Velocity Fields of Barred Spiral Galaxies from Fabry-Perot \\Observations

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Session 76 -- Spiral and Bar Structure in Galaxies
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[76.07] Velocity Fields of Barred Spiral Galaxies from Fabry-Perot \\Observations

B. J. Weiner, T. B. Williams, J. A. Sellwood (Rutgers University)

\def\kms{$\rm {km}~\rm s^{-1}$} \def\ha{H$\alpha$}

We present 2-dimensional velocity fields of gas in the barred spiral galaxies NGC 1832 and NGC 3095, obtained by mapping the H$\alpha$ emission line with the Rutgers Imaging Fabry-Perot Interferometer at CTIO. The data for each galaxy are 12--15 narrow-band images spaced across the H$\alpha$ emission line, separated by approximately 1 \AA\ (50 \kms). For each pixel, we thus have measurements of the flux as a function of wavelength, to which we fit a line profile, obtaining the continuum, intensity, wavelength, and kinetic broadening of the line. In regions of strong \ha\ emission we obtain velocity precision of 5 \kms\ and spatial resolution of 1\arcsec--2\arcsec, limited only by the seeing. In regions of diffuse emission we average the data spatially to obtain precision of $\sim$\,15 \kms\ at spatial resolution of 3\arcsec--4\arcsec; this allows us to obtain velocities over the full extent of the disk.

The velocity fields show global deviations from axisymmetry, exhibiting the $S$-shaped isovelocity contours characteristic of barred disk galaxies. These data will enable us to constrain mass models of barred spirals, through fluid-dynamical simulations of the gas flow.

The maps also reveal dynamically interesting small-scale velocity structure. In NGC 3095, we obtain velocities from diffuse \ha\ emission over the entire bar. Direct imaging shows typical straight, offset dust lanes along the bar; we detect a strong velocity gradient (100-150 \kms\ over 3\arcsec) across the width of the bar, coincident with the dust lanes. This provides evidence that dust lanes in bars are the locations of shocks.

In the inner bulge of NGC 1832, we have detected a fast-rotating, nuclear ring structure of intense \ha\ emission. The $B$-band image and the continuum at \ha\ show a smooth, centrally-peaked bulge, but the \ha\ intensity map reveals a ring of radius 0.8\arcsec\ (70$h^{-1}$ pc if the galaxy is at its Hubble distance) with the line-of-sight component of the rotation velocity equal to 100 \kms. We conjecture that this gas has sunk to the center of the bulge due to outward angular momentum transport by the bar.

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