PATRICIA B. TISSERA
Institute for Astronomy and Space PhysicsArgentina
i
Observational motivationsModelResults
gas cooling and condensation
star formation and stellar evolution
supernova feedback:chemical + energy release
environmental effects:starvationstrangulation, etc
GALAXY FORMATION In the last years, studies of chemical elements obtained in the Local Universeand at high redshifts have improved dramatically.
Chemical patterns are the result of different mechanisms which contribute togalaxy formation
growth of the structure:Collapse, infall and mergers
THE MILKY WAY
BULGE
DM HALO
THIN DISCTHICK DISC
STELLAR HALO
Patricia B. Tissera
Milky Way
BULGEhz ~ 2 kpc; averged age ~ 10 Gyr for stars with hz >
400 pc
metallicity peak: [Fe/H] ~ -0.3 dex ( Zoccali et al.
2003).
there are young stars and on-going star formation
( Van Loon et al. 2003)
Stellar Halor:J/M ~ 0 (Freeman 1987); sopported
by dispersion
<[Fe/H] > ~ -1.5 dex (Ryan & Nories
1991;Chiba & Beers (2000
(σr, σphi, σz ) ~ (141, 106, 94) km/s
THIN DISCRotationally supported: σ/V <<1.
Scale-length ~ 2-2.5 kpc (Siegel et al. 2001), hz ~ 280 pc
Stellar age distribution ~ [2,14]Gyr and [Fe/H] peaks at ~ -0.2
(Nordstrom et al. 2004)
THICK DISCscale-lenght ~ 3 kpc , hz ~ 1 kpc (assuming a double
exponential) .
t_median ~ 12.5 +- 1.4 Gyr (Liu &Chaboyer 2000)
-2.2 < [Fe/H] <0.5 with <[Fe/H]> ~ -0.6 (Chiba & Beers
2000)
higher [O/Fe] than the stars in the thin disc.
Luminosity-metallicity and mass-metallicity relations:
There are well-known LMR and MMR in the local Universe.Observations suggest evolution in the zero point and slope of both relations.
SDSS: Tremonti et al .2004
Erb et al 2006: z~2.5
CHEMICAL FEEDBACKSome references on chemical modeling in cosmological simulations:
Raiteri et al. (1996; also Berczik 1999) SNII & SNIa; Fe & HMosconi, Tissera, Lambas & Cora. (2001): SNII & SNIa, Eth. Lia, Portinari & Carraro (2002):detailed SE; diffusion Kawata & Gibson (2003): SNII, SNIa,IS; Eth +Ekin Springel & Hernquist (2003): Z + Twophases +Ekin Kobayashi (2004; et al. 2006):detailedSE; Eth +Ekin Scannapieco et al. (2005, 2006): SNII & SNIa + Multiphase+SNEOkamoto et al. 2006: SNII+SNIa+Twophases+Ekin (+top heavy Imf) Oppenhaimer & Dave (2006): SNII &SNIa + Twophases + Ekin Stinson et al. (2006): SNII&SNIa + cooling off Martinez-Serrano et al. (2008): detailedSE; diffusionWiersma et al. (2009): detailedSE; smoothed metals+ Ekin
Supernova Feedback
CHEMICAL ENRICHMENT HYDRODYNAMICAL HEATING
SN: Main source of heavy elements
Change the cooling time
evaporates cold-dense gas galactic winds which can results in outflows or galactic fountains
•Regulates the star formation activity and enriches the ISM and IGM•Affects the gas dynamics: disc formation
•This might leave chemical fossils which can be used •to track the formation history of a galaxy
Intermediate mass stars
CHEMICAL FEEDBACK
Numerical space Physical space NeedStar particles Stellar populations
↔
IMF:SNelong-lived stars
M* > 8 Mo; typical life-times: ~ 106 yrType II Sne
Typical life-times: ~ GyrMain source of iron (Fe)Type Ia Sne
Produce most O, Si, Ca, etc
YIELDS
Mosconi, Tissera, Lambas & Cora 2001
Chemical evolution: the fossil records
from Zocalli 2008
Relative abundances of alfa elements over Fe:
Relative abundances of SNII with respecto to SNIaFormation timescale of the systems
Mosconi, Tissera, Lambas & Cora 2001
When SN explosions take place, they distribute metals according to the SPH technique. For a given chemical element x at a particle i,
Exploding star particle
Gaseous neighbours
CHEMICAL FEEDBACK
Mxi = ∑j mj/ρj Mxi W(rij,hij)
Mxj =mj/ρj Mxi W(rij,hij)
Each neigbhour will receive
i j
★ A GADGET-3 (Springel 2005) with:
Stochastic star formation (Springel & Hernquist 2002)
Chemical enrichment from Type II and Ia Supernovae and metal dependent cooling
Multiphase gas model: allows overlap of dense and diffuse gas
Supernova feedback: distributes energy separately for cold and hot pre-defined phases (thermal feedback + reservoir for cold phases) within the context of the Multiphase gas model.
All this implemented without scale-dependent parameters well suited to run cosmological simulations where systems of different mass form simultaneously.
Scannapieco, Tissera, White & Springel 2005,2006,2008
Scannapieco et al. 2006
Aquarius haloes
8 galazy-sized haloes of 1012 Mo (Springel et al. 2008) selected
from a Λ-CDM cosmological volume of 100 Mpc/h box , with mild
isolation criterion.
ICs have been modified to include baryons.
approx half a millons particle per specie
Run with GADGET-3 including chemical evolution.
Can these simulations reproduce general trends?
Can we link the chemical properties to their histories of assembly?
Tissera, White & Scannapieco in prepration
Scannapieco et al. 2008
Aquarius galaxies
T=
(U
2 +
W2 )
Bulge Disc Inner H Outer H
V (km/s)
Disc cont. 16%Bar/T(p) = 0.23
Disc cont. 7.5%Bar/T(p) = 0
Disc cont. 12 %Bar/T(p) = 0.34
Re-defining the disc components
r (kpc/h) r (kpc/h) r (kpc/h)
r (kpc/h) r (kpc/h) r (kpc/h)
[Fe/
H]
[Fe/
H]
[Fe/
H]
Aq-E-5
Star formation histories of each component
Age Gyr
Aq-A-5
Disc
Bulge
Inner Halo
Outer Halo
Aq-C-5 Aq-D-5
Age Gyr
f
Aq-F-5Aq-G-5
f
f
Aq-A-5 Aq-C-5 Aq-D-5
Aq-E-5 Aq-G-5 Aq-F-5
Disc Bulge Inner Halo Outer Halo
The hierarchical building up of the structure
log z +1 log z + 1
log z + 1 log z + 1
Fraction of stellar mass formed in the progenitor and in substructure
Ste
llar
mas
s fr
actio
n in
Bul
ge
Ste
llar
mas
s fr
actio
n in
Dis
c
Ste
llar
mas
s fr
actio
n in
Inne
r H
alo
Ste
llar
mas
s fr
actio
n in
Out
er H
alo
In situ
In satellites
Disc
Bulge
Inner Halo
Outer Halo
Median Fe enrichment for each component
Disc
Bulge
Inner Halo
Outer Halo
Median alfa-enhacement for each component
There is a
correlation between
the fraction of stellar
mass formed in situ
and the fraction of
stellar mass formed
in massive satellites
(M > 0.5 1010 Mo/h).
The level of enrichment of stars in the halo tend to correlates with the fraction of mass formed in massive satellites:
the larger this fraction, the higher the median abundance of the halo
Metallicity gradients
Observations from Dutil et al. 1997
Metallicity gradientes and history of formation
Mean age of Bulges
The faster the bulge formed its stars, the steeper and higher its Oxygen abundances and the higher its [alfa-Fe] content.
Nevertheless, there is important dispersion in the correlations.
Median age Median age Median age
S(O
/H)
(O/H
)c
Med
ian
[O/F
e]
[Fe/H] [Fe/H]sat [O/Fe] [O/Fe]sat Age Age_sat σ/vtan σ/vtanAq-C -0.93 -1.23 -0.17 0.27 8.19 12.23 0.55 0.70
Aq-D -0.91 -1.02 -0.078 0.16 8.21 10.93 0.65 0.73
Aq-G -1.01 -1.07 -0.11 0.02 8.65 10.34 0.57 0.71 (Gyr)
DISC COMPONENT
Median properties of stars formed in situ and stars formed in satellites
Stars on the disc coming from satellites tend to have lower metallicity and higher[alfa-Fe] than those formed in situ.
Kinematically they are, on average, more consistent with belonging to a thick disc
Stellar mass fraction with very low metallicity
The fraction of
old metal-rich
stars show NO
correlation with
the history of
formation.
Stellar mass fraction of old and metal-rich stars
The satellite systems
100 kpc/h
The satellite systems: star formation histories
Aq-B-5Aq-A-5
Aq-F-5Aq-D-5 Aq-G-5
Age (Gyr)
Ste
llar
mas
s fr
actio
nS
tella
r m
ass
frac
tion
Aq-C-5
Chemical properties of the satellites which contribute to the formation of the main galaxies are different from those of the surviving satellites.
The satellite systems: chemical properties
Surviving satellites
Stripped stars
Bulges formed mainly in situ. Some might receive contribution from stars formed insubtructures. The level of enrichmnet and [alfa/Fe] anticorrelates with this fraction: Systems formed mainly by infall have older stellar populations, larger [alfa-Fe] , higher O/H abundances and speeper gradients.
Haloes formed mainly by contribution from substructure. Stars tend to be old with lowerlevel of enrichment. The median abundances correlate with the fraction of stars formedin massive satellites. It matter how they were assembly. The have very flat gradients.
The disc component formed mainly in situ and in several starbursts resulting in a population with lower [O/Fe] content. There could be contribution from satellites (~15%) and these stars are older, alfa enhanced and high velocity dispersion than those stars formed on the disc. Simulated gradients are consistent with observations.
Satellites that contribute to the formation of the main galaxies have very different chemical properties than those that survive in the haloes.
Some conclusions ...
Dynamics and chemistry: new interesting results coming soon..