1,882 research outputs found
Evolution in the Clustering of Galaxies for Z < 1
Measuring the evolution in the clustering of galaxies over a large redshift
range is a challenging problem. For a two-dimensional galaxy catalog, however,
we can measure the galaxy-galaxy angular correlation function which provides
information on the density distribution of galaxies. By utilizing photometric
redshifts, we can measure the angular correlation function in redshift shells
(Brunner 1997, Connolly et al. 1998) which minimizes the galaxy projection
effect, and allows for a measurement of the evolution in the correlation
strength with redshift. In this proceedings, we present some preliminary
results which extend our previous work using more accurate photometric
redshifts, and also incorporate absolute magnitudes, so that we can measure the
evolution of clustering with either redshift or intrinsic luminosity.Comment: 6 pages, 6 figures requires paspconf.sty. To be published in
"Photometric Redshifts and High Redshift Galaxies", eds. R. Weymann, L.
Storrie-Lombardi, M. Sawicki & R. Brunner, (San Francisco: ASP Conference
Series
Exploring the Use of Virtual Worlds as a Scientific Research Platform: The Meta-Institute for Computational Astrophysics (MICA)
We describe the Meta-Institute for Computational Astrophysics (MICA), the
first professional scientific organization based exclusively in virtual worlds
(VWs). The goals of MICA are to explore the utility of the emerging VR and VWs
technologies for scientific and scholarly work in general, and to facilitate
and accelerate their adoption by the scientific research community. MICA itself
is an experiment in academic and scientific practices enabled by the immersive
VR technologies. We describe the current and planned activities and research
directions of MICA, and offer some thoughts as to what the future developments
in this arena may be.Comment: 15 pages, to appear in the refereed proceedings of "Facets of Virtual
Environments" (FaVE 2009), eds. F. Lehmann-Grube, J. Sablating, et al., ICST
Lecture Notes Ser., Berlin: Springer Verlag (2009); version with full
resolution color figures is available at
http://www.mica-vw.org/wiki/index.php/Publication
Towards More Precise Photometric Redshifts: Calibration Via CCD Photometry
We present the initial results from a deep, multi-band photometric survey of
selected high Galactic latitude redshift fields. Previous work using the
photographic data of Koo and Kron demonstrated that the distribution of
galaxies in the multi-dimensional flux space U B R I is nearly planar. The
position of a galaxy within this plane is determined by its redshift,
luminosity and spectral type. Using recently acquired deep CCD photometry in
existing, published redshift fields, we have redetermined the distribution of
galaxies in this four-dimensional magnitude space. Furthermore, from our CCD
photometry and the published redshifts, we have quantified the
photometric-redshift relation within the standard AB magnitude system. This
empirical relation has a measured dispersion of approximately 0.02 for z < 0.4.
With this work we are reaching the asymptotic intrinsic dispersions that were
predicted from simulated distributions of galaxy colors.Comment: submitted to the Astrophysical Journal Letter
Simultaneous Multicolor Detection of Faint Galaxies in the Hubble Deep Field
We present a novel way to detect objects when multiband images are available.
Typically, object detection is performed in one of the available bands or on a
somewhat arbitrarily co-added image. Our technique provides an almost optimal
way to use all the color information available. We build up a composite image
of the N passbands where each pixel value corresponds to the probability that
the given pixel is just sky. By knowing the probability distribution of sky
pixels (a chi-square distribution with N degrees of freedom), the data can be
used to derive the distribution of pixels dominated by object flux. From the
two distributions an optimal segmentation threshold can be determined. Clipping
the probability image at this threshold yields a mask, where pixels unlikely to
be sky are tagged. After using a standard connected-pixel criterion, the
regions of this mask define the detected objects. Applying this technique to
the Hubble Deep Field data, we find that we can extend the detection limit of
the data below that possible using linearly co-added images. We also discuss
possible ways of enhancing object detection probabilities for certain well
defined classes of objects by using various optimized linear combinations of
the pixel fluxes (optimal subspace filtering).Comment: 8 pages, 5 figures (4 postscript, 1 JPEG). To be published in A
Optimal multihump filter for photometric redshifts
We propose a novel type filter for multicolor imaging to improve on the
photometric redshift estimation of galaxies. An extra filter - specific to a
certain photometric system - may be utilized with high efficiency. We present a
case study of the Hubble Space Telescope's Advanced Camera for Surveys and show
that one extra exposure could cut down the mean square error on photometric
redshifts by 34% over the z<1.3 redshift range.Comment: 9 pages, 3 figures, LaTeX AASTeX, accepted to A
The National Virtual Observatory
As a scientific discipline, Astronomy is rather unique. We only have one
laboratory, the Universe, and we cannot, of course, change the initial
conditions and study the resulting effects. On top of this, acquiring
Astronomical data has historically been a very labor-intensive effort. As a
result, data has traditionally been preserved for posterity. With recent
technological advances, however, the rate at which we acquire new data has
grown exponentially, which has generated a Data Tsunami, whose wave train
threatens to overwhelm the field. In this conference proceedings, we present
and define the concept of virtual observatories, which we feel is the only
logical answer to this dilemma.Comment: 5 pages, uses newpasp.sty (included), to appear in "Extragalactic Gas
at Low Redshfit", ASP Conf. Series, J. S. Mulchaey and J. T. Stocke (eds.
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