Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths

By A. Feltre, S. Charlot, Julia Gutkin. 2015

204 citations recorded by the source corpus.

In the context of observations of the rest-frame ultraviolet and optical emission from distant galaxies, we explore the emission-line properties of photoionization models of active and inactive galaxies. Our aim is to identify new line-ratio diagnostics to discriminate between gas photoionization by active galactic nuclei (AGN) and star formation. We use a standard photoionization code to compute the emission from AGN narrow-line regions and compare this with calculations of the nebular emission from star-forming galaxies achieved using the same code. We confirm the appropriateness of widely used optical spectral diagnostics of nuclear activity versus star formation and explore new diagnostics at ultraviolet wavelengths. We find that combinations of a collisionally excited metal line or line multiplet, such as CIV 1548,1551, OIII]1661,1666, NIII]1750, [SiIII]1883+[SiIII]1892 and [CIII]1907+CIII]1909, with the HeII 1640 recombination line are individually good discriminants of the nature of the ionizing source. Diagrams involving at least 3 of these lines allow an even more stringent distinction between active and inactive galaxies, as well as valuable constraints on interstellar gas parameters and the shape of the ionizing radiation. Several line ratios involving Ne-based emission lines, such as [NeIV]2424, [NeIII]3343 and [NeV]3426, are also good diagnostics of nuclear activity. Our results provide a comprehensive framework to identify the sources of photoionization and physical conditions of the ionized gas from the ultraviolet and optical nebular emission from galaxies. This will be particularly useful to interpret observations of high-redshift galaxies with future facilities, such as the James Webb Space Telescope and extremely large ground-based telescopes.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/302960f2316d3f9046d91facafe812d6734d4458

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Citations in the corpus

Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, methodology): “1 of MNRAS 000, 1–20 (2016) Feltre et al. 2016 for a graphical summary of the ionization potentials of the different species considered in Fig.”
SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs (2016, background): “However, it should be noted that more recent models have found that star forming galaxies can be characterised by line ratios extending beyond such demarcation (Feltre et al. 2016).”
Lyα and C iii] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems? (2016, background): “Observational efforts are now underway to establish how common such hard ionizing spectra are among reionization-era galaxies and to constrain the powering mechanism (AGN or metal poor stars) of the nebular CIV emission (e.g., Feltre et al. 2016).”
Active galactic nuclei: what’s in a name? (2017, methodology): “Finally, we are generally reliant on optical spectroscopy to provide con- firmation of a source as an AGN and to determine its redshift, while the presence of narrow emission lines in the spectra of galaxies and their ratios are indicative of the presence of an AGN (e.g. Feltre et al. 2016).”
The GLASS-JWST Early Release Science Program. I. Survey Design and Release Plans (2022, methodology): “In addition to metallicity and star formation conditions, the detection of these lines may aid in identifying high-z active galactic nuclei candidates, using diagnostic diagrams based on He II, C IV, and C III], and Lyα (Feltre et al. 2016; Nakajima et al. 2018; Laporte et al. 2017a).”