Impact of Cosmic Variance on the Galaxy-Halo Connection for Lyman-α\alpha Emitters

In this paper we study the impact of cosmic variance and observational uncertainties in constraining the mass and occupation fraction, $f_{\rm occ}$, of dark matter halos hosting Ly-$\alpha$ Emitting Galaxies (LAEs) at high redshift. To this end, we construct mock catalogs from an N-body simulation to match the typical size of observed fields at $z=3.1$ ($\sim 1 {\rm deg^2}$). In our model a dark matter halo with mass in the range $M_{\rm min}<M_{\mathrm h}<M_{\rm max}$ can only host one detectable LAE at most. We proceed to explore the parameter space determined by $M_{\rm min}$,$M_{\rm max}$ and $f_{\rm occ}$ with a Markov Chain Monte-Carlo algorithm using the angular correlation function (ACF) and the LAEs number density as observational constraints. We find that the preferred minimum and maximum masses in our model span a wide range $10^{10.0}h^{-1}{\rm{M_{\odot}}}\leq M_{\rm min} \leq 10^{11.1}h^{-1}{\rm{M_{\odot}}}$ , $10^{11.0}h^{-1}{\rm{M_{\odot}}}\leq M_{\rm max} \leq 10^{13.0}h^{-1}{\rm{M_{\odot}}}$; followed by a wide range in the occupation fraction $0.02\leq f_{\rm occ} \leq 0.30$. As a consequence the median mass, $M_{50}$, of all the consistent models has a large uncertainty $M_{50} = 3.16^{+9.34}_{-2.37}\times 10^{10}$$h^{-1}{\rm{M_{\odot}}}$. However, we find that the same individual models have a relatively tight $1\sigma$ scatter around the median mass $\Delta M_{1\sigma} = 0.55^{+0.11}_{-0.31}$ dex. We are also able to show that \focc\ is uniquely determined by $M_{\rm min}$, regardless of $M_{\rm max}$. We argue that upcoming large surveys covering at least $25$ deg$^{2}$ should be able to put tighter constraints on $M_{\rm min}$ and $f_{\rm occ}$ through the LAE number density distribution width constructed over several fields of $\sim 1$ deg$^{2}$.Comment: 7 Pages, 5 figures. Accepted for publication in Ap

Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes

We study the alignment of dark matter haloes with the cosmic web characterized by the tidal and velocity shear fields. We focus on the alignment of their shape, angular momentum and peculiar velocities. We use a cosmological N-body simulation that allows to study dark matter halos spanning almost five orders of magnitude in mass ($10^{9}$-$10^{14}$) $h^{-1}$$M_{\odot}$ and spatial scales of $(0.5$-$1.0)$ $h^{-1}$ Mpc to define the cosmic web. We find that the halo shape presents the strongest alignment along the smallest tidal eigenvector, e.g. along filaments and walls, with a signal that gets stronger as the halo mass increases. In the case of the velocity shear field only massive halos $>10^{12}$ $h^{-1}$$M_{\odot}$ tend to have their shapes aligned along the largest tidal eigenvector; that is, perpendicular to filaments and walls. For the angular momentum we find alignment signals only for halos more massive than $10^{12}$ $h^{-1}$$M_{\odot}$ both in the tidal and velocity shear webs where the preferences are for it to be parallel to the middle eigenvector; perpendicular to filaments and parallel to walls. Finally, the peculiar velocities show a strong alignment along the smallest tidal eigenvector for all halo masses; halos move along filaments and walls. In the velocity shear the same alignment is present but weaker and only for haloes less massive than $10^{12}$ $h^{-1}$$M_{\odot}$. Our results clearly show that the two different algorithms we used to define the cosmic web describe different physical aspects of non-linear collapse and should be used in a complementary way to understand the effect of the cosmic web on galaxy evolution.Comment: 14 pages, 5 figures, MNRAS accepte

Mechanisms of Overyielding and Coexistence in Diverse Tallgrass Prairie Communities

Plants compete for the same basic nutrient and water resources. According to the competitive exclusion principle, when a substantial overlap in resource pools exists, the best competitor for resources should drive all other species to extinction. The ability for plants to coexist in violation of the competitive exclusion principle is the “biodiversity paradox”. Coexistence is actually beneficial for plants: as species diversity increases, you typically see increases in plant biomass production (known as the biodiversity-productivity relationship). The mechanisms behind coexistence and the biodiversity-productivity relationship remain an ecological mystery. One hypothesis is that plants obtain water and nutrients from different places in the soil, which reduces competition and results in plants coexisting and thriving by exploiting more spaces in the soil. Another hypothesis is that plants alter the soil in which they grow to their own detriment by accumulating species-specific soil pathogens or reducing soil nutrient levels. These plant-altered soils reduce the growth of species that are becoming too dominant in a plant community, creating a plant-soil feedback (PSF) effect that maintains biodiversity and increases productivity. I explored the role of PSFs and niche partitioning in coexistence and the biodiversity-productivity relationship. I investigated 1) how PSFs affect the biodiversity-productivity relationship in controlled greenhouse experiments, 2) whether greenhouse experiments are the best method to measure the role of PSFs in biodiverse communities in the field, 3) how PSFs affect the biodiversity-productivity relationship in diverse plant communities in the field, and 4) how partitioning of soil nitrogen and soil water affect coexistence and plant productivity. Greenhouse experimentation suggested PSFs influence productivity and the biodiversity-productivity relationship, but PSFs when measured in the greenhouse were not correlated with PSFs that were measured in the field. This implies PSFs should be measured in the field when trying to predict coexistence or the biodiversity-productivity relationship as observed in the field. Our ability to predict coexistence and productivity in the field was slightly improved by the inclusion of PSFs. However, partitioning of soil water and soil nitrogen was strongly correlated with landscape productivity in the same system, indicating that PSFs are not the dominant mechanism of these phenomena

Systematic uncertainties from halo asphericity in dark matter searches

Although commonly assumed to be spherical, dark matter halos are predicted to be non-spherical by N-body simulations and their asphericity has a potential impact on the systematic uncertainties in dark matter searches. The evaluation of these uncertainties is the main aim of this work, where we study the impact of aspherical dark matter density distributions in Milky-Way-like halos on direct and indirect searches. Using data from the large N-body cosmological simulation Bolshoi, we perform a statistical analysis and quantify the systematic uncertainties on the determination of local dark matter density and the so-called $J$ factors for dark matter annihilations and decays from the galactic center. We find that, due to our ignorance about the extent of the non-sphericity of the Milky Way dark matter halo, systematic uncertainties can be as large as 35%, within the 95% most probable region, for a spherically averaged value for the local density of 0.3-0.4 GeV/cm$^3$. Similarly, systematic uncertainties on the $J$ factors evaluated around the galactic center can be as large as 10% and 15%, within the 95% most probable region, for dark matter annihilations and decays, respectively.Comment: 29 pages, 6 artistic figures, version accepted for publication in JCA

Influencia del uso del suelo en la diversidad y composición de artrópodos edáficos en la Granja Tunguavita

The modification of the landscape, the intense&nbsp;exploitation of natural resources through intensive&nbsp;agriculture and the advance of the agricultural frontier&nbsp;result in the homogenization of the landscape and alteration of soil physicochemical conditions.&nbsp;These soil alterations cause changes in the composition and&nbsp;diversity of edaphic arthropod communities that can be&nbsp;used as biomonitoring and diagnostic tools in local areas.&nbsp;The objective of the study was to evaluate the&nbsp;diversity of edaphic arthropods and their association to different&nbsp;physicochemical parameters (i.e., pH, real density, bulk&nbsp;density, %OC, %OM and gravimetric and volumetric&nbsp;humidity) in three soil uses (permanent crop,&nbsp;rotational crop and pasture) in the experimental farm Tunguavita&nbsp;Paipa - Boyacá. The plot sampling technique was used to obtain data on biological and physicochemical variables. Samples were&nbsp;taken in three soil uses, permanent crop, rotational crop and&nbsp;cattle ranch. The edaphic arthropods and physicochemical&nbsp;variables were determined in the soil laboratory of the&nbsp;Universidad Pedagógica y Tecnológica de Colombia. The highest&nbsp;diversity of edaphic arthropods (309 individuals) was&nbsp;recorded in the permanent crop plot, followed by the&nbsp;rotational crop plot, both with high average&nbsp;values of %OM (1.82 - 1.90) and %OC (1.05 - 1.10). The&nbsp;Oligochaeta, Diplopoda and Araneae group were the major&nbsp;contributors to the biological differentiation between land uses.&nbsp;The changes in the abundance of edaphic arthropods were&nbsp;related to % gravimetric humidity, %volumetric humidity, pH,&nbsp;%OM and %OC, while the values of real density and bulk density did not correlate to a great extent with the changes in abundance.&nbsp;These variations allow the differentiation of land uses in an&nbsp;intervention gradient. &nbsp;La modificación del paisaje, la intensa explotación de&nbsp;recursos naturales mediante agricultura intensiva y el avance de la&nbsp;frontera agrícola da resultado la homogeneización del paisaje y&nbsp;alteración de condiciones fisicoquímicas del suelo. Estas&nbsp;alteraciones en el suelo provocan cambios en la composición y&nbsp;diversidad de las comunidades de artrópodos edáficos que&nbsp;pueden ser utilizados como herramientas de biomonitoreo y&nbsp;diagnostico en zonas locales. El objetivo del estudio fue evaluar&nbsp;la diversidad de artrópodos edáficos y su asociación a diferentes&nbsp;parámetros fisicoquímicos (i.e., pH, densidad real, densidad aparente, CO, MO y humedad gravimétrica y volumétrica)&nbsp;en tres usos del suelo (cultivo permanente, cultivo rotativo y&nbsp;pastoreo) en la granja experimental Tunguavita Paipa – Boyacá. Para&nbsp;obtener los datos de las variables biológicas y fisicoquímicas se&nbsp;usó la técnica de muestreo por parcela. Las muestras fueron&nbsp;tomadas en tres usos de suelo, cultivo permanente, cultivo&nbsp;rotativo y lote de ganadería. Los artrópodos edáficos y se determinó&nbsp;las variables fisicoquímicas en el laboratorio de suelos de la&nbsp;Universidad Pedagógica y Tecnológica de Colombia. La mayor&nbsp;diversidad de artrópodos edáficos (309 individuos), se registró en el lote de cultivo permanente, seguido del cultivo rotativo&nbsp;ambos con valores promedio altos de %MO (1.82 – 1.90) y&nbsp;%CO (1.05 – 1.10). El grupo de Oligochaeta, Diplopoda y&nbsp;Araneae fueron los que contribuyeron en mayor proporción a la&nbsp;diferenciación biológica entre usos de suelo. Los cambios en la&nbsp;abundancia de artrópodos edáficos, se relacionaron con %&nbsp;Humedad gravimétrica, %Humedad volumétrica, pH, %MO y&nbsp;%CO, mientras que los valores de densidad real y densidad&nbsp;aparente, no se correlacionaron en gran medida con los cambios de&nbsp;abundancia. Estas variaciones permiten la diferenciación de usos&nbsp;de suelo en un gradiente de intervención

Identifying networks with common organizational principles

Many complex systems can be represented as networks, and the problem of network comparison is becoming increasingly relevant. There are many techniques for network comparison, from simply comparing network summary statistics to sophisticated but computationally costly alignment-based approaches. Yet it remains challenging to accurately cluster networks that are of a different size and density, but hypothesized to be structurally similar. In this paper, we address this problem by introducing a new network comparison methodology that is aimed at identifying common organizational principles in networks. The methodology is simple, intuitive and applicable in a wide variety of settings ranging from the functional classification of proteins to tracking the evolution of a world trade network.Comment: 26 pages, 7 figure

The kinematics of the Local Group in a cosmological context

Recent observations constrained the tangential velocity of M31 with respect to the Milky Way (MW) to be v_tan<34.4 km/s and the radial velocity to be in the range v_rad=-109+/- 4.4 km/s (van der Marel et al. 2012). In this study we use a large volume high resolution N-body cosmological simulation (Bolshoi) together with three constrained simulations to statistically study this kinematics in the context of the LCDM. The comparison of the ensembles of simulated pairs with the observed LG at the 1-sigma level in the uncertainties has been done with respect to the radial and tangential velocities, the reduced orbital energy (e_tot), angular momentum (l_orb) and the dimensionless spin parameter, lambda. Our main results are: (i) the preferred radial and tangential velocities for pairs in LCDM are v_rad=-80+/-20 km/s, v_tan=50+/-10 km/s, (ii) pairs around that region are 3 to 13 times more common than pairs within the observational values, (iii) 15%to 24% of LG-like pairs in LCDM have energy and angular momentum consistent with observations while (iv) 9% to 13% of pairs in the same sample show similar values in the inferred dimensionless spin parameter. It follows that within current observational uncertainties the quasi-conserved quantities that characterize the orbit of the LG, i.e. e_tot, r_orb and lambda, do not challenge the standard LCDM model, but the model is in tension with regard to the actual values of the radial and tangential velocities. This might hint to a problem of the LCDM model to reproduce the observed LG.Comment: 6 pages, 2 figures, 3 tables, accepted for publication in ApJ Letters. For full data and source code (IPython notebook) to reproduce the results, see: https://github.com/forero/LG_Kinematic