high-redshift galaxies in cluster fields wei zheng, larry bradley, and the clash high-z search group
TRANSCRIPT
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High-Redshift Galaxies
in Cluster Fields
Wei Zheng, Larry Bradley, and the CLASH high-z
search group
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High-Redshift Galaxies
Key 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?
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Galaxy Clusters as Cosmic Telescopes
Strong 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
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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)
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Lyman Break Color Selection
Rest-frame UV Continuum Color
Lym
an B
reak
Colo
r
Low-mass stars
(M, L, T-dwarfs):
exclude point sources in
z850
z~7 (z-dropouts)
Bouwens et al. 2008
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LBG at z ~ 7.6 ± 0.4
HAB = 24.7 (observed)
HAB = 27.1 (intrinsic)
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NASA, Bradley et al. STScI PRC08-08a
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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
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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)
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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)
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Abell 2261
AB~25.5
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Another Dropout Candidate in Abell 2261 that Shows Multiple
Components
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Dropout Candidate in MS2137
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MACS0744
F125WF160W
F814WF775W
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More Candidates in Cluster Fields?
Orbits Z~7 Candidates
CLASH 50 ~10
HIPPIES 130 3
UDF 96 16
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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