Browsing by Author "Purcell, GB"

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    INTRINSIC BAR RING MISALIGNMENT AND A STARBURST NUCLEAR RING IN THE PECULIAR SPIRAL GALAXY ESO-565-11
    (American Institute of Physics, 1995-10) Buta, R; Purcell, GB; Crocker, DA; California Institute of Technology; University of Texas System; University of Texas Austin; University of Alabama Tuscaloosa
    The southern galaxy ESO 565-11 is a very clear example of a nearly face-on ringed barred spiral where the bar axis and the major axis of the inner ring are significantly misaligned. The object is important because the normal configuration is alignment, based on statistics of apparent bar/ring position angles for large samples of ringed galaxies. In this paper, we verify, using deep CCD surface photometry and Fabry-Perot interferometry, that the bar/ring misalignment of 60 degrees seen in ESO 565 - 11 is intrinsic. We show that ESO 565-11 has two important nonaxisymmetric components: the primary bar, and a luminous oval distortion which contains a greater proportion of the total luminosity. The primary bar is of the ''ansae'' type, showing bright enhancements at the ends, The inner pseudoring is a minor contribution to the total light at the rim of the oval distortion. Thus, ESO 565 - 11 can also be characterized as a misaligned bar/oval galaxy, There is a very faint outer pseudoring beyond the oval distortion. In the center of the galaxy, a starburst nuclear ring of collosal physical size dominates the morphology. The ring is about 3.5 times the average size of such features and is defined by ten giant and at least three lesser I-I II regions which contribute 77% of the total H alpha luminosity of the galaxy. The position angle of the major axis of the ring changes by 23 degrees in the direction of rotation from H alpha to B to I, and in the latter filter is aligned nearly perpendicular to the bar in projection. The ring is also imbedded in a more extended disk of diffuse H alpha emission. The inner pseudoring is defined by much fainter discrete H II regions. (C) 1995 American Astronomical Society.
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    NGC 3081: Surface photometry and kinematics of a classic resonance ring barred galaxy
    (University of Chicago Press) Buta, R; Purcell, GB; University of Alabama Tuscaloosa
    This paper presents a detailed photometric and kinematic study of the well-known Seyfert 2 galaxy NGC 3081, one of the best examples of a resonance ring barred galaxy in the sky. Improved optical images compared to previous studies reveal that NGC 3081 is a classic R1R2' galaxy, a type that shows a distinctive outer ring/pseudoring pattern at large radii that can be linked to orbit families at the outer Lindblad resonance (OLR). Together with an exceptionally strong inner ring and a blue nuclear ring, NGC 3081 has the rare distinction of having all four of the main types of resonance rings that have been predicted by test-particle models of barred spirals. Near-infrared imaging of NGC 3081 reveals clear old rings connected to the inner ring and the R, outer ring. Objective comparison of the B-and H-band positions of the inner ring indicates no significant difference in shape, major-axis position angle, or major-axis radius between the two passbands, in spite of the different stellar populations each band emphasizes. Imaging Fabry-Perot interferometry provides an intriguing picture of star formation in the galaxy and of the dynamics of the system. H alpha emission is strong in the inner ring and is confined to a bounded elliptical annulus of diffuse emission whose ellipticity increases from the inner edge to the outer edge. A few H II regions are connected to the strong R-1-type outer ring, particularly just off the major axis of the inner ring where "dimples," typical of the R-1 morphology, are found. There is bright emission in an oval zone in the inner 10'' radius, but no enhancement of emission is associated with the blue-light nuclear ring. Since most of the emission is connected with the intrinsically oval inner ring and the bright center, the global dynamics of the galaxy are uncertain. Nevertheless, using a combination of the gravitational potential derived from the H-band light distribution and a simple halo model, we estimate the pattern speed and the location of all major resonances in the disk of NGC 3081. We find that NGC 3081 fits extremely well into recent ideas of barred galaxy dynamics.
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    An optical and H I study of NGC 5850: Victim of a high-speed encounter?
    (IOP Publishing, 1998) Higdon, JL; Buta, RJ; Purcell, GB; Commonwealth Scientific & Industrial Research Organisation (CSIRO); University of Alabama Tuscaloosa
    We present optical CCD surface photometry and VLA H I observations of NGC 5850, one of the largest and brightest barred spirals of the inner ring variety in the sky. The broadband images reveal numerous morphological peculiarities, particularly in the spiral arms. Structural asymmetries are more obvious in H I, the most pronounced being a large-scale displacement of gas to the west and northwest of the nucleus. Most of the (3.3 +/- 0.1) x 10(9) M-circle dot of atomic hydrogen is concentrated in the prominent optical ring and faint spiral arms, with very low H I surface densities (Sigma(HI)) in the bulge and interarm regions. We detect approximately 2 x 10(7) M-circle dot of H I in the southwestern half of the nuclear ring. The H I surface density drops rapidly outside the arms, and we find no evidence for either large-scale tidal features or an extended gas disk above 0.05 M-circle dot pc(-2) (3 sigma). Overall, the intensity-weighted H I velocity field appears fairly regular, yet still shows clear deviations from circular rotation that we attribute to a warped oval disk and streaming motions across the arms. Radio continuum emission at 20 cm is dominated by a faint bulge component that peaks at the optical nucleus. The spiral arms are not detected. The absence of extended X-ray emission throughout the NGC 5846 group and the close similarity between NGC 5850's optical and H I morphologies argue against ram pressure stripping through a dense intergalactic medium as the cause of the galaxy's peculiar morphology. We attribute it instead to a high-speed encounter with the massive elliptical galaxy NGC 5846. We identify the peculiar spiral arms as a disrupted outer pseudoring. Star formation in NGC 5850 has not been enhanced relative to other intermediate field spirals, nor have significant gas masses been transported to the nucleus. This may be attributed to the recent (less than or similar to 200 Myr) nature of the interaction.
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    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.
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    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.