Local Late Galactic Evolution (LOLA-GE) CHEMICAL EVOLUTION in the Galaxy, LMC, SMC and other dwarfs (overview) ISSI, February 23-27 2004 Monica Tosi INAF – Osservatorio Astronomico di Bologna

observational constraints 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 !

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)

The parameters are many, but not really free. Star Formation Law and Rate e.g. SFR  e-t/ or SFR  gn Gas flows in and out 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) The parameters are many, but not really free. Correct approach is to always compare the model predictions with all the available observational constraints.

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.

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 ?

chemical evolution models of dwarfs

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

we are entering a new exciting era 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.

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

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

dSphs in the Local Group Tolstoy et al 03

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

(Lanfranchi & Matteucci 2004) 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

(Romano, Tosi, Matteucci 2004) chemical evolution models for late-type dwarfs (Romano, Tosi, Matteucci 2004) NGC1569 NGC1705 SF and IMF from HST CMDs => high SF efficiency, high wind efficiency

chemical evolution of MW and dwarfs: comparison 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:

what do we know today on infall, winds and SF from models and from observations ?

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).

need for metal poor infall: three examples abundance gradients (HII regions) models with no infall models with metal free infall local G-dwarfs 1 Zinfall/Zsun=0 0.5 Tosi 1988 dots: F stars local AMR (F stars) Tosi 1988 Tinsley’s intuition in late 70’s

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 gas density dark = dense, white = empty 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 20 15 10 5 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)

galactic winds abundance tracer white = SN ejecta, black = unpolluted 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 20 15 10 5 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)

Star Formation Sandage 1986

from chromosferic age of dwarfs SF in the Milky Way solar neighbourhood present epoch 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)

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

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

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 ? 7 6 5 4 3 2 1 now Annibali et al. 03

the end

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

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