Narrow band imaging and long slit spectroscopy of UGC 5101

UGC 5101 (z = 0.04; D is approximately equal to 240 Mpc) is one of the so called Ultraluminous IRAS sources. Two important properties of the members of this group are their L(sub IR) is greater than or equal to 10(exp 12) solar luminosity, and their space density in the universe up to z is less than 0.1 is equal or even larger than the space density of the quasars. Further noteworthy features of the Ultraluminous IRAS sources are their being morphologically peculiar and the fact that they all seem to host active nuclei in their center. We have observed UGC 5101 in an effort to study the interplay between the gas ionized by the central active nucleus and that gas ionized by other processes which may hold important clues to the understanding of the entire picture of this object. In particular these other ionizing processes could well be massive stars formed recently after the galactic encounter and shocks possibly also related to the galaxy collision. The data that we discuss were obtained between Dec. 1989 and Jan. 1992 with the WHT 4.2 m telescope using the two-arm spectrograph ISIS. Several spectral frames were obtained at three different position angles: PA 84--along the tail of the galaxy; PA 32--along the dust lane; and PA 110. The blue spectra are centered on the H beta line, while the red spectra are centered on the H alpha line. In the configuration we used for the long slit spectra, the spectral scale was 0.74 A per pixel, and the spatial scale was .37 arcsec per pixel; we also observed the H alpha region with a spectral scale of .37 A per pixel, at position angle 84. The narrow band images were obtained at the auxiliary port of ISIS, with a scale of .2 arcsec per pixel, and were centered at the H alpha wavelength, and on the adjacent continuum. The H alpha images and the spectra support the following model. UGC 5101 hosts an active nucleus; the NLR extends up to about 1.5 kpc and shows a complex velocity field, superimposed on the rotation curve of the galaxy. Besides the NLR, in the H alpha image are visible tow bright cones that extend up to 3 kpc along PA 32. The long slit spectra at PA 32 show that the velocity field of the gas in these regions is peculiar, while the ionization structure of the gas is similar to that of the NLR

Long slit spectroscopy of NGC 5506

The galaxy NGC 5506 hosts an active nucleus, that presents characteristics that are intermediate between Sy1 and Sy2. We discuss long slit spectra of NGC 5506 in the ranges 4675-5475 A and 6300-7125 A, that were obtained at three different position angles, in Apr. 1991 at the WHT 4.2 m telescope. The peculiar kinematics of the emitting gas has already been observed by other researchers; following the model proposed by the other researchers, that the emitting gas is located in two cones, we determined the aperture of the cones. The data, moreover, support the hypothesis that the gas is receding from the nucleus. We modelled the intensity and the ratios of the emission lines, and verified that the active nucleus of NGC 5506 can be described as a Sy1 nucleus, with the UV-X source that is partially obscured to our line of sight. On the contrary, a good fraction of the interstellar gas of the galaxy is directly illuminated and photoionized by the central source. Our data show evidence of star formation close to the nucleus; we estimated the star formation rate, that is high with respect to 'normal' spirals, but not high enough to be comparable to star formation rates in a starburst galaxy

STEPS TOWARD DETERMINATION OF THE SIZE AND STRUCTURE OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI .5. VARIABILITY OF THE ULTRAVIOLET CONTINUUM AND EMISSION-LINES OF NGC-3783

We report on the result of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variability was observed in both continuum and emission-line fluxes. The light curves for the continuum fluxes exhibited two well-defined local minima or ''dips,'' the first lasting less than or similar to 20 days and the second less than or similar to 4 days, with additional episodes of relatively rapid flickering of approximately the same amplitude. As in the case of NGC 5548 (the only other Seyfert galaxy that has been the subject of such an intensive, sustained monitoring effort), the largest continuum variations were seen at the shortest wavelengths, so that the continuum became ''harder'' when brighter. The variations in the continuum occurred simultaneously at all wavelengths (Delta t <2 days). Generally, the amplitude of variability of the emission lines was lower than (or comparable to) that of the continuum. Apart from Mg II (which varied little) and N V (which is relatively weak and badly blended with Ly alpha), the light curves of the emission lines are very similar to the continuum light curves, in each case with a small systematic delay or ''lag'' As for NGC 5548, the highest ionization lines seem to respond with shorter lags than the lower ionization lines. The lags found for NGC 3783 are considerably shorter than those obtained for NGC 5548, with values of(formally) similar to 0 days for He II + O III], and similar to 4 days for Ly alpha and C IV. The data further suggest lags of similar to 4 days for Si IV + O IV] and 8-30 days for Si III] + C III]. Mg II lagged the 1460 Angstrom continuum by similar to 9 days, although this result depends on the method of measuring the line flux and may in fact be due to variability of the underlying Fe II lines. Correlation analysis further shows that the power density spectrum contains substantial unresolved power over timescales of less than or similar to 2 days, and that the character of the continuum variability may change with time