The KBSS–KCWI survey: the connection between extended Ly α haloes and galaxy azimuthal angle at z ∼ 2–3
The KBSS–KCWI survey: the connection between extended Ly α haloes and galaxy azimuthal angle at z ∼ 2–3
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DOI：
10.1093/mnras/stab2383
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发表时间：
2021-04
影响因子：
4.8
通讯作者：
Yuguang Chen;C. Steidel;D. Erb;D. Law;R. Trainor;N. Reddy;A. Shapley;A. Pahl;A. Strom;N. Lamb;Zhihui Li;G. Rudie
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作者：
Yuguang Chen;C. Steidel;D. Erb;D. Law;R. Trainor;N. Reddy;A. Shapley;A. Pahl;A. Strom;N. Lamb;Zhihui Li;G. Rudie
在Keck重子结构调查(KBSS)中，我们首次使用Keck宇宙网络成像仪(KCWI)对z=2-3星系周围的运动学分辨的、空间扩展的$\rMLy\α$发射进行了统计分析。我们的样本包括59个恒星形成星系(Zmed=2.29)，包括典型的KCW积分时间为∼5小时的子集，以及来自哈勃太空望远镜和/或自适应光学辅助积分场光谱的现有成像数据。高分辨率图像被用来评估在≲30适当的kpc的银心距离内弥散的Lyα辐射相对于恒星连续体的方位依赖关系。我们引入了柱面投影2D谱(CP2D)，它作为星系周围撞击参数的函数，映射了特定方位角范围内的平均谱轮廓。所有星系的平均CP2D谱都显示出流出气体共振散射的明显特征。我们将单个星系的CP2D光谱叠加在相对于其主轴的方位角范围内。沿星系主轴扩展的$rM Ly\α$发射在统计上是不可区分的，剩余的不对称性为积分$\rM Ly\α$发射的≤2%(∼2σ)。这一对称性表明，在30kpc以内，Lyα散射介质以各方向的外流为主。同时，我们发现在发射相对较弱的星系中，Lyα发射的蓝移分量沿星系短轴方向略强。我们推测，只有当逃逸分数较低时，这种弱的方向依赖关系才能被分辨出来。这些发现突显了在使用$\rMLy\α$辐射传输模型进行模拟时进行类似分析的必要性。
We present the first statistical analysis of kinematically resolved, spatially extended $\rm Ly\alpha$ emission around z = 2–3 galaxies in the Keck Baryonic Structure Survey (KBSS) using the Keck Cosmic Web Imager (KCWI). Our sample of 59 star-forming galaxies (zmed = 2.29) comprises the subset with typical KCWI integration times of ∼5 h and with existing imaging data from the Hubble Space Telescope and/or adaptive optics-assisted integral field spectroscopy. The high-resolution images were used to evaluate the azimuthal dependence of the diffuse $\rm Ly\alpha$ emission with respect to the stellar continuum within projected galactocentric distances of ≲30 proper kpc. We introduce cylindrically projected 2D spectra (CP2D) that map the averaged $\rm Ly\alpha$ spectral profile over a specified range of azimuthal angle, as a function of impact parameter around galaxies. The averaged CP2D spectrum of all galaxies shows clear signatures of $\rm Ly\alpha$ resonant scattering by outflowing gas. We stacked the CP2D spectra of individual galaxies over ranges of azimuthal angle with respect to their major axes. The extended $\rm Ly\alpha$ emission along the galaxy principal axes is statistically indistinguishable, with residual asymmetry of ≤2 per cent (∼2σ) of the integrated $\rm Ly\alpha$ emission. The symmetry implies that the $\rm Ly\alpha$ scattering medium is dominated by outflows in all directions within 30 kpc. Meanwhile, we find that the blueshifted component of $\rm Ly\alpha$ emission is marginally stronger along galaxy minor axes for galaxies with relatively weak $\rm Ly\alpha$ emission. We speculate that this weak directional dependence of $\rm Ly\alpha$ emission becomes discernible only when the $\rm Ly\alpha$ escape fraction is low. These discoveries highlight the need for similar analyses in simulations with $\rm Ly\alpha$ radiative transfer modelling.