| 1. |
- Bisbas, T.G., et al.
(författare)
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GMC Collisions as Triggers of Star Formation. V. Observational Signatures
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 850:1, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- © 2017. The American Astronomical Society. All rights reserved.. We present calculations of molecular, atomic, and ionic line emission from simulations of giant molecular cloud (GMC) collisions. We post-process snapshots of the magnetohydrodynamical simulations presented in an earlier paper in this series by Wu et al. of colliding and non-colliding GMCs. Using photodissociation region (PDR) chemistry and radiative transfer, we calculate the level populations and emission properties of the transitions of 12 CO J = 1-0, [C i] at 609 μm, [C ii] 158 μm, and [O i] at 63 μm. From emission maps of integrated intensity and position-velocity diagrams, we find that fine-structure lines, particularly [C ii] 158 μm, can be used as a diagnostic tracer for cloud-cloud collision activity. These results hold even in more evolved systems in which the collision signature in molecular lines has been diminished.
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| 2. |
- Bisbas, T. G., et al.
(författare)
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The inception of star cluster formation revealed by [C ii] emission around an Infrared Dark Cloud
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society: Letters. - : Oxford University Press (OUP). - 1745-3925 .- 1745-3933. ; 478:1, s. L54-L59
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Tidskriftsartikel (refereegranskat)abstract
- We present SOFIA-upGREAT observations of [C ii] emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such clouds. Several velocity components of [C ii] emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the 13CO(2-1) emission of the IRDC, but offset by ∼3 km s-1 and with a larger velocity width of ∼9 km s-1. The spatial distribution of the [C ii] emission of this component is also offset predominantly to one side of the dense filamentary structure of the IRDC. The C ii column density is estimated to be of the order of ∼1017-1018 cm-2. We compare these results to the [C ii] emission from numerical simulations of magnetized, dense gas filaments formed from giant molecular cloud (GMC) collisions, finding similar spatial and kinematic offsets. These observations and modellingof [C ii] add further to the evidence that IRDC G035.39-00.33 has been formed by a process of GMC-GMC collision, which may thus be an important mechanism for initiating star cluster formation.
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| 3. |
- Krips, M., et al.
(författare)
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ACA CI observations of the starburst galaxy NGC 253
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592:L3
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Tidskriftsartikel (refereegranskat)abstract
- Context. Carbon monoxide (CO) is widely used as a tracer of the molecular gas in almost all types of environments. However, several shortcomings of CO complicate usaging it as H-2 tracer, such as its optical depth effects, the dependence of its abundance on metallicity, or its susceptibility to dissociation in highly irradiated regions. Neutral carbon emission has been proposed to overcome some of these shortcomings and hence to help revealing the limits of CO as a measure of the molecular gas. Aims. We aim to study the general characteristics of the spatially and spectrally resolved carbon line emission in a variety of extragalactic sources and evaluate its potential as complementary H-2 tracer to CO. Methods. We used the Atacama Compact Array to map the [CI](P-3(1)-P-3(0)) line emission in the nearby starburst galaxy NGC 253 at unprecedented angular resolution (similar to 3 ''). This is the first well-resolved interferometric [CI] map of an extragalactic source. Results. We have detected the [CI] line emission at high significance levels along the central disk of NGC 253 and its edges where expanding shells have previously been found in CO. Globally, the distribution of the [CI] line emission strongly resembles that of CO, confirming the results of previous Galactic surveys that [CI] traces the same molecular gas as CO. However, we also identify a significant increase of [CI] line emission with respect to CO in (some of) the outflow or shocked regions of NGC 253, namely the bipolar outflow emerging from the nucleus. A first-order estimate of the [CI] column densities indicates abundances of [CI] that are very similar to the abundance of CO in NGC 253. Interestingly, we find that the [CI] line is marginally optically thick within the disk. Conclusions. The enhancement of the [CI]/CO line ratios (similar to 0.4-0.6) with respect to Galactic values (
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| 4. |
- Yang, Chentao, 1988, et al.
(författare)
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SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 680
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the nature of high-redshift dusty galaxies requires a comprehensive view of their interstellar medium (ISM) and molecular complexity. However, the molecular ISM at high redshifts is commonly studied using only a few species beyond 12C16O, limiting our understanding. In this paper, we present the results of deep 3 mm spectral line surveys using the NOrthern Extended Millimeter Array (NOEMA) targeting two strongly lensed dusty galaxies observed when the Universe was less than 1.8 Gyr old: APM 08279+5255, a quasar at redshift z = 3.911, and NCv1.143 (H-ATLAS J125632.7+233625), a z = 3.565 starburst galaxy. The spectral line surveys cover rest-frame frequencies from about 330 to 550 GHz for both galaxies. We report the detection of 38 and 25 emission lines in APM 08279+5255 and NCv1.143, respectively. These lines originate from 17 species, namely CO, 13CO, C18O, CN, CCH, HCN, HCO+, HNC, CS, C34S, H2O, H3O+, NO, N2H+, CH, c-C3H2, and the vibrationally excited HCN and neutral carbon. The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. By comparing the spectra of the two sources and combining the analysis of the molecular gas excitation, we find that the physical properties and the chemical imprints of the ISM are different: the molecular gas is more excited in APM 08279+5255, which exhibits higher molecular gas temperatures and densities compared to NCv1.143; the molecular abundances in APM 08279+5255 are akin to the values of local active galactic nuclei (AGN), showing boosted relative abundances of the dense gas tracers that might be related to high-temperature chemistry and/or the X-ray-dominated regions, while NCv1.143 more closely resembles local starburst galaxies. The most significant differences between the two sources are found in H2O: the 448 GHz ortho-H2O(423 - 330) line is significantly brighter in APM 08279+5255, which is likely linked to the intense far-infrared radiation from the dust powered by AGN. Our astrochemical model suggests that, at such high column densities, far-ultraviolet radiation is less important in regulating the ISM, while cosmic rays (and/or X-rays and shocks) are the key players in shaping the molecular abundances and the initial conditions of star formation. Both our observed CO isotopologs line ratios and the derived extreme ISM conditions (high gas temperatures, densities, and cosmic-ray ionization rates) suggest the presence of a top-heavy stellar initial mass function. From the ~330-550 GHz continuum, we also find evidence of nonthermal millimeter flux excess in APM 08279+5255 that might be related to the central supermassive black hole. Such deep spectral line surveys open a new window into the physics and chemistry of the ISM and the radiation field of galaxies in the early Universe.
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