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Register a new userMorphological Properties of Lyman Alpha Emitters at Redshift 4.86 in the COSMOS Field: Clumpy Star Formation or Merger?
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Masakazu Kobayashi Dr.
Publication date
2016
fields
Physics
and research's language is
English
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We investigate morphological properties of 61 Lyman-alpha 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 the 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 PSF half-light radius of 0.07 (~ 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 which 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 A) is inevitable to decipher which interpretation is adequate for our LAE sample.
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We search for bright Ly$rm alpha$ emitters among Spitzer SMUVS galaxies at z > 2.9 with homogeneous MUSE data. Although it only covers a small region of COSMOS, MUSE has the unique advantage of providing spectral information over the entire field, without the need of target pre-selection. This gives an unbiased detection of all the brightest Ly$rm alpha$ emitters among SMUVS sources, which by design are stellar-mass selected galaxies. Within the studied area, ~14% of the SMUVS galaxies at z > 2.9 have Ly$rm alpha$ fluxes F$rm _lambda$ > 7 x 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$. These Ly$rm alpha$ emitters are characterized by three types of emission, 47% show a single line profile, 19% present a double peak or a blue bump and 31% show a red tail. One object (3%) shows both a blue bump and a red tail. We also investigate the spectral energy distribution (SED) properties of the SMUVS MUSE-detected galaxies and MUSE non-detections. After stellar-mass matching both populations, we find that MUSE detected galaxies have generally lower extinction than SMUVS-only objects, while there is no clear intrinsic difference in the mass and age distributions. For the MUSE-detected SMUVS galaxies, we compare the instantaneous SFR lower limit given by Ly$rm alpha$ flux with its past average derived from SED fitting, and find evidence for rejuvenation in some of our oldest objects. We also study the spectra of those Ly$rm alpha$ emitters which are not detected in SMUVS in the same field. We find different distributions of the emission line profiles, which could be ascribed to the fainter Ly$rm alpha$ luminosities of the MUSE-only sources and an intrinsically different mass distribution. Finally, we search for the presence of galaxy associations. MUSEs integral coverage is 20 times more likely to find associations than all other existing spectral data in COSMOS, biased by target pre-selection.
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