wfc3 ebl collaborators: –tim dolch, ranga-ram chary, asantha cooray, anton koekemoer, swara...
DESCRIPTION
Background We have resolved % 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+ 06TRANSCRIPT
• 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