Large binocular telescope observations of new six compact star-forming galaxies with [Ne  v ] λ3426 Å emission

Journal Article · 02 October 2021 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/stab2798 · OSTI ID:1826212

Izotov, Y. I. ; Thuan, T. X.; Guseva, N. G.

ABSTRACT We report the discovery of [Ne v] λ3426 emission, in addition to He ii λ4686 emission, in six compact star-forming galaxies. These observations considerably increase the sample of eight such galaxies discovered earlier by our group. For four of the new galaxies, the optical observations are supplemented by near-infrared spectra. All galaxies, but one, have H ii regions that are dense, with electron number densities of ∼ 300–700 cm−3. They are all characterized by high H β equivalent widths EW(H β) ∼ 190–520 Å and high O32 = [O iii] λ5007/[O ii] λ3727 ratios of 10–30, indicating young starburst ages and the presence of high ionization radiation. All are low-metallicity objects with 12 + logO/H = 7.46–7.88. The spectra of all galaxies show a low-intensity broad component of the H α line and five of six objects show Wolf–Rayet features. Comparison with photoionization models shows that pure stellar ionization radiation from massive stars is not hard enough to produce such strong [Ne v] and He ii emission in our galaxies. The [Ne v] λ3426/He ii λ4686 flux ratio of ∼1.2 in J1222+3602 is consistent with some contribution of active galactic nucleus ionizing radiation. However, in the remaining five galaxies, this ratio is considerably lower, $$\lesssim$$ 0.4. The most plausible models are likely to be non-uniform in density, where He ii and [Ne v] lines are emitted in low-density channels made by outflows and illuminated by harder ionizing radiation from radiative shocks propagating through these channels, whereas [O iii] emission originates in denser regions exposed to softer stellar ionizing sources.

• Sponsoring Organization: USDOE
• OSTI ID: 1826212
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 508; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English