48x36 poster template

1
Non-Thermal Radiation from Intergalactic
Shocks Uri Keshet1, Eli Waxman1, Abraham Loeb2,
Volker Springel3, and Lars Hernquist2 1) Weizmann
Institute of Science 2) Harvard University 3)
Max Planck Institute for Astrophysics
Max Planck Institute for Astrophysics
GAMMA-RAY SIGNAL
Spectrum
Source Number Count

• Conclusions
• IGM 10 of EGRB flux
• gt a dozen GLAST sources for ?egt0.03
• Cross-correlation with LSS (e.g. Scharf
  Mukherjee 2002)

CONCEPT
TREE-SPH COSMOLOGICAL SIMULATION
EGRET
non-calibrated
N(gtF)
?e5
GLAST
EGRET
?e5
Intergalactic shocks emit radiation in the
following process
non-calibrated
calibrated
Converging flows during structure formation (SF)
simulation
J ? ?e
Electron acceleration
Collisionless shocks
calibrated model
simulation
Inverse-Compton (of CMB photons) and synchrotron
emission
The emission from strong shocks dominates the
radiation from the periphery of galaxy clusters
and from galaxy filaments traces LSS
Fph s-1 cm-2
RADIO SKY
SHOCK IDENTIFICATION
ANALYTICAL MODEL
Radio sky brightness
Intensity fluctuations dIl on 00.5 scales
Cooling is inefficient in the relevant regions
(panel 1) Adiabatic simulations suffice
Entropy changes (panel 2) of SPH
particles trace the shocks (panel 4)
Approximations 1) Large scale structure (LSS)
composed of halos 2) Halo mass distribution
isothermal sphere 3) Strong shocks only
e.g. according to the Press-Schechter halo mass
function
Panel 1 phase space with tcool/tH contours
Panel 2 histogram of entropy change ?S ?S/CV
accumulated by SPH particles in the epoch 0ltzlt2
IGM shocks
?dN/d?S
very dense, beyond shocks
?
dN/d?S
10-1
104
?
Galactic synchrotron ?l-1/2
10-2
const for 400ltllt4000
Halo Parameters M - mass T - temperature rsh
- shock radius - mass accretion rate
103
discrete sources ?l
total
CMB
e-
e-
M
M
Translates ?S to Mach number M
102
10-3
M,T
Particles with ?S above the cutoff trace all
shocks of Mach number Mgt4
ERB estimates
Galactic
101
10-4
M4
synchrotron
already cold
rsh
IGM shocks
CMB
21 cm tomography
?
100
?
Halo Dimensional Analysis
Panel 3 density slice (100x100x10 Mpc)
ncm-3
Bremsstrahlung from Lya clouds
ncm-3
Panel 4 same density slice as shown in panel 3,
but including the Mgt4 shocked particles only
MHz
? MHz
isothermal sphere
IGM fluctuation dominate on 1-00.5 scales
IGM shocks significant fraction of the ERB
Mpc
Mpc
facc
EXTRAGALACTIC GAMMA-RAY BACKGROUND
Shock fronts may be identified
velocity dispersion
fT
modeled EGRB ref 7
408 MHz

• Previous EGRB estimates are
• Non isotropic on large scale
• Correlated with Galactic tracers
• High ( total polar intensity)

Previous estimate
unknown dimensionless parameters
Hubbles coefficient
Mpc
Mpc
effective mass
fr
(Sreekumar et al. 1998)
INTEGRATED EMISSION
Relativistic Electron Distribution
Fit EGRET latitude profile as a sum of 2
components one linear in a Galactic gas tracer
and the other linear in a synchrotron tracer
EGRET gt100 MeV
Results Robust EGRB flux upper limit (1/3 of
previous estimates)
Strong shocks
70 syn. tracer (22 GHz)
Simulated sky
J/ltJgt

• Conclusions
• gt10 sources well resolved by GLAST (for
  ?e0.05)
• ?-ray clusters targets for MAGIC, HESS, VERITAS
• ?-ray morphology accretion rings with bright
  emission at filament intersections

30 gas tracer (21 cm)
gt100 MeV
North
??42
South
Parameterization (no complete model)
log10T
J/ltJgt
gt10 GeV
electron energy ?e5 (2.5-7.5) magnetic
energy ?B1 (0.05-2)
SNR observations
CONCLUSIONS AND IMPLICATIONS
out of shock thermal energy
Bcluster 0.1µG
??12
deg

• Conclusions
• ?-ray sources detectable by GLAST and Cerenkov
  detectors
• Signal fluctuations dominate the radio sky on
  1-0.50 scales
• Indirect detection, e.g. cross correlations with
  LSS tracers
• Extragalactic backgrounds EGRB low, ERB unknown
• Calibrated analytical model, fast shock
  identification in SPH

• Implications of signal detection
• First identification of intergalactic shocks
• Reconstruction of large-scale flows
• Tracer of warm-hot IGM (WHIM)
• Probe of intergalactic magnetic fields

Emitted Radiation
halo luminosity
deg
Mpc
MODEL CALIBRATION
Integration over halo abundance (images the
integrands in the mass-redshift plane)
Model halo parameters (column 1) are calibrated
with various features of the simulation (column
2). Agreement between the radiation fields
extracted from the simulation and from the
calibrated model (column 3) provides an
independent check of the calibration scheme.
BIBLIOGRAPHY

• Cosmic ?-ray background from structure formation
  in the intergalactic medium, Loeb and Waxman
  2000, Nature, 405, 156-158
• Fluctuations in the radio background from
  intergalactic synchrotron emission, Waxman and
  Loeb 2000, The Astrophysical Journal, 545,
  L11-L14
• Gamma rays from intergalactic shocks Keshet,
  Waxman, Loeb, Springel and Hernquist 2003, The
  Astrophysical Journal, 585, 128-150
• The case for a low extragalactic gamma-ray
  background Keshet, Waxman and Loeb 2004,
  Journal of Cosmology and Astrophysics, 04 (006)
• Imprint of Intergalactic shocks on the radio
  sky Keshet, Waxman and Loeb 2004, submitted to
  ApJ astro-ph/0402320
• A statistical detection of ?-ray emission from
  galaxy clusters, Scharf Mukherjee 2002, The
  Astrophysical Journal 580, 154-163
• EGRET observations of the extragalactic
  gamma-ray emission, Sreekumar et al. 1998, The
  Astrophysical Journal 494, 523-534

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