Cold Dark Matter Substructure and Galactic Disks

We perform a set of high-resolution, dissipationless N-body simulations to investigate the influence of cold dark matter (CDM) substructure on the dynamical evolution of thin galactic disks. Our method combines cosmological simulations of galaxy-sized CDM halos to derive the properties of substructure populations and controlled numerical experiments of consecutive subhalo impacts onto initially-thin, fully-formed disk galaxies. We demonstrate that close encounters between massive subhalos and galactic disks since z~1 should be common occurrences in LCDM models. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. One typical host halo merger history is used to seed controlled N-body experiments of subhalo-disk encounters. As a result of these accretion events, the disk thickens considerably at all radii with the disk scale height increasing in excess of a factor of 2 in the solar neighborhood. We show that interactions with the subhalo population produce a wealth of distinctive morphological signatures in the disk stars including: conspicuous flares; bars; low-lived, ring-like features in the outskirts; and low-density, filamentary structures above the disk plane. We compare a resulting dynamically-cold, ring-like feature in our simulations to the Monoceros ring stellar structure in the MW. The comparison shows quantitative agreement in both spatial distribution and kinematics, suggesting that such observed complex stellar components may arise naturally as disk stars are excited by encounters with subhalos. These findings highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution.Comment: 10 pages, 4 figures. To appear in the proceedings of the IAU Symposium No. 254 "The Galaxy Disk in Cosmological Context", Copenhagen 9-13 June 2008, Denmark, (Eds.) J. Andersen, J. Bland-Hawthorn & B. Nordstrom, Cambridge University Pres

Tennessee Forest Roundtable : analysis of a multiple stakeholder dialogue on forest resource policy

Like other states, Tennessee has experienced some conflict over forest resource management that has or could result in courtroom litigation, legislative action, and/or protests. Responding to this confrontational atmosphere, a diverse, national coalition of forest stakeholders developed a model for convening local roundtables to provide preliminary input to the Seventh American Forest Congress, planned for February of 1996. This process was designed to bring diverse groups of stakeholders in America\u27s forests together to seek common ground on the future use and management of forests and associated resources. A committee of eleven diverse individuals organized and executed one of these meetings, the Tennessee Forest Roundtable, on November 11, 1995. To their credit, the organizing committee succeeded in planning and executing the roundtable with tight constraints on time, but time pressures prohibited all committee members from actively contributing in all decisions and may have limited the group\u27s cohesiveness. Thirty-nine individuals representing a range of stakeholders in Tennessee\u27s forest resources attended the program, and through the facilitated process developed some common ground. This study examines the Tennessee Forest Roundtable as a process for developing common ground between diverse stakeholders and examines the content of the resulting consensus statements and unresolved issues. The process proved to be one effective way to engage this group of stakeholders in dialogue about the resources that they all value. Though the participants did not represent the \u27ideal\u27 distribution envisioned by the organizing committee, they did represent a broad range of stakeholders. The only group identified in the \u27ideal\u27 that was not represented was that of recreation/tourism interests. Several other groups identified in the \u27ideal\u27 were under represented, and the participants did not reflect the general demographics of Tennessee regarding sex, race, or age. Overall, the process\u27s use of small groups and facilitators worked effectively, but not all participants were equally satisfied with the quality of facilitators. Time constraints limited the program from its conception and continued to be important throughout the program. The day\u27s planned activities were cut short which is thought to have limited the range of common ground which was identified. Facilitators, committee members, and participants all suggested that more time would be beneficial in developing common ground and understanding. Despite these constraints, participants did develop forty-three consensus statements. This common ground clearly demonstrated that these participants believe strongly in both using and caring for forests and their resources, i.e., using the forest to meet human wants and needs but maintaining forest health and sustainability. The remaining comments, on which participants did not deliberate or could not agree, suggest that stakeholders have great interest in forest policy, management, and use. These unresolved issues also suggest that disagreements remain about how society is to balance the needs of human and natural communities. They also display the ambivalence surrounding how society is to balance private and public rights and responsibilities. Both the process and content analysis suggest that though these forest stakeholders have taken some crucial first steps toward developing a collaborative community, more time and energy must be invested if the stakeholders in Tennessee\u27s forest resources are to truly collaborate on the use and management of these resources which so many value

Through a Smoother Lens: An expected absence of LCDM substructure detections from hydrodynamic and dark matter only simulations

A fundamental prediction of the cold dark matter cosmology is the existence of a large number of dark subhalos around galaxies, most of which should be entirely devoid of stars. Confirming the existence of dark substructures stands among the most important empirical challenges in modern cosmology: if they are found and quantified with the mass spectrum expected, then this would close the door on a vast array of competing theories. But in order for observational programs of this kind to reach fruition, we need robust predictions. Here we explore substructure predictions for lensing using galaxy lens-like hosts at z=0.2 from the Illustris simulations both in full hydrodynamics and dark matter only. We quantify substructures more massive than ~ 10^9 M_sun, comparable to current lensing detections derived from HST, Keck, and ALMA. The addition of full hydrodynamics reduces the overall subhalo mass function by about a factor of two. Even for the dark matter only runs, most (~ 85%) lines of sight through projected cylinders of size close to an Einstein radius contain no substructures larger than 10^9 M_sun. The fraction of empty sight lines rises to ~ 95% in full physics simulations. This suggests we will likely need hundreds of strong lensing systems suitable for substructure studies, as well as predictions that include the effects of baryon physics on substructure, to properly constrain cosmological models. Fortunately, the field is poised to fulfill these requirements.Comment: 11 pages, 9 figure

Forward-Looking Review of the CGIAR Challenge Program on Water and Food (2013-2014)

The Challenge Program on Water and Food (CPWF) was a 10-year (January 1, 2004–December 31, 2013) investment by the CGIAR, conducted over two phases and aimed at an overarching goal of raising water productivity and improving food security while helping alleviate poverty, improve health, and attain environmental security. This review, undertaken between November 2013 and March 2014, was commissioned by CPWF to assess CPWF’s achievements, but also to identify lessons to take forward by CGIAR Research Programs (CRPs) and other research and development stakeholders

Cosmological Constraints from Primordial Black Holes

Primordial black holes may form in the early Universe, for example from the collapse of large amplitude density perturbations predicted in some inflationary models. Light black holes undergo Hawking evaporation, the energy injection from which is constrained both at the epoch of nucleosynthesis and at the present. The failure as yet to unambiguously detect primordial black holes places important constraints. In this article, we are particularly concerned with the dependence of these constraints on the model for the complete cosmological history, from the time of formation to the present. Black holes presently give the strongest constraint on the spectral index $n$ of density perturbations, though this constraint does require $n$ to be constant over a very wide range of scales.Comment: 8 pages LaTeX file, using elsart.sty, with three figures incorporated using epsf. To appear, proceedings of DM98, Los Angeles (ed D Cline, Elsevier

GPS Surveys and the Internet

ITS has been pioneering the use of GPS to provide more accurate data on where and when people travel, their routes, travel distance, and travel time. GPS provides no information on the number of people travelling together, trip purposes, and travel costs. ITS has pioneered the development of a method of collecting this additional information called the prompted recall survey, designed to be conducted some days after the GPS data are collected, using maps and tabular presentations from the GPS records to prompt the respondent’s memory. We describe these surveys and document some of the results. As an improvement on the paper and pencil version, we developed an internet-based survey. This provides animation of each GPS trip, and gives respondents the ability to stop the trip part way through to indicate a trip end that the analysis of the GPS data had not detected, to restart the trip, and to indicate that a stop was only a traffic stop, not a destination. The paper describes the animation, shows the types of data that can be collected, and describes the advantages offered. Some examples are provided of the results of people using the prompted recall survey version

Cold Dark Matter Substructure and Galactic Disks I: Morphological Signatures of Hierarchical Satellite Accretion

(Abridged) We conduct a series of high-resolution, dissipationless N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the LCDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach. Substructure properties are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. In contrast to what can be inferred from statistics of the present-day substructure populations, accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z~1 should be common occurrences. One host halo merger history is subsequently used to seed controlled numerical experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a ring-like feature in the outskirts; a significant flare; a central bar; and faint filamentary structures that (spuriously) resemble tidal streams. The final distribution of disk stars exhibits a complex vertical structure that is well-described by a standard ``thin-thick'' disk decomposition. We conclude that satellite-disk encounters of the kind expected in LCDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way, M31, and in other disk galaxies. These results highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution. Upcoming galactic structure surveys and astrometric satellites may be able to distinguish between competing cosmological models by testing whether the detailed structure of galactic disks is as excited as predicted by the CDM paradigm.Comment: Accepted version to appear in ApJ, 24 pages, 8 figures, LaTeX (uses emulateapj.cls). Comparison between the simulated ring-like features and the Monoceros ring stellar structure in the Milky Way performed; conclusions unaltere