Properties ofz~ 3–6 Lyman break galaxies

Abstract

Context. To gain insight on the mass assembly and place constraints on the star formation history (SFH) of Lyman break galaxies (LBGs), it is important to accurately determine their properties. Aims. We estimate how nebular emission and different SFHs affect parameter estimation of LBGs.Methods. We present a homogeneous, detailed analysis of the spectral energy distribution (SED) of ∼1700 LBGs from the GOODS-MUSIC catalogue with deep multi-wavelength photometry from the U band to 8 μm to determine stellar mass, age, dust attenuation, and star formation rate. Using our SED fitting tool, which takes into account nebular emission, we explore a wide parameter space. We also explore a set of different star formation histories. Results. Nebular emission is found to significantly affect the determination of the physical parameters for the majority of z ∼ 3−6 LBGs. We identify two populations of galaxies by determining the importance of the contribution of emission lines to broadband fluxes. We find that ∼65% of LBGs show detectable signs of emission lines, whereas ∼35% show weak or no emission lines. This distribution is found over the entire redshift range. We interpret these groups as actively star-forming and more quiescent LBGs, respectively. We find that it is necessary to considerer SED fits with very young ages (<50 Myr) to reproduce some colours affected by strong emission lines. Other arguments favouring episodic star formation and relatively short star formation timescales are also discussed. Considering nebular emission generally leads to a younger age, lower stellar mass, higher dust attenuation, higher star formation rate, and a large scatter in the SFR-M relation. Our analysis yields a trend of increasing specific star formation rate with redshift, as predicted by recent galaxy evolution models. Conclusions. The physical parameters of approximately two thirds of high redshift galaxies are significantly modified when we account for nebular emission. The SED models, which include nebular emission shed new light on the properties of LBGs with numerous important implications.

The ionizing photon production efficiency of compactz~ 0.3 Lyman continuum leakers and comparison with high-redshift galaxies

“…Our z ∼ 0.3 sources are also in line with the average relation between stellar mass and UV magnitude derived at high redshifts, which indicates a stellar mass M ∼ 10 9 M for M 1500 ∼ −20 (cf. Duncan et al 2014;de Barros et al 2014;Grazian et al 2015). Figure 2 shows for illustration the SED fit of the first of our LyC leakers, J0925+1403 from I16a, to the broad-band photometry from the SDSS and the two GALEX bands.…”

“…The fit was obtained with a version of the Hyperz code including nebular emission, described in Schaerer & de Barros (2009, 2010, which has been used extensively to fit large samples of high-z LBGs (cf. de Barros et al 2014). Since the attenuation law and the metallicity are constrained or measured (I16a), we used the SMC law and a metallicity =1/5 solar, the closest value available for the Bruzual & Charlot (2003) models.…”

SPITZER ULTRA FAINT SURVEY PROGRAM (SURFS UP). II. IRAC-DETECTED LYMAN-BREAK GALAXIES AT 6 ≲ z ≲ 10 BEHIND STRONG-LENSING CLUSTERS

“…Recent works suggest that, at least in a subset of high-z galaxies, strong nebular emission lines (most notably Hα, Hβ, [O III] λ5007, and [O II] λ3727) with rest-frame equivalent widths ∼200 Å or higher contribute significantly to their IRAC fluxes (e.g., Schaerer & De Barros 2009;Shim et al 2011;De Barros et al 2014;Smit et al 2014). The galaxies with extreme nebular emission line strengths are most likely starbursts younger than 100 Myr; such galaxies are also being found in increasing numbers at z∼2-3 (e.g., Atek et al 2011;van der Wel et al 2011).…”

“…The inferred stellar masses of these z  6 galaxy candidates range from ∼10 9 to ∼10 11 M e , surprisingly large for a universe younger than 1 Gyr old. It is likely that the majority of IRAC-detected z  6 galaxies are at the high-mass end of the stellar mass function, although some of these galaxies likely have their IRAC fluxes boosted by strong nebular emission lines like [O III], Hα, and Hβ (e.g., Finkelstein et al 2013;De Barros et al 2014;Smit et al 2014).…”

The Galaxy UV Luminosity Function Before the Epoch of Reionization

“…Our modeling results are consistent with the picture emerging from multiple recent studies that combine HST and Spitzer/IRAC data and find that the majority of z ∼ > 4 galaxies to have old stellar populations (> 100 Myr) and relatively low specific SFR (∼ 100 M yr −1 ) (Oesch et al 2013a;Straatman et al 2014; see also González et al 2011 for earlier studies reaching the same conclusion but without accounting for nebular emission lines). However, other independent studies based mostly on overlapping datasets reached the different conclusion that z ∼ > 4 galaxies have a high chance of being young systems (ages < 50 Myr) with high specific SFRs (de Barros et al 2014;Finkelstein et al 2015a), suggesting that improved observational constraints are needed to evaluate the fidelity of stellar ages predicted by our model.…”