http://arxiv.org/abs/1403.0732
We present diffuse Ly$\alpha$ halos (LAHs) identified in the composite Subaru narrowband images of $100-3600 $ Ly$\alpha$ emitters (LAEs) at $z=2.2$, $3.1$, $3.7$, $5.7$, and $6.6$. First, we carefully examine potential artifacts mimicking LAHs that include a large-scale point-spread function (PSF) made by instrumental and atmospheric effects. Based on our critical test with composite images of non-LAE samples whose narrowband-magnitude and source-size distributions are the same as our LAE samples, we confirm that no artifacts can produce a diffuse extended feature similar to our LAHs. After this test, we measure the scale lengths of exponential profile for the LAHs estimated from our $z=2.2-6.6$ LAE samples of $L_{\rm Ly\alpha}\gtrsim 2\times 10^{42}$ erg s$^{-1}$. We obtain the scale lengths of $\simeq 5-10$ kpc at $z=2.2-5.7$, and find no evolution of scale lengths 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 $z=2.2-5.7$. On the other hand, the scale length of our $z=6.6$ LAH is larger than $5-10$ kpc, and there is a hint that the scale lengths of LAHs would increase from $z=5.7$ to $6.6$. This may be a signature of increasing fraction of neutral hydrogen scattering Ly\alpha$ photons, due to cosmic reionization, although larger data are needed for a definitive conclusion.
R. Momose, M. Ouchi, K. Nakajima, et. al.
Wed, 5 Mar 14
16/75