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  • 1
    Electronic Resource
    Electronic Resource
    A class of compact dwarf galaxies from disruptive processes in galaxy clusters (2003)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 423 (2003), S. 519-521 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Dwarf galaxies have attracted increased attention in recent years, because of their susceptibility to galaxy transformation processes within rich galaxy clusters. Direct evidence for these processes, however, has been difficult to obtain, with a small number of diffuse light trails and ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01666
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    Paper (German National Licenses)
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  • 2
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    Bars formed in galaxy merging and their classification with deep learning (2020)
    EDP Sciences
    Details
    Publication Date: 2020-09-01
    Description: Context. Stellar bars are a common morphological feature of spiral galaxies. While it is known that they can form in isolation, or be induced tidally, few studies have explored the production of stellar bars in galaxy merging. We look to investigate bar formation in galaxy merging using methods from deep learning to analyse our N-body simulations. Aims. The primary aim is to determine the constraints on the mass ratio and orientations of merging galaxies that are most conducive to bar formation. We further aim to explore whether it is possible to classify simulated barred spiral galaxies based on the mechanism of their formation. We test the feasibility of this new classification schema with simulated galaxies. Methods. Using a set of 29 400 images obtained from our simulations, we first trained a convolutional neural network to distinguish between barred and non-barred galaxies. We then tested the network on simulations with different mass ratios and spin angles. We adapted the core neural network architecture for use with our additional aims. Results. We find that a strong inverse relationship exists between the mass ratio and the number of bars produced. We also identify two distinct phases in the bar formation process; (1) the initial, tidally induced formation pre-merger and (2) the destruction and/or regeneration of the bar during and after the merger. Conclusions. Mergers with low mass ratios and closely-aligned orientations are considerably more conducive to bar formation compared to equal-mass mergers. We demonstrate the flexibility of our deep learning approach by showing it is feasible to classify bars based on their formation mechanism.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 3
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    The transformation and quenching of simulated gas-rich dwarf satellites within a group environment (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-14
    Description: The underlying mechanisms driving the quenching of dwarf-mass satellite galaxies remain poorly constrained, but recent studies suggest they are particularly inefficient for those satellites with stellar mass 10 9 M . We investigate the characteristic evolution of these systems with chemodynamical simulations and idealized models of their tidal/hydrodynamic interactions within the 10 $^{\rm 13{\rm -}13.5}$ -M group-mass hosts in which they are preferentially quenched. Our fiducial simulations highlight the role played by secular star formation and stellar bars, and demonstrate a transition from a gas-rich to passive, H i -deficient state (i.e. SFR ≤ –1, def $_{\rm H\, {\small {I}}}$  ≥ 0.5) within 6 Gyr of first infall. Furthermore, in the 8–10 Gyr in which these systems have typically been resident within group hosts, the bulge-to-total ratio of an initially bulgeless disc can increase to 0.3 〈 B/T 〈 0.4, its specific angular momentum R reduce to ~0.5, and strong bisymmetries formed. Ultimately, this scenario yields satellites resembling dwarf S0s, a result that holds for a variety of infall inclinations/harassments albeit with broad scatter. The key assumptions here lie in the rapid removal of the satellite's gaseous halo upon virial infall, and the satellite's local intragroup medium density being defined by the host's spherically averaged profile. We demonstrate how quenching can be greatly enhanced if the satellite lies in an overdensity, consistent with recent cosmological-scale simulations but contrasting with observationally inferred quenching mechanisms/time-scales; an appraisal of these results with respect to the apparent preferential formation of dS0s/S0s in groups is also given.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Formation of emission line dots and extremely metal-deficient dwarfs from almost dark galaxies (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-25
    Description: Recent observations have discovered a number of extremely gas-rich very faint dwarf galaxies possibly embedded in low-mass dark matter haloes. We investigate star formation histories of these gas-rich dwarf (‘almost dark’) galaxies both for isolated and interacting/merging cases. We find that although star formation rates (SFRs) are very low (〈10 –5 M  yr –1 ) in the simulated dwarfs in isolation for the total halo masses ( M h ) of 10 8 -10 9 M , they can be dramatically increased to be ~10 –4 M  yr –1 when they interact or merge with other dwarfs. These interacting faint dwarfs with central compact H ii regions can be identified as isolated emission line dots (‘ELdots’) owing to their very low surface brightness envelopes of old stars. The remnant of these interacting and merging dwarfs can finally develop central compact stellar systems with very low metallicities ( Z /Z  〈 0.1), which can be identified as extremely metal-deficient (‘XMD’) dwarfs. These results imply that although there would exist many faint dwarfs that can be hardly detected in the current optical observations, they can be detected as isolated ELdots or XMD dwarfs, when they interact with other galaxies and their host environments. We predict that nucleated ultrafaint dwarfs formed from the darkest dwarf merging can be identified as low-mass globular clusters owing to the very low surface brightness stellar envelopes.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    The global warming of group satellite galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-26
    Description: Recent studies adopting Re , a proxy for specific angular momentum, have highlighted how early-type galaxies (ETGs) are composed of two kinematical classes for which distinct formation mechanisms can be inferred. With upcoming surveys expected to obtain Re from a broad range of environments (e.g. SAMI, MaNGA), we investigate in this numerical study how the Re – e distribution of fast-rotating dwarf satellite galaxies reflects their evolutionary state. By combining N -body/SPH simulations of progenitor disc galaxies (stellar mass ~=10 9 M ), their cosmologically-motivated sub-halo infall history and a characteristic group orbit/potential, we demonstrate the evolution of a satellite ETG population driven by tidal interactions (e.g. harassment). As a general result, these satellites remain intrinsically fast-rotating oblate stellar systems since their infall as early as z = 2; mis-identifications as slow rotators often arise due to a bar/spiral lifecycle which plays an integral role in their evolution. Despite the idealistic nature of its construction, our mock Re – e distribution at z 〈 0.1 reproduces its observational counterpart from the ATLAS 3D /SAURON projects. We predict therefore how the observed Re – e distribution of a group evolves according to these ensemble tidal interactions.
    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 VMC Survey - XXI. New star cluster candidates discovered from infrared photometry in the Small Magellanic Cloud (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-27
    Description: We report the first search for new star clusters performed using the VISTA near-infrared YJK s Magellanic Clouds survey (VMC) data sets. We chose a pilot field of ~0.4 deg 2 located in the South-west of the Small Magelllanic Cloud bar, where the star field is among the densest and highest reddened region in the galaxy. In order to devise an appropriate automatic procedure we made use of dimensions and stellar densities observed in the VMC data sets of the known clusters in this area. We executed different kernel density estimations over a sample of more than 358 000 stars with magnitudes measured in the three YJK s filters. We analysed the new cluster candidates whose colour–magnitude diagrams (CMDs), cleaned from field star contamination, were used to assess the clusters’ reality and estimate reddenings and ages of the genuine systems. As a result 38 objects ( a 55 per cent increase in the known star clusters located in the surveyed field) of 0.15–0.40 arcmin (2.6–7.0 pc) in radius resulted to have near-infrared CMD features which resemble those of star clusters of young to moderate intermediate age (log( t  yr –1 ) ~7.5–9.0). Most of the new star cluster candidates are hardly recognizable in optical images without the help of a sound star field decontaminated CMD analysis. For highly reddened star cluster candidates ( E ( B – V ) ≥ 0.6 mag) the VMC data sets were necessary in order to recognize them.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Coevolution of dust, gas and stars in galaxies - I. Spatial distributions and scaling-relations of dust and molecular hydrogen (2013)
    Oxford University Press
    Details
    Publication Date: 2013-06-09
    Description: We investigate the time evolution of dust properties, molecular hydrogen (H 2 ) contents and star formation histories in galaxies by using our original chemodynamical simulations. The simulations include the formation of dust in the stellar winds of supernovae and asymptotic giant branch (AGB) stars, the growth and destruction processes of dust in the interstellar medium (ISM), the formation of polycyclic aromatic hydrocarbon (PAH) dust in carbon-rich AGB stars, the H 2 formation on dust grains and the H 2 photodissociation due to far-ultraviolet light in a self-consistent manner. We focus mainly on disc galaxies with the total masses ranging from 10 10 to 10 12 M in this preliminary study. The principal results are as follows. The star formation histories of disc galaxies can be regulated by the time evolution of interstellar dust, mainly because the formation rates of H 2 can be controlled by dust properties. The observed correlation between dust-to-gas-ratios ( D ) and gas-phase oxygen abundances [ A O   12 + log (O/H)] can be reproduced reasonably well in the present models. The discs show negative radial gradients (i.e. larger in inner regions) of H 2 fraction ( $f_{\rm H_2}$ ), PAH-to-dust mass ratio ( f PAH ), D and A O , and these gradients evolve with time. The surface mass densities of dust ( dust ) are correlated more strongly with the total surface gas densities ( gas ) than with those of H 2 ( $\Sigma _{\rm H_2}$ ). Local gaseous regions with higher D are more likely to have higher $f_{\rm H_2}$ in individual discs and total H 2 masses ( $M_{\rm H_2}$ ) correlate well with total dust masses ( M dust ). More massive disc galaxies are more likely to have higher D , f PAH and $f_{\rm H_2}$ , and smaller dust-to-stellar mass ratios ( R dust  = M dust / M star ). Early-type E/S0 galaxies formed by major galaxy merging can have lower R dust than isolated late-type disc galaxies. We also compare between galactic star formation histories in the metallicity-dependent and dust-dependent star formation models and find no major differences. Based on these results, we discuss the roles of dust in chemical and dynamical evolution of galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Erratum: Global properties of 'ordinary early-type galaxies: photometry and spectroscopy of stars and globular clusters in NGC 4494 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-01
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Dust-regulated galaxy formation and evolution: a new chemodynamical model with live dust particles (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-27
    Description: Interstellar dust plays decisive roles in the conversion of neutral to molecular hydrogen (H 2 ), the thermodynamical evolution of interstellar medium (ISM), and the modification of spectral energy distributions (SEDs) of galaxies. These important roles of dust have not been self-consistently included in previous numerical simulations of galaxy formation and evolution. We have therefore developed a new model by which one can investigate whether and how galaxy formation and evolution can be influenced by dust-related physical processes such as photoelectric heating, H 2 formation on dust, and stellar radiation pressure on dust in detail. A novel point of the model is that different dust species in a galaxy are represented by ‘live dust’ particles (i.e. not test particles). Therefore, dust particles in a galaxy not only interact gravitationally with all four components of the galaxy (i.e. dark matter, stars, gas, and dust) but also are grown and destroyed through physical processes of ISM. First, we describe a way to include dust-related physical processes in N -body+hydrodynamical simulations of galaxy evolution in detail. Then, we show some preliminary results of dust-regulated galaxy evolution. The preliminary results suggest that the evolution of dust distributions driven by radiation pressure of stars is very important for the evolution of star formation rates, chemical abundances, H 2 fractions, and gas distributions in galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The distance and properties of hydrogen clouds in the Leading Arm of the Magellanic System (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-02
    Description: We present a high-resolution study of five high-velocity clouds in the Magellanic Leading Arm region. This is a follow-up study of our widefield Parkes survey of the region in order to probe the multiphase structures of the clouds and to give an insight to their origin, evolution and distance. High-resolution data were obtained from the Australia Telescope Compact Array. By combining with single-dish data from the Galactic All-Sky Survey, we are able to probe compact and diffuse emission simultaneously. We identify resolved and unresolved clumps. Physical parameters were derived for both diffuse structure and compact clumps. The latter are cold with typical velocity linewidths of 5 km s –1 . We find a gradient in thermal halo pressure, hydrogen density and H i column density of high-velocity clouds as a function of Galactic latitude. This is possibly the first observational evidence of varying distance in the Leading Arm region, with the leading part of the Leading Arm (LA II and III) probably being closer to the Galactic disc than the trailing end (LA I).
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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