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Prospects of observing a quasar HII region during the Epoch ofReionization with redshifted 21cm
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
(English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966Article in journal (Refereed) Submitted
Abstract [en]

We present a study of the impact of a bright quasar on the redshifted 21cm signal during theEpoch of Reionization (EoR). Using three different cosmological radiative transfer simula-tions, we investigate if quasars are capable of substantially changing the size and morphologyof the H II regions they are born in. We choose stellar and quasar luminosities in a way that isfavourable to seeing such an effect. We find that even the most luminous of our quasar modelsis not able to increase the size of its native H II region substantially beyond those of largeH II regions produced by clustered stellar sources alone. However, the quasar H II region isfound to be more spherical. We next investigate the prospects of detecting such H II regionsin the redshifted 21cm data from the Low Frequency Array (LOFAR) by means of a matchedfilter technique. We find that H II regions with radii ∼ 25 comoving Mpc or larger shouldhave a sufficiently high detection probability for 1200 hours of integration time. Although thematched filter can in principle distinguish between more and less spherical regions, we findthat when including realistic system noise this distinction can no longer be made. The strongforegrounds are found not to pose a problem for the matched filter technique. We also demon-strate that when the quasar position is known, the redshifted 21cm data can still be used toset upper limits on the ionizing photon rate of the quasar. If both the quasar position and itsluminosity are known, the redshifted 21 cm data can set new constrains on quasar lifetimes.

National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-74229OAI: oai:DiVA.org:su-74229DiVA: diva2:507271
Available from: 2012-03-02 Created: 2012-03-02 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Simulations of Cosmic Reionization: Shapes & Sizes of H II regions around Galaxies and Quasars
Open this publication in new window or tab >>Simulations of Cosmic Reionization: Shapes & Sizes of H II regions around Galaxies and Quasars
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

After the era of recombination, roughly 360 000 years after the big bang (redshift 1100), the universe was neutral, continued to expand and eventually the first gravitationally collapsed structures capable of forming stars, formed. Observations show that approximately 1 billion years later (redshift 6), the Universe had become highly ionized. The transition from a neutral intergalactic medium to a highly ionized one, is called the epoch of Reionization (EoR). Although quasar spectra and polarization power-spectra from cosmic microwave background experiments set some time-constrains on this epoch, the details of this process are currently not known.

New radio telescopes operating at low frequencies aim at measuring directly the neutral hydrogen content between redshifts 6 - 10 via the HI spin-flip line at 21cm. The interpretation of these first measurements is not going to be trivial. Therefore, simulations of the EoR are useful to test the many ill-constrained parameters such as the properties of the sources responsible for reionization. This thesis contributes to such simulations.

It addresses different source models and discusses different measures to quantify their effect on the shapes and sizes of the emerging H II regions. It also presents a new version of the widely used radiative transfer code C2-Ray which is capable of handling the ionizing radiation produced by energetic sources such as quasars. Using this new version we study whether 21cm experiments could detect the signature of a quasar.

We find that different size measures of ionized regions can distinguish between different source models in the simulations and that a topological measure of the ionized fraction field confirms the inside-out (i.e. overdense regions ionize first) reionization scenario. We find that the HII regions from luminous quasars may be detectable in 21cm, but that it might not be possible to distinguish them from the largest HII regions produced by clustered galaxies.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2012. 47 p.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-72409 (URN)978-91-7447-448-0 (ISBN)
Public defence
2012-03-29, lecture room FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Submitted. Available from: 2012-03-07 Created: 2012-02-10 Last updated: 2012-03-05Bibliographically approved

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