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  • 1
    Digitale Medien
    Digitale Medien
    Accretion of low-metallicity gas by the Milky Way (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 402 (1999), S. 388-390 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] Models of the chemical evolution of the Milky Way suggest that the observed abundances of elements heavier than helium (‘metals’) require a continuous infall of gas with metallicity (metal abundance) about 0.1 times the solar value. An infall rate integrated over the entire disk of ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/46498
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  • 2
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    The BaLROG project - II. Quantifying the influence of bars on the stellar populations of nearby galaxies (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-06-24
    Beschreibung: We continue the exploration of the BaLROG (Bars in Low Redshift Optical Galaxies) sample: 16 large mosaics of barred galaxies observed with the integral field unit Spectrographic Areal Unit for Research on Optical Nebulae. We quantify the influence of bars on the composition of the stellar component. We derive line-strength indices of H β, Fe5015 and Mg b . Based on single stellar population (SSP) models, we calculate ages, metallicities and [Mg/Fe] abundances and their gradients along the bar major and minor axes. The high spatial resolution of our data allows us to identify breaks among index and SSP profiles, commonly at 0.13 ± 0.06 bar length, consistent with kinematic features. Inner gradients are about 10 times steeper than outer gradients and become larger when there is a central rotating component, implying that the gradients are not independent of dynamics and orbits. Central ages appear to be younger for stronger bars. Yet, the bar regions are usually old. We find a flattening of the iron (Fe5015) and magnesium (Mg b ) outer gradients along the bar major axis, translating into a flattening of the metallicity gradient. This gradient is found to be 0.03 ± 0.07 dex kpc –1 along the bar major axis while the mean value of the bar minor axis compares well with that of an unbarred control sample and is significantly steeper, namely –0.20 ± 0.04 dex kpc –1 . These results confirm recent simulations and discern the important localized influence of bars. The elevated [Mg/Fe] abundances of bars and bulges compared to the lower values of discs suggest an early formation, in particular for early-type galaxies.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 3
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    The void galaxy survey: Star formation properties (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-03-08
    Beschreibung: We study the star formation properties of 59 void galaxies as part of the Void Galaxy Survey (VGS). Current star formation rates are derived from H α and recent star formation rates from near-UV imaging. In addition, infrared 3.4, 4.6, 12 and 22 μm Wide-field Infrared Survey Explorer emission is used as star formation and mass indicator. Infrared and optical colours show that the VGS sample displays a wide range of dust and metallicity properties. We combine these measurements with stellar and $\rm {H\,\small {I}}$ masses to measure the specific SFRs (SFR/ M * ) and star formation efficiencies ( $\rm {SFR/{\it M }_{H\,\small {I}}}$ ). We compare the star formation properties of our sample with galaxies in the more moderate density regions of the cosmic web, ‘the field’. We find that specific SFRs of the VGS galaxies as a function of stellar and $\rm {H\,\small {I}}$ mass are similar to those of the galaxies in these field regions. Their SFR α is slightly elevated than the galaxies in the field for a given total $\rm {H\,\small {I}}$ mass. In the global star formation picture presented by Kennicutt–Schmidt, VGS galaxies fall into the regime of low average star formation and correspondingly low $\rm {H\,\small {I}}$ surface density. Their mean $\rm {SFR\,\alpha /{\it M}_{H\,\small {I}}}$ and SFR α/ M * are of the order of 10 – 9.9 yr – 1 . We conclude that while the large-scale underdense environment must play some role in galaxy formation and growth through accretion, we find that even with respect to other galaxies in the more mildly underdense regions, the increase in star formation rate is only marginal.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 4
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    Star formation in the outer regions of the early-type galaxy NGC 4203 (2015)
    Oxford University Press
    Details
    Publikationsdatum: 2015-05-24
    Beschreibung: NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H i disc. In this paper, we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the H i disc consists of two distinct components: an inner star-forming ring with radius from ~1 to ~3 R eff and an outer disc. The outer H i disc is nine times more massive than the inner H i ring. At the location of the inner H i ring, we detect spiral-like structure both in the deep g ' –  r ' image and in the 8 μm Spitzer -Infrared Array Camera image, extending in radius up to ~ 3 R eff . These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner H i ring and accretion from the inter galactic medium for the outer H i disc. The low-level star formation efficiency in the outer H i disc is not enough to change the morphology of NGC 4203, making the depletion time of the H i gas much too long.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 5
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    Star formation in the outer regions of the early-type galaxy NGC 4203 (2015)
    Oxford University Press
    Details
    Publikationsdatum: 2015-06-12
    Beschreibung: NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H i disc. In this paper, we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the H i disc consists of two distinct components: an inner star-forming ring with radius from ~1 to ~3 R eff and an outer disc. The outer H i disc is nine times more massive than the inner H i ring. At the location of the inner H i ring, we detect spiral-like structure both in the deep g ' –  r ' image and in the 8 μm Spitzer -Infrared Array Camera image, extending in radius up to ~ 3 R eff . These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner H i ring and accretion from the inter galactic medium for the outer H i disc. The low-level star formation efficiency in the outer H i disc is not enough to change the morphology of NGC 4203, making the depletion time of the H i gas much too long.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 6
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    Establishing the level of cylindrical rotation in boxy/peanut bulges (2015)
    Oxford University Press
    Details
    Publikationsdatum: 2015-12-19
    Beschreibung: We present SAURON integral-field observations of a sample of 12 mid-to-high-inclination disc galaxies, to unveil hidden bars on the basis of their kinematics, i.e. the correlation between velocity and h 3 profiles, and to establish their degree of cylindrical rotation. For the latter, we introduce a method to quantify cylindrical rotation that is robust against inner disc components. We confirm high levels of cylindrical rotation in boxy/peanut bulges, but also observe this feature in a few galaxies with rounder bulges. We suggest that these are also barred galaxies with end-on orientations. Re-analysing published data for our own Galaxy using this new method, we determine that the Milky Way bulge is cylindrically rotating at the same level as the strongest barred galaxy in our sample. Finally, we use self-consistent three-dimensional N -body simulations of bar-unstable discs to study the dependence of cylindrical rotation on the bar's orientation and host galaxy inclination.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 7
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    The HST/ACS Coma Cluster Survey - X. Nuclear star clusters in low-mass early-type galaxies: scaling relations (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-10-22
    Beschreibung: We present scaling relations between structural properties of nuclear star clusters and their host galaxies for a sample of early-type dwarf galaxies observed as part of the Hubble Space Telescope ( HST ) Advanced Camera for Surveys (ACS) Coma Cluster Survey. We have analysed the light profiles of 200 early-type dwarf galaxies in the magnitude range 16.0 〈  m F 814 W  〈 22.6 mag, corresponding to –19.0 〈  M F 814 W  〈 –12.4 mag. Nuclear star clusters are detected in 80 per cent of the galaxies, thus doubling the sample of HST -observed early-type dwarf galaxies with nuclear star clusters. We confirm that the nuclear star cluster detection fraction decreases strongly towards faint magnitudes. The luminosities of nuclear star clusters do not scale linearly with host galaxy luminosity. A linear fit yields $L_{\rm nuc} \sim L_{\rm gal}^{0.57\pm 0.05}$ . The nuclear star cluster–host galaxy luminosity scaling relation for low-mass early-type dwarf galaxies is consistent with formation by globular cluster (GC) accretion. We find that at similar luminosities, galaxies with higher Sérsic indices have slightly more luminous nuclear star clusters. Rounder galaxies have on average more luminous clusters. Some of the nuclear star clusters are resolved, despite the distance of Coma. We argue that the relation between nuclear star cluster mass and size is consistent with both formation by GC accretion and in situ formation. Our data are consistent with GC inspiralling being the dominant mechanism at low masses, although the observed trend with Sérsic index suggests that in situ star formation is an important second-order effect.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 8
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    Stellar population synthesis models between 2.5 and 5 {mu}m based on the empirical IRTF stellar library (2015)
    Oxford University Press
    Details
    Publikationsdatum: 2015-04-06
    Beschreibung: We present the first single-burst stellar population models in the infrared wavelength range between 2.5 and 5 μm which are exclusively based on empirical stellar spectra. Our models take as input 180 spectra from the stellar IRTF (Infrared Telescope Facility) library. Our final single-burst stellar population models are calculated based on two different sets of isochrones and various types of initial mass functions of different slopes, ages larger than 1 Gyr and metallicities between [Fe/H] = –0.70 and 0.26. They are made available online to the scientific community on the MILES web page. We analyse the behaviour of the Spitzer [3.6]–[4.5] colour calculated from our single stellar population models and find only slight dependences on both metallicity and age. When comparing to the colours of observed early-type galaxies, we find a good agreement for older, more massive galaxies that resemble a single-burst population. Younger, less massive and more metal-poor galaxies show redder colours with respect to our models. This mismatch can be explained by a more extended star formation history of these galaxies which includes a metal-poor or/and young population. Moreover, the colours derived from our models agree very well with most other models available in this wavelength range. We confirm that the mass-to-light ratio determined in the Spitzer [3.6] μm band changes much less as a function of both age and metallicity than in the optical bands.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 9
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    The HST/ACS Coma Cluster Survey - VII. Structure and assembly of massive galaxies in the centre of the Coma cluster (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-05-31
    Beschreibung: We constrain the assembly history of galaxies in the projected central 0.5 Mpc of the Coma cluster by performing structural decomposition on 69 massive ( M *  ≥ 10 9 M ) galaxies using high-resolution F 814 W images from the Hubble Space Telescope ( HST ) Treasury Survey of Coma. Each galaxy is modelled with up to three Sérsic components having a free Sérsic index n . After excluding the two cDs in the projected central 0.5 Mpc of Coma, 57 per cent of the galactic stellar mass in the projected central 0.5 Mpc of Coma resides in classical bulges/ellipticals while 43 per cent resides in cold disc-dominated structures. Most of the stellar mass in Coma may have been assembled through major (and possibly minor) mergers. Hubble types are assigned based on the decompositions, and we find a strong morphology–density relation; the ratio of (E+S0):spirals is (91.0 per cent):9.0 per cent. In agreement with earlier work, the size of outer discs in Coma S0s/spirals is smaller compared with lower density environments captured with SDSS (Data Release 2). Among similar-mass clusters from a hierarchical semi-analytic model, no single cluster can simultaneously match all the global properties of the Coma cluster. The model strongly overpredicts the mass of cold gas and underpredicts the mean fraction of stellar mass locked in hot components over a wide range of galaxy masses. We suggest that these disagreements with the model result from missing cluster physics (e.g. ram-pressure stripping), and certain bulge assembly modes (e.g. mergers of clumps). Overall, our study of Coma underscores that galaxy evolution is not solely a function of stellar mass, but also of environment.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 10
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    The void galaxy survey: Star formation properties (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-03-08
    Beschreibung: We study the star formation properties of 59 void galaxies as part of the Void Galaxy Survey (VGS). Current star formation rates are derived from H α and recent star formation rates from near-UV imaging. In addition, infrared 3.4, 4.6, 12 and 22 μm Wide-field Infrared Survey Explorer emission is used as star formation and mass indicator. Infrared and optical colours show that the VGS sample displays a wide range of dust and metallicity properties. We combine these measurements with stellar and $\rm {H\,\small {I}}$ masses to measure the specific SFRs (SFR/ M * ) and star formation efficiencies ( $\rm {SFR/{\it M }_{H\,\small {I}}}$ ). We compare the star formation properties of our sample with galaxies in the more moderate density regions of the cosmic web, ‘the field’. We find that specific SFRs of the VGS galaxies as a function of stellar and $\rm {H\,\small {I}}$ mass are similar to those of the galaxies in these field regions. Their SFR α is slightly elevated than the galaxies in the field for a given total $\rm {H\,\small {I}}$ mass. In the global star formation picture presented by Kennicutt–Schmidt, VGS galaxies fall into the regime of low average star formation and correspondingly low $\rm {H\,\small {I}}$ surface density. Their mean $\rm {SFR\,\alpha /{\it M}_{H\,\small {I}}}$ and SFR α/ M * are of the order of 10 – 9.9 yr – 1 . We conclude that while the large-scale underdense environment must play some role in galaxy formation and growth through accretion, we find that even with respect to other galaxies in the more mildly underdense regions, the increase in star formation rate is only marginal.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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