Testing the universal stellar IMF on the metallicity distribution in the bulges of the Milky Way and M31

We test whether the universal initial mass function (UIMF) or the integrated galaxial IMF (IGIMF) can be employed to explain the metallicity distribution (MD) of giants in the Galactic bulge. We make use of a single-zone chemical evolution model developed for the Milky Way bulge in the context of an inside-out model for the formation of the Galaxy. We checked whether it is possible to constrain the yields above 80 M_{\sun} by forcing the UIMF and required that the resulting MD matches the observed ones. We also extended the analysis to the bulge of M31 to investigate a possible variation of the IMF among galactic bulges. Several parameters that have an impact on stellar evolution (star-formation efficiency, gas infall timescale) are varied. We show that it is not possible to satisfactorily reproduce the observed metallicity distribution in the two galactic bulges unless assuming a flatter IMF ($x \leq 1.1$) than the universal one. We conlude that it is necessary to assume a variation in the IMF among the various environments.Comment: 9 pages, 4 figures, accepted for publication in A&

Abundance Patterns in Stars in the Bulge and Galactic Center

We discuss oxygen and iron abundance patterns in K and M red-giant members of the Galactic bulge and in the young and massive M-type stars inhabiting the very center of the Milky Way. The abundance results from the different bulge studies in the literature, both in the optical and the infrared, indicate that the [O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with [O/Fe] values falling above those of the disk. Based on these elevated values of [O/Fe] extending to large Fe abundances, it is suggested that the bulge underwent a rapid chemical enrichment with perhaps a top-heavy initial mass function. The Galactic Center stars reveal a nearly uniform and slightly elevated (relative to solar) iron abundance for a studied sample which is composed of 10 red giants and supergiants. Perhaps of more significance is the fact that the young Galactic Center M-type stars show abundance patterns that are reminiscent of those observed for the bulge population and contain enhanced abundance ratios of alpha-elements relative to either the Sun or Milky Way disk at near-solar metallicities.Comment: requires iaus.cls; to appear in Formation and Evolution of Galaxy Bulges, Proceedings IAU Symposium No. 245, 2007, M. Bureau et al. eds., in pres

The Evolution of Oxygen and Magnesium in the Bulge and Disk of the Milky Way

We show that the Galactic bulge and disk share a similar, strong, decline in [O/Mg] ratio with [Mg/H]. The similarity of the [O/Mg] trend in these two, markedly different, populations suggests a metallicity-dependent modulation of the stellar yields from massive stars, by mass loss from winds, and related to the Wolf-Rayet phenomenon, as proposed by McWilliam & Rich (2004). We have modified existing models for the chemical evolution of the Galactic bulge and the solar neighborhood with the inclusion of metallicity-dependent oxygen yields from theoretical predictions for massive stars that include mass loss by stellar winds. Our results significantly improve the agreement between predicted and observed [O/Mg] ratios in the bulge and disk above solar metallicity; however, a small zero-point normalization problem remains to be resolved. The zero-point shift indicates that either the semi-empirical yields of Francois et al. (2004) need adjustment, or that the bulge IMF is not quite as flat as found by Ballero et al. (2007); the former explanation is preferred. Our result removes a previous inconsistency between the interpretation of [O/Fe] and [Mg/Fe] ratios in the bulge, and confirms the conclusion that the bulge formed more rapidly than the disk, based on the over-abundances of elements produced by massive stars. We also provide an explanation for the long-standing difference between [Mg/Fe] and [O/Fe] trends among disk stars more metal-rich than the sun.Comment: 22 pages including 5 figures. Submitted to the Astronomical Journa

Plants and traditional knowledge: An ethnobotanical investigation on Monte Ortobene (Nuoro, Sardinia)

<p>Abstract</p> <p>Background</p> <p>Most of the traditional knowledge about plants and their uses is fast disappearing as a consequence of socio-economic and land use changes. This trend is also occurring in areas that are historically exposed to very few external influences, such as Sardinia (Italy). From 2004 to 2005, an ethnobotanical investigation was carried out in the area of Monte Ortobene, a mountain located near Nuoro, in central Sardinia.</p> <p>Methods</p> <p>Data were collected by means of semi-structured interviews. All the records – defined as 'citations', i.e. a single use reported for a single botanical species by a single informant – were filed in a data base ('analytical table'), together with additional information: i.e. local names of plants, parts used, local frequencies, and habitats of plants, etc. In processing the data, plants and uses were grouped into general ('categories') and detailed ('secondary categories') typologies of use. Some synthetic indexes have also been used, such as Relative Frequency of Citation (RFC), Cultural Importance Index (CI), the Shannon-Wiener Index (H'), and Evenness Index (J).</p> <p>Results</p> <p>Seventy-two plants were cited by the informants as being traditionally used in the area. These 72 'ethnospecies' correspond to 99 botanical taxa (species or subspecies) belonging to 34 families. Three-hundred and one citations, 50 secondary categories of use, and 191 different uses were recorded, most of them concerning alimentary and medicinal plants.</p> <p>For the alimentary plants, 126 citations, 44 species, and 13 different uses were recorded, while for the medicinal plants, there were 106 citations, 40 species, and 12 uses. Few plants and uses were recorded for the remaining categories. Plants and uses for each category of use are discussed. Analyses of results include the relative abundance of botanical families, wild vs. cultivated species, habitats, frequency, parts of plant used, types of use, knowledge distribution, and the different cultural importance of the species in question.</p> <p>Conclusion</p> <p>The study provides examples of several interesting uses of plants in the community, which would seem to show that the custom of using wild plants is still alive in the Monte Ortobene area. However, many practices are no longer in use, and survive only as memories from the past in the minds of elderly people, and often only in one or just a few informants. This rapidly vanishing cultural diversity needs to be studied and documented before it disappears definitively.</p

The Richness and Beauty of the Physics of Cosmological Recombination: The Contributions from Helium

The physical ingredients to describe the epoch of cosmological recombination are amazingly simple and well-understood. This fact allows us to take into account a very large variety of processes, still finding potentially measurable consequences. In this contribution we highlight some of the detailed physics that were recently studied in connection with cosmological hydrogen and helium recombination. The impact of these considerations is two-fold: (i) the associated release of photons during this epoch leads to interesting and unique deviations of the Cosmic Microwave Background (CMB) energy spectrum from a perfect blackbody, which, in particular at decimeter wavelength, may become observable in the near future. Despite the fact that the abundance of helium is rather small, it also contributes a sizeable amount of photons to the full recombination spectrum, which, because of differences in the dynamics of the helium recombinations and the non-trivial superposition of all components, lead to additional distinct spectral features. Observing the spectral distortions from the epochs of hydrogen and helium recombination, in principle would provide an additional way to determine some of the key parameters of the Universe (e.g. the specific entropy, the CMB monopole temperature and the pre-stellar abundance of helium), not suffering from limitations set by cosmic variance. Also it permits us to confront our detailed understanding of the recombination process with direct observational evidence. (ii) with the advent of high precision CMB data, e.g. as will be available using the Planck Surveyor or CMBpol, a very accurate theoretical understanding of the ionization history of the Universe becomes necessary for the interpretation of the CMB temperature and polarization anisotropies. (abridged)Comment: 16 pages, 11 figures, proceedings of the conference: "A Century of Cosmology: Past, Present and Future

Evolution of chemical abundances in Seyfert galaxies

We computed the chemical evolution of spiral bulges hosting Seyfert nuclei, based on updated chemical and spectro-photometrical evolution models for the bulge of our Galaxy, made predictions about other quantities measured in Seyferts, and modeled the photometry of local bulges. The chemical evolution model contains detailed calculations of the Galactic potential and of the feedback from the central supermassive black hole, and the spectro-photometric model covers a wide range of stellar ages and metallicities. We followed the evolution of bulges in the mass range 10^9 - 10^{11} Msun by scaling the star formation efficiency and the bulge scalelength as in the inverse-wind scenario for elliptical galaxies, and considering an Eddington limited accretion onto the central supermassive black hole. We successfully reproduced the observed black hole-host bulge mass relation. The observed nuclear bolometric luminosity is reproduced only at high redshift or for the most massive bulges; in the other cases, at z = 0 a rejuvenation mechanism is necessary. The black hole feedback is in most cases not significant in triggering the galactic wind. The observed high star formation rates and metal overabundances are easily achieved, as well as the constancy of chemical abundances with redshift and the bulge present-day colours. Those results are not affected if we vary the index of the stellar IMF from x=0.95 to x=1.35; a steeper IMF is instead required in order to reproduce the colour-magnitude relation and the present K-band luminosity of the bulge.Comment: 17 pages, 15 figures, 3 tables, accepted for publication in A&

Formation & evolution of the Galactic bulge: constraints from stellar abundances

We compute the chemical evolution of the Galactic bulge in the context of an inside-out model for the formation of the Milky Way. The model contains updated stellar yields from massive stars. The main purpose of the paper is to compare the predictions of this model with new observations of chemical abundance ratios and metallicity distributions in order to put constraints on the formation and evolution of the bulge. We computed the evolution of several alpha-elements and Fe and performed several tests by varying different parameters such as star formation efficiency, slope of the initial mass function and infall timescale. We also tested the effect of adopting a primary nitrogen contribution from massive stars. The [alpha/Fe] abundance ratios in the Bulge are predicted to be supersolar for a very large range in [Fe/H], each element having a different slope. These predictions are in very good agreement with most recent accurate abundance determinations. We also find a good fit of the most recent Bulge stellar metallicity distributions. We conclude that the Bulge formed on a very short timescale (even though timescales much shorter than about 0.1 Gyr are excluded) with a quite high star formation efficiency of about 20 Gyr$^{-1}$ and with an initial mass function more skewed toward high masses (i.e. x <= 0.95) than the solar neighbourhood and rest of the disk. The results obtained here are more robust than previous ones since they are based on very accurate abundance measurements.Comment: 26 pages, 9 figures, accepted for publication in A&

The Radio - X-ray relation as a star formation indicator: Results from the VLA--E-CDFS Survey

In order to trace the instantaneous star formation rate at high redshift, and hence help understanding the relation between the different emission mechanisms related to star formation, we combine the recent 4 Ms Chandra X-ray data and the deep VLA radio data in the Extended Chandra Deep Field South region. We find 268 sources detected both in the X-ray and radio band. The availability of redshifts for $\sim 95$ of the sources in our sample allows us to derive reliable luminosity estimates and the intrinsic properties from X-ray analysis for the majority of the objects. With the aim of selecting sources powered by star formation in both bands, we adopt classification criteria based on X-ray and radio data, exploiting the X-ray spectral features and time variability, taking advantage of observations scattered across more than ten years. We identify 43 objects consistent with being powered by star formation. We also add another 111 and 70 star forming candidates detected only in the radio or X-ray band, respectively. We find a clear linear correlation between radio and X-ray luminosity in star forming galaxies over three orders of magnitude and up to $z \sim 1.5$. We also measure a significant scatter of the order of 0.4 dex, higher than that observed at low redshift, implying an intrinsic scatter component. The correlation is consistent with that measured locally, and no evolution with redshift is observed. Using a locally calibrated relation between the SFR and the radio luminosity, we investigate the L_X(2-10keV)-SFR relation at high redshift. The comparison of the star formation rate measured in our sample with some theoretical models for the Milky Way and M31, two typical spiral galaxies, indicates that, with current data, we can trace typical spirals only at z<0.2, and strong starburst galaxies with star-formation rates as high as $\sim 100 M_\odot yr^{-1}$, up to $z\sim 1.5$.Comment: 21 pages, 10 figures, 5 table

Chemical similarities between Galactic bulge and local thick disk red giant stars

The evolution of the Milky Way bulge and its relationship with the other Galactic populations is still poorly understood. The bulge has been suggested to be either a merger-driven classical bulge or the product of a dynamical instability of the inner disk. To probe the star formation history, the initial mass function and stellar nucleosynthesis of the bulge, we performed an elemental abundance analysis of bulge red giant stars. We also completed an identical study of local thin disk, thick disk and halo giants to establish the chemical differences and similarities between the various populations. High-resolution infrared spectra of 19 bulge giants and 49 comparison giants in the solar neighborhood were acquired with Gemini/Phoenix. All stars have similar stellar parameters but cover a broad range in metallicity. A standard 1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O and Fe. A homogeneous and differential analysis of the bulge, halo, thin disk and thick disk stars ensured that systematic errors were minimized. We confirm the well-established differences for [O/Fe] (at a given metallicity) between the local thin and thick disks. For the elements investigated, we find no chemical distinction between the bulge and the local thick disk, which is in contrast to previous studies relying on literature values for disk dwarf stars in the solar neighborhood. Our findings suggest that the bulge and local thick disk experienced similar, but not necessarily shared, chemical evolution histories. We argue that their formation timescales, star formation rates and initial mass functions were similar.Comment: Accepted for publication in A&A, 5 page