Spitzer Extragalactic First Look Survey 3.6um 8um 24um • 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.
Spitzer 24micron Observationsof (R - K > 5.3) Selected Extremely Red Galaxies at z ~ 1 - 2:Evidence for Assembly of Massive Galaxies? June 2004 ApJS Spitzer Special Issue 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
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?? 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 & Thompson 2003; Moustakas etal 2004). Choi et al. 2004 in prep. Yan & 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 ?? 24um With optical/near-IR photometry alone, It is difficult to separate two types. Spitzer 24um data directly answer this question! HR10
Use Data in ELAIS N1: 24um: 3sigma 40uJy, EROs with (R-K>5.3), K<20.2 (6sigma). 24um K
RESULTS: • 129 EROs with (R - Ks > 5.3) and K<20.2, 65(50+-6%) have 24um emission brighter than 40uJy. The mean <f(24um)>=167uJy
I).What are the total infrared luminosities of 24um-detected EROs?? <f(24um)>=167uJy, at z=1, vLv(24um obs) = 3x1010 L_sun ==> L(IR) = 3x1011 L_sun. @ z=1.5, L(IR) = 1012 L_sun. (LIRGs or ULIGs) II). What are the SFRs?? <SFR> (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 <Mass>=SFR*T = 5x109 -- 2x1010 Msun Soifer et al. 1989; Chary & Elbaz 2001
Conclusions and Implications 1).50% of EROs at z ~ 1 - 2 are luminous infrared galaxies with (R - Ks >5.3) , Ks< 20.2(>5.6uJy) and f(24um) > 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 > 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 & 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: • Spitzer 24um revealed a population of 24um sources (13-23%) which are extremely faint in optical. They are candidates for LIRGs/ULIRGs @z>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
1). Detailed spectroscopic follow-up on these 24um sources ===> mass, spectral properties, metallicities etc.
SFR (optical) versus SFR (FIR) Extinction uncorrected Extinction corrected [OII] Extinction uncorrected H-beta H-alpha
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. 24um-detected EROs 1.5”
R 3.6um 8.0um 24um FLS main R K 8.0um 24um ELAIS N1 3sigma R = 25.5mag, 3sigma K=21mag.