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  • 1
    Electronic Resource
    Electronic Resource
    Neuropeptide Y is an inhibitor of neural function in the myenteric plexus of the guinea-pig ileum
    Amsterdam : Elsevier
    Peptides 7 (1986), S. 623-629 
    Details
    ISSN: 0196-9781
    Keywords: Cholecystokinin ; Guinea-pig ileum ; Neuropeptide Y ; Opioids ; Somatostatin
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0196-9781(86)90037-9
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    Paper (German National Licenses)
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  • 2
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    Larger λR in the disc of isolated active spiral galaxies than in their non-active twins (2020)
    EDP Sciences
    Details
    Publication Date: 2020-07-01
    Description: We present a comparison of the spin parameter λR, measured in a region dominated by the galaxy disc, between 20 pairs of nearby (0.005 〈  z 〈  0.03) seemingly isolated twin galaxies differing in nuclear activity. We find that 80−82% of the active galaxies show higher values of λR than their corresponding non-active twin(s), indicating larger rotational support in the active galactic nuclei (AGN) discs. This result is driven by the 11 pairs of unbarred galaxies, for which 100% of the AGN show larger λR than their twins. These results can be explained by a more efficient angular momentum transfer from the inflowing gas to the disc baryonic matter in the case of the active galaxies. This gas inflow could have been induced by disc or bar instabilities, although we cannot rule out minor mergers if these are prevalent in our active galaxies. This result represents the first evidence of galaxy-scale differences between the dynamics of active and non-active isolated spiral galaxies of intermediate stellar masses (1010 〈  M* 〈  1011 M⊙) in the Universe.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 3
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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
    Publication Date: 2016-06-24
    Description: 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
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Tests of model predictions for the responses of stellar spectra and absorption-line indices to element abundance variations (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-26
    Description: A method that is widely used to analyse stellar populations in galaxies is to apply the theoretically derived responses of stellar spectra and line indices to element abundance variations, which are hereafter referred to as response functions. These are applied in a differential way, to base models, in order to generate spectra or indices with different abundance patterns. In this paper, sets of such response functions for three different stellar evolutionary stages are tested with new empirical [Mg/Fe] abundance data for the medium-resolution Isaac Newton Telescope library of empirical spectra (MILES). Recent theoretical models and observations are used to investigate the effects of [Fe/H], [Mg/H] and overall [Z/H] on spectra, via ratios of spectra for similar stars. The global effects of changes in abundance patterns are investigated empirically through direct comparisons of similar stars from MILES, highlighting the impact of abundance effects in the blue part of the spectrum, particularly for lower temperature stars. It is found that the relative behaviour of iron-sensitive line indices are generally well predicted by response functions, whereas Balmer line indices are not. Other indices tend to show large scatter about the predicted mean relations. Implications for element abundance and age studies in stellar populations are discussed and ways forward are suggested to improve the match with the behaviour of spectra and line-strength indices observed in real stars.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Evolutionary stellar population synthesis with MILES - II. Scaled-solar and {alpha}-enhanced models (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-26
    Description: We present models that predict spectra of old- and intermediate-aged stellar populations at 2.51 Š(FWHM) with varying [α/Fe] abundance. The models are based on the MILES library and on corrections from theoretical stellar spectra. The models employ recent [Mg/Fe] determinations for the MILES stars and BaSTI scaled-solar and α-enhanced isochrones. We compute models for a suite of initial mass function (IMF) shapes and slopes, covering a wide age/metallicity range. Using BaSTI, we also compute ‘base models’ matching the Galactic abundance pattern. We confirm that the α-enhanced models show a flux excess with respect to the scaled-solar models blueward ~4500 Å, which increases with age and metallicity. We also confirm that both [MgFe] and [MgFe]' indices are [α/Fe]-insensitive. We show that the sensitivity of the higher order Balmer lines to [α/Fe] resides in their pseudo-continua, with narrower index definitions yielding lower sensitivity. We confirm that the α-enhanced models yield bluer (redder) colours in the blue (red) spectral range. To match optical colours of massive galaxies, we require both α-enhancement and a bottom-heavy IMF. The comparison of globular cluster line-strengths with our predictions match the [Mg/Fe] determinations from their individual stars. We obtain good fits to both full spectra and indices of galaxies with varying [α/Fe]. Using thousands of SDSS galaxy spectra, we obtain a linear relation between a proxy for the abundance, [ Z Mg / Z Fe ] SS(BaSTI) , using solely scaled-solar models and the [Mg/Fe] derived with models with varying abundance ([Mg/Fe] = 0.59[ Z Mg / Z Fe ] SS(BaSTI) ). Finally, we provide a user-friendly, web-based facility, which allows composite populations with varying IMF and [α/Fe].
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    No direct coupling between bending of galaxy disc stellar age and light profiles (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-25
    Description: We study the stellar properties of 44 face-on spiral galaxies from the Calar Alto Legacy Integral Field Area survey via full spectrum fitting techniques. We compare the age profiles with the surface brightness distribution in order to highlight differences between profile types (type I, exponential profile; and II, down-bending profile). We observe an upturn (‘U-shape’) in the age profiles for 17 out of these 44 galaxies with reliable stellar information up to their outer parts. This ‘U-shape’ is not a unique feature for type II galaxies but can be observed in type I as well. These findings suggest that the mechanisms shaping the surface brightness and stellar population distributions are not directly coupled. This upturn in age is only observable in the light-weighted profiles while it flattens out in the mass-weighted profiles. Given recent results on the outer parts of nearby systems and the results presented in this Letter, one of the most plausible explanations for the age upturn is an early formation of the entire disc (~10 Gyr ago) followed by an inside-out quenching of the star formation.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Dissecting galactic bulges in space and time - I. The importance of early formation scenarios versus secular evolution (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-03
    Description: The details of bulge formation via collapse, mergers, secular processes or their interplay remain unresolved. To start answering this question and quantify the importance of distinct mechanisms, we mapped a sample of three galactic bulges using data from the integral field spectrograph WiFeS on the ANU's 2.3-m telescope in Siding Spring Observatory. Its high-resolution gratings ( R  ~ 7000) allow us to present a detailed kinematic and stellar population analysis of their inner structures with classical and novel techniques. The comparison of those techniques calls for the necessity of inversion algorithms in order to understand complex substructures and separate populations. We use line-strength indices to derive single stellar population equivalent ages and metallicities. Additionally, we use full spectral fitting methods, here the code steckmap , to extract their star formation histories. The high quality of our data allows us to study the 2D distribution of different stellar populations (i.e. young, intermediate and old). We can identify their dominant populations based on these age-discriminated 2D light and mass contribution. In all galactic bulges studied, at least 50 per cent of the stellar mass already existed 12 Gyr ago, more than currently predicted by simulations. A younger component (age between ~1 and ~8 Gyr) is also prominent and its present day distribution seems to be affected much more strongly by morphological structures, especially bars, than the older one. This in-depth analysis of the three bulges supports the notion of increasing complexity in their evolution, likely to be found in numerous bulge structures if studied at this level of detail, which cannot be achieved by mergers alone and require a non-negligible contribution of secular evolution.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Spiral-induced velocity and metallicity patterns in a cosmological zoom simulation of a Milky Way-sized galaxy (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-26
    Description: We use a high-resolution cosmological zoom simulation of a Milky Way-sized halo to study the observable features in velocity and metallicity space associated with the dynamical influence of spiral arms. For the first time, we demonstrate that spiral arms, that form in a disc in a fully cosmological environment with realistic galaxy formation physics, drive large-scale systematic streaming motions. In particular, on the trailing edge of the spiral arms the peculiar galactocentric radial and azimuthal velocity field is directed radially outward and azimuthally backward, whereas it is radially inward and azimuthally forward on the leading edge. Owing to the negative radial metallicity gradient, this systematic motion drives, at a given radius, an azimuthal variation in the residual metallicity that is characterized by a metal-rich trailing edge and a metal-poor leading edge. We show that these signatures are theoretically observable in external galaxies with integral field unit instruments such as VLT/MUSE, and if detected, would provide evidence for large-scale systematic radial migration driven by spiral arms.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Gaseous-phase metallicities and stellar populations in the centres of barred galaxies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-26
    Description: Numerical simulations predict that bars represent a very important agent for triggering gas inflows, which in turn could lead to central star formation. Bars thus are thought to contribute to the formation of the bulge. This process changes both the gaseous -phase and the stellar -phase metallicities in the centres of galaxies. With the aim of quantifying the importance of this process, we present a comparative study of the gaseous-phase and stellar-phase metallicities in the centres of members of a sample of barred and unbarred galaxies from SDSS. We do not find a significant difference in the metallicity (neither gaseous nor stellar) between barred and unbarred galaxies, but we find different trends in the metallicities of early- and late-type galaxies, with larger differences in the metallicity in the early-type subsample. Our results contradict some previous research in this field, but we find a possible origin of the discrepancies between previous works and our results.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    PPAK Wide field Integral Field Spectroscopy of NGC 628 - III. Stellar population properties (2013)
    Oxford University Press
    Details
    Publication Date: 2013-12-18
    Description: We present a stellar population analysis of the nearby, face-on, SA(s)c galaxy, NGC 628, which is part of the PPAK Integral Field Spectroscopy Nearby Galaxies Survey. The data cover a field of view of ~6 arcmin in diameter with a sampling of ~2.7 arcsec per spectrum and a wavelength range (3700–7000 Å). We apply spectral inversion methods to derive 2D maps of star formation histories and chemical enrichment. We present maps of the mean (luminosity- and mass-weighted) age and metallicity that reveal the presence of structures such as a nuclear ring, previously seen in molecular gas. The disc is dominated in mass by an old stellar component at all radii sampled by our data, while the percentage of young stars increase with radius. The mean stellar age and metallicity profiles have a two defined regions, an inner one with flatter gradients (even slightly positive) and an external one with a negative, steeper one, separated at ~60 arcsec. This break in the profiles is more prominent in the old stellar component. The young component shows a metallicity gradient that is very similar to that of the gas, and that is flatter in the whole disc. The agreement between the metallicity gradient of the young stars and the gas, and the recovery of the measured colours from our derived star formation histories validate the techniques to recover the age–metallicity and the star formation histories in disc galaxies from integrated spectra. We speculate about the possible origin of the break and conclude that the most likely scenario is that we are seeing, in the centre of NGC 628, a dissolving bar, as predicted in some numerical simulations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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