Engineering topics

Antonucci, R. R. J.

Publications and source records attributed to Antonucci, R. R. J..

5 records

NASA NTRS1991

The featureless continua and hydrogen lines of Seyfert 2 galaxies

Optical and ultraviolet spectra taken in similar sized large apertures for 15 Seyfert 2 galaxies are presented. Measurements of emission-line strengths of Ly-alpha, H-alpha, and H-beta are used together with measurements of the ultraviolet slopes to estimate the ratio of recombination photons to ionizing photons. The photon ratios indicate that the ionizing continuum is being emitted anisotropically for at least six of the eight objects with UV slope measurements. The median value of the UV slope is indistinguishable from the UV slope of Seyfert 1 galaxies. This result suggests that in the occultation/reflection picture of Seyfert nuclei, the reflecting particles are free electrons and not dust. Previous observations of variability in Mrk 477 are verified, and it is shown that this galaxy exhibits characteristics of both Seyfert 1 and Seyfert 2 galaxies.

Kinney, A. L.↗

NASA NTRS1991

FOS spectroscopy of resolved structure in the nucleus of NGC 1068

The results of FOS spectroscopy of the continuum peak of NGC 1068 in the wavelength range 2200-7000 A are reported. Detailed analysis reveals the emission lines to be complex in shape and to consist of a number of different velocity components. Both the Balmer lines and the strong forbidden lines have a contribution from a component with full width at half-maximum on the order of 2200 km/s. However, the broad H-beta emission observed in polarized light is not detected. This implies that the continuum peak is not the mirror which reflects light from the hidden Seyfert I nucleus. It could possibly contribute some of the reflected light, but the equivalent width of the H-beta BLR line, if present at all, is much weaker than expected from the ground-based nuclear polarized-flux spectrum.

Caganoff, S.↗

NASA NTRS1991

HST imaging of the inner 3 arcseconds of NGC 1068 in the light of forbidden O III 5007 A

The Planetary Camera aboard HST has been used to obtain a high spatial resolution forbidden O III 5007 A image of the nucleus of the barred spiral galaxy NGC 1068. This image shows more detail than any previously published images and resolves the NLR into several distinct clouds arranged in an apparently conical geometry. The individual emission-line regions appear to be resolved with sizes of 0.1-0.2 arcsec. There is a strong apparent correspondence between the 1.3 cm radio structure and several of the forbidden O III 5007 A clouds, although there are also bright emission-line clouds for which there are no radio counterparts. In particular, the radio 'triple' of Ulvestad et al. (1987) appears to correspond directly to the forbidden O III 5007 A clouds A-D. It is concluded that the distribution of the clouds is consistent with ionization core models. The hidden nucleus is located somewhere in the southern radio component and may be coincident with the H2O megamaser.

Evans, I. N.↗

NASA NTRS1989

The Lyman edge test of the quasar emission mechanism

The Lyman edge region in the spectra of 11 high-redshift quasars is studied using data designed to detect broadened Lyman edge absorption predicted by thermal models of the 'big blue bump' continuum component, especially thin accretion disks. Three objects have broadened, partial edges near the systemic redshifts, as expected for thermal models. In two cases, however, narrow Lyamn lines with the edge absorption, ruling out the disk interpretation. Thus, the data are negative for thermal models, at least for opaque thin accretion disks.

Antonucci, R. R. J.↗

NASA NTRS1986

Blazars with arcminute-scale radio halos

About 10-arcsec resolution 20-cm wavelength maps are presented for three nearby BL Lac objects: Mkn 180, whose halo has a linear size of 85 kpc, 2155-304, with a halo about 375 kpc across, and 1727 + 502, whose one-sided diffuse emission extends to a distance of about 145 kpc from its radio core. Little evidence is found for strong radio variability in the cores of the three blazars; these and other results obtained are consistent with the assertion that the three objects should be classified as normal low luminosity double radio galaxies with optically dull nuclei, if seen from other directions.

Ulvestad, J. S.↗