Journal Article

Direct observation of cosmic strings via their strong gravitational lensing effect – II. Results from the <i>HST</i>/ACS image archive

Eric Morganson, Phil Marshall, Tommaso Treu, Tim Schrabback and Roger D. Blandford

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 4, pages 2452-2472
Published in print August 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16562.x
Direct observation of cosmic strings via their strong gravitational lensing effect – II. Results from the HST/ACS image archive

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We have searched 4.5 deg2 of archival Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) images for cosmic strings, identifying close pairs of similar, faint galaxies and selecting groups whose alignment is consistent with gravitational lensing by a long, straight string. We find no evidence for cosmic strings in five large-area HST treasury surveys (covering a total of 2.22 deg2) or in any of 346 multifilter guest observer images (1.18 deg2). Assuming that simulations accurately predict the number of cosmic strings in the Universe, this non-detection allows us to place upper limits on the dimensionless Universal cosmic string tension of Gμ/c2 < 2.3 × 10−6 and cosmic string density of Ωs < 2.1 × 10−5 at the 95 per cent confidence level (marginalizing over the other parameter in each case). We find four dubious cosmic string candidates in 318 single-filter guest observer images (1.08 deg2), which we are unable to conclusively eliminate with existing data. The confirmation of any of these candidates as cosmic strings would imply Gμ/c2≈ 10−6 and Ωs≈ 10−5. However, we estimate that there is at least a 92 per cent chance that these string candidates are random alignments of galaxies. If we assume that these candidates are indeed false detections, our final limits on Gμ/c2 and Ωs fall to 6.5 × 10−7 and 7.3 × 10−6, respectively. Due to the extensive sky coverage of the HST/ACS image archive, the above limits are universal. They are quite sensitive to the number of fields being searched and could be further reduced by more than a factor of 2 using forthcoming HST data.

Keywords: gravitational lensing: strong; surveys; cosmology: observations

Journal Article.  14232 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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