Title: Constraining Populations of Extragalactic Gamma-ray Sources with the Extragalactic Gamma-ray Background
1Constraining Populations of Extragalactic
Gamma-ray Sources with the Extragalactic
Gamma-ray Background
- Vasiliki PavlidouUniversity of Chicago
- Tonia Venters University
of Chicago and APC (Paris 7) - Jennifer Siegal-Gaskins University of
Chicago - Brian Fields
University of Illinois - Angela Olinto University
of Chicago and APC (Paris 7) - Carolyn Brown University of
Chicago
2Extragalactic Gamma-ray Emitters1. Classes with
already detected members
- Blazars
- AGNs with jet aligned with line-of-sight
- Most populated class of EGRET identified sources
- Only class with identified members at high z
- Normal galaxies
- EGRET detected only 2 Milky Way, LMC
- GLAST will detect only 3 more SMC, M31, M33?
- Unidentified EGRET sources
- Likely to include many extragalactic sources
- More numerous than blazars!
3Extragalactic Gamma-ray Emitters2. Theorized
but yet-undetected classes
- Starburst galaxies
- GLAST will likely detect 10 (Torres et a
2004) - Merging / accreting clusters of galaxies and
large-scale filaments - Dark matter density peaks
- Insert your own here
4How do we make progress on extragalactic source
classes with no identified members?
- Theorize, then theorize some more.
- Use observations of the isotropic diffuse
background to constraint properties of
yet-undetected classes / exotic physics - However
- unresolved members of established classes
(blazars, normal galaxies, extragalactic
unidetified sources) also have some guaranteed
contribution to background - These contributions need to be modeled and
subtracted - Task involves formidable uncertainties!
5How do we make progress on extragalactic source
classes with no identified members?
- Use information on background spectral shape
6How confident are we in the spectra of
unresolved emission from established source
classes?
- Unresolved emission spectra
- calculated from spectral index distributions of
detected sources - implicit assumption spectra of unresolved
sources similar to spectra of resolved sources - but also uncertainty involved in spectral index
distribution of resolved sources (low number
statistics, large measurement error in individual
spectral indices)
7GLAST can help!
- GLAST will detect between 1,000 - 10,000 blazars
(EGRET detected 60) - v
Unresolved FSRQ emission using EGRET data
Unresolved FSRQ emission using GLAST data
(simulated)
8Conclusions
- Extragalactic diffuse emission encodes valuable
information on (a) unresolved members of
established classes(b) theorized, yet-undetected
classes of extragalactic gamma-ray sources - Spectral shapes of different components /
observed emission powerful tool
complementary to studies of relative emission
intensity involves different, independent
uncertainties - GLAST will allow us to make much more confident
predictions for spectral shape of known classes,
and place much stricter constraints on
properties of undetected classes