117 research outputs found
Winter precipitation over the Iberian peninsula and its relationship to circulation indices
International audienceWinter precipitation variability over the Iberian peninsula was investigated by obtaining the spatial and temporal patterns. Empirical Orthogonal Functions were used to describe the variance distribution and to compress the precipitation data into a few modes. The corresponding spatial patterns divide the peninsula into climatic regions according to precipitation variations. The associated time series were related to large scale circulation indices and tropical sea surface temperature anomalies by using lag cross-correlation and cross-spectrum. The major findings are: the most influential indices for winter precipitation were the North Atlantic Oscillation and the East Atlantic/West Russian pattern; coherent oscillations were detected at about eight years between precipitation and the North Atlantic Oscillation and some dynamic consequences of the circulation on precipitation over the Iberian peninsula were examined during drought and wet spells. In the end statistical methods have been proposed to downscale seasonal precipitation prediction. Keywords: Winter precipitation, circulation indices, Iberian peninsula climate, climate variations, precipitation tren
CANDELS Sheds Light on the Environmental Quenching of Low-mass Galaxies
We investigate the environmental quenching of galaxies, especially those with
stellar masses (M*), beyond the local universe. Essentially
all local low-mass quenched galaxies (QGs) are believed to live close to
massive central galaxies, which is a demonstration of environmental quenching.
We use CANDELS data to test {\it whether or not} such a dwarf QG--massive
central galaxy connection exists beyond the local universe. To this purpose, we
only need a statistically representative, rather than a complete, sample of
low-mass galaxies, which enables our study to . For each low-mass
galaxy, we measure the projected distance () to its nearest massive
neighbor (M*) within a redshift range. At a given redshift
and M*, the environmental quenching effect is considered to be observed if the
distribution of QGs () is significantly skewed toward
lower values than that of star-forming galaxies (). For galaxies
with , such a difference between
and is detected up to . Also, about 10\%
of the quenched galaxies in our sample are located between two and four virial
radii () of the massive halos. The median projected distance from
low-mass QGs to their massive neighbors, , decreases with
satellite M* at , but increases with satellite M*
at . This trend suggests a smooth, if any,
transition of the quenching timescale around at
.Comment: 8 pages, 5 figures. ApJL accepted. Typos correcte
Gas Accretion and Star Formation Rates
Cosmological numerical simulations of galaxy evolution show that accretion of
metal-poor gas from the cosmic web drives the star formation in galaxy disks.
Unfortunately, the observational support for this theoretical prediction is
still indirect, and modeling and analysis are required to identify hints as
actual signs of star-formation feeding from metal-poor gas accretion. Thus, a
meticulous interpretation of the observations is crucial, and this
observational review begins with a simple theoretical description of the
physical process and the key ingredients it involves, including the properties
of the accreted gas and of the star-formation that it induces. A number of
observations pointing out the connection between metal-poor gas accretion and
star-formation are analyzed, specifically, the short gas consumption time-scale
compared to the age of the stellar populations, the fundamental metallicity
relationship, the relationship between disk morphology and gas metallicity, the
existence of metallicity drops in starbursts of star-forming galaxies, the
so-called G dwarf problem, the existence of a minimum metallicity for the
star-forming gas in the local universe, the origin of the alpha-enhanced gas
forming stars in the local universe, the metallicity of the quiescent BCDs, and
the direct measurements of gas accretion onto galaxies. A final section
discusses intrinsic difficulties to obtain direct observational evidence, and
points out alternative observational pathways to further consolidate the
current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
Astro2020: Empirically Constraining Galaxy Evolution
Over the past decade, empirical constraints on the galaxy-dark matter halo
connection have significantly advanced our understanding of galaxy evolution.
Past techniques have focused on connections between halo properties and galaxy
stellar mass and/or star formation rates. Empirical techniques in the next
decade will link halo assembly histories with galaxies' circumgalactic media,
supermassive black holes, morphologies, kinematics, sizes, colors,
metallicities, and transient rates. Uncovering these links will resolve many
critical uncertainties in galaxy formation and will enable much higher-fidelity
mock catalogs essential for interpreting observations. Achieving these results
will require broader and deeper spectroscopic coverage of galaxies and their
circumgalactic media; survey teams will also need to meet several criteria
(cross-comparisons, public access, and covariance matrices) to facilitate
combining data across different surveys. Acting on these recommendations will
continue enabling dramatic progress in both empirical modeling and galaxy
evolution for the next decade.Comment: Science white paper submitted to the Astro2020 Decadal Surve
Definition of a temporal distribution index for high temporal resolution precipitation data over Peninsular Spain and the Balearic Islands: the fractal dimension; and its synoptic implications
Precipitation on the Spanish mainland and in the Balearic archipelago exhibits a high degree of spatial and temporal variability, regardless of the temporal resolution of the data considered. The fractal dimension indicates the property of self-similarity, and in the case of this study, wherein it is applied to the temporal behaviour of rainfall at a fine (10-min) resolution from a total of 48 observatories, it provides insights into its more or less convective nature. The methodology of Jenkinson & Collison which automatically classifies synoptic situations at the surface, as well as an adaptation of this methodology at 500 hPa, was applied in order to gain insights into the synoptic implications of extreme values of the fractal dimension. The highest fractal dimension values in the study area were observed in places with precipitation that has a more random behaviour over time with generally high totals. Four different regions in which the atmospheric mechanisms giving rise to precipitation at the surface differ from the corresponding above-ground mechanisms have been identified in the study area based on the fractal dimension. In the north of the Iberian Peninsula, high fractal dimension values are linked to a lower frequency of anticyclonic situations, whereas the opposite occurs in the central region. In the Mediterranean, higher fractal dimension values are associated with a higher frequency of the anticyclonic type and a lower frequency of the advective type from the east. In the south, lower fractal dimension values indicate higher frequency with respect to the anticyclonic type from the east and lower frequency with respect to the cyclonic type
Angular Momentum of Early- and Late-type Galaxies: Nature or Nurture?
We investigate the origin, the shape, the scatter, and the cosmic evolution
in the observed relationship between specific angular momentum and
the stellar mass in early-type (ETGs) and late-type galaxies (LTGs).
Specifically, we exploit the observed star-formation efficiency and chemical
abundance to infer the fraction f_\rm inf of baryons that infall toward the
central regions of galaxies where star formation can occur. We find f_\rm
inf\approx 1 for LTGs and for ETGs with an uncertainty of about
dex, consistent with a biased collapse. By comparing with the locally
observed vs. relations for LTGs and ETGs we estimate the
fraction of the initial specific angular momentum associated to the
infalling gas that is retained in the stellar component: for LTGs we find
, in line with the classic disc formation
picture; for ETGs we infer , that can be
traced back to a evolution via dry mergers. We also show that the
observed scatter in the vs. relation for both galaxy
types is mainly contributed by the intrinsic dispersion in the spin parameters
of the host dark matter halo. The biased collapse plus mergers scenario implies
that the specific angular momentum in the stellar components of ETG progenitors
at is already close to the local values, in pleasing agreement with
observations. All in all, we argue such a behavior to be imprinted by nature
and not nurtured substantially by the environment
Galaxy And Mass Assembly (GAMA): Gas Fuelling of Spiral Galaxies in the Local Universe II. – Direct Measurement of the Dependencies on Redshift and Host Halo Mass of Stellar Mass Growth in Central Disk Galaxies
We present a detailed analysis of the specific star formation rate – stellar mass (sSFR − M*) of z ≤ 0.13 disk central galaxies using a morphologically selected mass-complete sample (M* ≥ 109.5M⊙). Considering samples of grouped and ungrouped galaxies, we find the sSFR − M* relations of disk-dominated central galaxies to have no detectable dependence on host dark-matter halo (DMH) mass, even where weak-lensing measurements indicate a difference in halo mass of a factor ≳ 5. We further detect a gradual evolution of the sSFR − M* relation of non-grouped (field) central disk galaxies with redshift, even over a Δz ≈ 0.04 (≈5 · 108yr) interval, while the scatter remains constant. This evolution is consistent with extrapolation of the ”main-sequence-of-star-forming-galaxies” from previous literature that uses larger redshift baselines and coarser sampling. Taken together, our results present new constraints on the paradigm under which the SFR of galaxies is determined by a self-regulated balance between gas inflows and outflows, and consumption of gas by star-formation in disks, with the inflow being determined by the product of the cosmological accretion rate and a fuelling-efficiency –
M ˙ b,halo ζ
M˙b,haloζ
. In particular, maintaining the paradigm requires
M ˙ b,halo ζ
M˙b,haloζ
to be independent of the mass Mhalo of the host DMH. Furthermore, it requires the fuelling-efficiency ζ to have a strong redshift dependence (∝(1 + z)2.7 for M* = 1010.3M⊙ over z = 0 − 0.13), even though no morphological transformation to spheroids can be invoked to explain this in our disk-dominated sample. The physical mechanisms capable of giving rise to such dependencies of ζ on Mhalo and z for disks are unclea
The importance of innovative projects and network for the advances of innovation in Science Teaching: the case of on IRES network teacher
Este articulo presenta la descripción y análisis del Modelo de Investigación en la Escuela que fundamenta el
Proyecto IRES (Investigación y Renovación Escolar) y el análisis en profundidad de una entrevista a un maestro
en el área de ciencias que pertenece a la red de este proyecto: Red IRES. Los resultados ponen en evidencia la
importancia que ha tenido para este profesor la pertenencia al proyecto y al colectivo de docentes que lo
impulsan, así como la pertinencia del modelo para sustentar los cambios introducidos en el aula. Destaca también
la relevancia, para su evolución profesional, del diálogo entre docentes de todos los niveles del sistema educativo,
incluida la universidad. Proponemos que estas experiencias sean más reconocidas y valoradas en el ámbito de la
Enseñanza de las Ciencias y en las instancias gubernamentales.This article presents the description and analysis of the Research Model in the School that bases the IRES Project
(Research and School Renovation) and the in-depth analysis of an interview with a science teacher belonging to
the network of this project: IRES Network. The results show how important it is for this teacher to belong to the
project and to the group of teachers that promote it, as well as the relevance of the model to support the changes
introduced in the classroom. It also highlights the relevance, for its professional evolution, of the dialogue
between teachers at all levels of the education system, including the university. We propose that these
experiences be more recognized and valued in the field of Science Teaching and in governmental instances
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