Fast Molecular Cloud Destruction Requires Fast Cloud Formation

A large fraction of the gas in the Galaxy is cold, dense, and molecular. If all this gas collapsed under the influence of gravity and formed stars in a local free-fall time, the star formation rate in the Galaxy would exceed that observed by more than an order of magnitude. Other star-forming galaxies behave similarly. Yet observations and simulations both suggest that the molecular gas is indeed gravitationally collapsing, albeit hierarchically. Prompt stellar feedback offers a potential solution to the low observed star formation rate if it quickly disrupts star-forming clouds during gravitational collapse. However, this requires that molecular clouds must be short-lived objects, raising the question of how so much gas can be observed in the molecular phase. This can occur only if molecular clouds form as quickly as they are destroyed, maintaining a global equilibrium fraction of dense gas. We therefore examine cloud formation timescales. We first demonstrate that supernova and superbubble sweeping cannot produce dense gas at the rate required to match the cloud destruction rate. On the other hand, Toomre gravitational instability can reach the required production rate. We thus argue that, although dense, star-forming gas may last only around a single global free-fall time, the dense gas in star-forming galaxies can globally exist in a state of dynamic equilibrium between formation by gravitational instability, and disruption by stellar feedback. At redshift z >~ 2, the Toomre instability timescale decreases, resulting in a prediction of higher molecular gas fractions at early times, in agreement with observations.Comment: 7 pages, no figures, ApJL accepted; v3: corrected several errors, added discussion, no change in conclusion

Una evaluación del Plan de Consolidación Integral de la Macarena (PCIM)

Este artículo presenta una descripción de la nueva estrategia de la lucha contra las drogas implementada en Colombia desde el año 2007. El Salto Estratégico, como ha llamado el gobierno colombiano a este programa, o la Iniciativa de Desarrollo Estratégico, como lo llama USAID (la agencia del gobierno de Estados Unidos para la ayuda a los países en desarrollo) es un paso hacia adelante en el diseño de políticas anti-droga más sostenibles y efectivas en el mediano plazo. Actualmente, se está implementando un plan piloto en la Sierra de la Macarena, en el departamento del Meta (suroriente de Bogotá), donde los cultivos de coca y las actividades ilícitas eran la norma hace unos pocos años. El Estado colombiano, con financiación parcial de los gobiernos de Estados Unidos y países de Europa, consolida su presencia en la zona con las diferentes instancias y programas del aparato estatal para recuperar el control territorial y combatir la producción de drogas ilícitas. Pero más importante aun es que esta nueva aproximación de las políticas antidroga se ha fundamentado en un plan de desarrollo económico regional, para evitar que los campesinos se vinculen con actividades ilícitas asociadas a los primeros eslabones de la producción y tráfico de cocaína. El adecuado funcionamiento de esta estrategia puede ser un punto de referencia para otros países que enfrentan problemas de producción de drogas ilícitas y de conflicto asociado a estas actividades.Macarena, Plan de Consolidación, Colombia, Políticas antidroga.

Dust charge distribution in the interstellar medium

We investigate the equilibrium charge distribution of dust grains in the interstellar medium (ISM). Our treatment accounts for collisional charging by electrons and ions, photoelectric charging due to a background interstellar radiation field, the collection of suprathermal cosmic ray electrons and photoelectric emission due to a cosmic ray induced ultraviolet radiation field within dense molecular clouds. We find that the charge equilibrium assumption is valid throughout the multi-phase ISM conditions investigated here, and should remain valid for simulations with resolutions down to AU scales. The charge distribution of dust grains is size, composition, and ISM environment dependent: local radiation field strength, $G$, temperature, $T$, and electron number density, $n_{\mathrm{e}}$. The charge distribution is tightly correlated with the `charging parameter', $G\sqrt{T}/n_{\mathrm{e}}$. In the molecular medium, both carbonaceous and silicate grains have predominantly negative or neutral charges with narrow distributions. In the cold neutral medium, carbonaceous and silicate grains vary from negative and narrow distributions, to predominantly positive and wide distributions depending on the magnitude of the charging parameter. In the warm neutral medium, grains of all sizes are positively charged with wide distributions. We derive revised parametric expressions that can be used to recover the charge distribution function of carbonaceous and silicate grains from 3.5 {\AA} to 0.25 $\mu$m as a function of the size, composition and ambient ISM parameters. Finally, we find that the parametric equations can be used in environments other than Solar neighborhood conditions, recovering the charge distribution function of dust grains in photon dominated regions.Comment: 13 pages and 9 figures. Accepted for publication in MNRAS. Code developed in this paper can be found: https://github.com/jcibanezm/DustCharg

Dust charge distribution in the interstellar medium

We investigate the equilibrium charge distribution of dust grains in the interstellar medium (ISM). Our treatment accounts for collisional charging by electrons and ions, photoelectric charging due to a background interstellar radiation field, the collection of suprathermal cosmic ray electrons and photoelectric emission due to a cosmic ray induced ultraviolet radiation field within dense molecular clouds. We find that the charge equilibrium assumption is valid throughout the multi-phase ISM conditions investigated here, and should remain valid for simulations with resolutions down to AU scales. The charge distribution of dust grains is size, composition, and ISM environment dependent: local radiation field strength, $G$, temperature, $T$, and electron number density, $n_{\mathrm{e}}$. The charge distribution is tightly correlated with the `charging parameter', $G\sqrt{T}/n_{\mathrm{e}}$. In the molecular medium, both carbonaceous and silicate grains have predominantly negative or neutral charges with narrow distributions. In the cold neutral medium, carbonaceous and silicate grains vary from negative and narrow distributions, to predominantly positive and wide distributions depending on the magnitude of the charging parameter. In the warm neutral medium, grains of all sizes are positively charged with wide distributions. We derive revised parametric expressions that can be used to recover the charge distribution function of carbonaceous and silicate grains from 3.5 {\AA} to 0.25 $\mu$m as a function of the size, composition and ambient ISM parameters. Finally, we find that the parametric equations can be used in environments other than Solar neighborhood conditions, recovering the charge distribution function of dust grains in photon dominated regions.Comment: 13 pages and 9 figures. Accepted for publication in MNRAS. Code developed in this paper can be found: https://github.com/jcibanezm/DustCharg

TRIBUNAL ARBITRAL DE CSS CONSTRUCTORES S.A. VS. AGENCIA NACIONAL DE INFRAESTRUCTURA - ANI

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Evolutionary scenarios associated with the Pteronotus parnellii cryptic species-complex (Chiroptera: Mormoopidae).

One of the major challenges to understanding the evolution of Neotropical bats concerns our capacity to successfully scrutinize phylogenetic patterns associated with cases of cryptic species complexes. In this study Pteronotus parnellii is examined as a selected example of a known lineage of mormoopid bat that potentially contains several cryptic species. A samples of 452 individuals from 83 different localities, essentially covering its entire mainland distribution, was evaluated using two genetic markers: COI (mitochondrial) and DBY (nuclear) genes. The findings of this study strongly support the hypothesis of high genetic variability and identify at least six lineages within P. parnellii, some of which appear to be cryptic species.Peer reviewe

Modelling the supernova-driven ISM in different environments

We use hydrodynamical simulations in a (256 pc)3 periodic box to model the impact of supernova (SN) explosions on the multiphase interstellar medium (ISM) for initial densities n=0.5-30cm−3 and SN rates 1-720Myr−1. We include radiative cooling, diffuse heating, and the formation of molecular gas using a chemical network. The SNe explode either at random positions, at density peaks, or both. We further present a model combining thermal energy for resolved and momentum input for unresolved SNe. Random driving at high SN rates results in hot gas (T≳106K) filling >90 per cent of the volume. This gas reaches high pressures (10450 per cent), residing in small, dense clumps. Such a model might resemble the dense ISM in high-redshift galaxies. Peak driving results in huge radiative losses, producing a filamentary ISM with virtually no hot gas, and a small molecular hydrogen mass fraction (≪1 per cent). Varying the ratio of peak to random SNe yields ISM properties in between the two extremes, with a sharp transition for equal contributions. The velocity dispersion in H i remains≲10 km s−1 in all cases. For peak driving, the velocity dispersion in Hα can be as high as 70 km s−1 due to the contribution from young, embedded SN remnant

Qualidade de vida e percepção de saúde em idosos com doença crônica

Introduction: A subject’s representation of quality of life is considered good or bad according to experience. Objective: To determine the quality of life and health-disease perception among the elderly people with chronic non-transmissible diseases. Methods: A study with sequential, explanatory, mixed design of a population of 44 elderly persons with chronic disease in 2017 from two care programs in Tunja. The variables were: sociodemographic, health perception, disease perception and quality of life, SF-36 questionnaires, IPQ-B and focus group were applied. The analysis was with Spearman’s correlation, logistic regression, existential phenomenological analysis and triangulation. Results: The average global quality of life was 59.5 % with mental health at 93.2 %. The understanding of disease with 7.3 ± 2.2 stands out in its perception, the highest correlation was personal control and overall health with 0.770 (p = 0.000) and recognized categories were: the disease as social and family marginalization, family and divine support, the influence of the health system, need for self-care, the importance of support networks and quality of life. Conclusions: Quality of life and the perception of health and disease are correlated, in addition to being influenced by experience and coping methods.Introducción. La representación de calidad de vida de un sujeto se considera buena o mala según la experiencia. Objetivo. Determinar la calidad de vida y la percepción de la salud-enfermedad en la persona mayor con enfermedad crónica no transmisible. Métodos. Estudio con diseño mixto explicativo secuencial, en una población de personas mayores, con enfermedad crónica y pacientes de dos programas de atención en Tunja en 2017. Se elaboró una muestra de 44 personas y las variables fueron sociodemográficas, percepción de la salud, percepción de la enfermedad y calidad de vida. Se aplicaron los cuestionarios SF-36 y el IPQ-B, se realizó un grupo focal y el análisis fue con correlación de Spearman, regresión logística, análisis fenomenológico existencial y triangulación. Resultados. La calidad de vida global promedio fue de 59,5 % y predominó la salud mental con un 93,2 %. En la percepción de la enfermedad sobresale la comprensión de la misma con 7,3±2,2. La correlación más alta fue el control personal y la salud en general con 0,770 (p=0,000). Las categorías reconocidas fueron: la enfermedad como marginación social y familiar, el apoyo familiar y divino, la influencia del sistema de salud, la necesidad del autocuidado, la importancia de las redes de apoyo y la calidad de vida. Conclusiones. La calidad de vida y la percepción de la salud y enfermedad se correlacionan; además están influenciadas por la experiencia y los métodos de afrontamientoIntrodução. A representação da qualidade de vida de um sujeito é considerada boa ou ruim de acordo com a experiência. Objetivo. Determinar a qualidade de vida e a percepção de saúde-doença em idosos com doença crônica não transmissível. Métodos. Estudo com desenho misto explicativo sequencial, numa população de idosos, com doença crónica e doentes de dois programas de cuidados em Tunja em 2017. Foi elaborada uma amostra de 44 pessoas e as variáveis foram sociodemográficas, percepção de saúde, percepção de doença e qualidade de vida. Aplicouse os questionários SF-36 e IPQ-B, realizouse um grupo focal e a análise foi com correlação de Spearman, regressão logística, análise fenomenológica existencial e triangulação. Resultados. A qualidade de vida global média foi de 59,5% e a saúde mental predominou com 93,2%. Na percepção da doença, destacase a compreensão da mesma com 7,3±2,2. A maior correlação foi controle pessoal e saúde geral com 0,770 (p=0,000). As categorias reconhecidas foram: doença como marginalização social e familiar, apoio familiar e divino, influência do sistema de saúde, necessidade de autocuidado, importância das redes de apoio e qualidade de vida. Conclusões. A qualidade de vida e a percepção de saúde e doença estão correlacionadas; eles também são influenciados pela experiência e métodos de enfrentamento

Modelling the supernova-driven ISM in different environments

We use hydrodynamical simulations in a $(256\;{\rm pc})^3$ periodic box to model the impact of supernova (SN) explosions on the multi-phase interstellar medium (ISM) for initial densities $n = 0.5-30$ cm$^{-3}$ and SN rates $1-720$ Myr$^{-1}$. We include radiative cooling, diffuse heating, and the formation of molecular gas using a chemical network. The SNe explode either at random positions, at density peaks, or both. We further present a model combining thermal energy for resolved and momentum input for unresolved SNe. Random driving at high SN rates results in hot gas ($T\gtrsim 10^6$ K) filling $> 90$% of the volume. This gas reaches high pressures ($10^4 < P/k_\mathrm{B} < 10^7$ K cm$^{-3}$) due to the combination of SN explosions in the hot, low density medium and confinement in the periodic box. These pressures move the gas from a two-phase equilibrium to the single-phase, cold branch of the cooling curve. The molecular hydrogen dominates the mass ($>50$%), residing in small, dense clumps. Such a model might resemble the dense ISM in high-redshift galaxies. Peak driving results in huge radiative losses, producing a filamentary ISM with virtually no hot gas, and a small molecular hydrogen mass fraction ($\ll 1$%). Varying the ratio of peak to random SNe yields ISM properties in between the two extremes, with a sharp transition for equal contributions. The velocity dispersion in HI remains $\lesssim 10$ km s$^{-1}$ in all cases. For peak driving the velocity dispersion in H$_\alpha$ can be as high as $70$ km s$^{-1}$ due to the contribution from young, embedded SN remnants.Comment: 19 pages, 12 figures, 2 tables. Accepted for publication in MNRAS. Minor revisions to match published versio

Molecular Cloud Evolution VI. Measuring cloud ages

This article has been published in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.In previous contributions, we have presented an analytical model describing the evolution and star formation rate (SFR) of molecular clouds (MCs) undergoing hierarchical gravitational contraction. The cloud’s evolution is characterized by an initial increase in its mass, density, SFR, and star formation efficiency (SFE), as it contracts, followed by a decrease of these quantities as newly formed massive stars begin to disrupt the cloud. The main parameter of the model is the maximum mass reached by the cloud during its evolution. Thus, specifying the instantaneous mass and some other variable completely determines the cloud’s evolutionary stage. We apply the model to interpret the observed scatter in SFEs of the cloud sample compiled by Lada et al. as an evolutionary effect so that, although clouds such as California and Orion A have similar masses, they are in very different evolutionary stages, causing their very different observed SFRs and SFEs. The model predicts that the California cloud will eventually reach a significantly larger total mass than the Orion A cloud. Next, we apply the model to derive estimated ages of the clouds since the time when approximately 25 per cent of their mass had become molecular. We find ages from ∼1.5 to 27 Myr, with the most inactive clouds being the youngest. Further predictions of the model are that clouds with very low SFEs should have massive atomic envelopes constituting the majority of their gravitational mass, and that low-mass clouds (M ∼ 103–104M⊙) end their lives with a mini-burst of star formation, reaching SFRs ∼300–500M⊙ Myr−1. By this time, they have contracted to become compact (∼1 pc) massive star-forming clumps, in general embedded within larger giant molecular clouds.Peer reviewe