莱曼-α参比样品：I. Markarian 259的调查大纲和初步结果
The Lyman-alpha Reference Sample: I. Survey outline and first results for Markarian 259
摘要：
莱曼α参考样本（英语：Lyman alpha reference sample，LARS）是哈勃太空望远镜（HST）的一个项目，提供了一个本地宇宙实验室星系的样本，以研究氢的莱曼α（Lyman alpha，Lya）线的可见度和强度的天体物理学。本文概述了调查，其选择功能和HST成像观测。样品选自GALEX+SDSS目录中z=0.028-0.19处，以便允许在HST/ACS的日盲通道（SBC）中用长通滤波器的组合捕获Lya。此外，LARS还利用了Halpha和Hbeta窄波段成像，以及ACS和WFC 3的U、B、i宽带成像。为了研究产生大量Lya光子的星系，我们要求Halpha等效宽度> 100 nm。14个星系的样本覆盖远紫外（FUV）光度与高z Lya发射体和莱曼布雷克星系（LBG）重叠。我们提出了用于获得Lya图像的减少步骤，包括我们的LARS提取软件（LaXs），该软件利用逐像素光谱合成拟合来减去Lya处的连续体。我们证明，使用SBC长通滤波器显着增加的信号噪声相比，在SBC的标称Lya滤波器。为了证明这一点，我们给出了Mrk 259的结果。这个不规则星系显示出扩展但强烈不对称的Lya辐射。HST/COS的光谱显示中性ISM和不对称Lya剖面中的适度流出。辐射转移建模能够再现Lya线轮廓，确认流出的存在。积分测光法提供的Lya光度为1.3E42 erg/s，等效宽度W（Lya）= 45 μ m，FUV绝对星等为-19.2。因此，在高z Lya和LBG调查中可以检测到Mrk 259。总Lya逃逸分数为12%，类似于在z>4处观察到的。（缩短）
英文摘要：
The Lyman-alpha reference sample (LARS) is a program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the astrophysics of the visibility and strength of the Lyman-alpha (Lya) line of hydrogen. This article presents an overview of the survey, its selection function and HST imaging observations. The sample was selected from the GALEX+SDSS catalogue at z=0.028-0.19, in order to allow Lya to be captured with combinations of long pass filters in the Solar Blind Channel (SBC) of HST/ACS. In addition, LARS utilises Halpha and Hbeta narrow, and U, B, i broad-band imaging with ACS and WFC3. In order to study galaxies in which large numbers of Lya photons are produced we demanded an Halpha equivalent width > 100Å. The sample of 14 galaxies covers far UV (FUV) luminosities that overlaps with those of high-z Lya emitters and Lyman Break Galaxies (LBGs). We present the reduction steps used to obtain the Lya images, including our LARS eXtraction software (LaXs) which utilises pixel-by-pixel spectral synthesis fitting to subtract the continuum at Lya. We demonstrate that the use of SBC long pass filters dramatically increase the signal to noise compared to the nominal Lya filter in SBC. To exemplify, we present results for Mrk 259. This irregular galaxy shows extended but strongly asymmetric Lya emission. Spectroscopy from HST/COS show a moderate outflow in the neutral ISM and an asymmetric Lya profile. Radiative transfer modeling is able to reproduce the Lya line profile, confirming the presence of an outflow. The integrated photometry provides a Lya luminosity of 1.3E42 erg/s an equivalent width W(Lya) =45Å and a FUV absolute magnitude -19.2. Mrk 259 would hence be detectable in high-z Lya and LBG surveys. The total Lya escape fraction is 12%, similar to that observed at z>4. (shortened)
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