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arXiv 1605.03014astro-ph.GA
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超大质量致密早型星系:z=1.6以来的速度色散和数密度演化

Ultramassive dense early-type galaxies: velocity dispersions and number density evolution since z=1.6

A. Gargiulo, P. Saracco, S. Tamburri, I. Lonoce, F. Ciocca

摘要:

本文研究了超大质量(Mstar > 10^11Msun)致密(Sigma = Mstar/(2*pi*Re^2)> 2500 Msun/pc^2)早型星系(ETG)在过去9 Gyr的质量聚集历史。我们追踪了超大质量致密ETG的数密度ρ的演化,并在0 < z < 1.6的红移范围内比较了它们的结构(有效半径Re和恒星质量Mstar)和动力学(速度色散σ_e)参数。我们已经从MUNICS和GOODS-South巡天中得到了1.6 < z < 1处的数密度,而我们已经使用COSMOS和SDSS光谱巡天来探测中间和局部红移范围。为了比较动力学参数和结构参数,我们收集了1.2 < z < 1.6的超大质量致密ETG,其中11个ETG的速度色散测量是可用的。对于其中的4个,我们提出了未发表的估计sigma_e。我们使用Saglia等人(2010),Zahid等人(2015)和Thomas等人(2010)的ETG样本探测中间红移范围和局部宇宙。我们发现超大质量致密ETG的数密度演化为rho(z)= K*(1 + z)^(0.3 \pm 0.8),这意味着自z = 1.6以来,人口减少了约25%。通过比较0 < z < 1.6范围内超重质量稠密ETG的Re、Mstar和sigma_e值,我们发现所有的高z ETG在局域宇宙中都有对应的ETG。这意味着大多数(约70%)的超大质量致密ETG已经在z = 1.4时完成了组装和成形<z>,或者,如果它们中的很大一部分在尺寸上演变,新的超大质量致密ETG必须在z &lt; 1.5时形成,以保持它们的数量密度几乎恒定。在z &lt; 1.5时,很难为这些新的致密ETG识别出好的祖先,而局部超大质量致密ETG的恒星星族性质指向第一种假设。

英文摘要:

In this paper we investigate the mass assembly history of ultramassive (Mstar > 10^11Msun) dense (Sigma = Mstar/(2*pi*Re^2) > 2500 Msun/pc^2) early-type galaxies (ETGs) over the last 9 Gyr. We have traced the evolution of the number density rho of ultramassive dense ETGs and have compared their structural (effective radius Re and stellar mass Mstar) and dynamical (velocity dispersion sigma_e) parameters over the redshift range 0 < z < 1.6. We have derived the number density at 1.6 < z < 1 from the MUNICS and GOODS-South surveys, while we have used the COSMOS and SDSS spectroscopic surveys to probe the intermediate and local redshift range. For the comparison of the dynamical and structural parameters, we have collected the ultramassive dense ETGs at 1.2 < z < 1.6 for which velocity dispersion measurements are available (11 ETGs). For 4 of them we present unpublished estimates of sigma_e. We probe the intermediate redshift range, and the local universe using the samples of ETGs by Saglia et al. (2010), Zahid et al. (2015), and by Thomas et al. (2010). We find that the number density of ultramassive dense ETGs evolves as rho(z) = K*(1 + z)^(0.3\pm0.8) implying a decrease of ~ 25% of the population since z = 1.6. By comparing the values of Re, Mstar, and sigma_e of ultramassive dense ETGs over the range 0 < z < 1.6 we find that all the high-z ETGs have a counterpart in the local universe. This implies either that the majority (~70%) of ultramassive dense ETGs has already completed its assembly and its shaping at <z> = 1.4, or that, if a significant fraction of them evolves in size, new ultramassive dense ETGs must form at z < 1.5 to maintain their number density almost constant. The difficulty into identify good progenitors for these new dense ETGs at z < 1.5, and the stellar populations properties of local ultramassive dense ETGs point toward the first hypothesis.

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