Optical Spectroscopy and Ionization Models of the Diffuse Ionized Gas in M33, M51/NGC 5195, and M81*

摘要: We report the results of a spectroscopic investigation diffuse ionized gas (DIG) in M33, M81, and M51. All three galaxies have enhanced [S II]/Hα [N ratios DIG compared to H II regions, agreement with predictions photoionization models. The all also has [O III]/Hβ equal or greater than that neighboring regions. II]/[N II] ratio does not vary Hα surface brightness is similar both regions DIG. tentatively detected He I λ5876 line bright near NGC 604, indicating contribution from O7 hotter stars ionizing spectrum at location. M33 lower M51 Galaxy, most likely because low N abundance M33. used CLOUDY models test feasibility two sources for DIG: (1) diluted continua massive ("standard" models) (2) transmitted density-bounded ("leaky region" models). leaky region produce higher II]/Hα, standard same stellar temperatures. This alleviates somewhat problem producing high However, no single model can simultaneously reproduce ratios. conclude either combination necessary other ionization heating mechanisms play role powering Finally, we on associated companion M51, 5195. around 5195 very forbidden-line broad widths (~ 500 km s-1 FWHM), indicative shock-ionized gas. At some locations emission lines split into velocity components, suggesting an expanding structure outflow. ratios, morphology, kinematics show interstellar medium disturbed.