K-DRIFT Science Theme: Galaxies in the Faint Universe

TL;DR

K-DRIFT introduces a dedicated ultra-deep, wide-field optical survey to map low-surface-brightness features around nearby galaxies, addressing the challenge of reaching depths around $29{-}30$ mag arcsec$^{-2}$. By employing an off-axis freeform two-telescope design and rolling-dithering, it delivers uniform sensitivity over ${\sim}11.5$ deg$^2$ and targets a core sample of ~400 galaxies to study tidal structures, stellar halos, and dwarf populations. The paper outlines a broad science program spanning streams, tails, shells, UDGs, DMDGs, void galaxies, XUV disks, and ML-based detection, and emphasizes synergies with HI data and IFU spectroscopy to illuminate merger histories and DM-related galaxy evolution. The project seeks to constrain small-scale $\Lambda$CDM predictions, quantify merger-induced processes, and establish ML-driven pipelines for robust LSB discovery across diverse environments.

Abstract

Low-surface-brightness (LSB) structures serve as evidence of the intricate mass assembly of galaxies, and dedicatedly studying them promises to give us profound insights into the evolutionary history of galaxies. Furthermore, delving into the properties of star formation (SF) in the LSB regime can broaden our understanding of SF activity in regions characterized by low surface gas density, thereby shedding light on fundamental cosmic processes. However, systematic uncertainties may hamper the exploration of the LSB universe by limiting detectable SB levels. Indeed, despite dedicated advancements in telescope and observing techniques over decades, achieving ultra-deep photometric depths in optical wavelengths remains a formidable challenge. To overcome this challenge and explore the LSB universe that we have yet to see, we have been developing a novel telescope called K-DRIFT. This paper outlines the telescope's specification and describes various LSB features we aim for, explicitly focusing on nearby individual galaxies. To further advance the capabilities of the K-DRIFT survey, focused on LSB detection, we present several feasible research topics that utilize other survey data together and discuss the role of LSB observation in understanding the evolution of galaxies.

Figures (14)

• Figure 1: Example observation of the Andromeda Galaxy (M31) obtained with K-DRIFT G1. This single image was captured using the $L$ filter with an exposure time of 300 sec. No data reduction or post-processing was applied, but a false-color (cubehelix) scheme was used for visual clarity.
• Figure 2: Coverage of a single observation sequence using the rolling dithering method. The color represents the integration time. Since the dithering offset is up to $\sim$40$^\prime$, the effective area with the longest integration time is $\sim$11.5 deg$^2$. The camera's position angle rotating by 160$^\circ$ is also shown in the upper left corner.
• Figure 3: Stellar structures of merging galaxies adopted from the GRT (top) and NewHorizon2 (bottom) simulations. The SB limits of each panel are denoted in the upper left corner. The color-coded pixels in the right panel represent the pixels above 27 mag arcsec$^{-2}$, which is the same as in the left panel.
• Figure 4: Stellar stream structure associated with NGC 5907 2022PASP..134h4101B. Bright sources are masked, while color-coded pixels highlight the disk of NGC 5907 brighter than 27 mag arcsec$^{-2}$. A prominent, curved stellar stream extends to the east of the galaxy.
• Figure 5: Tidal tail structures within the Antennae Galaxies, which are in the process of colliding with each other. The FoV of the image is $\sim$$16^\prime\times12^\prime$. Credit: KPNO/NOIRLab/NSF/AURA/Bob and Bill Twardy/Adam Block