New insights into the stellar content and physical conditions of star-forming galaxies at z = 2-3 from spectral modelling

By J. Brinchmann, M. Pettini, Stephane Charlot Caup Porto, I. Cambridge, Iap, Leiden. 2008

198 citations recorded by the source corpus.

We have used extensive libraries of model and empirical galaxy spectra [assembled, respectively, from the population synthesis code of Bruzual and Charlot and the fourth data release of the Sloan Digital Sky Survey (SDSS)] to interpret some puzzling features seen in the spectra of high-redshift star-forming galaxies. We show that a stellar He ii λ1640 emission line, produced in the expanding atmospheres of Of and Wolf–Rayet stars, should be detectable with an equivalent width of 0.5–1.5 A in the integrated spectra of star-forming galaxies, provided the metallicity is greater than about half solar. Our models reproduce the strength of the He ii λ1640 line measured in the spectra of Lyman-break galaxies for established values of their metallicities. With better empirical calibrations in local galaxies, this spectral feature has the potential of becoming a useful diagnostic of massive star winds at high, as well as low redshifts. We also uncover a relationship in SDSS galaxies between their location in the [O iii]/Hβ versus [N ii]/Hα diagnostic diagram (the BPT diagram) and their excess specific star formation rate relative to galaxies of similar mass. We infer that an elevated ionization parameter U is at the root of this effect, and propose that this is also the cause of the offset of high-redshift star-forming galaxies in the BPT diagram compared to local ones. We further speculate that higher electron densities and escape fractions of hydrogen ionizing photons may be the factors responsible for the systematically higher values of U in the H ii regions of high-redshift galaxies. The impact of such differences on abundance determinations from strong nebular lines are considered and found to be relatively minor.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/3d3d65a323d967023de7489e7cfb172b9c69ef1a

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. R. Dav'e
4. C. Conroy
5. P. V. van Dokkum
6. M. Franx
7. R. Somerville
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In Instrumentation

1. P. V. van Dokkum
2. C. Conroy
3. M. Franx
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6. I. Labbé
7. R. Bouwens
8. L. Hernquist

Citations in the corpus

• THEORETICAL EVOLUTION OF OPTICAL STRONG LINES ACROSS COSMIC TIME (2013, background): “The broad He II feature has been attributed to a significant contribution from O and Wolf-Rayet stars to the ionizing EUV radiation field at low metallicity (Brinchmann et al. 2008a).”
• Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio (2016, background): “…that galaxies with higher electron densities (ne ∼ 10 2 cm−3) exhibit higher log([N II]/Hα) and log([O III]/Hβ) than typical SDSS galaxies (e.g. Brinchmann et al. 2008; Liu et al. 2008; Yuan et al. 2010), often associated with higher inferred ionization parameters and differences in ISM…”
• Ionization state of inter-stellar medium in galaxies: evolution, SFR-M * -Z dependence, and ionizing photon escape (2013, background): “Nakajima et al. (2013) have pointed out a possibility that fesc positively correlates with ionization parameter, since an optically thin nebula could show a high [O III]/[O II] ratio (e.g. Giammanco, Beckman & Cedrés 2005; Brinchmann et al. 2008; Kewley et al. 2013b).”
• OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, background): “…galaxies in the nearby universe, and may not be applicable at higher redshift where the physical conditions in galaxies may differ dramatically from physical conditions in local galaxies (Shapley et al. 2005; Liu et al. 2008; Brinchmann et al. 2008; Hainline et al. 2009; Lehnert et al. 2009).”
• PHYSICAL CONDITIONS IN A YOUNG, UNREDDENED, LOW-METALLICITY GALAXY AT HIGH REDSHIFT (2010, methodology): “…weak emission in the composite shown in Figure 9 has equivalent width W0 ∼ 0.6 Å, and He II emission is clearly seen in the composite spectrum of z ∼ 3 Lyman break galaxies analyzed by Shapley et al. (2003), with W0 = 1.3 ± 0.3 Å (as measured by Brinchmann et al. 2008b) and FWHM ∼ 1500 km s−1 .”
• SDSS-IV MaNGA : the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements (2016, unknown): “2006; Liu et al. 2008; Brinchmann et al. 2008; Hainline et al. 2009; Wright et al. 2010; Trump et al. 2011 Kewley et al. 2013a,b; Steidel et al. 2014).”
• Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for Their Progenitors (2020, background): “…FRB hosts occupy a distinct region of the BPT diagram from the dominant locus of SF galaxies: the majority of FRB hosts show an excess in the [N II]/Hα ratio compared to the ridge line tracing the highest density of local SF galaxies (Brinchmann et al. 2008), with many located in the LINER region.”
• Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, background): “…of H ii regions and galaxies in the nearby Universe, which increasingly appear as inappropriate to study the star formation and ISM conditions of chemically young galaxies (e.g., Erb et al. 2010; Steidel et al. 2014, 2016; Shapley et al. 2015; see also Brinchmann et al. 2008; Shirazi et al. 2014).”
• A NEW DIAGNOSTIC OF ACTIVE GALACTIC NUCLEI: REVEALING HIGHLY ABSORBED SYSTEMS AT REDSHIFT >0.3 (2011, background): “Some attributed this trend to varying HII region conditions (Liu et al. 2008; Brinchmann et al. 2008; Hainline et al. 2009) while others claim that additional AGN contribution may be the driving factor (Groves et al. 2006; Wright et al. 2010).”
• A fundamental relation between mass, SFR and metallicity in local and high redshift galaxies (2010, background): “For this reason the absence of systematic differences between these two line ratios with SSFR is an indication that the dependence of measured metallicity on density or U, if present, is small, in agreement with the findings of Liu et al. (2008) and Brinchmann et al. (2008).”
• THE ORIGIN AND OPTICAL DEPTH OF IONIZING RADIATION IN THE “GREEN PEA” GALAXIES (2013, methodology): “The blue bump emission of WNE stars comes from Nv λ4603-4620, and the WNE stars have weaker blue bump luminosities than the WNL stars (Brinchmann et al. 2008).”
• VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES, (2011, methodology): “We note that using the BPT diagram to classify low-metallicity dwarf galaxies with high sSFR can be somewhat ambiguous (Brinchmann et al. 2008; Izotov & Thuan 2008).”
• Galaxies with Wolf-Rayet signatures in the low-redshift Universe. A survey using the Sloan Digital Sky Survey (2008, background): “It is of considerable interest to understand the properties of the interstellar medium (ISM) of galaxies with very strong star formation activity since this might give important insights into the ISM of actively star forming galaxies at all redshifts (e.g. Brinchmann et al. 2008; Liu et al. 2008).”
• Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, methodology): “The first, presented here for comparison with our own earlier work is the Brinchmann et al. (2008) sample of WR galaxies selected from SDSS.”
• THE MOSFIRE DEEP EVOLUTION FIELD (MOSDEF) SURVEY: REST-FRAME OPTICAL SPECTROSCOPY FOR ∼1500 H-SELECTED GALAXIES AT 1.37 ≤ z ≤ 3.8 ?> (2014, background): “The origin of these differences may reflect fundamental differences in distant H ii regions (e.g., Liu et al. 2008; Brinchmann et al. 2008) and may have severe implications for metallicity measurements of galaxies.”
• LSD: Lyman-break galaxies Stellar populations and Dynamics – I. Mass, metallicity and gas at z∼ 3.1 (2009, background): “Nevertheless, several authors (Brinchmann et al. 2008; Liu et al. 2008) conclude that the influence of different ionization conditions on the derived metallicities is likely to be low, of the order of 0.1 dex.”