The MOSDEF Survey: Optical AGN Diagnostics at z~2.3

Abstract

We present results from the MOSFIRE Deep Evolution Field (MOSDEF) survey on rest-frame optical AGN identification and completeness at z~2.3. With our sample of 50 galaxies and 10 X-ray and IR-selected AGN with measured H-beta, [OIII], H-alpha, and [NII] emission lines, we investigate the location of AGN in the BPT, MEx (mass-excitation), and CEx (color-excitation) diagrams. We find that the BPT diagram works well to identify AGN at z~2.3 and that the z~0 AGN/star-forming galaxy classifications do not need to shift substantially at z~2.3 to robustly separate these populations. However, the MEx diagram fails to identify all of the AGN identified in the BPT diagram, and the CEx diagram is substantially contaminated at high redshift. We further show that AGN samples selected using the BPT diagram have selection biases in terms of both host stellar mass and stellar population, in that AGN in low mass and/or high specific star formation rate galaxies are difficult to identify using the BPT diagram. These selection biases become increasingly severe at high redshift, such that optically-selected AGN samples at high redshift will necessarily be incomplete. We also find that the gas in the narrow-line region appears to be more enriched than gas in the host galaxy for at least some MOSDEF AGN. However, AGN at z~2 are generally less enriched than local AGN with the same host stellar mass.

21 pages, 11 figures, updated to match ApJ accepted version

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• Nebular Emission Line Ratios in z~2-3 Star-Forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio
• The MOSDEF Survey: the Variation of the Dust Attenuation Curve with Metallicity
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• Closing in on the sources of cosmic reionization: first results from the GLASS-JWST program
• ZFIRE: A KECK/MOSFIRE Spectroscopic Survey of Galaxies in Rich Environments at z~2
• The Grism Lens-Amplified Survey from Space (GLASS) X. Sub-kpc resolution gas-phase metallicity maps at cosmic noon behind the Hubble Frontier Fields cluster MACS1149.6+2223
• Early results from GLASS-JWST. IV: Spatially resolved metallicity in a low-mass $z\sim 3$ galaxy with NIRISS
• The MOSDEF Survey: Metallicity Dependence of the PAH Emission at High Redshift and Implications for 24 micron-inferred IR Luminosities and Star Formation Rates at z~2
• JWST/NIRSpec Measurements of the Relationships Between Nebular Emission-line Ratios and Stellar Mass at z~3-6
• The mass-metallicity relation at z~1-2 and its dependence on star formation rate
• Metallicity in Quasar Broad Line Regions at Redshift $\sim$ 6
• The MOSDEF Survey: Environmental dependence of the gas-phase metallicity of galaxies at $1.4\le z\le 2.6$
• The average dust attenuation curve at z~1.3 based on HST grism surveys
• First Census of Gas-phase Metallicity Gradients of Star-forming Galaxies in Overdense Environments at Cosmic Noon
• IR SED and Dust Masses of Sub-solar Metallicity Galaxies at z~2.3
• Stellar populations and star formation histories of the most extreme [OIII] emitters at $z=1.3-3.7$
• Evidence for gas-phase metal deficiency in massive protocluster galaxies at z~2.2
• The MOSDEF Survey: An Improved Voronoi Binning Technique on Spatially Resolved Stellar Populations at z~2
• The MOSDEF-LRIS Survey: Detection of Inflowing Gas Towards Three Star-forming Galaxies at z ~ 2
• The MOSDEF Survey: The Dependence of H$\alpha$-to-UV SFR Ratios on SFR and Size at $z\sim 2$
• A Spatially-Resolved Survey of Distant Quasar Host Galaxies: II. Photoionization and Kinematics of the ISM
• The MOSDEF Survey: Calibrating the relationship between H$\alpha$ star-formation rate and radio continuum luminosity at $1.4<z<2.6$
• Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators
• Gas-Phase metallicity for the Seyfert galaxy NGC 7130
• The MOSDEF Survey: Probing Resolved Stellar Populations at $z\sim 2$ Using a New Bayesian-defined Morphology Metric Called Patchiness
• Does the lockstep growth between black holes and bulges create their mass relation?