No temperature fluctuations in the giant HII region H 1013

Abstract

While collisionally excited lines in HII regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature fluctuations casts some doubt on the derived abundances. To provide new insights into this question, we have carried out a detailed study of a giant HII region, H 1013, located in the galaxy M101, for which many observational data exist and which has been claimed to harbour temperature fluctuations at a level of t^2 = 0.03-0.06. We have first complemented the already available optical observational datasets with a mid-infrared spectrum obtained with the Spitzer Space Telescope. Combined with optical data, this spectrum provides unprecedented information on the temperature structure of this giant HII region. A preliminary analysis based on empirical temperature diagnostics suggests that temperature fluctuations should be quite weak. We have then performed a detailed modelling using the pyCloudy package based on the photoionization code Cloudy. We have been able to produce photoionization models constrained by the observed Hb surface brightness distribution and by the known properties of the ionizing stellar population than can account for most of the line ratios within their uncertainties. Since the observational constraints are both strong and numerous, this argues against the presence of significant temperature fluctuations in H 1013. The oxygen abundance of our best model is 12 + log O/H = 8.57, as opposed to the values of 8.73 and 8.93 advocated by Esteban et al. (2009) and Bresolin (2007), respectively, based on the significant temperature fluctuations they derived. However, our model is not able to reproduce the intensities of the oxygen recombination lines . This cannot be attributed to observational uncertainties and requires an explanation other than temperature fluctuations.

accepted in Astronomy & Astrophysics

References in corpus (7)

• Resolving the electron temperature discrepancies in HII Regions and Planetary Nebulae: kappa-distributed electrons
• Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
• On the abundance discrepancy problem in HII regions
• The oxygen abundance in the inner HII regions of M101. Implications for the calibration of strong-line metallicity indicators
• Enrichment of the ISM by metal-rich droplets and the abundance bias in HII regions
• Ionized gas diagnostics from protoplanetary discs in the Orion Nebula and the abundance discrepancy problem
• Cloudy_3D, a new pseudo-3D photoionization code

Cited by in corpus (9)

• Metallicity inhomogeneities in local star-forming galaxies as sign of recent metal-poor gas accretion
• Chemical distribution of HII regions towards the Galactic anticentre
• Towards A Removal of Temperature Dependencies from Abundance Determinations
• Correlation between the gas-phase metallicity and ionization parameter in extragalactic HII regions
• Accurate Oxygen Abundance of Interstellar Gas in Mrk 71 from Optical and Infrared Spectra
• Metal-poor dwarf galaxies in the SIGRID galaxy sample. II. The electron temperature-abundance calibration and the parameters that affect it
• Gas-phase Fe/O and Fe/N abundances in Star-Forming Regions. Relations between nucleosynthesis, metallicity and dust
• CHAOS V: Recombination Line Carbon Abundances in M101
• SDSS-V LVM: Resolving Physical Conditions in the Trifid Nebula