ISO spectroscopy of compact HII regions in the Galaxy

Martín-Hernández, N. L.; Peeters, E.; Morisset, Charles; Tielens, A. G. G. M.; Cox, P.; Roelfsema, P. R.; Baluteau, J. P.; Schaerer, D.; Mathis, J. S.; Damour, F; Churchwell, E.; Kessler, M. F.

doi:10.1051/0004-6361:20011504

Cited by 131 publications

(208 citation statements)

References 66 publications

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“…This expression assumes that 1) the nebula is homogeneous with constant electron temperature and density; 2) all the line photons emitted in the nebula escape without absorption and therefore without causing further upward transitions; and 3) the volume occupied by X +i and H + is the same. The emission coefficients depend on T e , n e and the relevant atomic parameters (Martín-Hernández et al 2002a). Adopting T e = 12 000 K (see Sect.…”

Section: Ionic Abundancesmentioning

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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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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Section: Ionic Abundancesmentioning

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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“…> 0.69 are similar to the most extreme example of ultra-compact H II regions in our Galaxy. The ratios indicate that the radiation field is extremely hard and corresponds to an effective stellar temperature of T eff ≥ 4 × 10 4 K, assuming solar abundance (see Martin-Hernandez et al 2002). This would suggest that the absence of PAHs results from their destruction by the hard UV photons and strong winds produced by the massive stars (i.e.…”

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confidence: 97%

Early Results from the Infrared Spectrograph on the Spitzer Space Telescope

Houck

Charmandaris

Brandl

2005

The Initial Mass Function 50 Years Later

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The Infrared spectrograph, IRS, on the Spitzer Space Telescope has greatly improved the sensitivity in the thermal infrared and opened many new avenues in infrared astronomy over the range of 5.5 to 38 microns. With the IRS an object with midinfrared flux of ∼1 mJy can produce a usable low resolution spectrum in an hour of telescope time.The midinfrared study of star formation at low metallicity has been enabled by this new sensitivity.

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“…A description of the reduction techniques as well as a catalogue of the line intensities will be given in Peeters et al (in preparation) and the first results of this study will be presented in Martin-Hernandez et al (in preparation) -see also a preliminary report in Martin-Hernandez et al (2000). This report will summarize the problems related to the determination of the N/O abundance ratio and give some results obtained on the dust properties.…”

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confidence: 99%

“…There are indications that the dust properties change in the surroundings of compact HII regions. For instance, the large number of HI recombination lines in K3-50A has been used to derive the extinction towards this object which has been found to deviate from the 'standard' extinction curve (Martin-Hernandez et al 2000). The attenuation is higher than expected and clearly lacks the deep minimum near 7 /xm, indicating that, either the properties of the dust surrounding K3-50A are very different from those of the typical interstellar dust, or that there are geometrical effects.…”

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confidence: 99%

Studies of Compact HII Regions with ISO

Cox

2002

Highlights astron.

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Abstract.We summarize results of a study of combined ISO SWS-LWS grating spectra of compact HII regions in our Galaxy.Compact HII regions, which are the result of the ionizing radiation of newly formed massive stars, are either completely embedded in their natal molecular clouds or in the process of breaking out. These regions consist of ionized material from the local interstellar medium (ISM) and therefore, are excellent probes of the ISM and can be used to trace the spatial distribution of chemical elements in galaxies. Abundance determination methods based on infrared observations present clear advantages over optical studies as the infrared fine-structure lines are not very sensitive to large changes in the electron temperature and do not suffer from high extinction.Using the Infrared Space Observatory (ISO), we observed with the SWS and LWS in the grating mode 45 compact HII regions sampling the galactic plane from the center to the outer regions. The spectra cover a range from 2.5 to 196 fim with resolving powers A/AA between 150 and 1500. The complete spectral coverage gives access to nearly all the atomic fine-structure lines in the infrared range. For some elements, different ionization stages are measured, which alleviates the problem of applying ionization correction factors for unseen ions. In addition to the atomic emission lines, the spectra are dominated by strong dust continua and a series of dust bands, as well as absorption bands from molecular ice species (see Fig. 1).The data have been reduced using up-to-date SWS and LWS reduction software. A description of the reduction techniques as well as a catalogue of the line intensities will be given in Peeters et al. (in preparation) and the first results of this study will be presented in Martin-Hernandez et al. (in preparation) -see also a preliminary report in Martin-Hernandez et al. (2000). This report will summarize the problems related to the determination of the N/O abundance ratio and give some results obtained on the dust properties.The abundance ratio N/O has a special significance for galactic nucleosynthesis models because the main stellar source of N is still unclear. Simple chemical evolution models predicts that its dominant isotope ( 14 N) originates principally from primary nucleosynthesis (through H-burning of carbon newlygenerated within the star), but, how much 14 N is produced from secondary nucleosyntheis (i.e. through the CNO cycle where the carbon is already present in the star) is still an open question.

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ISO spectroscopy of compact HII regions in the Galaxy

Cited by 131 publications

References 66 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

Early Results from the Infrared Spectrograph on the Spitzer Space Telescope

Studies of Compact HII Regions with ISO

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