LBT observations of compact star-forming galaxies with extremely high [O iii]/[O ii] flux ratios: He i emission-line ratios as diagnostics of Lyman continuum leakage

Izotov, Y. I.; Thuan, T. X.; Гусева, Н. Г.

doi:10.1093/mnras/stx1629

Cited by 71 publications

(82 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…16 Fig. 15; in practice, data are available only for a few candidate LyC leakers (Jaskot & Oey 2013;Izotov et al 2017) and an AGN (Dors et al 2014). The benchmark ionization-bounded models appear to overlap with the data in this diagram, as do density-bounded models, eventually combined with an AGN or radiative-shock component.…”

Section: Agn and Radiative Shocksmentioning

confidence: 87%

“…However, while the WR phase of the model with Z = 0.002 hardly reaches the high observed He λ4686/Hβ ≈ 0.01 around EW(Hβ) ≈ 200 Å (Fig. 13d), none of the reference SSP models can account for the extreme He λ4686/Hβ ≈ 0.02 of galaxies with EW(Hβ) ≈ 500 Å in the Izotov et al (2017) sample (Figs 13b, 13d and 13f). Increasing the ionization parameter from log U = −2 to −1 (grey curves) significantly boosts EW(He λ1640) and He λ4686/Hβ in Fig.…”

Section: Stellar Populationsmentioning

confidence: 95%

“…As mentioned in Section 2.2 above, this leakage is generally thought to occur either through holes carved into the neutral ISM by extreme galactic outflows or through density-bounded (i.e. optically thin to LyC photons) (Jaskot & Oey 2013;Nakajima et al 2016;Vanzella et al 2016;Izotov et al 2017;Nanayakkara et al 2019). Among these studies, Izotov et al (2017) caution that the [O ]λ5007/[O ]λ3727 ratio alone is not a certain indicator of LyC leakage, as it depends also on other parameters, such as the ionization parameter, the hardness of ionizing radiation and metallicity.…”

Section: Lyc Leakersmentioning

confidence: 99%

See 2 more Smart Citations

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

Plat

Charlot

Bruzual³

et al. 2019

Monthly Notices of the Royal Astronomical Society

117

133

View full text Add to dashboard Cite

We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionizationbounded and density-bounded H regions, active-galactic-nucleus (AGN) narrow-line regions and radiative shocks computed all using the same physically-consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous exploration of more spectral diagnostics than typically available at once for individual subsamples. We confirm that current single-and binary-star population synthesis models do not produce hard-enough radiation to account for the high-ionization emission of the most metal-poor galaxies. Introducing either an AGN or radiative-shock component brings models into agreement with observations. A published model including X-ray binaries is an attractive alternative to reproduce the observed rise in He λ4686/Hβ ratio with decreasing oxygen abundance in metal-poor star-forming galaxies, but not the high observed He λ4686/Hβ ratios of galaxies with large EW(Hβ). A source of harder ionizing radiation appears to be required in these extreme objects, such as an AGN or radiative-shock component, perhaps linked to an initial-mass-function bias toward massive stars at low metallicity. This would also account for the surprisingly high [O ]/[O ] ratios of confirmed LyC leakers relative to ionization-bounded models. We find no simple by-eye diagnostic of the nature of ionizing sources and the escape of LyC photon, which require proper simultaneous fits of several lines to be discriminated against. galactic nuclei (AGN), arising from gas accretion onto primordial black holes; radiative shocks, induced by large-scale gas flows; and the leakage of Lyman-continuum (LyC) photons through a porous interstellar medium (ISM), contributing to reionization (see, e.g., the review by Stark 2016). In waiting for advent of the James Webb Space Telescope (JWST), which will enable deep rest-frame ultraviolet and optical emission-line spectroscopy of galaxies into the reionization era at redshifts z ∼ 10-15, more nearby metal-poor galaxies approaching the properties of primeval galaxies offer a useful laboratory in which to test our ability to interpret emission-line spectra.

show abstract

Section: Agn and Radiative Shocksmentioning

confidence: 87%

Section: Stellar Populationsmentioning

confidence: 95%

Section: Lyc Leakersmentioning

confidence: 99%

See 1 more Smart Citation

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

Plat

Charlot

Bruzual³

et al. 2019

Monthly Notices of the Royal Astronomical Society

117

133

View full text Add to dashboard Cite

show abstract

“…3 by an open triangle the location of the compact SFG J0159+0751 with a M⋆/Lg ratio far below the model predictions. This SFG, with an oxygen abundance 12+logO/H = 7.55, is characterised by a very high [O iii]λ5007/[O ii]λ3727 flux ratio of 39 and an EW(Hβ) = 347Å, indicative of a very young starburst (Izotov, Thuan & Guseva 2017). However, subtracting the nebular line emission would put J0159+0751 in the region allowed by models (shown by an upward arrow in Fig.…”

Section: Mass-to-luminosity Ratiomentioning

confidence: 96%

J0811+4730: the most metal-poor star-forming dwarf galaxy known

Izotov

Thuan

Гусева

et al. 2017

Monthly Notices of the Royal Astronomical Society

Self Cite

114

131

View full text Add to dashboard Cite

We report the discovery of the most metal-poor dwarf star-forming galaxy (SFG) known to date, J0811+4730. This galaxy, at a redshift z=0.04444, has a Sloan Digital Sky Survey (SDSS) g-band absolute magnitude M g = −15.41 mag. It was selected by inspecting the spectroscopic data base in the Data Release 13 (DR13) of the SDSS. LBT/MODS spectroscopic observations reveal its oxygen abundance to be 12 + log O/H = 6.98 ± 0.02, the lowest ever observed for a SFG. J0811+4730 strongly deviates from the main-sequence defined by SFGs in the emission-line diagnostic diagrams and the metallicity -luminosity diagram. These differences are caused mainly by the extremely low oxygen abundance in J0811+4730, which is ∼ 10 times lower than that in main-sequence SFGs with similar luminosities. By fitting the spectral energy distributions of the SDSS and LBT spectra, we derive a stellar mass of M ⋆ = 10 6.24 − 10 6.29 M ⊙ (statistical uncertainties only), and we find that a considerable fraction of the galaxy stellar mass was formed during the most recent burst of star formation.

show abstract

“…Verhamme et al 2015Verhamme et al , 2017. On the other hand, O 32 depends on several other parameters such as metallicity and ionization parameter, in addition to the column density of the neutral gas (Jaskot & Oey 2013;Nakajima & Ouchi 2014;Stasińska et al 2015;Izotov et al 2017). The relation described by Eq.…”

Section: Lyc Escape Fraction Of J1154+2443mentioning

confidence: 99%

J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons

Izotov

Schaerer

Worseck

et al. 2017

Monthly Notices of the Royal Astronomical Society

235

285

View full text Add to dashboard Cite

We report the detection of the Lyman continuum (LyC) radiation of the compact starforming galaxy (SFG) J1154+2443 observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope. This galaxy, at a redshift of z = 0.3690, is characterized by a high emission-line flux ratio O 32 = [O iii]λ5007/[O ii]λ3727 = 11.5. The escape fraction of the LyC radiation f esc (LyC) in this galaxy is 46 per cent, the highest value found so far in low-redshift SFGs and one of the highest values found in galaxies at any redshift. The narrow double-peaked Lyα emission line is detected in the spectrum of J1154+2443 with a separation between the peaks V sep of 199 km s −1 , one of the lowest known for Lyα-emitting galaxies, implying a high f esc (Lyα). Comparing the extinction-corrected Lyα/Hβ flux ratio with the case B value we find f esc (Lyα) = 98 per cent. Our observations, combined with previous detections in the literature, reveal an increase of O 32 with increasing f esc (LyC). We also find a tight anticorrelation between f esc (LyC) and V sep . The surface brightness profile derived from the COS acquisition image reveals a bright star-forming region in the centre and an exponential disc in the outskirts with a disc scale length α = 1.09 kpc. J1154+2443, compared to other known low-redshift LyC leakers, is characterized by the lowest metallicity, 12+logO/H = 7.65±0.01, the lowest stellar mass M = 10 8.20 M , a similar star formation rate SFR = 18.9 M yr −1 and a high specific SFR of 1.2×10 −7 yr −1 .

show abstract

LBT observations of compact star-forming galaxies with extremely high [O iii]/[O ii] flux ratios: He i emission-line ratios as diagnostics of Lyman continuum leakage

Cited by 71 publications

References 56 publications

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

J0811+4730: the most metal-poor star-forming dwarf galaxy known

J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons

Contact Info

Product

Resources

About