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CHEMICAL EVOLUTION MODELS

INFALL and OUTFLOWS from the point of view of. CHEMICAL EVOLUTION MODELS. and STELLAR POPULATIONS. STScI, March 7-9 2005. Monica Tosi INAF – Osservatorio Astronomico di Bologna.

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CHEMICAL EVOLUTION MODELS

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  1. INFALL and OUTFLOWS from the point of view of CHEMICAL EVOLUTION MODELS and STELLAR POPULATIONS STScI, March 7-9 2005 Monica Tosi INAF – Osservatorio Astronomico di Bologna

  2. Chemical evolution models have many parameters and provide no unique solution; however, their predictions on several aspects of galactic evolution have often been confirmed by subsequent observations or theories. Among the most successful predictions, I include those on gas flows: chemical evolution arguments have been the first in favour of long-term infall on spiral disks and of enriched winds in active dwarf galaxies

  3. In the early 80’s, following Larson (1972) and Lynden-Bell (1975), a number of authors assumed continuous infall of metal poor gas on the galactic disk, finding that its time scale should be long to better fit the observed MW properties. MW models (1) Tinsley (1980 and references therein): continuous metal poor infall needed to solve G-dwarf problem and explain radial metallicity gradients Chiosi (1980): continuous slow infall [tinf ≈ (2-3)  109 yr] after first rapid collapse to account for G-dwarfs and radial distribution of gas and SFR in the disk Twarog (1980): infall rate ≈ 1/2 SFR (with <SFR>/SFRnow≈ 2.5) needed to explain AMR => long lasting infall Tosi (1982 and 1988) almost constant infall of extragalactic metal poor gas (Zinf 0.2 Z) after disk formation to account for AMR and radial distribution of element abundances and abundance ratios, gas, SFR, etc. Current rate 1-2 M yr-1. Lacey & Fall (1985): radial gas flows make the observed gradients, but infall of metal-free gas is still needed to reproduce solar neighbourhood properties, with current rate 0.1-1 M yr-1.

  4. abundance gradients (HII regions) infall to reproduce properties of stellar populations models with no infall models with metal free infall local G-dwarfs 1 Zinfall/Zsun=0 0.5 data Shaver et al 83, models Tosi 88 dots: F stars local AMR (F stars) data Edvardsson et al 93, models Tosi88 Tinsley’s intuition in late 70’s

  5. MW models (2) Then, people started arguing that HVCs were not sufficient evidence of significant persisting infall and, for more than a decade, only very few of us kept insisting on its need. Until … Chiappini, Matteucci & Gratton (1997): proposed the two-infall model, with a rapid halo collapse, followed by a slow gas accretion from outside the Galaxy to explain both disk and halo observed properties. Inside-out disk formation. Boissier & Prantzos (1999): inside-out disk formation; infall time-scale radially varying [tinf, ≈ 7  109 yr] Very successful models that have triggered a variety of similar approaches (see e.g. Matteucci 2001 and references therein).

  6. two-infall model: infall rate in  neighbourhood Halo and thick disk formation thin disk formation Chiappini, Matteucci & Gratton (1997)

  7. MW models (3) Meanwhile, HVCs have become fashionable again ….. They have the right metallicity (≈ 0.2 Z) and possibly the right mass to provide 1 Myr-1 Nowadays, most people believe in long-term infall, but the issue is its continuity: a steady state accretion seems less likely than a discontinuous one. What is the effect of intermittent infall on Galactic chemical evolution ? E.g. Koppen & Hensler 05, Valle et al. 05

  8. other galaxies Chemical evolution models require infall also for other spirals (Díaz & Tosi1984-90, Mollà et al96), possibly with different time scales. The lower the galaxy luminosity class, the lower the infall need. Current belief of chemev modellers is that spirals keep accreting metal poor gas from outside for all their life. There may be fountains and satellite accretions as well, but without long-lasting infall these phenomena cannot explain the observed properties of their stellar/gaseous populations. Galactic winds seem unlikely, except possibly in early halo phases or in lowest mass spirals. What about dwarf galaxies ?

  9. Marconi, Matteucci, Tosi first models:Matteucci & Tosi (1985), Pilyugin (1993), Marconi et al (1994) Pilyugin • to reproduce observed abundances: • bursting SF • Salpeter’s IMF • differential galactic winds no winds non selective winds differential winds

  10. thanks to HST stellar populations have been resolved in several dwarf galaxies, both of early and late type, both in the Local Group and beyond) We thus have SF history, IMF and distance from the CMDs of the resolved populations as input of chemical evolution models a new generation of more accurate models for individual dwarfs in now possible. Among this new type of models: for early-type dwarfs, see e.g. Carigi et al. (2002), Lanfranchi & Matteucci (2004) for late-type dwarfs, see e.g. Romano et al (2005)

  11. WFPC2 – NIC2: V image WFPC2 – NIC2 : UBVI combined ACS: V and I combined NGC 1569 NGC 1705 IZw18 2.2 Mpc 5.1 Mpc 10 – 20 Mpc Strong starburst dIrr, evidence of galactic winds Strong starburst BCD, evidence of galactic winds Most metal poor BCD, winds ?

  12. Tosi et al. 01 Different regions in NGC 1705 T-RGB very well defined => (m-M)0 = 28.54 ± 0.26 => D = 5.1 ± 0.6 Mpc 7 6 5 4 3 2 1 0

  13. wind source NGC1705: a post-starburst BCD already back to SF activity • Some SF 5 - 1 Gyr ago • Some SF 1 - 0.02 Gyr ago • Strong central SF 17 - 10 Myr ago • No SF anywhere 10 - 3 Myr ago • Strong SF everywhere 3-0 Myr ago ? quiescent phase only 6-7 Myr long => rapid cooling 7 6 5 4 3 2 1 0 now Annibali et al. 03

  14. chemical evolution models for late-type dwarfs (Romano, Tosi, Matteucci 2005) NGC1705 NGC1569 SF and IMF from HST CMDs => high SF efficiency, high wind efficiency

  15. chemical evolution models for Local Group dSph’s (Lanfranchi & Matteucci 2004) Draco Sagittarius Sculptor Ursa Minor Salpeter’s IMF; SFH from CMDs => low SF efficiency; high wind efficiency

  16. chemical evolution of spirals and dwarfs: gas flows comparison spirals dwarfs RESULTS: long-term infall of metal poor gas needed to dilute metals and favour gradients. Fountains possible. Winds unlikely. RESULTS: winds very likely in lower mass active galaxies; infall likely, fountains unlikely. QUESTIONS: can the accretion rate be considered roughly continuous ? what is the effect on chemical evolution of its discontinuity ? QUESTIONS: what is the wind efficiency of SNe Ia and II ? what is the final fate of the ejected gas ?

  17. the end

  18. SN rates in Romano et al 2005 NGC 1705 NGC 1569 model 5aH’ model 4aH

  19. Best model parameters NGC 1569 (4aH) NGC 1705 (5aH’)

  20. chemical evolution models for late-type dwarfs NGC1569 (Romano et al. 2005) NGC1705 SF and IMF from HST CMDs => high SF efficiency, high wind efficiency

  21. infall from chemical evolution models, infall of metal poor gas appears to be necessary in some, not all, spirals infall is observed in HI in some spirals, like M33, M83, M101, NGC2403, NGC6946 (e.g. D’Odorico et al 1985, van der Hulst & Sancisi 1988, Fraternali et al 2003). In MW evidence is from VHVCs (e.g. Mirabel 1981, DeBoer & Savage 1983-4, Songaila et al 1988, Danly 1989); derived metallicity ~0.2 Zsun, rate 1-2 Moyr -1. gas infall on MW is predicted as residual of proto-galaxy collapse, as accretion from surrounding halo, and/or as intergalactic gas trapped by MW during motion toward Virgo (e.g. Songaila et al 1998, Blitz et al 1999). Magellanic Stream will eventually fall in too (e.g. Sofue 1994).

  22. THE MILKY WAY DISK Inside-Out formation and radially varying SFR efficiency required to reproduce observed SFR, gas and colour profiles (Scalelengths:RB4 kpc, RK2.6 kpc) (Boissier and Prantzos 1999)

  23. MW models (3b) Meanwhile, HVCs have become fashionable again ….. They have the right metallicity (≈ 0.2 Z) and possibly the right mass to provide 1 Myr-1 Nowadays, most people believe in long-term infall, but the issue is its continuity: a steady state accretion seems less likely than a discontinuous one. What is the effect of intermittent infall on Galactic chemical evolution ? Valle, Shore, Galli 2005

  24. chemical evolution scheme collapse of protogalaxy and/or mergers star formation gas inflow and/or outflow stellar evolution, nucleosynthesis mass and composition of ISM stellar mass loss and death from Tinsley (1980)

  25. To understand galaxy evolution theoretical models observational constraints galaxy formation chemical evolution dynamical evolution … chemical abundances gas/star/dark masses kinematics star formation history IMF … N.B. standard chemical evolution models account for large-scale, long-term phenomena: the climate, not the weather !

  26. Star Formation Law and Rate e.g. SFR  e-t/ or SFR  gn Gas flows in andout of the region (infall and wind) e.g. fi  e-t/, fw  ESN Initial Mass Function (m)  m- ;  m (m)dm=1 Stellar lifetimes and nucleosynthesis (yields) PARAMETERS The parameters are many, but not really free. Correct approach is to always compare the model predictions with all the available observational constraints.

  27. observational constraints in the Galaxy they largely outnumber the parameters: • current radial distribution of star density, • current radial distribution of gas density, • current radial distribution of SFR, • current radial distribution of element abundances as derived • from HII regions and B stars, • radial distribution of element abundances at slightly older • epochs as derived from PNe, • age-metallicity relation in solar neighbourhood (and • elsewhere), • metallicity distribution of G-dwarfs in solar neighbourhood, • Local Present-Day-Mass-Function, • relative abundance ratios (e.g. [O/Fe] vs [Fe/H] in disk and • halo stars.

  28. chemical evolution of MW Thanks to the wealth of accurate and reliable data and theoretical achievements, there are currently a number of chemical evolution models able to reproduce all the major properties observed in the Galaxy (see e.g. Prantzos’ and Romano’s talks) However: 1) the solution is not unique yet, 2) there are observed properties not understood yet (e.g. CNO isotopes and gradient evolution)

  29. chemical evolution of dwarf galaxies The chemical evolution of dwarf galaxies has been modeledby many groups, but the observational constraints were so far insufficient: SF continuous, gasping or bursting ? gas infall, gas outflows or both ?

  30. other spirals (2) Chemical evolution models by Díaz & Tosi (1984, 85, 86, 90) suggested that long-lasting infall of metal poor gas was necessary also in other spirals (M31, M33, M51, M83, M101, NGC2403, NGC6946, IC342). The lower the galaxy luminosity class, the lower the infall need. With different models Mollà et al (1996) suggest that gas collapse time varies from spiral to spiral (M31, M33, NGC300, NGC628, NGC3198, NGC6946) to explain differences in observed metallicity gradients. Models for low mass, low luminosity spirals (e.g. M33, NGC2403) seemed to indicate that they need both infall and winds.

  31. Hence, the current belief of chemical evolution modellers is that spirals keep accreting metal poor gas from outside for all their life. There may be fountains and satellite accretions as well, but without long-lasting infall these two phenomena cannot explain the observed properties. Galactic winds seem unlikely, except possibly in early halo phases or in lowest mass spirals. What about dwarf galaxies ?

  32. chemical evolution models of dwarfs

  33. understanding dwarf galaxies evolution: we are entering a new exciting era Thanks to new generation instruments (HST, Keck, VLT, etc.) it is becoming possible to obtain for nearby galaxies information as accurate as for the solar neighbourhood (or even better) on stars and gas properties. This will allow us to finally compute reliable evolution models for individual dwarfs.

  34. Effect of distance on star resolution on reachable lookback times

  35. IMF in MCs R136 in LMC Salpeter’s slope (Sirianni et al 2000)

  36. Shetrone et al 01 LG dSphs GGC SN: halo+disk (courtesy M. Shetrone)

  37. dSphs in the Local Group Tolstoy et al 03

  38. AMRs in nearby galaxies: entering a new era Carina Sculptor Fornax (Tolstoy et al 03)

  39. chemical evolution of MW and dwarfs: comparison MW dwarfs slowly decreasing with time; continuous (possibly as average of many contiguous episodes depending on morphological type, either very discontinuous (early types) or almost continuous (late types), but not as in MW SF: slightly flatter than Salpeter’s at low masses and slightly steeper at high masses roughly Salpeter’s => flatter than in MW at high masses ? IMF: infall of metal poor gas needed to dilute metals and favour gradient. Fountains possible. Winds unlikely. winds very likely in lower mass galaxies; infall likely, fountains unlikely. flows:

  40. galactic winds from chemical evolution models of galaxies, winds appear to be necessary in low mass Irr’s and BCGs, not in spirals winds are observed in H and X-rays in some Irr’s and BGCs, like NGC1569, NGC1705 (e.g. Waller 1991, Meurer et al. 1992, Della Ceca et al. 1997), not in spirals winds are predicted by hydrodynamics of SN ejecta in Irr’s and BCGs (e.g. DeYoung & Gallagher 1990, MacLow & Ferrara 1998, D’Ercole & Brighenti 1999, Recchi et al. 2002), with low mass and intense star formation. In massive galaxies, like spirals, SN ejecta fail to escape.

  41. gas density 20 15 10 5 dark = dense, white = empty galactic winds hydrodynamical evolution of SN ejecta and galactic gas in NGC 1569 (D’Ercole & Brighenti 1999) 10 Myr 30 Myr 20 15 • Mtot = 2 109 Mo • Mstar = 3.3 108 Mo • Mgas = 1.1 108 Mo • only SNeII • - SFR from CMD (Greggio et al 98) 10 5 z (kpc) 70 Myr 100 Myr 30000 SNe in 30 Myr => eject 106 Mo at 100 Myr 105 Mo (i.e. 10%) have fallen back, the rest is lost for ever 2 6 10 2 6 10 R (kpc)

  42. abundance tracer 20 15 10 5 white = SN ejecta, black = unpolluted galactic winds hydrodynamical evolution of SN ejecta and galactic gas in NGC 1569 (D’Ercole & Brighenti 1999) 10 Myr 30 Myr 20 15 • Mtot = 2 109 Mo • Mstar = 3.3 108 Mo • Mgas = 1.1 108 Mo • only SNeII • - SFR from CMD (Greggio et al 98) 10 5 z (kpc) 70 Myr 100 Myr 30000 SNe in 30 Myr => eject 106 Mo at 100 Myr 105 Mo (i.e. 10%) have fallen back, the rest is lost for ever 2 6 10 2 6 10 R (kpc)

  43. Star Formation Sandage 1986

  44. solar neighbourhood present epoch SF in the Milky Way from chromosferic age of dwarfs (Rocha-Pinto et al 2000) 5 10 R (kpc) T [SFR=Ae-t/15, A (gas/tot)] P [SFR=0.3gas/R/Ro)] F [multiphase SFR] M [SFR=A gas1.1tot0.1] C [SFR=A gas1.4tot0.4] from chemev models (Chiappini et al 01)

  45. Grebel 1998 gasping rather than bursting SF SF boxes:

  46. one or more SF bursts SF boxes in dSph’s: Grebel 1998

  47. stellar yields ideal set of yields (Z=0.02, Marigo 01+Portinari et al 95): homogeneous and complete

  48. mass gap 5 – 11 Mo spurious bump stellar yields no masses > 40 Mo typical set of yields (Z=0.02, Marigo 01 + WW95): inhomogeneous and incomplete

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