12 research outputs found
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
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, , temperature, , and electron
number density, . The charge distribution is tightly correlated
with the `charging parameter', . 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 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, , temperature, , and electron
number density, . The charge distribution is tightly correlated
with the `charging parameter', . 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 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
Peabody Picture Vocabulary Test-III: Normative data for Spanish-speaking pediatric population
OBJECTIVE: To generate normative data for the Peabody Picture Vocabulary Test-III (PPVT-III) in Spanish-speaking
pediatric populations.
METHOD: The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador,
Honduras, Guatemala, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the PPVT-III
as part of a larger neuropsychological battery. PPVT-III scores were normed using multiple linear regressions and standard
deviations of residual values. Age, age2, sex, and mean level of parental education (MLPE) were included as predictors in
the analyses.
RESULTS: The final multiple linear regression models showed main effects for age in all countries, such that scores increased
linearly as a function of age. In addition, age2 had a significant effect in all countries, except Guatemala and Paraguay. Models
showed that children whose parent(s) had a MLPE >12 years obtained higher scores compared to children whose parent(s)
had a MLPE ≤12 years in all countries, except for Cuba, Peru, and Puerto Rico. Sex affected scores for Chile, Ecuador,
Guatemala, Mexico, and Spain.
CONCLUSIONS: This is the largest Spanish-speaking pediatric normative study in the world, and it will allow neuropsychologists from these countries to have a more accurate interpretation of the PPVT-III when used in pediatric populations
Stroop Color-Word Interference Test: Normative data for Spanish-speaking pediatric population
OBJECTIVE: To generate normative data for the Stroop Word-Color Interference test in Spanish-speaking pediatric populations. METHOD: The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the Stroop Word-Color Interference test as part of a larger neuropsychological battery. The Stroop Word, Stroop Color, Stroop Word-Color, and Stroop Interference scores were normed using multiple linear regressions and standard deviations of residual values. Age, age2, sex, and mean level of parental education (MLPE) were included as predictors in the analyses. RESULTS: The final multiple linear regression models showed main effects for age on all scores, except on Stroop Interference for Guatemala, such that scores increased linearly as a function of age. Age2 affected Stroop Word scores for all countries, Stroop Color scores for Ecuador, Mexico, Peru, and Spain; Stroop Word-Color scores for Ecuador, Mexico, and Paraguay; and Stroop Interference scores for Cuba, Guatemala, and Spain. MLPE affected Stroop Word scores for Chile, Mexico, and Puerto Rico; Stroop Color scores for Mexico, Puerto Rico, and Spain; Stroop Word-Color scores for Ecuador, Guatemala, Mexico, Puerto Rico and Spain; and Stroop-Interference scores for Ecuador, Mexico, and Spain. Sex affected Stroop Word scores for Spain, Stroop Color scores for Mexico, and Stroop Interference for Honduras. CONCLUSIONS: This is the largest Spanish-speaking pediatric normative study in the world, and it will allow neuropsychologists from these countries to have a more accurate approach to interpret the Stroop Word-Color Interference test in pediatric populations
Stroop Color-Word Interference Test: Normative data for Spanish-speaking pediatric population
How do velocity structure functions trace gas dynamics in simulated molecular clouds?
In Chira et al. (subm.), we investigate the time evolution of gas dynamics
within simulated molecular clouds, as well as how velocity structure functions
trace the dominating driving sources of turbulence. The molecular clouds are
formed self-consistently within kiloparsec-scale numerical simulations of the
interstellar medium that include self-gravity, magnetic fields, supernovae-
driven turbulence, and radiative heating and cooling.
Here, we provide the underlying data for the analysis and plots presented in
the paper submitted to Astronomy & Astrophysics. The simulations are run using
an implementation of the Flash code. We present data for each of the, in total,
160 timesteps in HDF5 format, the final velocity structure functions as
functions of lag and time.
Note that due to technical problems we are currently able to offer the raw
data for those simulations that resolve the local Jeans length with 4 cells
only. We will upload the higher Jeans-resolved data as soon as possible
Supplemental Data: Effect of the heating rate on the stability of the three-phase interstellar medium
In Hill et al (2018), we investigated the impact of the far ultraviolet (FUV) heating rate on the stability of the three-phase interstellar medium using three-dimensional simulations of a 1 kpc^2, vertically-extended domain. We found that even absent a variable star formation rate regulating the FUV heating rate, the gas physics keeps the pressure in the regime in which the cold and warm neutral media coexist. Here, we provide the underlying data for the figures presented in the paper in The Astrophysical Journal. The simulations were run using an implementation of the Flash code version 4.2. We present data for one timestep from each of 22 different simulations in HDF5 format
Feeding versus Falling: The Growth and Collapse of Molecular Clouds in a Turbulent Interstellar Medium
Modified Wisconsin Card Sorting Test (M-WCST): Normative data for Spanish-speaking pediatric population
OBJECTIVE: To generate normative data for the Modified Wisconsin Card Sorting Test (M-WCST) in Spanish-speaking pediatric populations. METHOD: The sample consisted of 4,373 healthy children from nine countries in Latin America (Chile, Cuba, Ecuador, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico) and Spain. Each participant was administered the M-WCST as part of a larger neuropsychological battery. Number of categories, perseverative errors, and total error scores were normed using multiple linear regressions and standard deviations of residual values. Age, age 2, sex, and mean level of parental education (MLPE) were included as predictors in the analyses. RESULTS: The final multiple linear regression models indicated main effects for age on all scores, such that the number of categories correct increased and total number of perseverative errors and total number of errors decrease linearly as a function of age. Age 2 had a significant effect in Chile, Cuba, Ecuador, and Spain for numbers of categories; a significant effect for number of perseverative errors in Chile, Cuba, Mexico, and Spain; and a significant effect for number of total errors in Chile, Cuba, Peru, and Spain. Models showed an effect for MLPE in Cuba (total errors), Ecuador (categories and total errors), Mexico (all scores), Paraguay (perseverative errors and total error), and Spain (categories and total errors). Sex affected number of total errors for Ecuador. CONCLUSIONS: This is the largest Spanish-speaking pediatric normative study in the world, and it will allow neuropsychologists from these countries to have a more accurate way to interpret the M-WCST with pediatric populations. © 2017 - IOS Press and the authors. All rights reserved.Trabajo de investigació