High-Redshift Galaxies

in Cluster FieldsWei Zheng, Larry Bradley, and the CLASH high-z

search group

High-Redshift GalaxiesKey Science Questions: How do the first generations of galaxies build up and evolve

at the earliest times? Number densities, sizes/morphologies, UV slopes,

brightness distribution (UVLF), star-formation rates, masses, ages, metallicities

How do these quantities change with cosmic time (e.g. N(z), L(z), SFR(z), M(z))?

What are their stellar populations and how do they evolve: unique conditions in the early universe (e.g. low metallicities, no dust, top-heavy IMF)?

What is the contribution of star-forming galaxies to reionization?

Galaxy Clusters as Cosmic TelescopesStrong Lensing Basics: Galaxy cluster mass

density deforms local space-time

Pure geometrical effect with no dependence on photon energy

Provides large areas of high magnification (μ ~ 10)

Amplifies both galaxy flux and size while conserving surface brightness

Can have multiply-imaged background galaxies

Predicted by Einstein in 1915 (GR)

Observationally confirmed by Eddington during the 1919 solar

eclipse

Lyman Break “Dropout” Technique

V i z J H

Attenuated

Spectrum

Unattenuated

Spectrum

No detection Blue continuum

Star-forming galaxies are relatively

bright in the rest-frame UV (O & B

stars)

Redshift: Their spectra are shifted to

the red (longer wavelengths) due to

cosmological expansion:

Intervening Hydrogen attenuates the

UV spectrum creating a sharp

featured called the Lyman break

λobs = λem (z + 1)

Lyman Break Color Selection

Rest-frame UV Continuum Color

Lym

an B

reak

Col

or

Low-mass stars

(M, L, T-dwarfs):

exclude point sources in

z850

z~7 (z-dropouts)

Bouwens et al. 2008

LBG at z ~ 7.6 ± 0.4

HAB = 24.7 (observed)

HAB = 27.1 (intrinsic)

NASA, Bradley et al. STScI PRC08-08a

3.4 x 3.4 arcmin

WFC3/IR vs. NICMOS/NIC3

ACS/WFC

2.2 x 2.2 arcmin

WFC3/IR

NIC3

WFC3/IR is ~6x larger in area

than NICMOS and has much

higher sensitivity

WFC3/IR has a discovery efficiency ~30-

40x NICMOS

NICMOS required ~100 orbits to find one z

~ 7 galaxy, but it takes WFC3/IR only a

few orbits!

z ~ 7 galaxy comparisons

WFC3/IR

NICMOS/NIC3

2.2” x 2.2” cutouts Bouwens et al. 2010

WFC3/IR Bright Lensed z-dropouts

■ Abell 1703: 1 orbit each in

WFC3/IR F125W (J) and F160W

(H)

8 z-dropout candidates! (some

may be multiply-imaged)

μ ~ 3 - 40

Bradley et al. 2011 (arXiv1104.2035B)

WFC3/IR Bright Lensed z-dropouts

Brightest candidate: z ~ 6.7,

H160 ~ 24.0 AB! (brightest z

850-dropout candidate known)

A1703-zD6 spectroscopically

confirmed at z = 7.045 (zphot =

7.0) (Schenker et al. 2011,

arXiv1107.1251S)

Bradley et al. 2011 (arXiv1104.2035B)

Abell 2261

AB~25.5

Another Dropout Candidate in Abell 2261 that Shows Multiple

Components

Dropout Candidate in MS2137

MACS0744

F125WF160W

F814WF775W

More Candidates in Cluster Fields?

Orbits Z~7 Candidates

CLASH 50 ~10

HIPPIES 130 3

UDF 96 16

Summary We have found ~10 candidates at z~7 One or two of them are marginally

bright (AB~25) Work in progress towards fainter

candidates Many of the candidates display

multiple components Finding opportunity high

inhomogeneous among clusters Many more red objects. Spitzer data

important