arXiv subjects

F. Matteucci

Publications and source records attributed to F. Matteucci.

178 records · Page 10Linked to original sources

arXiv2000

The mass surface density in the local disk and the chemical evolution of the Galaxy

We have studied the effect of adopting different values of the total baryonic mass surface density in the local disk at the present time in a model for the chemical evolution of the Galaxy. We have compared our model results with the G-dwarf metallicity distribution, the amounts of gas, stars, stellar remnants, infall rate and SN rate in the solar vicinity, and with the radial abundance gradients and gas distribution in the disk. This comparison strongly suggests that the value of the total baryonic mass surface density in the local disk which best fits the observational properties should lie in the range 50-75 Msun pc-2, and that values outside this range should be ruled out.

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arXiv2000

An X-ray and optical study of the cluster A33

We report the first detailed X-ray and optical observations of the medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray and optical imaging and spectroscopic data allowed us to identify the X-ray source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint, $F_{2-10 keV} \approx 2.4 \times 10^{-13} \ergscm2$, X-ray source 1SAXJ0027.2-1930, $\sim 2$ arcmin away from the optical position of the cluster as given in the Abell catalogue, is identified with the central region of A33. Based on six cluster galaxy redshifts, we determine the redshift of A33, $z=0.2409$; this is lower than the value derived by Leir and Van Den Bergh (1977). The source X-ray luminosity, $L_{2-10 keV} = 7.7 \times 10^{43} \ergs$, and intracluster gas temperature, $T = 2.9$ keV, make this cluster interesting for cosmological studies of the cluster $L_X-T$ relation at intermediate redshifts. Two other X-ray sources in the A33 field are identified. An AGN at z$=$0.2274, and an M-type star, whose emission are blended to form an extended X-ray emission $\sim 4$ arcmin north of the A33 cluster. A third possibly point-like X-ray source detected $\sim 3$ arcmin north-west of A33 lies close to a spiral galaxy at z$=$0.2863 and to an elliptical galaxy at the same redshift as the cluster.

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arXiv1999

The Galactic Lithium Evolution Revisited

The evolution of the 7Li abundance in the Galaxy has been computed by taking into account several 7Li sources: novae, massive AGB stars, C-stars, Type II SNe and GCRs. The theoretical predictions for the evolution of the 7Li abundance in the solar neighborhood have been compared to a new compilation of data. A critical analysis of extant observations revealed a possible extension of the Li plateau towards higher metallicities (up to [Fe/H] = -0.5 or even -0.3) with a steep rise afterwards. We conclude that 1) the 7Li contribution from novae is required in order to reproduce the shape of the growth of A(Li) versus [Fe/H], 2) the contribution from Type II SNe should be lowered by at least a factor of two, and 3) the 7Li production from GCRs is probably more important than previously estimated, in particular at the highest metallicities.

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arXiv1999

Diffuse Thermal Emission from Very Hot Gas in Starburst Galaxies: Spatial Results

New BeppoSAX observations of the nearby prototypical starburst galaxies NGC 253 and M82 are presented. A companion paper (Cappi et al. 1998;astro-ph/9809325) shows that the hard (2-10 keV) spectrum of both galaxies, extracted from the source central regions, is best described by a thermal emission model with kT ~ 6-9 keV and abundances ~ 0.1-0.3 solar. The spatial analysis yields clear evidence that this emission is extended in NGC 253, and possibly also in M82. This quite clearly rules out a LLAGN as the main responsible for their hard X-ray emission. Significant contribution from point-sources (i.e. X-ray binaries (XRBs) and Supernovae Remnants (SNRs)) cannot be excluded; neither can we at present reliably estimate the level of Compton emission. However, we argue that such contributions shouldn't affect our main conclusion, i.e., that the BeppoSAX results show, altogether, compelling evidence for the existence of a very hot, metal-poor interstellar plasma in both galaxies.

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arXiv1998

Light and Heavy Elements in the Galactic Bulge

The chemical evolution of the Galactic bulge is treated here in the context of an inside-out model for the Galaxy formation. We assume that this central region evolved even faster than the Galactic halo and test the effect of changing the slope of the IMF on the predicted stellar metallicity distribution for bulge stars. An IMF favoring the formation of massive stars is found to improve the agreement with the most recently observed metallicity distribution of bulge K giants. Then, we make specific predictions about temporal evolution of several light and heavy species in the Galactic bulge. We predict that alpha-elements should be enhanced relative to Fe for most of the [Fe/H] range, with different degrees of enhancement due to the different nucleosynthetic history of each element, and show that Lithium abundance should follow a trend with metallicity similar to that found for the solar neighbourhood. Several possible stellar Li sources are discussed.

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arXiv1998

Diffuse Thermal Emission from Very Hot Gas in Starburst Galaxies: Spectral Results

New BeppoSAX observations of the nearby archetypical starburst galaxies (SBGs) NGC253 and M82 are presented. The main observational result is the unambiguous evidence that the hard (2-10 keV) component is (mostly) produced in both galaxies by thermal emission from a metal-poor (~ 0.1-0.3 solar), hot (kT \~ 6- 9 keV) and extended (see companion paper: Cappi et al. 1998) plasma. Possible origins of this newly discovered component are briefly discussed. A remarkable similarity with the (Milky Way) Galactic Ridge's X-ray emission suggests, nevertheless, a common physical mechanism.

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arXiv1998

BeppoSAX detection of the Fe K line in the nearby starburst galaxy NGC 253

We present BeppoSAX results on the nearby starburst galaxy NGC 253. Although extended, a large fraction of the X-ray emission comes from the nuclear region. Preliminary analysis of the LECS/MECS/PDS ~0.2-60 keV data from the central 4' region indicates that the continuum is well fitted by two thermal models: a ``soft'' component with kT ~ 0.9 keV, and a ``hard'' component with kT ~ 6 keV absorbed by a column density of ~ 1.2 x10**22 cm-2. For the first time in this object, the Fe K line at 6.7 keV is detected, with an equivalent width of ~ 300 eV. This detection, together with the shape of the 2--60 keV continuum, implies that most of the hard X-ray emission is thermal in origin, and constrains the iron abundances of this component to be ~0.25 of solar. Other lines clearly detected are Si, S and Fe L/Ne, in agreement with previous ASCA results. We discuss our results in the context of the starburst-driven galactic superwind model.

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arXiv1998

On the Trend of [Mg/Fe] among Giant Elliptical Galaxies

We revisit the problem of the flat slope of the Mg2 versus relationship found for nuclei of elliptical galaxies (Faber et al. 1992; Worthey et al. 1992; Carollo et al. 1993; Davies et al. 1993), indicating that the Mg/Fe ratio should increase with galactic luminosity and mass. We transform the abundance of Fe, as predicted by classic wind models and alternative models for the chemical evolution of elliptical galaxies, into the metallicity indices Mg2 and , by means of the more recent index calibrations and show that none of the current models for the chemical evolution of elliptical galaxies is able to reproduce exactly the observed slope of the versus Mg2 relation, although the existing spread in the data makes this comparison quite difficult. In other words, we can not clearly discriminate between models predicting a decrease (classic wind model) or an increase of such a ratio with galactic mass. The reason for this resides in the fact that the available observations show a large spread due mostly to the errors in the derivation of the index. In our opinion this fact prevents us from drawing any firm conclusion on the behaviour of Mg and Fe in these galaxies.

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arXiv1998

The Influence of Stellar Energetics and Dark Matter on the Chemical Evolution of Dwarf Irregulars

A chemical evolution model following the evolution of the abundances of H, He, C, N, O and Fe for dwarf irregular and blue compact galaxies is presented. This model takes into account detailed nucleosynthesis and computes in detail the rates of supernovae of type II and I. The star formation is assumed to have proceeded in short but intense bursts. The novelty relative to previous models is that the development of a galactic wind is studied in detail by taking into account the energy injected into the interstellar medium (ISM) from both supernovae and stellar winds from massive stars as well as the presence of dark matter halos. Both metal enriched and normal winds have been considered. Our main conclusions are: i) a substantial amount of dark matter (from 1 to 50 times larger than the luminous matter) is required in order to avoid the complete destruction of such galaxies during strong starbursts, and ii) the energy injected by stellar winds and type Ia supernovae into the ISM is negligible relative to the total thermal energy, and in particular to the type II supernovae, which in fact, dominate the energetics during starbursts.

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arXiv1998

BeppoSAX detection of the Fe K line in the starburst galaxy NGC253

Preliminary results obtained from BeppoSAX observation of the starburst galaxy NGC253 are presented. X-ray emission from the object is clearly extended but most of the emission is concentrated on the optical nucleus. Preliminary analysis of the LECS and MECS data obtained using the central 4' region indicates that the continuum is well fitted by two thermal components at 0.9 keV and 7 keV. Fe K line at 6.7 keV is detected for the first time in this galaxy; the line has an equivalent width of ~300eV. The line energy and the shape of the 2-10 keV continuum strongly support thermal origin of the hard X-ray emission of NGC253. From the measurement of the Fe K line the abundances can be unambiguously constrained to ~0.25 the solar value. Other lines clearly detected are Si, S and Fe XVIII/Ne, in agreement with ASCA results.

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arXiv1997

A possible theoretical explanation of metallicity gradients in elliptical galaxies

Models of chemical evolution of elliptical galaxies taking into account different escape velocities at different galactocentric radii are presented. As a consequence of this, the chemical evolution develops differently in different galactic regions; in particular, we find that the galactic wind, powered by supernovae (of type II and I) starts, under suitable conditions, in the outer regions and successively develops in the central ones. The rate of star formation (SFR) is assumed to stop after the onset of the galactic wind in each region. The main result found in the present work is that this mechanism is able to reproduce metallicity gradients, namely the gradients in the $Mg_2$ index, in good agreement with observational data. We also find that in order to honor the constant [Mg/Fe] ratio with galactocentric distance, as inferred from metallicity indices, a variable initial mass function as a function of galactocentric distance is required. This is only a suggestion since trends on abundances inferred just from metallicity indices are still uncertain.

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arXiv1996

Galaxy evolution: the effect of dark matter on the chemical evolution of ellipticals and galaxy clusters

In this paper we discuss the chemical evolution of elliptical galaxies and its consequences on the evolution of the intracluster medium (ICM). We use chemical evolution models taking into account dark matter halos and compare the results with previous models where dark matter was not considered. In particular, we examine the evolution of the abundances of some relevant heavy elements such as oxygen, magnesium and iron and conclude that models including dark matter halos and an initial mass function (IMF) containing more massive stars than the Salpeter (1955) IMF, better reproduce the observed abundances of Mg and Fe both in the stellar populations and in the ICM (ASCA results). We also discuss the origin of gas in galaxy clusters and conclude that most of it should have a primordial origin.

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arXiv1996

The Chemical Evolution of the Galaxy: the two-infall model

In this paper we present a new chemical evolution model for the Galaxy which assumes two main infall episodes for the formation of halo-thick disk and thin disk, respectively. We do not try to take into account explicitly the evolution of the halo but we implicitly assume that the timescale for the formation of the halo was of the same order as the timescale for the formation of the thick disk. The formation of the thin-disk is much longer than that of the thick disk, implying that the infalling gas forming the thin-disk comes not only from the thick disk but mainly from the intergalactic medium. The timescale for the formation of the thin-disk is assumed to be a function of the galactocentric distance, leading to an inside-out picture for the Galaxy building. The model takes into account the most up to date nucleosynthesis prescriptions and adopts a threshold in the star formation process which naturally produces a hiatus in the star formation rate at the end of the thick disk phase, as suggested by recent observations. The model results are compared with an extended set of observational constraints. Among these constraints, the tightest one is the metallicity distribution of the G-dwarf stars for which new data are now available. Our model fits very well these new data. We show that in order to reproduce most of these constraints a timescale $\le 1$ Gyr for the (halo)-thick-disk and of 8 Gyr for the thin-disk formation in the solar vicinity are required. We predict that the radial abundance gradients in the inner regions of the disk ($R< R_{\odot}$) are steeper than in the outer regions, a result confirmed by recent abundance determinations, and that the inner ones steepen in time during the Galactic lifetime.

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arXiv1996

Chemical evolution of DLA systems

High redshift DLA systems suggest that the relative abundances of elements might be roughly solar, although with absolute abundances of more than two orders of magnitude below solar. The result comes from observations of the [SII/ZnII] ratio, which is a reliable diagnostic of the true abundance, and from DLA absorbers with small dust depletion and negligible HII contamination. In particular, in two DLA systems nitrogen is detected and at remarkably high levels (Vladilo et al. 1995, Molaro et al. 1995, Green et al. 1995, Kulkarni et al. 1996). Here we compare the predictions from chemical evolution models of galaxies of different morphological type with the abundances and abundance ratios derived for such systems. We conclude that solar ratios and relatively high nitrogen abundances can be obtained in the framework of a chemical evolution model assuming short but intense bursts of star formation, which in turn trigger enriched galactic winds, and a primary origin for nitrogen in massive stars. Such a model is the most successful in describing the chemical abundances of dwarf irregular galaxies and in particular of the peculiar galaxy IZw18. Thus, solar ratios at very low absolute abundances, if confirmed, seem to favour dwarf galaxies rather than spirals as the progenitors of at least some of the DLA systems.

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arXiv1995

26Al and 60Fe From Supernova Explosions

Using recently calculated yields for Type II supernovae, along with models for chemical evolution and the distribution of mass in the interstellar medium, the current abundances and spatial distributions of two key gamma-ray radioactivities, $^{26}$Al and $^{60}$Fe, are determined. The estimated steady state production rates are 2.0 $\pm$ 1.0 M\sun \ Myr$^{-1}$ for $^{26}$Al and 0.75 $\pm$ 0.4 M\sun \ Myr$^{-1}$ for $^{60}$Fe. This corresponds to 2.2 $\pm$ 1.1 M\sun \ of $^{26}$Al and 1.7 $\pm$ 0.9 M\sun \ of $^{60}$Fe in the present interstellar medium. Sources of uncertainty are discussed, one of the more important being the current rate of core collapse supernovae in the Galaxy. Our simple model gives three per century, but reasonable changes in the star formation rate could easily accommodate a core collapse rate one-half as large, and thus one-half the yields. When these stellar and chemical evolution results are mapped into a three dimensional model of the Galaxy, the calculated 1809 keV gamma-ray flux map is consistent with the {\it Compton Gamma Ray Observatory} observations of a steep decline in the flux outside a longitude of $\pm$ 50$^\circ$ from the Galactic center, and the slight flux enhancements observed in the vicinity of spiral arms. Other potential stellar sources of $^{26}$Al and $^{60}$Fe are mentioned, especially the possibility of $^{60}$Fe synthesis in Type Ia supernovae. Predictions for the $^{60}$Fe mass distribution, total mass, and flux map are given.

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arXiv1993

Synthetic metal line indices for elliptical galaxies from super metal rich alpha-enhanced stellar models

There are strong indications from recent papers (e.g. Worthey et al. 1992) that the abundance ratio of Mg/Fe, and consequently also O/Fe in giant elliptical galaxies is not solar. The line strengths of two Fe lines at 5270 and 5335 A are weaker than one expects from the strength of the Mg b line if [Mg/Fe] = 0. We have synthesized absorption line indices to derive the Mg and Fe abundances of these galaxies. For these models we have calculated new evolutionary tracks of high metallicity stars with a range of Mg/Fe abundances. This is the first time that such tracks have been generated. Integrating along isochrones to synthesize metal line strengths we find that for a typical bright giant elliptical [Mg/Fe] has to be between +0.3 and +0.7. We show that this result is independent of other parameters such as age, total metal content and mixing length parameter. The total metal content is super-solar, but the iron metallicity of elliptical galaxies not necessarily has to be larger than solar. For the formation of elliptical galaxies our result on the Mg and Fe abundances has the implication that most of the enrichment of the gas has to come from SNe II, which have more massive progenitors and as such produce relatively more O and Mg than Fe. It means that most of the stars have to be formed within a period of $3 \times 10^8$ years, so that there can only be one major collapse phase of the galaxy.

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