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Session 70 - Cosmic Backgrounds and the Distant Universe.
Oral session, Thursday, June 11
Presidio,
We present near-infrared images of the nearby edge-on spiral galaxy NGC 4565 in a search for infrared emission from baryonic dark matter in the massive galactic halo. The observation was made with a liquid-helium-cooled rocket-borne telescope using a low-background 256 x 256 InSb focal plane array. The field of view subtended 1.2 x 1.2 degrees with 17" pixels to map extended emission out to large radii and to accurately measure and subtract the sky brightness. The images achieve near-background-limited performance at 3.5 - 5.5 \mum where emission from the zodiacal foreground is at a minimum. We are able to map the surface brightness of the galaxy to < 0.5 nW/m^2 sr (0.2 % of the zodiacal foreground). By measuring the surface brightness as a function of radius, we do not detect a component associated with the massive halo, obtaining a lower limit on the mass-to-light ratio of the halo M/L > 250. This observation places strong contraints on the fraction of stars near the hydrogen-burning limit in the galactic halo.
