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- Baan, Willem A., et al.
(författare)
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Dense gas in luminous infrared galaxies
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 477:3, s. 747-U73
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Molecules that trace the high-density regions of the interstellar medium have been observed in (ultra-) luminous (far-) infrared galaxies, in order to initiate multiple-molecule multiple-transition studies to evaluate the physical and chemical environment of the nuclear medium and its response to the ongoing nuclear activity.Methods. The HCN(1-0), HNC(1-0), HCO+ (1-0), CN(1-0) and CN(2-1), CO(2-1), and CS(3-2) transitions were observed in sources covering three decades of infrared luminosity including sources with known OH megamaser activity. The data for the molecules that trace the high-density regions were augmented with data available in the literature.Results. The integrated emissions of high-density tracer molecules show a strong relation to the far-infrared luminosity. Ratios of integrated line luminosities were used for a first-order diagnosis of the integrated molecular environment of the evolving nuclear starbursts. Diagnostic diagrams display significant differentiation among the sources that relate to the initial conditions and the radiative excitation environment. Initial differentiation was introduced between the FUV radiation field in photon-dominated-regions and the X-ray field in X-ray-dominated-regions. The galaxies displaying OH megamaser activity have line ratios typical of photon-dominated regions.
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| 2. |
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| 3. |
- Larsson, Bengt, et al.
(författare)
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Molecular oxygen in the rho Ophiuchi cloud
- 2007
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 466:3, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org
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| 4. |
- Lundgren, A.A., et al.
(författare)
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Star Formation and Molecular Gas in M83
- 2008
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Ingår i: Pathways Through an Eclectic Universe, Proc. of conf. April 2007 in Tenerife, Spain, Eds. J.H. Knapen, T.J. Mahoney, A. Vazdekis, ASP Conference Series, San Francisco. ; 390, s. 144-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We compare star formation rates and efficiencies, obtained from different star formation tracers, before and after compensation for internal extinction due to gas and dust, in the barred spiral galaxy M83 (NGC 5236). We use far-UV continuum, B-band continuum, and Hα line images to estimate the star formation rate in the disk of this galaxy at 25 arcsec resolution. We use the total gas map, derived from CO(J=1→ 0) and H I data, to compensate for internal extinction. We find that the star formation rate estimates based on the different data agree well when corrections for internal extinction have been made. The star formation rate is particularly high in the nuclear region, at the bar ends, and in the spiral arms. Combined with the total gas mass map, the star formation rates provide estimates of the star formation efficiencies in the disk at 25 arcsec resolution. The star formation efficiency map is more patchy than the star formation rate map. There is evidence of an increased star formation efficiency along the spiral arms, i.e., not only do the arms present regions of higher gas mass surface density, the efficiency for making stars is also increased in them.
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| 5. |
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