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 $z\sim 0$ with metallicities of 0.01--0.1 Z${}_{\odot }$. We conduct multi-component surface brightness (SB) profile fitting for the deep Subaru/HSC $i$-band images of the EMPGs with the {\sc Galfit} software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of $\log (M_{\ast }/{\mathrm{M}}_{\odot })=6.0$ have a median S{é}rsic index of $n=1.1$ and a median effective radius of $r_{\mathrm{e}}=200$ pc, suggesting that typical EMPGs have very compact disk. We compare the EMPGs with $z\sim 6$ galaxies and local galaxies on the size-mass ($r_{\mathrm{e}}$-$M_{\ast }$) diagram, and identify that the majority of the EMPGs have a $r_{\mathrm{e}}$-$M_{\ast }$ relation similar to $z\sim 0$ star-forming galaxies rather than $z\sim 6$ galaxies. Not every EMPG is a local analog of high-$z$ young galaxies in the $r_{\mathrm{e}}$-$M_{\ast }$ 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 $\hat{I}”V=101\pm 32$ km s${}^{-1}$. This moderately-large $\hat{I}”V$ 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.

ApJ in Press