The ages and star formation rates of massive galaxies at z=2-3

Details The ages and star formation rates of massive galaxies at z=2-3 The ages and star formation rates of massive galaxies at z=2-3

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30873l&link_type=abstract

Spitzer Proposal ID #30873

Computer Science

Scientific paper

Using deep multiwavelength surveys from MUSYC, GOODS, and FIRES, and IR selection techniques we are now able to select galaxies at z>2 by stellar mass. Detailed optical-to-infrared photometry has recently revealed that massive M > 10^11 Msun galaxies at z=2-3 are on average already surprisingly red (J_ab - K_ab ~ 1.5). Studies in FIRES and GOODS have demonstrated that IRAC and MIPS are critical to determine the origin of these red colors. Thanks to Spitzer we can now distinguish galaxies that are ``red and dead'' from those that are actively forming stars and enshrouded by dust. Nevertheless, inferences for galaxy formation scenarios are severely limited by field-to-field variance. Strong clustering causes density fluctuations by more than a factor of 3 on fields the size of GOODS. Worse, current estimates of the space densities of dead galaxies differ by a factor of 10. It is imperative to extend to new and larger fields. Unfortunately, the fundamental obstacle is the lack of sufficiently deep J and K-band imaging in available IRAC fields. Because deep wide area NIR imaging is excessively time-consuming to obtain, we face delays of years before we can improve on current results. Therefore, to immediately enhance the scientific return of IRAC and MIPS, we propose to observe the *only* substantial fields with deep NIR imaging in the J,H, and K-band that are available *now*: the MUSYC survey, comprising 4 fields of 100 arcmin^2 each. These fields are very compelling for follow-up with Spitzer, as they are also the main focus of our Gemini/GNIRS ``Key Science Program'' obtaining very deep NIR spectra on massive distant galaxies. This unique program is producing dozens of direct measurements of the Balmer/4000 A break and Balmer decrement in z=2-3 massive galaxies, providing independent estimates of the ages, star formation rates, and extinctions. Ultimately, such NIR spectra will be crucial to calibrate the constraints that IRAC and MIPS place on the stellar populations of high redshift galaxies.

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