Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.1911h&link_type=abstract
American Astronomical Society, AAS Meeting #212, #19.11; Bulletin of the American Astronomical Society, Vol. 40, p.532
Astronomy and Astrophysics
Astronomy
Scientific paper
We present our analysis of an occulting spiral galaxy pair, serendipitously discovered in ANGST (ACS Nearby Galaxy Survey Treasury) observations of NGC 253, taken with Hubble Space Telescope's Advanced Camera for Survey in F475W, F606W and F814W (SDSS-g, broad V and I). The pair's geometry is near ideal for this type of analysis; a face-on spiral in the foreground and a bright and smooth bulge as the background.
The foreground disk system (at z < 0.06 is notable for showing a dusty disk much more extended that the starlight, with spiral lanes seen out to 1.5 times de Vaucouleurs radius (about 6 half-light radii).
This extended dust disk shows typical extinction values A(F475W) 0.25, A(F606W) 0.25, and A(F814W) 0.15, with much higher values in the three spiral arms. The distribution of extinction values is well described by an exponential distribution with scales of 0.28, 0.15 and 0.09 for F475W, F606W and F814W respectively.
The extinction law inferred from these measures is similar to the local Milky Way Extinction Law, although the smoothing effects of sampling at limited spatial resolution (<57; pc, in these data) might flatten the observed function through mixing of regions with different extinction. This galaxy illustrates the diversity of dust distributions in spirals, and the limitations of adopting a single dust geometry model for optically similar galaxies.
Dalcanton Julianne J.
de Jong Roelof S.
Holwerda Benne Willem
Keel William C.
Williams Bruce
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