Los puntos clave no están disponibles para este artículo en este momento.
Growing observational evidence indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z ~ 5-7 galaxies. This line emission makes z ~ 5-7 galaxies appear more massive, with lower specific star-formation rates (sSFRs). However, corrections for this line emission have been difficult to perform reliably because of huge uncertainties on the strength of such emission at z ≳ 5. 5. In this paper, we present the most direct observational evidence thus far for ubiquitous high-equivalent-width (EW) O III + Hβ line emission in Lyman-break galaxies at z ~ 7, and we present a strategy for an improved measurement of the sSFR at z ~ 7. We accomplish this through the selection of bright galaxies in the narrow redshift window z ~ 6. 6-7. 0 where the Spitzer/Infrared Array Camera (IRAC) 4. 5 μm flux provides a clean measurement of the stellar continuum light, in contrast with the 3. 6 μm flux, which is contaminated by the prominent O III + Hβ lines. To ensure a high signal-to-noise ratio for our IRAC flux measurements, we consider only the brightest (H_ (160) < 26 mag) magnified galaxies we have identified behind galaxy clusters. It is remarkable that the mean rest-frame optical color for our bright seven-source sample is very blue, 3. 6-4. 5 = –0. 9 ± 0. 3. Such blue colors cannot be explained by the stellar continuum light and require that the rest-frame EW of O III + Hβ is greater than 637 Å for the average source. The four bluest sources from our seven-source sample require an even more extreme EW of 1582 Å. We can also set a robust lower limit of ≳ 4 Gyr^ (–1) on the sSFR of our sample based on the mean spectral energy distribution.
Smit et al. (Tue,) studied this question.