首次結合調適光學與重力透鏡之時間延遲研究宇宙學

Abstract

精準的測量哈伯常數是對於檢驗目前宇宙標準模型和指引可能出現的新物理非常重要的一環。藉由哈伯望遠鏡的影像，每個擁有時間延遲效應的強重力透鏡都可以利用哈伯望遠鏡來決定哈伯常數到一個標準差為7%的精確度。然而，因哈伯望遠鏡有使用年限，找尋替代方法來觀測重力透鏡是可預期的。調適性光學影像可以提供比哈伯望遠鏡更佳的解析度，但卻因為大氣的擾動而有未知的點擴散函數問題。為了讓調適性光學影像可以拿來研究宇宙學，我們發展出一套方法可以在重力透鏡影像中直接利用被重力所彎折的類星體重建出點擴散函數。在利用兩個已內建好宇宙學參數的模擬重力透鏡影像來測試此方法後，可以證實即使一開始不知道內建的參數，我們依然可以精確的利用模擬的影像來預測出重要的內建宇宙學參數 (時間延遲距離，外在剪力，質量分佈斜率，和總愛因斯坦半徑) 到一個標準差之內 。我們把這個方法應用在凱克天文台所觀測到的重力透鏡RXJ1131-1231調適性影像上發現，除了高簡併性因素造成無法精確的決定星系及其衛星的個別愛因斯坦半徑外，其他的重要參數都跟利用哈伯影像分析出來的結果在一個標準差之內。更重要的是，在都使用質量分布為幕次模型的前提下，利用解析度每像素為0.04角秒的調適性影像所得到的標準差比用每像素為0.05角秒的哈伯影像的標準差還小大約50%。

Accurate and precise measurements of the Hubble constant are critical for testing our current standard cosmological model and revealing possibly new physics. With Hubble Space Telescope (HST) imaging, each strong gravita- tional lens with time delays can allow one to determine the Hubble constant with an uncertainty of ~7%. However, since HST will not last forever, alter- native approaches for obtaining follow-up imagings of strong lenses are de- sirable. Adaptive-optics (AO) imaging can provide higher angular resolution than HST imaging but has an unknown point spread function (PSF) due to atmospheric distortion. To make AO imaging useful for time-delay-lens cos- mography, we develop a method to extract the unknown PSF directly from the imaging of the lensed quasar by iteratively reconstructing the PSF. In a blind test with two mock data sets with different PSFs, we are able to recover the important cosmological parameters (time-delay distance, external shear, mass profile slope, and total Einstein radius) within 1-� uncertainty. Our analysis of the Keck AO image of the strong lens system RXJ 1131�1231 shows that except for the highly degenerate Einstein radius of the main galaxy, other important parameters for cosmography agree with those based on HST imag- ing and modeling within 1-� uncertainty. Most importantly, the constraint on the model time-delay distance by using AO imaging with 0.0400 resolution is tighter by ~50% than the constraint of time-delay distance by using HST imaging with 0.0500 when a power-law mass distribution for the lens system is adopted.