论文标题
QUASTAR调查：在银河系的圆形介质中检测隐藏的低速气体
The QuaStar Survey: Detecting Hidden Low-Velocity Gas in the Milky Way's Circumgalactic Medium
论文作者
论文摘要
从我们嵌入银河系星际介质（ISM）中的位置，我们在扩展的银河光环中检测到低相对速度的气体的能力有限，因为这些光谱线与来自密集的前景气体的信号混合在一起。结果，在$ | v _ {\ rm lsr} | $ $ \ $ \ lysesim $ 150 km s $^{ - 1} $的情况下，银河系的圆环培养基（CGM）的内容受到限制。为了克服这一并发症，Quastar调查使用配对的类星体明星视线采用了一种频谱差异技术，以首次测量银河系CGM的模糊含量。我们介绍了CIV DOBLET的测量值（$λλ$1548Å，1550Å），这是一种在HST/COS Spectra中检测到的休息型UV金属线转变，该过渡均为30 Halo-Star/quasar对均匀分布在银河纬度上的天空中，$ | b | b | b | b | b |> 30^\ crir。 30个光环恒星具有良好约束的距离（D $ \ $ 5-14 kpc），并与类星体配对，分别是$ <$ 2.8 $^\ circ $。我们认为，类星体和恒星视线之间的吸收差异主要起源于银河系的扩展CGM，超过$ \ sim $ 10 kpc。对于银河系的延长，低速CGM（$ | V | <$ 150 km/s），我们对平均civ列密度的上限为$ \rmΔlogn_{lvcgm} <13.39 $，并找到$ f _ {\ rm civ，lvcgm} $ f _ $ f _ civ，lvcgm}（\ rm fogn）5。 [6/30]，一个值明显低于低红移的星形星系的覆盖部分。我们的结果表明，大部分的银河系CIV追踪的CGM位于低银河纬度，或者与低红色（$ z <0.1 $）星形的星系卤素相比，银河系的CGM缺乏温暖的电离材料。
From our position embedded within the Milky Way's interstellar medium (ISM), we have limited ability to detect gas at low relative velocities in the extended Galactic halo because those spectral lines are blended with much stronger signals from dense foreground gas. As a result, the content of the Milky Way's circumgalactic medium (CGM) is poorly constrained at $|v_{\rm LSR}|$ $\lesssim$ 150 km s$^{-1}$. To overcome this complication, the QuaStar Survey applies a spectral differencing technique using paired quasar-star sightlines to measure the obscured content of the Milky Way's CGM for the first time. We present measurements of the CIV doublet ($λλ$ 1548 Å, 1550 Å), a rest-frame UV metal line transition detected in HST/COS spectra of 30 halo-star/quasar pairs evenly distributed across the sky at Galactic latitudes $|b|>30^\circ$. The 30 halo stars have well-constrained distances (d$\approx$5-14 kpc), and are paired with quasars separated by $<$ 2.8$^\circ$. We argue that the difference in absorption between the quasar and stellar sightlines originates primarily in the Milky Way's extended CGM beyond $\sim$10 kpc. For the Milky Way's extended, low velocity CGM ($|v|<$150 km/s), we place an upper limit on the mean CIV column density of $\rm ΔlogN_{LVCGM} < 13.39$ and find a covering fraction of $f_{\rm CIV,LVCGM} (\rm logN>13.65)=$ 20% [6/30], a value significantly lower than the covering fraction for star-forming galaxies at low redshift. Our results suggest either that the bulk of Milky Way's CIV-traced CGM lies at low Galactic latitudes, or that the Milky Way's CGM is lacking in warm, ionized material compared to low-redshift ($z < 0.1$) star-forming galaxy halos.
