Evidence for ubiquitous high-equivalent-width nebular emission in z ∼ 7 galaxies : toward a clean measurement of the specific star-formation rate using a sample of bright, magnified galaxies
Articolo
Data di Pubblicazione:
2014
Citazione:
Evidence for ubiquitous high-equivalent-width nebular emission in z ∼ 7 galaxies : toward a clean measurement of the specific star-formation rate using a sample of bright, magnified galaxies / R. Smit, R.J. Bouwens, I. Labbé, W. Zheng, L. Bradley, M. Donahue, D. Lemze, J. Moustakas, K. Umetsu, A. Zitrin, D. Coe, M. Postman, V. Gonzalez, M. Bartelmann, N. Benítez, T. Broadhurst, H. Ford, C. Grillo, L. Infante, Y. Jimenez Teja, S. Jouvel, D.D. Kelson, O. Lahav, D. Maoz, E. Medezinski, P. Melchior, M. Meneghetti, J. Merten, A. Molino, L.A. Moustakas, M. Nonino, P. Rosati, S. Seitz. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - 784:1(2014), pp. 58.1-58.8. [10.1088/0004-637X/784/1/58]
Abstract:
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.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
evolution galaxies; formation galaxies; galaxies; high-redshift; space and planetary science; astronomy and astrophysics; nuclear and high energy physics
Elenco autori:
R. Smit, R.J. Bouwens, I. Labbé, W. Zheng, L. Bradley, M. Donahue, D. Lemze, J. Moustakas, K. Umetsu, A. Zitrin, D. Coe, M. Postman, V. Gonzalez, M. Bartelmann, N. Benítez, T. Broadhurst, H. Ford, C. Grillo, L. Infante, Y. Jimenez Teja, S. Jouvel, D.D. Kelson, O. Lahav, D. Maoz, E. Medezinski, P. Melchior, M. Meneghetti, J. Merten, A. Molino, L.A. Moustakas, M. Nonino, P. Rosati, S. Seitz
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