NED Abstract 
Copyright by American Astronomical Society.
Reproduced by permission

2001AJ....122.2969H

 HIGH-RESOLUTION H I MAPPING OF NGC 4038/39 ("THE ANTENNAE") AND ITS TIDAL
                          DWARF GALAXY CANDIDATES

                               J. E. HIBBARD
 National Radio Astronomy Observatory,1 520 Edgemont Road, Charlottesville,
                        VA 22903; jhibbard@nrao.edu

                            J. M. VAN DER HULST
     Kapteyn Astronomical Institute, Postbus 800, NL-9700 AV Groningen,
                     Netherlands; vdhulst@astro.rug.nl

                               J. E. BARNES
    Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive,
                 Honolulu, HI 96822; barnes@ifa.hawaii.edu

                                    AND
                                R. M. RICH
   Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562;
                             rmr@astro.ucla.edu
              Received 2001 April 30; accepted 2001 August 27

                                 ABSTRACT
   We present new VLA C + D array H I observations and optical and
near-infrared imaging of the well-known interacting system NGC 4038/39,
"The Antennae." At low spatial resolution (~40"), the radio data reach a 
limiting column density of ~10^19^ cm^-2^ (2.5 {sigma}), providing 
significantly deeper mapping of the tidal features than afforded by 
earlier H I maps. At relatively high spatial resolution (~10"), the radio 
data reveal a wealth of gaseous substructure both within the main bodies 
of the galaxies and along the tidal tails. In agreement with previous H I 
studies, we find that the northern tail has H I along its outer length but 
none along its base. We suggest that the H I at the base of this tail has 
been ionized by massive stars in the disk of NGC 4038. The gas in the 
southern tail has a bifurcated structure, with one filament lying along 
the optical tail and another running parallel to it but with no optical 
counterpart. The two filaments join just before the location of several 
star-forming regions near the end of the tail. The H I velocity field at 
the end of the tail is dominated by strong velocity gradients, which 
suggests that at this location the tail is bending away from us. We 
delineate and examine two regions within the tail previously identified as 
possible sites of a so-called tidal dwarf galaxy condensing out of the 
expanding tidal material. The tail velocity gradients mask any clear 
kinematic signature of a self-gravitating condensation in this region. A 
dynamical analysis suggests that there is not enough mass in gas alone for 
either of these regions to be self-gravitating. Conversely, if they are 
bound they require a significant contribution to their dynamical mass from 
evolved stars or dark matter. Even if there are no distinct dynamical tidal 
entities, it is clear that there is a unique concentration of gas, stars, 
and star-forming regions within the southern tail: the H I channel maps 
show clear evidence for a significant condensation near the tail 
star-forming regions, with the single-channel H I column densities higher 
than anywhere else in the system, including within the main disks. Finally, 
the data reveal H I emission associated with the edge-on "superthin" Scd 
galaxy ESO 572-G045, which lies just beyond the southern tidal tail of 
The Antennae, showing it to be a companion system.

Key words: galaxies: evolution - galaxies: individual (NGC 4038/39) - 
galaxies: interactions - galaxies: ISM - galaxies: kinematics and dynamics 
- galaxies: peculiar