K-DRIFT: Unveiling New Imagery of the Hidden Universe

TL;DR

The paper addresses the challenge of observing low-surface-brightness (LSB) structures, which are crucial for understanding galaxy formation and dark matter but are limited by atmospheric and instrumental systematics. It presents K-DRIFT, a framework pairing an off-axis freeform three-mirror telescope with a rolling-dithering observing strategy to achieve deep, wide LSB imaging, demonstrated by the completed K-DRIFT G1 and a planned southern survey. It outlines instrument design (optics, camera, filters, focuser, mount), a detailed site and field strategy, and four scientific themes (galaxy formation, small-scale $\Lambda$CDM tests, Milky Way substructures, and CGM/environmental effects), plus legacy-data and space-based extensions. The work establishes a path to ultra-deep, wide-field LSB studies that can constrain galaxy evolution and dark matter models, including a prospective space-based mission to reach $\sim$31 mag arcsec$^{-2}$ depths across the full sky.

Abstract

Low-surface-brightness (LSB) structures play a crucial role in understanding galaxy evolution by providing significant insights into galaxy interactions, the histories of mass assembly, and the distribution of dark matter. Nevertheless, their inherently faint nature, coupled with observational difficulties such as stray light interference and variations in the sky background, has significantly impeded comprehensive studies of LSB features. The KASI Deep Rolling Imaging Fast Telescope (K-DRIFT) project aims to address these observational challenges by developing off-axis freeform three-mirror telescopes and observational strategies specifically designed for LSB imaging surveys. The first generation of the K-DRIFT (K-DRIFT G1) has been successfully completed, and the forthcoming survey, scheduled to commence shortly, is expected to yield novel insights into the LSB universe. This paper outlines the scientific motivations of the project, discusses the technical challenges encountered, highlights the innovative solutions devised, and describes the future trajectory of the K-DRIFT.

Figures (9)

• Figure 1: Comparison of the 3$\sigma$ surface brightness limit at an angular scale of $10^{\prime\prime}\times10^{\prime\prime}$ as a function of the covered area for various imaging surveys. Surface brightness depths are estimated based on the $r$ band. The diamond shape represents space-based telescopes, while the circle shape represents ground-based telescopes. The K-DRIFT survey presented in this paper is indicated by a black star, with its depth and coverage varying along the black lines depending on the specific observation strategy. This figure is a reproduced version of Figure 12 in 2023AA...671A.141M. The imaging surveys shown in the figure include the following: SDSS 2000AJ....120.1579Y, SDSS Stripe 82 2014ApJS..213...12J2016MNRAS.456.1359F, HSC Wide Survey 2018ApJ...857..104G2022PASJ...74..247A, HSC Deep Survey 2022PASJ...74..247A, Euclid Wide and Deep Survey 2022AA...657A..92E, Dragonfly Ultrawide Survey 2024ApJ...976...75S, Dragonfly Wide Field Survey 2020ApJ...894..119D, Stellar Stream Legacy Survey 2023AA...671A.141M, Stellar Tidal Streams Survey 2019hsax.conf..146M, Next Generation Fornax Survey 2018ApJ...855..142E, Next Generation Virgo Survey 2012ApJS..200....4F, MATLAS 2015MNRAS.446..120D2022AA...662A.124S, Canada-France Imaging Survey 2022AA...662A.124S, LSST/Rubin 2019ApJ...873..111I, VEGAS/VST 2021arXiv210204950I, UGC00180/GTC 2016ApJ...823..123T, HST UDF 2006AJ....132.1729B, HST XDF 2013ApJS..209....6I.
• Figure 2: Left: Optical design of K-DRIFT G1. Right: Opto-mechanical configuration with system parameters. The overall mechanical dimensions, including the camera, are $1410 \times 1150 \times 624$ mm. The diameters of the entrance pupil and the primary mirror are 300 mm and 500 mm, respectively.
• Figure 3: Comparison of the FoV of K-DRIFT G1 (solid white box) with the Andromeda galaxy and the full moon. K-DRIFT G1 can capture nearly 100 times the area of the full moon in a single exposure, enabling efficient mapping of extended LSB structures. Credit: ESA/Hubble & Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)
• Figure 4: System throughput as a function of wavelength, showing contributions from the filter transmission (dashed color-coded lines), detector QE (solid black lines), and atmospheric transmission at 1.2 airmass (dotted black lines).
• Figure 5: Telescope rendering of the K-DRIFT G1. Two identical telescopes will conduct the initial LSB imaging survey at El Sauce Observatory in Chile.