發現強重力透鏡的新方法：成對光譜搜尋法及其在 DESI DR1 上的實作

Abstract

本研究提出一種搜尋強重力透鏡系統的新方法：成對光譜搜尋。利用光譜巡天資料，本研究對天球上位置彼此接近的光譜進行成對分析，並從暗能量光譜儀（Dark Energy Spectroscopic Instrument, DESI）第一版資料釋出（Data Release 1）中篩選出 26,621 筆光譜，逐一對其進行人工目視檢查。

排除不良數據後，本研究進一步人工檢視了這些光譜所對應之暗能量光譜儀遺產影像巡天（DESI Legacy Imaging Surveys）第十版資料釋出（Data Release 10）中的 11,848 張影像，並識別出 2046 個傳統型強重力透鏡候選系統，其中有 1906 個為全新的發現。這是迄今為止在光譜資料中所搜尋出最大規模的強重力透鏡候選系統樣本集。

除了傳統型強重力透鏡候選系統之外，本研究還發現一類新的系統，稱之為「酒窩透鏡」（dimple lenses）。這類系統以前景的低質量星系作為透鏡，相對於背景星系，其角尺寸較小、亮度也更為昏暗。理論預測，這些低質量前景星系將在背景星系的表面亮度分布上產生細微的凹陷結構。本研究共發現 318 個此類「酒窩透鏡」候選系統，推測其可能代表矮星系透鏡系統。此類系統將令後續觀測研究得以有機會探討其質量分布、恆星質量－暈質量關係，以及在 Mₕₐₗₒ ≲ 10¹³ M⊙ 範圍內的暈質量函數。透過這些方法，這類系統有潛力成為檢驗冷暗物質模型的新途徑。

總結兩者，本研究共回報了 2164 個新發現的強重力透鏡候選系統。本研究顯示成對光譜搜尋法在強重力透鏡搜尋上的強大潛力，並提供了一條可與影像搜尋方法及單一光譜搜尋法互補的研究途徑。

We present a new method to search for strong gravitational lensing systems by pairing spectra that are close together on the sky in a spectroscopic survey. We visually inspect 26,621 spectra in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 that are selected in this way.

We further inspect the 11,848 images corresponding to these spectra in the DESI Legacy Imaging Surveys Data Release 10, and obtain 2046 conventional strong gravitational lens candidates, of which 1906 are new. This constitutes the largest sample of lens candidates identified to date in spectroscopic data.

Besides the conventional candidates, we identify a new class of systems that we term “dimple lenses.” These systems have a low-mass foreground galaxy as a lens, typically smaller in angular extent and fainter compared with the lensed background source galaxy, producing subtle surface brightness indentations in the latter. We report the discovery of 318 of these “dimple lens” candidates. We suspect that these represent dwarf galaxy lensing. With follow-up observations, they could offer a new avenue to test the cold dark matter model by probing their mass profiles, stellar mass–halo mass relation, and halo mass function for Mₕₐₗₒ ≲ 10¹³ M⊙.

Thus, in total, we report 2164 new lens candidates. Our method demonstrates the power of pairwise spectroscopic analysis and provides a pathway complementary to imaging-based and single-spectrum lens searches.