Using the Big Ideas in Cosmology to Teach College Students

Recent advances in our understanding of the Universe have revolutionized our view of its structure, composition and evolution. However, these new ideas have not necessarily been used to improve the teaching of introductory astronomy students. In this project, we have conducted research into student understanding of cosmological ideas so as to develop effective web-based tools to teach basic concepts important to modern cosmology. The tools are intended for use at the introductory college level. Our research uses several instruments, including open-ended and multiple choice surveys conducted at multiple institutions, as well as interviews and course artifacts at one institution, to ascertain what students know regarding modern cosmological ideas, what common misunderstandings and misconceptions they entertain, and what sorts of materials can most effectively overcome student difficulties in learning this material. These data are being used to create a suite of interactive, web-based tutorials that address the major ideas in cosmology using real data. Having students engage with real data is a powerful means to help students overcome certain misconceptions. Students master the scientific concepts and reasoning processes that lead to our current understanding of the universe through interactive tasks, prediction and reflection, experimentation, and model building.Comment: 2012 Fermi Symposium proceedings - eConf C12102

CATS: CfAO Treasury Survey of distant galaxies, supernovae, and AGN's

The NSF Science and Technology Center for Adaptive Optics (CfAO) is supporting a major scientific legacy project called the CfAO Treasury Survey (CATS). CATS is obtaining near-infrared AO data in deep HST survey fields, such as GEMS, GOODS-N, & EGS. Besides summarizing the main objectives of CATS, we highlight some recent imaging work on the study of distant field galaxies, AGNs, and a redshift z = 1.32 supernova. CATS plans the first data release to the community in early 2007 (check http://www.astro.ucla.edu/~irlab/cats/index.shtml for more details on CATS and latest updates).Comment: 2 pages. Proceedings of the IAU Symposium 235, "Galaxy Evolution across the Hubble Time", F. Combes & J. Palous (eds.

Microtubules in hyaloclasts from the Hawaii Scientific Drilling Project #2 phase 1 core, Hilo, Hawaii: evidence of microbe-rock interactions

Minute tubules etched into basalt glass in hyaloclastites from the Hawaii Scientific Drilling Project #2 (HSDP) phase 1 borehole are interpreted as trace fossils formed by microbes, i.e. microendolithic borings. Such borings are one to a few micrometers in diameter and up to >100 µm long; they extend into glass shards from free surfaces (broken shards, vesicles, fractures). Morphologic characterization of microendolithic borings quantitatively describes them for comparison with other occurrences and aids in understanding the interactions between microorganisms and basaltic glass that result in the dissolution of the glass. The first step in working with these features as trace fossils was to modify the ichnofabric index of Droser and Bottjer (1986) for use with minute features that extend into homogeneous material. The modification includes six semiquantitative classes of disruption and is scale-independent, applicable to any size feature. The second step was to apply the new microendolithic ichnofabric index (MII) to the HSDP samples. Analysis of the HSDP samples using the MII showed that the abundance of bioerosion varied throughout the core. Assigned MII values ranged from 1 to 3, average MII values ranged from 1 to 2.44, while the mean MII value of 1.2. Areas with the most bioerosion were located between 1,365.9 and 1,478.8 mbsl and a section of the core centered around 2,117.0 mbsl. The MII values of these locations ranged from 2 to 2.5. Areas with low bioerosion (all samples 100 µm long; they extend into glass shards from free surfaces (broken shards, vesicles, fractures). Morphologic characterization of microendolithic borings quantitatively describes them for comparison with other occurrences and aids in understanding the interactions between microorganisms and basaltic glass that result in the dissolution of the glass. The first step in working with these features as trace fossils was to modify the ichnofabric index of Droser and Bottjer (1986) for use with minute features that extend into homogeneous material. The modification includes six semiquantitative classes of disruption and is scale-independent, applicable to any size feature. The second step was to apply the new microendolithic ichnofabric index (MII) to the HSDP samples. Analysis of the HSDP samples using the MII showed that the abundance of bioerosion varied throughout the core. Assigned MII values ranged from 1 to 3, average MII values ranged from 1 to 2.44, while the mean MII value of 1.2. Areas with the most bioerosion were located between 1,365.9 and 1,478.8 mbsl and a section of the core centered around 2,117.0 mbsl. The MII values of these locations ranged from 2 to 2.5. Areas with low bioerosion (all samples <2) were located between 1,079.0 and 1,320.0 mbsl, 1,799.0 and 1,900.0 mbsl, and all depths below 2,500.0 mbsl. Lastly, such features as length, diameter, ornamentation, density, and complexity and tortuosity were measured to better describe the interactions between microorganisms and basaltic hyaloclastite media. The shortest measured 0.907 µm and the longest measured 129.22 µm. Lengths were approximately log-normally distributed with a geometric mean of 18.9 µm. The tortuosity of borings had a median of 1.29 with a range of 1.227 to 1.37. The least tortuous measured 1.22 and the most tortuous measured 16.46. This was one of the first attempts to quantify the range of morphology and density, of euendolithic microborings in basalt glass. This study extends the sampling scale for ichnological study to what is near the minimum size range of trace fossils. It demonstrates that trace fossil abundance does not simply decrease with depth in ocean islands, unlike basalts of oceanic crust, but varies, probably as a result of variation of the rate of accumulation of suitable substrates

The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies

We investigate the influence of ram-pressure stripping on the internal gas kinematics of simulated spiral galaxies. Additional emphasis is put on the question of how the resulting distortions of the gaseous disc are visible in the rotation curve and/or the full 2D velocity field of galaxies at different redshifts. A Milky-Way type disc galaxy is modelled in combined N-body/hydrodynamic simulations with prescriptions for cooling, star formation, stellar feedback, and galactic winds. This model galaxy moves through a constant density and temperature gas, which has parameters similar to the intra-cluster medium (ICM). Rotation curves (RCs) and 2D velocity fields of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We find that the appearance of distortions of the gaseous disc due to ram-pressure stripping depends on the direction of the acting ram pressure. In the case of face-on ram pressure, the distortions mainly appear in the outer parts of the galaxy in a very symmetric way. In contrast, in the case of edge-on ram pressure we find stronger distortions. The 2D velocity field also shows signatures of the interaction in the inner part of the disc. At angles smaller than 45 degrees between the ICM wind direction and the disc, the velocity field asymmetry increases significantly compared to larger angles. Compared to distortions caused by tidal interactions, the effects of ram-pressure stripping on the velocity field are relatively low in all cases and difficult to observe at intermediate redshift in seeing-limited observations. (abridged)Comment: 9 pages, 11 figures, accepted for publication in A&

The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip

We present the quantitative rest-frame B morphological evolution and galaxy merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity evolution of 1.3 M_B per unit redshift. We find that the merger fraction remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3. The majority of z 10^11 L_sun are disk galaxies, and only ~ 15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate density since z ~ 1 is a result of declining star-formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.Comment: 24 pages, including 3 tables and 18 color figures; accepted to the Astrophysical Journal; high resolution version available at http://www.noao.edu/noao/staff/lotz/lotz_mergers.pd

The Butcher-Oemler Effect at Moderate Redshift

We present the results of Butcher-Oemler-style analysis of three moderate- redshift (0.1<z<0.2) clusters which have bimodal X-ray surface brightness profiles. We find that at least two of these clusters exhibit unusually high fractions of blue galaxies as compared to clusters at comparable redshifts studied by Butcher and Oemler (1984). This implies that star formation is occurring in a high fraction of the galaxies in the two clusters. Our results are consistent with hierarchical clustering models in which subcluster- subcluster mergers create shocks in the intracluster medium. The shocks, in turn, induce simultaneous starbursts in a large fraction of cluster galaxies. Our study therefore lends weight to the hypothesis that the Butcher-Oemler effect is an environmental, as well as evolutionary, phenomenon.Comment: 22 pages, 8 figures; accepted for publication in A

Spectroscopic Observations of Optically Selected Clusters of Galaxies from the Palomar Distant Cluster Survey

We have conducted a redshift survey of sixteen cluster candidates from the Palomar Distant Cluster Survey (PDCS) to determine both the density of PDCS clusters and the accuracy of the estimated redshifts presented in the PDCS catalog (Postman et. al. 1996). We find that the matched-filter redshift estimate presented in the PDCS has an error sigma_z = 0.06 in the redshift range 0.1 < z < 0.35 based on eight cluster candidates with three or more concordant galaxy redshifts. We measure the low redshift (0.1 < z < 0.35) space density of PDCS clusters to be 31.3^{+30.5}_{-17.1} * E-06 h^3 Mpc^-3 (68% confidence limits for a Poisson distribution) for Richness Class 1 systems. We find a tentative space density of 10.4^{+23.4}_{-8.4}* E-06 h^3 Mpc^-3 for Richness Class 2 clusters. These densities compare favorably with those found for the whole of the PDCS and support the finding that the space density of clusters in the PDCS is a factor of ~5 above that of clusters in the Abell catalog (Abell 1958; Abell, Corwin, and Olowin 1989). These new space density measurements were derived as independently as possible from the original PDCS analysis and therefore, demonstrate the robustness of the original work. Based on our survey, we conclude that the PDCS matched-filter algorithm is successful in detecting real clusters and in estimating their true redshifts in the redshift range we surveyed.Comment: 23 pages with 4 figures and 3 seperate tables. To be published in the November Issue of the Astronomical Journa