Program: GN-2006A-Q-56

Title:NIRI Spectroscopy of the Extreme R-[24]$\ge$14 Red Galaxy Population
PI:Arjun Dey
Co-I(s): Kate Brand, Michael Brown, Vandana Desai, Emeric Le Floc'H, Buell Jannuzi, Casey Papovich, Tom Soifer, Dan Weedman

Abstract

We have recently discovered a sample of IR-luminous objects of extreme color which may represent an early active phase in the formation of very massive galaxies. These objects are optically extremely faint ($R\gtrsim 25$), but nevertheless bright at mid-infrared wavelengths. Although only $<$1\% of the mid-IR source population at bright fluxes ($F_{24\mu m}\gtrsim 0.8$mJy), they are an increasing fraction of the source population at fainter flux densities ($\gtrsim 10$\% at $F_{24\mu m}\approx 0.3$). {\it Spitzer}/IRS spectra of the brightest sources (with $F_{24\mu m} > 0.8$mJy) suggest redshifts $z\sim 2$. We propose to extend our study of this population to fainter mid-IR flux densities ($F_{24\mu m}\approx 0.3$) currently beyond {\it Spitzer}'s reach. We will obtain near-IR spectra of 7 of these objects which are bright at $K$ and with $0.3 \le F_{24\mu m} < 0.8$ mJy in order to determine their redshifts and investigate their spectral properties. Constraints on the redshift distribution can help determine whether or not this population is responsible for the strong evolution observed in the mid-IR number counts.

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