Browsing by Author "Ryder, SD"

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    Dust in spiral galaxies: Comparing emission and absorption to constrain small-scale and very cold structures
    (IOP Publishing, 1999-10) Domingue, DL; Keel, WC; Ryder, SD; White, RE; University of Alabama Tuscaloosa
    The detailed distribution of dust in the disks of spiral galaxies is important to understanding the radiative transfer within disks and to measuring overall dust masses if significant quantities of dust are either very opaque or very cold. We address this issue by comparing measures of dust absorption, using the galaxy-overlap technique in the optical, with measures of the dust grains' thermal emission from 50-2000 mu m, using ISOPHOT on board Infrared Space Observatory (ISO) and SCUBA at the James Clerk Maxwell Telescope. We examine three spiral galaxies projected partially in front of E/S0 galaxies: AM 1316-241, NGC 5545, and NGC 5091 (for NGC 5091 we have only optical and ISO data). Adopting an empirical exponential model for the dust distribution, we compare column densities and dust masses derived from the absorption and emission techniques. This comparison is sensitive to the amount of dust mass in small, opaque structures, which would not contribute strongly to area-weighted absorption measures, and to very cold dust, which would contribute to optical absorption but provide only a small fraction of the submillimeter emission. In AM 1316-241, we find global dust masses of 2-5 x 10(7) M., with the two techniques agreeing at the 50% level. NGC 5545 has about half this dust mass. The concordance of dust masses is well within the errors expected from our knowledge of the radial distribution of dust and argues against any dominant part of the dust mass being so cold or opaque. The 50-2000 mu m data are well fitted by modified Planck functions with an emissivity law beta = -2, at 21 +/- 2 K; a modest contribution from warmer dust is required to fit only the 50 mu m measurement of NGC 5545. We incorporate empirical corrections to the flux scale of ISOPHOT P32 data, which can reach a factor 2 from comparison of IRAS and ISO fluxes for objects in two programs. We also present 12 mu m ISOCAM observations of these pairs. The light profiles at this wavelength exhibit shorter disk scale lengths than in the optical. Comparison of H alpha and 12 mu m images of NGC 5545 indicate that ISOCAM images are reliable tracers of star formation.
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    Dynamics of ringed barred spiral galaxies. I. Surface photometry and kinematics of NGC 1433 and NGC 6300
    (University of Chicago Press, 2001) Buta, R; Ryder, SD; Madsen, GJ; Wesson, K; Crocker, DA; Combes, F; University of Alabama Tuscaloosa; University of Wisconsin System; University of Wisconsin Madison; Duke University; UDICE-French Research Universities; Universite PSL; Observatoire de Paris
    This paper presents new near-infrared images and surface photometry and H alpha Fabry-Perot radial velocities for NGC 1433 and NGC 6300, two large and previously well-studied nearby ringed barred spiral galaxies. Stellar absorption-line radial velocities and new optical surface photometry are also presented for NGC 1433. The data are intended to set the stage for dynamical modeling of the two galaxies, with the principal goals being to derive mass distributions, bar mass-to-light ratios, bar pattern speeds, and resonance locations, parameters which have been derived for very few ringed disk galaxies. The presence of strong rings and pseudorings in the two galaxies allows the possibility to link specific orbital resonances with the observed rings. The new data allow us to derive a fairly complete composite rotation curve of NGC 1433, leading us to make some interesting preliminary judgments about the structure of the galaxy. The new data also verify the previous finding that the radial velocity of the Seyfert nucleus in NGC 6300 differs from the actual systemic velocity of the galaxy by nearly 100 km s(-1). We demonstrate in this paper that the offset is not an artifact of significant extinction in the inner regions of the galaxy.
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    Neutral hydrogen in the ringed barred galaxies NGC 1433 and NGC 6300
    (University of Chicago Press, 1996-04) Ryder, SD; Buta, RJ; Toledo, H; Shukla, H; StaveleySmith, L; Walsh, W; Commonwealth Scientific & Industrial Research Organisation (CSIRO); University of New South Wales Sydney; University of Alabama Tuscaloosa
    We have made observations of the H I in the southern ringed barred spiral galaxies NGC 1433 and NGC 6300 with the Australia Telescope Compact Array (ATCA), the main goal being to test the resonance theory for the origin of these rings. NGC 1433 is the prototypical ringed barred spiral and displays distinct H I counterparts to its nuclear ring, inner ring, outer pseudoring, and plumelike features. The L(4) and L(5) regions at corotation, as well as the bar itself, are relatively devoid of neutral atomic hydrogen. We use the Tully-Fisher relation to argue that the mean inclination of the disk of NGC 1433 is closer to 33 degrees than to 20 degrees, meaning that its outer pseudoring is intrinsically almost circular, while the inner ring is rather more elongated than the average (based on results from the Catalog of Southern Ringed Galaxies). Strong radio continuum emission is localized to the nucleus and the ends of the bar in NGC 1433, and we place an upper limit on the 1.38 GHz flux of the Type II SN 1985P a decade after the explosion, By associating the inner ring of NGC 1433 with the inner second harmonic resonance, and its outer pseudoring with the outer Lindblad resonance, we are able to infer a bar pattern speed for NGC 1433 of 26 +/- 5 km s(-1) kpc(-1). By way of contrast, NGC 6300 possesses a much more extended H I disk than NGC 1433, despite having a similar morphological type. There is a gas ring underlying the inner pseudoring, but it is both broader and slightly larger in diameter than the optical feature. The outer H I envelope has a 20 degrees kinematic warp as well. as a short tail, even though there are no nearby candidates for a recent interaction with NGC 6300. The noncircular motions inferred from optical emission-line spectra do not appear to extend beyond the bar region of NGC 6300. Barely 10% of the 1.38 GHz radio continuum emission in NGC 6300 originates in the type 2 Seyfert nucleus, with the rest coming from a disklike component internal to the ring. By again linking an inner ring feature to the inner second harmonic resonance, we derive a bar pattern speed for NGC 6300 of 27 +/- 8 kM s(-1) kpc(-1), but in this case, neither the outer pseudoring nor the nuclear ring predicted by the resonance ring theory can be identified in NGC 6300. Although it may be the case that the ring in NGC 6300 is not related to a resonance with the bar at all, we postulate instead that NGC 6300 is merely a less well developed example of a resonance ring galaxy than is NGC 1433.