Continuum radiation from ionised gas

Free-free (aka bremstrahlung = braking radiation) Not necessarily X-ray

í

See ` High energy Astrophysics’ (Melia) p.91

Bremsstrahlung examples X-ray bremsstrahlung in cluster of galaxies (Perseus) : T=10^8K

Radio bremsstrahlung (green) in star forming region NGC3603

cf

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

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  

Ionising radiation may photoevaporate protoplanetary

discs

Race  between  planet  forma<on  and  disc  dispersa?l  

Inverse Compton emission (= scattering of photons off

relativistic electrons)

Lab Electron frame Lab

hν   ~γhν   ~γhν   ~γ    hν  

Synchotron radiation

Non-relativistic case: balancing centrifugal and Lorentz force gives cyclotron frequency

Example: AGN NGC 4051

Red = disc component Green line = synchotron Blue line = inverse Compton

Optically thick accretion disc spectrum

ν

Protoplanetary discs show accretion disc spectra when in

outburst

But rest of time radiated energy is mainly reprocessed starlight

Lines from accretion discs

•  Colours = contours of equal projected velocity

Not obvious in raw spectrum because of forest of blended lines

•  Pick out double peaked structure via `cross-correlation analysis’