ar X iv : a st ro - p h / 01 06 05 6 v 1 4 J un 2 00 1 Seeing Galaxies though Thick and Thin . IV . The Superimposed Spiral Galaxies of NGC 3314 1

The superimposed pair of spiral galaxies comprising NGC 3314 offers a unique opportunity to trace the dust properties in a spiral galaxy. We analyze multicolor HST imaging, supported by ground-based near-IR imaging and fiber-array spectroscopy to measure dust extinction in the foreground Sc galaxy NGC 3314A, which is backlit by the Sb system NGC 3314B. The superposition allows us to measure extinctions over a wide range of galactocentric radii in the foreground galaxy, from 0.4-4.5 kpc. In the outer half of the disk, the extinction is strongly localized in discrete dust lanes, including some patches whose galactic setting is clear only because of associated Hα emission at the foreground velocity. These dust features show an extinction curve with a slope close to the Galactic mean (R = 3.5± 0.3) over a range in galactocentric radius from 1.6 to 3.8 kpc, with no radial trend. Using the I −K color of the background nucleus, we derive an extinction AI = 3.3 through the disk at a projected distance 400 pc from the nucleus of NGC 3314A. The extinction in even the inner disk of NGC 3314A is quite patchy, since background Hα emission is detected from all parts of the system. Local anticorrelations between foreground and background line emission demonstrate that the dust is concentrated to star-forming regions, as has been found for the blue light in several systems. Colors of dust lanes in NGC 3314A which are projected only partially against the background disk indicate that the dust scale height in the foreground disk is substantially smaller than that of the stars. The color-intensity behavior of the net light in these regions tracks the predictions of a thin-layer model closely. Subject headings: galaxies: ISM — galaxies: spiral — dust, extinction Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract No. NAS5-26555. Visiting astronomer, NASA Infrared Telescope Facility, Mauna Kea, Hawaii Visiting Astronomer, WIYN Observatory, which is owned and operated by the WIYN Consortium, Inc., which consists of the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatory (NOAO). NOAO is operated for the National Science Foundation by the Association of Universities for Research in Astronomy (AURA), Inc.