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Median value:

• 12+log(S/H)= 6.92 (DHR)

12+log(S/H)_max= 7.82±0.08

• ~5 times × 12+log(S/H)_⨀⁽¹⁾
• In region 11 of M83

⁽¹⁾ 12+log(S/H)_⨀= 7.12 (Asplund et al. 2009)

~ 25%

Total abundances

Median value:

• T_e([SIII])= 7900 K (DHR)

T_e([SIII])_min= 4860±340 K

On the use of Sulphur as a tracer for abundances in galaxies

Sulphur

Made in Córdoba

Sersic-Pastoriza galaxies

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Elena Terlevich (INAOE-Mexico)

Sandra Zamora (UAM-Spain)

Angeles Díaz (UAM-Spain)

Roberto Terlevich (INAOE-Mexico; IoA-Cambridge UK)

Marcelo Castellanos (Spain)

Guillermo Hägele (La Plata-Argentina)

Mónica Cardaci (La Plata-Argentina)

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M83

Sersic-Pastoriza galaxies

Sersic & Pastoriza,

``Peculiar nuclei of galaxies” 1965, PASP, 77, 287

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Circumnuclear star forming regions

What are they?

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“In the context of disk galaxies, a nuclear or circumnuclear ring is a region of large gas surface density and enhanced star formation, located within 2 kpc of the galactic nucleus”

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“A `circumnuclear starburst´ is a region composed of star condensations with individual masses ranging from a few ×10⁴ to greater than 10⁶ M_⊙, bright in the ultraviolet (UV) because they have recently emerged from their birth clouds (the nuclear galactic ring), and contain hot and massive O and/or B stars.”

(Wofford, Leitherer & Chandar, 2011, Apj 727, 100)

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Sersic-Pastoriza

(hot-spot) galaxies

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• Similar to luminous and large HII regions but more compact.
• They show higher peak surface brightness
• In many cases they contribute substantially to the emission of the entire nuclear region of the galaxy.

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• Determining chemical abundances is key for studies of galaxy evolution and star formation.
• Main source of information are the emission spectra of ionised gas.
• The direct method, based on the determination of ^T_e, is only possible by measuring auroral lines (e.g.: [OIII] λ4363 Å).
• These lines are weak, not detected in faint or metal rich objects.
• Then, empirical methods that allow to estimate oxygen abundance from the flux of intense emission lines of [OII], [OIII], [NII], [SII], [SIII], come to the rescue.

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Modelos de estructura de fotoionización

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High metallicity HII Regions

[OIII] 4363 Å not detected, but . . .

There is an anticorelation between the intensity of emission lines collissionaly excited and oxygen abundance

Empirical calibration

R₂₃ = log ([OII]+[OIII])/Hβ vs 12+log(O/H)

(Pagel et al. 1979: MNRAS, 189, 95)

Optical spectrum of a high metallicity HII region:

CCM72 en M 51

[OIII] nebular line

[OIII] auroral line

Límites de detección de T_e

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EL PARÁMETRO DE ABUNDANCIA R₂₃

R₂₃ = ([OII]+[OIII]) / Hβ

Rama inferior : Enfriamiento dominado por líneas de recombinación de hidrógeno

R₂₃ aumenta con la abundancia de oxígeno

Rama superior : Enfriamiento dominado por líneas colisionales de oxígeno

R₂₃ disminuye con la abundancia de oxígeno

LA RELACIÓN ES BIVALUADA

Empirical methods for abundance determination

Based on the cooling properties of the ionised regions

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When cooling is dominated by oxygen lines in the optical, T_e depends inversely on the oxygen abundance. As the intensities of collisionaly excited lines depend exponentially on the temperature, one expects a relation to exist between their intensity and the oxygen abundance.

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Calibración empírica del parámetro R₂₃ = O₂₃

Emprical calibrations rely on direct measurements of T_e in the low metallicity regime (high excitation) but require the use of theoretical models in the high metallicity regime (low excitation).

go to

Modelos de cúmulos de edad cero predicen que en la rama inferior R₂₃ depende sobre todo de U y en la rama superior los modelos convergen a una única línea (McGaugh 1991, ApJ 380, 140)

PERO... .

La situación es más complicada cuando se considera la evolución de los cúmulos: la evolución de las estrellas masivas es muy rápida y depende de la metalicidad y la temperatura del cúmulo ionizante no es una función monotónicamente decreciente de la edad, debido a la aparición de estrellas WR

EL PARÁMETRO ALTERNATIVO S₂₃

S₂₃ = ([SII]+[SIII]) / Hβ

S is also produced in massive stars. S/O constant. Spectroscopically the lines are analogous to those of O but, due to their longer wavelength, their contribution to the cooling is expected to be more important at lower temperatures.

Less sensitive to T_e , the inversion in the relation is expected to be produced at higher metallicities.

The relation remains single valued up to higher metallicity values.

Alternative parameter: S₂₃

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Calibration of the abundance parameter S₂₃

Díaz & Pérez-Montero 2000

Other abundance calibrations

• No uncertainties due to redenning or to flux calibration, uni-valued with metallicity over the whole range.
• Large dispersion due to an anti correlation with degree of ionisation and the uncertainty with N/O value.

N2 = I(6584 Å)/I(Hα) (Denicoló et al., 2001).

[NII]/[OII] and [NII]/[SII] could be metallicity indicators for 12+log(O/H)≥8.6 (Kewley and Dopita 2002).

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However, the observed dispersion is similar to that of N2, with the added problem that it is not valid at low metallicities.

• Los valores de [NII]/[OII] y [NII]/[SII], podrían ser indicadores de la metalicidad para 12+log(O/H) ≥ 8.6 (Kewley & Dopita, 2002).
• Sin embargo, la dispersión observacional es similar a la de N2, con el problema añadido de que no vale a metalicidades bajas.

El parámetro log [OIII]/[NII] , originalmente propuesto por Alloin et al en 1979 ha sido mas recientemente reivindicado por Pettini & Pagel (2004) para su uso en objetos a redshift intermedio.

The parameter log [OIII/[NII], originally proposed by Alloin et al. 1979, has been reivindicated by Pettini and Pagel (2004) for objects at intermediate redshifts.

S Ionisation Correction Fraction (ICF)

The fraction of S³⁺ is measurable through the [SIV] line at 10.52 μμ so S/H needs to be corrected by such contribution in optical and near IR obsevations.

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El ICF para el S

Similitud de potenciales de ionización de O⁺ y S²⁺.

Los modelos individuales no permiten decantarse por ninguno de los resultados de las secuencias de modelos, los cuales no tienen en cuenta la fracción de H⁺/H que puede hacer bajar el ICF de 1.

El único dato observacional, además indica una cantidad de S³⁺ mayor de lo prevista por los modelos.

[SIII] lines at 9069 y 9532 Å are clearly detected in both low and high metallicity regions.

Region A in NGC 604, low metallicity

Region CCM72 in M51, high metallicity

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(Sersic profile)

Circumnuclear star forming regions (Sersic-Pastoriza galaxies) are important for…

• Metallicity gradients in disk galaxies galactic chemical evolution.
• Stellar population analysis.
• Metallicity-luminosity (mass-metallicity) relation in dwarf galaxies with intense star formation.
• Abundance Empirical methods calibration.

Thank you!

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Sandra Zamora, PhD Thesis UAM,

Sept, 2023