Transcript LSST Galaxies - Penn State Department of Astronomy and

Near-Infrared Extragalactic Background
Fluctuations
Henry Ferguson (STScI)
• WFC3 EBL Collaborators:
– Tim Dolch, Ranga-Ram Chary, Asantha Cooray,
Anton Koekemoer, Swara Ravindranath
WFC3 H-band masked
Background
• We have resolved 30-100% of the EBL
• We do not know how much is due to:
•The night sky is bright
to galaxies!
– The wings of galaxies
compared– The faint end of the LF post reionization
– Sources at the epoch of reionization
Galaxies
Adapted from Leinert 1998
Bock+ 06
Fluctuations in the Near-IR from HST
• Thompson et al HST NICMOS:
– Detected sources emit 7 nW m2 sr-1 compared to DC-level
estimate of 70 nW m2 sr-1 from Matsumoto+ 2005
– Sources of the remaining fluctuations are probably at z<8
(even for the longer-wavelength IRAC data).
IRAC 3.6μm
NICMOS H band
WFC3 H-band
WFC3 H-band masked
NICMOS masking
from Thompson et al. 2007 (NICMOS )
Data Preparation
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Iteratively remove detector blemishes
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Create pure noise images in original detector
coordinates
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Combined dithered images with some masking
Transfer combined image back to original image
geometries and subtract
Smooth and detect blemishes or persistence
Mask and recombine for the final image
Gaussian statistics okay for these images; match sky
background
Predicted RMS matches measured RMS to within a few
percent
Combine these just as for the real images
Mask the detected sources
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Ideally -- subtract the galaxy wings (work in progress)
Analysis Procedure
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Create a shuffled version of the
image
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For both the shuffled and
unshuffled version:
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Unmasked pixels are randomly
shuffled, removing correlations
Convolve the masked images
with kernels of various sizes
Compute the histogram of pixel
intensities P(D)
Subtract the shuffled P(D) from
the unshuffled P(D).
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Excess is amplified when kernel
matches the characteristic size
of the sources
Simulated data
α=0.1,r=0.12”
α=0.1,r=0.36”
α=0.5,r=0.12”
α=0.5,r=0.36”
Validation
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Tests on simulated UDF
data
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Pure Gaussians:
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Recover power-law slope to about
σα=0.1
Recover size to about 10%
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(for an idealized model with
Gaussians all the same size)
Mixture of galaxy profiles:
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power-law biased low by -0.1 ± 0.1
Characteristic size biased high by
1.2 ± 0.2
Preliminary results
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Simple power-law model:
– N(M)~10αm
– Normalization fixed to match total counts
27<m<28
– Constant size modeled with Gaussians
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Best fit
– F105W: α = 0.7, r = 0.24’’
– F125W: α = 0.65, r = 0.24’’
– F160W: α = 0.65, r = 0.24’’
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Steep slope is intriguing
Pure noise simulation
Pure noise + simulated galaxies
N(M)~100.5m ; radius 0.24”
WFC3 H-band masked
Near-IR Galaxy counts
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Faint-end slope is:
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Much flatter than α=0.6
Similar in all three bands
Less than 5% of the galaxies at H>26.5 are identified
as Lyman-break galaxies at z>6.5
Correlations between bands
Correlation after convolution with 4-pixel (0.24”) Gaussian
Simulated data – identical colors for all galaxies
Correlation between J and H bands
Correlation between Y and H bands
Future Efforts
• Galaxy subtraction
• More sophisticated models
– Galaxy size magnitude relation with scatter
– Galaxy redshift and SED distributions
• Better calibration of hot pixels and
persistence
• More data
Hubble Multi-Cycle Treasury Program
• WFC3 IR observations of 5 well-studied reference
fields at high galactic latitude:
– The GOODS fields
• Encompass the deepest fields from HST, Spitzer, Chandra, the
VLA, and soon Herschel
– Carefully selected portions of
• The Extended Groth Strip
• the COSMOS field
• The UKIRT Ultradeep Survey Field
• Optimized for studies of galaxy evolution at z~2-10
• Optimized for supernova cosmology
Theories crumble, but good observations never fade.— Harlow Shapley
90 Co-investigators
Observing strategy
• Wide fields:
– ~750 sq. arcmin (44-45 tiles)
– 2/3 orbits J (F125W)
– 4/3 orbits H (F160W)
• GOODS Deep:
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~130 sq. arcmin
11 orbit depth 3+4+4
F105W+F125W+F160W
At least 12 orbits new ACS F814W
• UV (GOODS-N):
– ~70 sq. arcmin
– Lyman-escape fractions at z~2.5
– 2.6:1 ratio in F275W:F336W
Potential for EBL measurements
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HST Multicycle treasury program will cover 830 square arcminutes
at 1.2 and 1.6 microns to 27-28 magnitude
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Fluctuation measurements on larger scales will be possible
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Reionization Simulation from Trac and Cen 2007
Large θ   Small θ
The large angle (θ ~ 1/30 °)
peak (green curve) is a lineartheory prediction of clustering of
reionization sources.
Small scale power is sensitive to
the slope and normalization of
the luminosity function and the
sizes of the sources.
large area surveys with WFC3
can (barely) reach large angle
peak
Summary
• A new technique for analyzing the small-scale
structure in the EBL:
– Fit difference of P(D) and shuffled P(D) after
convolving with a kernel
– Constrains both the number-counts slope and the
power-law index 1-2 mag fainter than detection limit.
• Preliminary analysis suggests fluctuations well
in excess of extrapolation of observed counts
– In Y, J and H bands.
– Unlikely to be reionization sources
• Possible systematic effects remain
– Wings of galaxies; persistence