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  • 2015-2019  (44)
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  • 1
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    Accretion, radial flows and abundance gradients in spiral galaxies (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-25
    Description: The metal-poor gas continuously accreting on to the discs of spiral galaxies is unlikely to arrive from the intergalactic medium (IGM) with exactly the same rotation velocity as the galaxy itself and even a small angular momentum mismatch inevitably drives radial gas flows within the disc, with significant consequences to galaxy evolution. Here, we provide some general analytic tools to compute accretion profiles, radial gas flows and abundance gradients in spiral galaxies as a function of the angular momentum of the accreting material. We generalize existing solutions for the decomposition of the gas flows, required to reproduce the structural properties of galaxy discs, into direct accretion from the IGM and a radial mass flux within the disc. We then solve the equation of metallicity evolution in the presence of radial gas flows with a novel method, based on characteristic lines, which greatly reduces the numerical demand on the computation and sheds light on the crucial role of boundary conditions on the abundance profiles predicted by theoretical models. We also discuss how structural and chemical constraints can be combined to disentangle the contributions of inside-out growth and radial flows in the development of abundance gradients in spiral galaxies. Illustrative examples are provided throughout with parameters plausible for the Milky Way. We find that the material accreting on the Milky Way should rotate at 70–80 per cent of the rotational velocity of the disc, in agreement with previous estimates.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    The instantaneous radial growth rate of stellar discs (2015)
    Oxford University Press
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    Publication Date: 2015-06-15
    Description: We present a new and simple method to measure the instantaneous mass and radial growth rates of the stellar discs of spiral galaxies, based on their star formation rate surface density (SFRD) profiles. Under the hypothesis that discs are exponential with time-varying scalelengths, we derive a universal theoretical profile for the SFRD, with a linear dependence on two parameters: the specific mass growth rate $\nu _ {\rm M} \equiv \dot{M}_\star /M_\star$ and the specific radial growth rate $\nu _ {\rm R} \equiv \dot{R}_\star /R_\star$ of the disc. We test our theory on a sample of 35 nearby spiral galaxies, for which we derive a measurement of M and R . 32/35 galaxies show the signature of ongoing inside-out growth ( R  〉 0). The typical derived e-folding time-scales for mass and radial growth in our sample are ~10 and ~30 Gyr, respectively, with some systematic uncertainties. More massive discs have a larger scatter in M and R , biased towards a slower growth, both in mass and size. We find a linear relation between the two growth rates, indicating that our galaxy discs grow in size at ~0.35 times the rate at which they grow in mass; this ratio is largely unaffected by systematics. Our results are in very good agreement with theoretical expectations if known scaling relations of disc galaxies are not evolving with time.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    PinSnps: structural and functional analysis of SNPs in the context of protein interaction networks (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-11
    Description: : We present a practical computational pipeline to readily perform data analyses of protein–protein interaction networks by using genetic and functional information mapped onto protein structures. We provide a 3D representation of the available protein structure and its regions (surface, interface, core and disordered) for the selected genetic variants and/or SNPs, and a prediction of the mutants’ impact on the protein as measured by a range of methods. We have mapped in total 2587 genetic disorder-related SNPs from OMIM, 587 873 cancer-related variants from COSMIC, and 1 484 045 SNPs from dbSNP. All result data can be downloaded by the user together with an R-script to compute the enrichment of SNPs/variants in selected structural regions. Availability and Implementation: PinSnps is available as open-access service at http://fraternalilab.kcl.ac.uk/PinSnps/ Contact: franca.fraternali@kcl.ac.uk Supplementary information: Supplementary data are available at Bioinformatics online.
    Print ISSN: 1367-4803
    Electronic ISSN: 1460-2059
    Topics: Biology , Computer Science , Medicine
    Published by Oxford University Press
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  • 4
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    3D BAROLO: a new 3D algorithm to derive rotation curves of galaxies (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-20
    Description: We present $^{3\small {D}}$ barolo , a new code that derives rotation curves of galaxies from emission-line observations. This software fits 3D tilted-ring models to spectroscopic data cubes and can be used with a variety of observations: from H i and molecular lines to optical/IR recombination lines. We describe the structure of the main algorithm and show that it performs much better than the standard 2D approach on velocity fields. A number of successful applications, from high to very low spatial resolution data are presented and discussed. $^{3\small {D}}$ barolo can recover the true rotation curve and estimate the intrinsic velocity dispersion even in barely resolved galaxies (~2 resolution elements) provided that the signal to noise of the data is larger than 2–3. It can also be run automatically thanks to its source-detection and first-estimate modules, which make it suitable for the analysis of large 3D data sets. These features make $^{3\small {D}}$ barolo a uniquely useful tool to derive reliable kinematics for both local and high-redshift galaxies from a variety of different instruments including the new generation Integral Field Units, ALMA and the SKA pathfinders.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Efficiency of gas cooling and accretion at the disc-corona interface (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-05
    Description: In star-forming galaxies, stellar feedback can have a dual effect on the circumgalactic medium both suppressing and stimulating gas accretion. The trigger of gas accretion can be caused by disc material ejected into the halo in the form of fountain clouds and by its interaction with the surrounding hot corona. Indeed, at the disc–corona interface, the mixing between the cold/metal-rich disc gas ( T 10 4  K) and the hot coronal gas ( T 10 6  K) can dramatically reduce the cooling time of a portion of the corona and produce its condensation and accretion. We studied the interaction between fountain clouds and corona in different galactic environments through parsec-scale hydrodynamical simulations, including the presence of thermal conduction, a key mechanism that influences gas condensation. Our simulations showed that the coronal gas condensation strongly depends on the galactic environment, in particular it is less efficient for increasing virial temperature/mass of the haloes where galaxies reside and it is fully ineffective for objects with virial masses larger than 10 13 M . This result implies that the coronal gas cools down quickly in haloes with low-intermediate virial mass ( M vir 3  x  10 12 M ) but the ability to cool the corona decreases going from late-type to early-type disc galaxies, potentially leading to the switching off of accretion and the quenching of star formation in massive systems.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The Galactic fountain as an origin for the Smith Cloud (2016)
    Oxford University Press
    Details
    Publication Date: 2016-10-22
    Description: The recent discovery of an enriched metallicity for the Smith high-velocity H  i Cloud (SC) lends support to a Galactic origin for this system. We use a dynamical model of the galactic fountain to reproduce the observed properties of the SC. In our model, fountain clouds are ejected from the region of the disc spiral arms and move through the halo interacting with a pre-existing hot corona. We find that a simple model where cold gas outflows vertically from the Perseus spiral arm reproduces the kinematics and the distance of the SC, but is in disagreement with the cloud's cometary morphology, if this is produced by ram-pressure stripping by the ambient gas. To explain the cloud morphology, we explore two scenarios: (i) the outflow is inclined with respect to the vertical direction and (ii) the cloud is entrained by a fast wind that escapes an underlying superbubble. Solutions in agreement with all observational constraints can be found for both cases, the former requires outflow angles 〉40° while the latter requires 1000 km s –1 winds. All scenarios predict that the SC is in the ascending phase of its trajectory and has large – but not implausible – energy requirements.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    In silico identification of rescue sites by double force scanning (2018)
    Oxford University Press
    Details
    Publication Date: 2018-03-06
    Description: Motivation A deleterious amino acid change in a protein can be compensated by a second-site rescue mutation. These compensatory mechanisms can be mimicked by drugs. In particular, the location of rescue mutations can be used to identify protein regions that can be targeted by small molecules to reactivate a damaged mutant. Results We present the first general computational method to detect rescue sites. By mimicking the effect of mutations through the application of forces, the double force scanning (DFS) method identifies the second-site residues that make the protein structure most resilient to the effect of pathogenic mutations. We tested DFS predictions against two datasets containing experimentally validated and putative evolutionary-related rescue sites. A remarkably good agreement was found between predictions and experimental data. Indeed, almost half of the rescue sites in p53 was correctly predicted by DFS, with 65% of remaining sites in contact with DFS predictions. Similar results were found for other proteins in the evolutionary dataset. Availability and implementation The DFS code is available under GPL at https://fornililab.github.io/dfs/ Contact m.tiberti@qmul.ac.uk or a.fornili@qmul.ac.uk Supplementary information Supplementary dataSupplementary data are available at Bioinformatics online.
    Print ISSN: 1367-4803
    Electronic ISSN: 1460-2059
    Topics: Biology , Computer Science , Medicine
    Published by Oxford University Press
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  • 8
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    A very dark stellar system lost in Virgo: kinematics and metallicity of SECCO 1 with MUSE (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-13
    Description: We present the results of VLT-MUSE (Very Large Telescope-Multi Unit Spectroscopic Explorer) integral field spectroscopy of SECCO 1, a faint, star-forming stellar system recently discovered as the stellar counterpart of an ultracompact high-velocity cloud (HVC 274.68+74.0), very likely residing within a substructure of the Virgo cluster of galaxies. We have obtained the radial velocity of a total of 38 individual compact sources identified as H ii regions in the main and secondary bodies of the system, and derived the metallicity for 18 of them. We provide the first direct demonstration that the two stellar bodies of SECCO 1 are physically associated and that their velocities match the H i velocities. The metallicity is quite uniform over the whole system, with a dispersion lower than the uncertainty on individual metallicity estimates. The mean abundance, 〈12 + log(O/H)〉 = 8.44, is much higher than the typical values for local dwarf galaxies of similar stellar mass. This strongly suggests that the SECCO 1 stars were born from a pre-enriched gas cloud, possibly stripped from a larger galaxy. Using archival Hubble Space Telescope ( HST ) images, we derive a total stellar mass of ~=1.6 x 10 5 M for SECCO 1, confirming that it has a very high H i -to-stellar mass ratio for a dwarf galaxy, $M_{\rm H\,\small {I}}$ / M * ~ 100. The star formation rate, derived from the Hα flux, is a factor of more than 10 higher than in typical dwarf galaxies of similar luminosity.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Molecular outflow and feedback in the obscured quasar XID2028 revealed by ALMA (2018)
    EDP Sciences
    Details
    Publication Date: 2018-04-01
    Description: We imaged, with ALMA and ARGOS/LUCI, the molecular gas and dust and stellar continuum in XID2028, which is an obscured quasi-stellar object (QSO) at z = 1.593, where the presence of a massive outflow in the ionised gas component traced by the [OIII]5007 emission has been resolved up to 10 kpc. This target represents a unique test case to study QSO feedback in action at the peak epoch of AGN-galaxy co-evolution. The QSO was detected in the CO(5 − 4) transition and in the 1.3 mm continuum at ~30 and ~20σ significance, respectively; both emissions are confined in the central (
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 10
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    Highly ionized region surrounding SN Refsdal revealed by MUSE (2015)
    EDP Sciences
    Details
    Publication Date: 2015-12-10
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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