New Ionization Models and the Shocking Nitrogen Excess at z > 5

Abstract

The new era of galaxy evolution studies hearkened in by JWST has led to the discovery of z > 5 galaxies exhibiting excess nitrogen with log(N/O)~1 dex or more than expected from log(N/O) vs 12+log(O/H) trends in the local Universe. A variety of novel enrichment pathways have been presented to explain the apparent nitrogen excess, invoking a wide range of processes from very massive stars to stripped binaries to fine-tuned star-formation histories. However, understanding the excitation mechanism responsible for the observed nebular emission is necessary to accurately infer chemical abundances. As of yet, the ionization sources of these galaxies have not been thoroughly explored, with radiative shocks left out of the picture. We present a suite of homogeneous excitation models for star-forming galaxies, active galactic nuclei, and radiative shocks, with which we explore possible explanations for the apparent nitrogen excess. We propose new BPT-style diagnostics to classify galaxies at z > 5, finding that, when combined with O iii] 1660,66 and He ii 1640, N iii] 1747-54 / C iii] 1907,09 best selects shock-dominated galaxies while N iv] 1483,86 / C iii] 1907,09 best distinguishes between active black holes and star forming galaxies. From our diagnostics, we find that slow/intermediate radiative shocks (v = 75-150 km/s) are most consistent with observed UV emission line flux ratios in nitrogen-bright galaxies. Accounting for the effects of shocks can bring nitrogen estimates into better agreement with abundance patterns observed in the local Universe and may be attributable to Wolf Rayet populations actively enriching these galaxies with nitrogen and possibly driving winds responsible for these shocks.

submitted to MNRAS, 13 pages, 5 figures

References in corpus (43)

• The NumPy array: a structure for efficient numerical computation
• The Host Galaxies and Classification of Active Galactic Nuclei
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• The MAPPINGS III Library of Fast Radiative Shock Models
• PyNeb: a new tool for analyzing emission lines. I. Code description and validation of results
• The Effects of Stellar Rotation. II. A Comprehensive Set of Starburst99 Models
• CHIANTI -- an atomic database for emission lines -- Paper XVI: Version 10, further extensions
• Modelling the nebular emission from primeval to present-day star-forming galaxies
• Galaxies with Wolf-Rayet signatures in the low-redshift Universe - A survey using the Sloan Digital Sky Survey
• The SAMI Galaxy Survey: Shocks and Outflows in a normal star-forming galaxy
• Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
• The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters
• The localized chemical pollution in NGC 5253 revisited: Results from deep echelle spectrophotometry
• Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: II. Control of the \HII Region Parameters
• HST-COS Observations of AGN. II. Extended Survey of Ultraviolet Composite Spectra from 159 Active Galactic Nuclei
• Photoionization Models for the Semi-Forbidden C III] 1909 Emission in Star-Forming Galaxies
• The Sunburst Arc: Direct Lyman α escape observed in the brightest known lensed galaxy
• Far-infrared metallicity diagnostics: Application to local ultraluminous infrared galaxies
• CLASSY IV: Exploring UV diagnostics of the interstellar medium in local high-$z$ analogs at the dawn of the JWST era
• The Dependence of Theoretical Synthetic Spectra on $\alpha$-enhancement in Young, Binary Stellar Populations
• Kinematics and Optical Depth in the Green Peas: Suppressed Superwinds in Candidate LyC Emitters
• Chemical abundances of Seyfert 2 AGNs-III. Reducing the oxygen abundance discrepancy
• Very massive stars and Nitrogen emitting galaxies
• A physically-based model of the ionizing radiation from active galaxies for photoionization modeling
• Dense CO in Mrk 71-A: Superwind Suppressed in a Young Super Star Cluster
• Probing the Physics of Narrow Line Regions in Active Galaxies III: Accretion and Cocoon Shocks in the LINER NGC1052
• Large Binocular Telescope observations of new six compact star-forming galaxies with [NeV] 3426A emission
• Chemical abundances in Seyfert galaxies -- V. The discovery of shocked emission outside the AGN ionization axis
• The pressure confined wind of the massive and compact superstar cluster M82-A1
• The Te[N II]-Te[O III] temperature relation in H II regions and the reliability of strong-line methods
• Catastrophic Cooling in Superwinds: Line Emission and Non-equilibrium Ionization
• Shocked Gas in IRAS F17207-0014: ISM Collisions and Outflows
• Probing the physics of narrow-line regions of Seyfert galaxies I: The case of NGC 5427
• The connection between galactic outflows and the escape of ionizing photons
• Comparison of Theoretical Starburst Photoionisation Models for Optical Diagnostics
• Chemical abundances of Seyfert 2 AGNs IV. Composite models calculated by photoionization + shocks
• EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with $M_{\ast }=10^4-10^7{M}_{\odot }$: Weak Feedback in Low-Mass Galaxies?
• Hitting the slopes: A spectroscopic view of UV continuum slopes of galaxies reveals a reddening at z > 9.5
• Catastrophic Cooling in Superwinds. III. Non-equilibrium Photoionization
• On the universal validity of Case B recombination theory
• Constraints on the densities and temperature of Seyfert 2 NLR
• Shock fronts in the long GRB031203 host galaxy
• Dust emission from the bulk of galaxies at the Epoch of Reionization

Cited by in corpus (2)

• MAMMOTH-MOSFIRE: Environmental Effects on Galaxy Interstellar Medium at $z\sim 2$
• Extreme equivalent width-selected low-mass starbursts at $z=4-9$: insights into their role in cosmic reionization