Flashcards
Galaxy Lecture 7
Cards in this deck (8)
- 1HI Emission and AbsorptionEmission gives bigger picture
- 2Gas 2 CNMCold, but warmer than molecular clouds. T = 80-100K
n - 50cm/3
1-4%, scale height - 120pc - 3Gas 3 WNMHI=neutral hydrogen, T = 8000K, density has decreased to 0.5cm/3
30% of ISM by volume. Lower density = higher volume = higher scale height (400pc)
Well distributed through plane of MW. Scale height - measured from mid plane out. Thickness is double scale height
HI shells - diameter 360pc, v = 12km/s. SN moves - see effects of energy ejection of supernova - 4Gas 4 WIM HIIHII - ionised H
T - 6000-12000K
n - 0.1cm/3 - 10^5m/3
25% of ISM
Height - 1000pc - 1kpc
Primarily photo ionised as opposed to collisionally ionised
90% of HII in MW is in WIM only 10% in bright dense HII regions - 5What is H alpha and why does it trace ionised hydrogen?going from n=3 to n=2 with lambda = 656nm = visible. Recombination and reionisation.
- 6Gas 5: HIMHII, T = 10^5-10^6 K
n - <0.0003cm/3
50% of ISM by volume. Extremely tenuous
Scale Height - 3000 pc, 3kpc
Sometimes referred to as galaxy's corona. - 7What heats HIM?Supernovae - biggest energy source - dump energy in to ISM. Different to photoionisation of WIM - this is shock ionised by mechanical energy injected in to ISM
Seen by: absorption lines from ground states of highly ionised atoms (Ovi Nv) superposed on spectra of background stars
X ray emission - Wiens Law, High temperatures.
Buoyant (hot and low density): fountains, bubbles
ISM has the morphology of swiss cheese - 8Summary1. Molecular clouds - sites of star formation. Observe via dust extinction (IR and visible) , emission. Long wavelengths.
2. Neutral - observed via H 21cm emission line
4. WIM and HIM - h - alpha, UV absorption lines, x rays.
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- Flashcards on Galaxy Lecture 7, created by Lucy Mathieson on 09/11/2016.
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- Lucy Mathieson
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