arXiv subjects

Francesca Matteucci

Publications and source records attributed to Francesca Matteucci.

At least 127 records · Page 7Linked to original sources

arXiv2003

Chemical Evolution of Dwarf Spheroidal and Blue Compact Galaxies

We studied the chemical evolution of Dwarf Spheroidal (dSph) and Blue Compact Galaxies (BCGs) by means of comparison between the predictions of chemical evolution models and several observed abundance ratios. Detailed models with up to date nucleosynthesis taking into account the role played by supernovae of different types (II, Ia) were developed for both types of galaxies allowing us to follow the evolution of several chemical elements. The models are specified by the prescriptions of the star formation (SF) and galactic wind efficiencies chosen to reproduce the main features of these galaxies. We also investigated a possible connection in the evolution of dSph and BCGs and compared the predictions of the models to the abundance ratios observed in Damped Lyman alpha Systems (DLAs). The main conclusions are: i) the observed distribution of [alpha/Fe] vs. [Fe/H] in dSph is mainly a result of the SF rate coupled with the wind efficiency; ii) a low SF efficiency and a high wind efficiency are required to reproduce the observational data for dSph; iii) the low gas content of these galaxies is the result of the combined action of gas consumption by SF and gas removal by galactic winds; iv) the BCGs abundance ratios are reproduced by models with 2 to 7 bursts of SF with low efficiencies ; v) the low values of N/O observed in BCGs are the natural result of a bursting SF; vi) a connection between dSph and BCGs in an unified evolutionary scenario is unlikely; vii) the models for the dSph and BCGs imply different formation scenarios for the DLAs; viii) a suitable amount of primary N produced in massive stars can be perhaps an explanation for the low plateau in the [N/$α$] distribution observed in DLAs, if real.

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arXiv2003

Models of Chemical Evolution

The basic principles underlying galactic chemical evolution and the most important results of chemical evolution models are discussed. In particular, the chemical evolution of the Milky Way galaxy, for which we possess the majority of observational constraints, is described. Then, it is shown how different star formation histories influence the chemical evolution of galaxies of different morphological type. Finally, the role of abundances and abundance ratios as cosmic clocks is emphasized and a comparison between model predictions and abundance patterns in high redshift objects is used to infer the nature and the age of these systems.

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arXiv2003

Modelling the nova rate in galaxies

We compute theoretical nova rates as well as type Ia SN rates in galaxies of different morphological type (Milky Way, ellipticals and irregulars) by means of detailed chemical evolution models, and compare them with the most recent observations. The main difference among the different galaxies is the assumed history of star formation. In particular, we predict that the nova rates in giant ellipticals such as M87 are 100-300 nova/yr, about a factor of ten larger than in our Galaxy (25 nova/yr), in agreement with very recent estimates from HST data. The best agreement with the observed rates is obtained if the recurrence time of novae in ellipticals is assumed to be longer than in the Milky Way. This result indicates that the star formation rate in ellipticals, and in particular in M87, must have been very efficient at early cosmic epochs. We predict a nova rate for the LMC of 1.7 nova/yr, again in agreement with observations. We compute also the K- and B-band luminosities for ellipticals of different luminous mass and conclude that there is not a clear trend for the luminosity specific nova rate with luminosity among these galaxies. However, firm conclusions about ellipticals cannot be drawn because of possible observational biases in observing these objects. The comparison between the specific nova rates in the Milky Way and the LMC indicates a trend of increasing nova rate passing from the Galaxy towards late-type spirals and Magellanic irregulars.

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arXiv2003

Nova nucleosynthesis and Galactic evolution of the CNO isotopes

We study the role played both by novae and single stars in enriching the ISM of the Galaxy with CNO group nuclei, in the framework of a detailed successful model for the chemical evolution of both the Galactic halo and disc. Once all the nucleosynthesis sources of CNO elements are taken into account, we conclude that 13C, 15N and 17O are likely to have both a primary and a secondary origin, in contrast to previous beliefs. Given the uncertainties still present in the computation of theoretical stellar yields, our results can be used to put constraints on stellar evolution and nucleosynthesis models.

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arXiv2002

Chemical evolution of Elliptical Galaxies and the ICM

We present a new model for the chemical evolution of elliptical galaxies taking into account SN feedback, detailed nucleosynthesis and galactic winds. We discuss the effect of galactic winds on the chemical enrichment of the ICM and compute the energy per particle injected by the galaxies into the ICM.

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arXiv2002

What determines galactic evolution?

We are briefly introducing the most important ingredients to study galactic evolution. In particular the roles of star formation, nucleosynthesis and gas flows. Then we are discussing the two different approaches to galactic evolution: the stellar population approach (chemical evolution models) and the hierarchical clustering scenario for galaxy formation. It is shown that there are still some controversial points in the two approaches, as evident in the brief summary of the discussion.

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arXiv2002

Oxygen, Carbon and Nitrogen evolution in galaxies

We discuss the evolution of oxygen, carbon and nitrogen in galaxies of different morphological type by adopting detailed chemical evolution models with different star formation histories (continuous star formation or starbursts). We start by computing chemical evolution models for the Milky Way with different stellar nucleosynthesis prescriptions. Then, a comparison between model results and ``key'' observational constraints allows us to choose the best set of stellar yields. Once the best set of yields is identified for the Milky Way, we apply the same nucleosynthesis prescriptions to other spirals (in particular M101) and dwarf irregular galaxies. We compare our model predictions with the [C,N,O/Fe] vs. [Fe/H], log(C/O) vs. 12+ log(O/H), log(N/O) vs. 12+ log(O/H) and [C/O] vs. [Fe/H] relations observed in the solar vicinity, along the disk and in other galaxies. By taking into account the results obtained for all the studied galaxies (Milky Way, M101, dwarf galaxies and DLAs) our main conclusions are: a) once the available observational data are properly interpreted, there is no compelling evidence for requiring the production of primary N in massive stars (M>10Msun); b) both C and N we see today in the ISM come mainly from low- and intermediate-mass stars. In particular, there is no need to invoke strong stellar winds in massive stars in order to explain the evolution of C/O ratio in the solar neighborhood, as often claimed in the literature (abridged).

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arXiv2002

Evolution of Deuterium, 3He and 4He in the Galaxy

In this work we present the predictions of the ``two-infall model'' concerning the evolution of D, 3He and 4He in the solar vicinity, as well as their distribution along the Galactic disk. Our results show that, when adopting detailed yields taking into account the extra-mixing process in low and intermediate mass stars, the problem of the overproduction of 3He by the chemical evolution models is solved. The predicted distribution of 3He along the disk is also in agreement with the observations. We also predict the distributions of D/H, D/O and D/N along the disk, in particular D abundances close to the primordial value are predicted in the outer regions of the Galaxy. The predicted D/H, D/O and D/N abundances in the local interstellar medium are in agreement with the mean values observed by the Far Ultraviolet Spectroscopic Explorer mission, although a large spread in the D abundance is present in the data. Finally, by means of our chemical evolution model, we can constrain the primordial value of the deuterium abundance, and we find a value of (D/H)_p < 4 10(-5) which implies Omega_b h^2 > 0.017, in agreement with the values from the Cosmic Microwave Background radiation analysis. This value in turn implies a primordial 4He abundance Y_p > 0.244.

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arXiv2002

Outflows from ellipticals: the role of supernovae

Models of SN driven galactic winds for ellipticals are presented. We assume that ellipticals formed at high redshift and suffered an intense burst of star formation. The role of supernovae of type II and Ia in the chemical enrichment and in triggering galactic winds is studied. In particular, several recipes for SN feed-back together with detailed nucleosynthesis prescriptions are considered. It is shown that SNe of type II have a dominant role in enriching the interstellar medium of elliptical galaxies whereas type Ia SNe dominate the enrichment and the energetics of the intracluster medium.

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arXiv2002

SNe heating and the chemical evolution of the intra-cluster medium

We compute the chemical and thermal history of the intra-cluster medium in rich and poor clusters under the assumption that supernovae (I, II) are the major responsible both for the chemical enrichment and the heating of the intra-cluster gas. We assume that only ellipticals and S0 galaxies contribute to the enrichment and heating of the intra-cluster gas through supernova driven winds and explore several prescriptions for describing the feed-back between supernovae and the interstellar medium in galaxies. We integrate then the chemical and energetical contributions from single cluster galaxies over the cluster luminosity function and derive the variations of these quantities as functions of the cosmic time. We reach the following conclusions: i) while type II supernovae dominates the chemical enrichment and energetics inside the galaxies, type Ia supernovae play a predominant role in the intra-cluster medium, ii) galaxy models, which reproduce the observed chemical abundances and abundance ratios in the intra-cluster medium, predict a maximum of 0.3-0.4 keV per particle of energy input, a result obtained by assuming that type Ia supernovae contribute 100% of their initial blast wave energy whereas type II supernovae contribute only by a few percents of their initial energy.

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arXiv2002

Chemical evolution in a model for the joint formation of quasars and spheroids

Direct and indirect pieces of observational evidence point to a strong connection between high-redshift quasars and their host galaxies. In the framework of a model where the shining of the quasar is the episode that stops the formation of the galactic spheroid inside a virialized halo, it has been proven possible to explain the submillimetre source counts together with their related statistics and the local luminosity function of spheroidal galaxies. The time delay between the virialization and the quasar manifestation required to fit the counts is short and incresing with decresing the host galaxy mass. In this paper we compute the detailed chemical evolution of gas and stars inside virialized haloes in the framework of the same model, taking into account the combined effects of cooling and stellar feedback. Under the assumption of negligible angular momentum, we are able to reproduce the main observed chemical properties of local ellipticals. In particular, by using the same duration of the bursts which are required in order to fit the submillimetre source counts, we recover the observed increase of the Mg/Fe ratio with galactic mass. Since for the most massive objects the assumed duration of the burst is Tburst < 0.6 Gyr, we end up with a picture for elliptical galaxy formation in which massive spheroids complete their assembly at early times, thus resembling a monolithic collapse, whereas smaller galaxies are allowed for a more prolonged star formation, thus allowing for a more complicated evolutionary history.

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arXiv2001

The Origin of Blue Cores in Hubble Deep Fields E/S0 galaxies

In this letter we address the problem of the origin of blue cores and inverse color gradients in early-type galaxies reported in the Hubble Deep Field North and South (HDFs) by Menanteau, Abraham & Ellis 2001. We use a multi-zone single collapse model. This model accounts for the observed blue cores by adopting a broad spread in formation redshifts for ellipticals, allowing some of these galaxies begin forming no more than ~1 Gyr before the redshift of observation. The single-zone collapse model then produces cores that are bluer than the outer regions because of the increase of the local potential well toward the center which makes star-formation more extended in the central region of the galaxy. We compare the predicted V-I(r) color gradients with the observed ones using the redshift of formation ($z_F$) of the elliptical as the only free parameter. We find that the model can account with relatively good agreement for the blue cores and inverse color gradients found in many spheroidals and at the same time for the red and smooth colors profiles reported. Based on the model our analysis suggests two populations of field ellipticals, one formed recently, within $\lesssim1$Gyr and another much older formed $\gtrsim4$Gyr since the redshift of observation.

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arXiv2001

Chemical Evolution of Elliptical Galaxies as a Constraint to Galaxy Formation Scenarios

Elliptical galaxies are the main contributors to the chemical enrichment of the intracluster and intergalactic medium; understanding how they form and evolve enables us to get important hints on the amounts of energy and processed matter that they eject into the ICM/IGM. Recent pieces of observational evidence point to a strong connection between high redshift quasars and their host galaxies. The aim of this paper is to prove that the main aspects of the chemical evolution of the spheroids can be reproduced in the framework of a model where the shining of the quasar is intimately related to the formation of the galactic nucleus. A key assumption is that the quasars shone in an inverted order with respect to the hierarchical one (i.e., stars and black holes in bigger dark halos formed before those in smaller ones) during an early episode of vigorous star formation. This scenario closely resembles the so-called `inverse wind' model invoked to explain the observed increase of the [Mg/Fe] ratio in the nuclei of ellipticals with increasing the galactic mass, the only difference being that now the time for the occurrence of a galactic wind is not determined by the energy input from supernovae, but is indeed the energy injected by the quasar which regulates the onset of the wind phase.

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arXiv2001

The stellar origin of 7Li - Do AGB stars contribute a substantial fraction of the local Galactic lithium abundance?

We adopt up-to-date 7Li yields from asymptotic giant branch stars in order to study the temporal evolution of 7Li in the solar neighbourhood in the context of a revised version of the two-infall model for the chemical evolution of our galaxy. We consider several lithium stellar sources besides the asymptotic giant branch stars such as Type II supernovae, novae, low-mass giants as well as Galactic cosmic rays and low-mass X-ray binaries. We conclude that asymptotic giant branch stars cannot be considered as important 7Li producers as believed in so far and that the contribution of low-mass giants and novae is necessary to reproduce the steep rise of the 7Li abundance in disk stars as well as the meteoritic 7Li abundance. Lithium production in low-mass X-ray binaries hardly affects the temporal evolution of 7Li in the solar neighbourhood.

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arXiv2001

Abundance Gradients and the Formation of the Milky Way

In this paper we adopt a chemical evolution model, which is an improved version of the Chiappini, Matteucci and Gratton (1997) model, assuming two main accretion episodes for the formation of the Galaxy. The present model takes into account in more detail than previously the halo density distribution and explores the effects of a threshold density in the star formation process, during both the halo and disk phases. In the comparison between model predictions and available data, we have focused our attention on abundance gradients as well as gas, stellar and star formation rate distributions along the disk. We suggest that the mechanism for the formation of the halo leaves detectable imprints on the chemical properties of the outer regions of the disk, whereas the evolution of the halo and the inner disk are almost completely disentangled. This is due to the fact that the halo and disk densities are comparable at large Galactocentric distances and therefore the gas lost from the halo can substantially contribute to building up the outer disk. We also show that the existence of a threshold density for the star formation rate, both in the halo and disk phase, is necessary to reproduce the majority of observational data in the solar vicinity and in the whole disk. Moreover, we predict that the abundance gradients along the Galactic disk must have increased with time and that the average [alpha/Fe] ratio in stars (halo plus disk) slightly decrease going from 4 to 10 Kpcs from the Galactic center. We also show that the same ratios increase substantially towards the outermost disk regions and the expected scatter in the stellar ages decreases, because the outermost regions are dominated by halo stars.

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arXiv2001

Evolution of Lithium in the Milky Way

We adopt up-to-date 7Li yields from asymptotic giant branch stars in order to study the temporal evolution of this element in the solar neighbourhood. Several lithium stellar sources are considered besides the AGBs: Type II supernovae, novae, low-mass giants. Galactic cosmic ray nucleosynthesis is taken into account as well. We conclude that AGB stars do not substantially contribute to 7Li enrichment on a Galactic scale. Therefore, a significant 7Li production from novae and low-mass stars is needed to explain the late, steep rise of the 7Li abundance in disk stars and the meteoritic 7Li abundance.

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arXiv2000

Dynamical and chemical evolution of gas-rich dwarf galaxies

We study the effect of a single, instantaneous starburst on the dynamical and chemical evolution of a gas-rich dwarf galaxy, whose potential well is dominated by a dark matter halo. We follow the dynamical and chemical evolution of the ISM by means of an improved 2-D hydrodynamical code coupled with detailed chemical yields originating from type II SNe, type Ia SNe and single low and intermediate mass stars (IMS). In particular we follow the evolution of the abundances of H, He, C, N, O, Mg, Si and Fe. We find that for a galaxy resembling IZw18, a galactic wind develops as a consequence of the starburst and it carries out of the galaxy mostly the metal-enriched gas. In addition, we find that different metals are lost differentially in the sense that the elements produced by type Ia SNe are more efficiently lost than others. As a consequence of that we predict larger [$α$/Fe] ratios for the gas inside the galaxy than for the gas leaving the galaxy. A comparison of our predicted abundances of C, N, O and Si in the case of a burst occurring in a primordial gas shows a very good agreement with the observed abundances in IZw18 as long as the burst has an age of $\sim 31$ Myr and IMS produce some primary nitrogen. However, we cannot exclude that a previous burst of star formation had occurred in IZw18 especially if the preenrichment produced by the older burst was lower than $Z=0.01$ Z$_{\odot}$. Finally, at variance with previous studies, we find that most of the metals reside in the cold gas phase already after few Myr. This result is mainly due to the assumed low SNII heating efficiency, and justifies the generally adopted homogeneous and instantaneous mixing of gas in chemical evolution models.

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arXiv2000

Abundances and Evolution of Lithium in the Galactic Halo and Disk

We have measured the Li abundance of 18 stars with -2 <~ [Fe/H] ~< -1 and 6000 K <~ Teff <~ 6400 K, a parameter range that was poorly represented in previous studies. We examine the Galactic chemical evolution (GCE) of this element, combining these data with previous samples of turnoff stars over the full range of halo metallicities. We find that A(Li) increases from a level of \~2.10 at [Fe/H] = -3.5, to ~2.40 at [Fe/H] = -1.0, where A(Li) = log_10 (n(Li)/n(H)) + 12.00. We compare the observations with several GCE calculations, including existing one-zone models, and a new model developed in the framework of inhomogeneous evolution of the Galactic halo. We show that Li evolved at a constant rate relative to iron throughout the halo and old-disk epochs, but that during the formation of young-disk stars, the production of Li relative to iron increased significantly. These observations can be understood in the context of models in which post-primordial Li evolution during the halo and old-disk epochs is dominated by Galactic cosmic ray fusion and spallation reactions, with some contribution from the $ν$-process in supernovae. The onset of more efficient Li production (relative to iron) in the young disk coincides with the appearance of Li from novae and AGB stars. The major challenge facing the models is to reconcile the mild evolution of Li during the halo and old-disk phases with the more efficient production (relative to iron) at [Fe/H] > -0.5. We speculate that cool-bottom processing (production) of Li in low-mass stars may provide an important late-appearing source of Li, without attendant Fe production, that might explain the Li production in the young disk.

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