分类： 天文学 >> 天文学 提交时间： 2023-02-19
Alexandra Le Reste
John M. Cannon
Matthew J. Hayes
John L. Inoue
Amanda A. Kepley
Jens Melinder
Veronica Menacho
Angela Adamo
Arjan Bik
Timmy Ejdetjärn
Gyula I. G. Józsa
Göran Östlin
Sarah H. Taft
摘要： Around 400 million years after the big bang, ultraviolet emission (Lyman Continuum, LyC) from star-forming galaxies drove the reionization of the Universe. How this radiation escapes the cold neutral gas (HI) of galaxies with sufficiently little absorption to reionize the intergalactic medium is poorly understood. HI has never been mapped in confirmed LyC-emitters, leaving major uncertainties on how LyC photons escape galaxies and ionize the intergalactic medium. We imaged the 21cm HI emission of nearby reionization-era analog galaxy Haro 11 to identify how ionizing radiation escapes the neutral interstellar medium. We find that merger-driven interactions have tidally displaced up to 82% of the neutral gas from the ultraviolet emission production sites in the galaxy, allowing the escape of ionizing radiation to the intergalactic medium. Increased galaxy interactions in the early Universe predicted by cosmological models could contribute significantly to the reionization of the Universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jens Melinder
Göran Östlin
Matthew Hayes
Armin Rasekh
J. Miguel Mas-Hesse
John M. Cannon
Daniel Kunth
Peter Laursen
Axel Runnholm
E. Christian Herenz
Matteo Messa
Daniel Schaerer
Anne Verhamme
T. Emil Rivera-Thorsen
Lucia Guaita
Thomas Marquart
Johannes Puschnig
Alexandra Le Reste
Andreas Sandberg
Emily Freeland
摘要： We present Ly $\alpha$ imaging of 45 low redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates using far-ultraviolet (FUV) luminosity and \ha equivalent width criteria, but no constraints on Ly $\alpha$ luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum subtracted Ly $\alpha$, H $\alpha$ and H $\beta$ maps. We find that Ly $\alpha$ is less concentrated than FUV and optical line emission in almost all galaxies with significant Ly $\alpha$ emission. We present global measurements of Ly $\alpha$ and other quantities measured in apertures designed to capture all of the Ly $\alpha$ emission. We then show how the escape fraction of Ly $\alpha$ relates to a number of other measured quantities (mass, metallicity, star formation, ionisation parameter, and extinction). We find that the escape fraction is strongly anti-correlated with nebular and stellar extinction, weakly anti-correlated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Ly $\alpha$ escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present a star formation rate calibration based on Ly $\alpha$ luminosity, where the equivalent width of Ly $\alpha$ is used to correct for non-unity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Ly $\alpha$ for the galaxies that can be used to find aperture loss fractions at a given physical radius.
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