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Nature and Nurture? Comparing Lyα Detections in UV-bright and Fainter [O iii]+Hβ Emitters at z ∼ 8 with Keck/MOSFIRE

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jats:titleAbstract</jats:title> jats:pThe 100% detection rate of Lyjats:italicα</jats:italic> emission in a sample of four luminous jats:italicz</jats:italic> ∼ 8 galaxies with red Spitzer/IRAC colors suggests objects with unusual ionizing capabilities that created early ionized bubbles in a neutral era. Whether such bubbles reflect enhanced ionizing properties (nature) or an overdense environment (nurture), however, remains unclear. Here we aim to distinguish between these hypotheses via a search for Lyjats:italicα</jats:italic> emission in five fainter galaxies drawn from the CANDELS-GOODS fields using a similar IRAC excess and UV magnitudes that should reflect reduced clustering effects. Using Keck/MOSFIRE we tentatively detect >4jats:italicσ</jats:italic> line emission in only two targets at redshifts jats:italicz</jats:italic> jats:subLyjats:italicα</jats:italic> </jats:sub> = 7.1081 and 7.9622 with rest-frame EWs of 16–17 Å, ∼1.5× weaker compared to their brighter counterparts. Thus, we find a reduced rate for Lyjats:italicα</jats:italic> emission of jats:inline-formula jats:tex-math

</jats:tex-math> <mml:math xmlns:mml="" overflow="scroll"> mml:msubsup mml:mrow mml:mn0.40</mml:mn> </mml:mrow> mml:mrow mml:mo−</mml:mo> mml:mn0.25</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn0.30</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="" xlink:href="apjacc798ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> compared to jats:inline-formula jats:tex-math

</jats:tex-math> <mml:math xmlns:mml="" overflow="scroll"> mml:msubsup mml:mrow mml:mn1.00</mml:mn> </mml:mrow> mml:mrow mml:mo−</mml:mo> mml:mn0.44</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn0.00</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="" xlink:href="apjacc798ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> for more luminous examples. The lower rate agrees with predictions from simulations of a mostly neutral intergalactic medium and an intrinsic EWjats:sub0,Lyjats:italicα</jats:italic> </jats:sub> distribution for jats:italicz</jats:italic> ∼ 6 galaxies. However, even with an extreme EWjats:sub0,Lyjats:italicα</jats:italic> </jats:sub> model, it is challenging to match the detection rate for the luminous objects. Spectral energy distribution fitting of our fainter sample indicates young and star-forming systems, albeit with less extreme star formation rates and ionization parameters compared to their luminous counterparts. The enhanced Lyjats:italicα</jats:italic> rate in luminous galaxies is thus likely a byproduct of both extreme ionizing properties as well as environmental effects. Further studies with JWST may be required to resolve the physical nature of this puzzling population.</jats:p>



5101 Astronomical Sciences, 51 Physical Sciences

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American Astronomical Society