5,660 research outputs found
Evolution along the Great Rift Valley: phenotypic and genetic differentiation of East African white-eyes (Aves, Zosteropidae)
The moist and cool cloud forests of East Africa represent a network of isolated habitats that are separated by dry and warm lowland savannah, offering an opportunity to investigate how strikingly different selective regimes affect species diversification. Here, we used the passerine genus Zosterops (white-eyes) from this region as our model system. Species of the genus occur in contrasting distribution settings, with geographical mountain isolation driving diversification, and savannah interconnectivity preventing differentiation. We analyze (1) patterns of phenotypic and genetic differentiation in high- and lowland species (different distribution settings), (2) investigate the potential effects of natural selection and temporal and spatial isolation (evolutionary drivers), and (3) critically review the taxonomy of this species complex. We found strong phenotypic and genetic differentiation among and within the three focal species, both in the highland species complex and in the lowland taxa. Altitude was a stronger predictor of phenotypic patterns than the current taxonomic classification. We found longitudinal and latitudinal phenotypic gradients for all three species. Furthermore, wing length and body weight were significantly correlated with altitude and habitat type in the highland species Z.poliogaster. Genetic and phenotypic divergence showed contrasting inter- and intraspecific structures. We suggest that the evolution of phenotypic characters is mainly driven by natural selection due to differences in the two macro-habitats, cloud forest and savannah. In contrast, patterns of neutral genetic variation appear to be rather driven by geographical isolation of the respective mountain massifs. Populations of the Z.poliogaster complex, as well as Z.senegalensis and Z.abyssinicus, are not monophyletic based on microsatellite data and have higher levels of intraspecific differentiation compared to the currently accepted species
Resolving galaxies in time and space: II: Uncertainties in the spectral synthesis of datacubes
In a companion paper we have presented many products derived from the
application of the spectral synthesis code STARLIGHT to datacubes from the
CALIFA survey, including 2D maps of stellar population properties and 1D
averages in the temporal and spatial dimensions. Here we evaluate the
uncertainties in these products. Uncertainties due to noise and spectral shape
calibration errors and to the synthesis method are investigated by means of a
suite of simulations based on 1638 CALIFA spectra for NGC 2916, with
perturbations amplitudes gauged in terms of the expected errors. A separate
study was conducted to assess uncertainties related to the choice of
evolutionary synthesis models. We compare results obtained with the Bruzual &
Charlot models, a preliminary update of them, and a combination of spectra
derived from the Granada and MILES models. About 100k CALIFA spectra are used
in this comparison.
Noise and shape-related errors at the level expected for CALIFA propagate to
0.10-0.15 dex uncertainties in stellar masses, mean ages and metallicities.
Uncertainties in A_V increase from 0.06 mag in the case of random noise to 0.16
mag for shape errors. Higher order products such as SFHs are more uncertain,
but still relatively stable. Due to the large number statistics of datacubes,
spatial averaging reduces uncertainties while preserving information on the
history and structure of stellar populations. Radial profiles of global
properties, as well as SFHs averaged over different regions are much more
stable than for individual spaxels. Uncertainties related to the choice of base
models are larger than those associated with data and method. Differences in
mean age, mass and metallicity are ~ 0.15 to 0.25 dex, and 0.1 mag in A_V.
Spectral residuals are ~ 1% on average, but with systematic features of up to
4%. The origin of these features is discussed. (Abridged)Comment: A&A, accepte
The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes
Galaxies, which often contain ionised gas, sometimes also exhibit a so-called
low-ionisation nuclear emission line region (LINER). For 30 years this was
attributed to a central mass-accreting supermassive black hole (AGN) of low
luminosity, making LINER galaxies the largest AGN-sub-population, dominating in
numbers over higher luminosity Seyfert galaxies and quasars. This, however,
poses a serious problem. While the inferred energy balance is plausible, many
LINERs clearly do not contain any other independent signatures of an AGN. Using
integral field spectroscopic data from the CALIFA survey, we aim at comparing
the observed radial surface brightness profiles with what is expected from
illumination by an AGN. Essential for this analysis is a proper extraction of
emission-lines, especially weak lines such as the Balmer Hb line which is
superposed on an absorption trough. To accomplish this, we use the GANDALF code
which simultaneously fits the underlying stellar continuum and emission lines.
We show for 48 galaxies with LINER-like emission, that the radial emission-line
surface brightness profiles are inconsistent with ionisation by a central
point-source and hence cannot be due to an AGN alone. The most probable
explanation for the excess LINER-like emission is ionisation by evolved stars
during the short but very hot and energetic phase known as post-AGB. This leads
us to an entirely new interpretation. Post-AGB stars are ubiquitous and their
ionising effect should be potentially observable in every galaxy with gas
present and stars older than ~1 Gyr, unless a stronger radiation field from
young hot stars or an AGN outshines them. This means that galaxies with
LINER-like emission are in fact not a class defined by a property, but rather
by the absence of a property. It also explains why LINER emission is observed
mostly in massive galaxies with old stars and little star formation.Comment: 8 pages, 7 figure
Central star formation and metallicity in CALIFA interacting galaxies
We use optical integral-field spectroscopic (IFS) data from 103 nearby
galaxies at different stages of the merging event, from close pairs to merger
remnants provided by the CALIFA survey, to study the impact of the interaction
in the specific star formation and oxygen abundance on different galactic
scales. To disentangle the effect of the interaction and merger from internal
processes, we compared our results with a control sample of 80 non-interacting
galaxies. We confirm the moderate enhancement (2-3 times) of specific star
formation for interacting galaxies in central regions as reported by previous
studies; however, the specific star formation is comparable when observed in
extended regions. We find that control and interacting star-forming galaxies
have similar oxygen abundances in their central regions, when normalized to
their stellar masses. Oxygen abundances of these interacting galaxies seem to
decrease compared to the control objects at the large aperture sizes measured
in effective radius. Although the enhancement in central star formation and
lower metallicities for interacting galaxies have been attributed to tidally
induced inflows, our results suggest that other processes such as stellar
feedback can contribute to the metal enrichment in interacting galaxies.Comment: 9 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysic
Tracing kinematic (mis)alignments in CALIFA merging galaxies: Stellar and ionized gas kinematic orientations at every merger stage
We present spatially resolved stellar and/or ionized gas kinematic properties
for a sample of 103 interacting galaxies, tracing all merger stages: close
companions, pairs with morphological signatures of interaction, and coalesced
merger remnants. We compare our sample with 80 non-interacting galaxies. We
measure for the stellar and the ionized gas components the major (projected)
kinematic position angles (PA, approaching and receding)
directly from the velocity fields with no assumptions on the internal motions.
This method allow us to derive the deviations of the kinematic PAs from a
straight line (PA). Around half of the interacting
objects show morpho-kinematic PA misalignments that cannot be found in the
control sample. Those misalignments are present mostly in galaxies with
morphological signatures of interaction. Alignment between the kinematic sides
for both samples is similar, with most of the galaxies displaying small
misalignments. Radial deviations of the kinematic PA from a straight line in
the stellar component measured by PA are large for
both samples. However, for a large fraction of interacting galaxies the ionized
gas PA is larger than typical values derived from
isolated galaxies (48%), making this parameter a good indicator to trace the
impact of interaction and mergers in the internal motions of galaxies. By
comparing the stellar and ionized gas kinematic PA, we find that 42% (28/66) of
the interacting galaxies have misalignments larger than 16 degrees, compared to
10% from the control sample. Our results show the impact of interactions in the
internal structure of galaxies as well as the wide variety of their velocity
distributions. This study also provides a local Universe benchmark for
kinematic studies in merging galaxies at high redshift.Comment: 24 pages,11 Figures, Accepted for publication in Astronomy &
Astrophysics. The entire set of stellar and ionized gas velocity fields of
the interacting/merging sample will be available in the electronic version of
the journa
The dependence of oxygen and nitrogen abundances on stellar mass from the CALIFA survey
We analysed the optical spectra of HII regions extracted from a sample of 350
galaxies of the CALIFA survey. We calculated total O/H abundances and, for the
first time, N/O ratios using the semi-empirical routine HII-CHI-mistry, which,
according to P\'erez-Montero (2014), is consistent with the direct method and
reduces the uncertainty in the O/H derivation using [NII] lines owing to the
dispersion in the O/H-N/O relation. Then we performed linear fittings to the
abundances as a function of the de-projected galactocentric distances. The
analysis of the radial distribution both for O/H and N/O in the non-interacting
galaxies reveals that both average slopes are negative, but a non-negligible
fraction of objects have a flat or even a positive gradient (at least 10\% for
O/H and 4\% for N/O). The slopes normalised to the effective radius appear to
have a slight dependence on the total stellar mass and the morphological type,
as late low-mass objects tend to have flatter slopes. No clear relation is
found, however, to explain the presence of inverted gradients in this sample,
and there is no dependence between the average slopes and the presence of a
bar. The relation between the resulting O/H and N/O linear fittings at the
effective radius is much tighter (correlation coefficient = 0.80) than
between O/H and N/O slopes ( = 0.39) or for O/H and N/O in the
individual \hii\ regions ( = 0.37). These O/H and N/O values at the
effective radius also correlate very tightly (less than 0.03 dex of dispersion)
with total luminosity and stellar mass. The relation with other integrated
properties, such as star formation rate, colour, or morphology, can be
understood only in light of the found relation with mass.Comment: Accepted for publication in A&A. 20 pages, 19 figure
From Teamchef Arminius to Hermann Junior: glocalised discourse about a national foundation myth
If for much of the nineteenth and twentieth centuries, the ‘Battle of the Teutoburg Forest’, fought in 9 CE between Roman armies and Germanic tribes, was predominantly a reference point for nationalist and chauvinist discourses in Germany, the first decade of the twenty-first century has seen attempts to link public remembrance with local/regional identities on the one hand and international/intercultural contact on the other. In the run up to and during the ‘anniversary year’ of 2009, German media, sports institutions and various other official institutions articulating tourist, economic and political interests attempted to create a new ‘glocalised’ version of the public memory of the Teutoburg battle. Combining methods of Cognitive Linguistics and Critical Discourse Analysis, the paper analyses the narrative and argumentative topoi employed in this re-orientation of public memory, with a special emphasis on hybrid, post-national identity-construction. Das zweitausendjährige Gedenkjahr der „Schlacht im Teutoburger Wald“ im Jahr 2009 bot eine günstige Gelegenheit, die bis in die zweite Hälfte des 20. Jahrhunderts dominante Tradition nationalistisch–chauvinistischer Deutungen des Sieges von germanischen Stämmen über drei römische Legionen zu korrigieren und zu überwinden. Der Aufsatz analysiert mit Hilfe diskurslinguistischer Methoden die Anstrengungen regionaler Institutionen und Medien, die nationale Vereinnahmung des historischen Gedenkens kritisch zu thematisieren sowie neue, zum eine lokal situierte, zum andern international orientierte Identifikationsangebote anzubieten. Die Analyse zeigt, dass solche „de-nationalisierten“ Identifikationsangebote zwar teilweise auch früher verwendet wurden, aber heutzutage rekontextualisiert und auf innovative Weise in den Vordergrund gestellt werden
A new scaling relation for HII regions in spiral galaxies: unveiling the true nature of the mass-metallicity relation
We demonstrate the existence of a -local- relation between galaxy surface
mass density, gas metallicity, and star-formation rate density using
spatially-resolved optical spectroscopy of HII regions in the local Universe.
One of the projections of this distribution, -the local mass-metallicity
relation- extends over three orders of magnitude in galaxy mass density and a
factor of eight in gas metallicity. We explain the new relation as the combined
effect of the differential radial distributions of mass and metallicity in the
discs of galaxies, and a selective star-formation efficiency. We use this local
relation to reproduce -with remarkable agreement- the total mass-metallicity
relation seen in galaxies, and conclude that the latter is a scale-up
integrated effect of a local relation, supporting the inside-out growth and
downsizing scenarios of galaxy evolution.Comment: Accepted for publication in Astrophysical Journal Letters, 5 pages, 4
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