Faint Object Camera

Abstract: Low-ionization nuclear emission-line regions (LINERs), which exist in a large fraction of galaxies, may be the least luminous manifestation of quasar activity. As such, they may make possible the study of the active galactic nucleus (AGN) phenomenon in the nearest galaxies. The nature of LINERs has, however, remained controversial because an AGN-like nonstellar continuum source has not been directly observed in them. We report the detection of bright (greater than or approximately = 2 x 10(exp -16) ergs/s/sq cm/A), unresolved (full width at half maximum (FWHM) less than or approximately = 0.1 sec) point sources of UV (approximately 2300 A) emission in the nuclei of nine nearby galaxies. The galaxies were imaged using the Faint Object Camera (FOC) on the Hubble Space Telescope (HST), and seven of them are from a complete sample of 110 nearby galaxies that was observed with HST. Ground-based optical spectroscopy reveals that five of the nuclei are LINERs, three are starburst nuclei, and one is a Seyfert nucleus. The observed UV flux in each of the five LINERs implies an ionizing flux that is sufficient to account to the observed emission lines through photoionization. The detection of a strong UV continuum in the LINERs argues against shock excitation as the source of the observed emission lines, and supports the idea that photoionization excites the lines in at least some objects of this class. We have analyzed ground-based spectra for most of the northern-hemisphere galaxies in the HST sample and find that 26 of them are LINERs, among which only the above five LINERs have a detected nuclear UV source.

Abstract: A set of Hubble Space Telescope faint object camera images taken in the H 2 bands near 1550 A is used to infer the morphological properties of the steady state Jovian FUV aurorae. We focus on issues best addressed using the excellent spatial resolution available after correction of the spherical aberration, i.e., those related to high latitude or small auroral features. A thorough comparison of the emission loci with model ovals highlights the improvement of the VIP4 magnetic field model over previous ones at all latitudes. The northsouth conjugacy of the main oval is now correctly accounted for, and second-order discrepancies suggest non axially symmetric contributions of external origin. This oval is usually amazingly narrow (down to 80 ± 50 km) and very bright, although quite variable with time (100 kR to 1-2 MR, i.e., peak input flux of∼ 10-200 ergs cm -2 s -1 ). We discuss its structure, in latitude and longitude, and show that it is consistent with precipitation by pitch angle scattering. Fainter concentric narrow ovals are also present on the north polar cap, presumably at the footprint of open field lines. Both polar caps are partly covered by a faint diffuse emission, confined to the afternoon sector in magnetic local time. A bright extended feature, previously identified across the north polar cap along the 160° meridian, might be not a specific auroral feature but rather a region where inner arcs and diffuse polar cap emissions are intensified, maybe by a solar wind driven ionospheric process. Equatorward of the main oval, we identify a belt of moderate emission, attributed to a precipitation process distributed between the In torus and the distant magnetosphere. Longitudinally confined bright areas lie in the same latitude range and consist of series of short segments of concentric arcs. We also present the discovery of a narrow faint oval at the footprint of Io's orbit. Finally, we confirm that the FUV footprints of the Io flux tube are very small (a few hundreds of kilometers or less), implying an interaction close to Io. The input energy flux in this spots is huge and variable (0.8-5 x 10 11 W).

Abstract: Previous ground-based observations of the Seyfert 2 galaxy Mrk 78 revealed a double set of emission lines, similar to those seen in several active galactic nuclei (AGNs) from recent surveys. Are the double lines due to two AGNs with different radial velocities in the same galaxy, or are they due to mass outflows from a single AGN? We present a study of the outflowing ionized gas in the resolved narrow-line region (NLR) of Mrk 78 using observations from the Space Telescope Imaging Spectrograph (STIS) and Faint Object Camera aboard the Hubble Space Telescope as part of an ongoing project to determine the kinematics and geometries of AGN outflows. From the spectroscopic information, we determined the fundamental geometry of the outflow via our kinematics modeling program by recreating radial velocities to fit those seen in four different STIS slit positions. We determined that the double emission lines seen in ground-based spectra are due to an asymmetric distribution of outflowing gas in the NLR. By successfully fitting a model for a single AGN to Mrk 78, we show that it is possible to explain double emission lines with radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual supermassive black holes.

Abstract: [O III] λ5007 emission lines of 16 intracluster planetary nebula (PN) candidates in the Coma Cluster were detected with a multislit imaging spectroscopy technique using the Faint Object Camera and Spectrograph on the Subaru telescope. The identification of these faint emission sources as PNs is supported by (1) their pointlike flux distribution in both space and wavelength, with tight limits on the continuum flux; (2) the identification of the second [O III] λ4959 line in the only object at high enough velocity that this line too falls into the filter bandpass; (3) emission-line fluxes consistent with PNs at 100 Mpc distance, in the range 2.8 × 10-19 to 1.7 × 10-18 ergs s-1 cm-2; and (4) a narrow velocity distribution approximately centered on the systemic velocity of the Coma Cluster. Comparing with the velocities of galaxies in our field, we conclude that the great majority of these candidates would be intracluster PNs, free floating in the Coma Cluster core. Their velocity dispersion is ~760 km s-1, and their mean velocity is lower than that of the galaxies. The velocity distribution suggests that the intracluster stellar population has different dynamics from the galaxies in the Coma Cluster core.