Detection of a Large Population of Ultradiffuse Galaxies in Massive Galaxy Clusters: Abell S1063 and Abell 2744

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 ⊙ . 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 ⊙ , and only a few of them have total masses, M 200 = 10 11 to 10 12 M ⊙ . The total number of UDGs within the virial radius is estimated to be N(UDG)= 770 ± 114 for Abell S1063, and N(UDG)= 814 ± 122 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 ⊙ with a power law, N(UDG) = M 1.05±0.09 200. 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.

Intrinsic Morphology of Ultra-diffuse Galaxies

“…Indeed, the Rand r-band magnitudes/surface brightness levels only show a marginal difference. (Graham & Driver 2005), where m á ñ r e,abs ( ) and m á ñ r z e, ( ) are the mean surface brightness at z=0 and z, respectively, and the values of E(z) and K(z) are −0.36 and +0.11 for AS1063 and −0.32 and +0.09 for A2744, respectively (see Lee et al 2017), which corresponds to the surface brightness criterion of sample3, i.e., m á ñ> = r z e, 0.055 ( )…”

“…For the member UDGs in the low-density and high-density environments, they primarily populate the blue cloud and red sequence (RS) in the color-magnitude diagram, respectively (e.g., Mihos et al 2015;van der Burg et al 2016;Janssens et al 2017;Lee et al 2017;Román & Trujillo 2017aVenhola et al 2017;Spekkens & Karunakaran 2018;Rong et al 2020b); their morphologies are also distinct: the former ones are mostly irregular, while the latter ones usually have elliptical appearances (e.g., Yagi et al 2016;Leisman et al 2017;Román & Trujillo 2017a;Trujillo et al 2017;Conselice 2018;Eigenthaler et al 2018). A large fraction of UDGs in galaxy clusters exhibit unresolved nuclear star clusters (e.g., Mihos et al 2015;Yagi et al 2016;Eigenthaler et al 2018).…”

Ultra-diffuse galaxies in the Auriga simulations

“…(i) Clusters such as Coma (Koda et al 2015;Yagi et al 2016;Ruiz-Lara et al 2018), Virgo (Mihos et al 2015;Mihos et al 2017;Toloba et al 2018), Fornax (Muñoz et al 2015;Venhola et al 2017); 8 clusters in the redshift range of 0.044 < z < 0.063 (van der Burg et al 2016) and another 10 clusters with z 0.09 (Sifón et al 2018); Abell 168 (Román & Trujillo 2017a); Abell 2744 (Janssens et al 2017;Lee et al 2017); Email: shliao@nao.cas.cn Abell S1063 (Lee et al 2017); Pegasus I and Pegasus II (Shi et al 2017); and Perseus (Wittmann et al 2017).…”

“…To distinguish between the scenarios of failed L galaxies and genuine dwarfs, a useful probe are the galaxies' virial masses. Several methods have been used to determine virial masses of UDGs, for example, stellar kinematics from spectroscopy , dynamics of globular clusters van Dokkum et al 2018a), specific frequency of globular clusters Beasley & Trujillo 2016;Peng & Lim 2016;Amorisco et al 2018;Lim et al 2018;Toloba et al 2018), galaxy scaling relations (Lee et al 2017;Zaritsky 2017), HI rotation curves (Leisman et al 2017), width of HI lines (Trujillo et al 2017), and weak gravitational lensing (Sifón et al 2018). From these observations, show that one UDG in the Coma cluster, DF 44, has a virial mass of M200 ∼ 10 12 M 1 , and Toloba et al (2018) show that two UDGs in the Virgo cluster, VLSB-B and VCC615, are consistent with ∼ 10 12 M dark matter haloes.…”

Exploring the origin of ultra-diffuse galaxies in clusters from their primordial alignment

“…The UDGs in the Coma and Abell 1314 clusters show the radial alignment signals (Yagi et al 2016;Mancera Piña et al 2019), suggesting that the member UDGs in clusters may be the products of strong tidal stripping or remarkably affected by tides. However, UDGs in the other galaxy clusters, including Fornax (Venhola et al 2017;Rong et al 2019b) Lee et al 2017), show no radial alignment signals, implying that the orientations of most UDGs in clusters are not strongly affected by the environment. Yet the possible primordial alignment of cluster UDGs, which may reveal their origin and evolution, has never been studied to the present.…”