| 1. |
- Kohandel, M., et al.
(författare)
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Kinematics of z ≥ 6 galaxies from [C II] line emission
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 487:3, s. 3007-3020
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Tidskriftsartikel (refereegranskat)abstract
- We study the kinematical properties of galaxies in the Epoch of Reionization via the [C ii]158 μm line emission. The line profile provides information on the kinematics as well as structural properties such as the presence of a disc and satellites. To understand how these properties are encoded in the line profile, first we develop analytical models from which we identify disc inclination and gas turbulent motions as the key parameters affecting the line profile. To gain further insights, we use 'Althæa', a highly resolved (30\, \rm pc) simulated prototypical Lyman-break galaxy, in the redshift range z = 6-7, when the galaxy is in a very active assembling phase. Based on morphology, we select three main dynamical stages: (I) merger, (II) spiral disc, and (III) disturbed disc. We identify spectral signatures of merger events, spiral arms, and extra-planar flows in (I), (II), and (III), respectively. We derive a generalized dynamical mass versus [C ii]-line FWHM relation. If precise information on the galaxy inclination is (not) available, the returned mass estimate is accurate within a factor 2 (4). A Tully-Fisher relation is found for the observed high-z galaxies, i.e. L[C ii] (FWHM)1.80 ± 0.35 for which we provide a simple, physically based interpretation. Finally, we perform mock ALMA simulations to check the detectability of [C ii]. When seen face-on, Althæa is always detected at >5σ; in the edge-on case it remains undetected because the larger intrinsic FWHM pushes the line peak flux below detection limit. This suggests that some of the reported non-detections might be due to inclination effects.
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| 2. |
- Behrens, C., et al.
(författare)
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Ly alpha emission from galaxies in the Epoch of eionization
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 486:2, s. 2197-2209
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Tidskriftsartikel (refereegranskat)abstract
- The intrinsic strength of the Ly alpha line in young, star-forming systems makes it a special tool for studying high-redshift galaxies. However, interpreting observations remains challenging due to the complex radiative transfer involved. Here, we combine state-of-the-art hydrodynamical simulations of 'Althaea', a prototypical Lyman Break Galaxy (LBG; stellar mass M-star similar or equal to 10(10) M-circle dot) at z = 7.2, with detailed radiative transfer computations of dust/continuum, [C II] 158 mu m, and Ly alpha to clarify the relation between the galaxy properties and its Ly alpha emission. Althaea exhibits low (f(alpha) < 1 per cent) Ly alpha escape fractions and equivalent widths, EW less than or similar to 6 angstrom for the simulated lines of sight, with a large scatter. The correlation between escape fraction and inclination is weak, as a result of the rather chaotic structure of high-redshift galaxies. Low f(alpha) values persist even if we artificially remove neutral gas around star-forming regions to mimic the presence of H II regions. The high attenuation is primarily caused by dust clumps co-located with young stellar clusters. We can turn Althaea into a Lyman Alpha Emitter (LAE) only if we artificially remove dust from the clumps, yielding EWs up to 22 angstrom. Our study suggests that the LBG-LAE duty-cycle required by recent clustering measurements poses the challenging problem of a dynamically changing dust attenuation. Finally, we find an anticorrelation between the magnitude of Ly alpha-[C II] line velocity shift and Ly alpha luminosity.
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| 3. |
- Carniani, S., et al.
(författare)
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Constraints on high-J CO emission lines in z similar to 6 quasars
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 489:3, s. 3939-3952
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Tidskriftsartikel (refereegranskat)abstract
- We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of eight highly excited CO (J(up) > 8) lines and continuum emission in two z similar to 6 quasars: SDSS J231038.88+185519.7 (hereafter J2310), for which CO(8-7), CO(9-8), and CO(17-16) lines have been observed, and ULAS J131911.29+095951.4 (J1319), observed in the CO(14-13), CO(17-16), and CO(19-18) lines. The continuum emission of both quasars arises from a compact region (<0.9 kpc). By assuming a modified blackbody law, we estimate dust masses of log(M-dust/M-circle dot) = 8.75 +/- 0.07 and log(M-dust/M-circle dot) = 8.8 +/- 0.2 and dust temperatures of T-dust = 76 +/- 3 K and T-dust = 66(-10)(+15) K, respectively, for J2310 and J1319. Only CO(8-7) and CO(9-8) in J2310 are detected, while 3 sigma upper limits on luminosities are reported for the other lines of both quasars. The CO line luminosities and upper limits measured in J2310 and J1319 are consistent with those observed in local active galactic nuclei and starburst galaxies, and other z similar to 6 quasars, except for SDSS J1148+5251 (J1148), the only quasar at z = 6.4 with a previous CO(17-16) line detection. By computing the CO spectral line energy distributions normalized to the CO(6-5) line and far-infrared luminosities for J2310, J1319, and J1148, we conclude that different gas heating mechanisms (X-ray radiation and/or shocks) may explain the different CO luminosities observed in these z similar to 6 quasar. Future J(up) > 8 CO observations will be crucial to understand the processes responsible for molecular gas excitation in luminous high-z quasars.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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