Lessons on the high-z Universe from local Laboratories: Extreme Environments in Blueberry Galaxies

Yu Rong, Huan Yang, Hong-xin Zhang, Thomas H. Puzia, Igor V. Chilingarian, Paul Eigenthaler, Sangeeta Malhotra, James E. Rhoads, Junxian Wang, Yasna Ordens-briceno, Evelyn Johnston

Published 2018-06-26Version 1

A population of so-called "blueberry" dwarf galaxies with extremely blue colors, low-metallicities, and enormous ionization ratios, has recently been found by \cite{Yang17}. As a pilot study of these blueberries, we investigate two new blueberry candidates, RGG\,B and RGG\,5, which have Hubble Space Telescope high-resolution images.~We find that RGG\,B and RGG\,5 are likely to be merging dwarf galaxies; RGG\,B may have a close merging companion, and RGG\,5 presents shell-like outskirts.~Yet the current evidence still cannot exclude the possibility that RGG~B is just disturbed by in-situ star formation through, e.g., outflows, rather than undergoing a merger.~All of the blueberries, including RGG\,B and RGG\,5, are located close to the theoretical maximum-starburst-line in the BPT diagram, have very high ionization parameters, and relatively low hardness ionizing radiation fields, exhibit nitrogen overabundances, and show extremely red mid-IR colors, and reside in the so-called "ULIRGs/LINERs/Obscured AGN" region.~Their specific star formation rates (sSFR) range among the most extreme and compare with those of extreme starbursts at high redshifts.~The blueberry galaxies may not harbor AGN, which may be due to their very early phases of the galaxy merging process.