Nebular emission from star-forming galaxies

By S. Charlot, M. Longhetti. 2001

356 citations recorded by the source corpus.

We present a new model for computing consistently the line and continuum emission from galaxies, based on a combination of recent population synthesis and photoionization codes. We use effective parameters to describe the H ii regions and the diffuse gas ionized by single stellar generations in a galaxy, among which the most important ones are the zero-age effective ionization parameter, the effective gas metallicity and the effective dust-to-heavy element ratio. We calibrate the nebular properties of our model using the observed [O iii]/Hβ, [O ii]/[O iii], [S ii]/Hα and [N ii]/[S ii] ratios of a representative sample of nearby spiral and irregular, starburst and H ii galaxies. To compute whole (line plus continuum) spectral energy distributions, we include the absorption by dust in the neutral interstellar medium (ISM) using a recent simple prescription, which is consistent with observations of nearby starburst galaxies. Our model enables us to interpret quantitatively the observed optical spectra of galaxies in terms of stars, gas and dust parameters. We find that the range of ionized-gas properties spanned by nearby galaxies implies factors of 3.5 and 14 variations in the Hα and [O ii] luminosities produced per unit star formation rate (SFR). When accounting for stellar Hα absorption and absorption by dust in the neutral ISM, the actual uncertainties in SFR estimates based on the emergent Hα and [O ii] luminosities are as high as several decades. We derive new estimators of the SFR, the gas-phase oxygen abundance and the effective absorption optical depth of the dust in galaxies. We show that, with the help of other lines such as [O ii], Hβ, [O iii], [N ii] or [S ii], the uncertainties in SFR estimates based on Hα can be reduced to a factor of only 2–3, even if the Hα line is blended with the adjacent [N ii] lines. Without Hα, however, the SFR is difficult to estimate from the [O ii], Hβ and [O iii] lines. The reason for this is that the absorption by dust in the neutral ISM and the ionized-gas parameters are then difficult to constrain independently. This suggests that, while insufficient by itself, the Hα line is essential for estimating the star formation rate from the optical emission of a galaxy.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/78665deaf31f768b319bbe51a5c0c3f1e3d1c703

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

Nebular Continuum and Line Emission in Stellar Population Synthesis Models (2016, methodology): “Following the process of Charlot & Longhetti (2001), we use simple stellar populations (SSPs) as the ionizing source for the gas clouds using the photoionization code CLOUDY.”
Metallicities and Physical Conditions in Star-forming Galaxies at z ~ 1.0-1.5 (2008, methodology): “In an independent study, Brinchmann et al. (2008) have also analyzed the possible causes for the high-redshift galaxies’ offset in the BPT diagram, using theoretical models of nebu- lar emission from star-forming galaxies (Charlot & Longhetti 2001) and the SDSS DR4 data.”
Empirical determination of the shape of dust attenuation curves in star-forming galaxies (2011, methodology): “7 http://www.mpa-garching.mpg.de/SDSS/DR7/Data/stellarmass.html c© 0000 RAS, MNRAS000, 000–000 Gas phase metallicity: measured from a combination of the strongest optical emission line fluxes by Tremonti et al. (2004), using the method of Charlot & Longhetti (2001).”
Ionization state of inter-stellar medium in galaxies: evolution, SFR-M * -Z dependence, and ionizing photon escape (2013, background): “MNRAS 442, 900–916 (2014) Downloaded from https://academic.oup.com/mnras/article-abstract/442/1/900/1252695 by guest on 28 July 2018 ing of O2 + is more efficient than those in optical wavelength (e.g. Dopita et al. 2000; Charlot & Longhetti 2001).”
PRIMUS: CONSTRAINTS ON STAR FORMATION QUENCHING AND GALAXY MERGING, AND THE EVOLUTION OF THE STELLAR MASS FUNCTION FROM z = 0–1 (2013, methodology): “We draw µ from an order four Gamma distribution that ranges from zero to unity centered on a typical value 〈µ〉 = 0.3 (Charlot & Longhetti 2001; Wild et al. 2011) and the V -band optical depth from an order two Gamma distribution that peaks around AV ≈ 1.2 mag, with a tail to AV ≈ 6 mag.”
Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths (2015, background): “This makes the electronic temperature rise, and hence cooling through the optical transitions larger (Shields & Kennicutt 1995; Charlot & Longhetti 2001).”
Emission-line diagnostics of low-metallicity active galactic nuclei (2006, background): “Recent papers by Charlot & Longhetti (2001) and Kewley & Dopita (2002) have provided calibrated relationships between gas-phase oxygen abundance and combinations of strong emission lines that are obsrvable at optical wavelengths.”
Galaxy Star Formation as a Function of Environment in the Early Data Release of the Sloan Digital Sky Survey (2002, methodology): “As a result, only 85 galaxies satisfy the Charlot & Longhetti (2001) prescription.”
Spectral and photometric evolution of young stellar populations: The impact of gaseous emission at various metallicities (2003, methodology): “It differs from those of Charlot & Longhetti (2001), Moy et al. (2001), or Zackrisson et al. (2001), who assume electron densities and temperatures for the gas at low metallicities and couple a photoionisation code to their evolutionary synthesis model.”
The host galaxies of active galactic nuclei (2003, neutral): “1: starforming galaxies define a sequence in which the ratio [O III]/Hβ decreases and the ratio [N II]/Hα increases towards higher gas-phase metallicities (e.g. Charlot & Longhetti 2001).”
PHYSICAL PROPERTIES OF EMISSION-LINE GALAXIES AT z ∼ 2 FROM NEAR-INFRARED SPECTROSCOPY WITH MAGELLAN FIRE (2014, background): “However, ionization parameter scales weakly with electron density: U ∝ n 1/3 e (Charlot & Longhetti 2001), and the ∼4× higher electron density we find with respect to local samples is, therefore, probably not the only cause of the ∼0.5-1.0 dex higher ionization parameters in the high redshift…”
Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS (2003, methodology): “Uniform dust extinction will not affect the W0(Hα), though selective extinction around massive stars will (Charlot & Longhetti 2001).”
Inferring the star formation histories of massive quiescent galaxies with bagpipes: evidence for multiple quenching mechanisms (2017, methodology): “(iii) The transmission function of the ionized ISM, T+(a, λ), as defined by Charlot & Longhetti (2001), including absorption, line emission, ionized continuum emission and emission from warm dust within H ii regions (described in Section 3.1.3).”
Galaxies with Wolf-Rayet signatures in the low-redshift Universe. A survey using the Sloan Digital Sky Survey (2008, methodology): “At higher metallicity one might use one of several “strong-line” methods which are calibrated on photoionisation models (e.g. Osterbrock 1989; Charlot & Longhetti 2001; Kewley & Dopita 2002).”
A fundamental relation between mass, SFR and metallicity in local and high redshift galaxies (2010, background): “Others (Charlot & Longhetti 2001; Brinchmann et al. 2004) have discussed that systematic effects with mass and metallicity could be present.”
Bulge mass is king: the dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey (2014, methodology): “For the BPT selected star forming galaxies, SFRs are determined via fitting of their emission lines with Charlot & Longhetti (2001) models.”
The Environment of Active Galactic Nuclei in the Sloan Digital Sky Survey (2003, methodology): “AGN Fraction as a Function of Galaxy Morphology In this section, we study the fraction of AGNs in galaxies as a function of the morphology of the host galaxy.”
Deriving model-based Te-consistent chemical abundances in ionized gaseous nebulae (2014, background): “The main problem is that many of the most widely used calibrations based on models (e.g. McGaugh 1991; Charlot & Longhetti 2001; Kewley & Dopita 2002) give systematic overabundances in relation with the direct method.”
SEMI-ANALYTIC GALAXY EVOLUTION (SAGE): MODEL CALIBRATION AND BASIC RESULTS (2016, methodology): “Furthering this, Tremonti et al. (2004, and see references therein) showed there is a near quadratic relationship in logarithmic space for the oxygen abundance in galaxies, calculated based on the model of Charlot & Longhetti (2001), as a function of their stellar mass.”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, methodology): “…wide range of ionization parameter (−3.5 < log (U ) < −1.9), metallicity (0.0001 < Z < 0.05), and stellar effective temperature (McGaugh 1991; Dopita et al. 2000; Charlot & Longhetti 2001; Kewley et al. 2001a; Moy et al. 2001; Dopita et al. 2006a; Martı́n-Manjón et al. 2010; Levesque et al. 2010).”