UA cloudflare authentication

Browsing by Author "Cobb, ML"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    An optical, near-infrared, and kinematic study of four early-type resonance ring galaxies
    (University of Chicago Press, 1998) Buta, R; Alpert, AJ; Cobb, ML; Crocker, DA; Purcell, GB; University of Alabama Tuscaloosa; University of Pennsylvania; Muskingum University
    We present optical and near-infrared surface photometry of four early-type galaxies considered to have resonance ring phenomena on the basis of morphology. We also present kinematics and rotation curves for three of the galaxies. The four galaxies are exceptional examples of resonance ring galaxies, and from these observations we derive the characteristic light distributions, the colors of the rings, and the near-infrared disk mass-to-light ratios. We also deproject the galaxies to examine intrinsic ring shapes and bar/ring alignments. From models of the rotation curves, we compute the Lindblad precession frequencies to examine resonance locations in the disks of the galaxies. Under the assumption that the outer rings and pseudorings seen in these galaxies are linked to the outer Lindblad resonance, we iind that the inner rings of the sample galaxies lie near the inner 4:1 resonance and that the sharp ends of the bars lie on average at only 0.65 times the predicted radius of corotation.
  • Thumbnail Image
    Item
    The structure and dynamics of the early-type resonance ring galaxy IC 4214. I. Observations
    (University of Chicago Press, 1999) Buta, R; Purcell, GB; Cobb, ML; Crocker, DA; Rautiainen, P; Salo, H; University of Alabama Tuscaloosa; Muskingum University; University of Oulu
    The southern galaxy IC 4214 is a bright, nearby example of a multiple ring early-type spiral galaxy with a weak bar. The galaxy shows three strong pseudoring features, including a nuclear ring, an inner ring, and a prominent R-1' outer ring, each with distinctive characteristics. The galaxy is important because it is a classic resonance ring galaxy where the ring features can be linked to specific orbital resonances with the bar. We present in this paper a detailed UBVIH study of its photometric structure and a Fabry-Perot study of its kinematics to set the stage for a dynamical model in a separate paper. Despite the early Hubble type, ionized gas is well. distributed in the inner disk regions, providing a well-sampled velocity field. Rapid rotation is found in the vicinity of the nuclear ring, where the rotation curve reaches a maximum, and the rotation velocities drop off somewhat with increasing radius in the outer regions. Noncircular motions are clearly seen in the observed velocity held. Analysis of both the velocity held and the shapes of isophotes give discrepant values for the inclination of the system, ranging from 47 degrees to 50 degrees from photometry to 55 degrees to 58 degrees from kinematics. A likely value of the inclination could be 52 degrees if the inner and outer rings are intrinsically elongated and aligned perpendicular to each other.