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

2. 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 !

3. 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)

4. 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.

5. 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.

6. 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)

7. 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 ?

8. chemical evolution models of dwarfs

9. 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

10. 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.

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

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

13. dSphs in the Local Group
Tolstoy et al 03

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

15. (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

16. (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

17. 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:

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

19. 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 , 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).

20. 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

21. 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.

22. 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 = Mo
Mstar = Mo
Mgas = 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
R (kpc)

23. 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 = Mo
Mstar = Mo
Mgas = 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
R (kpc)

24. Star Formation
Sandage 1986

25. 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)

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

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

28. NGC1705: a post-starburst BCD already back to SF activity
Some SF Gyr ago
Some SF Gyr ago
Strong central SF Myr ago
No SF anywhere Myr ago
Strong SF everywhere 3-0 Myr ago ? 7 6 5 4 3 2 1
now
Annibali et al. 03

29. the end

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

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