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Session 73 - Spiral Galaxies.
Oral session, Thursday, June 11
Friars,
Using long-slit spectra centered in wavelength about H\alpha, we have obtained a velocity map of a 20\arcsec x 140\arcsec east-west box centered on the nuclear region of M101. The velocity resolution is 2.5 km/s and the spatial resolution is approximately 1\arcsec east-west and variable (3-4\arcsec on average) north-south. We have also obtained temperature, density, shock, and ionization fraction maps of the same region using the [NII](\lambda6548), [NII](\lambda6583), H\alpha, [SII](\lambda6717), and [SII](\lambda6731) lines. The temperatures range from 4100-14,000 K with an average temperature of 6200 K. The densities range from 6.6-36,600 cm^3 with an average density of 800 cm^3. Regions northeast and southwest of the nucleus have [NII](\lambda6583)/H\alpha ratios \geq 0.56 and [SII](\lambda\lambda6717+6731)/H\alpha ratios \geq 0.4 which are indicative of shock heating or power law photoionized gas. The gas in an S-shaped region, passing through the nucleus, has [NII](\lambda6583)/H\alpha ratios \leq 0.56 and [SII](\lambda\lambda6717+6731)/H\alpha ratios \sim 0.1 which is representative of gas photoionized by hot stars. The ionization fraction in this S-shaped region has an average value of 0.45 while the regions northeast and southwest of the nucleus have average values of 0.10. The velocity data are consistent with gas infalling toward the nucleus as part of streaming motions traveling west-to-east on the north side of the nucleus and east-to-west on the south side of the nucleus. However, there appears to be a local instability in which the motion southwest of the nucleus is moving west-to-east creating a collision of the two opposing gas motions in a region of relatively high density and temperature. A blue arc emanating from an unresolved source on or near the nucleus shows evidence of collision in this same high density and temperature region.
