The Stellar Content of Giant H<scp>ii</scp>Regions in NGC 7714

García-Vargas, María Luisa; Delgado, R. M. González; Pérez, E.; Alloin, D.; Díaz, Ángeles I.; Terlevich, Elena

doi:10.1086/303778

Cited by 61 publications

(91 citation statements)

References 36 publications

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“…In addition to the radiation field, the strength of these lines depends on the chemical composition, the density structure, and the geometry of the ionized gas. Even so, photoionization models of various starbursts and H ii regions can successfully constrain the stellar content (e.g., García-Vargas et al 1997 for the H ii regions of NGC 7714; González In the present study we perform a critical test of the inputs to the photoionization models, in particular the radiation field of the ionizing stars. The stellar ionizing spectrum is known a priori from the analysis of the UV spectra.…”

Section: Modeling the Nebular Linesmentioning

confidence: 99%

The Massive Stellar Content in the Starburst NGC 3049: A Test for Hot‐Star Models

Delgado

Leitherer

Stasińska

et al. 2002

ApJ

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The objective of this work is twofold. First, we seek evidence for or against the depletion of massive stars in metal-rich starbursts. A second, equally important goal is to perform a consistency test of the latest generation of starburst models in such a high-metallicity environment. We have obtained high spatial resolution ultraviolet and optical STIS spectroscopy and imaging of the metal-rich nuclear starburst in NGC 3049. The stellar continuum and the absorption-line spectrum in the ultraviolet are used to constrain the massive stellar population. The strong, blueshifted stellar lines of C iv and Si iv detected in the UV spectra indicate a metalrich, compact, massive ($10 6 M ) cluster of age 3-4 Myr emitting the UV-optical continuum. We find strong evidence against a depletion of massive stars in this metal-rich cluster. The derived age and the upper masslimit cutoff of the initial mass function are also consistent with the detection of Wolf-Rayet (W-R) features at optical wavelengths. As a second, independent constraint on the massive stellar content, the nebular emission-line spectrum is modeled with photoionization codes using stellar spectra from evolutionary synthesis models. The morphology of the nuclear starburst of NGC 3049 from the STIS images indicates a simple geometry for the nebular emission-line region. However, the nebular lines are badly reproduced by 3-4 Myr instantaneous bursts, as required by the UV line spectrum, when unblanketed W-R and/or Kurucz stellar atmospheres are used. The corresponding number of photons above 24 and 54 eV in the synthetic models is too high in comparison with values suggested by the observed line ratios. Since the ionizing spectrum in this regime is dominated by emission from W-R stars, this discrepancy between observations and models is most likely the result of incorrect assumptions about the W-R stars. Thus, we conclude that the nebular spectrum of high-metallicity starbursts is poorly reproduced by models for W-R-dominated populations. However, the new model set of Smith et al. with blanketed W-R and O atmospheres and adjusted W-R temperatures predicts a softer far-UV radiation field, providing a better match to the data.

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Section: Modeling the Nebular Linesmentioning

confidence: 99%

The Massive Stellar Content in the Starburst NGC 3049: A Test for Hot‐Star Models

Delgado

Leitherer

Stasińska

et al. 2002

ApJ

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“…There have already been detailed photoionization studies of some giant Hii regions (García-Vargas et al 1997;Stasińska & Schaerer 1999;Luridiana et al 1999Luridiana et al , 2003González Delgado & Pérez 2000;Luridiana & Peimbert 2001;Relaño et al 2002). In most cases, the models were not able to reproduce the observed temperature indicators correctly.…”

Section: Introductionmentioning

confidence: 99%

What is the temperature structure in the giant HII region NGC 588?

Jamet

Stasińska

Pérez³

et al. 2005

A&A

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We present the results of an exhaustive study of the ionized gas in NGC 588, a giant Hii region in the nearby spiral galaxy M 33. This analysis uses a high number of diagnostics in the optical and infrared ranges. Four temperature diagnostics obtained with optical lines agree with a gas temperature of 11 000 K, while the [Oiii] λ5007/λ88 µm ratio yields a much lower temperature of ≈8000 K. This discrepancy suggests the presence of large temperature inhomogeneities in the nebula. We investigated the cause of this discrepancy by constructing photoionization models of increasing complexity. In particular, we used the constraints from the Hα and Hβ surface brightness distributions and state-of-theart models of the stellar ionizing spectrum. None of the successive attempts was able to reproduce the discrepancy between the temperature diagnostics, so the thermal balance of NGC 588 remains unexplained. We give an estimate of the effect of this failure on the O/H and Ne/O estimates and show that O/H is known to within ±0.2 dex.

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“…Composite populations have been postulated for region A in NGC 3310 (Pastoriza et al 1993) and region A in NGC 7714 (García-Vargas et al 1997). Under this assumption, the equivalent widths, EW(WR) and EW(HeII), of the cluster with WR stars are increased to 6 and 4.8Å for region A in NGC 3310 and 3.6 and 2.5Å for region A in NGC 7714 which might still be compatible with Scharer & Vacca models.…”

Section: Discussionmentioning

confidence: 84%

“…Table 8 shows the values of the WR feature intensities and equivalent widths for 74C and other three well studied extragalac- † All the models are computed assuming a standard Salpeter IMF for the stellar ionizing cluster and using the photoionization code CLOUDY (Ferland 1996). tic HII regions: NGC 604 in M33 (Díaz et al 1987;Terlevich et al 1996), region A in NGC 3310 (Pastoriza et al 1993) and region A in NGC 7714 (García-Vargas et al 1997). Also given in the table are the metallicities of the regions in the form 12+log(O/H) and the effective temperature of the ionizing radiation estimated from single star photo-ionization models.…”

Section: Discussionmentioning

confidence: 99%

Chemical abundances and ionizing clusters of H ii regions in the LINER galaxy NGC 4258

Díaz¹,

Castellanos²,

Terlevich³

et al. 2000

Monthly Notices RAS

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We present long-slit observations in the optical and near infrared of eight H II regions in the spiral galaxy NGC 4258. Six of the observed regions are located in the SE inner spiral arms and the other two are isolated in the northern outer arms.A detailed analysis of the physical conditions of the gas has been performed. For two of the regions an electron temperature has been derived from the [SIII] λ 6312Å line. For the rest, an empirical calibration based on the red and near infrared sulphur lines has been used. The oxygen abundances derived by both methods are found to be significantly lower (by a factor of two) than previously derived by using empirical calibrations based on the optical oxygen lines.In the brightest region, 74C, the observation of a prominent feature due to WolfRayet stars provides an excellent constraint over some properties of the ionizing clusters. In the light of the current evolutionary synthesis models, no consistent solution is found to explain at the same time both the WR feature characteristics and the emission line spectrum of this region. In principle, the presence of WR stars could lead to large temperature fluctuations and also to a hardening of the ionizing radiation. None of these effects are found in region 74C for which the electron temperatures found from the [SIII] λ 6312Å line and the Paschen discontinuity at 8200Å are equal within the errors and the effective temperature of the ionizing radiation is estimated at around 35300 K.Both more observations of confirmed high metallicity regions and a finer metallicity grid for the evolutionary synthesis models are needed in order to understand the ionizing populations of HII regions.

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The Stellar Content of Giant HiiRegions in NGC 7714

Cited by 61 publications

References 36 publications

The Massive Stellar Content in the Starburst NGC 3049: A Test for Hot‐Star Models

The Massive Stellar Content in the Starburst NGC 3049: A Test for Hot‐Star Models

What is the temperature structure in the giant HII region NGC 588?

Chemical abundances and ionizing clusters of H ii regions in the LINER galaxy NGC 4258

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