HST探测z = 0.4大质量椭圆中的扩展中性氢
HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z = 0.4
摘要：
我们首次在一个z~0以外的大质量椭圆星系的星际介质中探测到了扩展中性氢气体。观测利用z_QSO = 1.676的类星体HE 0047 - 1756的双透镜图像作为z = 0.408的大质量（M_star~10^11 M_sun）椭圆透镜中ISM的吸收线探针，在透镜两侧的投影距离d = 3.3和4.6 kpc处探测气体。使用空间望远镜成像光谱仪（STIS），我们获得了透镜类星体的紫外吸收光谱，并确定了一个突出的流量不连续性和相关的吸收功能匹配的莱曼系跃迁z = 0.408在两个视线。在穿过透镜的两个位置，HI柱密度为log N（HI）= 19.6 - 19.7，与在附近椭圆星系的21厘米图像中看到的相当。HI气体的运动学是很好地匹配的运动学的FeII吸收复杂的地面上阶梯光栅的数据显示，整个星系的速度剪切360公里/秒。我们估计在这两个位置的ISM铁丰度为0.3 - 0.4太阳。包括可能的尘埃耗尽增加了估计的铁丰度太阳或超太阳，类似于热ISM和附近的椭圆星系的恒星。假设这种富铁气体的覆盖率为100%，我们推断在大质量椭圆透镜的冷ISM中的总Fe质量为M_cool（Fe）~（5 - 8）× 10^4 M_sun，这不超过在热ISM中观测到的总Fe质量的5%。
英文摘要：
We report the first detection of extended neutral hydrogen (HI) gas in the interstellar medium (ISM) of a massive elliptical galaxy beyond z~0. The observations utilize the doubly lensed images of QSO HE 0047-1756 at z_QSO = 1.676 as absorption-line probes of the ISM in the massive (M_star ~ 10^11 M_sun) elliptical lens at z = 0.408, detecting gas at projected distances of d = 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope Imaging Spectrograph (STIS), we obtain UV absorption spectra of the lensed QSO and identify a prominent flux discontinuity and associated absorption features matching the Lyman series transitions at z = 0.408 in both sightlines. The HI column density is log N(HI) = 19.6-19.7 at both locations across the lens, comparable to what is seen in 21 cm images of nearby ellipticals. The HI gas kinematics are well-matched with the kinematics of the FeII absorption complex revealed in ground-based echelle data, displaying a large velocity shear of 360 km/s across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at both locations. Including likely dust depletions increases the estimated Fe abundances to solar or supersolar, similar to those of the hot ISM and stars of nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas,we infer a total Fe mass of M_cool(Fe)~(5-8)x10^4 M_sun in the cool ISM of the massive elliptical lens, which is no more than 5% of the total Fe mass observed in the hot ISM.
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