Shadows in the Dark: Low-Surface-Brightness Galaxies Discovered in the Dark Energy Survey (2006.04294v2)

Abstract: We present a catalog of 23,790 extended low-surface-brightness galaxies (LSBGs) identified in $\sim 5000 \deg^2$ from the first three years of imaging data from the Dark Energy Survey (DES). Based on a single-component S\'ersic model fit, we define extended LSBGs as galaxies with $g$-band effective radii $R_{eff}(g) > 2.5''$ and mean surface brightness $\bar{\mu}{eff}(g) > 24.2 \,mag .arcsec^{-2}$. We find that the distribution of LSBGs is strongly bimodal in $(g-r)$ vs.\ $(g-i$) color space. We divide our sample into red ($g-i \geq 0.60$) and blue ($g-i<0.60$) galaxies and study the properties of the two populations. Redder LSBGs are more clustered than their blue counterparts and are correlated with the distribution of nearby ($z < 0.10$) bright galaxies. Red LSBGs constitute $\sim 33\%$ of our LSBG sample, and $\sim 30\%$ of these are located within 1 deg of low-redshift galaxy groups and clusters (compared to $\sim 8\%$ of the blue LSBGs). For nine of the most prominent galaxy groups and clusters, we calculate the physical properties of associated LSBGs assuming a redshift derived from the host system. In these systems, we identify 41 objects that can be classified as ultra-diffuse galaxies, defined as LSBGs with projected physical effective radii $R{eff} > 1.5 \,kpc$ and central surface brighthness $\mu_0(g) > 24.0\, mag \,arcsec^{-2}$. The wide-area sample of LSBGs in DES can be used to test the role of environment on models of LSBG formation and evolution.

Overview of "Shadows in the Dark: Low-Surface-Brightness Galaxies Discovered in the Dark Energy Survey"

The paper "Shadows in the Dark: Low-Surface-Brightness Galaxies Discovered in the Dark Energy Survey" presents a comprehensive catalog of low-surface-brightness galaxies (LSBGs) derived from the Dark Energy Survey (DES). This catalog reveals 23,790 LSBGs over a 5000 square degree area of the southern Galactic cap, making it the largest LSBG catalog of its kind.

Key Findings

1. LSBG Identification and Characterization: LSBGs were defined based on a single-component Sersic model fit with $g$-band effective radii $R_{(g)} > 2.5''$ and mean surface brightness $(g) > 24.2$ mag. The catalog was assembled through a multi-step process involving classical selection criteria, machine learning, and visual inspections to ensure high-purity detections.
2. Photometric and Structural Properties: The paper shows a bimodal distribution of LSBGs in color space, segregating the sample into red and blue subpopulations. Blue LSBGs generally have higher mean surface brightness compared to their red counterparts.
3. Distribution and Clustering: The spatial distribution analysis shows that red LSBGs are more clustered than blue ones. The paper applies the two-point correlation function to quantify this clustering, finding that red LSBGs exhibit higher clustering amplitude at scales less than three degrees. The results align with previous understandings that red LSBGs are often associated with dense environments, such as clusters and groups, indicating their likely role as satellite galaxies in massive halos.
4. Association with Galaxy Clusters: The clustering of LSBGs often corresponds with known galaxy clusters and groups. Specifically, 32 peaks in LSBG density were matched with Abell clusters, suggesting a strong environmental effect on the distribution and possibly on the formation of LSBGs.
5. Ultra-Diffuse Galaxies (UDGs): The catalog also identifies a subset of LSBGs that qualify as ultra-diffuse galaxies, characterized by a large effective radius and very low central surface brightness. These UDGs appear to be a continuation of the LSBG population in the size-luminosity domain.

Implications and Future Directions

The discovery and cataloging of such a large number of LSBGs have significant implications for our understanding of galaxy formation and evolution in different environments. The paper supports theories that suggest environmental factors like dark matter halos and cluster membership play a crucial role in the formation and evolution of LSBGs.

From a cosmological perspective, LSBGs provide a critical test for models of galaxy formation that link properties of galaxies to the dark matter halos they reside in. This catalog provides a valuable resource for further studies, including potential weak lensing analyses to constrain the mass distribution associated with these diffuse systems.

The paper also lays the groundwork for future surveys, such as those planned with the Vera C. Rubin Observatory, which will further explore the low-surface-brightness universe. Automating the detection of LSBGs with machine learning, as outlined in the paper, will be vital for handling the unprecedented data volume from such projects.

In summary, this research enriches our understanding of the role of LSBGs in the cosmic structure and provides a crucial dataset for refining models of galaxy evolution across diverse environments.