Classifying Intermediate Redshift Galaxies in SDSS: Alternative Diagnostic Diagrams

Abstract

We select a sample of 1,437 active galactic nuclei (AGN) from the catalog of the Sloan Digital Sky Survey (SDSS) galaxy properties from the Portsmouth group by detection of the high-ionization [Ne V] 3426 Å emission line. We compare the fluxes of [Ne III] 3869 Å, [O III] 5007 Å, [O II] 3726, 3728 Å, and [O I] 6300 Å to that of [Ne V]. All four lines show a strong linear correlation with [Ne V], although lines from ions with lower ionization potentials have a lower correlation coefficient. We investigate the use of two forbidden-line ratio (FLR) diagnostic diagrams that do not rely on H$\alpha$ in order to classify high redshift galaxies. These use the [Ne III]/[O II] line ratio plotted against [O III]/[O I] and [O III]/[O II] respectively. We use photo-ionization modeling to characterize the behavior of the narrow-line region in AGN and star-forming regions and test the validity of our diagnostic diagrams. We also use a luminosity cutoff of log L[OIII] [erg/s] = 42, which lowers the contamination of the AGN region by star-forming galaxies down to 10% but does not remove Green Pea and Purple Grape galaxies from the AGN region. We also investigate the OHNO diagram which uses [Ne III]/[O II] plotted against [O III]/H$\beta$. Using our new diagnostic diagrams, we are able to reliably classify AGN up to a redshift of z $\le$ 1.06, and add more than 822 new AGN to the [Ne V]-selected AGN sample.

Published February 12 2024 in ApJ, 15 pages, 10 figures

References in corpus (13)

• Evidence for TP-AGB stars in high redshift galaxies, and their effect on deriving stellar population parameters
• Galaxies with Wolf-Rayet signatures in the low-redshift Universe - A survey using the Sloan Digital Sky Survey
• Broad-line Balmer Decrements in Blue Active Galactic Nuclei
• AGN Emission Line Diagnostics and the Mass-Metallicity Relation up to Redshift z~2: the Impact of Selection Effects and Evolution
• Spitzer Uncovers Active Galactic Nuclei Missed by Optical Surveys in 7 Late-type Galaxies
• AEGIS: Demographics of X-ray and Optically Selected AGNs
• Neon and Argon optical emission lines in ionized gaseous nebulae: Implications and applications
• Constraining the AGN Contribution in a Multiwavelength Study of Seyfert Galaxies
• Kinematics and Optical Depth in the Green Peas: Suppressed Superwinds in Candidate LyC Emitters
• [Ne V] Emission in Optically Classified Starbursts
• Assessing the sources of reionisation: a spectroscopic case study of a 30$\times$ lensed galaxy at $z\sim 5$ with Lyα, CIV, MgII, and [NeIII]
• HST Emission Line Galaxies at z ~ 2: The Mystery of Neon
• Strong [OIII]λ5007 emission line compact galaxies in LAMOST DR9: Blueberries, Green Peas and Purple Grapes

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• Boosting the evolutionary picture of Cl 0024+17 and MS 0451-03: A case study at intermediate-redshift
• Star Formation Rates in [Ne V] 3426 Å Selected Active Galactic Nuclei: Evidence for a Decrease along the Main Sequence?
• Through the fog: a complementary optical galaxy classification scheme for 'intermediate' redshifts
• Extreme equivalent width-selected low-mass starbursts at $z=4-9$: insights into their role in cosmic reionization