Galaxies and the Universe - Stellar Content of Galaxies

Galaxies and the - Gala ie and he Uni e e S ella Con en of Gala ie Se a C e f Ga a ie Dec i g he c e f a ga a f b e ed e ie he e ca ge e a headi g

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Unformatted text preview: 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie Se a C e f Ga a ie Dec i g he c e f a ga a f b e ed e ie , he e ca ' ge e a headi g f spect ral s nt hesis. The ga a i i a e ea e i a ie a a fc e i hich ha e i i ic i i de i r( ) Li; i i f hi c e (i eg a i g r dV) f he ga a , f hich a e e hi g ab he ga a hi a be de i ed. The ga a ' a ii e e i di id a a , fa de he e (e i ed) a e e g h l a be e die he a , ea e i a c di i , a d a be i e ( he e r i a ec i i ); hich e e i i , i e he e a i f adia i e a fe , c eeb ac ica e e . Ob e a i a a a e e g h ca c ai , if ecif , he de i ie ri if he ha e di i g i hab e Li (l) - ha i a , if hei ec a a e "diffe e e gh". The i d f c e e a e i e e ed i i c de: S a : ai - e e ce, gia , e gia , h i a - b a ch, a a f c i f ec a e e ea ea d efe ab ih e e a ici i f a i . Red a d hi e d a f a e fai ha hei c ib i a e a a a ed b ce ai ie i e i ai .Sa ae e i e b e ed i di ec ia i i a i f di g ga ( a e a eb ae, H II egi ). Ga : See i i i ed f (H II egi , e a e a , e ic e i i egi a d ac i e c ei), e a ad ec a (H I, CO, he ec a ecie ), a d high- e e a e ga (high i i ed ecie ia ab ii ha , di ec ia X- a he a b eh ah g). Thi a dea i h a e g h i a ea ie ec e. D : de ec ed ei he b e adia i f ab bed UV- i ib e a igh i fa - IR begi e , ia ab i (l). We c e ed hi a idic e g h i he e i ec e. F hi i d ec a g. O e i a h ica h ef a ab a ga a f che e f ; if a e e ce fi di i c e iaa ' ca e. , e eed (1) i a ei i i he b e ed ec a e di i c e gh - ace - igh , a d ha de a d ( , l); a d (2) ha e a complet e ib a f c ie g d ge he ga e b ca ' e ha ' aa fc e f c i ( ec a), h i g ha he gi e ea i ee . S e ch edge i i ici i ch ab e ag i de a e a ic a a e e g h e ch The aigh f a d a ach e c e he a be d e (i ai E g i h, ea e he e i i i e ). C S a : di ec h ea he ic e i i he ea Ga : c d a (UV h i e , IR f (bi a X- a (H I, (e .a . a.ed /keel/gala ie / a .h ml ae he ) a e) d) , a ea ce ed e a e d ce , he dd SS 433 c ec a c (104 K, e i i - i e ga ) H II egi a e (2- 3 104 K) ada a i a ga a : gh id- IR) (e i i id acc e i ec a a e i e ha e aigh f ide ib e ce f adia i f eb ae a i e i i i g adia i ) , h c ed ga 1/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie ( ) (107 K) D X- : , ( - , ) ( ) - ( V ) , .C F . - , " ( "). A NGC 7714, (SED) NED, ), K - UV, L , - IR ( a. ) ' , .B A J 100, 147 (1944) M.W NGC 147 L G A J 100, 137 (1944) - bl e red. T 185; ' H- R . a.ed /keel/gala ie / a .h ml ' . T .a 9- . X- M32, , ( FUSE S .N ( , M31 .T 109 2/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie years) and old (say 1010 years) groups of stars. The young stars will have few red giants, and a main sequence reaching to blue colors and high temperatures, while the older population's brightest members will be red giants and the main sequence will be truncated at cooler temperatures (lower masses, redder colors) as stellar evolution eats away down the mass sequence. This figure (from Baade 1944 on M31/M32, courtesy the AAS) shows the difference. The population designations are chosen to make the Sun Population I. The best- studied Pop II systems are globular clusters (which fact seriously biassed our understanding until recently), which are old (1.0- 1.4 x 1010 years) and have low metallicity 0.01 solar - this especially is not a defining Pop II characteristic, as galactic bulges have ranges going up to strong- lined stars with above- solar metal abundances. Interpreting the details of a stellar population is complicated by such facts as: 4. (1) the giant branch shifts depending on metallicity, mass- loss history, surface mixing 5. (2) most galaxies are observable only in integrated light 6. (3) the horizontal branch shifts with metal abundance, important in the blue and UV 7. (4) we need the luminosity function along the giant branch 8. (5) age differences can mimic abundance differences 9. (6) a range of age and metallicity is usually present. Even with all this, kinematic and distribution differences between populations are unmistakeable in nearby galaxies. We can see where certain features of the H- R diagram are by direct observation in nearby galaxies, exemplified by the cases of the Leo II dwarf spheroidal galaxy (from Mighell and Rich 1996 AJ 111, 777) and the Carina dwarf galaxy (Hurley- Keller et al. 1998 AJ 115, 1840, courtesy AAS). In the Carina data, excerpted from a multipanel figure, the vertical axis in V magnitude runs from 17 to 26, and the horizontal axis represents B- V. .a . a.ed /keel/gala ie / a .h ml 3/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie Da a ch a he e, a d a - b - a ec c f Ga ac ic b ge gia (Whi f d, Rich, F ge ), e ab he i i f c i a d e a ici a ge f gia . The diffe e ca e a d a ba d h b c e cha ge i he e f he gia b a ch, b he diffe i g a e f he h i a b a ch i i c ea . N e a e , he di i c ie a i i Ca i a. S e f he c e i ie f he " a i 1/2" a ach he a ied ga a ie i h di e e a - f i g hi ie a e di c ed b H dge (1989 ARA&A 27, 139). F ea b ga a ie (a d b ,f e gia , " ea b " ca g a he a he Vi g c e ) e ca b e e he b igh e i di id a a , e i g e ha e ca e ac f i eg a ed igh . The e ie f he e a de e d hei a hi , a d h a ge e a ici . O he ai e e ce, he e e a e f a gi e a a d ec a e i be e f highe ab da ce , h i g a cha ge i he a ' di ib i ac he e HR diag a , i he e ci a i f di g H II egi , a d i he e a i e be f O a d WR a . The g i d i WR a a e a ge d i e b adia i ee e a i i hei a he e , he e a e be ie ed be e e a highe e a ici (a d he i d fea e a e, i deed, ge f highe - e a ici e, he i ha e ca e fa - UV i d i e a e a ici i dica ). Bei g ab e dee e i he a ed gia a i gi e he hi f a f ai e G i e ca e . I e di a ga a ie e b e ed e a ec .I ai ea e if (1) e effec a e ' i a , (3) a i e e int egrat ed light a d e f e id i ci e (i.e. a he a ica ea i g) e c d ec de a d a e d ci g ig ifica igh , (2) ge g e gh a e e g h ba e i e i b e ed, a d (4) f spect ral s nt hesis a ch he e he e a i e c ib i f e ica ( b c a i , edde i g) he da a a e "g d e gh". Thi a ach begi i h de a di g hich a e dh g he e he H- R diag a , a d ha hei ec a i e a he e ca i . We a f e di ib i f a aa g ha h b Ke ic ' Fig e 4 i St ellar Populat ions. The e d e ' ee be ch a fig e a ai ab e e ec ica ih ai i g c igh e i i , I' i a e he i i h hi Hipparcos HR diag a , h i g he de i f a i a i a f he c - ag i de d ai . Thi i f a b e ed a e i ' i i - eigh ed i a i a ia e a ac a ba e a he i , b ' ge he idea. .a . a.ed /keel/gala ie / a .h ml 4/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie T , , . A ) SFR, , , H- R 466, ev olut ionar s nt hesis ; " .S ( , SFR, populat ion s nt hesis " K 1983 (A J 269, . 12): I S , C 1984 (A J . 56, 257; IRAF ) G ,S 1981 (A J 249, 48) .S UV IUE -W . 1093, IUE Ult rav iolet Spect ral At las (NASA IUE N 22, 1), H . 1984, IUE Low Dispersion Ref erence At las (ESA: N ), F . 1990 (A J 364, 272). R ,L 12(PASP 108, 996, 1996) , .a , . a.ed /keel/gala ie / a .h ml J , ,H T 5/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie with the tables appearing in the AAS CD- ROM series (disk 7, 1996 part 2). Many of the difficulties found in dealing with galaxies may be traced to a lack of very high- metallicity stars in our neighborhood for inclusion in such compilations, and the often- subtle changes in late stages of stellar evolution with metallicity. Typical spectral synthesis results look like this (again shamelessly taken from Keel 1983): in which the observed spectrum is at the top, the model spectrum composed from solar- neighborhood stars below, and the difference at the bottom. The jump near 5600 is due to splicing together data with different grating settings; this kind of analysis tests one's ability to do absolute spectrophotometric calibrations. The fitting itself may use various algorithms and weighting schemes, which might stress line strengths or continuum shapes. For instance, some schemes have used only equivalent widths of various absorption lines, sometimes with the intensity of Balmer emission as a constraint on the total number of OB stars. Lines are selected to include sets which are sensitive to temperature, pressure (i.e. dwarfs, giant, supergiants), and metallicity. Note that any system composed of a mix of spectral types will have different kinds of stars dominating at different wavelengths - that's why this technique works at all. Once the behavior of a strong feature is well understood spectroscopically, it may be more efficient to map its spatial variation via narrow- band imaging (Baum, Thomsen, and Morgan 1986, ApJ 301, 83). A review by O'Connell in S ella Pop la ion outlines some cautions. Some important references for spectral synthesis are given in the table below. Some patterns have emerged. The V- band light from old populations (ellipticals, spiral nuclei and bulges) is about evenly split between red giants and main- sequence stars. It is particularly easy to recognize such populations with a single superimposed burst (so- called E+A systems; see Dressler and Gunn 1982 ApJ 270, 7). Much work has concentrated on ellipticals as the galaxies with the simplest star- formation history, presumably approximated by a single burst and subsequent passive evolution. Many ellipticals have shown an unexpected excess of UV flux shortward of about 1500 , indicating that there is a significant population of hot stars. These are widely thought to be evolved, post- asymptotic- giant- branch (PAGB) stars (aka planetary nebula nuclei); deep UV observations with HUT suggest that the dominant source of this UV light may be different for different luminosities/metallicities - Brown, Ferguson and Davidsen (1995 ApJL 454, L15) implicate the extreme horizontal branch for luminous ellipticals, while the M31 bulge UV component is hotter (Ferguson and Davidsen 1993 ApJ 408, 92), suggesting a stronger contribution from post- AGB stars. .a . a.ed /keel/gala ie / a .h ml 6/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie S i ad a d Ta J a dA dia 1971 A J S . 22,245 ( h 1973 A&A 26, 95 e ec ic, a a d e i ica ) 1976 A&A 50, 279 (h g a hic+b ad- ba d h 1972 A&A 20, 361 ech ica di c 1976 A J 206, 370 Gia e i ica Ti e 1976 A J 203, 63 Ba ic he Ti e a d G 1976 A J 203, 52 E i ica ga a ie , a Fabe O 'C G e ,S e & Ti e 1981 A J 249, 48 P i che a d Ca . c ei) i fe he i ia he i f e i ica 1980 A J 240, 768 R e f e ec i e ab da ce cha ge 1983 A J 273, 105 S ec a e Bica 1988 A&A 195, 76 Ue f a c eae G egg 1989 A J 337, 45 Diffe e ia he i a d S0 age B a & Cha 1993 A J 405, 538 De c i i W he 1994 A JS 95, 107 I B be E e , ga ac ic a i f ed e a ici a d i g edie a GISSEL he i f ae ae W he ' c de i a ai ab e he Web f dia - i e f ec a he i de . Rece he Pad a de (ac a he i ch e f Be e i e a . 1994 A&AS 97, 851 i h he W he e a de ) beca e i i a a ai ab e. The STScI g a ha a WWW ib a f g ai de . Ge e a be e ai : e ed a d e b e a a e e e e e ed i he ib a ie ; ei he a e e e aich g- i ed a . S he i e a be e i i e d . OB a ha e f hei igh i he i i i g UV, he a e ee h gh H II egi . We h ee i di ec ace f ( a i e- ) a f a i h gh hei effec he i e e a edi . S a cl e ca a be e f ace f he e a a i . G b a c e a e e ecia ice beca e he a e b igh , c ac ( h g- a i g) a d ca be ee a g a ff. The ce f g b a i a i ga a ie e e i e e i g a da ie ( a de Be gh 2000 PASP 112, 932 a d a ge be f hi ea ie a e ). The i i f ci fg b a c e i iig c i e f ga a ga a , gh Ga ia i h a ea a ab M =- 7.5 ( hich ha bee ed a a di a ce i dica ). H e e , he be f c e a ie e . Thi i f e a ified a he ecific f e e c S, he be f c e e i i i , he e f ecifici S=1 ce d a i g e c e e M =-15 f a igh . The a e a ge f S=0.5 i a e- e i a , h gh S=1 f Sa/Sb i a , 2.5 f ica i a ed e i ica , i h a e ab e 10 f e c e e be . O f hi , e ce a c e ga a ie a ge a high a 30. S ch a e ace i ge i i he hi ie f ga a ie , i a ic a he i f b i di g e i ica b i e e ge f di e . F he e, eg b a c e e h bi da c di ib i , gge i g f a i a di i c i e d i g he b i d f e a ( hich i i b ad acc d i h a e ge ce a i ). O he he ha d, he g b a - c e a i c e a e be e i h ga a e ie ha d be e ec ed f a e ge che e, eadi g idea i i g a ec d e ch f c e f ai f ga hich ha fa e bac f a ga ac ic i d a he ha a e a a e ga a (La e e a . 2001 AJ 121, 2974). The e ac e he , i he , c adic . Thei ha he Ga ia f c e a d fadi g e .a ee i a b , a d f e i e gi g e , aai a ei i g hi . Wi eda age bec e ha e ec g i e a a g b a c e ? E ide ce hi ii i i f ci f e e e b e he e a ee f e c e i ea b ga a ie , a he f g b a c e . T a e ch a a i i e i e a c bi a i f di i f fai e i e. The i i g e e e i bei g e ha he i i f c i i he g, b igh c e . a.ed /keel/gala ie / a .h ml 7/8 1/15/12 Gala ie and he Uni e e - S ella Con en of Gala ie is "normal", rather than being weighted toward the more massive stars that we actually see. Velocity dispersions of a couple of nearby examples (Ho and Filippenko 1996 ApJL 466, L83) suggest that indeed they do have large amounts of mass in low- mass stars, someday becoming old and rich globular clusters. In any case, star- cluster populations provide sets of coeval objects whose colors are systematic with age and metallicity, and therefore they can be used to provide some of the information sought from HR diagrams for galaxies at much greater distances. « Dust in galaxies | Star formation Course Home | Bill Keel's Home Page | Image Usage and Copyright Info | UA Astronomy k [email protected] Ls cags 920 at hne: /06 .a . a.ed /keel/gala ie / a .h ml . a.ed 20006 8/8 ...
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This note was uploaded on 01/15/2012 for the course AY 620 taught by Professor Williamkeel during the Fall '09 term at Alabama.

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