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• 1.
ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands .
Dense gas in luminous infrared galaxies2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 477, no 3, p. 747-762Article in journal (Refereed)

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.

• 2.
Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering. Computer Science.
Dense Molecular Gas in Luminous Infrared Galaxies: Diagnosing the ISM2008In: EAS Publications Series, ISSN 1633-4760, Vol. 31, p. 111-114Article in journal (Refereed)

The behavior of molecular tracers of the high-density star-forming ISM provides a diagnostics tool for luminous FIR galaxies. All molecules react differently to the physical and chemical environment and their collective behavior is indicative of the excitation of the ISM and its evolutionary state. This paper describes efforts to diagnose the nuclear medium through multiple-molecule studies.

• 3.
Linnaeus University, Faculty of Technology, Department of computer science and media technology (CM), Department of Computer Science. ASTRON, Netherlands;Shanghai Astron Observ, Peoples Republic of China.
ASTRON, Netherlands;Kapteyn Astron Inst, Netherlands. Kapteyn Astron Inst, Netherlands.
Multimolecular studies of Galactic star-forming regions2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 445, no 4, p. 3331-3344Article in journal (Refereed)

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 (similar to 300 K) mechanical heating-dominated region (MHDR) with a slightly lower density (10(4.5)-10(5) 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.

• 4. Loenen, A. F.
Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering. Computer Science.
Extragalactic Chemistry: HCN, HNC, and HCO+: M. , W. A. Baan, and R.2008In: EAS Publications Series, ISSN 1633-4760, Vol. 31, p. 183-185Article in journal (Refereed)

High- and low-density tracer molecules have been observed in (Ultra-) Luminous Infrared Galaxies in order to initiate multi-molecule multi-transition studies to evaluate the physical and chemical environment of the nuclear medium and the ongoing nuclear activity. The data, augmented with data available in the literature, are presented in Baan et al. (2007), which also presents a first order analysis. Here, we present the chemical analysis of the J=1–0 transition lines of HCN, HNC, and HCO+.

• 5. Loenen, A. F.
ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands .
Mechanical feedback in the molecular ISM of luminous IR galaxies2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 488, no 1, p. L5-L8Article in journal (Refereed)

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 = 104.5 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 = 104.5 cm-3) and mechanical feedback from supernova shocks dominates the heating budget.

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