Evolutionary Synthesis Models as a Tool and Guide Towards the First Galaxies

Schaerer, Daniel

doi:10.1007/978-3-642-32362-1_7

Cited by 13 publications

(12 citation statements)

References 126 publications

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“…We briefly address the presence of nebular He II emission in SSC-N. Guseva (Schaerer & Stasínska 1999). When the first W-R stars appear around 4 Myr, the photoionization models can produce log (He II 4686/H) = 1.5, consistent with the nebular emission observed in SSC-N.…”

Section: Properties Of the Super Nebulamentioning

confidence: 63%

“…The Infrared Space Observatory (ISO) and the Spitzer Space Telescope detected strong nebular [O IV] 25.9 μm emission (Lutz et al 1998;Hao et al 2009). [O IV] emission paired with the presence of nebular, narrow He II 4686 Å suggest a very peculiar stellar population, non-thermal processes such as shocks, or even some contribution from a non-stellar powering source (Schaerer & Stasínska 1999;Izotov et al 2012), since emission from these high ionization species is not typically associated with star formation powered by normal OB stars. Among all metal-poor BCDs with Spitzer data, II Zw 40 has the most extreme [Ne III] 15.6/[Ne II] 12.8 ratio, a ratio often used as an ionization parameter diagnostic.…”

Section: Introductionmentioning

confidence: 99%

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Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Leitherer

Byler

Lee

et al. 2018

ApJ

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We analyze far-ultraviolet spectra and ancillary data of the super star cluster SSC-N and its surrounding H II region in the nearby dwarf galaxy II Zw 40. From the ultraviolet spectrum, we derive a low internal reddening of E(B -V) = 0.07 ± 0.03, a mass of (9.1 ± 1.0)  10 5 M⊙, a bolometric luminosity of (1.1 ± 0.1)  10 9 L⊙, a number of ionizing photons of (6 ± 2)  10 52 s −1 , and an age of (2.8 ± 0.1) Myr. These parameters agree with the values derived from optical and radio data, indicating no significant obscured star formation, absorption of photons by dust, or photon leakage. SSC-N and its nebulosity are an order of magnitude more massive and luminous than 30 Doradus and its ionizing cluster. Photoionization modeling suggests a high ionization parameter and a C/O ratio where C is between primary and secondary. We calculate diagnostic emission-line ratios and compare SSC-N to local star-forming galaxies. The SSC-N nebula does not coincide with the locus defined by local galaxies. Rather, it coincides with the location of "Green Pea" galaxies, objects which are often considered nearby analogs of the galaxies reionizing the universe. Most stellar features are well-reproduced by synthetic spectra.However, the SSC-N cluster has strong, broad, stellar He II 1640 emission that cannot be reproduced, suggesting a deficit of He-enhanced stars with massive winds in the models. We discuss possible sources for the broad He II emission, including very massive stars and/or enhanced mixing processes.

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Section: Properties Of the Super Nebulamentioning

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Leitherer

Byler

Lee

et al. 2018

ApJ

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“…Also, for completeness, since the [O ] 25.9 µm line is often discussed in the same context as the He line (e.g. Schaerer & Stasińska 1999), we checked that the [O ] 25.9 µm/[O ]λ5007 ratio in our models behaves similarly to the He λ4686/Hβ ratio (this is even more true for the [O ] 25.9 µm/[O ] 51.8 µm ratio, which is less sensitive to electronic temperature).…”

Section: Discussionmentioning

confidence: 99%

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

Plat

Charlot

Bruzual³

et al. 2019

Monthly Notices of the Royal Astronomical Society

117

133

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We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionizationbounded and density-bounded H regions, active-galactic-nucleus (AGN) narrow-line regions and radiative shocks computed all using the same physically-consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous exploration of more spectral diagnostics than typically available at once for individual subsamples. We confirm that current single-and binary-star population synthesis models do not produce hard-enough radiation to account for the high-ionization emission of the most metal-poor galaxies. Introducing either an AGN or radiative-shock component brings models into agreement with observations. A published model including X-ray binaries is an attractive alternative to reproduce the observed rise in He λ4686/Hβ ratio with decreasing oxygen abundance in metal-poor star-forming galaxies, but not the high observed He λ4686/Hβ ratios of galaxies with large EW(Hβ). A source of harder ionizing radiation appears to be required in these extreme objects, such as an AGN or radiative-shock component, perhaps linked to an initial-mass-function bias toward massive stars at low metallicity. This would also account for the surprisingly high [O ]/[O ] ratios of confirmed LyC leakers relative to ionization-bounded models. We find no simple by-eye diagnostic of the nature of ionizing sources and the escape of LyC photon, which require proper simultaneous fits of several lines to be discriminated against. galactic nuclei (AGN), arising from gas accretion onto primordial black holes; radiative shocks, induced by large-scale gas flows; and the leakage of Lyman-continuum (LyC) photons through a porous interstellar medium (ISM), contributing to reionization (see, e.g., the review by Stark 2016). In waiting for advent of the James Webb Space Telescope (JWST), which will enable deep rest-frame ultraviolet and optical emission-line spectroscopy of galaxies into the reionization era at redshifts z ∼ 10-15, more nearby metal-poor galaxies approaching the properties of primeval galaxies offer a useful laboratory in which to test our ability to interpret emission-line spectra.

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“…Due to the very high-ionization potential of [Ne V] (97.1 eV) we consider its detection coincident with the galactic nucleus in mid-IR spectroscopy to be an almost unambiguous identifier of AGN activity. Theoretically, Schaerer & Stasińska (1999) (Armus et al 2006;Satyapal et al 2008;Dale et al 2009;GA09). However, these ratios are not necessarily strong tracers of the intrinsic power of the AGN.…”

Section: [Ne V] As An Unambiguous Agn Indicatormentioning

confidence: 99%

Towards a complete census of active galactic nuclei in nearby galaxies: the incidence of growing black holes

Goulding

Alexander

Lehmer

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We investigate the local supermassive black hole (SMBH) density function and relative mass accretion rates of all active galactic nuclei (AGNs) identified in a volume‐limited sample of infrared (IR) bright galaxies (LIR > 3 × 109 L⊙) to D < 15 Mpc. A data base of accurate SMBH mass (MBH) estimates is compiled from literature sources using physically motivated AGN modelling techniques (reverberation mapping, maser mapping and gas kinematics) and well‐established indirect MBH estimation methods (the M–σ* and MBH–LK,bul relations). For the three sources without previously published MBH estimates, we use Two Micron All Sky Survey (2MASS) K‐band imaging and galfit to constrain the bulge luminosities, and hence SMBH masses. In general, we find the AGNs in the sample host SMBHs which are spread over a wide mass range [MBH≈ (0.1–30) × 107 M⊙], but with the majority in the poorly studied MBH≈ 106–107 M⊙ region. Using sensitive hard X‐ray (2–10 keV) and mid‐IR constraints we calculate the bolometric luminosities of the AGNs (LBol,AGN) and use them to estimate relative mass accretion rates. We use these data to calculate the volume‐averaged SMBH growth rate of galaxies in the local Universe and find that the AGNs hosting SMBHs in the mass range MBH≈ 106–107 M⊙ are dominated by optically unidentified AGNs. These relatively small SMBHs are acquiring a significant proportion of their mass in the present day, and are amongst the most rapidly growing in the local Universe (SMBH mass‐doubling times of ≈6 Gyr). Additionally, we find tentative evidence for an increasing volume‐weighted AGN fraction with decreasing SMBH mass in the MBH≈ 106–108 M⊙ range. Overall, we conclude that significant mass accretion on to small SMBHs may be missed in even the most sensitive optical surveys due to absent or weak optical AGN signatures.

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Evolutionary Synthesis Models as a Tool and Guide Towards the First Galaxies

Cited by 13 publications

References 126 publications

Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

Towards a complete census of active galactic nuclei in nearby galaxies: the incidence of growing black holes

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