fine structure lines 
[S\III.] (33 \mm.), [Si\II.] (35 \mm.), [O\III.] (52, 88 \mm.), 
[O\I.] (63 \mm.), and [C\II.] (158 \mm.)
and the adjacent continua at these wavelengths 
in a strip crossing 
the E2 and W1 thermal radio filaments in the Galactic Center ``Arc''.
The properties of the two filaments are similar: 
the line and continuum fluxes peak in the vicinity of the radio ridges, 
and the contrast of the ridge fluxes relative to the off-ridge fluxes 
is greatest for the FIR continuum and doubly ionized lines, 
lower for the single-dish radio measurements (Sofue \etal. 1986) 
and smallest for the low excitation lines. 
The near spatial coincidence of the line and continuum emission maxima 
with the radio filaments 
demonstrates that the same excitation source 
must be responsible for both the line and the continuum emission. 
The peak FIR luminosity of $\sim 2.5\times10^5$ L\sun. per 30$''$ beam 
and the association of [O\III.] intensity with the filaments 
pose difficulties for shock and MHD models. 
Excitation by a string of stars is also unlikely,
but photoionization of molecular cloud edges 
by a quasi-uniform distribution of stars is the most plausible 
excitation source proposed. 
The peak ionized line intensity is shifted slightly eastward 
relative to the FIR continuum emission. 
The deduced excitation, 
as measured by the [O\III.] to [S\III.] line flux ratios, 
also peaks slightly east of the radio ridges. 
Together, these two measurements suggest 
a substantial contribution from an ionizing source to the east. 
The strengths of the [O\I.] and [C\II.] lines 
are consistent with their 
production in photodissociated molecular material 
adjacent to the photoionized gas, 
but the FIR luminosity and the [Si\II.] emission 
appear to originate predominantly in or very near to the ionized gas. 

\vskip0.5truein
\subjectheading{
Galaxy: center --- 
infrared: interstellar: lines --- 
infrared: interstellar: continuum 
}

\end


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