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
- Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
- Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21208 (United States)
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
- Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States)
- Institute of Astronomy and Astrophysics, Academia Sinica, P. O. Box 23-141, Taipei 10617, Taiwan (China)
- Institut fur Theoretische Astrophysik, ZAH, Albert-Ueberle-Straß e 2, 69120 Heidelberg (Germany)
- Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
- Instituto de Astrofisica de Andalucia (CSIC), C/Camino Bajo de Huetor 24, Granada 18008 (Spain)
- Department of Theoretical Physics, University of the Basque Country, P. O. Box 644, 48080 Bilbao (Spain)
- Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)
- Departamento de Astronoia y Astrofisica, Pontificia Universidad Catolica de Chile, V. Mackenna 4860, Santiago 22 (Chile)
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 {sub 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{sup –1} on the sSFR of our sample based on the mean spectral energy distribution.
- OSTI ID:
- 22351498
- Journal Information:
- Astrophysical Journal, Vol. 784, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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