Source evaluation and selection for interpretation in Sequoia and Kings Canyon National Parks

The purpose of this study is to aid interpreters in evaluation sources (research material) for use in interpretive presentations and programs in Sequoia and Kings Canyon National Parks. This was done by illustrating the need for source evaluation and then developing the guidelines for selecting, evaluating, and most effectively using various sources in the development of interpretive programs in the National Parks Services (NPS)

Characteristics of perrennial grasses [poster]

Growth Characteristics of perennial C3 grasses: this table presents information on a range of perennial grass species but it is not a recommendation for them. Consider species characteristics in relation to local conditions and then source specific variety information before making decisions. It is suggest you grow trial plots of grasses before planting large areas (see key below for rating system)

Private Revenge and its Relation to Punishment

In contrast to the vast literature on retributive theories of punishment, discussions of private revenge are rare in moral philosophy. This paper reviews some examples, from both classical and recent writers. It detects, both in the philosophical tradition and in contemporary moral discourse, uncertainty and equivocation over the ethical significance of acts of revenge, and in particular over their possible resemblances, in motive, purpose or justification, to acts of lawful punishment. A key problem for the coherence of our ethical conception of revenge, it suggests, is the consideration that certain acts of revenge may be just (at least in the minimal sense that the victim of revenge has no grounds for complaint against the revenger) and yet be generally agreed to be morally wrong. It argues that the challenge of explaining adequately why private revenge is morally wrong poses particular difficulty for purely retributive theories of punishment, since without invoking consequentialist reasons it does not seem possible adequately to motivate an objection to just and proportionate acts of revenge. The paper concludes by identifying some of the directions in which further reflection on the moral and political significance of revenge might proceed

Connecting Cluster Substructure in Galaxy Cluster Cores at z=0.2 With Cluster Assembly Histories

We use semi-analytic models of structure formation to interpret gravitational lensing measurements of substructure in galaxy cluster cores (R<=250kpc/h) at z=0.2. The dynamic range of the lensing-based substructure fraction measurements is well matched to the theoretical predictions, both spanning f_sub~0.05-0.65. The structure formation model predicts that f_sub is correlated with cluster assembly history. We use simple fitting formulae to parameterize the predicted correlations: Delta_90 = tau_90 + alpha_90 * log(f_sub) and Delta_50 = tau_50 + alpha_50 * log(f_sub), where Delta_90 and Delta_50 are the predicted lookback times from z=0.2 to when each theoretical cluster had acquired 90% and 50% respectively of the mass it had at z=0.2. The best-fit parameter values are: alpha_90 = (-1.34+/-0.79)Gyr, tau_90 = (0.31+/-0.56)Gyr and alpha_50 = (-2.77+/-1.66)Gyr, tau_50 = (0.99+/-1.18)Gyr. Therefore (i) observed clusters with f_sub<~0.1 (e.g. A383, A1835) are interpreted, on average, to have formed at z>~0.8 and to have suffered <=10% mass growth since z~0.4, (ii) observed clusters with f_sub>~0.4 (e.g. A68, A773) are interpreted as, on average, forming since z~0.4 and suffering >10% mass growth in the ~500Myr preceding z=0.2, i.e. since z=0.25. In summary, observational measurements of f_sub can be combined with structure formation models to estimate the age and assembly history of observed clusters. The ability to ``age-date'' approximately clusters in this way has numerous applications to the large clusters samples that are becoming available.Comment: Accepted by ApJL, 4 pages, 2 figure

Tracing Galaxy Formation with Stellar Halos I: Methods

If the favored hierarchical cosmological model is correct, then the Milky Way system should have accreted ~100-200 luminous satellite galaxies in the past \~12 Gyr. We model this process using a hybrid semi-analytic plus N-body approach which distinguishes explicitly between the evolution of light and dark matter in accreted satellites. This distinction is essential to our ability to produce a realistic stellar halo, with mass and density profile much like that of our own Galaxy, and a surviving satellite population that matches the observed number counts and structural parameter distributions of the satellite galaxies of the Milky Way. Our model stellar halos have density profiles which typically drop off with radius faster than those of the dark matter. They are assembled from the inside out, with the majority of mass (~80%) coming from the \~15 most massive accretion events. The satellites that contribute to the stellar halo have median accretion times of ~9 Gyr in the past, while surviving satellite systems have median accretion times of ~5 Gyr in the past. This implies that stars associated with the inner halo should be quite different chemically from stars in surviving satellites and also from stars in the outer halo or those liberated in recent disruption events. We briefly discuss the expected spatial structure and phase space structure for halos formed in this manner. Searches for this type of structure offer a direct test of whether cosmology is indeed hierarchical on small scales.Comment: 22 pages, 16 figures, submitted to Ap

Tidal stirring and the origin of dwarf spheroidals in the Local Group

N-Body/SPH simulations are used to study the evolution of dwarf irregular galaxies (dIrrs) entering the dark matter halo of the Milky Way or M31 on plunging orbits. We propose a new dynamical mechanism driving the evolution of gas rich, rotationally supported dIrrs, mostly found at the outskirts of the Local Group (LG), into gas free, pressure supported dwarf spheroidals (dSphs) or dwarf ellipticals (dEs), observed to cluster around the two giant spirals. The initial model galaxies are exponential disks embedded in massive dark matter halos and reproduce nearby dIrrs. Repeated tidal shocks at the pericenter of their orbit partially strip their halo and disk and trigger dynamical instabilities that dramatically reshape their stellar component. After only 2-3 orbits low surface brightness (LSB) dIrrs are transformed into dSphs, while high surface brightness (HSB) dIrrs evolve into dEs. This evolutionary mechanism naturally leads to the morphology-density relation observed for LG dwarfs. Dwarfs surrounded by very dense dark matter halos, like the archetypical dIrr GR8, are turned into Draco or Ursa Minor, the faintest and most dark matter dominated among LG dSphs. If disks include a gaseous component, this is both tidally stripped and consumed in periodic bursts of star formation. The resulting star formation histories are in good qualitative agreement with those derived using HST color-magnitude diagrams for local dSphs.Comment: 5 pages, 5 figures, to appear on ApJL. Simulation images and movies can be found at the Local Group web page at http://pcblu.uni.mi.astro.it/~lucio/LG/LG.htm

An analytical model for the accretion of dark matter subhalos

An analytical model is developed for the mass function of cold dark matter subhalos at the time of accretion and for the distribution of their accretion times. Our model is based on the model of Zhao et al. (2009) for the median assembly histories of dark matter halos, combined with a simple log-normal distribution to describe the scatter in the main-branch mass at a given time for halos of the same final mass. Our model is simple, and can be used to predict the un-evolved subhalo mass function, the mass function of subhalos accreted at a given time, the accretion-time distribution of subhalos of a given initial mass, and the frequency of major mergers as a function of time. We test our model using high-resolution cosmological $N$-body simulations, and find that our model predictions match the simulation results remarkably well. Finally, we discuss the implications of our model for the evolution of subhalos in their hosts and for the construction of a self-consistent model to link galaxies and dark matter halos at different cosmic times.Comment: 14 pages, 10 figures (caption for figure 10 fixed). Accepted for publication in Ap

New multi-zoom method for N-body simulations: application to galaxy growth by accretion

In this work we focus on the properties of accretion onto galaxies. Through numerical simulations we investigate the geometrical properties of accretion. To span the scale range required in these simulations we have developed a new numerical technique: the multi-zoom method. We run a series of Tree-SPH simulations in smaller and smaller boxes at higher and higher mass resolution, using data recorded at the previous level to account for the matter inflow and the tidal field from outside matter. The code is parallelized using OpenMP. We present a validation test to evaluate the robustness of the method: the pancake collapse. We apply this new multizoom method to study the accretion properties. Zooming in onto galaxies from a cosmological simulation, we select a sample of 10 well resolved galaxies (5000 baryonic particles or more). We sum up their basic properties and plot a Tully-Fisher relation. We find that smooth accretion of intergalactic cold gas dominates mergers for the mass growth of galaxies at z < 2. Next we study the baryonic accretion rate which shows different behaviours depending on the galaxy mass. The bias is also computed at different radii and epochs. Then we present galactocentric angular maps for the accretion integrated between z=2 and z=0, which reveal that accretion is highly anisotropic. Average accretion rates plotted against galactocentric latitude show a variety of behaviours. In general, accretion in the galactic plane is favored, even more for baryonic matter than for dark matter.Comment: Page lay out fix u

Reionization and the abundance of galactic satellites

One of the main challenges facing standard hierarchical structure formation models is that the predicted abundance of galactic subhalos with circular velocities of 10-30 km/s is an order of magnitude higher than the number of satellites actually observed within the Local Group. Using a simple model for the formation and evolution of dark halos, based on the extended Press-Schechter formalism and tested against N-body results, we show that the theoretical predictions can be reconciled with observations if gas accretion in low-mass halos is suppressed after the epoch of reionization. In this picture, the observed dwarf satellites correspond to the small fraction of halos that accreted substantial amounts of gas before reionization. The photoionization mechanism naturally explains why the discrepancy between predicted halos and observed satellites sets in at about 30 km/s, and for reasonable choices of the reionization redshift (z_re = 5-12) the model can reproduce both the amplitude and shape of the observed velocity function of galactic satellites. If this explanation is correct, then typical bright galaxy halos contain many low-mass dark matter subhalos. These might be detectable through their gravitational lensing effects, through their influence on stellar disks, or as dwarf satellites with very high mass-to-light ratios. This model also predicts a diffuse stellar component produced by large numbers of tidally disrupted dwarfs, perhaps sufficient to account for most of the Milky Way's stellar halo.Comment: 5 pages, 2 figures, Submitted to Ap

The descendents of Lyman Break Galaxies in galaxy clusters: spatial distribution and orbital properties

We combine semi-analytical methods with a ultra-high resolution simulation of a galaxy cluster (of mass 2.3 10^14h-1Msolar, and 4 10^6 particles within its virial radius) formed in a standard CDM universe to study the spatial distribution and orbital properties of the present-day descendents of Lyman Break Galaxies (LBGs). At the present time only five (out of 12) of halos containing LBGs survive as separate entities inside the cluster virial radius. Their circular velocities are in the range 200 - 550 km/sec. Seven halos merged together to form the central object at the very center of the cluster. Using semi-analytical modeling of galaxy evolution we show that descendents of halos containing LBGs now host giant elliptical galaxies. Galaxy orbits are radial, with a pericenter to apocenter ratio of about 1:5. The orbital eccentricities of LBGs descendents are statistically indistinguishable from those of the average galaxy population inside the cluster, suggesting that the orbits of these galaxies are not significantly affected by dynamical friction decay after the formation of the cluster's main body. In this cluster, possibly due to its early formation time, the descendents of LBGs are contained within the central 60% of the cluster virial radius and have an orbital velocity dispersion lower than the global galaxy population, originating a mild luminosity segregation for the brightest cluster members. Mass estimates based only on LBGs descendents (especially including the central cD) reflect this bias in space and velocity and underestimate the total mass of this well virialized cluster by up to a factor of two compared to estimates using at least 20 cluster members.Comment: 6 Pages, 2 Postscript figures. Submitted to Ap