Revisiting the hardening of the stellar ionizing radiation in galaxy discs

Pérez-Montero, E.; García-Benito, R.; Vı́lchez, J. M.

doi:10.1093/mnras/sty3330

Cited by 15 publications

(16 citation statements)

References 41 publications

(52 reference statements)

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“…As a consistency check, we also used the HII-CH-mistry pipeline (Pérez-Montero et al 2014) for the computation of the gas phase metallicity. Based on the diagnostic diagrams (see Sect.…”

Section: Determination Of the Oxygen Abundance And Ionisation Parameter With Hii-ch-mistrymentioning

confidence: 99%

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

Ciocan

Ziegler

Verdugo

et al. 2021

A&A

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We reveal the importance of ongoing in situ star formation in the brightest cluster galaxy (BCG) in the massive cool-core CLASH cluster MACS 1931.8-2635 at a redshift of z = 0.35 by analysing archival VLT-MUSE optical integral field spectroscopy. Using a multi-wavelength approach, we assessed the stellar and warm ionised medium components, which were spatially resolved by the VLT-MUSE spectroscopy, and linked them to the molecular gas by incorporating sub-mm ALMA observations. We measured the fluxes of strong emission lines such as: [O II] λ3727, Hβ, [O III] λ5007, Hα, [N II] λ 6584, and [S II] λ6718, 6732, which allowed us to determine the physical conditions of the warm ionised gas, such as electron temperature, electron density, extinction, ionisation parameter, (O/H) gas metallicities, star formation rates, and gas kinematics, as well as the star formation history of the system. Our analysis reveals the ionising sources in different regions of the galaxy. The ionised gas flux brightness peak corresponds to the location of the supermassive black hole in the BCG and the system shows a diffuse warm ionised gas tail extending 30 kpc in the north-east direction. The ionised and molecular gas are co-spatial and co-moving, with the gaseous component in the tail likely falling inward, providing fuel for star formation and accretion-powered nuclear activity. The gas is ionised by a mix of star formation and other energetic processes which give rise to LINER-like emission, with active galactic nuclei emission dominant only in the BCG core. We measured a star formation rate of ∼97 M⊙ yr−1, with its peak at the BCG core. However, star formation accounts for only 50–60% of the energetics needed to ionise the warm gas. The stellar mass growth of the BCG at z < 0.5 is dominated either by in situ star formation generated by thermally unstable intracluster medium cooling or by dry mergers, with these mechanisms accounting for the build-up of 20% of the stellar mass of the system. Our measurements reveal that the most central regions of the BCG contain the lowest gas-phase oxygen abundance, whereas the Hα arm exhibits slightly more elevated values, suggesting the transport of gas out to large distances from the centre as a result of active galactic nuclei outbursts. The galaxy is a dispersion-dominated system that is typical for massive, elliptical galaxies. The gas and stellar kinematics are decoupled, with the gaseous velocity fields being more closely related to the bulk motions of the intracluster medium.

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“…As a consistency check, we also used the HII-CH-mistry pipeline (Pérez-Montero et al 2014) for the computation of the gas phase metallicity. Based on the diagnostic diagrams (see Sect.…”

Section: Determination Of the Oxygen Abundance And Ionisation Parameter With Hii-ch-mistrymentioning

confidence: 99%

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

Ciocan

Ziegler

Verdugo

et al. 2021

A&A

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“…2. Alternatively, for such objects, we used the emission line ratio [S ii]/[O iii] for our calculations, which can also be used to provide a scale for T * (e.g., Pérez-Montero et al 2019b).…”

Section: The Softness Diagram Based On He Emission Linesmentioning

confidence: 99%

“…As described in Pérez-Montero et al (2019b), in the case of WM-Basic stellar atmospheres, it is possible to use a grid of models to perform a Bayesian-like comparison between the ob- In the case of our sample of He ii emitters, we update the code HCm-Teff to version 4.0 to take into account the emission-line ratio He i/He ii and using the same black-body models described in the above section.…”

Section: Using Hcm-teff To Derive T * In He II Emittersmentioning

confidence: 99%

Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram

Pérez-Montero

Kehrig

Vı́lchez

et al. 2020

A&A

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Aims. Star-forming galaxies with nebular He II emission contain very energetic ionizing sources of radiation, which can be considered as analogs to the major contributors of the reionization of the Universe in early epochs. It is therefore of great importance to provide a reliable absolute scale for the equivalent effective temperature (T*) for these sources. Methods. We study a sample of local (z < 0.2) star-forming galaxies showing optical nebular He II emission using the so-called softness diagrams, involving emission lines of two elements in two consecutive stages of ionization (e.g., [S II]/[S III] vs. [O II]/[O III]). We use for the first time the He I/He II ratio in these diagrams in order to explore the higher range of T* expected in these objects, and to investigate the role of possible mechanisms driving the distribution of galaxy points in these diagrams. We build grids of photoionization models covering different black-body temperatures, model cluster atmospheres, and density-bounded geometries to explain the conditions observed in the sample. Results. We verified that the use of the softness diagrams including the emission-line ratio He I/He II combined with black-body photoionization models can provide an absolute scale of T* for these objects. The application of a Bayesian-like code indicates T* in the range 50−80 kK for the sample of galaxies, with a mean value higher than 60 kK. The average of these high temperature values can only be reproduced using cluster model populations with nearly metal-free stars, although such ionizing sources cannot explain either the highest T* values, beyond 1σ, or the dispersion observed in the softness diagrams. According to our photoionization models, most sample galaxies could be affected to some extent by ionizing photon leaking, presenting a mean photon absorption fraction of 26% or higher depending on the metallicity assumed for the ionizing cluster. The entire range of He I/He II, [S II]/[S III], and [O II]/[O III] ratios for these HeII-emitting galaxies is reproduced with our models, combining nearly metal-free ionizing clusters and photon leaking under different density-bounded conditions.

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“…As shown in the right panel of Figure 7 and contrary to other high-to-low excitation emission-line intensity ratios such as O3O2 or Ne3O2, no correlation between oxygen abundance and the emis-sion line ratio [S ]/[S ] is observed (𝜌 = 0.06). This different behaviour could be due to the fact that O32 and Ne3O2 are not directly tracing the excitation of the gas, but the hardness of the ionizing radiation (Dors et al 2017;Pérez-Montero et al 2019a). On the contrary, the emission-line ratio [S ]/[S ] shows very little dependence on the equivalent effective temperature of the ionizing source and strongly depends on the ionization parameter (e.g.…”

Section: Parameters Based On [Sii] and [Siii] Emission Linesmentioning

confidence: 99%

Extreme Emission-Line Galaxies in SDSS. I. Empirical and model-based calibrations of chemical abundances

Pérez-Montero,

Amorín,

Almeida

et al. 2021

Preprint

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Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 Extreme Emission Line Galaxies (EELGs) at a redshift 0 𝑧 0.49, selected from the Sloan Digital Sky Survey (SDSS) to be local analogues of high-redshift galaxies, was used to analyze their most prominent emission lines and to derive total oxygen abundances and nitrogen-to-oxygen ratios following the direct method in the ranges 7.7 < 12+log(O/H) < 8.6 and -1.8 < log(N/O) < -0.8. They allow us to obtain new empirically calibrated strong-line methods and to evaluate other recipes based on photoionization models that can be later used for a chemical analysis of actively star-forming galaxies in very early stages of galaxy evolution. Our new relations are in agreement with others found for smaller samples of objects at higher redshifts. When compared with other relations calibrated in the local Universe, they differ when the employed strong-line ratio depends on the hardness of the ionizing radiation, such as O32 or Ne3O2, but they do not when the main dependence is on the ionization parameter, such as S23. In the case of strong-line ratios depending on [N ] lines, the derivation of O/H becomes very uncertain due to the very high N/O values derived in this sample, above all in the low-metallicity regime. Finally, we adapt the bayesian-like code HII-C -for the conditions found in this kind of galaxies and we prove that it can be used to derive within errors both O/H and N/O, in consistency with the direct method .

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Revisiting the hardening of the stellar ionizing radiation in galaxy discs

Cited by 15 publications

References 41 publications

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram

Extreme Emission-Line Galaxies in SDSS. I. Empirical and model-based calibrations of chemical abundances

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Revisiting the hardening of the stellar ionizing radiation in galaxy discs

Cited by 15 publications

References 41 publications

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy

Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram

Extreme Emission-Line Galaxies in SDSS. I. Empirical and model-based calibrations of chemical abundances

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Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram