Modelling the Chemical Enrichment of the ICM/IGM

Francesca MatteucciUniversity of Trieste

Leiden, May 25th 2009

Outline of the talk

• Modelling galaxy evolution: stellar nucleosynthesis, the roles of SNe (II, Ia, Ib/c) in galactic chemical enrichment

• Models for galaxies of different morphological type (E, Sp, Irr)

• Computing the chemical enrichment of the ICM and IGM

Chemical Evolution of Galaxies

• Main ingredients:• Initial Conditions• Stellar birthrate function: SFRxIMF• Stellar nucleosynthesis• Gas flows: infall, inflow, outflow• Equations containing all of this• A good model should take stellar lifetimes into

account

Stellar nucleosynthesis

• Low and intermediate mass stars (0.8-8 Msun): produce He, N, C and heavy s-process elements. They die as C-O white dwarfs, when single, and can die as Type Ia SNe when binaries

• Massive stars (M>8-10 Msun, core-collapse SNe): they produce mainly alpha-elements (O, Mg..), some Fe, light s-process elements and r-process elements and explode as core-collapse SNe (Type II, Ib/c)

• Type Ia SNe produce mainly Fe (0.6-0.7M_sun per SN)

Type Ia SN Progenitors• Single-degenerate

scenario (e.g. Whelan & Iben 1974; Han & Podsiadlowsky 2004): a binary system with a C-O WD accreting matter from a MS star. When WD reaches Chandraekhar mass it explodes

• First system explodes after 35-40 Myr

• The DTD (delay time distr. , FM & Recchi 2001)

Type Ia SN Progenitors• Double-Degenerate

scenario (Iben & Tutukov, 1984): two C-O WDs merge after loosing angular momentum due to gravitational wave radiation

• When the Chandrasekhar mass is reached C-deflagration occurs

• First system explodes after 35-40 Myr+1Myr

• The DTD (Greggio 2005)

Empirical DTD (Mannucci et al)• Mannucci & al. (2005;

2006, Scannapieco & Bildsten, 2005) proposed a DTD function as in figure

• 50% of all Type Ia SNe should explode before 100 Myr (prompt SNe Ia)

• In the other DTDs this fraction is 13% and 10% and better fits the abundances in the MW (FM & al. 2006)

How to model the Type Ia SN Rate

• The Type Ia SN rate can be expressed as the product of DTDxSFR (Greggio 2005):

• Where, psi(t) is the SFR and A is the fraction of Type Ia SN progenitors in the whole range of masses and kalpha:

SFRs in galaxies

• Predicted SFRs in galaxies of different morphological type

• These SFRs agree with measured SFRs (Kennicutt, 1998) and well reproduce the chemical and photometric properties of local galaxies

Typical timescales for the SN Ia enrichment

• The typical timescale for SN Ia enrichment ( the time for the maximum of the SN I rate) depends on the DTD and the SFR (FM & Recchi 2001)

• For a given DTD (either the single or double degenerate model) it is very short in ellipticals (0.3-0.5 Gyr) which suffer a very high SFR

• It is roughly 1Gyr for a SFR like in the solar vicinity, and 4-5 Gyr for irregulars with low SFR

Models for Elliptical Galaxies• Elliptical galaxies are the

most common in clusters. They formed stars very quickly with intense SF

• Star formation was soon stopped in E galaxies by the occurrence of galactic winds (feedback from SNe II and Ia) which devoid them of gas

• Galactic winds develop much before 1 Gyr (Pipino & FM, 2004)

•

Supernova Rates in Ellipticals• Predicted Type II (dotted)

and Type Ia (continuous) SN rates in an elliptical galaxy of 10^(11) Msun luminous mass (Pipino & FM 2004)

• The galactic wind occurs at 0.4 Gyr, then SF stops. Most of stars will have [alpha/Fe] >0, whereas in the wind the [alpha/Fe] ratios <0

[alpha/Fe] ratios in galaxies

• This diagram depends on the SFR, through the [Fe/H]

• And on the time-delayin the chemical enrichment between Type II and Ia supernovae

Modelling the chemical enrichment of the ICM

• The first work on chemical enrichment of the ICM was by Gunn & Gott (1972), then Larson & Dinerstein (1975), Vigroux (1977), White & Rees (1978), Himmes & Biermann (1988)

• Galactic winds as the main cause of the ICM enrichment: Matteucci & Vettolani (1988), David & al. (1991), Arnaud(1992), Renzini & al. (1993), Elbaz & al. (1995), Lowenstein & Mushotzsky (1996), Pipino & al. (2002), Moretti & al. (2003), Ettori (2005), Tornatore & al. (2004), Calura & al. (2007) plus others...........

Models for the ICM enrichment

• FM & Vettolani (1988) developed a method to compute the chemical enrichment of the ICM

• They integrated over a Schechter (1976) luminosity function the single contributions from galaxies in clusters to the enrichment in Fe, alpha elements (Mg, Si) and total gas

• They assumed that ellipticals are the main contributors of metals through galactic winds

MV88 Results• MV88 predicted the right

mass of Fe in clusters with a Salpeter IMF by assuming that all the Fe produced after SF stops is lost soon or later

• However, they found that the cluster galaxies are not able to provide all the ICM mass

• The predicted Fe mass divided by the observed ICM mass gives XFeICM=0.3-0.5XFesun

MV88 Results

• Same conclusion from David & al. (1991) and Renzini & al. (1993), Gibson & FM (1997)

• It seems natural that most of the ICM is primordial gas (not processed inside stars) since M_ICM/M_gal=5.45h^(-3/2) (White & al. 1993)

• The ICM mass is 5 times larger than the mass in galaxies in clusters!

Abundance ratios in the ICM

• Asimmetry in the [alpha/Fe] ratios is predicted ([alpha/Fe]>0 in ellipticals and [alpha/Fe]<0 in the ICM) (MV88, Renzini & al. 1993, Pipino & al.02)

• ASCA results suggested [alpha/Fe]_ICM >0 (Mutshotzky & al. 1996), but Ishimaru & Arimoto (1999) showed that [alpha/Fe]_ICM=0 if meteoritic solar Fe abundance is adopted

• FM & Gibson (1995) and Chiosi (2000) showed [alpha/Fe]_ICM>0 if a top-heavy IMF is adopted and there are only early winds (the bulk of Fe is bound to galaxies)

Interpretation of abundance ratios

• Abundance ratios have the advantage of not depending on the unknown fraction of primordial ICM

• They depend on stellar yields, IMF and stellar lifetimes

• The ratio of two abundances is equal to the ratio of the yields only if I.R.A. is assumed

• No firm conclusions on yields can be derived from abundance ratios in the ICM (FM & Chiappini 05)

• More recent data indicate different ratios in the cluster centers and outskirts

Fe vs.redshift in the ICM• Pipino et al. (2002)

computed the redshift evolution of the Fe mass in the ICM

• The different roles of SNe II and Ia are shown

• Type Ia SNe are the major contributors of Fe in the ICM

• Chemical enrichment of the ICM starts at z=4.5

Evolution of the Fe abundance in the ICM (Balestra & al. 2007)

• Thanks to deep X-ray observations from Chandra and XMM it has been possible to measure the Fe abundance out to a redshift z=1.3

• Tozzi & al. (2003) found that the average Fe abundance in the ICM at z=1 is comparable with the local value X_Fe=0.45 X_Fesun, with no evolution

• However, Balestra & al. (2007) extended Tozzi’s sample to 56 clusters and found a significant evidence of evolution for z<0.5 (present time Fe abundance is a factor of 2 higher), while Fe is constant for z>0.5

Possible interpretations

• If the Fe is produced only by passive evolving ellipticals no increase of Fe is predicted (Pipino & al. 2002)

• Calura, FM & Tozzi (2007) proposed that the increase in the Fe abundance is accounted for by gas stripped from the progenitors of S0 galaxies in the act of the tranformation into spirals

Evolution of the Fe abundance in the ICM (Calura & al. 2007)

Cosmic chemical enrichment in the IGM

• Calura & FM (2004) computed the comoving cosmic metal production and the mean metallicity in galaxies, IGM and the universe

• Where rho_B,k is the B luminosity density for the k-th morphological type and gamma_i,k is the rate of production of an element i by a stellar generation in a k-th galaxy type

Cosmic metal production• Evolution of the total

cosmic rates of He and metal production (E cont. Sp short dash, Irr long dash)

• By integrating these rates it is found that spheroids are the major producers of metal in the universe and in IGM (56% of metals from E, 42% from Sp and 2% from Irr)

Mean metallicities of galaxies

• We need the comoving densities of stars and gas in galaxies

• Then the mean metallicity of galaxies is <Z>=0.9Z_sun

Chemical enrichment of the IGM

• To compute the average metallicity of the IGM we start from all the metals residing in galaxies (stars +gas)

• Then by subtracting the metals locked in galaxies from the total produced metals we obtain the metals in the IGM, expressed in terms of the critical density of the universe

Mean metallicity of the IGM

Summary

• The Fe masses of the ICM can be reproduced by means of a substantial contribution of Type Ia SNe in ellipticals if a normal Salpeter IMF is adopted

• In this case, solar or undersolar [alpha/Fe] ratios are predicted. The [alpha/Fe] ratios decrease with cosmic time whereas Fe abundance increases

• The increase of X_Fe from z=0.5 to 0 (Balestra & al. 2007) can be easily explained by the contribution of the progenitors of S0 galaxies Calura & al. 2007)

Summary

• Cosmic metal production taking into account chemical enrichment of galaxies of different morphological type predicts that most of metals were produced by ellipticals at high z

• <Fe_IGM>=0.07Fe_sun (<Fe_ICM>=0.3Fe_sun)• A total <Z_IGM>=0.05 Z_sun• A mean metallicity in galaxies <Z_gal>=0.9Z_sun

and a <Z_univ>=0.13 Z_sun

Type Ia SN Cosmic Rates in Clusters:different DTDs