Radio relics in cosmological MHD simulations
Radio relics in cosmological MHD simulations - Michigan State ...
Radio relics in cosmological MHD simulations - Michigan State ...
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<strong>Radio</strong> <strong>relics</strong> <strong>in</strong> <strong>cosmological</strong><br />
<strong>MHD</strong> <strong>simulations</strong><br />
Brian O’Shea<br />
Michigan State University<br />
With Sam Skillman, Jack Burns (CU/<br />
Boulder), Eric Hallman (Tech-X), Hao<br />
Xu, Mike Norman (UCSD), David<br />
Coll<strong>in</strong>s, Hui Li (LANL)
Some questions<br />
• What produces a radio relic?<br />
• What are the plasma conditions <strong>in</strong>side the<br />
relic?<br />
• How can <strong>cosmological</strong> <strong>simulations</strong> <strong>in</strong>form<br />
observations?
Some questions<br />
• What produces a radio relic?<br />
✓<br />
• What are the plasma conditions <strong>in</strong>side the<br />
relic?<br />
• How can <strong>cosmological</strong> <strong>simulations</strong> <strong>in</strong>form<br />
observations?
Our <strong>simulations</strong><br />
• <strong>MHD</strong> <strong>cosmological</strong> calculations us<strong>in</strong>g the Enzo<br />
AMR code (O’Shea et al. 2005;<br />
http://enzo-project.org)<br />
• 256 Mpc/h box, 1010 M⨀ dark matter particles,<br />
Δxm<strong>in</strong> = 7.8 kpc/h. All cells with |B| > 5x10 -8 G<br />
ref<strong>in</strong>ed to Lmax.<br />
• Sims start at z ~ 100, AGN <strong>in</strong>ject magnetic<br />
fields at z ~ 3, cluster allowed to evolve to z ~ 0.<br />
Skillman et al. 2012, ApJ, submitted
Gas Density<br />
FOV<br />
8 Mpc
10 8 K<br />
Gas Temperature<br />
FOV<br />
10 7 K<br />
8 Mpc
<strong>Radio</strong> emission us<strong>in</strong>g Hoeft & Bruggen (2007) model<br />
dP (⌫ obs )<br />
d⌫<br />
=6.4 ⇥ 10 34 erg s 1 Hz 1 A n e<br />
Mpc 2 10 4 cm 3<br />
⇠ e<br />
0.05 ( ⌫ obs<br />
1.4GHz ) s/2 ⇥ ( T 2<br />
7keV )3/2<br />
(B/µG) 1+(s/2)<br />
(B CMB /µG) 2 +(B/µG) 2 (M).
<strong>Radio</strong> emission us<strong>in</strong>g Hoeft & Bruggen (2007) model<br />
Area of shock<br />
Post-shock<br />
density, temp.<br />
dP (⌫ obs )<br />
d⌫<br />
Electron<br />
acceleration<br />
efficiency<br />
=6.4 ⇥ 10 34 erg s 1 Hz 1 A n e<br />
Mpc 2 10 4 cm 3<br />
⇠ e<br />
0.05 ( ⌫ obs<br />
1.4GHz ) s/2 ⇥ ( T 2<br />
7keV )3/2<br />
(B/µG) 1+(s/2)<br />
(B CMB /µG) 2 +(B/µG) 2 (M).<br />
Magnetic field<br />
strength<br />
Acceleration efficiency<br />
as f(Mach)
Comb<strong>in</strong>ed X-ray and radio emission
Temp<br />
YSZ<br />
Density<br />
All radio
Temp<br />
YSZ<br />
|B|<br />
Density<br />
All radio
Typical relic plasma properties:<br />
• 0.1-1 μG B-fields<br />
• Mach 2-6 shocks<br />
• ~10 -27 - 10 -28 g/cm 3 baryon density<br />
(10 -3 - 10 -4 cm -3 )<br />
• ~5x10 7 - 2x10 8 K plasma temperature
Appearance depends strongly on view<strong>in</strong>g angle!
Spectral <strong>in</strong>dex<br />
Between 300 MHz - 1.4 GHz<br />
Edge on<br />
Face on
Polarization - edge on<br />
(E-vectors)
Polarization - edge on<br />
Smoothed<br />
(E-vectors)
Polarization - face on
Polarization - face on<br />
Smoothed
What do we learn?<br />
• Cosmological structure formation naturally<br />
produces radio <strong>relics</strong> as a result of halo mergers<br />
• Gas at Mach 2-6, low density, very high<br />
temperature primarily responsible for emission<br />
• Relics correlate well with jumps <strong>in</strong> T, X-ray, (to a<br />
lesser extent) SZ<br />
• We f<strong>in</strong>d reasonable spectral <strong>in</strong>dices, magnetic<br />
field behavior (when compared to, e.g., sausage,<br />
toothbrush <strong>relics</strong>)
Observers beware!<br />
• We don’t need spectral ag<strong>in</strong>g to get a spectral<br />
gradient! Observed “ag<strong>in</strong>g” is likely real + LOS<br />
effects.<br />
• Some radio halos are not radio halos! View<strong>in</strong>g<br />
angle impacts spectral <strong>in</strong>dex, polarization<br />
fraction - and thus classification.
Thank you!<br />
Skillman et al. 2012, ApJ, submitted
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