Comparison of the optical spectrum of the filaments with the spectrum of the central region of M82.

Linear polarization observations of the line [N ii] A6583 in the filamentary patch of RD M82 was measured with the Hale reflector at Palomar to be 27 percent at 54 . These values are nearly the same as those of the continuum and Ha line from the same patch, which rules out fluorescence as a plausible mechanism for the origin of Ha in the filaments. The emission-line spectrum and the continuum of the same filamentary patch RD have also been observed with the multichannel scanner. The observed Balmer decrement is steep, and it is interpreted as due to Whitfordlike reddening by dust, corresponding to a value of 2.2 mag at V. The dereddened fluxes of the forbidden lines [0 ii] A3727, [0 ii] A5007, [N ii] A6584, and [S ii] A6724 with respect to HP as well as the shape of the dereddened continuum from 3300 to 9000 A in the patch RD are found to agree with those of the luminous H ii region M82 A located in the central region of the galaxy. Further, the dereddened emission-line and continuum spectrum in the range 3300-9000 A of patch RD is nearly the same as that of M82 A dimmed by a factor of about 234. Considering that the polarization data suggest scattering of both the permitted and forbidden-line emission and the continuum from a source in the central region of the galaxy, we are convinced that our results support the H ii region M82 A located in the central region of the galaxy as the source of the scattered light in the filaments. However, the observed velocity field is still not understood on this simple scattering model with purely radial motions. Subject headings: galaxies, individual - interstellar matter - polarization - spectrophotometry