The Stellar Masses and Star Formation Histories of Galaxies at z ≈ 6: Constraints from Spitzer Observations in the Great Observatories Origins Deep Survey

Using the deep Spitzer Infrared Array Camera (IRAC) observations of the Great Observatories Origins Deep Survey (GOODS), we study the stellar masses and star formation histories of galaxies at z approx 6 based on the i_(775)-band dropout sample selected from the GOODS fields. In total, we derive stellar masses for 53 i_(775)-band dropouts that have robust IRAC detections. These galaxies have typical stellar masses of ~10^(10) M_⊙ and typical ages of a couple of hundred million years, consistent with earlier results based on a smaller sample of z ≈ 6 galaxies. The existence of such massive galaxies at z ≈ 6 can be explained by at least one set of N-body simulations of the hierarchical paradigm. We also study 79 i_(775)-band dropouts that are invisible in the IRAC data and find that they are typically less massive by a factor of 10. These galaxies are much bluer than those detected by the IRAC, indicating that their luminosities are dominated by stellar populations with ages ≾ 40 Myr. Based on our mass estimates, we derive a lower limit to the global stellar mass density at z ≈ 6, which is 1.1-6.7 × 10^6 M_⊙ Mpc^(-3). The prospect of detecting the progenitors of the most massive galaxies at yet higher redshifts is explored. We also investigate the implication of our results for reionization and find that the progenitors of the galaxies comparable to those in our sample, even in the most optimized (probably unrealistic) scenario, cannot sustain the reionization for a period longer than ~2 Myr. Thus most of the photons required for reionization must have been provided by other sources, such as the progenitors of the dwarf galaxies that are far below our current detection capability

Participatory Integrated Climate Services for Agriculture (PICSA): field manual. A step-by-step guide to using PICSA with farmers

Smallholder farmers are key to food security in sub-Saharan Africa where two thirds of the population depend on small-scale, rain-fed farming as their main source of food and income. Critical farming and household decisions depend upon the weather, for example, how much rain falls, the length and start date of the rainfall season and the timing of dry spells. Such aspects of the weather vary considerably from year to year. The Participatory Integrated Climate Services for Agriculture (PICSA) approach aims to facilitate farmers to make informed decisions based on accurate, location specific, climate and weather information; locally relevant crop, livestock and livelihood options; and with the use of participatory tools to aid their decision making. Considering farming and livelihood options in the context of climate is crucial for making good decisions. A farmer in Matumba village in central Tanzania expressed this notion perfectly when he said, “We should select crops that look like the climate”. The PISCA approach has been designed with field staff in mind, and aims to support you to do your job better by providing you with improved resources and information. This field manual is a step by step guide to working though the PICSA approach with farmer groups. It is primarily for the use of facilitators (e.g. NGO and extension field staff who have received training in the use of the PICSA approach). The PICSA approach is divided into twelve steps to be carried out with groups of farmers. Due to the location specific nature of PICSA there are a number of preparatory activities that need to be completed before field staff are trained in the approach. The details of these activities can be found in the document ‘Preparing for PICSA’ on the PICSA website (http://www.walker-institute.ac.uk/research/PICSA)

Spitzer Constraints on the z=6.56 Galaxy Lensed by Abell 370

We report on Spitzer IRAC observations of the spectroscopically confirmed z=6.56 lensed Ly-alpha emitting source HCM 6A which was found behind the cluster Abell 370. Detection of the source at 3.6 and 4.5 microns, corresponding to rest-frame optical emission, allows us to study the stellar population of this primeval galaxy. The broadband flux density at 4.5 microns is enhanced compared to the continuum at other wavelengths, likely due to the presence of strong H-alpha in emission. The derived H-alpha line flux corresponds to a star-formation rate of around 140 M_{sun}/yr, more than an order of magnitude larger than estimates from the ultraviolet continuum and Ly-alpha emission line. The dust extinction required to explain the discrepancy is A_V of about 1 mag. The inference of dust at such high redshifts is surprising and implies that the first epoch of star-formation in this galaxy occurred at z~20.Comment: 11 pages, 3 figures, ApJ Letters in pres

Manual of Criminal Law and Procedure

Intended to aid to Alaska law enforcement officers in the performance of their duties in the field, this manual was designed to provide brief, quick access to major points of substantive and procedural criminal law. The manual contained discussion and procedural guidelines for investigatory stops, identification procedures including line-ups, arrest, search and seizure, interrogation, as well as discussion of justification for the use of nondeadly and deadly force whether by peace officers or civilians, culpability, entrapment, trial preparation, and media relations. The section on substantive criminal law deals with a selection of crimes most likely to be encountered by "street" officers as defined with the recently enacted Revised Alaska Criminal Code (effective January 1, 1980), desribing elements of each crime, investigative hints, and differences with previous provisions of the criminal code, where relevant.Alaska Department of Law Grant No. 78-A-014Introduction / Criminal Procedures / Substantive Criminal Law / Justification / Culpability / Entrapment / Trial Preparation / Media Relations / Appendice

The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight

The limiting magnitude of the HST data set used by Cochran et al. (1995) to detect small objects in the Kuiper belt is reevaluated, and the methods used are described in detail. It is shown, by implanting artificial objects in the original HST images, and re-reducing the images using our original algorithm, that the limiting magnitude of our images (as defined by the 50% detectability limit) is $V=28.4$. This value is statistically the same as the value found in the original analysis. We find that $\sim50$ of the moving Kuiper belt objects with $V=27.9$ are detected when trailing losses are included. In the same data in which these faint objects are detected, we find that the number of false detections brighter than $V=28.8$ is less than one per WFPC2 image. We show that, primarily due to a zero-point calibration error, but partly due to inadequacies in modeling the HST'S data noise characteristics and Cochran et al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects in the HST dataset by over a factor of 2, and their conclusions are therefore invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe