Diffuse Lyα haloes around galaxies at z = 2.2–6.6: implications for galaxy formation and cosmic reionization

Abstract

We present diffuse Lyα halos (LAHs) identified in the composite Subaru narrowband 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 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 narrowbandmagnitude 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 Lyα 2 × 10 42 erg s −1 . We obtain the scale lengths of ≃ 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 UVcontinuum sizes is nearly constant at z = 2.2 − 5.7. The scale length of our z = 6.6 LAH is larger than 5 − 10 kpc just beyond the error bar, which is a hint that the scale lengths 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 scale length change at z 6 would be a signature of increasing fraction of neutral hydrogen scattering Lyα photons, due to cosmic reionization.

Lyα Profile, Dust, and Prediction of Lyα Escape Fraction in Green Pea Galaxies

“…Note that many Lyα galaxies have a very extended Lyα halo (e.g. Ostlin et al 2009;Hayes et al 2013;Momose et al 2014). For these Green Pea galaxies, their Lyα to UV size ratios are about 2−4 (Yang et al 2017).…”

The Lyman alpha reference sample

“…By stacking hundreds of z 2.2, z 3.1, z 3.7, and z 5.7 LAEs from deep ground-based imaging, Momose et al (2014) discovered extended Lyα emission, with scale lengths in the range of 5−10 kpc. However, by stacking their sample of LAEs Feldmeier et al (2013) just found a marginal detection at z ∼ 3.1 and a non-detection at z 2.07.…”

Small-scale Intensity Mapping: Extended Lyα, Hα, and Continuum Emission as a Probe of Halo Star Formation in High-redshift Galaxies

“…In addition, at such small distances, the profile of the central galaxy is significantly driven by the point-spread function of the instrument (Momose et al 2014). Owing to these uncertainties,here we ignore the central galaxy and limit our calculations to distances >10 pkpc.…”

“…Nowadays, this faint emission is being proved to be nearly ubiquitousin galaxies at high redshift,   z 3 5, by means of stacking analyses Matsuda et al 2012;Feldmeier et al 2013;Momose et al 2014Momose et al , 2016anddue to the sensitivity and spatial resolution improvement of instruments such as MUSE (Bacon et al 2014). A clear understanding ofthe origin of these extended Lyα halos (LAHs; hereafter) is relevant because it yields information about the physical conditions of the circumgalactic medium (CGM) and, in turn, on the processes governing the formation and evolution of galaxies (Bahcall & Spitzer 1969).…”

“…We perform calculations considering the spatially extended emission observed around LAEs at redshift z=3.1, which allowsa comparison with the results by Momose et al (2014) and Matsuda et al (2012). Our paper is structured as follows.In Section 2, we detail the formalism and adopted values for the parameters in the calculation of the surface brightness profiles for the continua, Hα and Lyα.…”