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This page contains information and references to all papers published related to HII-CHI-Mistry. When using the code, cite in your papers the original article Pérez-Montero (2014) and other papers related to the version of the code used.
Title: Deriving model-based T$_{e}$-consistent chemical abundances in ionized gaseous nebulae
Authors: E. Pérez-Montero
Abstract: The derivation of abundances in gaseous nebulae ionized by massive stars using optical collisionally excited emission lines is studied in this work, comparing the direct or Te method with updated grids of photoionization models covering a wide range of input conditions of O/H and N/O abundances and ionization parameter. The abundances in a large sample of compiled objects with at least one auroral line are re-derived and later compared with the
DOI: 10.1093/mnras/stu753
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Associated version: Main HII-CHI-Mistry
Title: A bayesian-like approach to derive chemical abundances in type-2 active galactic nuclei based on photoionization models
Authors: E. Pérez-Montero, O. L. Dors, J. M. Vílchez, R. García-Benito, M. V. Cardaci, G. F. Hägele
Abstract: We present a new methodology for the analysis of the emission lines of the interstellar medium in the narrow-line regions around type-2 active galactic nuclei. Our aim is to provide a recipe that can be used for large samples of objects in a consistent way using different sets of optical emission lines that takes into the account possible variations from the O/H-N/O relation to use [N II] lines. Our approach consists of a bayesian-like comparison between certain observed emission-line ratios sensitive to total oxygen abundance, nitrogen-to-oxygen ratio, and ionization parameter with the predictions from a large grid of photoionization models calculated under the most usual conditions in this environment. We applied our method to a sample of Seyfert 2 galaxies with optical emission-line fluxes and determinations of their chemical properties from detailed models in the literature. Our results agree within the errors with other results and confirm the high metallicity of the objects of the sample, with N/O values consistent with a large secondary production of N, but with a large dispersion. The obtained ionization parameters for this sample are much larger than those for star-forming object at the same metallicity.
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Associated version: From HCm_v4.0 to latest one. Usage of HCm for AGN.
Title: Extreme emission-line galaxies in SDSS - I. Empirical and model-based calibrations of chemical abundances
Authors: E. Pérez-Montero, R. Amorín, J. Sánchez Almeida, J. M. Vílchez, R. García-Benito, C. Kehrig
Abstract: 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 analyse 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 II] 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 H II-CHI-MISTRY 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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Associated version: From HCm_v5.1 to latest one. Usage of HCm for EELG.
Title: Chemical abundances in the nuclear region of nearby galaxies from the Palomar Survey
Authors: B. Pérez-Díaz, J. Masegosa, I. Márquez, E. Pérez-Montero
Abstract: We estimate chemical abundances and ionization parameters in the nuclear region of a sample of 143 galaxies from the Palomar Spectroscopic Survey, composed by star-forming galaxies (87), Seyferts 2 (16), and LINERs (40) using the HII-CHI-MISTRY code. We also study for each spectral type the correlation of the derived quantities with other different properties of the host galaxies, such as morphology, stellar mass, luminosity, and mass of their supermassive black holes. The results obtained for star-forming galaxies are used to check the soundness of our methodology. Then, we replicate a similar study for our sample of AGN, distinguishing between Seyferts 2 and LINERs. We report a saturation of Oxygen abundances for the nuclear regions of SFG. The correlations between chemical abundances and their host galaxy properties for SFG are in good agreement with previous studies. We find that Seyferts 2 present slightly higher chemical abundances but this result must be reexamined in larger samples of Seyfert galaxies. In contrast, we obtain lower chemical abundances for LINERs than for SFG. We confirm these relatively lower abundances for another sample of infrared luminous LINERs in the same stellar mass range. Our analysis of AGNs (both LINERs and Seyferts) shows that their host galaxy properties are not correlated with our estimated chemical abundances.
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Associated version: From HCm_v5.2 to latest one. Usage of HCm for Low-Ionization AGN.
Title: Using photo-ionisation models to derive carbon and oxygen gas-phase abundances in the rest UV
Authors: E. Pérez-Montero, R. Amorín
Abstract: We present a new method to derive oxygen and carbon abundances using the ultraviolet (UV) lines emitted by the gas phase ionized by massive stars. The method is based on the comparison of the nebular emission-line ratios with those predicted by a large grid of photoionization models. Given the large dispersion in the O/H-C/O plane, our method first fixes C/O using ratios of appropriate emission lines and, in a second step, calculates O/H and the ionization parameter from carbon lines in the UV. We find abundances totally consistent with those provided by the direct method when we apply this method to a sample of objects with an empirical determination of the electron temperature using optical emission lines. The proposed methodology appears as a powerful tool for systematic studies of nebular abundances in star-forming galaxies at high redshift.
DOI: 10.1093/mnras/stx186
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Associated version: From HCm-UV_v2.0 to latest one. Usage of HCm-UV for ultraviolet emission lines in HII regions.
Title: Assessing model-based carbon and oxygen abundance derivation from ultraviolet emission lines in AGNs
Authors: E. Pérez-Montero, R. Amorín, B. Pérez-Díaz, J. M. Vílchez, R. García-Benito
Abstract: We present an adapted version of the code HII-CHI-MISTRY-UV to derive chemical abundances from emission lines in the ultraviolet, for use in narrow line regions (NLR) of active galactic nuclei (AGN). We evaluate different ultraviolet emission line ratios and how different assumptions about the models, including the presence of dust grains, the shape of the incident spectral energy distribution, or the thickness of the gas envelope around the central source, may affect the final estimates as a function of the set of emission lines used. We compare our results with other published recipes for deriving abundances using the same emission lines and show that deriving the carbon-to-oxygen abundance ratio using C III] λ 1909 Å and O III] λ 1665 Å emission lines is a robust indicator of the metal content in AGN that is nearly independent of the model assumptions, similar to the case of star-forming regions. Moreover, we show that a prior determination of C/O allows for a much more precise determination of the total oxygen abundance using carbon UV lines, as opposed to assuming an arbitrary relationship between O/H and C/O, which can lead to non-negligible discrepancies.
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Associated version: From HCm-UV_v5.0 to latest one. Usage of HCm-UV for ultraviolet emission lines in AGNs.
Title: Measuring chemical abundances with infrared nebular lines: HII-CHI-MISTRY-IR
Authors: J. A. Fernández-Ontiveros, E. Pérez-Montero, J. M. Vílchez, R. Amorín, L. Spinoglio
Abstract: We provide a new method for deriving heavy element abundances taking advantage of the unique suite of fine-structure lines in the mid- to far-infrared (IR) range. Using grids of photo-ionisation models that cover a wide range in O/H and N/O abundances and ionisation parameter, our code HII-CHI-MISTRY-IR (HCM-IR) provides model-based abundances based on extinction-free and temperature-insensitive tracers. These are two significant advantages over optical diagnostics when they are applied to dust-obscured regions or unresolved (stratified) nebulae, typical conditions found in high-z galaxies. The performance of the code is probed using three different samples of galaxies that extend over a wide range in metallicity, 7.2 ≲ 12 + log(O/H) ≲ 8.9, with available mid- to far-IR spectroscopic observations from Spitzer and Herschel, respectively. The samples correspond to 28 low-metallicity dwarf galaxies, 19 nearby starbursts, and 9 luminous IR galaxies. The IR model-based metallicities obtained are robust within a scatter of 0.03 dex when the hydrogen recombination lines, which are typically faint transitions in the IR range, are not available. When compared to the optical abundances obtained with the direct method, model-based methods, and strong-line calibrations, HCM-IR estimates show a typical dispersion of ∼ 0.2 dex. This is in line with previous studies comparing IR and optical abundances and does not introduce a noticeable systematic above 12 + log(O/H) ≳ 7.6. This accuracy can be achieved by measuring the sulphur ([S IV]10.5 μm and [S III]18.7, 33.5 μm) and the neon lines ([Ne III]15.6 μm and [Ne II]12.8 μm). Additionally, HCM-IR provides an independent N/O measurement when the oxygen ([O III]52, 88 μm) and nitrogen ([N III]57 μm) transitions are measured. The derived abundances in this case do not rely on particular assumptions on the N/O ratio. Large uncertainties (∼ 0.4 dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like N/O ratio is adopted. Finally, the code has been applied to 8 galaxies located at 1.8 < z < 7.5 with ground-based detections of far-IR lines redshifted in the submillimetre range, revealing solar-like N/O and O/H abundances in agreement with recent studies. A script to derive chemical abundances with HCM-IR has been made publicly available online.
DOI: 10.1051/0004-6361/202039716
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Associated version: From HCm-IR_v1.1 to latest one. Usage of HCm-IR for infrared emission lines in HII regions.
Title: Measuring chemical abundances in AGN from infrared nebular lines: HII-CHI-MISTRY-IR for AGN
Authors: B. Pérez-Díaz, E. Pérez-Montero, J. A. Fernández-Ontiveros, J. M. Vílchez
Abstract: Context. Future and ongoing infrared and radio observatories such as JWST, METIS, and ALMA will increase the amount of rest-frame IR spectroscopic data for galaxies by several orders of magnitude. While studies of the chemical composition of the interstellar medium (ISM) based on optical observations have been widely spread over decades for star-forming galaxies (SFGs) and, more recently, for active galactic nuclei (AGN), similar studies need to be performed using IR data. In the case of AGN, this regime can be especially useful given that it is less affected by temperature and dust extinction, traces higher ionic species, and can also provide robust estimations of the chemical abundance ratio N/O. Aims: We present a new tool based on a Bayesian-like methodology (HII-CHI-MISTRY-IR) to estimate chemical abundances from IR emission lines in AGN. We use a sample of 58 AGN with IR spectroscopic data retrieved from the literature, composed by 43 Seyferts, eight ultraluminous infrared galaxies (ULIRGs), four luminous infrared galaxies (LIRGs), and three low-ionization nuclear emission line regions (LINERs), to probe the validity of our method. The estimations of the chemical abundances based on IR lines in our sample are later compared with the corresponding abundances derived from the optical emission lines in the same objects. Methods: HII-CHI-MISTRY-IR takes advantage of photoionization models, characterized by the chemical abundance ratios O/H and N/O, and the ionization parameter U, to compare their predicted emission-line fluxes with a set of observed values. Instead of matching single emission lines, the code uses some specific emission-line ratios that are sensitive to the above free parameters. Results: We report mainly solar and also subsolar abundances for O/H in the nuclear region for our sample of AGN, whereas N/O clusters are around solar values. We find a discrepancy between the chemical abundances derived from IR and optical emission lines, the latter being higher than the former. This discrepancy, also reported by previous studies of the composition of the ISM in AGN from IR observations, is independent of the gas density or the incident radiation field to the gas, and it is likely associated with dust obscuration and/or temperature stratification within the gas nebula.
DOI: 10.1051/0004-6361/202243602
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Associated version: From HCm-IR_v2.1 to latest one. Usage of HCm-IR for infrared emission lines in AGNs.
Title: Chemical abundances and deviations from the solar S/O ratio in the gas-phase interstellar medium of galaxies based on infrared emission lines
Authors: B. Pérez-Díaz, E. Pérez-Montero, J. A. Fernández-Ontiveros, J. M. Vílchez, A. Hernán-Caballero, R. Amorín
Abstract: Context. The infrared (IR) range is extremely useful in the context of chemical abundance studies of the gas-phase interstellar medium (ISM) due to the large variety of ionic species traced in this regime, the negligible effects from dust attenuation or temperature stratification, and the amount of data that has been and will be released in the coming years. Aims: Taking advantage of available IR emission lines, we analysed the chemical content of the gas-phase ISM in a sample of 131 star-forming galaxies (SFGs) and 73 active galactic nuclei (AGNs). In particular, we derived the chemical content via their total oxygen abundance in combination with nitrogen and sulphur abundances, and with the ionisation parameter. Methods: We used a new version of the code HII-CHI-MISTRY-IR v3.1, which allowed us to estimate log(N/O), 12+log(O/H), log(U) and, for the first time, 12+log(S/H) from IR emission lines, which can be applied to both SFGs and AGNs. We tested whether the estimates from this new version, which only considers sulphur lines for the derivation of sulphur abundances, are compatible with previous studies. Results: While most of the SFGs and AGNs show solar log(N/O) abundances, we find a large spread in the log(S/O) relative abundances. Specifically, we find extremely low log(S/O) values (1/10 solar) in some SFGs and AGNs with solar-like oxygen abundances. This result warns against the use of optical and IR sulphur emission lines to estimate oxygen abundances when no prior estimation of log(S/O) is provided
DOI: 10.1051/0004-6361/202348318
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Associated version: From HCm-IR_v3.01 to latest one. Usage of HCm-IR for infrared emission lines from both SFGs and AGNs.
Title: Revisiting the hardening of the stellar ionizing radiation in galaxy discs
Authors: E. Pérez-Montero, R. García-Benito, J. M. Vílchez
Abstract: In this work we explore accurate new ways to derive the ionization parameter (U) and the equivalent effective temperature (T*) in H II regions using emission-line intensities from the ionized gas. The so-called softness parameter (η), based on [O II], [O III], [S II], and [S III], has been proposed to estimate the hardening of the ionizing incident field of radiation, but the simplest relation of this parameter with T* also depends on U and metallicity (Z). Here we provide a Bayesian-like code (HCM-TEFF) that compares the observed emission lines of η with the predictions of a large grid of photoionization models giving precise estimations of both U and T* when Z is known. We also study the radial variation of these parameters in well-studied disc galaxies observed by the CHAOS collaboration. Our results indicate that the observed radial decreasing of η can be attributed to a radial hardening of T* across galactic discs as in NGC 628 and NGC 5457. On the other hand NGC 5194, which presents a positive slope of the fitting of the softness parameter, has a flat slope in T*. On the contrary the three galaxies do not seem to present large radial variations of the ionization parameter. When we inspect a larger sample of galaxies, we observe steeper radial variations of T* in less bright and later-type galaxies, mimicking a similar trend observed for Z, but the studied sample should be enlarged to obtain more statistically significant conclusions.
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Associated version: From HCm-Teff_v2.0 to latest one. Usage of HCm-Teff for models with plane-parallel or spherical geometry.
Title: Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram
Authors: E. Pérez-Montero, C. Kehrig, J. M. Vílchez, R. García-Benito, S. Duarte Puertas, J. Iglesias-Páramo
Abstract: 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.
DOI: 10.1051/0004-6361/202038509
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Associated version: From HCm-Teff_v4.0 to latest one. Usage of HCm-Teff with density-bounded models.
Title: The softness diagram for MaNGA star-forming regions: diffuse ionized gas contamination or local HOLMES predominance?
Authors: E. Pérez-Montero, I. A. Zinchenko, J. M. Vílchez, A. Zurita, E. Florido, B. Pérez-Díaz
Abstract: Aims: We explore the so-called softness diagram - whose main function is to provide the hardness of the ionizing radiation in star-forming regions - in order to check whether hot and old low-mass evolved stars (HOLMES) are significant contributors to the ionization within star-forming regions, as suggested by previous MaNGA data analyses. Methods: We used the code HCM-TEFF to derive both the ionization parameter and the equivalent effective temperature (T*), adopting models of massive stars and planetary nebulae (PNe), and exploring different sets of emission lines in the softness diagram to figure out the main causes of the observed differences in the softness parameter in the MaNGA and CHAOS star-forming region samples. Results: We find that the fraction of regions with a resulting T* > 60 kK, which are supposedly ionised by sources harder than massive stars, is considerably larger in the MaNGA (66%) than in the CHAOS (20%) sample when the [S II] λλ 6716,6731 Å emission lines are used in the softness diagram. However, the respective fractions of regions in this regime for both samples are considerably reduced (20% in MaNGA and 10% in CHAOS) when the [N II] emission line at λ 6584 Å is used instead. This may indicate that diffuse ionised gas (DIG) contamination in the lower resolution MaNGA data is responsible for artificially increasing the measured T* as opposed to there being a predominant role of HOLMES in the H II regions.
DOI: 10.1051/0004-6361/202244591
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Associated version: From HCm-Teff_v5.01 to latest one. Usage of HCm-Teff with [NII] emission lines.
Title: The softness diagram for MaNGA star-forming regions: diffuse ionized gas contamination or local HOLMES predominance?
Authors: E. Pérez-Montero, J. A. Fernández-Ontiveros, B. Pérez-Díaz, J. M. Vílchez, N. Kumari, R. Amorín
Abstract: Aims: We explored the softness parameter in the infrared, ηIR', whose main purpose is the characterisation of the hardness of the incident ionising radiation in emission-line nebulae. This parameter is obtained from the combination of mid-infrared wavelength range transitions corresponding to consecutive ionisation stages in star-forming regions. Methods: We compiled observational data from a sample of star-forming galaxies (SFGs), including luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs), to study the ηIR' and its equivalent expression in two dimensions, the softness diagram. We compared them with predictions from photoionisation models to determine the shape of the ionising continuum energy distribution in each case. We also used the measured emission-line ratios as input for HCMISTRY-TEFF-IR, a code that performs a Bayesian-like comparison with photoionisation model predictions in order to quantify the equivalent effective temperature (T*) and the ionisation parameter. Results: We found similar average values within the errors of ηIR' in (U)LIRGs (−0.57) in the rest of the SFGs (−0.51), which could be interpreted as indicative of a similar incident radiation field. This result is confirmed from the analysis using HCM-TEFF-IR, which simultaneously points to a slightly lower, although similar within the errors, T* scale for (U)LIRGs, even when a higher dust-to-gas mass ratio is considered in the models for these objects. These derived T* values are compatible with the ionisation from massive stars, without any need of harder ionising sources, both for (U)LIRGs and the rest of the SFGs. However, the derived T* in (U)LIRGs do not show any correlation with metallicity. This could be interpreted as a sign that their similar average T* values are due to the attenuation of the energetic incident flux from massive stars by the heated dust mixed with the gas. This is supported by the known very large amounts of small grains associated with the very high star formation rates measured in galaxies of this type.
DOI: 10.1051/0004-6361/202348089
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Associated version: From HCm-Teff-IR_v2.2 to latest one. Usage of HCm-Teff with infrared emission lines.
HII-CHI-Mistry has been made thanks to the financial support from the Spanish AYA Project Estallidos