XMP gas-rich dwarfs in nearby voids: results of BTA spectroscopy. (arXiv:2108.12065v2 [astro-ph.GA] UPDATED)

XMP gas-rich dwarfs in nearby voids: results of BTA spectroscopy. (arXiv:2108.12065v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Pustilnik_S/0/1/0/all/0/1">S. A. Pustilnik</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Egorova_E/0/1/0/all/0/1">E. S. Egorova</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Kniazev_A/0/1/0/all/0/1">A. Y. Kniazev</a> (3,4,2), <a href="http://arxiv.org/find/astro-ph/1/au:+Perepelitsyna_Y/0/1/0/all/0/1">Y. A. Perepelitsyna</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Tepliakova_A/0/1/0/all/0/1">A. L. Tepliakova</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Burenkov_A/0/1/0/all/0/1">A.N. Burenkov</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Oparin_D/0/1/0/all/0/1">D. V. Oparin</a> (1) ((1) Special Astrophysical Observatory of RAS, Russia, (2) Sternberg Astronomical Institute of Moscow State University, Russia, (3) South African Astronomical Observatory, Cape Town, South Africa, (4) Southern African Large Telescope Foundation, Cape Town, South Africa)

We present the second part of results of the on-going project of searching
for and studying eXtremely Metal-Poor (XMP, adopted as those with Z(gas) <~
Zo/30, or with 12+log(O/H) <~ 7.21~dex) very gas-rich blue dwarfs in voids.They
were first identified in course of the ‘unbiased’ study of galaxy population in
the nearby Lynx-Cancer void. These very rare and unusual galaxies seem to be
the best proxies of so-called Very Young Galaxies (VYGs) defined recently in
model simulations by Tweed et al. To date, for 16 preselected void XMP
candidates, we obtained with the SAO 6-m telescope (BTA) spectra suitable for
determination of O/H. For majority of the observed galaxies, the principal line
[OIII]4363 used for the direct classical T_e method of O/H determination, is
undetected. Therefore, to estimate O/H, we use a new ‘Strong-lines’ method by
Izotov et al. This appears the most accurate empirical O/H estimator for the
range of 12+log(O/H) < 7.4-7.5. For higher O/H objects, we use the
semi-empirical method by Izotov and Thuan with our modification accounting for
variance of the excitation parameter O32. Six of those 16 candidates are found
to be the confident XMP dwarfs. In addition, eight studied galaxies are
somewhat less metal-poor, with 12+log(O/H) = 7.24-7.33. They also can fall into
the category of VYG candidates. With account of the recently published by us
and previously known (9 prototype galaxies) XMP gas-rich void objects, the new
findings increase the number of this type galaxies to the total of 19.

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