Search for Very Thick Disks Around NGC 891 and NGC 5907 with the IRS PUI

Details Search for Very Thick Disks Around NGC 891 and NGC 5907 with the IRS PUI Search for Very Thick Disks Around NGC 891 and NGC 5907 with the IRS PUI

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20016b&link_type=abstract

Spitzer Proposal ID #20016

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Scientific paper

Flat galaxy rotation curves routinely observed out to large radii in HI and in optical emission lines are convincing evidence for the existence of dark matter. As yet, we know very little about the nature of this dark matter. An intriguing possibility is that a population of very cool objects - extreme brown dwarfs or "Jupiters'' - accounts for a significant part of its mass. Their intrinsic faintness at visible wavelengths would explain why they have not yet been clearly detected. IRAC GTO observations of two famous edge-on galaxies (NGC 891 and 5907) have yielded good evidence for such a very red, thick disk component that could comprise some of this "missing mass", but the mid-infrared colors as yet offer no clear discriminant of the thick disks' makeup. We propose to use the IRS PUI mode for follow-up observations of the thick disks seen in the two edge-on IRAC GTO program galaxies. By measuring the thick disk fluxes at 16 microns we can obtain crucial information for example about the temperature of the objects in these disks and hence get a better idea of their nature. As the expected signal is much smaller than the foreground emission from the zodiacal light, we propose to execute raster maps perpendicular to the midplanes of these galaxies without touching the regions of strong emission. The radiation from the thick disks will then appear as a surface brightness gradient measured as a function of distance on both sides of the galactic midplanes. Previous attempts to detect halo or thick disk material around edge-on galaxies concentrated on the near infrared; the observations proposed here would be the first ones at longer wavelengths which are aimed only at regions outside the visible disks. In addition to the proposed 16 micron images, we will obtain 22 micron images in parallel, from the other IRS peak-up array at similar positions relative to the galaxies. We request 2.1 hours to carry out this program.

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