The stellar kinematic fields of NGC 3379

Citation
Ts. Statler et T. Smecker-hane, The stellar kinematic fields of NGC 3379, ASTRONOM J, 117(2), 1999, pp. 839-854
Citations number
42
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMICAL JOURNAL
ISSN journal
00046256 → ACNP
Volume
117
Issue
2
Year of publication
1999
Pages
839 - 854
Database
ISI
SICI code
0004-6256(199902)117:2<839:TSKFON>2.0.ZU;2-1
Abstract
We have measured the stellar kinematic profiles of NGC 3379 along four posi tion angles, using absorption lines in spectra obtained with the Multiple M irror Telescope. We derive a far more detailed description of the kinematic fields through the main body of the galaxy than could be obtained from pre vious work. Our data extend 90" from the center, at essentially seeing-limi ted resolution out to 17". The derived mean velocities and dispersions have total errors (internal and systematic) better than +/-10 km s(-1), and fre quently better than 5 km s(-1), out to 55". We find very weak (3 km s(-1)) rotation on the minor axis interior to 12" and no detectable rotation above 6 km s(-1) from 12" to 50" or above 16 km s(-1) out to 90" (95% confidence limits). However, a Fourier reconstruction of the mean velocity field from all four sampled PAs does indicate a approximate to 5 degrees twist of the kinematic major axis, in the direction opposite to the known isophotal twi st. The h(3) and h(4) parameters are found to be generally small over the e ntire observed region. The azimuthally averaged dispersion profile joins sm oothly at large radii with the velocity dispersions of planetary nebulae. U nexpectedly, we find sharp bends in the major axis rotation curve, also vis ible (though less pronounced) on the diagonal position angles. The outermos t bend closely coincides in position with other sharp kinematic features: a n abrupt flattening of the dispersion profile, and local peaks in h(3) and h(4). All of these features are in a photometrically interesting region in which the surface brightness profile departs significantly from an r(1/4) l aw. Features such as these are not generally known in elliptical galaxies o wing to a lack of data at comparable resolution. Very similar behavior, how ever, is seen the kinematics of the edge-on SO galaxy NGC 3115. We discuss the suggestion that NGC 3379 could be a misclassified SO galaxy; preliminar y results from dynamical modeling indicate that it may be a flattened, weak ly triaxial system seen in an orientation that makes it appear round.