Wide field imaging of distant clusters

Wide field imaging is key to understanding the build-up of distant clusters and their galaxy population. By focusing on the so far unexplored outskirts of clusters, where infalling galaxies first hit the cluster potential and the hot intracluster medium, we can help separate cosmological field galaxy evolution from that driven by environment. I present a selection of recent advancements in this area, with particular emphasis on Hubble Space Telescope wide field imaging, for its superior capability to deliver galaxy morphologies and precise shear maps of distant clusters.Comment: Invited contribution. To appear in "Outskirts of galaxy clusters: intense life in the suburbs", A. Diaferio et al. eds. 7 pages, 5 figures. Refereed versio

On the average density profile of dark-matter halos in the inner regions of massive early-type galaxies

We study a sample of 39 massive early-type lens galaxies at redshift z < 0.3 to determine the slope of the average dark-matter density profile in the innermost regions. We keep the strong lensing and stellar population synthesis modeling as simple as possible to measure the galaxy total and luminous masses. By rescaling the values of the Einstein radius and dark-matter projected mass with the values of the luminous effective radius and mass, we combine all the data of the galaxies in the sample. We find that between 0.3 and 0.9 times the value of the effective radius the average logarithmic slope of the dark-matter projected density profile is -1.0 +/- 0.2 (i.e., approximately isothermal) or -0.7 +/- 0.5 (i.e., shallower than isothermal), if, respectively, a constant Chabrier or heavier, Salpeter-like stellar IMF is adopted. These results provide positive evidence of the influence of the baryonic component on the contraction of the galaxy dark-matter halos, compared to the predictions of dark matter-only cosmological simulations, and open a new way to test models of structure formation and evolution within the standard LCDM cosmological scenario.Comment: 5 pages, 2 figures, published in Astrophysical Journal Letters 747, L1

Service training in the agriculture equipment industry

Plan B Paper. 2012. Master of Science in Agricultural Education--University of Wisconsin-River Falls. Agricultural Education Department. 33 leaves. Includes bibliographical references (leaf 33).The demand for service training continues to increase in the agriculture equipment industry as technology is adopted and advancements continue to be made on equipment. Service technicians need to be prepared when servicing customer's equipment. In this study I investigated the structure of service training and components of service training. The survey provided feedback on service training from service managers at dealerships. This information will allow service training to be effective and efficient. The population surveyed consisted of service managers from AGCO, Case IH, John Deere and New Holland dealerships. For the first part of the study I sent out a survey to the service managers that asked questions related to the structure, location, and cost of service training. Then I conducted phone interviews with service managers about the structure and components of service training, while receiving feedback on instructor and web based training. This study showed that there is a similar structure in service training among the four major North American equipment manufacturers surveyed. There were similarities in materials used during instructor based courses, along with advantages and disadvantages of web based learning courses among the manufactures. I believe there will continue to be a mixture of instructor and web based service training courses because the research showed that hands on activities are an important part of learning

The Galaxy UV Luminosity Function Before the Epoch of Reionization

We present a model for the evolution of the galaxy ultraviolet (UV) luminosity function (LF) across cosmic time where star formation is linked to the assembly of dark matter halos under the assumption of a mass dependent, but redshift independent, efficiency. We introduce a new self-consistent treatment of the halo star formation history, which allows us to make predictions at $z>10$ (lookback time $\lesssim500$ Myr), when growth is rapid. With a calibration at a single redshift to set the stellar-to-halo mass ratio, and no further degrees of freedom, our model captures the evolution of the UV LF over all available observations ($0\lesssim z\lesssim10$). The significant drop in luminosity density of currently detectable galaxies beyond $z\sim8$ is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, we derive a reionization optical depth $\tau = 0.056^{+0.007}_{-0.010}$, fully consistent with the latest Planck measurement, implying that the universe is fully reionized at $z=7.84^{+0.65}_{-0.98}$. In addition, our model naturally produces smoothly rising star formation histories for galaxies with $L\lesssim L_*$ in agreement with observations and hydrodynamical simulations. Before the epoch of reionization at $z>10$ we predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope ($\alpha\sim-3.5$ at $z\sim16$). Finally, we construct forecasts for surveys with \JWST~and \WFIRST and predict that galaxies out to $z\sim14$ will be observed. Galaxies at $z>15$ will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.Comment: Accepted for publication in ApJ. 11 pages, 13 figures. Corrected mislabelled redshifts in Figure

The SL2S Galaxy-scale Gravitational Lens Sample. I. The alignment of mass and light in massive early-type galaxies at z=0.2-0.9

We study the relative alignment of mass and light in a sample of 16 massive early-type galaxies at z=0.2-0.9 that act as strong gravitational lenses. The sample was identified from deep multi-band images obtained as part of the Canada France Hawaii Telescope Legacy Survey as part of the Strong Lensing Legacy Survey (SL2S). Higher resolution follow-up imaging is available for a subset of 10 systems. We construct gravitational lens models and infer total enclosed mass, elongation, and position angle of the mass distribution. By comparison with the observed distribution of light we infer that there is a substantial amount of external shear with mean value $= 0.12 \pm 0.05$, arising most likely from the environment of the SL2S lenses. In a companion paper, we combine these measurements with follow-up Keck spectroscopy to study the evolution of the stellar and dark matter content of early-type galaxies as a function of cosmic time

Dark Matter Contraction and the Stellar Content of Massive Early-type Galaxies: Disfavoring "Light" Initial Mass Functions

We use stellar dynamics, strong lensing, stellar population synthesis models, and weak lensing shear measurements to constrain the dark matter (DM) profile and stellar mass in a sample of 53 massive early-type galaxies. We explore three DM halo models (unperturbed Navarro Frenk & White [NFW] halos and the adiabatic contraction models of Blumenthal and Gnedin) and impose a model for the relationship between the stellar and virial mass (i.e., a relationship for the star-formation efficiency as a function of halo mass). We show that, given our model assumptions, the data clearly prefer a Salpeter-like initial mass function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of the choice of DM halo. In addition, we find that the data prefer at most a moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is strongly disfavored) and are only consistent with no adiabatic contraction (i.e., a NFW halo) if a mass-dependent IMF is assumed, in the sense of a more massive normalization of the IMF for more massive halos.Comment: 6 pages, 3 figures; submitted to ApJL, including revisions based upon the referee repor

The initial mass function of early-type galaxies

We determine an absolute calibration of the initial mass function (IMF) of early-type galaxies, by studying a sample of 56 gravitational lenses identified by the SLACS Survey. Under the assumption of standard Navarro, Frenk & White dark matter halos, a combination of lensing, dynamical, and stellar population synthesis models is used to disentangle the stellar and dark matter contribution for each lens. We define an "IMF mismatch" parameter \alpha=M*(L+D)/M*(SPS) as the ratio of stellar mass inferred by a joint lensing and dynamical models (M*(L+D)) to the current stellar mass inferred from stellar populations synthesis models (M*(SPS)). We find that a Salpeter IMF provides stellar masses in agreement with those inferred by lensing and dynamical models (=0.00+-0.03+-0.02), while a Chabrier IMF underestimates them (=0.25+-0.03+-0.02). A tentative trend is found, in the sense that \alpha appears to increase with galaxy velocity dispersion. Taken at face value, this result would imply a non universal IMF, perhaps dependent on metallicity, age, or abundance ratios of the stellar populations. Alternatively, the observed trend may imply non-universal dark matter halos with inner density slope increasing with velocity dispersion. While the degeneracy between the two interpretations cannot be broken without additional information, the data imply that massive early-type galaxies cannot have both a universal IMF and universal dark matter halos.Comment: 10 pages 4 figures. Resubmitted to ApJ taking into account referee's comment