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

**Authors:** Y. I. Izotov (1, 2), N. G. Guseva (1, 2), K. J. Fricke (2 and, 3), C. Henkel (2, 4), D. Schaerer (5, 6) ((1) Main Astronomical, Observatory, Kyiv, Ukraine, (2) Max-Planck-Institut fuer Radioastronomie,, Bonn, Germany, (3) Institut fuer Astrophysik, Goettingen Universitat,, Goettingen, Germany, (4) Astronomy Department, King Abdulaziz University,, Jeddah, Saudi Arabia, (5) Observatoire de Geneve, Versoix, Switzerland, (6), IRAP/CNRS, Toulouse, France)

arXiv: 1702.02420 · 2023-05-03

## TL;DR

This study analyzes UV and IR data of low-redshift compact star-forming galaxies to understand their ionising photon production efficiency and dust extinction laws, with implications for cosmic reionisation.

## Contribution

It provides new insights into the UV extinction law variations and quantifies the ionising photon production efficiency in compact star-forming galaxies.

## Key findings

- UV magnitudes match GALEX data
- Different reddening laws needed for different EW(Hbeta)
- High ionising photon efficiency in certain 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 star-forming 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 GALEX magnitudes. It is found that galaxies with low and high equivalent widths EW(Hbeta) of the Hbeta emission line require different reddening laws with steeper slopes for galaxies with higher EW(H$\beta$). 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 mum 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 Hbeta luminosities and modelled SEDs in the UV range we derive efficiencies of ionising photon production \xi for the entire sample of CSFGs. It is found that $\xi$ in CSFGs with high EW(Hbeta) 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.

## Full text

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## Figures

24 figures with captions in the complete paper: https://tomesphere.com/paper/1702.02420/full.md

## References

66 references — full list in the complete paper: https://tomesphere.com/paper/1702.02420/full.md

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Source: https://tomesphere.com/paper/1702.02420