Computer Science
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50369k&link_type=abstract
Spitzer Proposal ID #50369
Computer Science
Scientific paper
To perform spatiall-resolved study of very small grains (VSGs) and PAHs in elliptical galaxies, we propose to observe the three elliptical galaxies, NGC4589, NGC4125, and IC3370, in a deep spectral mapping of central 1'x1' area with the IRS; the targets are carefully selected from our AKARI sample of nearby elliptical galaxies. With Spitzer, we have found that a considerable amount of PAHs as well as VSGs are present in nearby dusty elliptical galaxies, emitting very unusual features: usually strong features at 6.2, 7.7, and 8.6 micron are very faint in contrast to prominent features at 11.3 and 17 micron, which might be explained by a dominance of neutral PAHs over ionized ones due to very soft radiation fields from evolved stars. The Spitzer results have also exhibited the presence of warm molecular and ionized gases, which is apparently inconsistent with the dominance of neutral PAHs irradiated by soft radiation field. What are the supplying sources of the dust in elliptical galaxies? How are they related with the warm molecular and ionized gases? How can such small dust particles as PAHs and VSGs survive sputtering destruction in the hot plasma of the elliptical galaxies? The three elliptical galaxies have prominent PAH emissions at 11.3 and 17 micron as well as relatively strong mid-IR excess emission at wavelengths longer than 25 micron; however we have no spatial information. Our earlier IRS observations were performed in a staring mode by one pointing at the center of each galaxy. Spatial information is indispensable to disentangle various competing components and pursue follow-on studies of the above Spitzer discoveries. For example, if the distributions of the dust are more extended than the stellar distribution and smaller grains are abundant in outer regions, it will support that the dust is of external origin. The spatially-resolved IRS data can elucidate the origin and history of the dust, providing key information about the evolution of the elliptical galaxies.
Kaneda Hidehiro
Kitayama Tetsu
Okada Yoko
Onaka Takashi
Sakon Itsuki
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