Subaru/FOCAS IFU revealed the metallicity gradient of a local extremely metal-poor galaxy

Abstract

We present the first measurement of the metallicity gradient in extremely metal-poor galaxies (EMPGs). With Subaru/Faint Object Camera And Spectrograph (FOCAS) Integral Field Unit (IFU), we have observed a nearby, low-mass EMPG, HSC J1631+4426, whose oxygen abundance and stellar mass are known to be 12 + log (O/H) = 6.9 and log10(M∗/M⊙) = 5.8, respectively. The measured metallicity gradient is -0.36 ± 0.04 dex kpc-1 corresponding to -0.049 ± 0.006 dex R-1e for the continuum effective radius of Re = 0.14 kpc. Our observation has successfully demonstrated that threedimensional spectroscopy with 8m-class telescopes is powerful enough to reveal the metallicity distribution in local EMPGs, providing precious information on the baryon cycle in local analogs of primordial galaxies in the early Universe.