| 1. |
- Decataldo, D., et al.
(författare)
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Molecular clumps photoevaporation in ionized regions
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 471:4, s. 4476-4487
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Tidskriftsartikel (refereegranskat)abstract
- We study the photoevaporation of molecular clumps exposed to a UV radiation field including hydrogen-ionizing photons (h nu > 13.6 eV) produced by massive stars or quasars. We follow the propagation and collision of shockwaves inside clumps and take into account self-shielding effects, determining the evolution of clump size and density with time. The structure of the ionization-photodissociation region is obtained for different initial clump masses (M = 0.01- 10(4)M(circle dot)) and impinging fluxes (G(0) = 10(2)-10(5) in units of the Habing flux). The cases of molecular clumps engulfed in the HII region of an OB star and clumps carried within quasar outflows are treated separately. We find that the clump undergoes in both cases an initial shock-contraction phase and a following expansion phase, which lets the radiation penetrate in until the clump is completely evaporated. Typical evaporation time-scales are similar or equal to 0.01 Myr in the stellar case and 0.1 Myr in the quasar case, where the clump mass is 0.1 M-circle dot and 10(3)M(circle dot) , respectively. We find that clump lifetimes in quasar outflows are compatible with their observed extension, suggesting that photoevaporation is the main mechanism regulating the size of molecular outflows.
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| 2. |
- Decataldo, D., et al.
(författare)
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Photoevaporation of Jeans-unstable molecular clumps
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 487:3, s. 3377-3391
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Tidskriftsartikel (refereegranskat)abstract
- We study the photoevaporation of Jeans-unstable molecular clumps by isotropic FUV (6 eV < by < 13.6 eV) radiation, through 3D radiative transfer hydrodynamical simulations implementing a non-equilibrium chemical network that includes the formation and dissociation of H2. We run a set of simulations considering different clump masses (M = 10-200 Mo) and impinging fluxes (G0 = 2 x 103 to 8 x 104 in Habing units). In the initial phase, the radiation sweeps the clump as an R-type dissociation front, reducing the H2 mass by a factor 40-90 per cent. Then, a weak (.A4 2) shock develops and travels towards the centre of the clump, which collapses while losing mass from its surface, All considered clumps remain gravitationally unstable even if radiation rips off most of the clump mass, showing that external REV radiation is not able to stop clump collapse. However, the REV intensity regulates the final H2 mass available for star formation: for example, for Go < 104 more than 10 per cent of the initial clump mass survives, Finally, for massive clumps (?, 100 the H2 mass increases by 25-50 per cent during the collapse, mostly because of the rapid density growth that implies a more efficient H2 self-shielding.
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| 3. |
- Ferrara, A., et al.
(författare)
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A physical model for [C II] line emission from galaxies
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 489:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- A tight relation between the [C II] 158 mu m line luminosity and star formation rate is measured in local galaxies. At high redshift (z > 5), though, a much larger scatter is observed, with a considerable (15-20 per cent) fraction of the outliers being [C II]-deficient. Moreover, the [C II] surface brightness (Sigma([C II])) of these sources is systematically lower than expected from the local relation. To clarify the origin of such [C II]-deficiency, we have developed an analytical model that fits local [C II] data and has been validated against radiative transfer simulations performed with CLOUDY. The model predicts an overall increase of Sigma([C II]) with Sigma(SFR). However, for Sigma(SFR) greater than or similar to 1M(circle dot) yr(-1) kpc(-2), Sigma([C II]) saturates. We conclude that underluminous [C II] systems can result from a combination of three factors: (a) large upward deviations from theKennicutt-Schmidt relation (kappa(s) >> 1), parametrized by the 'burstiness' parameter kappa(s); (b) low metallicity; (e.g. CR7). Observations of [C II] emission alone cannot break the degeneracy among the above three parameters; this requires additional information coming from other emission lines (e.g. [OIII]88 mu m, C III]1909 degrees, CO lines). Simple formulae are given to interpret available data for low- and high- z galaxies.
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| 4. |
- Pallottini, A., et al.
(författare)
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Deep into the structure of the first galaxies : SERRA views
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 487:2, s. 1689-1708
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Tidskriftsartikel (refereegranskat)abstract
- We study the formation and evolution of a sample of Lyman break galaxies in the epoch of reionization by using high-resolution (similar to 10 pc), cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow the interstellar medium thermochemical non-equilibrium evolution and perform on-the-fly radiative transfer of the interstellar radiation field (ISRF). The simulation outputs are post-processed to compute the emission of far infrared lines ([C II], [N II], and [O III]). At z = 8, the most massive galaxy, 'Freesia', has an age t(star) similar or equal to 409 Myr, stellar mass M-star similar or equal to 4.2 x 10(9)M(circle dot), and a star formation rate (SFR), SFR similar or equal to 11.5M(circle dot) yr(-1), due to a recent burst. Freesia has two stellar components (A and B) separated by similar or equal to 2.5 kpc; other 11 galaxies are found within 56.9 +/- 21.6 kpc. The mean ISRF in the Habing band is G = 7.9G(0) and is spatially uniform; in contrast, the ionization parameter is U = 2(-2)(+20) x 10(-3), and has a patchy distribution peaked at the location of star-forming sites. The resulting ionizing escape fraction from Freesia is f(esc) similar or equal to 2 per cent. While [C II] emission is extended (radius 1.54 kpc), [O III] is concentrated in Freesia-Lambda (0.85 kpc), where the ratio Sigma([O III])/Sigma([C II]) similar or equal to 10. As many high-z galaxies, Freesia lies below the local [C II]-SFR relation. We show that this is the general consequence of a starburst phase (pushing the galaxy above the Kennicutt-Schmidt relation) that disrupts/photodissociates the emitting molecular clouds around star-forming sites. Metallicity has a sub-dominant impact on the amplitude of [C II]-SFR deviations.
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