Presentation on theme: "CHEMICAL EVOLUTION MODELS CHEMICAL EVOLUTION MODELS Monica Tosi INAF – Osservatorio Astronomico di Bologna STScI, March 7-9 2005 INFALL and OUTFLOWS from."— Presentation transcript:
CHEMICAL EVOLUTION MODELS CHEMICAL EVOLUTION MODELS Monica Tosi INAF – Osservatorio Astronomico di Bologna STScI, March 7-9 2005 INFALL and OUTFLOWS from the point of view of and STELLAR POPULATIONS
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
MW models (1) In the early 80’s 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. 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 [ nf ≈ (2-3) 10 9 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 now ≈ 2.5) needed to explain AMR => long lasting infall Tosi (1982 and 1988) almost constant infall of extragalactic metal poor gas (Z inf 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.
infall to reproduce properties of stellar populations abundance gradients (HII regions) models with no infall models with metal free infall Z infall/ Z sun =0 0.5 1 local AMR (F stars) dots: F stars local G-dwarfs data Shaver et al 83, models Tosi 88 data Edvardsson et al 93, models Tosi 88 Tinsley’s intuition in late 70’s
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 [ nf, ≈ 7 10 9 yr] Very successful models that have triggered a variety of similar approaches (see e.g. Matteucci 2001 and references therein).
two-infall model: infall rate in neighbourhood Halo and thick disk formation thin disk formation Chiappini, Matteucci & Gratton (1997)
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
other galaxies Chemical evolution models require infall also for other spirals ( Díaz & Tosi 1984-90, Mol ), possibly with different time scales. The lower the galaxy luminosity class, the lower the infall need. Chemical evolution models require infall also for other spirals ( Díaz & Tosi 1984-90, Mollà et al 96 ), 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 ?
first models: Matteucci & Tosi (1985), Pilyugin (1993), Marconi et al (1994) to reproduce observed abundances: - bursting SF - Salpeter’s IMF - differential galactic winds Pilyugin no winds non selective winds Marconi, Matteucci, Tosi differential winds
stellar populations have been resolved thanks to HST thanks to HST 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)
IZw18 WFPC2 – NIC2: V image NGC 1569 WFPC2 – NIC2 : UBVI combined NGC 1705 ACS: V and I combined 2.2 Mpc 5.1 Mpc 10 – 20 Mpc Strong starburst BCD, evidence of galactic winds Most metal poor BCD, winds ? Strong starburst dIrr, evidence of galactic winds
Different regions in NGC 1705 Tosi et al. 01 7 6 5 4 3 2 1 0 T-RGB very well defined => (m-M) 0 = 28.54 ± 0.26 => D = 5.1 ± 0.6 Mpc
NGC1705: a post-starburst BCD already back to SF activity 1) 1)Some SF 5 - 1 Gyr ago 2) 2)Some SF 1 - 0.02 Gyr ago 3) 3)Strong central SF 17 - 10 Myr ago 4) 4)No SF anywhere 10 - 3 Myr ago 5) 5)Strong SF everywhere 3-0 Myr ago Annibali et al. 03 now ? 7654321076543210 wind source quiescent phase only 6-7 Myr long => rapid cooling
(Romano, Tosi, Matteucci 2005) chemical evolution models for late-type dwarfsNGC1569 SF and IMF from HST CMDs => high SF efficiency, high wind efficiency NGC1705
(Lanfranchi & Matteucci 2004) chemical evolution models for Local Group dSph’s Draco Sagittarius SculptorUrsa Minor Salpeter’s IMF; SFH from CMDs => low SF efficiency; high wind efficiency
gas flows comparison chemical evolution of spirals and dwarfs: spirals RESULTS: long-term infall of metal poor gas needed to dilute metals and favour gradients. Fountains possible. Winds unlikely. dwarfs 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 ?
SN rates in Romano et al 2005 NGC 1705 NGC 1569 model 5aH’ model 4aH
Best model parameters NGC 1569 (4aH) NGC 1705 (5aH’) NGC 1569 (4aH) NGC 1705 (5aH’)
(Romano et al. 2005) chemical evolution models for late-type dwarfsNGC1569 SF and IMF from HST CMDs => high SF efficiency, high wind efficiency NGC1705
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 Z sun, rate 1-2 M o yr -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 ).
Inside-Out formation and radially varying SFR efficiency required to reproduce observed SFR, gas and colour profiles (Scalelengths: R B 4 kpc, R K 2.6 kpc) (Boissier and Prantzos 1999) THE MILKY WAY DISK
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
chemical evolution scheme collapse of protogalaxy and/or mergers mass and composition of ISM gas inflow and/or outflow star formation stellar evolution, nucleosynthesis stellar mass loss and death from Tinsley (1980)
galaxy evolution To understand theoretical modelsobservational 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 !
PARAMETERS The parameters are many, but not really free. Correct approach is to always compare the model predictions with all the available observational constraints. Star Formation Law and Rate e.g. SFR e -t/ or SFR g n e.g. SFR e -t/ or SFR g n Gas flows in and out of the region (infall and wind) e.g. f i e -t/ , f w E SN Initial Mass Function (m) m - ; m (m)dm=1 Stellar lifetimes and nucleosynthesis (yields)
observational constraints in the Galaxy they largely outnumber the parameters: current radial distribution of star density,current radial distribution of star density, current radial distribution of gas density,current radial distribution of gas density, current radial distribution of SFR,current radial distribution of SFR, current radial distribution of element abundances as derivedcurrent radial distribution of element abundances as derived from HII regions and B stars, from HII regions and B stars, radial distribution of element abundances at slightly olderradial distribution of element abundances at slightly older epochs as derived from PNe, epochs as derived from PNe, age-metallicity relation in solar neighbourhood (andage-metallicity relation in solar neighbourhood (and elsewhere), elsewhere), metallicity distribution of G-dwarfs in solar neighbourhood,metallicity distribution of G-dwarfs in solar neighbourhood, Local Present-Day-Mass-Function,Local Present-Day-Mass-Function, relative abundance ratios (e.g. [O/Fe] vs [Fe/H] in disk andrelative abundance ratios (e.g. [O/Fe] vs [Fe/H] in disk and halo stars. halo stars.
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)
chemical evolution of dwarf galaxies The chemical evolution of dwarf galaxies has been modeled by many groups, but the observational constraints were so far insufficient: SF continuous, gasping or bursting ? gas infall, gas outflows or both ?
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.
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 ?
we are entering a new exciting era understanding dwarf galaxies evolution: 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.
Effect of distance on star resolution on reachable lookback times
IMF in MCs R136 in LMC (Sirianni et al 2000) Salpeter’s slope
Shetrone et al 01 SN: halo+disk GGC LG dSphs (courtesy M. Shetrone)
AMRs in nearby galaxies: entering a new eraCarina Fornax Sculptor (Tolstoy et al 03)
comparison chemical evolution of MW and dwarfs: MW SF: slowly decreasing with time; continuous (possibly as average of many contiguous episodes IMF: IMF: slightly flatter than Salpeter’s at low masses and slightly steeper at high masses flows: flows: infall of metal poor gas needed to dilute metals and favour gradient. Fountains possible. Winds unlikely. dwarfs depending on morphological type, either very discontinuous (early types) or almost continuous (late types), but not as in MW roughly Salpeter’s => flatter than in MW at high masses ? winds very likely in lower mass galaxies; infall likely, fountains unlikely.
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.
galactic winds R (kpc) 2 6 10 201510 5 20 15 10 5 z (kpc) gas density 10 Myr30 Myr 70 Myr100 Myr hydrodynamical evolution of SN ejecta and galactic gas in NGC 1569 (D’Ercole & Brighenti 1999) - - M tot = 2 10 9 M o - - M star = 3.3 10 8 M o - - M gas = 1.1 10 8 M o - - only SNeII - SFR from CMD (Greggio et al 98) 30000 SNe in 30 Myr => eject 10 6 M o at 100 Myr 10 5 M o (i.e. 10%) have fallen back, the rest is lost for ever dark = dense, white = empty
galactic winds R (kpc) 2 6 10 201510 5 20 15 10 5 z (kpc) abundance tracer 10 Myr30 Myr 70 Myr100 Myr hydrodynamical evolution of SN ejecta and galactic gas in NGC 1569 (D’Ercole & Brighenti 1999) - - M tot = 2 10 9 M o - - M star = 3.3 10 8 M o - - M gas = 1.1 10 8 M o - - only SNeII - SFR from CMD (Greggio et al 98) 30000 SNe in 30 Myr => eject 10 6 M o at 100 Myr 10 5 M o (i.e. 10%) have fallen back, the rest is lost for ever white = SN ejecta, black = unpolluted
SF in the Milky Way T [SFR=Ae -t/15, A ( gas / tot )] P [SFR=0.3 gas /R/R o )] F [multiphase SFR] M [SFR=A gas 1.1 tot 0.1 ] C [SFR=A gas 1.4 tot 0.4 ] present epoch 510 R (kpc) from chromosferic age of dwarfs (Rocha-Pinto et al 2000) from chemev models (Chiappini et al 01) solar neighbourhood
SF boxes: Grebel 1998 gasping rather than bursting SF
SF boxes in dSph’s: Grebel 1998 one or more SF bursts
stellar yields ideal set of yields (Z=0.02, Marigo 01+Portinari et al 95): homogeneous and complete
stellar yields typical set of yields (Z=0.02, Marigo 01 + WW95): inhomogeneous and incomplete mass gap 5 – 11 M o spurious bump no masses > 40 M o