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Limits on Lyman Continuum Escape from z = 2.2 Hα-emitting Galaxies
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
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2015 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 814, no 1, L10Article in journal (Refereed) Published
Abstract [en]

The leakage of Lyman continuum (LyC) photons from star-forming galaxies is an elusive parameter. When observed, it provides a wealth of information on star formation in galaxies and on the geometry of the interstellar medium, and puts constraints on the role of star-forming galaxies in the reionization of the universe. Hα-selected galaxies at  trace the highest star formation population at the peak of cosmic star formation history, providing a base for directly measuring LyC escape. Here we present this method and highlight its benefits as well as caveats. We also use the method on 10 Hα emitters in the Chandra Deep Field South at  also imaged with the Hubble Space Telescope in the ultraviolet. We find no individual LyC detections, and our stack puts a 5σ upper limit on the average absolute escape fraction of <24%, consistent with similar studies. With future planned observations, the sample sizes should rapidly increase and the method presented here should provide very robust constraints on the escape fraction.

Place, publisher, year, edition, pages
2015. Vol. 814, no 1, L10
Keyword [en]
dark ages, reionization, first stars, galaxies: evolution, ultraviolet: galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-123705DOI: 10.1088/2041-8205/814/1/L10ISI: 000365035400010OAI: oai:DiVA.org:su-123705DiVA: diva2:876042
Available from: 2015-12-02 Created: 2015-12-02 Last updated: 2016-01-15Bibliographically approved
In thesis
1. Observing Lyman alpha emitters - How does Lyman alpha escape from galaxies?
Open this publication in new window or tab >>Observing Lyman alpha emitters - How does Lyman alpha escape from galaxies?
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Lyman alpha (Lyα) emission line has grown to become one of the most successful tools for finding galaxies at high redshift. At redshifts corresponding to the early cosmic times of reionization and primeval galaxy formation, the wavelength of Lyα is still accessible with ground-based facilities. Lyα is a resonance line which undergoes a complicated radiative transfer process through the neutral gas inside galaxies. This process is still not fully understood. The precise distribution and kinematics of stars, gas and dust all seem to affect the amount of Lyα that eventually escapes the galaxy. Observational studies of Lyα emitting galaxies are necessary for understanding this process in detail.

From previous observations and simulations, it is evident that outflows of neutral gas can facilitate the escape of Lyα photons, as the Doppler effect shifts the frequency out of resonance. In Paper I we explore the connection between Lyα escape and outflows of neutral gas as measured with the Na D absorption feature in two nearby Lyα emitting galaxies. We find suprisingly little evidence for such a connection, and speculate how the Na D absorption is perhaps not measuring the velocity of the gas which is the most important for Lyα escape.

Papers II and III address LARS - the Lyman Alpha Reference Sample - a project in which 14 nearby galaxies and their Lyα emission are studied in detail using the Hubble Space Telescope. The two papers describe how we directly image the Lyα emission and absorption in these galaxies, and relate it to their physical properties. We find that Lyα escape is more probable in galaxies with younger age, and lower mass, dust content and instantaneous star formation rate, whereas the total Lyα luminosity appears to be independent of these factors.

Papers IV and V then turn to higher redshifts, exploring Lyα and Lyman Continuum escape at z ∼ 2. In Paper IV we find 25 Lyα-emitting galaxies (LAEs) using the photometric narrow-band technique, and we explore their multi-wavelength properties. Our results are well in line with similar studies at this redshift. We also find several luminous infrared galaxies (LIRGs) in the sample, which may seem surprising given their high dust content, but we also review similar previous findings in the literature.

Paper V describes the method of using Hα-emitting galaxies (HAEs) in order to accurately ascertain the Lyman Continuum escape fraction from a galaxy population, a number which is crucial for the understanding of the role of galaxies during the epoch of reionization. An Hα-selected sample is less biased towards dust-free systems than UV-selected samples, which are typically used for this type of study. We also use the method on 10 strongly clustered HAEs and constrain the Lyman Continuum escape fraction to <24%, but stress that this number is strongly affected by cosmic variance and that further studies of HAEs could provide very robust constraints on the escape fraction.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2016. 52 p.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-125604 (URN)978-91-7649-336-6 (ISBN)
Public defence
2016-03-10, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
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Available from: 2016-02-16 Created: 2016-01-14 Last updated: 2016-02-03Bibliographically approved

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Andreas, SandbergÖstlin, GöranMelinder, JensBik, Adrianus
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