[Paper Review] Hubble captures multiply-imaged ionizing radiation from strongly lensed galaxy at z=2.4

T. Emil Rivera-Thorsen, Håkon Dahle+8 more|arXiv (Cornell University)|Apr 17, 2019

Astronomy and Astrophysical Research5 references4 citations

TL;DR

Using gravitational lensing magnification, Hubble captures the clearest view yet of ionizing radiation escaping a strongly lensed galaxy at z=2.4, revealing multiple images of a compact stellar region emitting through a narrow channel in optically thick gas. This provides unprecedented insight into the escape of ionizing photons during the epoch of re-ionization, probing intergalactic neutral hydrogen on small scales.

ABSTRACT

The early Universe was ionized by hard ultraviolet radiation from hot, young stars in the first galaxies. These galaxies contain absorbing neutral Hydrogen which must be configured favorably to allow ionizing escape; only a few dozen cases have been detected at any redshift. Here we present Hubble observations of the brightest known lensed galaxy, the Sunburst Arc, revealing bright, multiply-imaged escape from a compact stellar region through a narrow channel in an optically thick gas. Gravitational lensing magnification has allowed the clearest view yet of how ionizing photons escape galaxies, providing a unique window to the last major phase transition of the Universe, the epoch of re-ionization. The multiple sight lines to the source probe absorption by intergalactic neutral Hydrogen on unprecedentedly small scales.

Motivation & Objective

• To study the escape of ionizing radiation from high-redshift galaxies during the epoch of re-ionization.
• To understand the role of gas geometry and absorption in enabling ionizing photons to escape.
• To leverage strong gravitational lensing to achieve higher resolution and sensitivity than possible with unlensed observations.
• To probe intergalactic neutral hydrogen absorption on small spatial scales using multiple sight lines.

Proposed method

• Utilized Hubble Space Telescope observations to capture high-resolution imaging of the strongly lensed Sunburst Arc galaxy at z=2.4.
• Exploited gravitational lensing magnification to enhance sensitivity and spatial resolution, enabling detection of faint, multiply-imaged ionizing radiation.
• Analyzed multiple sight lines to the source to probe absorption by intergalactic neutral hydrogen on sub-kiloparsec scales.
• Identified a narrow channel in optically thick gas that allows ionizing photons to escape from a compact stellar region.
• Compared observed multiple images to model the geometry of gas and radiation escape paths.
• Used the lensing magnification to achieve the clearest view of ionizing photon escape to date.

Experimental results

Research questions

• RQ1 How do ionizing photons escape from high-redshift galaxies despite surrounding optically thick gas?
• RQ2 What is the role of gas geometry and density structures in enabling photon escape?
• RQ3 Can gravitational lensing reveal small-scale absorption features in intergalactic neutral hydrogen?
• RQ4 What fraction of ionizing radiation escapes through narrow channels in dense gas?
• RQ5 How does the lensed view improve constraints on the escape fraction and escape mechanisms?

Key findings

• The Sunburst Arc is the brightest known lensed galaxy, enabling the clearest observation of ionizing radiation escape at z=2.4.
• Multiple images reveal that ionizing radiation escapes through a narrow channel in an optically thick gas structure.
• The observed escape is consistent with a compact stellar region emitting ionizing photons through a low-density path in a surrounding neutral hydrogen envelope.
• The multiple sight lines probe intergalactic neutral hydrogen absorption on unprecedentedly small spatial scales.
• The lensing magnification provides a unique, high-resolution view of the escape mechanism, crucial for understanding the epoch of re-ionization.
• This system offers direct observational evidence of how ionizing photons can escape galaxies despite high neutral hydrogen column densities.