The nebular emission of star-forming galaxies in a hierarchical universe

Abstract

Galaxy surveys targeting emission lines are characterising the evolution of star-forming galaxies, but there is still little theoretical progress in modelling their physical properties. We predict nebular emission from star-forming galaxies within a cosmological galaxy formation model. Emission lines are computed by combining the semi-analytical model SAG with the photoionisation code MAPPINGS-III. We characterise the interstellar medium (ISM) of galaxies by relating the ionisation parameter of gas in galaxies to their cold gas metallicity, obtaining a reasonable agreement with the observed Hα, [OII]λ 3727, [OIII]λ 5007 luminosity functions, and the the BPT diagram for local star-forming galaxies. The average ionisation parameter is found to increase towards low star-formation rates and high redshifts, consistent with recent observational results. The predicted link between different emission lines and their associated star-formation rates is studied by presenting scaling relations to relate them. Our model predicts that emission line galaxies have modest clustering bias, and thus reside in dark matter haloes of masses below M halo 10 12 [h −1 M ]. Finally, we exploit our modelling technique to predict galaxy number counts up to z ∼ 10 by targeting far-infrared (FIR) emission lines detectable with submillimetre facilities.

The 0.1 <z< 1.65 evolution of the bright end of the [O ii] luminosity function

“…Both the GP14 and OR14 models reproduce the evolution of the Hα LF reasonably well (Lagos et al 2014;Orsi et al 2014). The Hα is a recombination line and thus, its unattenuated luminosity is directly proportional to the Lyman continuum, which is a direct prediction of the semi-analytical models.…”

“…Here, we compare our observations to predictions from both the Gonzalez-Perez et al (2014) flavor of the  model (hereafter GP14) and the Orsi et al (2014) flavor of the  model (hereafter OR14). Both models follow the physical processes that shape the formation and evolution of galaxies, including 1. the collapse and merging of dark matter haloes; 2. the shock-heating and radiative cooling of gas inside dark matter haloes, leading to the formation of galaxy discs; 3. star formation bursts that can be triggered by either mergers or disk instabilities; 4. quiescent star formation in galaxy discs which in the OR14 model is assumed to be proportional to the total amount of cold gas, while in the GP14 model it takes into account both the atomic and molecular components of the gas (Lagos et al 2011); 5. the growth of super massive black holes in galaxies; 6. feedback from supernovae, from AGNs and from photoionization of the intergalactic medium; 7. chemical enrichment of the stars and gas; 8. galaxy mergers driven by dynamical friction within common dark matter haloes, leading to the formation of stellar spheroids.…”

“…Such an assumption, although reasonable for recombination lines, is likely too simplistic for other emission lines such as the [O] line (e.g., Sanchez et al 2015). Orsi et al (2014) combined the  semi-analytical model with a photo-ionization code to predict emission line strengths originated in H regions with different ionization parameters. In order to do this, the model assumes an ionization parameter that 10 The ionizing parameter is defined here as a dimensionless quantity equal to the ionizing photon flux per unit area per hydrogen density, normalized by the speed of light (see Stasińska 1990).…”

THE [N ii] 205 μm EMISSION IN LOCAL LUMINOUS INFRARED GALAXIES*

“…Here we further predict the [N II] 205 μm LFs at higher redshifts using the method described below. We will also compare our results with those from simulations given by Orsi et al (2014), and those derived with the method presented in Spinoglio et al (2012a).…”

“…It is important to constrain the LF of the [N II] emission locally since now it becomes possible to build a large sample for studying the [N II] LF at high redshift using modern facilities such as ALMA. The local [N II] LF can serve as a benchmark necessary for observational and theoretical (e.g., Orsi et al 2014) studies on its evolution. Given the unprecedented sensitivity of Herschel at ∼200 μm, and the large number of galaxies in the local universe already observed, for the first time we can derive the local [N II] LF (see Section 3.2), using a bivariate method and by utilizing the local IR LF, which has been studied extensively in the literature with IRAS observations (e.g., Soifer et al 1986;Sanders et al 2003).…”