The efficiency of ionizing photon production and the radiation energy balance in compact star-forming galaxies

Abstract

We derive apparent and absolute ultraviolet (UV) magnitudes, and luminosities in the infrared (IR) range of a large sample of low-redshift (0 < z < 1) compact starforming galaxies (CSFGs) selected from the Data Release 12 of the Sloan Digital Sky Survey (SDSS). These data are used to constrain the extinction law in the UV for our galaxies and to compare the absorbed radiation in the UV range with the emission in the IR range. We find that the modelled far-and near-UV apparent magnitudes are in good agreement with the observed Galaxy Evolution Explorer (GALEX) magnitudes. It is found that galaxies with low and high equivalent widths EW(Hβ) of the Hβ emission line require different reddening laws with steeper slopes for galaxies with higher EW(Hβ). This implies an important role of the hard ionising radiation in shaping the dust grain size distribution. The IR emission in the range of 8 -1000 µm is determined using existing data obtained by various infrared space telescopes. We find that the radiation energy absorbed in the UV range is nearly equal to the energy emitted in the IR range leaving very little room for hidden star formation in our galaxies. Using extinction-corrected Hβ luminosities and modelled SEDs in the UV range we derive efficiencies of ionising photon production ξ for the entire sample of CSFGs. It is found that ξ in CSFGs with high EW(Hβ) are among the highest known for low-and high-redshift galaxies. If galaxies with similar properties existed at redshifts z = 5 -10, they could be considered as promising candidates for the reionisation of the Universe.

The GREATS H β + [O iii] luminosity function and galaxy properties at z ∼ 8: walking the way of JWST

“…The constraints that we obtain on the ionizing photon production efficiency at z ∼ 8 are consistent with results obtained for the bluest (i.e., least dust attenuated) LBGs and Lyman-α Emitters at z ∼ 2 (Shivaei et al 2018;Sobral et al 2018;Tang et al 2018) as well as results obtained for lowredshift compact star-forming galaxies (Izotov et al 2017), and for LBGs at z ∼ 4 − 5 Lam et al 2019;Ceverino et al 2019). The observed ionizing photon production efficiency that we find is also consistent with the observed value found for z ∼ 0.3 Lyman continuum emitters (ξ ion = 25.6 − 26, Schaerer et al 2016).…”

Kinematics and Optical Depth in the Green Peas: Suppressed Superwinds in Candidate LyC Emitters*

“…The strong stellar N v λ1240 P-Cygni profile observed in the extreme GP J1608 further indicates an age < 3 Myr ( § 3.2). With young ages, the GPs may be at their peak LyC production (cf., Schaerer et al 2016;Izotov et al 2017a). By ionizing the surrounding nebular gas, this intense radiation may ensure its own escape.…”

Semi-analytic forecasts for JWST – III. Intrinsic production efficiency of Lyman-continuum radiation

“…We compare our predictions to the results from the First-Light simulations, which is a set of high-resolution zoom-in simulations based on cosmological boxes of 10, 20, and 40 Mpc h −1 on a side, resolving galaxies in halos with circular velocities spanning the range between 50-250 km s −1 at z 5 (Ceverino et al 2017(Ceverino et al , 2019 Typical values adopted in analytic calculations are highlighted by the grey band. We also show the range derived from a large sample of SDSS galaxies at 0 < z < 1 (Izotov et al 2017). The lower bound of this range extends to ξ ion = 24 (not shown).…”

“…These may be biased towards objects at the extreme tails of the distribution of physical properties, or towards rare starbursting galaxies. The large sample of lower redshift galaxies (0 < z < 1) studied by Izotov et al (2017) show a broad range of values of ξion, and suggest the strong sensitivity in this parameter to recent bursts.…”