722 research outputs found
Cambios en la representaciĂłn polĂnica de los ecosistemas fluvio-marinos de transiciĂłn del entorno de la RĂa de Vigo durante los Ășltimos 1500 años
XV lnternational A.P.L.E. Symposium of Palynolog
First high-resolution multi-proxy palaeoenvironmental record of the Late Glacial to Early Holocene transition in the RĂa de Arousa (Atlantic margin of NW Iberia)
A 322-cm-long sedimentary sequence obtained in the shallow marine basin of the RĂa de Arousaâa submerged unglaciated river valley on the Atlantic margin of northwestern Iberiaâwas analysed using a multi-proxy approach to study how climatic and sea level changes affected the coastal ecosystems during the Last GlacialâInterglacial Transition. Past sedimentation, vegetation and marine productivities were inferred from palynological, radiocarbon, seismic and lithological data. A substantial reduction in the pollen and dinoflagellate cyst accumulation rates is observed at âŒ12,700 to 11,700âŻcal a BP, suggesting lower marine and vegetation productivities likely as a response to the Younger Dryas cooling event. Overall, the regional vegetation changed from cold-tolerant open woodlands (Pinus sylvestris/P. nigra and Betula) dominating before âŒ10,200âŻcal a BP to coastal wetlands and the regional spread of Quercus-dominated forests after âŒ9800âŻcal a BP. Cluster analysis and principal component analysis allowed the identification of several small environmental oscillations, such as the 11.4 ka and 10.5 ka cooling events. After that, a conspicuous heath expansion was likely favoured by the palaeotopography, the increased precipitation and the relative sea level rise, which might have caused a profound change in the coastal configuration. Concurrently, both the dinoflagellate cyst and non-pollen palynomorph records reveal variations in the marine productivity and coastal hydrodynamics that also agree with a period of marked marine transgression, warming and increasing river flow. New sedimentary data highlight the high sensitivity of the ria's ecosystems to environmental oscillations and show a close temporal correspondence between terrestrial and marine responses to climate change
Radial distribution of stars, gas and dust in SINGS galaxies. I. Surface photometry and morphology
We present ultraviolet through far-infrared surface brightness profiles for
the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The
imagery used to measure the profiles includes GALEX UV data, optical images
from KPNO, CTIO and SDSS, near-IR data from 2MASS, and mid- and far-infrared
images from Spitzer. Along with the radial profiles, we also provide
multi-wavelength asymptotic magnitudes and several non-parametric indicators of
galaxy morphology: the concentration index (C_42), the asymmetry (A), the Gini
coefficient (G) and the normalized second-order moment of the brightest 20% of
the galaxy's flux (M_20). Our radial profiles show a wide range of morphologies
and multiple components (bulges, exponential disks, inner and outer disk
truncations, etc.) that vary not only from galaxy to galaxy but also with
wavelength for a given object. In the optical and near-IR, the SINGS galaxies
occupy the same regions in the C_42-A-G-M_20 parameter space as other normal
galaxies in previous studies. However, they appear much less centrally
concentrated, more asymmetric and with larger values of G when viewed in the UV
(due to star-forming clumps scattered across the disk) and in the mid-IR (due
to the emission of Polycyclic Aromatic Hydrocarbons at 8.0 microns and very hot
dust at 24 microns).Comment: 66 pages in preprint format, 14 figures, published in ApJ. The
definitive publisher authenticated version is available online at
http://dx.doi.org/10.1088/0004-637X/703/2/156
Radial distribution of stars, gas and dust in SINGS galaxies. III. Modeling the evolution of the stellar component in galaxy disks
(Abridged) We analyze the evolution of 42 spiral galaxies in the Spitzer
Infrared Nearby Galaxies Survey, using extinction-corrected UV, optical and
near-infrared radial profiles to probe the emission of stars of different ages
as a function of radius. We fit these profiles with models that describe the
chemical and spectro-photometric evolution of spiral disks within a
self-consistent framework. These backward models succesfully reproduce the
multi-wavelength profiles of our galaxies, except the UV profiles of some
early-type disks. From the model fitting we infer the maximum circular velocity
of the rotation curve (Vc) and the dimensionless spin parameter (lambda). The
values of Vc are in good agreement with the velocities measured in HI rotation
curves. While our sample is not volume-limited, the resulting distribution of
spins is close to the lognormal function obtained in cosmological N-body
simulations, peaking at ~0.03 regardless of the total halo mass. We do not find
any evident trend between spin and Hubble type, besides an increase in the
scatter for the latest types. According to the model, galaxies evolve along a
roughly constant mass-size relation, increasing their scale-lengths as they
become more massive. The radial scale-length of most disks in our sample seems
to have increased at a rate of 0.05-0.06 kpc/Gyr, being now 20-25% larger than
at z=1.Comment: Accepted for publication in ApJ. 32 pages in emulateapj format, 25
figures. The whole figureset of Fig. 2 can be downloaded from
http://www.cv.nrao.edu/~jmunoz/f2_all.p
Star formation in the extended gaseous disk of the isolated galaxy CIG 96
We study the Kennicutt-Schmidt star formation law and efficiency in the
gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on
its unusually large atomic gas (HI) disk (r_HI/r_25 = 3.5, r_25 = 1.'85). We
present deep GALEX near and far ultraviolet observations, used as a recent star
formation tracer, and we compare them with new, high resolution (16", or 1.6
kpc) VLA HI observations. The UV and HI maps show good spatial correlation
outside the inner 1', where the HI phase dominates over H_2. Star-forming
regions in the extended gaseous disk are mainly located along the enhanced HI
emission within two (relatively) symmetric giant gaseous spiral arm-like
features, which emulate a HI pseudo-ring at a r \simeq 3' . Inside such
structure, two smaller gaseous spiral arms extend from the NE and SW of the
optical disk and connect to the previously mentioned HI pseudo-ring.
Interestingly, we find that the (atomic) Kennicutt-Schmidt power law index
systematically decreases with radius, from N \simeq 3.0 +- 0.3 in the inner
disk (0.'8 - 1.'7) to N = 1.6 +- 0.5 in the outskirts of the gaseous disk (3.'3
- 4.'2). Although the star formation efficiency (SFE), the star formation rate
per unit of gas, decreases with radius where the HI component dominates as is
common in galaxies, we find that there is a break of the correlation at r = 1.5
r_25. At radii 1.5 r_25 < r < 3.5 r_25, mostly within the HI pseudo-ring
structure, there exist regions whose SFE remains nearly constant, SFE \simeq
10^-11 yr^-1. We discuss about possible mechanisms that might be triggering the
star formation in the outskirts of this galaxy, and we suggest that the
constant SFE for such large radii r > 2 r_25 and at such low surface densities
might be a common characteristic in extended UV disk galaxies.Comment: 12 pages, 7 figures, 1 table. Accepted for publication in Ap
Matching microscopic and macroscopic responses in glasses
We first reproduce on the Janus and Janus II computers a milestone experiment
that measures the spin-glass coherence length through the lowering of
free-energy barriers induced by the Zeeman effect. Secondly we determine the
scaling behavior that allows a quantitative analysis of a new experiment
reported in the companion Letter [S. Guchhait and R. Orbach, Phys. Rev. Lett.
118, 157203 (2017)]. The value of the coherence length estimated through the
analysis of microscopic correlation functions turns out to be quantitatively
consistent with its measurement through macroscopic response functions.
Further, non-linear susceptibilities, recently measured in glass-forming
liquids, scale as powers of the same microscopic length.Comment: 6 pages, 4 figure
Integral Field Spectroscopy and multi-wavelength imaging of the nearby spiral galaxy NGC5668: an unusual flattening in metallicity gradient
We present the analysis of the full bi-dimensional optical spectral cube of
the nearby spiral galaxy NGC 5668, observed with the PPAK IFU at the Calar Alto
observatory 3.5m telescope. We make use of broad-band imaging to provide
further constraints on the evolutionary history of the galaxy. This dataset
will allow us to improve our understanding of the mechanisms that drive the
evolution of disks. We investigated the properties of 62 H II regions and
concentric rings in NGC 5668 and derived maps in ionized-gas attenuation and
chemical (oxygen) abundances. We find that, while inwards of
r\,\,4.4kpc\,\,0.36\, the derived
O/H ratio follows the radial gradient typical of spiral galaxies, the abundance
gradient beyond r flattens out. The analysis of the multi-wavelength
surface brightness profiles of NGC 5668 is performed by fitting these profiles
with those predicted by chemo-spectrophotometric evolutionary models of galaxy
disks. From this, we infer a spin and circular velocity of =0.053 and
v=167\,km\,s, respectively. The metallicity gradient and rotation
curve predicted by this best-fitting galaxy model nicely match the values
derived from the IFU observations, especially within r\,\sim36\arcsec. The
same is true for the colors despite of some small offsets and a reddening in
the bluest colors beyond that radius. On the other hand, deviations of some of
these properties in the outer disk indicate that a secondary mechanism,
possibly gas transfer induced by the presence of a young bar, must have played
a role in shaping the recent chemical and star formation histories of NGC 5668.Comment: 44 pages, 13 figures, Accepted for publication in ApJ. arXiv admin
note: text overlap with arXiv:astro-ph/020649
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