Kinematics of Galaxies in the Hubble Deep Field South: Discovery of a
Very Massive Spiral at z=0.6
ArXiv astro-ph/0207457 (2002)
Authors:
D Rigopoulou, A Franceschini, H Aussel, R Genzel, N Thatte, CJ Cesarsky
Abstract:
We report the first results from a study of the internal kinematics, based on
spatially resolved H_alpha velocity profiles, of three galaxies at redshift
z~0.6 and one at redshift z~0.8, detected by ISOCAM in the Hubble Deep Field
South. The kinematics are derived from high resolution near-infrared VLT
spectroscopy. One of the galaxies is a massive spiral which possesses a very
large rotational velocity of 460 km/s and contains a mass of 10^12 M_solar
(within 20 kpc), significantly higher than the dynamical masses measured in
most other local and high redshift spirals. Two of the galaxies comprise a
counter-rotating interacting system, while the fourth is also a large spiral.
The observed galaxies are representative examples of the morphologies
encountered among ISOCAM galaxies. The mass-to-light (M /L_bol) ratios of
ISOCAM galaxies lie between those of local luminous IR galaxies and massive
spirals. We measure an offset of 1.6+/-0.3 mag in the rest frame B-band and of
0.7+/-0.3 mag in the rest frame I-band when we compare the four ISOCAM galaxies
to the local Tully-Fisher B and I-band relations. We conclude that the large IR
luminosity of the ISOCAM population results from a combination of large mass
and efficient triggering of star formation. Since ISOCAM galaxies contribute
significantly to the Cosmic Infrared Background our results imply that a
relatively small number of very massive and IR luminous objects contribute
significantly to the IR background and star formation activity near z~0.7.
