GHOSTS -大质量盘状星系的凸起、晕和解析的恒星边缘
GHOSTS - Bulges, Halos, and the Resolved Stellar Outskirts of Massive Disk Galaxies
摘要：
我们的GHOSTS巡天测量了14个邻近盘状星系的恒星包络特性，通过使用HST/ACS&WFPC2对它们的分辨恒星星族进行成像。样本中的大部分大质量星系（Vrot >200 km/s）具有非常扩展的恒星包层，在外部区域具有Sersic定律轮廓或μ（r）~r^-2.5幂律轮廓。对于这些大质量星系，我们可以用同一个Sersic轮廓拟合出30 kpc的中心球光和外晕，轮廓的恒星表面密度与哈勃类型和球盘比相关。这表明，中央隆起和内晕是在同一过程中形成的。较小的星系（Vrot ~100 km/s）有更小的恒星包层，但根据几何形状，它们仍然可能比分层星系形成模型中的卫星残骸更明亮。或者，它们可以通过小的暗物质子晕的轰击通过盘加热而产生。我们拟合的晕是高度平坦的，具有较小轴与较大轴的比率c/a=0.6。晕圈比分层模型预测更紧凑。在30 kpc以下，晕的金属丰度梯度很小，大质量星系的[Fe/H]为-0.8。我们在许多星系中发现了晕子结构的迹象，但有些晕似乎非常光滑。
英文摘要：
Our GHOSTS survey measures the stellar envelope properties of 14 nearby disk galaxies by imaging their resolved stellar populations with HST/ACS&WFPC2. Most of the massive galaxies in the sample (Vrot >200 km/s) have very extended stellar envelopes with Sersic law profiles or mu(r)~r^-2.5 power law profiles in the outer regions. For these massive galaxies we can fit the central bulge light and the outer halo out to 30 kpc with one and the same Sersic profile and the stellar surface density of the profiles correlate with Hubble type and bulge- to-disk ratio. This suggests that the central bulges and inner halos are created in the same process. Smaller galaxies (Vrot ~100 km/s) have much smaller stellar envelopes, but depending on geometry, they could still be more luminous than expected from satellite remnants in hierarchical galaxy formation models. Alternatively, they could be created by disk heating through the bombardment of small dark matter sub-halos. The halos we fit are highly flattened, with minor- over-ma jor axis ratios c/a=0.6. The halos are somewhat more compact than hierarchical model predictions. The halos show small metallicity gradient out to 30 kpc and the massive galaxies have typical [Fe/H]~-0.8. We find indications of halo substructure in many galaxies, but some halos seem remarkable smooth.
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