# Presentation: 126610

## Spitzer  Extragalactic First Look Survey

- <date/time>

- 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?

- <date/time>

- Spitzer 24micron Observations of (R - K > 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)

- <date/time>

- 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??

- <date/time>

-   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 ??

- <date/time>

- 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).

- <date/time>

- Use Data in ELAIS N1: 24um: 3sigma 40uJy, EROs with (R-K>5.3), K<20.2 (6sigma).

- 24um

- K

## RESULTS:

- <date/time>

- 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

## What are the nature of these 24um-detected red galaxies?

- <date/time>

##  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) 

- <date/time>

-  I).What are the total infrared luminosities of 24um-detected   EROs?? ***<f(*****24um)>=167uJy,     at z=1,  *****vL******v******(24um obs) = 3x10******10 ******L_sun             ==>   L(IR) = 3x10******11 ******L_sun. @ z=1.5,  L(IR) = 10******12****** 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 ~ 10****8**** yr, then a lower limit on the mean mass of these galaxies is**
**<Mass>=SFR*T = 5x10****9**** -- 2x10****10 ****Msun**

- Soifer et al. 1989; Chary & Elbaz 2001

## Conclusions and Implications

- <date/time>

- 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:

- <date/time>

**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

- <date/time>

- 1). Detailed spectroscopic follow-up on these 24um sources ===> mass, spectral properties, metallicities etc.

## SFR (optical) versus SFR (FIR)

- <date/time>

- Extinction uncorrected

- Extinction corrected

- Extinction uncorrected

- H*-alpha*

- H-beta

- [OII]

## HST/ACS/NICMOS Morphologies:

- <date/time>

-  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

- <date/time>

-     R                        3.6um                 8.0um               24um

- FLS
- main

- ELAIS
- N1

-      R                        K                8.0um               24um

- 3sigma R = 25.5mag, 3sigma K=21mag.