EMPRESS. III. Morphology, stellar population, and dynamics of extremely metal-poor galaxies (EMPGs): Are EMPGs local analogs of high-z young galaxies?

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_e. 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 ΔV = 101 ± 32 km s^-1. This moderately large ΔV 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.