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arXiv · 1909.09212

RELICS: Spectroscopy of gravitationally-lensed $z\simeq 2$ reionization-era analogs and implications for CIII] detections at $z>6$

Ramesh Mainali·Daniel P Stark·Mengtao Tang·Jacopo Chevallard·Stéphane Charlot·Keren Sharon·Dan Coe·Brett Salmon·Larry D. Bradley·Traci L. Johnson·Brenda Frye·Roberto J. Avila·Sara Ogaz·Adi Zitrin·Maruša Bradač·Brian C. Lemaux·Guillaume Mahler·Rachel Paterno-Mahler·Victoria Strait·Felipe Andrade-Santos
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Abstract

Recent observations have revealed the presence of strong CIII] emission (EW$_{\rm{CIII]}}>20$ \r{A}) in $z>6$ galaxies, the origin of which remains unclear. In an effort to understand the nature of these line emitters, we have initiated a survey targeting CIII] emission in gravitationally-lensed reionization era analogs identified in HST imaging of clusters from the RELICS survey. Here we report initial results on four galaxies selected to have low stellar masses (2-8$\times$10$^7$ M$_\odot$) and J$_{125}$-band flux excesses indicative of intense [OIII]+H$\beta$ emission (EW$_{\rm{[OIII]+H\beta}}$=500-2000 \r{A}), similar to what has been observed at $z>6$. We detect CIII] emission in three of the four sources, with the CIII] EW reaching values seen in the reionization era (EW$_{\rm{CIII]}}\simeq 17-22$ \r{A}) in the two sources with the strongest optical line emission (EW$_{\rm{[OIII]+H\beta}}\simeq 2000$ \r{A}). We have obtained a Magellan/FIRE near-infrared spectrum of the strongest CIII] emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense CIII] and optical line emission for extremely young (2-3 Myr) and metal poor (0.06-0.08 Z$_\odot$) stellar populations, as would be expected after a substantial upturn in the SFR of a low mass galaxy. The sources in this survey are among the first for which CIII] has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to $z>6$ with current facilities, using CIII] to measure redshifts of objects with IRAC excesses indicating EW$_{\rm{[OIII]+H\beta}}\simeq 2000$ \r{A}, providing a method of spectroscopic confirmation independent of Ly$\alpha$.

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Ramesh Mainali, Daniel P Stark, Mengtao Tang, Jacopo Chevallard, Stéphane Charlot, Keren Sharon, Dan Coe, Brett Salmon, Larry D. Bradley, Traci L. Johnson, Brenda Frye, Roberto J. Avila, Sara Ogaz, Adi Zitrin, Maruša Bradač, Brian C. Lemaux, Guillaume Mahler, Rachel Paterno-Mahler, Victoria Strait, Felipe Andrade-Santos. 2019-09-19. RELICS: Spectroscopy of gravitationally-lensed $z\simeq 2$ reionization-era analogs and implications for CIII] detections at $z>6$. https://doi.org/10.1093/mnras%2Fstaa751

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