809 research outputs found
The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6m photometry for > 2000
galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue
Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which
is populated by irregular and spiral galaxies, and is mainly driven by changes
in the formation timescale () and a degeneracy between and dust
reddening. The tightness of the GBS provides an unprecedented way of
identifying star-forming galaxies and objects that are just evolving to (or
from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS,
at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated
by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the
optical red sequence. We find no such dichotomy in terms of stellar mass
(measured by ), since both massive () blue and red sequence galaxies are identified. The type that is
proportionally more often found in the GGV are the S0-Sa's and most of these
are located in high-density environments. We discuss evolutionary models of
galaxies that show a rapid transition from the blue to the red sequence on
timescale of years.Comment: 7 pages, 4 figures, 1 table. Accepted for publication in ApJ
Spread of the invasive alga Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta) along the Mediterranean Coast of the Murcia region (SE Spain)
The aim of this paper was to document the appearance and spread of the green alga Caulerpa racemosa along the coast of Murcia in south–eastern Spain. It was found for the first time in the area in 2005 and over the next two years the number of new sightings increased almost exponentially. In the period 2005–2007 the total surface area colonised by the alga in the region was estimated to be at least 265 ha. Benthic assemblages colonised by the alga were rocky bottoms with photophilic algae, dead P. oceanica rhizomes, infralittoral and circalittoral soft bottoms and maerl beds. No penetration of the alga was observed in P. oceanica meadows, except in one locality. Biometric analysis indicated high vegetative development in the established colonies in comparison to those described in other Mediterranean areas. Rapid spreading dynamics observed in the Murcia region is a potential threat for native benthic communities.
Key words: Biological invasions, Caulerpa racemosa var. cylindracea, Colonised surface area, Distribution, Mediterranean Sea, Spain.En el presente trabajo se documenta la aparición y dispersión del alga verde Caulerpa racemosa a lo largo de la costa de Murcia, región situada en el sureste español. El alga fue detectada por primera vez en el año 2005 y durante los dos años consecutivos se observó un crecimiento casi exponencial en el número de áreas colonizadas. La superficie total colonizada por el alga en Murcia durante el periodo 2005–2007 ha sido estimada en 265 ha., siendo las comunidades bentónicas afectadas algas fotófilas sobre sustrato rocoso, "mata muerta" de P. oceanica, fondos blandos infralitorales y circalitorales y fondos con comunidades de maërl. La presencia del alga dentro de praderas de P. oceanica solamente fue detectada en una localidad. Los estudios biométricos realizados muestran un elevado desarrollo vegetativo de las poblaciones de C. racemosa en Murcia en comparación con colonias de otras áreas del Mediterráneo, siendo esta rápida dinámica de expansión una amenaza potencial para las comunidades bentonicas nativas.
Palabras clave: Invasiones biológicas, Caulerpa racemosa var. cylindracea, Superficie colonizada, Mar
Mediterraneo, España.The aim of this paper was to document the appearance and spread of the green alga Caulerpa racemosa along the coast of Murcia in south–eastern Spain. It was found for the first time in the area in 2005 and over the next two years the number of new sightings increased almost exponentially. In the period 2005–2007 the total surface area colonised by the alga in the region was estimated to be at least 265 ha. Benthic assemblages colonised by the alga were rocky bottoms with photophilic algae, dead P. oceanica rhizomes, infralittoral and circalittoral soft bottoms and maerl beds. No penetration of the alga was observed in P. oceanica meadows, except in one locality. Biometric analysis indicated high vegetative development in the established colonies in comparison to those described in other Mediterranean areas. Rapid spreading dynamics observed in the Murcia region is a potential threat for native benthic communities.
Key words: Biological invasions, Caulerpa racemosa var. cylindracea, Colonised surface area, Distribution, Mediterranean Sea, Spain
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
Efficient training of energy-based models via spin-glass control
[EN] We introduce a new family of energy-based probabilistic graphical models for efficient unsupervised learning. Its definition is motivated by the control of the spin-glass properties of the Ising model described by the weights of Boltzmann machines. We use it to learn the Bars and Stripes dataset of various sizes and the MNIST dataset, and show how they quickly achieve the performance offered by standard methods for unsupervised learning. Our results indicate that the standard initialization of Boltzmann machines with random weights equivalent to spin-glass models is an unnecessary bottleneck in the process of training. Furthermore, this new family allows for very easy access to low-energy configurations, which points to new, efficient training algorithms. The simplest variant of such algorithms approximates the negative phase of the log-likelihood gradient with no Markov chain Monte Carlo sampling costs at all, and with an accuracy sufficient to achieve good learning and generalization.ML and AA groups acknowledge the Spanish Ministry MINECO and State Research Agency AEI (FIDEUA PID2019-106901GBI00/10.13039/501100011033, Severo Ochoa Grant Nos. SEV-2015-0522 and CEX2019-000910-S, FPI), the European Social Fund, Fundacio Cellex, Fundacio Mir-Puig, Generalitat de Catalunya (AGAUR Grant Nos. 2017 SGR 1341 and SGR 1381, CERCA program, QuantumCAT U16-011424, co-funded by ERDF Operational Program of Catalonia 2014-2020), ERC AdG NOQIA and CERQUTE, EU FEDER, MINECO-EU QUANTERA MAQS (funded by the State Research Agency AEI PCI2019-111828-2/10.13039/501100011033), the National Science Centre, Poland-Symfonia Grant No. 2016/20/W/ST4/00314 and the AXA Chair in Quantum Information Science. A P-K acknowledges funding from Fundacio Obra Socialla Caixa' (LCF/BQ/ES15/10360001) and the European Union's Horizon 2020 research and innovation programme-Grant Agreement No. 648913. G M-G acknowledges funding from Fundacio Obra Social 'la Caixa' (LCF-ICFO grant). M A G-M acknowledges funding from the Spanish Ministry of Education and Vocational Training (MEFP) through the Beatriz Galindo program 2018 (BEAGAL18/00203).Pozas-Kerstjens, A.; Muñoz-Gil, G.; Piñol, E.; Garcia March, MA.; AcÃn, A.; Lewenstein, M.; Grzybowski, PR. (2021). Efficient training of energy-based models via spin-glass control. Machine Learning: Science and Technology. 2(2). https://doi.org/10.1088/2632-2153/abe8070250262
A Multi-wavelength analysis of M81: insight on the nature of Arp's loop
Context: The optical ring like structure detected by Arp (1965) around M81
(commonly referenced as "Arp's loop") represents one of the most spectacular
feature observed in nearby galaxies. Arp's loop is commonly interpreted as a
tail resulting from the tidal interaction between M81 and M82. However, since
its discovery the nature of this feature has remained controversial. Aims: Our
primary purpose was to identify the sources of optical and infrared emission
observed in Arp's loop. Methods: The morphology of the Arp's loop has been
investigated with deep wide-field optical images. We also measured its colors
using IRAS and Spitzer-MIPS infrared images and compared them with those of the
disk of M81 and Galactic dust cirrus that fills the area where M81 is located.
Results: Optical images reveal that this peculiar object has a filamentary
structure characterized by many dust features overlapping M81's field. The
ratios of far-infrared fluxes and the estimated dust-to-gas ratios indicate the
infrared emission of Arp's loop is dominated by the contribution of cold dust
that is most likely from Galactic cirrus. Conclusions: The above results
suggest that the light observed at optical wavelengths is a combination of
emission from i) a few recent star forming regions located close to M81, where
both bright UV complexes and peaks in the HI distribution are found, ii) the
extended disk of M81 and iii) scattered light from the same Galactic cirrus
that is responsible for the bulk of the far infrared emission.Comment: 7 pages, 7 figures, accepted for publication by A&
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
Updating known distribution models for forecasting climate change impact on endangered species
To plan endangered species conservation and to design adequate management programmes, it is necessary to predict their
distributional response to climate change, especially under the current situation of rapid change. However, these
predictions are customarily done by relating de novo the distribution of the species with climatic conditions with no regard
of previously available knowledge about the factors affecting the species distribution. We propose to take advantage of
known species distribution models, but proceeding to update them with the variables yielded by climatic models before
projecting them to the future. To exemplify our proposal, the availability of suitable habitat across Spain for the endangered
Bonelli’s Eagle (Aquila fasciata) was modelled by updating a pre-existing model based on current climate and topography to
a combination of different general circulation models and Special Report on Emissions Scenarios. Our results suggested that
the main threat for this endangered species would not be climate change, since all forecasting models show that its
distribution will be maintained and increased in mainland Spain for all the XXI century. We remark on the importance of
linking conservation biology with distribution modelling by updating existing models, frequently available for endangered
species, considering all the known factors conditioning the species’ distribution, instead of building new models that are
based on climate change variables only.Ministerio de Ciencia e Innovación and FEDER (project CGL2009-11316/BOS
On the Nature of Star Formation at Large Galactic Radii
We have compared far-ultraviolet (FUV), near-ultraviolet (NUV), and Halpha
measurements for star forming regions in 21 galaxies, in order to characterise
the properties of their discs at radii beyond the main optical radius (R25). In
our representative sample of extended and non-extended UV discs we find that
half of the extended UV discs also exhibit extended Halpha emission. We find
that extended UV discs fall into two categories, those with a sharp truncation
in the Halpha disc close to the optical edge (R25), and those with extended
emission in Halpha as well as in the ultraviolet. Although most galaxies with
strong Halpha truncations near R25 show a significant corresponding falloff in
UV emission (factor 10--100), the transition tends to be much smoother than in
Halpha, and significant UV emission often extends well beyond this radius,
confirming earlier results by Thilker et al. (2007) and others. After
correcting for dust attenuation the median fraction of total FUV emission from
regions outside of R25 is 1.7%, but it can be as high as 35% in the most
extreme cases. The corresponding fractions of Halpha emission are approximately
half as large on average. This difference reflects both a slightly lower ratio
of Halpha to UV emission in the HII regions in the outer discs, as well as a
lower fraction of star clusters showing HII regions. Most HII regions in the
extended disc have fluxes consistent with small numbers of ionising O-type
stars, and this poor sampling of the upper initial mass function in small
clusters can probably account for the differences in the emission properties,
consistent with earlier conclusions by Zaritsky & Christlein (2007), without
needing to invoke a significant change in the stellar IMF itself. Consistent
Ha/FUV ratios and brightest HII region to total Halpha fluxes in the inner and
extended discs across our whole galaxy sample demonstrate no evidence for a
change in the cluster luminosity function or the IMF in the low gas density
outer disc.Comment: Accepted for publication in MNRAS. 21 Pages, 13 Figures, 2 Table
The structure of the R2TP complex defines a platform for recruiting diverse client proteins to the HSP90 molecular chaperone system
The R2TP complex, comprising the Rvb1p-Rvb2p AAA-ATPases, Tah1p, and Pih1p in yeast, is a special- ized Hsp90 co-chaperone required for the assembly and maturation of multi-subunit complexes. These include the small nucleolar ribonucleoproteins, RNA polymerase II, and complexes containing phosphati- dylinositol-3-kinase-like kinases. The structure and stoichiometry of yeast R2TP and how it couples to Hsp90 are currently unknown. Here, we determine the 3D organization of yeast R2TP using sedimenta- tion velocity analysis and cryo-electron microscopy. The 359-kDa complex comprises one Rvb1p/Rvb2p hetero-hexamer with domains II (DIIs) forming an open basket that accommodates a single copy of Tah1p-Pih1p. Tah1p-Pih1p binding to multiple DII do- mains regulates Rvb1p/Rvb2p ATPase activity. Using domain dissection and cross-linking mass spectro- metry, we identified a unique region of Pih1p that is essential for interaction with Rvb1p/Rvb2p. These data provide a structural basis for understanding how R2TP couples an Hsp90 dimer to a diverse set of client proteins and complexes
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