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14-The Evolution of Stars and Gas in Galaxies

14-The Evolution of Stars and Gas in Galaxies. Elliptical Galaxies. Spiral Galaxies. Barred Spiral. Lenticular. Irregular ( L arge M agellanic C loud). Dwarf Spheroidal Galaxy. The Hubble Sequence. Corrected mean galaxy colors according to de Vaucouleurs (1961)

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14-The Evolution of Stars and Gas in Galaxies

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  1. 14-The Evolution of Stars and Gas in Galaxies

  2. Elliptical Galaxies

  3. Spiral Galaxies

  4. Barred Spiral Lenticular Irregular (Large Magellanic Cloud) Dwarf Spheroidal Galaxy

  5. The Hubble Sequence

  6. Corrected mean galaxy colors according to de Vaucouleurs (1961) ---------------------------------------------------------------------------------------------------------------------------- E S0 Sa Sb Sbc Sc Sm/Im ---------------------------------------------------------------------------------------------------------------------------- <B-V>0 0.92 0.92 0.82 0.81 0.63 0.52: 0.50 <U-B>0 0.50 0.48 0.28 0.27 -0.02 -0.12 -0.20 ---------------------------------------------------------------------------------------------------------------------------- Normalized frequency distribution of spiral galaxies in the Revised Shapley-Ames Catalog ------------------------------------------------------------------------------------------------------------------------------------------ MB Sa Sab Sb Sbc Sc Scd Sdm Sm + Im ------------------------------------------------------------------------------------------------------------------------------------------ -23.75 0.01 -23.25 0.01 0.03 0.02 0.04 0.01 -22.75 0.03 0.10 0.19 0.01 0.03 -22.25 0.13 0.10 0.12 0.12 0.05 -21.75 0.13 0.15 0.24 0.22 0.17 -21.25 0.29 0.21 0.13 0.29 0.16 -20.75 0.17 0.21 0.14 0.14 0.20 0.08 -20.25 0.16 0.21 0.07 0.10 0.15 0.15 0.10 -19.75 0.08 0.04 0.04 0.12 0.23 0.08 0.10 -19.25 0.03 0.02 0.04 0.06 0.15 0.17 -18.75 0.01 0.01 0.03 0.23 0.17 0.10 -18.25 0.01 0.08 0.17 0.10 -17.75 0.08 0.17 -17.25 0.08 0.20 -16.75 0.10 -16.25 0.08 0.10 -15.75 -15.25 0.20 -14.75 0.08 ------------------------------------------------------------------------------------------------------------

  7. Luminosity distributions for Shapley-Ames galaxies (Sandage & Tammann 1981) as a function of Hubble type. Objects of types Sd-Sm-Im are seen to be much less luminous than those with types Sa-Sb-Sc.

  8. Isochrone - 4x109 yrs Isochrone - 2.5x108 yrs

  9. IMF in the ρ Oph Association

  10. IMF - Summary (Meyer et al. 2000, PPIV = Protostars & Planets IV)

  11. Is the IMF Universal in Space and Time? • The situation is complicated! • Doesn’t seem to be tremendously different within the Milky Way Galaxy, although some obvious differences exist • M/L in other galaxies - tricky - L is dominated by late-type giants, while M is dominated by dwarf stars and dark matter • However, the presence of metals in high-z systems might require a flatter IMF with more massive stars than local IMF

  12. What about the Star-Formation Rate? Stars more massive than 2 Msun evolve so quickly they are a good indicator of current SFR. The past SFR needs to include lower-mass stars - much harder to do (don’t know ages!) Oort Limit (kinematic) - stars are 70-95 Msun pc-2. Guessing the time dependence gives 1.5 < SFR < 25 Msun pc-2 Gyr -1 (but we don’t really know if SFR is currently decreasing or increasing!) Star counts give 43-144 Msun pc-2 and 3 < SFR < 7 Msun pc-2 Gyr -1 Rough mean of these 2 methods: SFR ~ 10 (+10/-5) Msun pc-2 Gyr -1

  13. The SFR Depends on Location in the MWG! • Current MWG star formation is dominated by 2 regions: • Innermost 1 kpc • Ring between 5-8 kpc of center And the actual rate is probably dominated by a wide variety of (often) little understood processes: gas density, shock conditions (local sound speed, shock frequency & strength), global and local gas rotation and shear, magnetic field strength, gas metal abundance (cooling!) and the background star density. May need to depend on more general ideas based on relevant factors - a complete analytic description is probably beyond hope at this point.

  14. Nucleosynthesis & Chemical Enrichment • Main Sequence • M<1.1Msun - pp chain makes He from H • M>1.1Msun - CNO makes He from H, while N builds up at expense of CO (Note that this requires pre-existing C) • Post-MS • Low-mass stars: Red Giant Tip through Horizontal Branch to Asymptotic Giant Branch - He converted to C and O - winds & PN • High-mass stars: He converted to C and O heavy metals produced through Fe - winds & SN II • Some WD stars in binaries also return heavies - SN I

  15. “G-DwarfProblem”(There is a deficit of metal poor G stars) • Solar neighborhood can be modeled as a closed system • It started as 100% metal-free gas • The IMF is constant • The gas is chemically homogeneous with time • Infall - most stars formed after significant enrichment • Pregalactic burst of massive stars • Variable IMF • ISM chemically inhomogeneous

  16. Clouds Above the Galactic Plane • Galactic Fountains? • Primordial Local Group Mini-Clouds • Tail-End of MWG Formation • Tidally-Stripped Gas from Passing Small Galaxy

  17. Magellanic Stream

  18. Abundance Gradients in the Galaxy??

  19. Rosolowsky & Simon (2007)

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