We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J = 4-3 through J = 13-12, 6 H sub(2)O rotational lines, and ...CI and NII fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H sub(2) upsilon = 1-0 S(1) and nu = 2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity nu sub(s) = 10 km s super(-1) and a pre-shock density n sub(H) = 5 x 10 super(4) cm super(-3). We find that the solution best fitting the H sub(2) lines is degenerate. The shock velocities and number densities range between nu sub(s) = 17-47 km s super(-1) and n sub(H) = 10 super(7)-5 x 10 super(4) cm super(-3), respectively. The H sub(2) lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s super(-1)) shocks while only a small fraction (<, ~1%) of the interstellar medium is exposed to the high-velocity shocks. This implies that the gas is rapidly losing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
Dense gas in luminous infrared galaxies Baan, W. A.; Henkel, C.; Loenen, A. F. ...
Astronomy & astrophysics,
01/2008, Letnik:
477, Številka:
3
Journal Article
Recenzirano
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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), ${\rm HCO}^+$(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.
We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk 231. In total 25 lines are detected, including CO J = 5–4 through J = 13–12, 7 rotational lines of ...H2O, 3 of OH+ and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J = 8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J = 8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk 231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk 231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J = 8. X-rays from the accreting supermassive black hole in Mrk 231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk 231. The extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of X-ray driven excitation and chemistry in this region.
Context. The molecular interstellar medium in extreme environments, such as Arp 220, but also NGC 253 appears to have extremely high cosmic ray (CR) rates (103−104 × Milky Way) and substantial ...mechanical heating from supernova driven turbulence. Aims. We explore the consequences of high CR rates and mechanical heating on the chemistry of the clouds. Methods. PDR model predictions are made for low, n = 103, and high, n = 105.5 cm-3, density clouds using well-tested chemistry and radiation transfer codes. Column densities of relevant species are discussed, and special attention is given to water-related species. Fluxes are shown for fine-structure lines of O, C+, C, and N+, and molecular lines of CO, HCN, HNC, and HCO+. A comparison is made with an X-ray dominated region model. Results. Fine-structure lines of CII, CI, and OI are remarkably similar for different mechanical heating and CR rates, when already exposed to large amounts of UV. Both HCN and H2O abundances are boosted for very high mechanical heating rates, while ionized species are relatively unaffected. Both OH+ and H2O+ are enhanced for very high CR rates ζ ≥ 5 × 10-14 s-1. A combination of OH+, OH, H2O+, H2O, and H3O+ traces the CR rates, and is able to distinguish between enhanced cosmic rays and X-rays.
Aims. Molecular emission lines originating in the nuclei of luminous infra-red galaxies are used to determine the physical properties of the nuclear ISM in these systems. Methods. A large ...observational database of molecular emission lines is compared with model predictions that include heating by UV and X-ray radiation, mechanical heating, and the effects of cosmic rays. Results. The observed line ratios and model predictions imply a separation of the observed systems into three groups: XDRs, UV-dominated high-density ($n \geq 10^5$ cm-3) PDRs, and lower-density ($n = 10^{4.5}$ cm-3) PDRs that are dominated by mechanical feedback. Conclusions. The division of the two types of PDRs follows naturally from the evolution of the star formation cycle of these sources, which evolves from deeply embedded young stars, resulting in high-density ($n \geq 10^5$ cm-3) PDRs, to a stage where the gas density has decreased ($n = 10^{4.5}$ cm-3) and mechanical feedback from supernova shocks dominates the heating budget.
Molecular emission-line observations of isolated Galactic star-forming regions are used to model the physical properties of the molecular interstellar medium in these systems. Observed line ratios ...are compared with the results predicted by models that incorporate gas-phase chemistry and the heating by stellar radiation and non-radiative feedback processes. The line ratios of characteristic tracer molecules may be interpreted using the contributions of two distinct components: a cold (40–50 K) and high-density (105–105.5 cm−3) photon-dominated region (PDR) with a nominal UV flux density and a warm (∼300 K) mechanical heating-dominated region (MHDR) with a slightly lower density (104.5–105 cm−3). The relative contributions of these structural components are used to model the observed line ratios. Ionized species may be better modelled by adopting an increase of the cosmic ray flux towards the Galactic Centre and the sulphur abundance should depleted by a factor of 200–400 relative to solar values. The line ratios of the Galactic sample are found to be very similar to those of the integrated signature of prominent (ultra)luminous IR Galaxies. The PDRs and MHDRs in the isolated Galactic regions may be modelled with slightly higher mean densities than in extragalactic systems and a higher MHDR temperature resulting from non-radiative mechanical heating. Multimolecular studies are effective in determining the physical and chemical properties of star formation regions by using characteristic line ratios to diagnose their environment. The addition of more molecular species will reduce the existing modelling redundancy.
Aims. Molecules that trace the high-density regions of the interstellar medium may be used to evaluate the changing physical and chemical environment during the ongoing nuclear activity in ...(ultra-)luminous infrared galaxies (ULIRGs). Methods. The changing ratios of the HCN (1-0), HNC (1-0), HCO+ (1-0), CN (1-0) and CN (2-1), and CS (3-2) transitions were compared with the HCN (1-0)/CO (1-0) ratio, which is proposed to represent the progression time scale of the starburst. These diagnostic diagrams were interpreted using the results of theoretical modeling with a large physical and chemical network to describe the state of the nuclear ISM in the evolving galaxies. Results. Systematic changes are seen in the line ratios as the sources evolve from early stage for the nuclear starburst (ULIRGs) to later stages. These changes result from changing environmental conditions and particularly from the lowering of the average density of the medium. A temperature rise due to mechanical heating of the medium by feedback explains the lowering of the ratios at later evolutionary stages. Infrared pumping may affect the CN and HNC line ratios during early evolutionary stages. Conclusions. Molecular transitions display a behavior that relates to changes of the environment during an evolving nuclear starburst. Molecular properties may be used to designate the evolutionary stage of the nuclear starburst. The HCN(1-0)/CO(1-0) and HCO+(1-0)/HCN(1-0) ratios serve as indicators of the time evolution of the outburst.
BACKGROUND: An optimal range of LH concentrations for achieving pregnancy has not been established. The aim of this study was to investigate the effect of various LH levels induced by different GnRH ...antagonist doses on IVF outcome. METHODS: This was a prospective, single centre study including 144 IVF patients, stimulated with recombinant FSH from cycle day 2, and co-treated with daily GnRH antagonist (antide/Iturelix) (2 mg/2 ml, 1 mg/ml, 0.5 mg/ml, 0.5 mg/0.5 ml or 0.25 mg/ml) from cycle day 7 onwards. Serum samples were taken three times daily. RESULTS: Clinical pregnancies were only observed within a particular range of change in LH levels. The upper and lower thresholds for the mean LH area under the curve (AUC), adjusted for the baseline LH level before the antagonist was started (LH AUC−S6; S6=stimulation day 6) were −2.2 and 12.4 (IU/l) respectively (a negative value=below baseline levels). There were no clinical pregnancies outside these threshold values. Similar results were found for progesterone, the threshold levels of progesterone AUC−S6 were 3.98 and −1.21 ng/ml. Moreover, there were no pregnancies with progesterone levels >0.26 ng/ml/follicle on the day of hCG. CONCLUSIONS: Excessive or insufficient suppression of LH and progesterone levels during GnRH antagonist administration and high progesterone/follicle on hCG day seems to be associated with impaired clinical pregnancy rates.
This paper presents emission line intensities of CO and Cdegrees from the compact circumnuclear disk in the center of NGC 5128 (Centaurus A) obtained with the Herschel Space Observatory in the ...400-1000 GHz range as well as previously unpublished measurements obtained with the ground-based observatories SEST, JC MT and APEX in the 90-800 GHz range. The CO surface brightness of the compact circumnuclear disk (CND) is significantly higher than that of the much more extended thin disk (ETD) in the same line of sight. The total gas mass of the CND is MsubCND = 8.4 10sup 7 M, uncertain by a factor of two. The CO-Hsub 2 conversion factor (XsubCND) is 4 10sup 20 (K km s-sup -1 )sup -1 also within a factor of two.
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