EMPRESS. III. Morphology, Stellar Population, and Dynamics of Extremely Metal-poor Galaxies (EMPGs): Are EMPGs Local Analogs of High-z Young Galaxies?*

Abstract

We present the morphology and stellar population of 27 extremely metal-poor galaxies (EMPGs) at z ∼ 0 with metallicities of 0.01–0.1 Z ⊙ . We conduct multicomponent surface brightness (SB) profile fitting for the deep Subaru/Hyper Suprime-Cam i -band images of the EMPGs with the Galfit software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of log ( M * / M ⊙ ) = 6.0 have a median Sérsic index of n = 1.1 and a median effective radius of r e = 200 pc, suggesting that typical EMPGs have a very compact disk. We compare the EMPGs with z ∼ 6 galaxies and local galaxies on the size–mass ( r e – M * ) diagram, and identify that the majority of the EMPGs have an r e – M * relation similar to z ∼ 0 star-forming galaxies rather than z ∼ 6 galaxies. Not every EMPG is a local analog of high- z young galaxies in the r e – M * relation. A spectrum of one pair of EMPG and tail, so far available, indicates that the tail is dynamically related to the EMPG with a median velocity difference of Δ V = 101 ± 32 km s −1 . This moderately large Δ V cannot be explained by the dynamics of the tail, but likely by the infall on the tail. For the first time, we may identify the metal-poor star-forming system just now infalling into the tail.