166 research outputs found
Addressing the Crisis in Fundamental Physics
I present the case for fundamental physics experiments in space playing an
important role in addressing the current "dark energy'' crisis. If cosmological
observations continue to favor a value of the dark energy equation of state
parameter w=-1, with no change over cosmic time, then we will have difficulty
understanding this new fundamental physics. We will then face a very real risk
of stagnation unless we detect some other experimental anomaly. The advantages
of space-based experiments could prove invaluable in the search for the a more
complete understanding of dark energy. This talk was delivered at the start of
the Fundamental Physics Research in Space Workshop in May 2006.Comment: 11 pages, Opening talk presented at the 2006 Workshop on Fundamental
Physics in Space. Submitted to Int'l Journal of Modern Physics,
Using Elliptical Galaxy Kinematics to Compare of the Strength of Gravity in Cosmological Regions of Differing Gravitational Potential -- A First Look
Various models of modified gravity invoke ``screening'' mechanisms that are
sensitive to the value of the local gravitational potential. This could have
observable consequences for galaxies. These consequences might be seen by
comparing two proxies for galaxy mass -- their luminosity and their internal
kinematics -- as a function of local galaxy density. Motivated by this
prospect, we have compared the observed properties of luminous red galaxies
(LRGs) inside and outside of voids in the cosmic large scale structure. We used
archival measurements of line widths, luminosities, redshifts, colors, and
positions of galaxies in conjunction with recent void catalogs to construct
comparison LRG samples inside and outside of voids. We fitted these two samples
to the well-established fundamental plane of elliptical galaxies to constrain
any differences between the inferred value of the Newtonian gravitational
constant G for the two samples. We obtained a null result, with an upper limit
on any fractional difference in G within and outside of cosmological voids to
be 40\%. This upper bound is dominated by the
small-number statistics of our N 100 within-void LRG sample. With the
caveat that environmental effects could influence various parameters such as
star formation, we estimate that a 1\% statistical limit on could be
attained with data from 10 elliptical galaxies within voids. This is
within the reach of future photometric and spectroscopic surveys, both of which
are required to pursue this method
Sky Variability in the y Band at the LSST Site
We have measured spatial and temporal variability in the y band sky
brightness over the course of four nights above Cerro Tololo near Cerro Pachon,
Chile, the planned site for the Large Synoptic Survey Telescope (LSST). Our
wide-angle camera lens provided a 41 deg field of view and a 145 arcsec pixel
scale. We minimized potential system throughput differences by deploying a deep
depletion CCD and a filter that matches the proposed LSST y_3 band (970 nm-1030
nm). Images of the sky exhibited coherent wave structure, attributable to
atmospheric gravity waves at 90 km altitude, creating 3%-4% rms spatial sky
flux variability on scales of about 2 degrees and larger. Over the course of a
full night the y_3 band additionally showed highly coherent temporal
variability of up to a factor of 2 in flux. We estimate the mean absolute sky
level to be approximately y_3 = 17.8 mag (Vega), or y_3 = 18.3 mag (AB). While
our observations were made through a y_3 filter, the relative sky brightness
variability should hold for all proposed y bands, whereas the absolute levels
should more strongly depend on spectral response. The spatial variability
presents a challenge to wide-field cameras that require illumination correction
strategies that make use of stacked sky flats. The temporal variability may
warrant an adaptive y band imaging strategy for LSST, to take advantage of
times when the sky is darkest.Comment: 8 pages, 5 figures, accepted to PASP. Minor changes from referee
report and editor's revisions
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