Age Determination of HII Regions of the LMC and SMC

Copetti, M. V. F.; Dottori, H.; Bica, E.; Pastoriza, M. G.

doi:10.1007/978-94-010-9801-4_78

Cited by 30 publications

(38 citation statements)

References 2 publications

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“…There could be two reasons for this: The most recent episode of star formation is younger in Hubble V or the ionizing stars are hotter, and therefore, more massive. A comparison of the equivalent width of Hβ, E v (Hβ), supports the first possibility, provided this parameter traces the age of the region for a given IMF (Copetti et al 1986). This is in agreement with the conclusion by Wilson (1992).…”

Section: The Excitation Structurementioning

confidence: 75%

The chemical abundances in a sample of dwarf irregular galaxies

Hidalgo-Gámez

Olofsson

Masegosa³

2001

A&A

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Abstract. Deep groundbased spectra of Hubble V and Hubble X, the two largest and brightest H ii regions in the Local Group dwarf galaxy, NGC 6822, are presented. The extinction, excitation and ionization are studied on scales as small as 4 pc. The chemical composition of some elements within the regions as well as possible small scale variations in the abundances of helium, nitrogen, oxygen and neon over the face of the two regions are investigated. The detection of the emission lines [OI] and [ClIII] are probably related to shock-heating from gas ejected from supernova explosions and planetary nebula ejections, respectively, although the contribution to the total ionization is very small. No significant differences in chemical composition was found between Hubble V and Hubble X. However, some small scale variations in the abundances of oxygen, and possibly nitrogen and helium, over the face of both H ii regions were noted, although different physical conditions could apply within the regions, such as local fluctuations in the temperature.

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Section: The Excitation Structurementioning

confidence: 75%

The chemical abundances in a sample of dwarf irregular galaxies

Hidalgo-Gámez

Olofsson

Masegosa³

2001

A&A

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“…In a case of a single stellar population formed in an instantaneous star formation burst, EW (Hβ) has a maximum at the onset of the star formation and then gradually decreases with time. This method was originally suggested by Copetti, Pastoriza & Dottori (1986) and later discussed by Schaerer & Vacca (1998) and Stasińska & Leitherer (1996). gave some expressions to determine the burst age for different metallicities (Z/Z ⊙ = 0.05, 0.2, 0.4, 1.0, 2.0).…”

Section: Agesmentioning

confidence: 99%

Optical and infrared emission of H ii complexes as a clue to the PAH life cycle

Khramtsova¹,

Wiebe²,

Lozinskaya³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 H ii complexes in nine galaxies. Spectra obtained with the 6-m telescope of SAO RAS are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied H ii complexes. Physical properties (age, radiation field parameters, metallicity) are related to the F 8 /F 24 ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in H ii complexes. The well-known correlation between the F 8 /F 24 ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [O iii]λ5007/Hβ ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [O iii]λ5007/Hβ and metallicity. In separate metallicity bins, the F 8 /F 24 ratio is found to correlate with an age of an H ii complex, which is estimated from the equivalent width of Hβ line. The correlation is positive for low metallicity complexes and negative for high metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within H ii complexes, but this is not necessarily due to their destruction. If PAHs can also form in H ii complexes due to some processes like aromatisation, photodestruction, shattering and sputtering of very small grains, the net F 8 /F 24 ratio is determined by a balance between all these processes that can be different at different metallicities.

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“…Summing up, EW(Hβ) is a "good enough" indicator of the age of an H ii region (Copetti et al 1986) once the covering factor is known. EW(Hβ) depends mainly on the metallicity (Cerviño & Mas-Hesse 1994) and age of the cluster with almost no variations due to the size of the cluster, if sampling effects are not considered (but see Cerviño et al 2000Cerviño et al , 2002b.…”

Section: Hβ Equivalent Widthmentioning

confidence: 99%

On emission-line spectra obtained from evolutionary synthesis models

Villaverde

Cerviño

Luridiana

2010

A&A

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Aims. In this paper we study the influence of the ionizing cluster mass on the emission line spectrum of H ii regions in order to determine the influence of low mass clusters on the integrated emission line spectra of galaxies. Methods. For this purpose, we present a grid of photoionization models that covers metallicities from Z = 0.001 to Z = 0.040, ages from 0.1 to 10 Ma (with a time step of 0.1 Ma), and cluster initial masses from 1 to 10 7 M . The stellar masses follow a Salpeter initial mass function (IMF) in an instantaneous burst mode of star formation. We obtain power-law scale-relations between emission-line luminosities and ionizing cluster masses from the grids and we evaluate the dependences on the ionizing cluster mass for some line luminosities, equivalent widths and line ratios. Results. Power-law scale-relations are shown to be useful tools to obtain robust diagnostics, as examples: (a) Hα/Hβ ratio varies from the usually assumed value of 2.86, these variations imply the existence of a lower limit to the attainable precision in extinction star formation rate indicator for ages older than ∼4.5 Ma. We also show that the ionizing cluster mass dependence explains why empirical calibrations produce more reliable diagnostics of some emission lines than photoionization models grids. Finally, we show preliminary results about the contribution of low mass clusters (M < 10 4 M ) to the integrated emission line spectra of galaxies, which can be as high as 80% for some relevant lines.

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Age Determination of HII Regions of the LMC and SMC

Cited by 30 publications

References 2 publications

The chemical abundances in a sample of dwarf irregular galaxies

The chemical abundances in a sample of dwarf irregular galaxies

Optical and infrared emission of H ii complexes as a clue to the PAH life cycle

On emission-line spectra obtained from evolutionary synthesis models

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