Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821
Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821
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DOI：
10.1111/j.1365-2966.2009.15134.x
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发表时间：
2009-05
影响因子：
4.8
通讯作者：
A. Weijmans;M. Cappellari;R. Bacon;P. Zeeuw;E. Emsellem;J. Falcón-Barroso;H. Kuntschner;R. McDermid-R.-M
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文献类型：
--
作者：
A. Weijmans;M. Cappellari;R. Bacon;P. Zeeuw;E. Emsellem;J. Falcón-Barroso;H. Kuntschner;R. McDermid-R.-M
我们使用积分场摄谱仪 SAURON 来测量早期星系 NGC 3379 和 NGC 821 中四个有效半径 (Re) 的恒星视线速度分布和吸收线强度。利用我们新开发的观测技术，我们现在可以探测星系中的这些微弱区域，而这些区域以前是用传统的长缝光谱无法到达的。我们充分利用了光谱仪的大视场和高通量：通过将所有 1400 个小透镜的信号添加到一个光谱中，我们在几个小时的观察时间内获得了足够的信噪比，以可靠地测量大半径的吸收线运动学和线强度。我们发现之前在 1 Re 内观察到的谱线强度梯度在至少 4 Re 范围内保持恒定，这对这些星系的合并历史施加了限制。恒星晕族群古老且缺乏金属。通过构建基于轨道的史瓦西动力学模型，我们发现暗物质对于解释 NGC 3379 和 NGC 821 中观察到的运动学是必要的，总物质的 30 - 50% 在 4 Re 范围内是暗物质。由于轨道结构的差异，我们的最佳拟合光晕模型中的径向各向异性小于没有光晕的模型。光晕也会对 Mg b - Vesc 关系产生影响：当模型中添加暗物质光晕时，其斜率会更陡。
We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii (Re) in the early-type galaxies NGC 3379 and NGC 821. With our newly developed observing technique we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all �1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius. We find that the line strength gradients previously observed within 1 Re remain constant out to at least 4 Re, which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal-poor. By constructing orbitbased Schwarzschild dynamical models we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and NGC 821, with 30 - 50 per cent of the total matter being dark within 4 Re. The radial anisotropy in our best-fit halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the Mg b - Vesc relation: its slope is steeper when a dark matter halo is added to the model.