Fabry-Perot Absorption-Line Spectroscopy of NGC 7079: Kinematics and Bar Pattern Speed

Abstract

We present Fabry-Perot absorption-line spectroscopy of the SB0 galaxy NGC 7079. This is the first use of Fabry-Perot techniques to measure the two-dimensional stellar kinematics of an early-type disk galaxy. We scan the infrared CaII line using the Rutgers Fabry-Perot (RFP), to obtain kinematic data extending to $I$-band surface brightness ${\mu }_I\simeq 21$ mag./arcsec^-2, in a field of radius $\sim 40\arcsec$. The kinematic data, consisting of line-of-sight velocities and velocity dispersions, are in good agreement with data obtained along the major axis of the disk with standard slit spectroscopy. Comparison of the exposure times required for slit and RFP spectroscopy to reach the same limiting magnitude shows that the RFP is significantly more efficient for mapping absorption-line galaxy kinematics. We use the velocity data, together with our own deep broad-band photometry,to measure the bar pattern speed, ${\Omega }_p$, of NGC 7079 with the model-independent Tremaine-Weinberg (TW) method. We find ${\Omega }_p=8.4\pm 0.2$ km/s/arcsec; this is the best-constrained pattern speed ever measured for a bar using the TW method. From the rotation curve, corrected for asymmetric drift, we calculate the co-rotation radius and find that the bar ends just inside this radius. The two-dimensional character of these data allow us to show that the TW method is sensitive to errors in the position angle (PA) of the disk. For example, a PA error of $2\degrees$ can give errors $\sim \pm 25$ in ${\Omega }_p$.

Accepted to ApJ. 30 pages, 10 figures. Postscript version with high resolution figures is available at: http://www.exp-astro.phys.ethz.ch/debattista/personal/ms.ps