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CASS Astrophysics Seminar

The Astrophysics Seminar takes place on WED.
280 SERF from 4:00 - 5:00 p.m.

FALL 2009





Special day Tuesday 27 Oct.

Michael Rauch, Carnegie Observatories

" "Faint Lyman alpha Emitters, Damped Lyman Alpha Absorbers, and their Relation to Other High Redshift Sources" "

" I will talk about some recent attempts at measuring very faint Lyman alpha emission from the general intergalactic medium at redshift 3. I'll describe how a recently detected population of faint emitters may help us to understand the nature of other classes of high redshift objects, in particular damped Lyman alpha absorption systems, and what they may tell us about the properties of dwarf galaxies at high redshift. approach, and discuss the implications of these results for the accretion history of the Universe. "

21 Oct.

James Aird, UCSD-CASS Postdoctoral Scholar

" "The evolution of AGN activity across cosmic time" "

" Determining the distribution and evolution of accretion activity in Active Galactic Nuclei (AGN) throughout the history of the Universe, traced by the luminosity function, is essential to constrain models of supermassive black-hole formation and growth, the triggering and fuelling of AGN and their co-evolution with galaxies. I will present new results on the evolution of the X-ray luminosity function (XLF) of AGN utilising data from the Chandra Deep Fields and the AEGIS survey, using new methods to account for uncertainties in photometric redshifts, selection effects and incompleteness. I will also present an alternative method of determining the XLF at high redshifts (z~2-3) using a rest-frame UV color pre-selection approach, and discuss the implications of these results for the accretion history of the Universe. "

07 Oct.


" Cosmological Constraints from Gravitational Lens Time Delays "

" Future large ensembles of time delay lenses have the potential to provide nteresting cosmological constraints complementary to those of other methods. Current constraints from 10-16 time delay lenses already yield the Hubble constant (h) in agreement with and to roughly the same level of precision (10%) as the HST Key Project which analyzed 40 Cepheids. Future surveys (Pan-STARRS, LSST, JDEM / IDECS, SKA, OMEGA) will yield hundreds or even thousands of lenses with well-measured time delays. We find in a flat universe with constant w including a Planck prior, LSST time delay measurements for ~4,000 lenses should constrain h to 0.007 (~1%), Omega_de to ~0.005, and w to ~0.026 (all 1-sigma precisions). Similar constraints could be obtained by a dedicated space-based gravitational lens observatory (OMEGA) which would obtain precise time delay and mass model measurements for ~100 lenses with spectroscopic redshifts. Constraints for a general cosmology are presented as well. We compare these to the "optimistic Stage IV" constraints expected from weak lensing, supernovae, baryon acoustic oscillations, and cluster counts, as calculated by the Dark Energy Task Force. As with any method, there are systematics we must learn to control, and we discuss these issues. "

Spring 2009





01 April

Naveen Reddy, NOAO, Tucson, AZ

" Multi-Wavelength Luminosity Functions and Implications for the Cosmic Star Formation History "

" I will review some of the recent efforts to constrain the star formation history of the Universe based on UV measurements, and will discuss what we have learned about the dust properties of typical star forming galaxies at high redshift based on detailed studies at z~2-3. I will present recent results that indicate a very steep slope of the UV luminosity function at z~2-3 that has interesting implications for both the evolution of the faint-end slope and the consequences for the shape of the stellar mass function and budget of total stellar mass at high redshift. "

08 April 4:00-5:00 PM

Dennis Zaritsky University of Arizona

" Galactic Structure"

" Unlike stellar structure, galactic structure has no well understood, simple physical model. In analogy to the development of the stellar color-magnitude diagram, and in particular to the stellar main sequence, I will describe the simple scaling relations that we have found that may lead to a simple theory of the structure of stellar systems. "

15 April

Hsiao-Wen Chen, University of Chicago

" The origin of QSO absorption-line systems and halo occupation of dark baryons"

" Observations of QSO absorption-line systems have revealed a wealth of information for the intergalactic medium from the nearby universe all the way to the epoch of reionization. These absorbers offer a powerful tool for mapping the dark universe, but their correlation with known stellar populations has always been ambiguous. I will describe on-going surveys of absorbers and galaxies along common lines of sight toward background quasars, for quantifying the cross-correlation between stars and gas. I will also introduce a new technique we have developed for constraining the baryon content of known dark matter halos based on absorption-line statistics."

24 April Noon-1:00PM

Jonathan Williams, Institute for Astronomy, Hawaii

" Clouds, cores, and disks: a potpourri of results from the submillimeter telescopes on Mauna Kea"

" Mauna Kea is the best site for observations at submillimeter wavelengths in the northern hemisphere. I will present a broad overview of a range of programs in star and planet formation that we have carried out through our unique access to all three submillimeter telescopes (CSO, JCMT, SMA) on the summit. Topics to be covered include a large 1.1mm survey of the Galactic plane, CO mapping of interstellar bubbles, starless cores in cluster forming regions, and circumstellar disks in Orion. I will end with some thoughts on how the cosmochemical discovery of 60Fe in our Solar System ties these subjects together. "

29 April

Ian McLean, UCLA

" Lifting the Cosmic Veil: celebrating 20 years of the UCLA IR Lab"

" The UCLA Infrared Lab was founded in 1989, only three years after the first infrared array detectors were introduced into astronomy. Within ten years we had jumped to megapixel arrays and provided NIRSPEC - the first high-resolution echelle spectrograph for the Keck telescope. Today, the lab is involved in two major instruments, MOSFIRE for Keck and GPI for Gemini-South. I will review all these developments and describe results from one of the NIRSPEC Key Programs - the Brown Dwarf Spectroscopic Survey (BDSS). In addition, I will give an up-to-date report on MOSFIRE, the cryogenic multi-object IR spectrograph which is due for delivery about 12 months from now, and look forward to IRIS, an instrument concept for the TMT. "

06 May

JD Smith, University of Toledo, Ohio

" Stars, Gas, and Dust in Galaxies: Spitzer's Incredible Legacy"

" With Spitzer's five year cold mission drawing to a close, I will highlight its remarkable (and continuing) successes in forming a more complete picture of the distribution and conditions of warm and cool gas and dust in galaxies, with an emphasis on the small PAH grains which dominate the mid-infrared energy output from star formation. I will also address the impact of AGN -- both strong and weak -- on a galaxy's dust emission, and the bright future prospects for infrared diagnostics of dust and gas in galaxies near and far. "

13 May

Greg Aldering, LBNL

" Supernovae as Probes of Dark Energy"

" The use of Type Ia supernovae as distance indicators led to the discovery of the accelerating expansion of the Universe more than a decade ago. Large 2nd generation surveys have significantly increased the size and quality of the high-redshift sample. The critical low-redshift reference sample useful for cosmology remains small however. The Nearby Supernova Factory (SNfactory) is using new nearby Type Ia supernovae to strengthen the measurement of the dark energy equation of state, with an emphasis on controlling systematic uncertainties and better understanding the underlying physics associated with Type Ia supernovae as distance indicators. To meet these goals the SNfactory has developed two new approaches to the problem -- an ultra-wide-field CCD survey at Palomar Observatory and replacement of filter-based supernova lightcurves with full spectral time series. In this talk I will discuss recent progress in measuring the dark energy equation of state with both high- and low-redshift supernovae, focusing on recent results from the Nearby Supernova Factory. "

20 May 4:00-5:00 PM

Mike Brown, CalTech

" The Dwarf Planets of the Outer Solar System"

" The past few years have seen an explosion in the discoveries of Pluto- and near Pluto-sized bodies in the outer solar system, giving rise to a new classification of "dwarf planets." Like Pluto, each of these largest dwarf planets has a unique story to tell about the history and evolution of the solar system. I'll discuss the discoveries of these objects and the new views of giant collisions, stellar encounters, and planetary rearrangement that we are gaining from their study."

27 May

Annick Pouquet, NCAR

" Turbulence in the presence of magnetic fields: Breakdown of universality?"

" Theories and concepts developed for fluid turbulence may well be applicable, mutatis mutandis, to the coupling with a magnetic field in the magnetohydrodynamics (MHD) approach valid for velocities small compared to the speed of light, as for example the phenomenology of Kolmogorov and its variants or the theory of weak turbulence in the presence of waves. In this talk, I shall first review some of the observations concerning the dynamics of magnetic fields. I shall then comment on some of the developments that are taking place presently in MHD, in particular concerning the possible breakdown of universality in MHD turbulence. In so doing, I will mention the results of high-resolution numerical simulations up to grids of 15363 points, and more implementing symmetries in special cases. "

03 June

Eugene Chiang, Depts. of Astronomy/Earth Planetary Science, UC Berkeley

" Planet Formation in Transitional and Debris Disks "

" Myriad processes operate in circumstellar disks to give birth to planets. New insights are afforded by transitional T Tauri disks and debris disks. Transitional disks resemble classical T Tauri disks but have central AU-sized clearings that are swept clean of dust. They age into debris disks in which the dust is entirely optically thin. The decline in optical depth almost certainly reflects the accumulation of micron-sized rains into planets. In connection with these systems we offer progress reports on several problems in disk physics, planet formation, and planet-disk interaction: (1) How do T Tauri disks accrete and dissipate? (2) As dust grains sediment to disk midplanes, what maximum densities can they achieve? Are dust concentrations large enough for planetesimals to form by gravitational instability? (3) What physics underlies the surface brightness profiles of debris disks? In particular, how can we use the observed shapes of debris disks to infer the properties of attendant planets, such as the newly imaged extrasolar planet orbiting Fomalhaut? "









































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