# Detection of a Large Population of Ultra Diffuse Galaxies in Massive Galaxy Clusters: Abell S1063 and Abell 2744

## TL;DR

This study identifies and characterizes a large population of ultra diffuse galaxies in two massive galaxy clusters, revealing their properties, distribution, and potential origins, and establishing a relation between UDG numbers and host mass.

## Contribution

It presents the first extensive detection and analysis of UDGs in Abell S1063 and Abell 2744, including their properties and a new scaling relation with host cluster mass.

## Key findings

- Detected 87 UDGs in two galaxy clusters.
- Most UDGs have stellar masses between 10^8 and 10^9 solar masses.
- Number of UDGs scales with host mass as M^{1.05}.

## Abstract

We present the detection of a large population of ultra diffuse galaxies (UDGs) in two massive galaxy clusters, Abell S1063 at $z=0.348$ and Abell 2744 at $z=0.308$, based on F814W and F105W images in the Hubble Frontier Fields Program. We find 47 and 40 UDGs in Abell S1063 and Abell 2744, respectively. Color-magnitude diagrams of the UDGs show that they are mostly located at the faint end of the red sequence. From the comparison with simple stellar population models, we estimate their stellar mass to range from $10^8$ to $10^9 M_\odot$. Radial number density profiles of the UDGs show a turnover or a flattening in the central region at $r<100$ kpc. We estimate the total masses of the UDGs using the galaxy scaling relations. A majority of the UDGs have total masses, $M_{200} = 10^{10}$ to $10^{11}~M_\odot$, and only a few of them have total masses, $M_{200} = 10^{11}$ to $10^{12}~M_\odot$. The total number of UDGs within the virial radius is estimated to be N(UDG)$=770\pm114$ for Abell S1063, and N(UDG)$=814\pm122$ for Abell 2744. Combining these results with data in the literature, we fit the relation between the total numbers of UDGs and the masses of their host systems for $M_{200}>10^{13} M_\odot$ with a power law, N(UDG) $= M_{200}^{1.05\pm0.09}$. These results suggest that a majority of the UDGs have a dwarf galaxy origin, while only a small number of the UDGs are massive $L_*$ galaxies that failed to form a normal population of stars.