Diffuse Lyα haloes around galaxies at z = 2.2-6.6: implications for galaxy formation and cosmic reionization
Abstract
We present diffuse Lyα haloes (LAHs) identified in the composite Subaru narrow-band images of 100-3600 Lyα emitters (LAEs) at z = 2.2, 3.1, 3.7, 5.7, and 6.6. First, we carefully examine potential artefacts mimicking LAHs that include a large-scale point-spread function made by instrumental and atmospheric effects. Based on our critical test with composite images of non-LAE samples whose narrow-band-magnitude and source-size distributions are the same as our LAE samples, we confirm that no artefacts can produce a diffuse extended feature similar to our LAHs. After this test, we measure the scalelengths of exponential profile for the LAHs estimated from our z = 2.2-6.6 LAE samples of LLyα ≳ 2 × 1042 erg s-1. We obtain the scalelengths of ≃5-10 kpc at z = 2.2-5.7, and find no evolution of scalelengths in this redshift range beyond our measurement uncertainties. Combining this result and the previously known UV-continuum size evolution, we infer that the ratio of LAH to UV-continuum sizes is nearly constant at z = 2.2-5.7. The scalelength of our z = 6.6 LAH is larger than 5-10 kpc just beyond the error bar, which is a hint that the scalelengths of LAHs would increase from z = 5.7 to 6.6. If this increase is confirmed by future large surveys with significant improvements of statistical and systematical errors, this scalelength change at z ≳ 6 would be a signature of increasing fraction of neutral hydrogen scattering Lyα photons, due to cosmic reionization.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2014
- DOI:
- 10.1093/mnras/stu825
- arXiv:
- arXiv:1403.0732
- Bibcode:
- 2014MNRAS.442..110M
- Keywords:
-
- galaxies: evolution;
- galaxies: haloes;
- galaxies: high-redshift;
- dark ages;
- reionization;
- first stars;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 13 pages, 9 figures, 1 table. Accepted by MNRAS