58 research outputs found
A multiscale approach to environment
Physical processes influencing the properties of galaxies can be traced by
the dependence and evolution of galaxy properties on their environment. A
detailed understanding of this dependence can only be gained through comparison
of observations with models, with an appropriate quantification of the rich
parameter space describing the environment of the galaxy. We present a new,
multiscale parameterization of galaxy environment which retains an
observationally motivated simplicity whilst utilizing the information present
on different scales. We examine how the distribution of galaxy (u-r) colours in
the Sloan Digital Sky Survey (SDSS), parameterized using a double gaussian (red
plus blue peak) fit, depends upon multiscale density. This allows us to probe
the detailed dependence of galaxy properties on environment in a way which is
independent of the halo model. Nonetheless, cross-correlation with the group
catalogue constructed by Yang et al, 2007 shows that galaxy properties trace
environment on different scales in a way which mimics that expected within the
halo model. This provides independent support for the existence of virialized
haloes, and important additional clues to the role played by environment in the
evolution of the galaxy population. This work is described in full by Wilman et
al., 2010, MNRAS, acceptedComment: A brief summary of the work presented by Wilman et al., 2010, MNRAS,
accepted; LaTeX, 4 pages, 2 figures. To appear in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista & C.C. Popescu, AIP Conference Serie
Searchable Sky Coverage of Astronomical Observations: Footprints and Exposures
Sky coverage is one of the most important pieces of information about
astronomical observations. We discuss possible representations, and present
algorithms to create and manipulate shapes consisting of generalized spherical
polygons with arbitrary complexity and size on the celestial sphere. This shape
specification integrates well with our Hierarchical Triangular Mesh indexing
toolbox, whose performance and capabilities are enhanced by the advanced
features presented here. Our portable implementation of the relevant spherical
geometry routines comes with wrapper functions for database queries, which are
currently being used within several scientific catalog archives including the
Sloan Digital Sky Survey, the Galaxy Evolution Explorer and the Hubble Legacy
Archive projects as well as the Footprint Service of the Virtual Observatory.Comment: 11 pages, 7 figures, submitted to PAS
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
Objective Identification of Informative Wavelength Regions in Galaxy Spectra
Understanding the diversity in spectra is the key to determining the physical
parameters of galaxies. The optical spectra of galaxies are highly convoluted
with continuum and lines which are potentially sensitive to different physical
parameters. Defining the wavelength regions of interest is therefore an
important question. In this work, we identify informative wavelength regions in
a single-burst stellar populations model by using the CUR Matrix Decomposition.
Simulating the Lick/IDS spectrograph configuration, we recover the widely used
Dn(4000), Hbeta, and HdeltaA to be most informative. Simulating the SDSS
spectrograph configuration with a wavelength range 3450-8350 Angstrom and a
model-limited spectral resolution of 3 Angstrom, the most informative regions
are: first region-the 4000 Angstrom break and the Hdelta line; second
region-the Fe-like indices; third region-the Hbeta line; fourth region-the G
band and the Hgamma line. A Principal Component Analysis on the first region
shows that the first eigenspectrum tells primarily the stellar age, the second
eigenspectrum is related to the age-metallicity degeneracy, and the third
eigenspectrum shows an anti-correlation between the strengths of the Balmer and
the Ca K and H absorptions. The regions can be used to determine the stellar
age and metallicity in early-type galaxies which have solar abundance ratios,
no dust, and a single-burst star formation history. The region identification
method can be applied to any set of spectra of the user's interest, so that we
eliminate the need for a common, fixed-resolution index system. We discuss
future directions in extending the current analysis to late-type galaxies.Comment: 36 Pages, 13 Figures, 4 Tables. AJ Accepte
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