Strongly star forming galaxies in the local Universe with nebular He iiλ4686 emission
By M. Shirazi, J. Brinchmann. 2012
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We present a sample of 2865 emission-line galaxies with strong nebular emissions in the Sloan Digital Sky Survey Data Release 7 and use this sample to investigate the origin of this line in star-forming galaxies. We show that star-forming galaxies and galaxies dominated by an active galactic nucleus form clearly separated branches in the versus diagnostic diagram and derive an empirical classification scheme which separates the two classes. We also present an analysis of the physical properties of 189 star-forming galaxies with strong emissions. These star-forming galaxies provide constraints on the hard ionizing continuum of massive stars. To make a quantitative comparison with observation, we use photoionization models and examine how different stellar population models affect the predicted emission. We confirm previous findings that the models can predict emission only for instantaneous bursts of 20 per cent solar metallicity or higher, and only for ages of ∼4–5 Myr, the period when the extreme-ultraviolet continuum is dominated by emission from Wolf–Rayet stars. We find, however, that 83 of the star-forming galaxies (40 per cent) in our sample do not have Wolf–Rayet features in their spectra despite showing strong nebular emission. We discuss possible reasons for this and possible mechanisms for the emission in these galaxies.
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/0968437a08ae11f989986d12f37e1985889bab1f
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In Astronomy and Astrophysics
Citations in the corpus
- HIGH-DENSITY CIRCUMSTELLAR INTERACTION IN THE LUMINOUS TYPE IIn SN 2010jl: THE FIRST 1100 DAYS (2013, methodology): “For the Milky Way reddening we use the extinction law by Cardelli et al. (1989) and being a star forming galaxy with WR features (Shirazi & Brinchmann 2012) we use the star burst extinction from Calzetti et al. (1994) for the host galaxy.”
- THE ORIGIN AND OPTICAL DEPTH OF IONIZING RADIATION IN THE “GREEN PEA” GALAXIES (2013, methodology): “Figure 11 shows the Shirazi & Brinchmann (2012) diagnostic for the Green Peas with He ii λ4686 detections.”
- BAT AGN Spectroscopic Survey. I. Spectral Measurements, Derived Quantities, and AGN Demographics (2017, methodology): “Finally, we also apply the [O III] λ5007/[O II] λ3727 and He II λ4686/Hβ diagnostics, defined by Shirazi & Brinchmann (2012).”
- EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION (2015, background): “…on e.g. radio galaxies: De Breuck et al. 2000), with typical FWHM of lines being ∼ 1000 km s−1; 2) Wolf-Rayet (WR) stars (many cases known in e.g. SDSS: Shirazi & Brinchmann 2012; or see Erb et al. (2010) for a higher redshift example), with typical FWHM of lines being ∼ 3000 km s−1; 3) Direct…”
- RECONCILING THE STELLAR AND NEBULAR SPECTRA OF HIGH-REDSHIFT GALAXIES (2016, background): “Massive star binaries naturally produce a harder ionizing-UV spectrum with a higher duty cycle than single star models, which can produce He II-ionizing photons only during brief intervals when very high mass Wolf-Rayet stars are present (see, e.g., Shirazi & Brinchmann 2012; Crowther et al. 2016).”
- Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, background): “…spectra of several dwarf star forming galaxies in our sample have a substantial flux of photons with energiesin xcess of 47.9 eV, similar to what is often inferred from spectroscopy of nearby blue compact dwarf galaxies (e.g., Guseva et al. 2000, Thuan & Izotov 2005, Shirazi & Brinchmann 2012).”