A Census of Oxygen in Star-Forming Galaxies: An Empirical Model Linking Metallicities, Star Formation Rates, and Outflows

Abstract

In this contribution we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates at z = 0.07, 0.8 and 2.26, including the SDSS and DEEP2 surveys. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and star formation rate observed in our three samples. We show that the observed relation between stellar mass and star formation rate for our three samples is consistent with other samples in the literature. The massmetallicity relation is well established for our three samples and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the star formation rates and metallicities of galaxies over cosmic time allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies.

Formation of disc galaxies in preheated media: a preventative feedback model

“…Metallicity measurements of low-mass galaxies may provide useful constraints to the model (e.g. Zahid et al 2012). Moreover, the preheated media at the present time implied by our model may be detected by QSO absorption line systems of highly ionized elements, such as CIV and OVI, and may indeed be the 'missing' baryons we are looking for (e.g.…”

Star formation sustained by gas accretion

“…Even for large returned fractions R = 0.5 (e.g., Edmunds 2005; Leitner and Kravtsov 2011;Torrey et al 2012) and moderate outflows w = 0.2 (e.g., Zahid et al 2012; see also Sect. 2.3), SFR gf /SFR is as large as 58 %.…”

The slow flow model of dust efflux in local star-forming galaxies

“…The AGB phase of intermediate mass stars (1 M⊙ 8) and massive stars ( 8M⊙) which end their lives as Type II supernovae (SNe) are considered the dominant source of stellar dust production in star-forming galaxies while dust in the ISM may also form in situ from accretion of enriched gas processed by stars (Dwek 1998). Dust forms from metals and a strong correlation between gas-phase oxygen abundance and dust content is observed in local (Heckman et al 1998;Boissier et al 2004;Asari et al 2007;Garn & Best 2010;Xiao et al 2012;Zahid et al 2012b) and high redshifts galaxies Domínguez et al 2013).…”

“…The small scatter (∼ 0.25 dex) of the relation is independent of redshift suggesting that secular processes such as cosmological gas accretion dominate over mergers in building up the stellar mass of galaxies since at least z ∼ 2 − 3. The observed stellar mass-SFR relation (MSR) places strong constraints on the star formation histories of galaxies (Noeske et al 2007a;Conroy & Wechsler 2009;Leitner 2012;Zahid et al 2012b). The observed MSR at several epochs implies that the majority of local starforming galaxies are best characterized by continuous star formation histories.…”

“…The well defined MSRs and MZRs observed over cosmological time provide purely empirical constraints for continuous stellar mass growth and chemical enrichment of galaxies as they evolve (see Zahid et al 2012b). We attempt to understand trends in the metal and dust distribution of local galaxies in the context of this empirical framework.…”