A Long‐Slit Spectral Analysis of the Nuclear Region of M101 and M33 and a Search for Nonnuclear Seyfert Activity in M33

Abstract

Using long-slit spectra centered in wavelength about Ha, a velocity map of a box centered on the nuclear ′′ ′′ 20 # 140 region of M101 has been obtained. The velocity resolution is 2.5 km s , and the spatial resolution is approximately 1 eastwest and 3 –4 north-south. Also obtained are temperature, density, and shock maps of the same region using the [N ii] (l6548), [N ii] (l6583), Ha, [S ii] (l6717), and [S ii] (l6731) lines. Temperatures range from 4100 to 14,100 K, with an average temperature of 6200 K. Densities range from 7.0 to 36,600 cm , with an average density of 800 cm . Regions northeast and southwest of the nucleus have [N ii] (l6583)/ Ha and [S ii] (ll6717 6731)/Ha , ratios ≥ 0.56 ratios ≥ 0.4 which are indicative of shock-heated or power-law photoionized gas. Gas in a S-shaped region, passing through the nucleus, has [N ii] (l6583)/Ha and [S ii] (ll6717 6731)/ ratios ! 0.56 Ha , which are representative of gas in H ii regions. ratios ≈ 0.1 The velocity data are consistent with gas infalling toward the nuclear region as part of streaming motions. However, there is a local instability in which the motion southwest of the nucleus is moving contrary to the streaming motion, creating a collision of the two opposing gas motions in a region of 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. A long-slit spectral analysis has also been carried out on a box centered on an “hourglass”-shaped object of ′′ ′′ 30 # 185 nonbroadened Ha emission in M33; this object is centered 38 southeast of the nucleus. Utilizing the same [N ii], [S ii], and Ha lines as in the M101 study, velocity, temperature, density, and shock maps have been acquired. The velocity and spatial resolution is 0.2 km s 1 and 0 .7 respectively along each slit. Temperatures range from 5500 to 20,600 K with an average temperature of 8700 K. Densities range from 8.0 to 38,600 cm 3 with an average density of 1400 cm . The overall sampled region reveals a suppressed [N ii] (l6583)/Ha and [S ii] (ll6717 6731)/Ha ratios. Regions near the center of the hourglass-shaped object and regions 50 north of this center, have [N ii] (l6583)/Ha and [S ii] (ll6717 6731)/Ha ratios indicative of shock heating. In addition, the area 30 south of the central region exhibits elevated [S ii] (ll6717 6731)/Ha ratios. To aid in the analysis of this object, a medium-resolution WIYN image, centered on the nucleus, was obtained. 6 .5 # 6 .5 An enlargement of this image (Fig. 1) reveals the finer details of the object’s northern and southern lobes. A faint line of gas extending through the center of the object, oriented at 55 west of north is also evident. The morphology of the object, coupled with the data, is utilized to present a model. In addition to the long-slit spectral analysis of M33, ultranarrowband ( A) Hb onand off-line images have FWHM ≈ 8.5 been obtained of this galaxy. Using an image multiplicationsubtraction method, maps that differentiate between H ii regions, OB associations, and broad-line Hb regions were created. Using these maps, a spectra of the broad-line Hb regions can be obtained to determine if Seyfert-like activity is present.