SMILES: Potentially Higher Ionizing Photon Production Efficiency in Overdense Regions
Yongda Zhu, Stacey Alberts, Jianwei Lyu, Jane Morrison, G. H. Rieke, Yang Sun, Jakob M. Helton, Zhiyuan Ji, Rachana Bhatawdekar, Nina Bonaventura, Andrew J. Bunker, Xiaojing Lin, Marcia Rieke, Pierluigi Rinaldi, Irene Shivaei, Christopher N. A. Willmer, Junyu Zhang
Abstract
Abstract The topology of reionization and the environments where galaxies efficiently produce ionizing photons are key open questions. For the first time, we investigate the trend between ionizing photon production efficiency, ξ ion , and galaxy overdensity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>δ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> . We analyze the ionizing properties of 79 galaxies between 1.0 < z < 5.2 using JWST NIRSpec medium-resolution spectra from the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES) program. Among these, 67 galaxies have H α coverage, spanning 1.0 < z < 3.1. The galaxy overdensity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>δ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> , is measured using the JADES photometric catalog, which covers the SMILES footprint. For the subset with H α coverage, we find that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">ion</mml:mi> </mml:mrow> </mml:msub> </mml:math> is positively correlated with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>δ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> , with a slope of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.9</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.46</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.46</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . Additionally, the mean ξ ion for galaxies in overdense regions ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>δ</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>></mml:mo> <mml:mn>0.1</mml:mn> </mml:math> ) is 2.43 times that of galaxies in lower density regions ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>δ</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo><</mml:mo> <mml:mn>0.1</mml:mn> </mml:math> ). This strong trend is found to be independent of redshift evolution. Furthermore, our results confirm the robust correlations between ξ ion and the rest-frame equivalent widths of the [O iii ] or H α emission lines. Our results suggest that galaxies in high-density regions are efficient producers of ionizing photons.