1,519 research outputs found
The Angular Power Spectra of Photometric SDSS LRGs
We construct new galaxy angular power spectra based on the extended, updated
and final SDSS II Luminous Red Galaxy (LRG) photometric redshift survey: MegaZ
DR7. Encapsulating 7746 deg^{2} we utilise 723,556 photometrically determined
LRGs between 0.45 < z < 0.65 in a 3.3 (Gpc h^{-1})^3 spherical harmonic
analysis of the galaxy distribution. By combining four photometric redshift
bins we find preliminary parameter constraints of f_{b} = \Omega_{b}/\Omega_{m}
= 0.173 +/- 0.046 and \Omega_{m} = 0.260 +/- 0.035 assuming H_{0} = 75 km
s^{-1} Mpc^{-1}, n_{s}=1 and \Omega_{k} = 0. These limits are consistent with
the CMB and the previous data release (DR4). The C_{\ell} are sensitive to
redshift space distortions and therefore we also recast our constraints into a
measurement of \beta ~ \Omega_{m}^{0.55}/b in different redshift shells. The
robustness of these power spectra with respect to a number of potential
systematics such as extinction, photometric redshift and ANNz training set
extrapolation are examined. The latter includes a cosmological comparison of
available photometric redshift estimation codes where we find excellent
agreement between template and empirical estimation methods. MegaZ DR7
represents a methodological prototype to next generation surveys such as the
Dark Energy Survey (DES) and, furthermore, is a photometric precursor to the
spectroscopic BOSS survey. Our galaxy catalogue and all power spectra data can
be found at http://zuserver2.star.ucl.ac.uk/~sat/MegaZ/MegaZDR7.tar.gz.Comment: MNRAS Accepted: 20 pages - Galaxy catalogue and power spectra
included onlin
Dissecting the Red Sequence--II. Star Formation Histories of Early-Type Galaxies Throughout the Fundamental Plane
This analysis uses spectra of ~16,000 nearby SDSS quiescent galaxies to track
variations in galaxy star formation histories along and perpendicular to the
Fundamental Plane (FP). We sort galaxies by their FP properties (sigma, R_e,
and I_e) and construct high S/N mean galaxy spectra that span the breadth and
thickness of the FP. From these spectra, we determine mean luminosity-weighted
ages, [Fe/H], [Mg/H], and [Mg/Fe] based on single stellar population models
using the method described in Graves & Schiavon (2008). In agreement with
previous work, the star formation histories of early-type galaxies are found to
form a two-parameter family. The major trend is that mean age, [Fe/H], [Mg/H],
and [Mg/Fe] all increase with sigma. However, no stellar population property
shows any dependence on R_e at fixed sigma, suggesting that sigma and not
dynamical mass (M_dyn ~ sigma^2 R_e) is the better predictor of past star
formation history. In addition to the main trend with sigma, galaxies also show
a range of population properties at fixed sigma that are strongly correlated
with surface brightness residuals from the FP, such that higher surface
brightness galaxies have younger mean ages, higher [Fe/H], higher [Mg/H], and
lower [Mg/Fe] than lower-surface brightness galaxies. These latter trends are a
major new constraint on star-formation histories.Comment: 23 pages, 14 figures. Accepted to Ap
Measuring Redshift-Space Distortions using Photometric Surveys
We outline how redshift-space distortions (RSD) can be measured from the
angular correlation function w({\theta}), of galaxies selected from photometric
surveys. The natural degeneracy between RSD and galaxy bias can be minimized by
comparing results from bins with top-hat galaxy selection in redshift, and bins
based on the radial position of galaxy pair centres. This comparison can also
be used to test the accuracy of the photometric redshifts. The presence of RSD
will be clearly detectable with the next generation of photometric redshift
surveys. We show that the Dark Energy Survey (DES) will be able to measure
f(z){\sigma}_8(z) to a 1{\sigma} accuracy of (17 {\times} b)%, using galaxies
drawn from a single narrow redshift slice centered at z = 1. Here b is the
linear bias, and f is the logarithmic rate of change of the linear growth rate
with respect to the scale factor. Extending to measurements of w({\theta}) for
a series of bins of width 0.02(1 + z) over 0.5 < z < 1.4 will measure {\gamma}
to a 1{\sigma} accuracy of 25%, given the model f = {\Omega}_m(z)^{\gamma}, and
assuming a linear bias model that evolves such that b = 0.5 + z (and fixing
other cosmological parameters). The accuracy of our analytic predictions is
confirmed using mock catalogs drawn from simulations conducted by the MICE
collaboration.Comment: Accepted by MNRAS, revisions include fixing of typos and
clarification of the tex
The stellar evolution of Luminous Red Galaxies, and its dependence on colour, redshift, luminosity and modelling
We present a series of colour evolution models for Luminous Red Galaxies
(LRGs) in the 7th spectroscopic data release of the Sloan Digital Sky Survey
(SDSS), computed using the full-spectrum fitting code VESPA on high
signal-to-noise stacked spectra. The colour-evolution models are computed as a
function of colour, luminosity and redshift, and we do not a-priori assume that
LRGs constitute a uniform population of galaxies in terms of stellar evolution.
By computing star-formation histories from the fossil record, the measured
stellar evolution of the galaxies is decoupled from the survey's selection
function, which also evolves with redshift. We present these evolutionary
models computed using three different sets of Stellar Population Synthesis
(SPS) codes. We show that the traditional fiducial model of purely passive
stellar evolution of LRGs is broadly correct, but it is not sufficient to
explain the full spectral signature. We also find that higher-order corrections
to this model are dependent on the SPS used, particularly when calculating the
amount of recent star formation. The amount of young stars can be
non-negligible in some cases, and has important implications for the
interpretation of the number density of LRGs within the selection box as a
function of redshift. Dust extinction, however, is more robust to the SPS
modelling: extinction increases with decreasing luminosity, increasing
redshift, and increasing r-i colour. We are making the colour evolution tracks
publicly available at http://www.icg.port.ac.uk/~tojeiror/lrg_evolution/.Comment: 29 pages, 34 figures, re-submitted to MNRAS after addressing the
referee's repor
Interpreting large-scale redshift-space distortion measurements
The simplest theory describing large-scale redshift-space distortions (RSD),
based on linear theory and distant galaxies, depends on the growth of
cosmological structure, suggesting that strong tests of General Relativity can
be constructed from galaxy surveys. As data sets become larger and the expected
constraints more precise, the extent to which the RSD follow the simple theory
needs to be assessed in order that we do not introduce systematic errors into
the tests by introducing inaccurate simplifying assumptions. We study the
impact of the sample geometry, non-linear processes, and biases induced by our
lack of understanding of the radial galaxy distribution on RSD measurements.
Using LasDamas simulations of the Sloan Digital Sky Survey II (SDSS-II)
Luminous Red Galaxy (LRG) data, these effects are shown to be important at the
level of 20 per cent. Including them, we can accurately model the recovered
clustering in these mock catalogues on scales 30 -- 200 Mpc/h. Applying this
analysis to robustly measure parameters describing the growth history of the
Universe from the SDSS-II data, gives
and
when no prior is imposed on the
growth-rate, and the background geometry is assumed to follow a CDM
model with the WMAP + SNIa priors. The standard WMAP constrained CDM
model with General Relativity predicts
and
, which is fully consistent with
these measurements.Comment: 20 pages, 17 figures, 1 tabl
Stellar Population Trends in S0 Galaxies
We present stellar population age and metallicity trends for a sample of 59
S0 galaxies based on optical SDSS and NIR J & H photometry. When combined with
optical g and r passband imaging data from the SDSS archive and stellar
population models, we obtain radial age and metallicity trends out to at least
5 effective radii for most of the galaxies in our sample. The sample covers a
range in stellar mass and light concentration. We find an average central
light-weighted age of ~ 4 Gyr and central metallicity [Z/H] ~ 0.2 dex. Almost
all galaxies show a negative metallicity gradient from the center out, with an
average value of Delta[Z/H]/Delta(log(r/Re)) = -0.6. An age increase, decrease,
and minimal change with radius is observed for 58%, 19%, and 23%, respectively,
for a mean age gradient of Delta(age)/Delta(log(r/Re)) = 2.3 Gyr dex^{-1}. For
14 out of 59 galaxies, the light-weighted age of the outer region is greater
than 10 Gyr. We find that galaxies with both lower mass and lower concentration
have younger light-weighted ages and lower light-weighted metallicities. This
mass-metallicity relation extends into the outer regions of our S0 galaxies.
Our results are consistent with the formation of S0 galaxies through the
transformation of spiral galaxy disks. Determining the structural component
that makes up the outer region of galaxies with old outksirts is a necessary
step to understand the formation history of S0 galaxies.Comment: accepted to MNRA
The Sol Genomics Network (SGN)--from genotype to phenotype to breeding
The Sol Genomics Network (SGN, http://solgenomics.net) is a web portal with genomic and phenotypic data, and analysis tools for the Solanaceae family and close relatives. SGN hosts whole genome data for an increasing number of Solanaceae family members including tomato, potato, pepper, eggplant, tobacco and Nicotiana benthamiana. The database also stores loci and phenotype data, which researchers can upload and edit with user-friendly web interfaces. Tools such as BLAST, GBrowse and JBrowse for browsing genomes, expression and map data viewers, a locus community annotation system and a QTL analysis tools are available. A new tool was recently implemented to improve Virus-Induced Gene Silencing (VIGS) constructs called the SGN VIGS tool. With the growing genomic and phenotypic data in the database, SGN is now advancing to develop new web-based breeding tools and implement the code and database structure for other species or clade-specific databases.Peer reviewe
Hubble Space Telescope studies of low-redshift Type Ia supernovae: Evolution with redshift and ultraviolet spectral trends
We present an analysis of the maximum light, near ultraviolet (NUV; 2900-5500
A) spectra of 32 low redshift (0.001<z<0.08) Type Ia supernovae (SNe Ia),
obtained with the Hubble Space Telescope (HST). We combine this spectroscopic
sample with high-quality gri light curves obtained with robotic telescopes to
measure photometric parameters, such as stretch, optical colour, and
brightness. By comparing our data to a comparable sample of SNe Ia at
intermediate-z (0.4<z<0.9), we detect modest spectral evolution (3-sigma), in
the sense that our mean low-z NUV spectrum has a depressed flux compared to its
intermediate-z counterpart. We also see a strongly increased dispersion about
the mean with decreasing wavelength, confirming the results of earlier surveys.
These trends are consistent with changes in metallicity as predicted by
contemporary SN Ia spectral models. We also examine the properties of various
NUV spectral diagnostics in the individual spectra. We find a general
correlation between stretch and the velocity (or position) of many NUV spectral
features. In particular, we observe that higher stretch SNe have larger Ca II
H&K velocities, that also correlate with host galaxy stellar mass. This latter
trend is probably driven by the well-established correlation between stretch
and stellar mass. We find no trends between UV spectral features and optical
colour. Mean spectra constructed according to whether the SN has a positive or
negative Hubble residual show very little difference at NUV wavelengths,
indicating that the NUV evolution and variation we identify do not directly
correlate with Hubble residuals. Our work confirms and strengthens earlier
conclusions regarding the complex behaviour of SNe Ia in the NUV spectral
region, but suggests the correlations we find are more useful in constraining
progenitor models than improving the use of SNe Ia as cosmological probes.Comment: 22 pages, 14 figures, accepted in MNRAS with minor changes - Spectra
are available on WISeREP, http://www.weizmann.ac.il/astrophysics/wiserep
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measurements of the growth of structure and expansion rate at z=0.57 from anisotropic clustering
We analyze the anisotropic clustering of massive galaxies from the Sloan
Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (BOSS) Data
Release 9 (DR9) sample, which consists of 264,283 galaxies in the redshift
range 0.43 < z < 0.7 spanning 3,275 square degrees. Both peculiar velocities
and errors in the assumed redshift-distance relation ("Alcock-Paczynski
effect") generate correlations between clustering amplitude and orientation
with respect to the line-of-sight. Together with the sharp baryon acoustic
oscillation (BAO) standard ruler, our measurements of the broadband shape of
the monopole and quadrupole correlation functions simultaneously constrain the
comoving angular diameter distance (2190 +/- 61 Mpc) to z=0.57, the Hubble
expansion rate at z=0.57 (92.4 +/- 4.5 km/s/Mpc), and the growth rate of
structure at that same redshift (d sigma8/d ln a = 0.43 +/- 0.069). Our
analysis provides the best current direct determination of both DA and H in
galaxy clustering data using this technique. If we further assume a LCDM
expansion history, our growth constraint tightens to d sigma8/d ln a = 0.415
+/- 0.034. In combination with the cosmic microwave background, our
measurements of DA, H, and growth all separately require dark energy at z >
0.57, and when combined imply \Omega_{\Lambda} = 0.74 +/- 0.016, independent of
the Universe's evolution at z<0.57. In our companion paper (Samushia et al.
prep), we explore further cosmological implications of these observations.Comment: 19 pages, 11 figures, submitted to MNRAS, comments welcom
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
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