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  • 1
    Electronic Resource
    Electronic Resource
    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
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [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 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/46498
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    Paper (German National Licenses)
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  • 2
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    Star formation in the outer regions of the early-type galaxy NGC 4203 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-24
    Description: 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
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Star formation in the outer regions of the early-type galaxy NGC 4203 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-12
    Description: 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
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Establishing the level of cylindrical rotation in boxy/peanut bulges (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-19
    Description: 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
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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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
    Publication Date: 2014-10-22
    Description: 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
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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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
    Publication Date: 2015-04-06
    Description: 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
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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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
    Publication Date: 2014-05-31
    Description: 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.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Star formation associated with neutral hydrogen in the outskirts of early-type galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-10-17
    Description: About 20 per cent of all nearby early-type galaxies ( M * 6 x 10 9 M ) outside the Virgo cluster are surrounded by a disc or ring of low-column-density neutral hydrogen (H i ) gas with typical radii of tens of kpc, much larger than the stellar body. In order to understand the impact of these gas reservoirs on the host galaxies, we analyse the distribution of star formation out to large radii as a function of H i properties using GALEX UV and SDSS optical images. Our sample consists of 18 H i -rich galaxies as well as 55 control galaxies where no H i has been detected. In half of the H i -rich galaxies, the radial UV profile changes slope at the position of the H i radial profile peak. To study the stellar populations, we calculate the FUV–NUV and UV–optical colours in two apertures, 1–3 and 3–10 R eff . We find that H i -rich galaxies are on average 0.5 and 0.8 mag bluer than the H i -poor ones, respectively. This indicates that a significant fraction of the UV emission traces recent star formation and is associated with the H i gas. Using FUV emission as a proxy for star formation, we estimate the integrated star formation rate in the outer regions ( R 〉 1 R eff ) to be on average ~6 x 10 –3 M yr –1 for the H i -rich galaxies. This rate is too low to build a substantial stellar disc and, therefore, change the morphology of the host. We find that the star formation efficiency and the gas depletion time are similar to those at the outskirts of spirals.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The void galaxy survey: photometry, structure and identity of void galaxies (2016)
    Oxford University Press
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    Publication Date: 2016-10-20
    Description: We analyse photometry from deep B -band images of 59 void galaxies in the Void Galaxy Survey (VGS), together with their near-infrared 3.6 μm and 4.5 μm Spitzer photometry. The VGS galaxies constitute a sample of void galaxies that were selected by a geometric-topological procedure from the Sloan Digital Sky Survey Data Release 7 data release, and which populate the deep interior of voids. Our void galaxies span a range of absolute B -magnitude from M B = –15.5 to –20, while at the 3.6 μm band their magnitudes range from M 3.6 = –18 to –24. Their B –[3.6] colour and structural parameters indicate these are star-forming galaxies. A good reflection of the old stellar population, the near-infrared band photometry also provide a robust estimate of the stellar mass, which for the VGS galaxies we confirm to be smaller than 3 x 10 10 M . In terms of the structural parameters and morphology, our findings align with other studies in that our VGS galaxy sample consists mostly of small late-type galaxies. Most of them are similar to Sd-Sm galaxies, although a few are irregularly shaped galaxies. The sample even includes two early-type galaxies, one of which is an AGN. Their Sérsic indices are nearly all smaller than n = 2 in both bands and they also have small half-light radii. In all, we conclude that the principal impact of the void environment on the galaxies populating them mostly concerns their low stellar mass and small size.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    A surprising consistency between the far-infrared galaxy luminosity functions of the field and Coma (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-13
    Description: We present new deep images of the Coma Cluster from the ESA Herschel Space Observatory at wavelengths of 70, 100 and 160 μm, covering an area of 1.75 1.0 square degrees encompassing the core and south-west infall region. Our data display an excess of sources at flux densities above 100 mJy compared to blank-field surveys, as expected. We use extensive optical spectroscopy of this region to identify cluster members and hence produce cluster luminosity functions in all three photometric bands. We compare our results to the local field galaxy luminosity function, and the luminosity functions from the Herschel Virgo Cluster Survey. We find consistency between the shapes of the Coma and field galaxy luminosity functions at all three wavelengths; however, we do not find the same level of agreement with that of the Virgo Cluster.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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