THE Lyα REFERENCE SAMPLE. I. SURVEY OUTLINE AND FIRST RESULTS FOR MARKARIAN 259
THE Lyα REFERENCE SAMPLE. I. SURVEY OUTLINE AND FIRST RESULTS FOR MARKARIAN 259
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DOI：
10.1088/0004-637x/797/1/11
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发表时间：
2014-09
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通讯作者：
G. Östlin;M. Hayes;F. Duval;A. Sandberg;T. Rivera-Thorsen;T. Marquart;T. Marquart;I. Orlitová;I. Orlitová;A. Adamo;J. Melinder;L. Guaita;H. Atek;J. Cannon;P. Gruyters;E. C. Herenz;D. Kunth;P. Laursen;J. Mas-Hesse;G. Micheva;G. Micheva;H. Otí-Floranes;S. Pardy;S. Pardy;M. Roth;D. Schaerer;A. Verhamme
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作者：
G. Östlin;M. Hayes;F. Duval;A. Sandberg;T. Rivera-Thorsen;T. Marquart;T. Marquart;I. Orlitová;I. Orlitová;A. Adamo;J. Melinder;L. Guaita;H. Atek;J. Cannon;P. Gruyters;E. C. Herenz;D. Kunth;P. Laursen;J. Mas-Hesse;G. Micheva;G. Micheva;H. Otí-Floranes;S. Pardy;S. Pardy;M. Roth;D. Schaerer;A. Verhamme
Lyα 参考样本 (LARS) 是哈勃太空望远镜 (HST) 的一项重要计划，提供本地宇宙实验室星系样本，用于研究中性氢 Lyα 线的可见度和强度的详细天体物理学。 Lyα 是用于表征高红移 (z) 星系的主要谱线。本文概述了该调查、其选择功能和 HST 成像观测。样本是从 z = 0.028–0.19 的 GALEX+Sloan 数字巡天目录中选取的，以便能够使用 HST 上的高级巡天相机 (ACS) 的日盲通道 (SBC) 中的长通滤光片组合来捕获 Lyα。此外，LARS 利用 ACS 和广角相机 3 (WFC3) 进行 Hα 和 Hβ 窄带以及 u、b、i 宽带成像。为了研究产生大量 Lyα 光子（无论它们是否逃逸）的星系，我们要求 Hα 等效宽度 W(Hα) ⩾100 Å。 14 个星系的最终样本涵盖了远紫外（FUV，λ ∼ 1500 Å）光度，与高 z Lyα 发射体 (LAE) 和莱曼断裂星系 (LBG) 的光度重叠，使 LARS 成为有效的比较样本。我们提出了用于获取 Lyα 图像的简化步骤，包括我们的 LARS eXtraction 软件 (LaXs)，该软件利用能量分布的逐像素光谱合成拟合来确定和减去 Lyα 处的连续体。我们证明，与 SBC 中可用的标称 Lyα 滤波器相比，使用 SBC 长通滤波器组合可将信噪比提高一个数量级。为了举例说明 LARS 的科学潜力，我们还展示了单个星系 Mrk 259（LARS #1）的一些初步结果。这个不规则星系显示出明亮且延伸的（表明共振散射）但强烈不对称的 Lyα 发射。以最亮的紫外结为中心的 HST 上的宇宙起源摄谱仪的光谱显示，中性星际介质中存在适度的流出（通过低电离级吸收特征探测），并且 Lyα 发射具有不对称轮廓。辐射传输模型能够重现 Lyα 线剖面的基本特征并确认流出的存在。通过积分光度测量，我们测量到 Lyα 光度为 LLyα=1.3 × 1042 erg s−1，等效宽度 W(Lyα) = 45 Å 和 FUV 绝对星等 MFUV = −19.2 (AB)。因此，Mrk 259 在高 z Lyα 和 LBG 巡天中可以被检测到。总 Lyα 逃逸分数为 12%。该数字高于低 z 平均值，但与 z > 4 时的数字相似，表明 LARS 为高 z 星系研究提供了有效的比较样本。
The Lyα Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Lyαline of neutral hydrogen. Lyα is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028–0.19, in order to allow Lyα to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes Hα and Hβ narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Lyα photons are produced (whether or not they escape), we demanded an Hα equivalent width W(Hα) ⩾100 Å. The final sample of 14 galaxies covers far-UV (FUV, λ ∼ 1500 Å) luminosities that overlap with those of high-z Lyα emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Lyα images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Lyα. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Lyα filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Lyα emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Lyα emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Lyα line profile and confirms the presence of an outflow. From the integrated photometry we measure an Lyα luminosity of LLyα=1.3 × 1042 erg s−1 an equivalent width W(Lyα) = 45 Å and an FUV absolute magnitude MFUV = −19.2 (AB). Mrk 259 would hence be detectable in high-z Lyα and LBG surveys. The total Lyα escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies.