The build-up of the cD halo of M 87: evidence for accretion in the last Gyr
The build-up of the cD halo of M 87: evidence for accretion in the last Gyr
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DOI：
10.1051/0004-6361/201526282
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发表时间：
2015-04
影响因子：
6.5
通讯作者：
A. Longobardi;M. Arnaboldi;O. Gerhard;J. C. Mihos
中科院分区：
文献类型：
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作者：
A. Longobardi;M. Arnaboldi;O. Gerhard;J. C. Mihos
目标。我们提出的运动学和光度证据吸积事件的晕的cD星系M87在最后一个陀螺。方法.利用M87晕中1000个行星状星云（PN）的速度，我们在PN相空间中识别出一个人字形的子结构。我们实现了一个概率高斯混合模型来识别属于V形的PN。通过对M87深V波段图像的分析，我们发现人字形PN密度最高的区域在光照下是一个冠状亚结构。结果我们分配了一个总NPN，sub = 54的子结构，它延伸超过1050 kpc沿着主轴，我们还观察到径向变化的椭圆率分布和颜色梯度。亚结构在半径为70kpc左右的20kpc × 60kpc区域内表面亮度最高。在该区域中，亚结构导致表面亮度增加60%。吸积事件与一个V带光度L = 2.8 ± 1.0 × 10 9 L？，V，色（B − V）= 0.76 ± 0.05，恒星质量M = 6.4 ± 2.3 × 10 9 M？的祖先星系相一致。结论.这个前身星系的吸积导致了M87在最后一个Gyr的外晕的重要修改。这一结果提供了强有力的证据表明，星系的cD晕是通过吸积较小的星系的层次星系演化模型预测的增长。
Aims. We present kinematic and photometric evidence for an accretion event in the halo of the cD galaxy M 87 in the last Gyr. Methods. Using velocities for ∼300 planetary nebulas (PNs) in the M 87 halo, we identify a chevron-like substructure in the PN phasespace. We implement a probabilistic Gaussian mixture model to identify PNs that belong to the chevron. From analysis of deep V-band images of M 87, we find that the region with the highest density of chevron PNs is a crown-shaped substructure in the light. Results. We assign a total of NPN,sub = 54 to the substructure, which extends over ∼50 kpc along the major axis where we also observe radial variations of the ellipticity profile and a colour gradient. The substructure has highest surface brightness in a 20 kpc × 60 kpc region around 70 kpc in radius. In this region, the substructure causes an increase in surface brightness by 60%. The accretion event is consistent with a progenitor galaxy with a V-band luminosity of L = 2.8 ± 1.0 × 10 9 L� ,V , a colour of (B − V) = 0.76 ± 0.05, and a stellar mass of M = 6.4 ± 2.3 × 10 9 M� . Conclusions. The accretion of this progenitor galaxy has caused an important modification of the outer halo of M 87 in the last Gyr. This result provides strong evidence that the galaxy’s cD halo is growing through the accretion of smaller galaxies as predicted by hierarchical galaxy evolution models.