modelling the chemical enrichment of the igm
TRANSCRIPT
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Modelling the Chemical Enrichment of the ICM/IGM
Francesca MatteucciUniversity of Trieste
Leiden, May 25th 2009
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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
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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
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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)
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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)
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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)
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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)
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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:
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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
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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
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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)
•
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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
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[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
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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...........
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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
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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
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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!
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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)
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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
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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
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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
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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
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Evolution of the Fe abundance in the ICM (Calura & al. 2007)
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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
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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)
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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
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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
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Mean metallicity of the IGM
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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)
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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
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Type Ia SN Cosmic Rates in Clusters:different DTDs