Hubble Space Telescope Paα and 1.9 Micron Imaging of Sagittarius A West
Hubble Space Telescope Paα and 1.9 Micron Imaging of Sagittarius A West
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哈勃太空望远镜 Paα 和人马座 A West 的 1.9 微米成像
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发表时间：
2003
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影响因子：
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通讯作者：
F. Yusef
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作者：
N. Scoville;S. Stolovy;M. Rieke;M. Christopher;F. Yusef
本文给出了Hubble Space Telescope/NICMOS在0.2 ″分辨率下（Nyquist采样于中心19 ′）银河系中心以非热射电源Sgr A* 为中心的70′′（α）× 90′′（δ）区域的H I Paα发射线图像。大部分的辐射来自中央秒差距的微旋区的电离气体。在26个恒星源中也观测到了Paα辐射，推测这些恒星是具有质量损失风的早期型恒星。新的数据揭示了小涡旋电离气体中显著的小尺度结构（≤1′′ ~ 1.2 × 1017 cm）;低表面亮度发射特征也是首次被发现。利用观测到的Paα辐射与6厘米射电连续辐射的比值，导出了电离气体在中央秒差距上的消光图。AV从20到50等不等，中值AV = 31.1等，与早期对恒星源的估计非常一致。使用H92α重组线数据独立得出的消光值与6 cm连续谱得出的消光值非常一致。在IRS 16星团的区域内，有一个很宽的消光极小区，向东北-西南方向延伸约30'，包括Paα和射电连续谱的峰值通量区。沿着电离气体的外围沿着可以看到消光的大幅增加，特别是在西臂的方向，这表明电离气体部分地被电离区域外部分子云中的尘埃吸收;然而，H II不可能完全在分子云的后面，因为吸收会大得多。Sgr A ~* 40'半径范围内的最小莱曼连续谱发射率为3.9 × 10 ~（50）s ~（-1）或LLyC ~* 2.7 × 10 ~（60）L ~（-1），其中20'半径范围内的发射率为50%。电离气体中的小尺度非线性结构的自由热膨胀时间仅为3000年;来自热发射线恒星的磁场或质量损失风可能包含电离细丝。（在Paα中还发现了八颗新的发射线星。对于电离气体和恒星连续体，发射的质心（消光校正）保持在从2'到40'的半径的±1'内。这提供了进一步的证据，证明Sgr A*（假定的中心黑洞）确实位于或非常接近（≤0.04秒差距或1.2 × 1017厘米）银河系核心恒星分布的中心，并且可能是银河系的动力学中心。1.9 μm的表面亮度向内增加到0.″9半径，并在接近Sgr A* 时表现出降低或趋于平稳，可能表明中心恒星分布的核心半径或晚型恒星在中心黑洞附近因恒星碰撞而耗尽。
We present Hubble Space Telescope/NICMOS images at 0.″2 resolution (Nyquist-sampled in the central 19') of the H I Paα emission line in a 70′′(α) × 90′′(δ) region of the Galactic center centered on the nonthermal radio source Sgr A*. The majority of the emission arises from ionized gas in the minispiral in the central parsec. Paα emission is also seen from 26 stellar sources, presumably early-type stars with mass-loss winds. The new data reveal significant small-scale structure (≤1′′ ~ 1.2 × 1017 cm) in the ionized gas of the minispiral; low surface brightness emission features are also seen for the first time. The ratio of observed Paα emission to 6 cm radio continuum emission is used to derive an extinction map for the ionized gas over the central parsec. AV varies from 20 to 50 mag with a median value of AV = 31.1 mag, in excellent agreement with earlier estimates derived for the stellar sources. Extinctions, independently derived using H92α recombination-line data, were in excellent agreement with those derived from the 6 cm continuum. A broad minimum in the extinction extends ~30' northeast-southwest over the area of the IRS 16 cluster, including the area of peak flux in Paα and radio continuum. Large increases in extinction are seen along the periphery of the ionized gas, particularly in the direction of the western arm, suggesting that the ionized gas is partially extincted by dust in the molecular clouds at the outside of the ionized region; however, the H II cannot be entirely behind the molecular clouds since the extinctions would then be much greater. The minimum Lyman continuum emission rate within 40' radius of Sgr A* is 3.9 × 1050 s-1 or LLyC ≃ 2.7 × 106 L☉, half of this within 20' radius. The small-scale, filamentary structures in the ionized gas have a free thermal expansion time of only ~3000 yr; either magnetic fields or mass-loss winds from the hot emission line stars may contain the ionized filaments. (Eight new emission-line stars were also detected in Paα.) For both the ionized gas and stellar continuum, the centroids of the emission (corrected for extinction) remain within ~±1' from a radius of 2' out to 40'. This provides further evidence that Sgr A* (the putative central black hole) is indeed at or extremely close (≤0.04 pc or 1.2 × 1017 cm) to the center of the Galactic nucleus stellar distribution and presumably the dynamical center of the Galaxy. The 1.9 μm surface brightness increases inwards to 0.″9 radius and exhibits a decrease or leveling off closer to Sgr A*, possibly indicating the core radius of the central stellar distribution or depletion of the late-type stars by stellar collisions near the central black hole.