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Measuring the Diffuse Extragalactic Background Light as a function ofredshift
Cosmic History of Star Formation:Holy Grail of Observational Cosmology(a “geological record” of all energy generated throughout history of Universe)
GLAST will be a BLAST!
Matt Malkan, UCLA
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Malkan and Stecker 1998; 2001
DIRB Predictions of “Backwards Evolution” Models
Start with local IR Luminosity functions, and local Spectral Energy Distributions,Extended into optical/UV
Then add the tricky part…
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Pure luminosity evolution still not bad approximation, with all L’s evolving with cosmic star formation history
Eg: MRR 1999, with extinction corrections included
MM +Stecker 98,“Fast”
Dust-corrected Global SFR History
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Redshifts z=0,1,2,3 Fancy surface plot, also SMS ’05Simple extension down to Lyman limit
Model predictions of Diffuse Photon Spectra
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Models for z=0* D O/IRB are getting Well-constrained by COBE and deep counts
Either “baseline” or “fast” evolution is currently consistent with observations
SMS ‘05*Too late to getDirect measurementsAt any higher z’s
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Stecker,MM,Scully 2005
Predicted total optical depths as fcn of received energy(at least 2 wiggles in LAT spectra expected)
Z=3, with CMWB separated / Summed optical depth as fcn of Z
*O/NIR bump: starlight cool dust reradiation
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LAT well designed to do most redshifts from 0.1 up to peak of cosmic energy generation
Differences between some models (eg fast vs. baseline) are subtleGood SNR at highest energies becomes crucial
Energy (received) at which total = 1
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A few test cases show that this “works” on nearby TeV sources, such as PKS 2155-304 (z=0.17)
With simultaneous wide energy coverage, fit absorbed (intrinsically straight) power law;
This could also work with GRB spectra, with z known
SMS ‘05
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What are potential ambiguities?DIRB(z) is a convolution of:
LF, SFR history over redshift, stellar population and dust properties:
Expect an increasingly focused search
through model parameter space ; Role of Air Shower Experiments is Crucial in filling
in lower z’s
We assume that Blazar AGN spectra are featureless power laws,
but there could be intrinsic (variable) curvature, Or internal absorption (Elliptical galaxy, hot AGN dust?)
Study statistical samples of Blazar spectra at each z
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What if the observed Gamma-ray absorptionIs shown to disagree with Independent DIRB Estimates?
Don’t Worry! An explanation has
already been published. It has something to do
with broken symmetries.
If that turns out, they’ll be looking for cheap airfares to Stockholm (Floyd hasn’t been yet)
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IR Luminosity functions of galaxies at z up to 2.5:Great improvement from Spitzer;Herschel will soon do the same For far-IR
=
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MS98 models
More luminous spirals have FIR peaks which are stronger and hotter (IRAS)
Trend continues into sub-mm: ISOPHOT
(Spinoglio, Malkan, Andreani 2002)
Starlight peakDust reradiation peak
Huge SFR: ultraluminous starburst, at 25-60um
Very low SFR, hardly any young stars