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Published March 1, 2016 | Submitted + Published
Journal Article Open

Morphological Properties of Lyα Emitters at Redshift 4.86 in the Cosmos Field: Clumpy Star Formation or Merger?


We investigate morphological properties of 61 Lyα emitters (LAEs) at z = 4.86 identified in the COSMOS field, based on Hubble Space Telescope Advanced Camera for Surveys (ACS) imaging data in the F814W band. Out of the 61 LAEs, we find the ACS counterparts for 54 LAEs. Eight LAEs show double-component structures with a mean projected separation of 0".63 (~4.0 kpc at z = 4.86). Considering the faintness of these ACS sources, we carefully evaluate their morphological properties, that is, size and ellipticity. While some of them are compact and indistinguishable from the point-spread function (PSF) half-light radius of 0f".07 (~0.45 kpc), the others are clearly larger than the PSF size and spatially extended up to 0".3 (~1.9 kpc). We find that the ACS sources show a positive correlation between ellipticity and size and that the ACS sources with large size and round shape are absent. Our Monte Carlo simulation suggests that the correlation can be explained by (1) the deformation effects via PSF broadening and shot noise or (2) the source blending in which two or more sources with small separation are blended in our ACS image and detected as a single elongated source. Therefore, the 46 single-component LAEs could contain the sources that consist of double (or multiple) components with small spatial separation (i.e., ≾ 0".3 or 1.9 kpc). Further observation with high angular resolution at longer wavelengths (e.g., rest-frame wavelengths of ≳4000 Å) is inevitable to decipher which interpretation is adequate for our LAE sample.

Additional Information

© 2016 The American Astronomical Society. Received 2015 February 10; accepted 2016 January 19; published 2016 February 24. We would like to thank both the Subaru and HST staff for their invaluable help, all members of the COSMOS team, Tsutomu T. Takeuchi at Nagoya University for his help in running our Monte Carlo simulations using his computers, and Shinki Oyabu at Nagoya University for providing valuable suggestions/comments. We would also like to thank the anonymous referees for useful comments. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work was in part financially supported by JSPS (15340059 and 17253001).

Attached Files

Published - apj_819_1_25.pdf

Submitted - 1601.05878v1.pdf


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