Chemically Decoupled Nuclei in the Spiral Galaxies NGC 4216 and NGC 4501
Chemically Decoupled Nuclei in the Spiral Galaxies NGC 4216 and NGC 4501
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螺旋星系 NGC 4216 和 NGC 4501 中的化学解耦核
DOI：
10.1086/300733
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
V. Vlasyuk
中科院分区：
文献类型：
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作者：
O. Sil’chenko;A. Burenkov;V. Vlasyuk
通过使用6米望远镜获得的室女座螺旋NGC4216和NGC4501的二维光谱数据，我们在这些星系中发现了化学上不同的富金属核。在核群和球体群年龄相等的假设下，估计了星系中核与其周围环境之间的金属丰度差为2倍。但我们也在NGC4216中发现了核与球体之间的年龄差：年龄-金属丰度解缠图(Hβ，Mgb)，(Hβ，[mGFe])和(Hβ，⟨Fe⟩)导致核年龄估计为8-12Gyr，球体年龄老了1.5-2倍；因此，自洽的金属丰度差估计是一个因子3。星系核中的太阳镁铁比表明，产生化学上不同的恒星子系统的次级核恒星形成爆发持续了很长时间。对NGC4216和4501中心的恒星和气体结构进行了详细的形态和运动学分析，发现存在半径为数百秒的绕核恒星气体盘，它表现出快速的轴对称自转，恰好位于主星系盘的平面上。
By using bidimensional spectral data obtained at the 6 m telescope for the Virgo spirals NGC 4216 and NGC 4501, we have found chemically distinct metal-rich nuclei in these galaxies. Under the assumption of equal ages for the nuclear and bulge stellar populations, the metallicity difference between the nuclei and their environments in the galaxies is estimated as a factor of 2. But we have also found an age difference between the nucleus and the bulge in NGC 4216: age-metallicity disentangling on the diagrams (Hβ, Mg b), (Hβ, [MgFe]), and (Hβ, ⟨Fe⟩) results in an age estimate for the nucleus of 8–12 Gyr, the bulge being older by a factor of 1.5–2; the self-consistent metallicity difference estimate is then a factor of 3. The solar magnesium-to-iron ratios in the galactic nuclei show evidence for long duration of the secondary nuclear star formation bursts that produced the chemically distinct stellar subsystems. Detailed morphological and kinematic analyses made for the stellar and gaseous structures in the centers of NGC 4216 and 4501 have revealed the presence of circumnuclear stellar-gaseous disks with radii of some hundreds of parsecs that demonstrate fast axisymmetric rotation and lie exactly in the planes of the main galactic disks.