Hintze Centre for Astrophysical Surveys

Abstract:

We present SAURON integral-field observations of the S0 galaxy NGC 7332. Existing broadband ground-based and Hubble Space Telescope (HST) photometry reveals a double-disc structure and a boxy bulge interpreted as a bar viewed close to edge-on. The SAURON two-dimensional stellar kinematic maps confirm the existence of the bar and inner disc but also uncover the presence of a cold counter-rotating stellar component within the central 250 pc. The Hβ and [O III] emission line maps show that the ionized gas has a complex morphology and kinematics, including both a component counter-rotating with respect to the stars and a fainter corotating one. Analysis of the absorption line-strength maps show that NGC 7332 is young everywhere. The presence of a large-scale bar can explain most of those properties, but the fact that we see a significant amount of unsettled gas, together with a few peculiar features in the maps, suggests that NGC 7332 is still evolving. Interactions as well as bar-driven processes must thus have played an important role in the formation and evolution of NGC 7332, and presumably of S0 galaxies in general.

Abstract:

Results of the commissioning of the first Gemini Multi-Object Spectrograph (GMOS) are described. GMOS and the Gemini-North telescope act as a complete system to exploit a large 8 m aperture with improved image quality. Key GMOS design features such as the on-instrament wave-front sensor (OIWFS) and active flexure compensation system maintain very high image quality and stability, allowing precision observations of many targets simultaneously while reducing the need for frequent recalibration and reacquisition of targets. In this paper, example observations in imaging, long-slit, and multiobject spectroscopic modes are presented and verified by comparison with data from the literature. The expected high throughput of GMOS is confirmed from standard star observations; it peaks at about 60% when imaging in the r′ and i′ bands, and at 45%-50% in spectroscopic mode at 6300 Å. Deep GMOS photometry in the g′, r′, and i′ filters is compared to data from the literature, and the uniformity of this photometry across the GMOS field is verified. The multiobject spectroscopic mode is demonstrated by observations of the galaxy cluster A383. Centering of objects in the multislit mask was achieved to an rms accuracy of 80 mas across the 5′.5 field, and an optimized setup procedure (now in regular use) improves this to better than 50 mas. Stability during these observations was high, as expected: the average shift between object and slit positions was 5.3 mas hr -1, and the wavelength scale drifted by only 0.1 Å hr -1 (in a setup with spectral resolution of 6 Å). Finally, the current status of GMOS on Gemini-North is summarized, and future plans are outlined.