Massive Star Formation and Evolution in Starburst Galaxies: Mid‐infrared Spectroscopy with the<i>ISO</i>Short Wavelength Spectrometer

Thornley, M. D.; Schreiber, N. M. Förster; Lutz, D.; Genzel, R.; Spoon, H. W. W.; Kunze, D.; Sternberg, A.

doi:10.1086/309261

Cited by 204 publications

(325 citation statements)

References 95 publications

(119 reference statements)

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“…Schaerer 2003). Although Thornley et al (2000) estimate a diffuse contribution to be insignificant, this remains to be demonstrated observationally.…”

Section: Introductionmentioning

confidence: 88%

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High spatial resolution mid-infrared spectroscopy of NGC 5253: The stellar content of the embedded super-star cluster

Martín-Hernández

Schaerer

Sauvage³

2004

A&A

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Abstract. We present the N-band (8-13 µm) spectrum of the hidden compact radio super-star cluster in NGC 5253, C2, obtained with TIMMI2 on the ESO 3.6 m telescope. The spectrum is characterised by a rising continuum due to warm dust, a silicate absorption and a strong [S ] line at 10.5 µm. Weaker lines of [Ar ] at 9.0 µm and [Ne ] at 12.8 µm are also present.The continuum can be modelled by an optically thick emission from hot (T d = 253 ± 1 K) dust emission extinguished by a cold foreground dust screen and a silicate absorption feature with A sil = 0.73 ± 0.05 mag. We show how the spatial scale of the observations greatly determine the mid-IR appearance of NGC 5253 and the important implications that this has on the interpretation of line fluxes in terms of the properties (age, IMF, etc.) of the embedded cluster. We have modelled the observed line fluxes towards C2 using photoionisation models with the most recent spectral energy distributions available to describe the integrated properties of the stellar cluster. The detailed dependence of the mid-IR lines on parameters such as the cluster age, upper mass cutoff and power law index of the IMF, as well as the local abundance, the presence of internal dust and the density structure is largely discussed. Strong constraints on the geometry based on high spatial resolution observations at different wavelengths -near-IR (HST and Keck), mid-IR (TIMMI2) and radio (VLA) -allows us to restrain the ionisation parameters to values log U ≥ −0.5 dex. This constraint on U leads to two possible solutions for the age and upper mass cutoff of C2: 1) a young (<4 Myr) cluster with a "non-standard" IMF having a low upper mass cutoff M up < 50 M ; and 2) a cluster of ∼5−6 Myr with a standard high upper mass cutoff (M up ∼ 100 M ). A young age of <4 Myr would agree with the lack of supernovae signatures in C2 and in case of being confirmed, would be the first indication for a "non-standard", low upper mass cutoff of the IMF for an individual massive cluster. An older age of ∼5-6 Myr would imply that it is possible to "contain" and hide such a compact cluster for a longer time that what it is generally thought. Arguments in favour and against these two scenarios are presented.The origin of the [O ] 25.9 µm emission measured by ISO and the possible presence of an intermediate mass black hole inside C2 are also addressed.

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“…Schaerer 2003). Although Thornley et al (2000) estimate a diffuse contribution to be insignificant, this remains to be demonstrated observationally.…”

Section: Introductionmentioning

confidence: 88%

“…Thornley et al 2000) is not completely clear and has led to somewhat conflicting or inconsistent interpretations. Thornley et al (2000) argue e.g.…”

Section: Introductionmentioning

confidence: 99%

High spatial resolution mid-infrared spectroscopy of NGC 5253: The stellar content of the embedded super-star cluster

Martín-Hernández

Schaerer

Sauvage³

2004

A&A

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“…Thornley et al (2000) used the mid-infrared line ratio of [Ne iii] 15.6/ [Ne ii] 12.8 to measure the hardness of the stellar ionizing radiation. They found that, on average, stars with masses above about 40 M are not present in starburst galaxies, either because they were never formed or because they have already disappeared as a result of aging effects.…”

Section: Introductionmentioning

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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“…With regard to this, Thornley et al (2000) carried out detailed starburst modelling of the [Ne III] 15.6 µm / [Ne II] 12.8 µm ratio of H II regions ionized by clusters of stars. As was shown above, the hottest stars in such models are responsible for producing large nebular [Ne III] 15.6 µm / [Ne II] 12.8 µm ratios.…”

Section: Spectral Energy Distributions Of Time-evolving Stellar Clustersmentioning

confidence: 99%

Hot Stars: Old-Fashioned or Trendy?

Pauldrach¹

Reviews in Modern Astronomy 16

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Massive Star Formation and Evolution in Starburst Galaxies: Mid‐infrared Spectroscopy with theISOShort Wavelength Spectrometer

Cited by 204 publications

References 95 publications

High spatial resolution mid-infrared spectroscopy of NGC 5253: The stellar content of the embedded super-star cluster

High spatial resolution mid-infrared spectroscopy of NGC 5253: The stellar content of the embedded super-star cluster

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

Hot Stars: Old-Fashioned or Trendy?

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