Published on August 29, 2007
Spitzer Extragalactic First Look Survey: Spitzer Extragalactic First Look Survey FLS main: ~2o x 2o centered @ 17:18:0 +59:30:0, ~ 80 sec/pix for MIPS (24,70,160um), ~60sec/pix for IRAC (3.6,4.5,5.8,8.0um). 5sigma flux limits: 6uJy @3.6um, 30uJy @8.0um, 110uJy @24um FLS verification: 0.2o x 1o, ~400sec/pix for MIPS and 600sec/pix for IRAC ELAIS N1: 10’ x 10’, ~4000sec/pix for MIPS 24um and ~4000sec/pix for IRAC. 5sigma flux limits: 0.5uJy @3.6um, 40uJy @24um. 8um 24um 3.6um Spitzer 24micron Observations of (R - K > 5.3) Selected Extremely Red Galaxies at z ~ 1 - 2: Evidence for Assembly of Massive Galaxies?: Spitzer 24micron Observations of (R - K andgt; 5.3) Selected Extremely Red Galaxies at z ~ 1 - 2: Evidence for Assembly of Massive Galaxies? Lin Yan, P. Choi, D. Fadda, F. Marleau, Tom Soifer, Lee Armus, Lisa Storrie-lombardi, Harry Telplitz, Gillian Wilson, and the FLS team Spitzer Science Center, Caltech June 2004 ApJS Spitzer Special Issue Near-IR observations probe stellar masses, optical/near-IR colors are widely used to select massive galaxies at z ~ 1 - 2 (if dust negligible), for example GDDS, LCIR, K20 surveys(Abraham et al. 2004; Glazebrook et al. 2004; McCarthy et al. 2002; Cimatti et al. 2002): Near-IR observations probe stellar masses, optical/near-IR colors are widely used to select massive galaxies at z ~ 1 - 2 (if dust negligible), for example GDDS, LCIR, K20 surveys (Abraham et al. 2004; Glazebrook et al. 2004; McCarthy et al. 2002; Cimatti et al. 2002) CWW SEDs What do we know about EROs??: What do we know about EROs?? 1). Wide area imaging survey: EROs are 10% of the total population at K=19.5, and more at fainter K. (McCarthy et al. 2001) 2). Optical Spectroscopy: EROs are indeed at z ~ 1 - 2 (Yan, Thompson, Soifer 2004; Cimatti etal. 2002; Glazebrook et al. 2004; Choi et al. 2004). ~50% EROs have emission lines and ~ 50% have pure absorption lines. 3). HST morphologies: 30-40% EROs are bulge dominated, ~50% are disk dominated or interacting/mergers (Yan andamp; Thompson 2003; Moustakas etal 2004). Choi et al. 2004 in prep. Yan andamp; Thompson 2003 ApJ, 5 HOWEVER,The red (R - K) color could due to either old stars or dust reddening in starbursts. What is the relative contribution of the two types ??: HOWEVER, The red (R - K) color could due to either old stars or dust reddening in starbursts. What is the relative contribution of the two types ?? With optical/near-IR photometry alone, It is difficult to separate two types. Spitzer 24um data directly answer this question! HR10 24um Use Data in ELAIS N1: 24um: 3sigma 40uJy, EROs with (R-K>5.3), K<20.2 (6sigma).: Use Data in ELAIS N1: 24um: 3sigma 40uJy, EROs with (R-Kandgt;5.3), Kandlt;20.2 (6sigma). 24um K RESULTS:: RESULTS: 129 EROs with (R - Ks andgt; 5.3) and Kandlt;20.2, 65 (50+-6%) have 24um emission brighter than 40uJy. The mean andlt;f(24um)andgt;=167uJy Slide8: What are the nature of these 24um-detected red galaxies? Slide9: I).What are the total infrared luminosities of 24um-detected EROs?? andlt;f(24um)andgt;=167uJy, at z=1, vLv(24um obs) = 3x1010 L_sun ==andgt; L(IR) = 3x1011 L_sun. @ z=1.5, L(IR) = 1012 L_sun. (LIRGs or ULIGs) II). What are the SFRs?? andlt;SFRandgt; (FIR) = 50-170 M_sun/yr SFR(limit) ~ 12M_sun/yr, more sensitive than the deepest 20cm data (Smail etal 2002). III). What is the lower limit on the masses? If a typical time scale for starbursting phase T ~ 108 yr, then a lower limit on the mean mass of these galaxies is andlt;Massandgt;=SFR*T = 5x109 -- 2x1010 Msun Soifer et al. 1989; Chary andamp; Elbaz 2001 Conclusions and Implications: Conclusions and Implications 1). 50% of EROs at z ~ 1 - 2 are luminous infrared galaxies with (R - Ks andgt;5.3) , Ksandlt; 20.2(andgt;5.6uJy) and f(24um) andgt; 40uJy limit. 2). Deep 24um observations have revealed a population of infrared luminous galaxies at z ~ 1 -- 2, some of these are starbursts with SFR andgt; 50 -- 170 Msun/yr. 3). It is possible that these 24um-detected EROs are in the midst of violent transformation to become massive early type galaxies we see today (Kormendy andamp; Sanders 1992). 4). The high fraction of EROs being infrared luminous suggests that many more high-z galaxies are undergoing starbursting phase. Exciting Future with Spitzer Data:: Exciting Future with Spitzer Data: Spitzer 24um revealed a population of 24um sources (13-23%) which are extremely faint in optical. They are candidates for LIRGs/ULIRGs @zandgt;1 (Yan et al. 2004, ApJS) Spectroscopic follow-up (optical and MIR) would be necessary in order to measure the evolution of LF, number density as well as spectral properties. HST high resolution morphologies will be useful to define the nature of these high-z IR luminous sources. R 24um Slide12: 1). Detailed spectroscopic follow-up on these 24um sources ===andgt; mass, spectral properties, metallicities etc. Slide13: SFR (optical) versus SFR (FIR) Extinction uncorrected Extinction corrected Extinction uncorrected H-alpha H-beta [OII] HST/ACS/NICMOS Morphologies:: HST/ACS/NICMOS Morphologies: we have HST/NICMOS NIC2 images of 50 EROs within the FLS verification. The ACS observations were done in the parallel mode. 1.5' 24um-detected EROs Slide15: R 3.6um 8.0um 24um FLS main ELAIS N1 R K 8.0um 24um 3sigma R = 25.5mag, 3sigma K=21mag.