Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
ON THE (NON-) ENHANCEMENT OF THE Ly alpha EQUIVALENT WIDTH BY A MULTIPHASE INTERSTELLAR MEDIUM
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Copenhagen, Denmark.
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).
2013 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 766, no 2, 124- p.Article in journal (Refereed) Published
Abstract [en]

It has been suggested that radiative transfer effects may explain the unusually high equivalent widths (EWs) of the Ly alpha line, observed occasionally from starburst galaxies, especially at high redshifts. If the dust is locked up inside high-density clouds dispersed in an empty intercloud medium, the Ly alpha photons could scatter off of the surfaces of the clouds, effectively having their journey confined to the dustless medium. The continuum radiation, on the other hand, does not scatter, and would thus be subject to absorption inside the clouds. This scenario is routinely invoked when Ly alpha EWs higher than what is expected theoretically are observed, although the ideal conditions under which the results are derived usually are not considered. Here we systematically examine the relevant physical parameters in this idealized framework, testing whether any astrophysically realistic scenarios may lead to such an effect. It is found that although clumpiness indeed facilitates the escape of Ly alpha, it is highly unlikely that any real interstellar media should result in a preferential escape of Ly alpha over continuum radiation. Other possible causes are discussed, and it is concluded that the observed high EWs are more likely to be caused by cooling radiation from cold accretion and/or anisotropic escape of the Ly alpha radiation.

Place, publisher, year, edition, pages
2013. Vol. 766, no 2, 124- p.
Keyword [en]
galaxies: ISM, radiative transfer, scattering
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-89706DOI: 10.1088/0004-637X/766/2/124ISI: 000316320900058OAI: oai:DiVA.org:su-89706DiVA: diva2:620541
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note

AuthorCount:3;

Available from: 2013-05-08 Created: 2013-05-06 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Lyman-alpha radiative transfer in Star-forming galaxies
Open this publication in new window or tab >>Lyman-alpha radiative transfer in Star-forming galaxies
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on the intrinsically strongest spectral signature of star-forming galaxies: the Lyman alpha recombination line of the hydrogen atom (hereafter Lya). Located at the wavelength of 1215.67 Å in the restframe far-ultraviolet spectra of star-forming galaxies, the Lya line proves to be a vital tracer and a powerful emission-line window to discover and to study the remote young star-forming galaxies of the early the Universe.

Although intrinsically very strong, the Lya line is also a resonant line. As a consequence, the transport of Lya photons inside the interstellar medium (ISM) of star-forming galaxies is very complex and depends on many ISM quantities (HI mass, dust content, HI gas kinematics and ISM clumpiness). All this process has serious effects on the emergent features of the Lya line (strength, equivalent width and line profile) that need to be understood for ensuring a proper interpretation of all very promising Lya-oriented studies in astrophysics and cosmology. This is precisely the aim of this thesis to go deeper into our understanding of the complex radiative transport experienced by the Lya line in star-forming galaxies.

In this work, we carry out both numerical and observational studies of Lya transport inside the ISM of galaxies.

In Paper I and II, we perform detailed numerical studies that examine the effects of a clumpy ISM on the strength and the shape of the Lya line. Although poorly studied until now, the effects of a clumpy ISM on Lya have been routinely invoked to explain the origin of anomalously strong Lya line observed from high-redshift galaxies. Some analytical studies suggest indeed an higher transmission of Lya photons over UV continuum ones from clumpy ISMs, resulting in an enhanced Lya equivalent width EW(Lya). Our results show that although clumpiness facilitates the escape of Lya, it is highly unlikely that any real ISM should result in any enhancement of EW(Lya). Other possible causes are discussed in our papers, leading to the conclusion that the observed high EW(Lya) are more likely produced by cooling radiation or anisotropic escape of Lya radiation.

Both Paper III and IV are related to the LARS project. This is an ambitious observational program in which 14 nearby star-forming galaxies have been observed with the Hubble Space Telescope (HST) with the aim to investigate how Lya is transported out of galaxies and what effects each ISM quantity produces on the Lya line. While Paper III examines the Lya properties and morphology of individual galaxies, Paper IV presents a detailed study of the surprising Lya emission line of Mrk1486 (the fifth galaxy of the sample).

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2015. 84 p.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-111550 (URN)978-91-7649-087-7 (ISBN)
Public defence
2015-02-12, FA31, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

Available from: 2015-01-21 Created: 2015-01-04 Last updated: 2015-01-20Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Duval, FlorentÖstlin, Göran
By organisation
Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
In the same journal
Astrophysical Journal
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 36 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf