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1. A Catalog of 71 Coronal Line Galaxies in MaNGA: [Ne v] Is an Effective AGN Tracer

   https://doi.org/10.3847/1538-4357/acb772  

   Negus, James ; Comerford, Julia M. ; Sánchez, Francisco Müller ; Revalski, Mitchell ; Riffel, Rogemar A. ; Bundy, Kevin ; Nevin, Rebecca ; Rembold, Sandro B. ( March 2023 , The Astrophysical Journal)

   Despite the importance of active galactic nuclei (AGNs) in galaxy evolution, accurate AGN identification is often challenging, as common AGN diagnostics can be confused by contributions from star formation and other effects (e.g., Baldwin–Phillips–Terlevich diagrams). However, one promising avenue for identifying AGNs is “coronal emission lines” (“CLs”), which are highly ionized species of gas with ionization potentials ≥100 eV. These CLs may serve as excellent signatures for the strong ionizing continuum of AGNs. To determine if CLs are in fact strong AGN tracers, we assemble and analyze the largest catalog of optical CL galaxies using the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) catalog. We detect CL emission in 71 MaNGA galaxies, out of the 10,010 unique galaxies from the final MaNGA catalog, with ≥5σconfidence. In our sample, we measure [Nev]λ3347,λ3427, [Fevii]λ3586,λ3760,λ6086, and [Fex]λ6374 emission and crossmatch the CL galaxies with a catalog of AGNs that were confirmed with broad-line, X-ray, IR, and radio observations. We find that [Nev] emission, compared to [Fevii] and [Fex] emission, is best at identifying high-luminosity AGNs. Moreover, we find that the CL galaxies with the least dust extinction yield the most iron CL detections. We posit that the bulk of the iron CLs are destroyed by dust grains in the galaxies with the highest [Oiii] luminosities in our sample, and that AGNs in the galaxies with low [Oiii] luminosities are possibly too weak to be detected using traditional techniques.

    

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2. Using [Ne v]/[Ne iii] to Understand the Nature of Extreme-ionization Galaxies

   https://doi.org/10.3847/1538-4357/acde55  

   Cleri, Nikko J. ; Olivier, Grace M. ; Hutchison, Taylor A. ; Papovich, Casey ; Trump, Jonathan R. ; Amorín, Ricardo O. ; Backhaus, Bren E. ; Berg, Danielle A. ; Fernández, Vital ; Finkelstein, Steven L. ; et al ( July 2023 , The Astrophysical Journal)

   Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 eV photons: the energy needed to ionize helium into He²⁺fully and emit Heiirecombination lines. Spectroscopic studies of EIGs can probe exotic stellar populations or accretion onto intermediate-mass black holes (∼10²–10⁵M_⊙), which are the possibly key contributors to the reionization of the Universe. To facilitate the use of EIGs as probes of high-ionization systems, we focus on ratios constructed from several rest-frame UV/optical emission lines: [Oiii]λ5008, Hβ, [Neiii]λ3870, [Oii]λλ3727, 3729, and [Nev]λ3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62, and 97.12 eV, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use the ratios of these lines ([Nev]/[Neiii] ≡ Ne53, [Oiii]/Hβ, and [Neiii]/[Oii]), which are nearby in wavelength, mitigating the effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed fromCloudythat use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and JWST of galaxies with strong high-ionization emission lines atz∼ 0,z∼ 2, and 5 <z< 8.5. We show that the Ne53 ratio can separate galaxies with ionization from “normal” stellar populations from those with active galactic nuclei and even “exotic” Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.

    

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3. CLEAR: Emission-line Ratios at Cosmic High Noon

   https://doi.org/10.3847/1538-4357/ac3919  

   Backhaus, Bren E. ; Trump, Jonathan R. ; Cleri, Nikko J. ; Simons, Raymond ; Momcheva, Ivelina ; Papovich, Casey ; Estrada-Carpenter, Vicente ; Finkelstein, Steven L. ; Matharu, Jasleen ; Ji, Zhiyuan ; et al ( February 2022 , The Astrophysical Journal)

   We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies atz∼ 1.5 in the CANDELS LyαEmission at Reionization survey. We compare [Oiii]/Hβversus [Sii]/(Hα+ [Nii]) as an “unVO87” diagram for 461 galaxies and [Oiii]/Hβversus [Neiii]/[Oii] as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Nev] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures atz> 1. The OHNO diagram does effectively separate X-ray AGN and [Nev]-emitting galaxies from the rest of the population. We find that the [Oiii]/Hβline ratios are significantly anticorrelated with stellar mass and significantly correlated with$\log (L_{\mathrm{H}\beta })$, while [Sii]/(Hα+ [Nii]) is significantly anticorrelated with$\log (L_{\mathrm{H}\beta })$. Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [Oiii]/Hβversus [Neiii]/[Oii] will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope.

    

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4. The Physical Conditions of Emission-line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

   https://doi.org/10.3847/1538-4357/acba8a  

   Trump, Jonathan R. ; Arrabal Haro, Pablo ; Simons, Raymond C. ; Backhaus, Bren E. ; Amorín, Ricardo O. ; Dickinson, Mark ; Fernández, Vital ; Papovich, Casey ; Nicholls, David C. ; Kewley, Lisa J. ; et al ( March 2023 , The Astrophysical Journal)

   We present rest-frame optical emission-line flux ratio measurements for fivez> 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliablerelativeflux calibration of emission lines that are closely separated in wavelength, despite the uncertainabsolutespectrophotometry of the current version of the reductions. Compared toz∼ 3 galaxies in the literature, thez> 5 galaxies have similar [Oiii]λ5008/Hβratios, similar [Oiii]λ4364/Hγratios, and higher (∼0.5 dex) [NeIII]λ3870/[OII]λ3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [NeIII]λ3870/[OII]λ3728, [Oiii]λ4364/Hγ, and [Oiii]λ5008/Hβemission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization ($\log (Q)\simeq 8-9$, units of cm s⁻¹), low metallicity (Z/Z_⊙≲ 0.2), and very high pressure ($\log (P/k)\simeq 8-9$, units of cm⁻³). The combination of [Oiii]λ4364/Hγand [Oiii]λ(4960 + 5008)/Hβline ratios indicate very high electron temperatures of$4.1<\log (T_e/\mathrm{K})<4.4$, further implying metallicities ofZ/Z_⊙≲ 0.2 with the application of low-redshift calibrations for “T_e-based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies at cosmic dawn.

    

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5. An Excess of Active Galactic Nuclei Triggered by Galaxy Mergers in MaNGA Galaxies of Stellar Mass ∼10 11 M ⊙

   https://doi.org/10.3847/1538-4357/ad1a15  

   Comerford, Julia M. ; Nevin, Rebecca ; Negus, James ; Barrows, R. Scott ; Eracleous, Michael ; Müller-Sánchez, Francisco ; Roy, Namrata ; Stemo, Aaron ; Storchi-Bergmann, Thaisa ; Wylezalek, Dominika ( February 2024 , The Astrophysical Journal)

   To facilitate new studies of galaxy-merger-driven fueling of active galactic nuclei (AGNs), we present a catalog of 387 AGNs that we have identified in the final population of over 10,000z< 0.15 galaxies observed by the Sloan Digital Sky Survey-IV (SDSS-IV) integral field spectroscopy survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). We selected the AGNs via mid-infrared Wide-field Infrared Survey Explorer colors, Swift/Burst Alert Telescope ultra-hard X-ray detections, NRAO Very Large Array Sky Survey and Faint Images of the Radio Sky at Twenty centimeters radio observations, and broad emission lines in SDSS spectra. By combining the MaNGA AGN catalog with a new SDSS catalog of galaxy mergers that were identified based on a suite of hydrodynamical simulations of merging galaxies, we study the link between galaxy mergers and nuclear activity for AGNs above a limiting bolometric luminosity of 10^44.4erg s⁻¹. We find an excess of AGNs in mergers, relative to nonmergers, for galaxies with stellar mass ∼10¹¹M_⊙, where the AGN excess is somewhat stronger in major mergers than in minor mergers. Further, when we combine minor and major mergers and sort by merger stage, we find that the highest AGN excess occurs in post-coalescence mergers in the highest-mass galaxies. However, we find no evidence of a correlation between galaxy mergers and AGN luminosity or accretion rate. In summary, while galaxy mergers overall do appear to trigger or enhance AGN activity more than nonmergers, they do not seem to induce higher levels of accretion or higher luminosities. We provide the MaNGA AGN Catalog and the MaNGA Galaxy Merger Catalog for the community here.

    

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