1,221 research outputs found
Clustering of red Galaxies near the Radio-loud Quasar 1335.8+2834 at z=1.1
We have obtained new deep optical and near-infrared images of the field of
the radio-loud quasar 1335.8+2834 at where an excess in the surface
number density of galaxies was reported by Hutchings et al. [AJ, 106, 1324]
from optical data. We found a significant clustering of objects with very red
optical-near infrared colors, and near the quasar. The colors and magnitudes of the reddest objects
are consistent with those of old (12 Gyr old at z=0) passively-evolving
elliptical galaxies seen at , clearly defining a `red envelope' like
that found in galaxy clusters at similar or lower redshifts. This evidence
strongly suggests that the quasar resides in a moderately-rich cluster of
galaxies (richness-class ). There is also a relatively large fraction
of objects with moderately red colors () which have a
distribution on the sky similar to that of the reddest objects. They may be
interpreted as cluster galaxies with some recent or on-going star formation.Comment: 14 pages text, 5 PostScript figures, 1 GIF figure, and 1 combined PS
file. Accepted for ApJ, Letter
Dark Matter Halo Properties vs. Local Density and Cosmic Web Location
We study the effects of the local environmental density and the cosmic web
environment (filaments, walls, and voids) on key properties of dark matter
halos using the Bolshoi-Planck LCDM cosmological simulation. The z = 0
simulation is analysed into filaments, walls, and voids using the SpineWeb
method and also the VIDE package of tools, both of which use the watershed
transform. The key halo properties that we study are the specific mass
accretion rate, spin parameter, concentration, prolateness, scale factor of the
last major merger, and scale factor when the halo had half of its z = 0 mass.
For all these properties, we find that there is no discernible difference
between the halo properties in filaments, walls, or voids when compared at the
same environmental density. As a result, we conclude that environmental density
is the core attribute that affects these properties. This conclusion is in line
with recent findings that properties of galaxies in redshift surveys are
independent of their cosmic web environment at the same environmental density
at z ~ 0. We also find that the local web environment of the Milky Way and the
Andromeda galaxies near the centre of a cosmic wall does not appear to have any
effect on the properties of these galaxies' dark matter halos except for their
orientation, although we find that it is rather rare to have such massive halos
near the centre of a relatively small cosmic wall.Comment: 23 page
Economic Efficiency of Rice Farmers in a Rainfed Lowland Environment Before and During the Financial Crisis
IndonesianPenelitian ini bertujuan untuk menilai efisiensi ekonomi dari petani padi lahan sawah tadah hujan sebelum dan selama krisis ekonomi di Jawa Tengah. Data yang digunakan dalam analisis adalah panel data dari 90 petani responden yang mencakup musim tanam 1997 dan 1999. Teknik analisa yang digunakan adalah analisa pendapatan dan biaya, uji beda nilai tengah, dan analisa regresi. Hasil regresi dari fungsi keuntungan menunjukkan bahwa harga gabah, pupuk dan tenaga kerja secara statistik nyata pengaruhnya terhadap keuntungan USAhatani baik pada musim hujan maupun musim kemarau. Petani secara ekonomi ternyata lebih efisien dalam memproduksi padi selama krisis dari pada sebelum krisis ekonomi. Efisiensi ekonomi pada musim hujan ternyata lebih tinggi dari pada musim kemarau karena infestasi hama dan kompetisi gulma lebih rendah serta air cukup. Efisiensi ekonomi meningkat selama krisis ekonomi seiring dengan meningkatnya harga sarana produksi terutama pupuk, herbisida dan insektisida. Efisiensi ekonomi sangat dipengaruhi oleh tingkat pendidikan, krisis ekonomi, dan musim tanam. Pengalaman USAhatani, ukuran rumah tangga, dan status penguasaan lahan tidak nyata pengaruhnya terhadap efisiensi ekonomi.EnglishThis study assessed the economic efficiency of rainfed lowland rice farmers before and during the financial crisis in Central Java. Panel data from 90 farmers were gathered by means of a structured questionnaire covering the 1997 and 1999 crop seasons. The analytical techniques employed in this study were costs and returns analysis, statistical test of means, and regression analysis. Regression results of the unit profit model showed that the prices of rough rice, fertilizer and labor were statistically significant for both the wet season and the dry season. Regardless of cropping season, the farmers were more economically efficient in producing rice during the period of financial crisis than before the financial crisis. Economic efficiency in the wet season was higher than in the dry season because of lower pest infestation and weed competition and because of sufficient water supply. Economic efficiency was significantly affected by level of education, financial crisis and cropping season. It increased during the financial crisis despite the price increase of input factors, especially fertilizer, herbicide and insecticide. During the wet season, farmers were found to be more economically efficient than in the dry season. Farming experience, household size, and tenure status did not significantly affect farmers\u27 economic efficiency
How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging
We present the results of applying new object classification techniques to
difference images in the context of the Nearby Supernova Factory supernova
search. Most current supernova searches subtract reference images from new
images, identify objects in these difference images, and apply simple threshold
cuts on parameters such as statistical significance, shape, and motion to
reject objects such as cosmic rays, asteroids, and subtraction artifacts.
Although most static objects subtract cleanly, even a very low false positive
detection rate can lead to hundreds of non-supernova candidates which must be
vetted by human inspection before triggering additional followup. In comparison
to simple threshold cuts, more sophisticated methods such as Boosted Decision
Trees, Random Forests, and Support Vector Machines provide dramatically better
object discrimination. At the Nearby Supernova Factory, we reduced the number
of non-supernova candidates by a factor of 10 while increasing our supernova
identification efficiency. Methods such as these will be crucial for
maintaining a reasonable false positive rate in the automated transient alert
pipelines of upcoming projects such as PanSTARRS and LSST.Comment: 25 pages; 6 figures; submitted to Ap
A Rich Cluster of Galaxies Near the Quasar B2 1335+28 at z=1.1: Color Distribution and Star-Formation Properties
We previously reported a significant clustering of red galaxies (R-K=3.5--6)
around the radio-loud quasar B2 1335+28 at z=1.086. In this paper, we establish
the existence of a rich cluster at the quasar redshift, and study the
properties of the cluster galaxies through further detailed analysis of the
photometric data. The color distribution of the galaxies in the cluster is
quite broad and the fraction of blue galaxies (\sim 70%) is much larger than in
intermediate-redshift clusters. Using evolutionary synthesis models, we show
that this color distribution can be explained by galaxies with various amounts
of star-formation activity mixed with the old stellar populations. Notably,
there are about a dozen galaxies which show very red optical-NIR colors but
also show significant UV excess with respect to passive-evolution models. They
can be interpreted as old early-type galaxies with a small amount of star
formation. The fact that the UV-excess red galaxies are more abundant than the
quiescent red ones suggests that a large fraction of old galaxies in this
cluster are still forming stars to some extent. However, a sequence of
quiescent red galaxies is clearly identified on the R-K versus K
color-magnitude (C-M) diagram. The slope and zero point of their C-M relation
appear to be consistent with those expected for the precursors of the C-M
relation of present-day cluster ellipticals when observed at z=1.1. We estimate
the Abell richness class of the cluster to be R \sim 1. New X-ray data
presented here place an upper limit of L_x < 2 10^{44} erg s^{-1} for the
cluster luminosity. Inspections of the wider optical images reveal some lumpy
structure, suggesting that the whole system is still dynamically young.Comment: 54 pages including 13 Postscript figures, 1 jpg figure, and 1 table,
uses aasms4.sty and epsf.sty. Accepted for publication in ApJ: Replaced as
the older verison was missed to include the figure 2c, 2d, and figure
Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 < z < 0.9
(Abridged) We analyze photometry and spectroscopy of a sample of 63 clusters
at 0.3<z<0.9 drawn from the Las Campanas Distant Cluster Survey to empirically
constrain models of cluster galaxy evolution. Specifically, by combining data
on our clusters with those from the literature we parametrize the redshift
dependence of 1) M*_I in the observed frame; 2) the V-I color of the E/S0 red
sequence in the observed frames; and 3) the I-K' color of the E/S0 red sequence
in the observed frame. Using the peak surface brightness of the cluster
detection, S, as a proxy for cluster mass, we find no correlation between S and
M* or the location of the red envelope in V-I. We suggest that these
observations can be explained with a model in which luminous early type
galaxies (or more precisely, the progenitors of current day luminous early type
galaxies) form the bulk of their stellar populations at high redshift (>~ 5)
and in which many of these galaxies, if not all, accrete mass either in the
form of evolved stellar populations or gas that causes only a short term
episode of star formation at lower redshifts (1.5 < z < 2). Our data are too
crude to reach conclusions regarding the evolutionary state of any particular
cluster or to investigate whether the morphological evolution of galaxies
matches the simple scenario we discuss, but the statistical nature of this
study suggests that the observed evolutionary trends are universal in massive
clusters.Comment: 35 pages, accepted for publication in Ap
B3 0003+387: AGN Marked Large-Scale Structure at z=1.47?
We present evidence for a significant overdensity of red galaxies, as much as
a factor of 14 over comparable field samples, in the field of the z=1.47 radio
galaxy B3 0003+387. The colors and luminosities of the brightest red galaxies
are consistent with their being at z>0.8. The radio galaxy and one of the red
galaxies are separated by 5" and show some evidence of a possible interaction.
However, the red galaxies do not show any strong clustering around the radio
galaxy nor around any of the brighter red galaxies. The data suggest that we
are looking at a wall or sheet of galaxies, possibly associated with the radio
galaxy at z=1.47. Spectroscopic redshifts of these red galaxies will be
necessary to confirm this large-scale structure.Comment: 19 pages, 7 figures, LaTeX2e/AASTeX v5.0.2. The full photometric
catalog is included as a separate deluxetable file. To appear in the
Astronomical Journal (~Nov 00
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at =1.31, and a fifth lies in the foreground at
z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.Comment: 37 pages including 11 Postscript figures. To appear in the June 2000
issue of the Astronomical Journa
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