We analyze a sample of 25 [Ne
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 ≥5
- NSF-PAR ID:
- 10401692
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 945
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 127
- Size(s):
- Article No. 127
- Sponsoring Org:
- National Science Foundation
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Abstract v ] (λ 3426) emission-line galaxies at 1.4 <z < 2.3 using Hubble Space Telescope/Wide Field Camera 3 G102 and G141 grism observations from the CANDELS Lyα Emission at Reionization (CLEAR) survey. [Nev ] emission probes extremely energetic photoionization (creation potential of 97.11 eV) and is often attributed to energetic radiation from active galactic nuclei (AGNs), shocks from supernovae, or an otherwise very hard ionizing spectrum from the stellar continuum. In this work, we use [Nev ] in conjunction with other rest-frame UV/optical emission lines ([Oii ]λ λ 3726, 3729, [Neiii ]λ 3869, Hβ , [Oiii ]λ λ 4959, 5007, Hα +[Nii ]λ λ 6548, 6583, [Sii ]λ λ 6716, 6731), deep (2–7 Ms) X-ray observations (from Chandra), and mid-infrared imaging (from Spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. The majority of the [Nev ]-detected galaxies have properties consistent with ionization from AGNs. However, for our [Nev ]-selected sample, the X-ray luminosities are consistent with local (z ≲ 0.1) X-ray-selected Seyferts, but the [Nev ] luminosities are more consistent with those fromz ∼ 1 X-ray-selected QSOs. The excess [Nev ] emission requires either reduced hard X-rays or a ∼0.1 keV excess. We discuss possible origins of the apparent [Nev ] excess, which could be related to the “soft (X-ray) excess” observed in some QSOs and Seyferts and/or be a consequence of a complex/anisotropic geometry for the narrow-line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. We also consider implications for future studies of extreme high-ionization systems in the epoch of reionization (z ≳ 6) with the James Webb Space Telescope. -
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v ] mid-infrared emission detected by Spitzer, and based on Chandra X-ray imaging, it has since been argued to host either a heavily obscured AGN or a supernova remnant. Galaxy J0851+3926 was originally identified as an AGN based on its Wide-Field Infrared Survey Explorer mid-IR colors, and follow-up near-infrared spectroscopy previously revealed a hidden broad-line region, offering compelling evidence for an optically elusive AGN. Neither AGN is detected within the new NuSTAR imaging, and we derive upper limits on the hard X-ray 10–24 keV fluxes of <7.41 × 10−14and <9.40 × 10−14erg cm−2s−1for the AGNs in NGC 4178 and J0851+3926, respectively. If these nondetections are due to large absorbing columns along the line of sight, the nondetections in NGC 4178 and J0851+3926 could be explained with column densities of log(N H/cm2) > 24.2 and 24.1, respectively. The nature of the nuclear activity in NGC 4178 remains inconclusive; it is plausible that the [Nev ] traces a period of higher activity in the past, but that the AGN is relatively quiescent now. The nondetection in J0851+3926 and multiwavelength properties are consistent with the AGN being heavily obscured.
