The Hubble Space Telescope Quasar Absorption Line Key Project. XV. Milky Way Absorption Lines
The Hubble Space Telescope Quasar Absorption Line Key Project. XV. Milky Way Absorption Lines
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DOI：
10.1086/313420
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发表时间：
2000-08
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通讯作者：
B. Savage;B. Wakker;B. Jannuzi;J. Bahcall;J. Bergeron;A. Boksenberg;G. Hartig;S. Kirhakos;E. Murphy;W. L. W. Sargent-W.-L.-W.-Sargent-2244025916;D. Schneider;D. Turnshek;A. Wolfe
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作者：
B. Savage;B. Wakker;B. Jannuzi;J. Bahcall;J. Bergeron;A. Boksenberg;G. Hartig;S. Kirhakos;E. Murphy;W. L. W. Sargent-W.-L.-W.-Sargent-2244025916;D. Schneider;D. Turnshek;A. Wolfe
本文对哈勃空间望远镜（HST）类星体吸收线重点项目数据库中的83个类星体（G190 H和G270 H光栅）的银河系吸收线进行了分析，其中16个类星体也用G130 H光栅观测到。HST关键项目的观测得到了高质量的21 cm H I发射线观测的补充，这些观测主要是用NRAO 43 m射电望远镜获得的。银河系晕气体表现出“混合电离”吸收，其中Si IV和C IV的高电离吸收明显弱于Si III、Si II、C II、Mg II和Fe II的极强中电离和低电离吸收。对于一个样本的16个类星体观察到的远紫外线，中值速度相当宽度的非常强的线的硅IV，硅III，和硅II分别为60，180和180公里s-1。Si III和Si II的速度等效宽度如此之大，意味着存在高速色散的中等（Si III）和低电离（Si II）气体沿着许多路径穿过银河系晕。通过对14个类星体的银河系阻尼Lyα线的测量，可以通过银河系的气体盘和晕来确定N（H I）Lyα。N（H I）Lyα值为0.64 × 1020 ~ 3.37 × 1020 cm-2，N（H I）Lyα值为0.64 × 1020 ~ 3.37 × 1020 cm-2，|罪B|平均（1.29 ± 0.49）× 1020 cm-2。N（H I）Lyα与N（H I）21 cm的比较表明，在N（H I）Lyα值不受地冕辐射显著影响的10条视线上，N（H I）Lyα/N（H I）21 cm的范围为0.62 ~ 0.91。这种差异可能是由系统误差和随机误差的组合以及H I分布中的小角尺度结构的贡献产生的。当用紫外线（类星体的角尺寸）中的无限小光束对气体进行采样时，与NRAO 43 m射电望远镜的大得多的21′光束相比，这种结构可以产生不同的柱密度。Mg II λλ2796和2803吸收的总体强度似乎与沿视线沿着的高速气体的存在相关。与麦哲伦流中高速气体相关的速度分辨Mg II吸收被检测到朝向八个类星体，包括PKS 0003+15，PG 0043+039，PKS 0637-75，3C 454.3，PKS 2251+11，PG 2302+029，PKS 2340-36和PKS 2344+09。速度分辨Mg II吸收朝向15类星体是不伴随着相关的H I发射的存在。此类别中有趣的对象包括PKS 0232-04（l = 174.°5，B =-56. ° 2），在Mg II和PG 1116+215中检测到v_（max）+270 km s-1的高速云（HVC）（l = 223.°3，B = 68.°2），在Mg II、C II、Si IV（可能还有C IV）中检测到+200 km s-1的HVC。朝向PKS 0232-04的HVC是有趣的，因为在天空的这个一般区域中所有已知的H I HVC都具有负速度而不是正速度。对于15类星体已知的谎言在H I HVC的方向，镁II线有非常强的主吸收成分，这表明混合低速和高速吸收的检测。这些视线意味着检测镁II吸收的高速气体在HVC复合物C和A，在外银河系翘曲，并在麦哲伦流，以及对三个较小的云。有11个类星体视线非常强的镁II吸收，没有证据表明高速H I排放。然而，这些视线中的六个位于已知的HI HVC附近。有38个类星体具有弱的Mg II主吸收，没有已知的H I HVC。这些天体提供了远离HIVCs的盘和晕气体的HIVCs吸收特性的信息。高速Mg II的天空覆盖因子很大，有41和71条类星体视线显示出分辨的高速Mg II吸收或主吸收，其强度如此之大，以至于建议混合低速和高速Mg II吸收。
This paper presents the results of an analysis of the Milky Way absorption lines found in the Hubble Space Telescope (HST) Quasar Absorption Line Key Project database for 83 QSOs observed with the Faint Object Spectrograph G190H and G270H gratings, of which 16 QSOs are also observed with the G130H grating. The HST Key Project observations are supplemented with high-quality 21 cm H I emission-line observations mostly obtained with the NRAO 43 m radio telescope. The Milky Way halo gas exhibits "mixed ionization" absorption with high-ionization absorption from Si IV and C IV substantially weaker than the extremely strong intermediate- and low-ionization absorption from Si III, Si II, C II, Mg II, and Fe II. For a sample of 16 QSOs observed in the far-UV, the median velocity equivalent widths of very strong lines of Si IV, Si III, and Si II are 60, 180, and 180 km s-1, respectively. Velocity equivalent widths this large for Si III and Si II imply the existence of high velocity dispersion moderate- (Si III) and low-ionization (Si II) gas along many paths through the Galactic halo. Measures of the Galactic damped Lyα line toward 14 QSOs permit the determination of N(H I)Lyα through the gaseous disk and halo of the Galaxy. The values of N(H I)Lyα range from 0.64 × 1020 to 3.37 × 1020 cm-2 with N(H I)Lyα| sin b| averaging (1.29 ± 0.49) × 1020 cm-2. A comparison of N(H I)Lyα with N(H I)21 cm reveals that N(H I)Lyα/N(H I)21 cm for the 10 sight lines where the value of N(H I)Lyα is not significantly affected by geocoronal emission ranges from 0.62 and 0.91. This difference is probably produced by a combination of systematic and random errors and contribution from the small angular scale structure in the H I distribution. Such structure can produce different column densities when sampling gas with an infinitesimal beam in the UV (the angular size of the QSO) compared to the much larger 21′ beam of the NRAO 43 m radio telescope. The overall strength of the Mg II λλ2796 and 2803 absorption appears to be correlated with the presence of high-velocity gas along the line to sight. Velocity-resolved Mg II absorption associated with high-velocity gas in the Magellanic Stream is detected toward eight QSOs, including PKS 0003+15, PG 0043+039, PKS 0637-75, 3C 454.3, PKS 2251+11, PG 2302+029, PKS 2340-36, and PKS 2344+09. Velocity-resolved Mg II absorption toward 15 QSOs is not accompanied by the existence of associated H I emission. Interesting objects in this category include PKS 0232-04 (l = 174.°5, b = -56.°2), which has a high-velocity cloud (HVC) at v ∼ +270 km s-1 detected in Mg II, and PG 1116+215 (l = 223.°3,b = 68.°2) with a HVC at +200 km s-1 detected in Mg II, C II, Si IV, and possibly C IV. The HVC toward PKS 0232-04 is interesting because all known H I HVCs in this general region of the sky have negative velocity rather than positive velocity. For 15 QSOs known to lie in the direction of H I HVCs, the Mg II lines have extremely strong principal absorption components, suggesting the detection of blended low- and high-velocity absorption. These lines of sight imply the detection of Mg II absorption by the high-velocity gas in HVC complexes C and A, in the outer Galaxy warp, and in the Magellanic Stream, as well as toward three smaller clouds. There are 11 QSO sight lines with very strong Mg II absorption for which there is no evidence for high-velocity H I emission. However, six of these sight lines lie near known H I HVCs. There are 38 QSOs with weak Mg II principal absorption and no known H I HVCs. These objects provide information about the H I absorption characteristics of disk and halo gas well away from H I HVCs. The sky covering factor of high-velocity Mg II is large, with 41 and 71 QSO lines of sight showing either resolved high-velocity Mg II absorption or principal absorption that is so strong that blended low- and high-velocity Mg II absorption is suggested.