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Continuum radiation from ionised gas
Free-free (aka bremstrahlung = braking radiation) Not necessarily X-ray
í
See ` High energy Astrophysics’ (Melia) p.91
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Bremsstrahlung examples X-ray bremsstrahlung in cluster of galaxies (Perseus) : T=10^8K
Radio bremsstrahlung (green) in star forming region NGC3603
cf
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The importance of measuring L_ion • Measuring star
formation rate in external galaxies
0.5 1 1.5 2
35
40
45
50
Log Φ ion
Log M_*
cf
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The importance of measuring L_ion
• Ionising luminosity of young stars with discs
Protoplanetary disc HL Tau imaged with ALMA 2015
Free-‐free emission from ionised gas (flat spectrum)
ì é
Thermal emission from cold dust
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Ionising radiation may photoevaporate protoplanetary
discs
Race between planet forma<on and disc dispersa?l
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Inverse Compton emission (= scattering of photons off
relativistic electrons)
Lab Electron frame Lab
hν ~γhν ~γhν ~γ hν
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Synchotron radiation
Non-relativistic case: balancing centrifugal and Lorentz force gives cyclotron frequency
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Example: AGN NGC 4051
Red = disc component Green line = synchotron Blue line = inverse Compton
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Optically thick accretion disc spectrum
ν
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Protoplanetary discs show accretion disc spectra when in
outburst
But rest of time radiated energy is mainly reprocessed starlight
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Lines from accretion discs
• Colours = contours of equal projected velocity
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Not obvious in raw spectrum because of forest of blended lines
• Pick out double peaked structure via `cross-correlation analysis’