Cosmology via Extragalactic Background Light

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Cosmology via Extragalactic Background Light

• Daniel Mazin1
• Martin Raue2
• 1 IFAE, Barcelona
• 2 MPI für Kernphysik, Heidelberg

24 January 2008 CTA kick-off, Barcelona
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Overview of the talk

• Intro Extragalactic Background Light
• Status of the measurements
• Status of the constraints
• CTA potential
• Resolving contribution of unexpected EBL sources
• Constraining EBL in MIR - FIR
• Measurement of the distances ? Hubble parameter

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AGN emission passes through EBL
?max 1.24 ?m(E/TeV)

• Imprint of the EBL density and shape in the
  measured GeV-TeV spectra
• GeV-TeV spectra can be used to test EBL density
  under certain assumptions about the intrinsic
  GeV-TeV spectra

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Extragalactic Background Light (EBL)

• Unique imprint of the history of the universe
• Test of star formation and galaxy evolution
  models
• Cosmological evolution models have to explain
  current EBL
• Opacity source for GeV-TeV photons

Redshifted star light
Redshifted dust emission
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Extragalactic Background Light (EBL)
NIR
MIR
FIR

• Direct measurements are difficult
• Lower limits from source counts and stacking
• Upper limits from fluctuation analyses and direct

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VHE ?-rays as probes of the EBL
UV-optical
NIR
MIR
FIR
1 TeV
10 TeV
100 TeV
0.1 TeV

• HEGRA, CAT, Whipple sensitive for 1 ?m to 30 ?m
• HESS, MAGIC and VERITAS 0.4 - 30 ?m
• HESS II and MAGIC II 0.2 - 30 ?m

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EBL constraints from VHE ?-rays

• Upper limits using VHE spectra assumptions
  about AGN physics
• Recent constraints are already very tight
• HESS II, MAGIC II and GLAST will remove these
  uncertainties
• Constraints above 10?m rely on a single
  measurement of Mkn 501 done by HEGRA in 1997
  need more!
• References
• Aharonian et al, Nature 440
• MazinRaue, AA 471
• Aharonian et al., AA 475

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Current view

• Either the sources of EBL are resolved by HST,
  Spitzer and ISOCAM and there is no big
  contribution from exotic sources (e.g. POPIII
  stars)
• Or AGN assumptions are wrong and current blazar
  paradigm has to be revised.
• Need more sources at different redshifts
• Need GLAST and low energies
• Need extensive Multiwavelength Campaigns

This issue is addressed to the next generation
HESS II and MAGIC II
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What can CTA do?
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Goal 1 EBL evolution

• Star and galaxy evolution is largely unknown
• CTA can measure blazar spectra up to redshift z
  2
• Such sources are behind the main star formation
  epoch ? beacons
• Using the sources with zlt2, the EBL evolution can
  be resolved!
• Need gt100 sources

Star formation rate
Madau, 1998
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Goal 2 EBL at Mid- and Far-Infrared
COBE data (Hauser Dwek, 2001)

• EBL in mid- and far-infrared are crucial for
  understanding star and galaxy formation
• How much dust?
• What is dust contents?
• How many galaxy populations?
• No direct measurement in the near future
• CTA (high energy array!!) is the only experiment
  to test Mid Far-Infrared
• Need a few sources

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Goal 3 distance Hubble parameter
Based on Blanch Martinez, 2001

• If one knows
• Intrinsic AGN spectrum and
• EBL density
• determine distance to the sources using the EBL
  signature in the measured spectra
• Can cover range from z0.004 to z gt 2

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Goal 3 distance Hubble parameter
Based on Blanch Martinez, 2001

• Determination of cosmological parameters
• Independent method
• Required precision 5-10 (in dz/z)
• High potential to determine evolution of Hubble
  parameter
• need gt100 sources

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Conclusions

• EBL carries essential cosmological information
• VHE spectra put strong limits on the EBL density
• HESS II and MAGIC II will resolve the hard
  spectra issue
• CTA will
• provide beacons behind the main galaxy formation
  epoch (z gt 2)
• measure Mid and Far-infrared EBL
• independent distance measurements
• ? cosmology, Hubble parameter