131 research outputs found
Understanding the faint red galaxy population using large-scale clustering measurements from SDSS DR7
We use data from the SDSS to investigate the evolution of the large-scale
galaxy bias as a function of luminosity for red galaxies. We carefully consider
correlation functions of galaxies selected from both photometric and
spectroscopic data, and cross-correlations between them, to obtain multiple
measurements of the large-scale bias. We find, for our most robust analyses, a
strong increase in bias with luminosity for the most luminous galaxies, an
intermediate regime where bias does not evolve strongly over a range of two
magnitudes in galaxy luminosity, and no evidence for an upturn in bias for
fainter red galaxies. Previous work has found an increase in bias to low
luminosities that has been widely interpreted as being caused by a strong
preference for red dwarf galaxies to be satellites in the most massive halos.
We can recover such an upturn in bias to faint luminosities if we push our
measurements to small scales, and include galaxy clustering measurements along
the line-of-sight, where we expect non-linear effects to be the strongest. The
results that we expect to be most robust suggest that the low luminosity
population of red galaxies is not dominated by satellite galaxies occupying the
most massive haloes.Comment: Matches version accepted by MNRA
Photometric Catalogue of Quasars and Other Point Sources in the Sloan Digital Sky Survey
We present a catalogue of about 6 million unresolved photometric detections
in the Sloan Digital Sky Survey Seventh Data Release classifying them into
stars, galaxies and quasars. We use a machine learning classifier trained on a
subset of spectroscopically confirmed objects from 14th to 22nd magnitude in
the SDSS {\it i}-band. Our catalogue consists of 2,430,625 quasars, 3,544,036
stars and 63,586 unresolved galaxies from 14th to 24th magnitude in the SDSS
{\it i}-band. Our algorithm recovers 99.96% of spectroscopically confirmed
quasars and 99.51% of stars to i 21.3 in the colour window that we study.
The level of contamination due to data artefacts for objects beyond is
highly uncertain and all mention of completeness and contamination in the paper
are valid only for objects brighter than this magnitude. However, a comparison
of the predicted number of quasars with the theoretical number counts shows
reasonable agreement.Comment: 16 pages, Ref. No. MN-10-2382-MJ.R2, accepted for publication in
MNRAS Main Journal, April 201
The Cluster Mass Function from Early SDSS Data: Cosmological Implications
The mass function of clusters of galaxies is determined from 400 deg^2 of
early commissioning imaging data of the Sloan Digital Sky Survey; ~300 clusters
in the redshift range z = 0.1 - 0.2 are used. Clusters are selected using two
independent selection methods: a Matched Filter and a red-sequence color
magnitude technique. The two methods yield consistent results. The cluster mass
function is compared with large-scale cosmological simulations. We find a
best-fit cluster normalization relation of sigma_8*omega_m^0.6 = 0.33 +- 0.03
(for 0.1 ~< omega_m ~< 0.4), or equivalently sigma_8 = (0.16/omega_m)^0.6. The
amplitude of this relation is significantly lower than the previous canonical
value, implying that either omega_m is lower than previously expected (omega_m
= 0.16 if sigma_8 = 1) or sigma_8 is lower than expected (sigma_8 = 0.7 if
omega_m = 0.3). The best-fit mass function parameters are omega_m = 0.19
(+0.08,-0.07) and sigma_8 = 0.9 (+0.3,-0.2). High values of omega_m (>= 0.4)
and low sigma_8 (=~ 2 sigma.Comment: AASTeX, 25 pages, including 7 figures, accepted for publication in
ApJ, vol.585, March 200
Linking human tick bite risk with tick abundance in the environment: a novel approach to quantify tick bite risk using orienteers in Scotland
The rate that people are bitten by ticks is critical in determining the risk of tick-borne infections but is rarely quantified accurately. Often tick abundance in the environment is used as a proxy for tick bite risk, but the relationship with risk is poorly understood. We used a novel citizen science approach to measure tick bite rate in orienteers, to assess the relationship between tick abundance and tick bite risk and to identify risk factors for tick bites. Eleven orienteering events were attended in Scotland between August 2018 and September 2019. The number of tick bites in orienteers, and the time and distance of activity were collected using an online questionnaire. Tick abundance in the same areas used for the orienteering events was estimated by surveying ticks on ground vegetation using blanket drags. Among orienteers, mean incidence was 409 tick bites per 1,000 person-hours. Tick abundance and tick bite rate were strongly correlated, indicating that data from questing tick surveys is a useful proxy for the risk of human tick bites. Tick bite rate was better explained by the activity duration than distance covered and was higher in orienteers that ran earlier in the day, exposed to higher temperatures and in woodland habitats. This study highlights the value of the citizen science approach used, which crucially included submission of activity reports both with and without ticks, to generate robust data on tick bite rate. Accurately measuring tick bite rate and understanding environmental factors that influence it are essential in mitigating the risk of tick-borne diseases
A Merged Catalog of Clusters of Galaxies from Early SDSS Data
We present a catalog of 799 clusters of galaxies in the redshift range z_est
= 0.05 - 0.3 selected from ~400 deg^2 of early SDSS commissioning data along
the celestial equator. The catalog is based on merging two independent
selection methods -- a color-magnitude red-sequence maxBCG technique (B), and a
Hybrid Matched-Filter method (H). The BH catalog includes clusters with
richness \Lambda >= 40 (Matched-Filter) and N_gal >= 13 (maxBCG), corresponding
to typical velocity dispersion of \sigma_v >~ 400 km s^{-1} and mass (within
0.6 h^{-1) Mpc radius) >~ 5*10^{13} h^{-1} M_sun. This threshold is below Abell
richness class 0 clusters. The average space density of these clusters is
2*10^{-5} h^3 Mpc^{-3}. All NORAS X-ray clusters and 53 of the 58 Abell
clusters in the survey region are detected in the catalog; the 5 additional
Abell clusters are detected below the BH catalog cuts. The cluster richness
function is determined and found to exhibit a steeply decreasing cluster
abundance with increasing richness. We derive observational scaling relations
between cluster richness and observed cluster luminosity and cluster velocity
dispersion; these scaling relations provide important physical calibrations for
the clusters. The catalog can be used for studies of individual clusters, for
comparisons with other sources such as X-ray clusters and AGNs, and, with
proper correction for the relevant selection functions, also for statistical
analyses of clusters.Comment: AASTeX, 62 pages, including 14 figures and 4 tables, submitted to
ApJS. Paper with full-resolution figures at
http://astro.princeton.edu/~feng/sdss_cluster.p
The Morphology of Galaxies in the Baryon Oscillation Spectroscopic Survey
We study the morphology of luminous and massive galaxies at 0.3<z<0.7
targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly
available Hubble Space Telescope imaging from COSMOS. Our sample (240 objects)
provides a unique opportunity to check the visual morphology of these galaxies
which were targeted based solely on stellar population modelling. We find that
the majority (74+/-6%) possess an early-type morphology (elliptical or S0),
while the remainder have a late-type morphology. This is as expected from the
goals of the BOSS target selection which aimed to predominantly select slowly
evolving galaxies, for use as cosmological probes, while still obtaining a fair
fraction of actively star forming galaxies for galaxy evolution studies. We
show that a colour cut of (g-i)>2.35 selects a sub-sample of BOSS galaxies with
90% early-type morphology - more comparable to the earlier Luminous Red Galaxy
(LRG) samples of SDSS-I/II. The remaining 10% of galaxies above this cut have a
late-type morphology and may be analogous to the "passive spirals" found at
lower redshift. We find that 23+/-4% of the early-type galaxies are unresolved
multiple systems in the SDSS imaging. We estimate that at least 50% of these
are real associations (not projection effects) and may represent a significant
"dry merger" fraction. We study the SDSS pipeline sizes of BOSS galaxies which
we find to be systematically larger (by 40%) than those measured from HST
images, and provide a statistical correction for the difference. These details
of the BOSS galaxies will help users of the data fine-tune their selection
criteria, dependent on their science applications. For example, the main goal
of BOSS is to measure the cosmic distance scale and expansion rate of the
Universe to percent-level precision - a point where systematic effects due to
the details of target selection may become important.Comment: 18 pages, 11 figures; v2 as accepted by MNRA
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