The properties of the brightest Lyα emitters at ★

Abstract

We use deep Very Large Telescope (VLT) optical and near‐infrared spectroscopy and deep Spitzer/IRAC imaging to examine the properties of two of the most luminous Lyα emitters at z= 5.7. The continuum redward of the Lyα line is clearly detected in both objects, thus facilitating a relatively accurate measurement (10–20 per cent uncertainties) of the observed rest‐frame equivalent widths, which are around 160 Å for both objects. Through detailed modelling of the profile of the Lyα line with a 3D Monte Carlo radiative transfer code, we estimate the intrinsic rest‐frame equivalent width of Lyα and find values that are around 300 Å, which is at the upper end of the range allowed for very young, moderately metal‐poor star‐forming galaxies. However, the uncertainties are large and values as high as 700 Å are permitted by the data. Both Lyα emitters are detected at 3.6 m in deep images taken with the Spitzer Space Telescope. We use these measurements, the measurement of the continuum redward of Lyα and other photometry to constrain the spectral energy distributions of these very luminous Lyα emitters and to compare them with three similar Lyα emitters from the literature. The contribution from nebular emission is included in our models: excluding it results in significantly higher masses. Four of the five Lyα emitters have masses of the order of ∼109 M⊙ and fairly high specific star formation rates (≳10–100 Gyr−1). While our two Lyα emitters appear similar in terms of the observed Lyα rest‐frame equivalent width, they are quite distinct from each other in terms of age, mass and star formation history. Evidence for dust is found in all objects, and emission from nebular lines often makes a dominant contribution to the rest‐frame 3.6 m flux. Rich in emission lines, these objects are prime targets for the next generation of extremely large telescopes, the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA).

The reionization of carbon

“…In particular, Oppenheimer et al (2009) (hereafter ODF09) find that C II absorbers at z = 6 are associated with galaxies with stellar masses of ∼ 10 7 M⊙ whereas C IV is seen near galaxies with M * ∼ 10 8 M⊙ (their Figures 21 and 23). The latter prediction is supported by observations that the two strongest C IV absorbers at z ∼ 6 are physically associated with Lyman-α emitters (Díaz et al 2014), whose stellar mass is characteristically 10 8 -10 10 M⊙ (Lidman et al 2012). The tendency for low-ionization metal absorbers to trace predominantly lower-mass galaxies (Becker et al 2011;Finlator et al 2013;Kulkarni et al 2013) immediately promotes them to a critical constraint on the origin of the UVB and of cosmological reionization because current models for reionization tend to rely heavily on low-mass galaxies to provide the required flux of ionizing photons (Finlator et al 2011;Alvarez et al 2012;Kuhlen & Faucher-Giguère 2012;Jaacks et al 2012;Robertson et al 2013;Duffy et al 2014;Wise et al 2014).…”

Using Lyman-αto detect galaxies that leak Lyman continuum

“…In the left panel we show the emerging profile from a clumpy shell with the following fiducial values for the four physical parameters: v exp = 150 km s −1 , log(N HI ) = 20, b = 20 km s −1 , and E(B − V) = 0.1 These values correspond to the most common best-fit values in our studies fitting observed spectra with our library of homogeneous shells (Verhamme et al 2008;Dessauges-Zavadsky et al 2010;Lidman et al 2012;Orlitová et al, in prep. ;Hashimoto et al, in prep.).…”

A CLOSE COMPARISON BETWEEN OBSERVED AND MODELED LyαLINES FORz∼ 2.2 LyαEMITTERS

“…Thus, combinations of seven free parameters are fitted to the data. This library of Lyα spectra has been successfully used to reproduce various observed Lyα line profiles of z > 3 LBGs, from strong emission to broad absorption Dessauges-Zavadsky et al 2010;Vanzella et al 2010;Lidman et al 2012). …”