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Register a new userA new comprehensive set of elemental abundances in DLAs - II. Data analysis and chemical variation studies
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Miroslava Dessauges-Zavadsky
Publication date
2005
fields
Physics
and research's language is
English
Authors
M. Dessauges-Zavadsky
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We present new elemental abundance studies of seven damped Lyman-alpha systems (DLAs). Together with the four DLAs analyzed in Dessauges-Zavadsky et al. (2004), we have a sample of eleven DLA galaxies with uniquely comprehensive and homogeneous abundance measurements. These observations allow one to study the abundance patterns of 22 elements and the chemical variations in the interstellar medium of galaxies outside the Local Group. Comparing the gas-phase abundance ratios of these high redshift galaxies, we found that they show low RMS dispersions, reaching only up 2-3 times the statistical errors for the majority of elements. This uniformity is remarkable given that the quasar sightlines cross gaseous regions with HI column densities spanning over one order of magnitude and metallicities ranging from 1/55 to 1/5 solar. The gas-phase abundance patterns of interstellar medium clouds within the DLA galaxies detected along the velocity profiles show, on the other hand, a high dispersion in several abundance ratios, indicating that chemical variations seem to be more confined to individual clouds within the DLA galaxies than to integrated profiles. The analysis of the cloud-to-cloud chemical variations within seven individual DLAs reveals that five of them show statistically significant variations, higher than 0.2 dex at more than 3 sigma. The sources of these variations are both the differential dust depletion and/or ionization effects; however, no evidence for variations due to different star formation histories could be highlighted. These observations place large constraints on the mixing timescales of protogalaxies and on scenarios of galaxy formation within the CDM hierarchical theory. Finally, we provide an astrophysical determination of the oscillator strength of the NiII 1317 transition.
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We obtained comprehensive sets of elemental abundances for eleven damped Ly-alpha systems (DLAs) at z_DLA=1.7-2.5. In Paper I of this series, we showed for three DLA galaxies that we can derive their star formation histories and ages from a detailed comparison of their intrinsic abundance patterns with chemical evolution models. We determine in this paper the star formation properties of six additional DLA galaxies. The derived results confirm that no single star formation history explains the diverse sets of abundance patterns in DLAs. We demonstrate that the various star formation histories reproducing the DLA abundance patterns are typical of local irregular, dwarf starburst and quiescent spiral galaxies. Independent of the star formation history, the DLAs have a common characteristic of being weak star forming galaxies; models with high star formation efficiencies are ruled out. All the derived DLA star formation rates per unit area are moderate or low, with values between -3.2 < log SFR < -1.1 M_sol yr^{-1} kpc^{-2}. The DLA abundance patterns require a large spread in ages ranging from 20 Myr up to 3 Gyr. The oldest DLA in our sample is observed at z_DLA=1.864 with an age estimated to more than 3 Gyr; it nicely indicates that galaxies were already forming at z_f>10. But, most of the DLAs show ages much younger than that of the Universe at the epoch of observation. Young galaxies thus seem to populate the high redshift Universe at z>2, suggesting relatively low redshifts of formation (z~3) for most high-redshift galaxies. The DLA star formation properties are compared with those of other high-redshift galaxies identified in deep imaging surveys with the aim of obtaining a global picture of high-redshift objects.
Results from high-resolution spectral analyses of a selected sample of CH stars are presented. Detailed chemical composition studies of these objects, which could reveal abundance patterns that in turn provide information regarding nucleosynthesis and evolutionary status, are scarce in the literature. We conducted detailed chemical composition studies for these objects based on high resolution (R ~ 42000) spectra. The spectra were taken from the ELODIE archive and cover the wavelength range from 3900 to 6800 A, in the wavelength range. We estimated the stellar atmospheric parameters, the effective temperature Teff, the surface gravity log g, and metallicity [Fe/H] from Local thermodynamic equilibrium analyses using model atmospheres. Estimated temperatures of these objects cover a wide range from 4550 K to 6030 K, the surface gravity from 1.8 to 3.8 and metallicity from -0.18 to -1.4. We report updates on elemental abundances for several heavy elements and present estimates of abundance ratios of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu and Dy with respect to Fe. For the object HD 188650 we present the first abundance analyses results based on a high resolution spectrum. Enhancements of heavy elements relative to Fe, that are characteristic of CH stars are evident from our analyses for most of the objects. A parametric model based study is performed to understand the relative contributions from the s- and r-processes to the abundances of the heavy elements.
By combining our UVES-VLT spectra of a sample of four damped Ly-alpha systems (DLAs) toward the quasars Q0100+13, Q1331+17, Q2231-00 and Q2343+12 with the existing HIRES-Keck spectra, we covered the total spectral range from 3150 to 10000 A for the four quasars. This large wavelength coverage and the high quality of the spectra allowed us to measure the column densities of up to 21 ions, namely of 15 elements - N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Mn, Fe, Ni, Zn. Such a large amount of information is necessary to constrain the photoionization and dust depletion effects, two important steps in order to derive the intrinsic chemical abundance patterns of DLAs. We evaluated the photoionization effects with the help of the Al+/Al++, Fe+/Fe++, N0/N+ and Ar/Si,S ratios, and computed dust corrections. Our analysis revealed that the DLA toward Q2343+12 requires important ionization corrections. The access to the complete series of relatively robust intrinsic elemental abundances in the other three DLAs allowed us to constrain their star formation history, their age and their star formation rate by a detailed comparison with a grid of chemical evolution models for spiral and dwarf irregular galaxies. Our results show that the galaxies associated with these three DLAs in the redshift interval z_abs = 1.7-2.5 are either outer regions of spiral disks (radius >= 8 kpc) or dwarf irregular galaxies (with a bursting or continuous star formation history) with ages varying from some 50 Myr only to >~ 3.5 Gyr and with moderate star formation rates per unit area of -2.1 < log psi < -1.5 M_{sol} yr^{-1} kpc^{-2}.
(Abridged) We present the abundance analysis of 12 PNe ionized by [WC]-type stars and wels obtained from high-resolution spectrophotometric data. Our main aims are to determine the chemical composition of the PNe and to study the behaviour of the abundance discrepancy problem (ADF) in this type of planetary nebulae. The detection of a large number of optical recombination lines (ORLs) and collisionally excited lines (CELs) from different ions were presented previously. Most of the ORLs were reported for the first time in these PNe. Ionic abundances were derived from the available CELs and ORLs, using previously determined physical conditions. Based on these two sets of ionic abundances, we derived the total chemical abundances in the nebulae using suitable ICFs (when available). In spite of the [WC] nature of the central stars, moderate ADF(O^++), in the range from 1.2 to 4, were found for all the objects. We found that when the quality of the spectra is high enough the ORLs O^++/H^+ abundance ratios obtained from different multiplets excited mainly by recombination are very similar. Possible dependence of ADFs with some nebular characteristics were analysed, finding no correlation. Abundances derived from CELs were corrected by determining the t^2 parameter. O abundances for PNe, derived from ORLs, are in general larger than the solar abundance. We derived the C/O ratio from ORLs and N/O and alpha-element/O ratios from CELs and found that these PNe are, in average, N-and C-richer than the average of large PN samples. About half of our sample is C-rich (C/O>1). The alpha-elements grow in lockstep with O abundance. Comparing the N/O and C /O ratios with those derived from stellar evolution models, we estimate that about half of our PNe have progenitors with initial masses > 4 M_sun. No correlation was found between the stellar [WC]-type and the nebular abundances.
Filaments are very common physical phenomena on the Sun and are often taken as important proxies of solar magnetic activities. The study of filaments has become a hot topic in the space weather research. For a more comprehensive understanding of filaments, especially for an understanding of solar activities of multiple solar cycles, it is necessary to perform a combined multifeature analysis by constructing a data set of multiple solar cycle data. To achieve this goal, we constructed a centennial data set that covers the H$alpha$ data from five observatories around the world. During the data set construction, we encountered varieties of problems, such as data fusion, accurate determination of the solar edge, classifying data by quality, dynamic threshold, and so on, which arose mainly due to multiple sources and a large time span of data. But fortunately, these problems were well solved. The data set includes seven types of data products and eight types of feature parameters with which we can implement the functions of data searching and statistical analyses. It has the characteristics of better continuity and highly complementary to space observation data, especially in the wavelengths not covered by space observations, and covers many solar cycles (including more than 60 yr of high-cadence data). We expect that this new comprehensive data set as well as the tools will help researchers to significantly speed up their search for features or events of interest, for either statistical or case study purposes, and possibly help them get a better and more comprehensive understanding of solar filament mechanisms.
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