• WFC3 EBL Collaborators:– Tim Dolch, Ranga-Ram Chary, Asantha Cooray,

Anton Koekemoer, Swara Ravindranath

Near-Infrared Extragalactic Background Fluctuations

Henry Ferguson (STScI)

WFC3 H-band masked

Background• We have resolved 30-100% of the EBL• We do not know how much is due to:

– The wings of galaxies– The faint end of the LF post reionization– Sources at the epoch of reionization

•The night sky is bright compared to galaxies!

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• Iteratively remove detector blemishes

– 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

• Create pure noise images in original detector coordinates

– 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

– Ideally -- subtract the galaxy wings (work in progress)

Analysis Procedure• Create a shuffled version of the

image– Unmasked pixels are randomly

shuffled, removing correlations• For both the shuffled and

unshuffled version:– 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).– Excess is amplified when kernel

matches the characteristic size of the sources

Simulated dataα=0.1,r=0.12” α=0.1,r=0.36”

α=0.5,r=0.12” α=0.5,r=0.36”

Validation

• Tests on simulated UDF data• Pure Gaussians:

– Recover power-law slope to about σα=0.1

– Recover size to about 10% • (for an idealized model with

Gaussians all the same size)

• Mixture of galaxy profiles:– power-law biased low by -0.1 ± 0.1– Characteristic size biased high by

1.2 ± 0.2

Preliminary results• Simple power-law model:

– N(M)~10αm

– Normalization fixed to match total counts 27<m<28

– Constant size modeled with Gaussians• Best fit

– F105W: α = 0.7, r = 0.24’’– F125W: α = 0.65, r = 0.24’’– F160W: α = 0.65, r = 0.24’’

• Steep slope is intriguing

Pure noise simulation

Pure noise + simulated galaxiesN(M)~100.5m ; radius 0.24”

WFC3 H-band masked

Near-IR Galaxy counts

• Faint-end slope is:– 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

Simulated data – identical colors for all galaxies

Correlation after convolution with 4-pixel (0.24”) Gaussian

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:– ~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• HST Multicycle treasury program will cover 830 square arcminutes

at 1.2 and 1.6 microns to 27-28 magnitude

• Fluctuation measurements on larger scales will be possible

Reionization Simulation from Trac and Cen 2007

• The large angle (θ ~ 1/30 °) peak (green curve) is a linear-theory 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

Large θ Small θ

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