Physics – Optics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30240s&link_type=abstract
Spitzer Proposal ID #30240
Physics
Optics
Scientific paper
Our program to identify luminous galaxies with apparently old stellar populations in radio source fields has discovered a number of such galaxies at z ~ 2.5. We have been engaged in obtaining high-resolution imaging of these objects with HST NICMOS and with ground-based adaptive optics on 8 to 10 m telescopes. The results for the small sample we have been able to observe so far are (1) that massive disks of old stars seem to predominate, in some cases with no evidence for any bulge component at all; and (2) that, for some objects, it is difficult to distinguish between radial-surface-brightness models because the galaxies, though highly luminous (2--3 L*), have effective radii as small as 500 pc. In both cases, the galaxies look nothing at all like present-epoch ellipticals. These morphologies have strong implications for mechanisms for the formation of massive galaxies in the early universe, but it is important at this point to nail down the spectral-energy distributions of the stellar populations in these galaxies better than we can from ground-based observations alone. We are proposing deep Spitzer IRAC (all bands) and MIPS (24 micron) observations of 6 fields for which we have our best examples of luminous galaxies with apparently pure old stellar populations. The Spitzer observations can do 3 important things: (1) By greatly extending the baseline on the longward side of the 4000 A break beyond the short H to K interval, the IRAC observations can help define the dominant stellar population and its age much better; (2) the IRAC photometry can also check for evidence for a highly reddened young-to-moderate-age population that would have no effect at optical and near-IR wavelengths; and (3) the MIPS 24 micron photometry can test for the presence of a highly luminous but heavily obscured starburst.
McGrath Elizabeth
Stockton Alan
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