Calibrating galaxy redshifts using absorption by the surrounding intergalactic medium
Calibrating galaxy redshifts using absorption by the surrounding intergalactic medium
复制标题
利用周围星系间介质的吸收来校准星系红移
DOI：
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发表时间：
2010
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通讯作者：
G. Rudie
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作者：
Olivera Rakic;J. Schaye;C. Steidel;G. Rudie
恒星形成星系的静止帧紫外光谱线系统地偏离星系的系统红移，可能是因为大规模的外流。利用背景天体光谱中星系周围的平均H i Lyα吸收轮廓，如果星系相对于背景天体的视线是随机取向的，那么星系周围的平均H i Lyα吸收轮廓必须相对于真实的星系红移是对称的这一事实，我们校准了由静止坐标系紫外线测量的星系红移.我们使用15个明亮的类星体在z = 2.5-3和600多个前景星系的光谱红移在z = 1.9-2.5。所有的星系都在2百万秒差距内，从视线到背景类星体。我们发现Lyα发射和ISM吸收红移分别需要Δ ν_Lyα =-295 ^（+35）_（-35）和Δ ν_ISM = 145^（+70）_（-35）km s^（-1）的系统位移。假设一个高斯分布，我们把可能的随机红移偏移的上限设为1σ，Lyα <220 km s^（-1），ISM红移<420 km s^（-1）。对于已经获得近红外光谱的星系的一小部分（<10%），我们可以将我们的结果与基于静止坐标系光学星云发射线的直接测量结果进行比较，我们证实这些测量结果标记了系统红移。虽然我们的ΔvISM与直接测量结果一致，但我们的Δv_Lyα要小得多。然而，当我们将我们的方法应用于其特征在于略有不同的选择效应的近红外子样本时，最佳拟合速度偏移与直接测量一致。这证实了我们的方法的有效性，并意味着没有一个单一的数字适当地描述了整个人口的星系，线偏移取决于星系光谱形态的观察。这种方法提供了精确的红移校准，并将使研究的环星系周围的物质，静止框架光学观测是不可用的。
Rest-frame UV spectral lines of star-forming galaxies are systematically offset from the galaxies' systemic redshifts, probably because of large-scale outflows. We calibrate galaxy redshifts measured from rest-frame UV lines by utilizing the fact that the mean H i Lyα absorption profiles around the galaxies, as seen in spectra of background objects, must be symmetric with respect to the true galaxy redshifts if the galaxies are oriented randomly with respect to the lines of sight to the background objects. We use 15 bright QSOs at z≈2.5–3 and more than 600 foreground galaxies with spectroscopic redshifts at z≈1.9–2.5. All galaxies are within 2 Mpc proper from the lines of sight to the background QSOs. We find that Lyα emission and ISM absorption redshifts require systematic shifts of ∆ν_Lyα = -295^(+35)_(-35) and ∆ν_ISM = 145^(+70)_(-35) km s^(-1), respectively. Assuming a Gaussian distribution, we put 1σ upper limits on possible random redshift offsets of <220 km s^(-1) for Lyα and <420 km s^(-1) for ISM redshifts. For the small subset (<10 per cent) of galaxies for which near-IR spectra have been obtained, we can compare our results to direct measurements based on rest-frame optical, nebular emission lines, which we confirm to mark the systemic redshifts. While our ΔvISM agrees with the direct measurements, our Δv_Lyα is significantly smaller. However, when we apply our method to the near-IR subsample which is characterized by slightly different selection effects, the best-fitting velocity offset comes into agreement with the direct measurement. This confirms the validity of our approach, and implies that no single number appropriately describes the whole population of galaxies, in line with the observation that the line offset depends on galaxy spectral morphology. This method provides accurate redshift calibrations and will enable studies of circumgalactic matter around galaxies for which rest-frame optical observations are not available.