The transition from Population III to normal galaxies: Lyα and He II emission and the ionising properties of high redshift starburst galaxies

By Daniel Schaerer. 2002

445 citations recorded by the source corpus.

Using new sets of stellar evolution models at very low metallicities (Z = 10 −7 ,1 0 −5 ) and previously published grids we examine spectral properties of the ionising continua, the Lyman-break, and the Lyα and He  λ1640 recombination lines in starbursts. The metallicity dependence of these properties, especially the transition from primordial galaxies (Population III) to currently observed metallicities, is examined for various IMFs and star formation histories. For the average properties of starbursts, approximated by a model with constant star formation, the main findings are: - The Lyman continuum flux Q(H) increases with decreasing metallicity. For a universal Salpeter IMF from 1-100 Mthe enhancement reaches typically a factor of ∼3 between solar metallicity and Pop III objects. - While for metallicities Z > 1/50 Zthe amplitude of the Lyman-break depends little on Z, a reduction by a factor ∼ 2i s found at lower metallicities, due to the strong increase of the average stellar temperature. - Using theoretical models and empirical constraints we discuss the expected evolution of the hardness of He + to H ionising photons, Q(He + )/Q(H), with metallicity and possible uncertainties. Over the metallicity range Z = 0t o∼10 −4 the hardness decreases from log(Q(He + )/Q(H)) ∼− 1.4 .. .−2.3 by ∼1.5-2 or more orders of magnitude, depending strongly on the upper mass cut-off of the IMF. From empirical constraints we derive a hardness log(Q(He + )/Q(H)) ∼ -3.2 to -2.6 for metal-poor starbursts (1/25 1/50 Zto 400-850 A or higher at Z between 10 −5 and 0 (Pop III) for the same Salpeter IMF. However, for well known reasons, the Lyα emission predicted likely represents an upper limit. Non-negligible He  λ1640 emission due to stellar photoionisation appears to be limited to very small metallicities (log(Z/Z� ) < −5.3) and Population III objects. The predictions, available on the Web through the CDS and at http://webast.ast.obs-mip.fr/sfr/, should be useful for a variety of studies regarding high redshift galaxies, cosmological reionisation, and others.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d7c721e0f4083d07e29236acf461b148e0592dcf

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Citations in the corpus

EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION (2015, methodology): “Given these observations, Lyα searches should also be able to find metalfree, PopIII stellar populations (since galaxies dominated by PopIII emit large amounts of Lyα photons, e.g. Schaerer 2002, 2003).”
Spectral population synthesis including massive binaries (2009, background): “It has been suggested such lines indicate the presence of population III stars (Schaerer 2003).”
UV-CONTINUUM SLOPES AT z ∼ 4–7 FROM THE HUDF09+ERS+CANDELS OBSERVATIONS: DISCOVERY OF A WELL-DEFINED UV COLOR–MAGNITUDE RELATIONSHIP FOR z ⩾ 4 STAR-FORMING GALAXIES (2011, result): “This blue β is also not inconsistent with what one can achieve with standard stellar population modeling (where the UV -continuum slope β can become as steep as ∼−2.7: Schaerer 2003; Bouwens et al. 2010a; Robertson et al. 2010).”
Keck spectroscopy of faint 3 < z < 7 Lyman break galaxies – I. New constraints on cosmic reionization from the luminosity and redshift-dependent fraction of Lyman α emission (2010, background): “As has been demonstrated in previous studies (Schaerer 2003), topheavy IMFs can boost the equivalent widths of Lyα relative to that expected for normal stellar populations.”
The impact of nebular emission on the ages of z~6 galaxies (2009, methodology): “Continuum emission is added to the stellar SED, as in our synthesis models (cf. Schaerer & Vacca 1998; Leitherer et al. 1999; Schaerer 2003).”
ON THE REDSHIFT EVOLUTION OF THE Lyα ESCAPE FRACTION AND THE DUST CONTENT OF GALAXIES (2010, background): “One would also assume that a relatively higher fraction of genuine primeval galaxies would be discovered as redshift increases, and a substantial (∼ 3-fold) enhancement of Lyα/UV may arise from preferential selection of extremely young systems (e.g. Charlot & Fall 1993; Schaerer 2003).”
High-Ionization Emission in Metal-deficient Blue Compact Dwarf Galaxies (2005, background): “…hard ionizing radiation have been proposed, such as massive main-sequence stars (Schaerer & de Koter 1997), Wolf-Rayet stars (Schaerer 1996), primordial zero-metallicity stars (Schaerer 2002, 2003), high-mass X-ray binaries (Garnett et al. 1991) and fast radiative shocks (Dopita & Sutherland 1996).”
LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z ⩾ 5–8 FROM THE HUDF09 WFC3/IR OBSERVATIONS (2011, background): “%) of low metallicity stars expected to make up galaxies in the early universe, we assume 1053.2 photons s−1 per M⊙ yr −1 (Schaerer 2003).”
Predicted UV properties of very metal-poor starburst galaxies (2010, methodology): “2 in Schaerer 2003).”
Stellar population effects on the inferred photon density at reionization (2015, background): “However our models differ from those of Schaerer (2003) and Raiter, Schaerer, & Fosbury (2010) in that we generate this photon flux at a continuum luminosity typically 0.1 dex lower.”
Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies (2011, methodology): “Therefore, this emission line is proposed as the signature of Pop III stars (e.g., Schaerer 2002, 2003).”
CLASH: THREE STRONGLY LENSED IMAGES OF A CANDIDATE z ≈ 11 GALAXY (2012, background): “The ionizing efficiency could be increased by a factor of ∼1.8 for a Chabrier (2003) IMF or ∼3 for a top-heavy IMF (Bruzual & Charlot 2003; Schaerer 2003; Stiavelli et al. 2004), with the latter generally realized in simulations of high-redshift galaxies (e.g., Abel et al. 2002; Bromm et al. 2002).”
The contribution of high-redshift galaxies to cosmic reionization: New results from deep WFC3 imaging of the Hubble Ultra Deep Field (2009, background): “Such blue slopes could be explained through low metallicity, or a top-heavy IMF, which can produce between 3 and 10 times as many ionizing photons for the same 1500 Å UV luminosity (Schaerer 2003 – see also Stiavelli, Fall & Panagia 2004).”
The origin of the galaxy mass-metallicity relation and implications for galactic outflows (2007, background): “The young galaxies also drive much of their enriched gas out via galactic superwinds, lac- ing the IGM with heavy elements (Adelberger et al. 2005b, 2003; Schaerer 2003) while suppressing their own star formation (Springel & Hernquist 2003b; Oppenheimer & Davé 2006).”
CRITICAL STAR FORMATION RATES FOR REIONIZATION: FULL REIONIZATION OCCURS AT REDSHIFT z ≈ 7 (2012, methodology): “Schaerer (2002, 2003) also computed models of Population III and lowmetallicity stars based on non-LTE model atmospheres and new stellar evolution tracks and evolutionary synthesis models.”
Mass, metal, and energy feedback in cosmological simulations (2007, background): “…of momentum-driven winds is that they do not have the same energy budget limitations as do supernova (SN) energy-driven winds, where the maximum is ∼ 1051 ergs per SN, because the UV photon energy generated over the main sequence lifetime of massive stars is ∼ 100× greater (Schaerer 2003).”
The birth of a galaxy – III. Propelling reionization with the faintest galaxies (2014, background): “We consider a monochromatic spectrum with an energy of 21.6 eV (Schaerer 2003).”