PYA0 Sior Sophistr Physics of th Itrstllar ad Itrgalactic Mdium Lctur 7: II gios Dr Graham M. arpr School of Physics, TCD
Follow-up radig for this ad t lctur Chaptr 5: Dyso ad Williams (lss dtaild) Chaptr 5: Spitzr (ovrlaps matrial hr) Chaptr 7: Tils (ovrlaps matrial hr) Chaptr 5: Drai (graduat lvl)
7. Photoioizatio gios II rgios ad platary bula II rgios physical procsss Siz of II rgio Ioizatio balac withi bula ow sharp is th dg? Effct of havy lmts Stratificatio of bula Tmpratur adio missio Fr-fr combiatio lis Pulsar disprsio masurs Uiformity of ISM ad bula Iitial pasio phas
II gios Trac th spiral arms - foud i/ar star formig rgios
Youg stars photoioizig thir viros S-55 (radius.7 pc) Courtsy of th UK Schmidt Tlscop (copyright i which is owd by th Particl Physics ad Astroomy sarch Coucil of th UK ad th Aglo-Australia Tlscop oard) ad th Southr Sky Survy as cratd by th SuprCOSMOS masurig machi. 5
Stllar ursry: ioiz whol rgios Multipl hot youg stars ca photoioiz th iitial molcular cloud, ad thir II rgios mrg ad joi up clarig larg volums 6
Physical procsss - ydrog ioizatio Photoioizatio rat 0 J d h 8 0 6.0 cm Cas radiativ rcombiatio cof. at.60 0 T.6 0 0.75 0 T cm s 0.75 s
Lyma cotiuum photos Cout th total th umbr of photoioizig photos N Lyc 0 L h d L, N ar th stllar lumiosity ad umbr of photoioizig photos Will d th ma itsity J ν to calculat th iozatio rat AND th hatig rat. First writ th lumiosity i trms of surfac flu L F T I T Isotropic missio Spcific Itsity of star is just th Plack fuctio (i blackbody appro.)
Th ma itsity J Dfiitio of ma itsity, ad approimatio for II rgios W(z) is th radiatio dilutio factor: sky fractio of solid agl subtdd by star * L z W T z W T d I J J J d I d I d I J star Diff star star star Ω (solid agl) Star poit i bula
Ioizatio alac alac btw photoioizatio ad rcombiatio i bula I Dfiitios 0 I 0 Diff J J d T h J d h I dsity of utral hydrog atoms, p ( p = II ) dsity of lctros ad protos, rspctivly total umbr of utral ad ioizd hydrog: p + I J* ma itsity from hot star J diff diffus ma itsity from bula α A, α radiativ rcombibatio cofficit (cm s - ) σ photoioizatio cross-sctio (cm ) p p T A O-th-spot approimatio
Strömgr radius of a II rgio Cosidr uiform II rgio hydrog is prdomiatly ioizd with a ioizatio fractio = [= fully ioizd, =0 utral] s Lyc N,, wh p p I II p Lyc s N alac total # ioizatios with ffctiv umbr of rcombiatios givs (gt) Strömgr s radius, sttig = (ioizd) Strömgr,., 99, ApJ, 89, 56
Typical Ioizatio alac Eampl: Adoptig typical dsity = 000 cm -, O star: r 0. 5pc 0 r F Lyc photos cm - s - With typical cross-sctio ad rcombiatio rats 0 Assumptio that hydrog is mostly ioizd is good (dpds o gas dsity)
Strömgr radius of a II rgio Lyma cotiuum lumiosity of O, stars: O: N(LyC) = 0 50 phot s - T = 60,000 K O5: N(LyC) = 0 9 phot s - T = 6,000 K O7: N(LyC) = 7 0 8 phot s - T = 5,000 K O9: N(LyC) = 0 8 phot s - T =,000 K 0: N(LyC) = 5 0 7 phot s - T = 0,000 K : N(LyC) = 5 0 5 phot s - T = 0,000 K Thortical valus N(LyC) ucrtai NLTE/LTE, li blaktig Eampl: Adoptig typical dsity = 000 cm -, O5 star: S ~ 0 8 cm ~ pc Mass of II rgio M II S m N Lyc m **Lowr dsitis mor mass**
ow sharp is th dg? Ma fr path of ioizig photo L I cosidr =0.5 th L 0 0.5 0 pc ΔL << S a vry sharp dg. ydari-malayri t al. (00, A&A, 7, 95)
Ioizatio balac (i mor dtail) p p p 0 0 * Lyc p I N d h L W T d h L W Writ ma itsity i trms of stllar lumiosity Lyc T N * p Attuatio by utral hydrog
Ioizatio balac Substitutig i th ioizatio balac quatio bcoms Lyc Lyc N T T N * p p p z S S z Dfi a ormalizd radius
Ioizatio balac p z S d [ A] d dz [ ] S Dfi Strömgr optical dpth (utral hydrog) S S s 0 0 cm NLyc 9 50 phot. s A S z p d dz S
Ioizatio balac 5 Elimiat - by combiig [A] ad [] d dz p d z dz z p Sttig ~ i th abov w obtai th solutio, l z Diffrtiatig, th with quatio [] givs th utral fractio d dz S z z S
Oio layrs I ( 0 ) 50Å photoioizatio cross-sctio E.g., O9 star N( Lyc) = 0 8 phot s - N( Lyc) = 0 7 phot s - II Strömgr radius is 75% of th II Strömgr radius For O star ad Strömgr radii ar about th sam siz small + shll ar to th star Shlls isid II rgio for abudat mtals with similar ioizatio pottials C, N, O mor compl atomic physics ivolvd Dust prst i cloud will absorb photos Last ffcts rduc siz of II rgio