Ly$\mathsf{\alpha}$ emitters in the GOODS-S field

Abstract

Context. The Great Observatories Origins Deep Survey (GOODS) has provided us with one of the deepest multi-wavelength views of the distant universe. The combination of multi-band photometry and optical spectroscopy has resulted in the identification of sources whose redshifts extend to values in excess of six. Amongst these distant sources are Lyα emitters whose nature must be deduced by clearly identifying the different components that contribute to the measured SED. Aims. From a sample of Lyα emitters in the GOODS-S field with uncontaminated photometry and optical (red) spectroscopy, we select a spatially compact object at a redshift of 5.563 (Lyα) that shows a second emission line, identified as N iv] 1486 Å. The SED is modelled in a way that accounts for both the N iv] line emission and the photometry in a self-consistent way.Methods. The photoionization code CLOUDY is used to calculate a range of nebular models as a function of stellar ionizing source temperature, ionization parameter, density and nebular metallicity. We compare the theoretical and observed magnitudes and search for the model parameters that also reproduce the observed N iv] luminosity and equivalent width.Results. A nebular model with a hot blackbody ionizing source of around 100 kK and a nebular metallicity of ∼5% of solar is able to fit the observed SED and, in particular, explain the large apparent Balmer break which is inferred from the pure stellar population model fitting conventionally applied to multi-band photometric observations. In our model, an apparent spectral break is produced by strong [O iii] 4959, 5007 Å emission falling in one of the IR bands (IRAC1 in this case). A lower limit on the total baryonic mass of a model of this type is 3.2 × 10 8 M . Conclusions. It is argued that objects with Lyα emission at high redshift that show an apparent Balmer break may have their SED dominated by nebular emission and so could possibly be identified with very young starbursting galaxies rather than massive evolved stellar populations. Detailed studies of these emission nebulae with large telescopes will provide a unique insight into very early chemical evolution.

The unusual N IV] -emitter galaxy GDS J033218.92-275302.7: star formation or AGN-driven winds from a massive galaxy atz= 5.56

“…5. Such a discontinuity is consistent with estimates available in the literature for the same object (FIREWORKS, Wuyts et al 2008;Stark et al 2007;Wiklind et al 2008;Raiter et al 2010).…”

“…As noted recently by Schaerer & de Barros (2009) and Raiter et al (2010), strong nebular emission lines may bias the result of the SED-fitting of high-redshift galaxies (e.g. [O iii] 4959−5007, Hα).…”

Predicted UV properties of very metal-poor starburst galaxies

“…The effect of this is to increase the line and nebular continuum emission relative to any observable stellar continuum. In extreme cases (e.g., Raiter et al 2010) the nebular emission may completely dominate the UV/visible/NIR spectrum. Also, if low metallicity objects and/or different IMFs are relevant for the sources of cosmic reionization, their intrinsic Lyman continuum flux, generally estimated from UV restframe observations, may need to be revised accordingly.…”

The nature ofz ~ 2.3 Lyman-αemitters

“…Recent publications show that nebular emission lines can play an extremely important role in fitting SEDs (Zackrisson et al 2008;Schaerer & de Barros 2009;Raiter et al 2010). In order to properly take into account this potentially large effect of gas emission in young, star-bursting galaxies, an add-on to the GALAXEV code was created.…”