Very Bright, Very Blue, and Very Red: JWST CAPERS Analysis of Highly Luminous Galaxies with Extreme Ultraviolet Slopes at <i>z</i> = 10
Callum T. Donnan, Mark Dickinson, Anthony J. Taylor, Pablo Arrabal Haro, Steven L. Finkelstein, T M Stanton, Intae Jung, Casey Papovich, Hollis B. Akins, Anton M. Koekemoer, D J McLeod, Lorenzo Napolitano, R. Amorín, R Begley, D. Burgarella, Adam C. Carnall, Caitlin M. Casey, Antonello Calabrò, Fergus Cullen, J. S. Dunlop, Richard S. Ellis, Vital Fernández, Mauro Giavalisco, Michaela Hirschmann, Weida Hu, G. D. Illingworth, Jeyhan S. Kartaltepe, Dale D. Kocevski, Vasily Kokorev, Ho-Hin Leung, Ray A. Lucas, Alexa M. Morales, R. J. McLure, L. Pentericci, Pablo G. Pérez‐González, Rachel S. Somerville, Struan Stevenson, Jonathan R. Trump, L. Y. Aaron Yung, Jorge A. Zavala
Abstract
Abstract We present JWST/NIRSpec PRISM observations of three luminous ( M UV < −20) galaxies at z ∼ 10 observed with the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS) Cycle 3 program. These galaxies exhibit extreme UV slopes compared to typical galaxies at z = 10. Of the three sources, two of them are a close pair (0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 22) of blue galaxies at z = 9.800 ± 0.003 and z = 9.808 ± 0.002 with UV slopes of β = −2.87 ± 0.15 and β = −2.46 ± 0.10, respectively, selected from PRIMER COSMOS NIRCam imaging. We perform spectrophotometric modeling of the galaxies, which suggests extremely young stellar ages and a lack of dust attenuation. For the bluest galaxy, its UV slope also suggests significant Lyman continuum escape. In contrast, the third source (selected from CEERS NIRCam imaging) at z = 9.942 ± 0.002 exhibits a red UV slope with β = −1.51 ± 0.08. We rule out the possibility of a strong nebular continuum due to the lack of a Balmer jump and find no evidence to support the presence of an active galactic nucleus continuum due to a lack of strong UV emission lines and no broad component to H γ or H β . Instead, it is most likely that the red UV slope is due to dust reddening ( A V ≃ 0.9) implying a significant level of dust-obscured star formation only ≃480 Myr after the Big Bang. Under standard assumptions for dust attenuation, EGS-25297 would be the most intrinsically UV-luminous galaxy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">UV</mml:mi> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">corr</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≃</mml:mo> <mml:mo>−</mml:mo> <mml:mn>22</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) yet spectroscopically confirmed at z ∼ 10. This work highlights that luminous galaxies at z ≳ 10 have a diversity of dust properties and that spectroscopy of these galaxies is essential to fully understand star formation at z ≳ 10.