共查询到20条相似文献，搜索用时 15 毫秒
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Leonid Pilyugin 《Astrophysics and Space Science》2003,284(2):775-778
Spiral galaxies with a reported bend in the slope of the oxygen abundance O/HR
23, derived with the traditionally used R23-method, are examined. It is shown that the artificial origin of the reported bends can be naturally explained. Two causes
of the false bend in the slope of O/HR
23 are indicated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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S. D. Ryder Y. Fenner B. K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,358(4):1337-1351
We describe the technique of absorption-line imaging of galaxy discs using the Taurus Tunable Filter on the Anglo-Australian Telescope and demonstrate its sensitivity to the behaviour of spectral features associated with Mg and Fe. Radial profiles of Mg2 and Fe5270 line strengths are presented for a sample of eight face-on spiral galaxies spanning a range of Hubble types. Signatures of phenomena including merger-induced star formation, H ii rings and galactic bars are also reported. This study demonstrates the capacity of tunable filters to measure Mg and Fe line strengths across the face of spiral galaxies, which can ultimately reveal clues about the star formation history and chemical evolution. 相似文献
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Gustavo A. Lanfranchi Francesca Matteucci Gabriele Cescutti 《Monthly notices of the Royal Astronomical Society》2006,365(2):477-488
By means of a detailed chemical evolution model, we follow the evolution of barium (Ba) and europium (Eu) in four Local Group Dwarf Spheroidal (dSph) galaxies, in order to set constraints on the nucleosynthesis of these elements and on the evolution of this type of galaxies compared with the Milky Way. The model, which is able to reproduce several observed abundance ratios and the present-day total mass and gas mass content of these galaxies, adopts up-to-date nucleosynthesis and takes into account the role played by supernovae (SNe) of different types (II, Ia) allowing us to follow in detail the evolution of several chemical elements (H, D, He, C, N, O, Mg, Si, S, Ca, Fe, Ba and Eu). By assuming that Ba is a neutron-capture element produced in low-mass asymptotic giant branch stars by s-process but also in massive stars (in the mass range 10–30 M⊙ ) by r-process, during the explosive event of SNe of Type II, and that Eu is a pure r-process element synthesized in massive stars also in the range of masses 10–30 M⊙ , we are able to reproduce the observed [Ba/Fe] and [Eu/Fe] as functions of [Fe/H] in all four galaxies studied. We confirm also the important role played by the very low star formation (SF) efficiencies (ν= 0.005–0.5 Gyr−1 ) and by the intense galactic winds (6–13 times the star formation rate) in the evolution of these galaxies. These low SF efficiencies (compared to the one for the Milky Way disc) adopted for the dSph galaxies are the main reason for the differences between the trends of [Ba/Fe] and [Eu/Fe] predicted and observed in these galaxies and in the metal-poor stars of our Galaxy. Finally, we provide predictions for Sagittarius galaxy for which data of only two stars are available. 相似文献
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F. Xiang E. Rudometkin E. Churazov W. Forman H. Böhringer 《Monthly notices of the Royal Astronomical Society》2009,398(2):575-582
We evaluate the impact of gas shock heating by a central active galactic nuclei (AGN) in M87 on the radial distribution of heavy elements. The propagation of a shock creates an inverted entropy profile, and the subsequent rearrangement of the gaseous atmosphere transports metal-rich gas from the central region to larger radii. We show that for the parameters of the relatively weak shock, recently found in M87, the abundance profile is not strongly affected by the redistribution of the shock heated gas (except for the very central region). At the same time, the energetics of the source is fully sufficient to broaden the metal distribution to match the observations, strongly suggesting that mechanisms other than direct shock heating must operate in cluster cores. The absence of a very strong abundance peak at the very centre of M87 suggests that the central AGN produces frequent (every few 10 Myr) and relatively weak outbursts, rather than rarer (every few 100 Myr) and an order of magnitude more powerful events. 相似文献
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Antonio Pipino Francesca Matteucci 《Monthly notices of the Royal Astronomical Society》2006,365(4):1114-1122
The effects of late gas accretion episodes and subsequent merger-induced starbursts on the photochemical evolution of elliptical galaxies are studied and compared to the picture of galaxy formation occurring at high redshift with a unique and intense starburst modulated by a very short infall, as suggested by Pipino and Matteucci in Paper I. By means of the comparison with the colour–magnitude relations (CMRs) and the [〈Mg/Fe〉 V ]–σ relation observed in ellipticals, we conclude that either bursts involving a gas mass comparable to the mass already transformed into stars during the first episode of star formation (SF) and occurring at any redshift, or bursts occurring at low redshift (i.e. z ≤ 0.2) and with a large range of accreted mass, are ruled out. These models fail in matching the above relations even if the initial infalling hypothesis is relaxed, and the galaxies form either by means of more complicated SF histories or by means of the classical monolithic model. On the other hand, galaxies accreting a small amount of gas at high redshift (i.e. z ≥ 3) produce a spread in the model results, with respect to the best model of Paper I, which is consistent with the observational scatter of the CMRs, although there is only marginal agreement with the [〈Mg/Fe〉 V ]–σ relation. Therefore, only small perturbations to the standard scenario seem to be allowed. We stress that the strongest constraints to galaxy-formation mechanisms are represented by the chemical abundances, whereas the colours can be reproduced under several different hypotheses. 相似文献
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A generalization of the multiphase chemical evolution model applied to a wide set of theoretical galaxies is shown. This set
of models has been computed by using the so-called Universal Rotation Curve from (Persic, Salucci and Steel, 1996) to calculate
the radial mass distributions of each theoretical galaxy. By assuming that the molecular cloud and star formation efficiencies
depend on the morphological type of each galaxy, we construct a bi-parametric grid of models whose results are valid in principle
for any spiral galaxy, of given maximum rotation velocity or total mass, and morphological type.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Paul A. Crowther Raman K. Prinja Max Pettini Charles C. Steidel 《Monthly notices of the Royal Astronomical Society》2006,368(2):895-902
We reconsider the use of the equivalent width of C iv λ1549, EW(C iv ), as an indicator of the oxygen abundance in star-forming galaxies, as proposed by Heckman et al. for nearby starbursts. We refine the local calibration of EW(C iv ) versus log (O/H) by using a restricted wavelength window which minimizes blending with interstellar absorption lines. When applied to the stellar component only of the complex C iv λ1549 features in two high-redshift galaxies with good quality spectra, MS 1512−cB58 ( z = 2.7268) and Q1307−BM1163 ( z = 1.4105) , the local calibration gives values of the oxygen abundance which are in good agreement with other metallicity determinations based on nebular emission and interstellar absorption lines. Our main conclusion is that for this method to give reliable results at high redshifts, it should only be used on data of sufficiently high spectral resolution ( R ≳ 1000) for stellar and interstellar C iv components to be clearly separated. Oxygen abundances will be systematically overestimated if the local calibration is applied to spectra of high-redshift galaxies obtained with the low resolving powers ( R ≃ 200–300) of many current wide-field surveys. It will also be necessary to understand better the causes of the scatter in the local relation, before we can be confident of inferences from it at high z . 相似文献
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Yong-Yun Chen Yan-Mei Chen Qiu-Sheng Gu Yong Shi Long-Ji Bing Xiao-Ling Yu 《天文和天体物理学研究(英文版)》2019,(6):51-62
We select 107 blue-core galaxies from the MaNGA survey, studying their morphology, kinematics as well as the gas-phase metallicity. Our results are as follows:(i) In our sample, 26% of blue-core galaxies have decoupled gas-star kinematics, indicating external gas accretion;15% have bar-like structure and 8% show post-merger features, such as tidal tails and irregular gas/star velocity field. All these processes/features, such as accreting external misaligned gas, interaction and bar, can trigger gas inflow. Thus the central star-forming activities lead to bluer colors in their centers(blue-core galaxies).(ii) By comparing with the SDSS DR7 star-forming galaxy sample, we find that the blue-core galaxies have higher central gas-phase metallicity than what is predicted by the local mass-metallicity relation. We explore the origin of the higher metallicity, finding that not only the blue-core galaxies, but also the flat-gradient and red-core galaxies all have higher metallicity. This can be explained by the combined effect of redshift and galaxy color. 相似文献
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GlendaDenicoló RobertoTerlevich † ElenaTerlevich ‡ 《Monthly notices of the Royal Astronomical Society》2002,330(1):69-74
We present a simple metallicity estimator based on the logarithmic [N ii ] λ 6584/H α ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in a metallicity sequence from redshift survey-quality data even for moderately low spectral resolution.
We have calibrated the N2 estimator using a compilation of H ii galaxies having accurate oxygen abundances, plus photoionization models covering a wide range of abundances. The comparison of models and observations indicates that both primary and secondary nitrogen are important for the relevant range of metallicities.
The N2 estimator follows a linear relation with log(O/H) that holds for the whole abundance range covered by the sample, from approximately 1/50th to twice the Solar value [7.2<12+log(O/H)<9.1] . We suggest that the ([S ii ] λλ 6717,6731/H α ) ratio (hereafter S2) can also be used as a rough metallicity indicator. Because of its large scatter the S2 estimator will be useful only in systems with very low metallicity, where [N ii ] λ 6584 is not detected or in low-resolution spectra where [N ii ] λ 6584 is blended with H α . 相似文献
We have calibrated the N2 estimator using a compilation of H ii galaxies having accurate oxygen abundances, plus photoionization models covering a wide range of abundances. The comparison of models and observations indicates that both primary and secondary nitrogen are important for the relevant range of metallicities.
The N2 estimator follows a linear relation with log(O/H) that holds for the whole abundance range covered by the sample, from approximately 1/50th to twice the Solar value [7.2<12+log(O/H)<9.1] . We suggest that the ([S ii ] λλ 6717,6731/H α ) ratio (hereafter S2) can also be used as a rough metallicity indicator. Because of its large scatter the S2 estimator will be useful only in systems with very low metallicity, where [N ii ] λ 6584 is not detected or in low-resolution spectra where [N ii ] λ 6584 is blended with H α . 相似文献
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A. Marcolini A. D'Ercole G. Battaglia B. K. Gibson 《Monthly notices of the Royal Astronomical Society》2008,386(4):2173-2180
Using three-dimensional hydrodynamical simulations of isolated dwarf spheroidal galaxies (dSphs), we undertake an analysis of the chemical properties of their inner regions, identifying the respective roles played by Type Ia supernovae (SNe Ia) and Type II supernovae (SNe II). The effect of inhomogeneous pollution from SNe Ia is shown to be prominent within two core radii, with the stars forming therein amounting to ∼20 per cent of the total. These stars are relatively iron-rich and α-element depleted compared to the stars forming in the rest of the galaxy. At odds with the projected stellar velocity dispersion radial profile, the actual three-dimensional one shows a depression in the central region, where the most metal-rich (i.e. [Fe/H]-rich) stars are partly segregated. This naturally results in two different stellar populations, with an anticorrelation between [Fe/H] and velocity dispersion, in the same sense as that observed in the Sculptor and Fornax dSphs. Because the most iron-rich stars in our model are also the most α depleted, a natural prediction and test of our model is that the same radial segregation effects should exist between [α/Fe] and velocity dispersion. 相似文献
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Agostino Renda Daisuke Kawata Yeshe Fenner Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,356(3):1071-1078
The chemical evolution history of a galaxy hides clues about how it formed and has been changing through time. We have studied the chemical evolution history of the Milky Way (MW) and Andromeda (M31) to find which are common features in the chemical evolution of disc galaxies as well as which are galaxy-dependent. We use a semi-analytic multizone chemical evolution model. Such models have succeeded in explaining the mean trends of the observed chemical properties in these two Local Group spiral galaxies with similar mass and morphology. Our results suggest that while the evolution of the MW and M31 shares general similarities, differences in the formation history are required to explain the observations in detail. In particular, we found that the observed higher metallicity in the M31 halo can be explained by either (i) a higher halo star formation efficiency (SFE), or (ii) a larger reservoir of infalling halo gas with a longer halo formation phase. These two different pictures would lead to (i) a higher [O/Fe] at low metallicities, or (ii) younger stellar populations in the M31 halo, respectively. Both pictures result in a more massive stellar halo in M31, which suggests a possible correlation between the halo metallicity and its stellar mass. 相似文献