L11 ISM, IGM, CGM

Question 1

M_gas vs M_dust in ISM?

Answer 1

M_gas ~ 10 x M_dust

Question 2

which gals have more ISM? why?

Answer 2

elliptical ~0%: tightly packed stellar sys: little to no ISM compared to stars

spiral: ISM <= 25%; ISM in spiral arms

irregular: 15-50% ISM: high in ISM

Question 3

sources of ISM gas?

Answer 3

ejected from SN, stars
remaining from galaxy formation
gas from outside, CGM accreted

Question 4

importance of ISM?

Answer 4

SF

observational: dynamics of galaxy, rotational vel through spectroscopy (also it goes further out then stars (i guess) )

Question 5

why are forbidden lines observable in ISM gas?

Answer 5

density low

collisional times much further apart

no transition back to lower state

Question 6

21 cm line is tracer of?

Answer 6

neutral H

Question 7

molecular gas clouds importance?

Answer 7

dense, cold, usually small
not easily observable (cold)

dense, carry most ISM mass
grav collapse: SF

massive ones have perturbative grav effects on galaxy