{\bf ABSTRACT}

We propose to use the NRAO 12m 
telescope
to search for CO (J = 1 - 0) emission from the tidal tails
of five merging or interacting galaxies.
These plumes are very HI-rich, and may contain star forming regions;
they may eventually evolve into independent dwarf galaxies.
Determining the molecular content of these plumes is important 
in understanding the issue of star formation in tidal
plumes,
as well as in understanding their
origin and
subsequent development.

{\bf I. Scientific Justification}

At low optical surface brightness levels, a subset of peculiar
galaxies show long thin streamers extending $\sim$100 kpc from 
the nucleus. 
These ``tidal tails'' are now recognized to be the endproduct of the merger (or 
close encounter) of two galaxies (Toomre and Toomre 1972).
It was hypothesized early on (Zwicky 1956) that such structures might be
able to form density concentrations that would eventually become independant dwarf galaxies. This idea has been revived recently on theoretical grounds
(Gerola et al. 1983; Barnes and Hernquist 1992; Elmegreen et al. 1993), 
and on the basis of optical observations of tidal tails (Mirabel et al. 1991, 1992). The formation of
a class of galaxies through tidal interactions has obvious implications for
our understanding of galaxy evolution, such as the question of how many
dwarfs have apparently avoided significant amounts of star formation over a 
Hubble time.

Radio HI observations of tidal tails show them to be gas rich, with
numerous clumps of high column density. The HI masses 
of these clumps are often $\sim$10$^{9}$ M$_{\odot}$, 
and several are known to possess faint star forming regions 
(Mirabel et al. 1991, 1992). The observed HI and optical properties of the
clumps are similar to those found in
dwarf galaxies (Hunter and Gallagher 1985; Kunth 1986). The presence of 
massive star formation associated 
with the HI clumps suggests that molecular material is also present, 
especially since the clump
HI column densities often exceed the self-shielding limit
($\sim$10$^{21}$ cm$^{-2}$; Federman et al. 1979). While a growing set of 
optical and radio observations exist, no CO studies have 
been published. Such information would be valuable to 
our understanding of the evolution of tidal plumes. 

{\bf II. Proposed Observations}

We propose to use the NRAO 12m 
telescope to search for molecular 
gas in the tidal tails of five peculiar galaxies using the
$^{12}$CO(1-0) line.
These galaxies are given in Table 1, along with their coordinates, 
the HI masses of the plumes, their velocities, and the reference for
the HI data.
These systems were chosen on the basis of their 
well developed plumes and the availability of HI data
indicating conditions favorable for star formation.
Their photographs in the Arp Atlas (1966) show 
long plumes characteristic of recent mergers or close encounters.
Clumpy HI counterparts of the optical tails have been discovered in each 
system, 
with HI column densities 
of
$\sim$4 $\times$ 10$^{20}$ cm$^{-2}$
over angular sizes comparable to the 
NRAO beam.  We intend to observe an average of two positions per
plume, at the HI maxima. 
Peak column densities at these
positions are above 10$^{21}$ cm$^{-2}$.
	
These observations will be made in conjunction with optical imaging
and spectroscopy to be done at McDonald Observatory, as part of our efforts
to determine the distribution and properties of star forming regions
in the plumes.

{\bf III. Signal Estimates}

To reach an average H$_2$/HI ratio of 0.2 for the HI concentrations in
the plumes (similar to that
found in many dwarf galaxies [Combes 1986; Tacconi and Young 1987],
assuming the Galactic conversion factor) requires a 3$\sigma$ 
level
of I(CO) $\sim$ 0.27 K km/s. Using the HI line widths
of $\sim$50 km s$^{-1}$ seen in these plumes and a 5 km s$^{-1}$ 
channel width, this 
requires an rms noise level of T$_R$$^*$ = 5.6 mK. Assuming Tsys = 350 K, 
a 2 MHz filter bank bandwidth, two polarizations, 
and an efficiency $\eta$  = 0.5, 
this requires an
integration time of 4.5 hours. 
We are requesting 54 hours of observing time for this project, allocating
4.5 hours per position, two positions per galaxy, 
with 9 additional hours 
for calibration and setup. 

\vskip 0.1in

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