Monday, 12/24/2012

A bit late, but this Monday had no astro-ph, so catching up! The first paper features our very own Eric P. as a co-author, so we can directly bug him with any questions. The second is interesting- experimentally determining CMB temp at intermed. redshift through molecular lines.

Single-Star HII Regions as a Probe of Massive Star Spectral Energy Distributions

Jordan Zastrow (1), M. S. Oey (1), E. W. Pellegrini (2) ((1) U. Michigan, (2) U. Toledo)
(Submitted on 21 Dec 2012)

The shape of the OB-star spectral energy distribution is a critical component in many diagnostics of the ISM and galaxy properties. We use single-star HII regions from the LMC to quantitatively examine the ionizing SEDs from widely available CoStar, TLUSTY, and WM-basic atmosphere grids. We evaluate the stellar atmosphere models by matching the emission-line spectra that they predict from CLOUDY photoionization simulations with those observed from the nebulae. The atmosphere models are able to reproduce the observed optical nebular line ratios, except at the highest energy transitions > 40 eV, assuming that the gas distribution is non-uniform. Overall we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rate of ionizing photons produced by the model SEDs is consistent with the rate derived from the \Halpha\ luminosity for standard, log(g) = 4.0 models adopted from the atmosphere grids. However, there is a systematic offset between the rate of ionizing photons from different atmosphere models that is correlated with the relative hardness of the SEDs. In general WM-basic and TLUSTY atmosphere models predict similar effective temperatures, while CoStar predicts effective temperatures that are cooler by a few thousand degrees. We compare our effective temperatures, which depend on the nebular ionization balance, to conventional photospheric-based calibrations from the literature. We suggest that in the future, spectral type to effective temperature calibrations can be constructed from nebular data.

Comments: Submitted to ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1212.5487 [astro-ph.GA]
(or arXiv:1212.5487v1 [astro-ph.GA] for this version)

A precise and accurate determination of the cosmic microwave background temperature at z=0.89

S. Muller (1), A. Beelen (2), J. H. Black (1), S. J. Curran (3,4), C. Horellou (1), S. Aalto (1), F. Combes (5), M. Guelin(6,7), C. Henkel (8,9) ((1) Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden (2) Institut d’Astrophysique Spatiale, Université Paris-Sud, Orsay Cedex, France (3) Sydney Institute for Astronomy, School of Physics, The University of Sydney, Australia (4) ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) (5) Observatoire de Paris, LERMA, CNRS, Paris, France (6) Institut de Radioastronomie Millimétrique, St Martin d’Hères, France (7) Ecole Normale Supérieure/LERMA, Paris, France (8) Max-Planck-Institut für Radioastonomie, Bonn, Germany (9) Astron. Dept., King Abdulaziz University, Jeddah, Saudi Arabia)
(Submitted on 21 Dec 2012)

According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. We aim at measuring the temperature of the CMB with an accuracy of a few percent at z=0.89 toward the molecular absorber in the galaxy lensing the quasar PKS1830-211. We adopt a Monte-Carlo Markov Chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation of a set of various molecular species directly from their spectra. We determine Tcmb=5.08 pm 0.10 K at 68% confidence level. Our measurement is consistent with the value Tcmb=5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of Tcmb at z>0 to date.

Comments: Accepted for publication in A&A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1212.5456 [astro-ph.CO]
(or arXiv:1212.5456v1 [astro-ph.CO] for this version)
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