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Published August 20, 2009 | Published
Journal Article Open

Hubble Space Telescope/Advanced Camera for Surveys Morphology of Lyα Emitters at Redshift 5.7 in the COSMOS Field


We present detailed morphological properties of Lyα emitters (LAEs) at z ≈ 5.7 in the COSMOS field based on Hubble Space Telescope Advanced Camera for Surveys (ACS) data. The ACS imaging in the F814W filter covered 85 LAEs of the 119 LAEs identified in the full two square degree field, and 47 LAEs of them are detected in the ACS images. Nearly half of them are spatially extended with a size larger than 0.15 arcsec (~0.88 kpc at z = 5.7) and up to 0.4 arcsec (~2.5 kpc at z = 5.7). The others are nearly unresolved compact objects. Two LAEs show double-component structures indicating interaction or merging of building components to form more massive galaxies. By stacking the ACS images of all the detected sources, we obtain a Sersic parameter of n ~ 0.7 with a half-light radius of 0.13 arcsec (0.76 kpc), suggesting that the majority of ACS detected LAEs have not spheroidal-like but disk-like or irregular light profiles. Comparing ACS F814W magnitudes (I _(814)) with Subaru/Suprime-Cam magnitudes in the NB816, i', and z' bands, we find that the ACS imaging in the F814W band mainly probes UV continuum rather than Lyα line emission. UV continuum sizes tend to be larger for LAEs with larger Lyα emission regions as traced by the NB816 imaging. The nondetection of 38 LAEs in the ACS images is likely due to the fact that their surface brightness is too low both in the UV continuum and Lyα emission. Estimating I_(814) for the ACS-undetected LAEs from the z' and NB816 magnitudes, we find that 16 of these are probably LAEs with a size larger than 0.15 arcsec in UV continuum. All these results suggest that our LAE sample contains systematically larger LAEs in UV continuum size than those previously studied at z ~ 6.

Additional Information

© 2009 American Astronomical Society. Print publication: Issue 2 (2009 August 20); received 2008 November 3, accepted for publication 2009 June 15; published 2009 July 28. We thank both the Subaru and HST staff for their invaluable help, and all members of the COSMOS team.We also thank the anonymous referee for his/her useful comments. This work was in part financially supported by JSPS (15340059 and 17253001).

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Published - Taniguchi2009p5715Astrophys_J.pdf


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