KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY

By D. Stark, M. Schenker, Richard S. Ellis, Brant Robertson, R. McLure, J. Dunlop. 2012

308 citations recorded by the source corpus.

The physical properties inferred from the spectral energy distributions (SEDs) of z > 3 galaxies have been influential in shaping our understanding of early galaxy formation and the role galaxies may play in cosmic reionization. Of particular importance is the stellar mass density at early times, which represents the integral of earlier star formation. An important puzzle arising from the measurements so far reported is that the specific star formation rates (sSFRs) evolve far less rapidly than expected in most theoretical models. Yet the observations underpinning these results remain very uncertain, owing in part to the possible contamination of rest-optical broadband light from strong nebular emission lines. To quantify the contribution of nebular emission to broadband fluxes, we investigate the SEDs of 92 spectroscopically confirmed galaxies in the redshift range 3.8 < z < 5.0 chosen because the Hα line lies within the Spitzer/IRAC 3.6 μm filter. We demonstrate that the 3.6 μm flux is systematically in excess of that expected from stellar continuum alone, which we derive by fitting the SED with population synthesis models. No such excess is seen in a control sample of spectroscopically confirmed galaxies with 3.1 < z < 3.6 in which there is no nebular contamination in the IRAC filters. From the distribution of our 3.6 μm flux excesses, we derive an Hα equivalent width distribution and consider the implications for both the derived stellar masses and the sSFR evolution. The mean rest-frame Hα equivalent width we infer at 3.8 < z < 5.0 (270 Å) indicates that nebular emission contributes at least 30% of the 3.6 μm flux and, by implication, nebular emission is likely to have a much greater impact for galaxies with z ≃ 6–7 where both warm IRAC filters are contaminated. Via our empirically derived equivalent width distribution, we correct the available stellar mass densities and show that the sSFR evolves more rapidly at z > 4 than previously thought, supporting up to a 5× increase between z ≃ 2 and 7. Such a trend is much closer to theoretical expectations. Given our findings, we discuss the prospects for verifying quantitatively the nebular emission line strengths prior to the launch of the James Webb Space Telescope.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/16ac0e846e1b9bcd594e1984e828d3e84450b4d2

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Citations in the corpus

REGULARITY UNDERLYING COMPLEXITY: A REDSHIFT-INDEPENDENT DESCRIPTION OF THE CONTINUOUS VARIATION OF GALAXY-SCALE MOLECULAR GAS PROPERTIES IN THE MASS-STAR FORMATION RATE PLANE (2013, unknown): “The most recent efforts have focused on quantifying the impact of nebular emission lines (e.g., Schaerer & de Barros 2010, Stark et al. 2013, de Barros et al. 2014, González et al. 2014) on stellar mass measurements.”
CONSTRAINING THE LOW-MASS SLOPE OF THE STAR FORMATION SEQUENCE AT 0.5 < z < 2.5 (2014, background): “This effect has recently been found to be particularly important for bright, blue galaxies discovered at 3 < z < 7 (Stark et al. 2013).”
STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS (2014, methodology): “In summary, the overestimate of the stellar mass when ignoring nebular emission at high redshift, as predicted by previous works (e.g., Stark et al. 2013; Schenker et al. 2013), is enhanced in particular redshift ranges where strong lines enter the near-IR filters and does not affect most of the…”
Identification of the brightest Lyα emitters at z = 6.6 : Implications for the evolution of the luminosity function in the reionization era (2015, background): “…or as a further evidence for the source being at z = 6.6, since at that redshift the [3.6] and [4.5] µm bands are contaminated in such a way that sources with strong nebular emission (EW > 1000 Å) are expected to have blue [3.6]− [4.5] colours (e.g. Stark et al. 2013; Smit et al. 2014a,b).”
The mass evolution of the first galaxies: stellar mass functions and star formation rates at 4 < z < 7 in the CANDELS GOODS-South field (2014, methodology): “This rate of stellar mass growth observed is higher than observed by González et al. (2011) over the same time period but comparable to that found by Stark et al. (2013) when the large uncertainty in the z ∼ 7 SMD is taken into account.”
THE SPECTRAL ENERGY DISTRIBUTIONS OF z ∼ 8 GALAXIES FROM THE IRAC ULTRA DEEP FIELDS: EMISSION LINES, STELLAR MASSES, AND SPECIFIC STAR FORMATION RATES AT 650 MYR (2012, methodology): “This technique has been applied successfully by looking for excess flux in the [3.6]−band due to Hα at z ∼ 4.5 (e.g. Shim et al. 2011, Stark et al. 2013) and by comparing the average observed IRAC colors over 4 < z < 6 (Gonzalez et al. 2012).”
THE KMOS3D SURVEY: DESIGN, FIRST RESULTS, AND THE EVOLUTION OF GALAXY KINEMATICS FROM 0.7 ⩽ z ⩽ 2.7 (2014, background): “…with the evolution of both quantities established observationally (molecular gas fractions: Tacconi et al. 2010, 2013; Daddi et al. 2010; Combes et al. 2011; Genzel et al. 2014a; sSFR: Bouché et al. 2010; Dutton et al. 2010; Whitaker et al. 2012b, 2014; Stark et al. 2013; González et al. 2014).”
THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ⩽ z ⩽ 6.5 IN CANDELS (2014, background): “Here we show the the observed UV absolute magnitude with no dust corrections in order to easily compare against previous studies (Stark et al. 2009, 2013; Lee et al. 2011, 2012).”
Herschel PEP/HerMES: the redshift evolution (0 ≤ z ≤ 4) of dust attenuation and of the total (UV+IR) star formation rate density (2013, background): “Stark et al.(2013) account for the nebular emission lines contribution to the broad-band fluxes used 3 Selecting option 1 or 2 does not impact on Fig.”
Lyα EMISSION FROM GREEN PEAS: THE ROLE OF CIRCUMGALACTIC GAS DENSITY, COVERING, AND KINEMATICS (2015, background): “As a comparison, inferred emission line contamination of Spitzer/ IRAC photometry provides tentative evidence for similar WHα in star-forming galaxies at z ∼ 4–7 (Shim et al. 2011; Labbé et al. 2013; Stark et al. 2013; Smit et al. 2014).”
Spectroscopic detection of C iv λ1548 in a galaxy at z = 7.045: implications for the ionizing spectra of reionization-era galaxies (2015, methodology): “…last several years, this technique has been used to characterize the equivalent width distribution of Hα in 3.8 < z < 5.0 galaxies (Shim et al. 2011; Stark et al. 2013) and [OIII]+Hβ in z ' 6.6−6.9 (Smit et al. 2014, 2015) and z ' 8 (Labbé et al. 2013) galaxies, revealing that typical [OIII] and…”
UNLEASHING POSITIVE FEEDBACK: LINKING THE RATES OF STAR FORMATION, SUPERMASSIVE BLACK HOLE ACCRETION, AND OUTFLOWS IN DISTANT GALAXIES (2013, background): “This is similar to what is observed at z 2 (Weinmann et al. 2011; Bouwens et al. 2012; Stark et al. 2013).”
A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING “MAIN SEQUENCE” FROM z ∼ 0–6 (2014, methodology): “When necessary, we include emission line effects on the masses using the conversion factors from Stark et al. (2013) and adjust for differences in cosmology using our assumed (h,ΩM ,ΩΛ) = (0.7, 0.3, 0.7) WMAP concordance cosmology (Spergel et al. 2003) and first-order volume corrections (see §…”
Stellar population effects on the inferred photon density at reionization (2015, background): “Such systems, observed at z ∼ 7, can form their current stellar mass in as little as 100Myr, assuming constant star formation at the observed rate (i.e. sSFR∼9.7Gyr−1, Stark et al. 2013).”
The bright end of the galaxy luminosity function at z≃7: before the onset of mass quenching? (2013, methodology): “We do not include models with nebular emission lines in our SED fitting analysis, which can result in underestimated masses by a factor of ' 2.4–4.4 (Stark et al. 2013), where the larger value assumes a continued evolution in the EW distribution of the contaminating lines beyond z = 5.”