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arXiv 0708.0533astro-ph
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局部宇宙恒星中金属和重子的普查

A census of metals and baryons in stars in the local Universe

Anna Gallazzi, Jarle Brinchmann, Stephane Charlot, Simon D. M. White

摘要:

我们结合恒星金属丰度和恒星质量的估计,从SDSS DR 2跨越广泛的物理性质的星系的大样本,以获得库存的总质量的金属和重子锁定在今天的恒星。物理参数的估计来自星系光谱与高S/N(>20)。在参数空间中,具有相似速度色散、r带绝对星等和4000个折点值的星系的叠加谱被用于那些单个谱具有较低信噪比的区域。我们估计了恒星中金属和重子的总密度,并由这两个量得到质量和体积平均的恒星金属丰度<Z_star>=1.04+-0.14 Z_sun,即与太阳一致。我们还研究了金属在星系中的分布,根据它们的质量,形态和年龄,然后我们比较这些分布与相应的恒星质量分布。我们发现,大部分的金属锁定在恒星在本地宇宙居住在大规模的,隆起为主的星系,红色和高4000年的突破值对应于旧的恒星星族。以膨胀为主的星系和以盘为主的星系对恒星总质量密度的贡献相似,但对恒星中金属质量密度的贡献不同,与质量-金属丰度关系一致。膨胀主导的星系含有大约40%的恒星金属总量,而盘主导的星系不到25%。最后,在一个给定的星系恒星质量,我们定义了两个特征年龄作为年龄的函数的质量和金属的分布的中位数。这些特征年龄从高质量到低质量星系逐渐减小,与大质量星系中恒星的高形成时期一致。

英文摘要:

We combine stellar metallicity and stellar mass estimates for a large sample of galaxies drawn from the SDSS DR2 spanning wide ranges in physical properties, in order to derive an inventory of the total mass of metals and baryons locked up in stars today. Physical parameter estimates are derived from galaxy spectra with high S/N (>20). Coadded spectra of galaxies with similar velocity dispersions, absolute r-band magnitudes and 4000Å-break values are used for those regions of parameter space where individual spectra have lower S/N. We estimate the total density of metals and of baryons in stars and, from these two quantities, we obtain a mass- and volume-averaged stellar metallicity of <Z_star>=1.04+-0.14 Z_sun, i.e. consistent with solar. We also study how metals are distributed in galaxies according to their mass, morphology and age, and we then compare these distributions with the corresponding distributions of stellar mass. We find that the bulk of metals locked up in stars in the local Universe reside in massive, bulge-dominated galaxies, with red colours and high 4000Å-break values corresponding to old stellar populations. Bulge-dominated and disc-dominated galaxies contribute similar amounts to the total stellar mass density, but have different fractional contributions to the mass density of metals in stars, in agreement with the mass-metallicity relation. Bulge-dominated galaxies contain roughly 40% of the total amount of metals in stars, while disc-dominated galaxies less than 25%. Finally, at a given galaxy stellar mass, we define two characteristic ages as the median of the distributions of mass and metals as a function of age. These characteristic ages decrease progressively from high-mass to low-mass galaxies, consistent with the high formation epochs of stars in massive galaxies.

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