464 research outputs found
Galaxy groups in the 2dF redshift survey: The catalogue
We construct a galaxy groups catalogue from the public 100K data release of
the 2dF galaxy redshift survey. The group identification is carried out using a
slightly modified version of the group finding algorithm developed by Huchra &
Geller. Several tests using mock catalogues allow us to find the optimal
conditions to increase the reliability of the final group sample. A minimum
number of 4 members, an outer number density enhancement of 80 and a linking
radial cutoff of , are the best obtained values from the
analysis. Using these parameters, approximately 90% of groups identified in
real space have a redshift space counterpart. On the other hand the level of
contamination in redshift space reaches to 30 % including a of
artificial groups and of groups associated with binaries or triplets
in real space. The final sample comprise 2209 galaxy groups covering the sky
region described by Colless et al. spanning over the redshift range of with a mean redshift of 0.1.Comment: Accepted for publication in the MNRAS. 8 figures 8 page
Methods for Rapidly Processing Angular Masks of Next-Generation Galaxy Surveys
As galaxy surveys become larger and more complex, keeping track of the
completeness, magnitude limit, and other survey parameters as a function of
direction on the sky becomes an increasingly challenging computational task.
For example, typical angular masks of the Sloan Digital Sky Survey contain
about N=300,000 distinct spherical polygons. Managing masks with such large
numbers of polygons becomes intractably slow, particularly for tasks that run
in time O(N^2) with a naive algorithm, such as finding which polygons overlap
each other. Here we present a "divide-and-conquer" solution to this challenge:
we first split the angular mask into predefined regions called "pixels," such
that each polygon is in only one pixel, and then perform further computations,
such as checking for overlap, on the polygons within each pixel separately.
This reduces O(N^2) tasks to O(N), and also reduces the important task of
determining in which polygon(s) a point on the sky lies from O(N) to O(1),
resulting in significant computational speedup. Additionally, we present a
method to efficiently convert any angular mask to and from the popular HEALPix
format. This method can be generically applied to convert to and from any
desired spherical pixelization. We have implemented these techniques in a new
version of the mangle software package, which is freely available at
http://space.mit.edu/home/tegmark/mangle/, along with complete documentation
and example applications. These new methods should prove quite useful to the
astronomical community, and since mangle is a generic tool for managing angular
masks on a sphere, it has the potential to benefit terrestrial mapmaking
applications as well.Comment: New version 2.1 of the mangle software now available at
http://space.mit.edu/home/tegmark/mangle/ - includes galaxy survey masks and
galaxy lists for the latest SDSS data release and the 2dFGRS final data
release as well as extensive documentation and examples. 14 pages, 9 figures,
matches version accepted by MNRA
ESO Imaging Survey: Infrared Deep Public Survey
This paper presents new J and Ks data obtained from observations conducted at
the ESO 3.5m New Technology Telescope using the SOFI camera. These data were
taken as part of the ESO Imaging Survey Deep Public Survey (DPS) and
significantly extend the earlier optical/infrared EIS-DEEP survey presented in
a previous paper. The DPS-IR survey comprises two observing strategies: shallow
Ks observations providing nearly full coverage of pointings with complementary
multi-band optical data and deeper J and Ks observations of the central parts
of these fields. The DPS-IR survey provides a coverage of roughly 2.1 square
degrees in Ks with 0.63 square degrees to fainter magnitudes and also covered
in J, over three independent regions of the sky. The goal of the present paper
is to describe the observations, the data reduction procedures, and to present
the final survey products. The astrometric solution with an estimated accuracy
of <0.15" is based on the USNO catalog. The final stacked images presented here
number 89 and 272, in J and Ks, respectively, the latter reflecting the larger
surveyed area. The J and Ks images were taken with a median seeing of 0.77" and
0.8". The images reach a median 5sigma limiting magnitude of J_AB~23.06 in an
aperture of 2", while the corresponding limiting magnitude in Ks_AB is ~21.41
and ~22.16 mag for the shallow and deep strategies. Overall, the observed
limiting magnitudes are consistent with those originally proposed. The quality
of the data has been assessed by comparing the measured magnitude of sources at
the bright end directly with those reported by the 2MASS survey and at the
faint end by comparing the counts of galaxies and stars with those of other
surveys to comparable depth and to model predictions. The final science-grade
catalogs and images are available at CDS.Comment: Accepted for publication in A&A, 14 pages, 8 figures, a full
resolution version of the paper is available from
http://www.astro.ku.dk/~lisbeth/eisdata/papers/5019.pd
AGN Environments in the Sloan Digital Sky Survey I: Dependence on Type, Redshift, and Luminosity
We explore how the local environment is related to the redshift, type, and
luminosity of active galactic nuclei (AGN). Recent simulations and observations
are converging on the view that the extreme luminosity of quasars is fueled in
major mergers of gas-rich galaxies. In such a picture, quasars are expected to
be located in regions with a higher density of galaxies on small scales where
mergers are more likely to take place. However, in this picture, the activity
observed in low-luminosity AGN is due to secular processes that are less
dependent on the local galaxy density. To test this hypothesis, we compare the
local photometric galaxy density on kiloparsec scales around spectroscopic Type
I and Type II quasars to the local density around lower luminosity
spectroscopic Type I and Type II AGN. To minimize projection effects and
evolution in the photometric galaxy sample we use to characterize AGN
environments, we place our random control sample at the same redshift as our
AGN and impose a narrow redshift window around both the AGN and control
targets. We find that higher luminosity AGN have more overdense environments
compared to lower luminosity AGN on all scales out to our 2\Mpchseventy
limit. Additionally, in the range , Type II
quasars have similarly overdense environments to those of bright Type I quasars
on all scales out to our 2\Mpchseventy limit, while the environment of dimmer
Type I quasars appears to be less overdense than the environment of Type II
quasars. We see increased overdensity for Type II AGN compared to Type I AGN on
scales out to our limit of 2\Mpchseventy in overlapping redshift ranges. We
also detect marginal evidence for evolution in the number of galaxies within
2\Mpchseventy of a quasar with redshift.Comment: 30 pages, 9 figures. Major revisions made for current version. Some
content in previous version has been removed to refocus content on redshift
and type effects. This content will be deferred to later work
The dust budget crisis in high-redshift submillimetre galaxies
We apply a chemical evolution model to investigate the sources and evolution of dust in a sample of 26 high-redshift (z > 1) submillimetre galaxies (SMGs) from the literature, with complete photometry from ultraviolet to the submillimetre. We show that dust produced only by low–intermediate-mass stars falls a factor 240 short of the observed dust masses of SMGs, the well-known ‘dust-budget crisis’. Adding an extra source of dust from supernovae can account for the dust mass in 19 per cent of the SMG sample. Even after accounting for dust produced by supernovae the remaining deficit in the dust mass budget provides support for higher supernova yields, substantial grain growth in the interstellar medium or a top-heavy IMF. Including efficient destruction of dust by supernova shocks increases the tension between our model and observed SMG dust masses. The models which best reproduce the physical properties of SMGs have a rapid build-up of dust from both stellar and interstellar sources and minimal dust destruction. Alternatively, invoking a top-heavy IMF or significant changes in the dust grain properties can solve the dust budget crisis only if dust is produced by both low-mass stars and supernovae and is not efficiently destroyed by supernova shocks
Nature and Environment of Very Luminous Galaxies
The most luminous galaxies in the blue passband have a larger correlation
amplitude than L* galaxies. They do not appear to be preferentially located in
rich clusters or groups, but a significant fraction of them seem to be in
systems which include fainter members.We present an analysis of fields centered
on 18 Very Luminous Galaxies (MB < -21) selected from the Southern Sky Redshift
Survey 2, based on new observations and public data of the 2dF Galaxy Redshift
Survey; we present also additional data on a CfA VLG and on Arp 127. We find
that all the selected VLGs are physically associated to fainter companions.
Moreover, there is a relation between the VLG morphology (early or late) and
the dynamical properties of the system, which reflects the morphology-density
relation. 6 out of the 18 SSRS2 VLGs are early type galaxies: 2 are in the
center of rich Abell clusters with velocity dispersion sigma ~600 km/s, and the
other 4 are in poor clusters or groups with sigma ~300. The VLG extracted from
the CfA catalog is also an elliptical in a Zwicky cluster. The remaining 2/3 of
the sample are late-type VLGs, generally found in poorer systems with a larger
spread in velocity dispersion, from ~100 up to ~750 km/s. The low velocity
dispersion, late-type VLG dominated systems appear to be the analogous of our
own Local Group. The possibile association of VLG systems to dark matter halos
with mass comparable to rich groups or clusters, as suggested by the comparable
correlation amplitude, would imply significant differences in the galaxy
formation process. This work also shows that observing fields around VLGs
represents an effective way of identifying galaxy systems which are not
selected through other traditional techniques.Comment: 21 pages, A&A, in pres
Ultrastructure of Sheep Primordial Follicles Cultured in the Presence of Indol Acetic Acid, EGF, and FSH
The aim of this study was to investigate the ultrastructural characteristics of primordial follicles after culturing of sheep ovarian cortical slices in the presence of indol acetic acid (IAA), Epidermal Growth Factor (EGF), and FSH. To evaluate ultrastructure of primordial follicles cultured in MEM (control) or in MEM containing IAA, EGF, and FSH, fragments of cultured tissue were processes for transmission electron microscopy. Except in the control, primordial follicles cultured in supplemented media for 6 d were ultrastructurally normal. They had oocyte with intact nucleus and the cytoplasm contained heterogeneous-sized lipid droplets and numerous round or elongated mitochondria with intact parallel cristae were observed. Rough endoplasmic reticulum (RER) was rarely found. The granulosa cells cytoplasm contained a great number of mitochondria and abundant RER. In conclusion, the presence of IAA, EGF, and FSH helped to maintain ultrastructural integrity of sheep primordial follicles cultured in vitro
Scale-invariance of galaxy clustering
Some years ago we proposed a new approach to the analysis of galaxy and
cluster correlations based on the concepts and methods of modern statistical
Physics. This led to the surprising result that galaxy correlations are fractal
and not homogeneous up to the limits of the available catalogs. The usual
statistical methods, which are based on the assumption of homogeneity, are
therefore inconsistent for all the length scales probed so far, and a new, more
general, conceptual framework is necessary to identifythe real physical
properties of these structures. In the last few years the 3-d catalogs have
been significatively improved and we have extended our methods to the analysis
of number counts and angular catalogs. This has led to a complete analysis of
all the available data that we present in this review. The result is that
galaxy structures are highly irregular and self-similar: all the available data
are consistent with each other and show fractal correlations (with dimension ) up to the deepest scales probed so far (1000 \hmp) and even more
as indicated from the new interpretation of the number counts. The evidence for
scale-invariance of galaxy clustering is very strong up to 150 \hmp due to
the statistical robustness of the data but becomes progressively weaker
(statistically) at larger distances due to the limited data. In These facts
lead to fascinating conceptual implications about our knowledge of the universe
and to a new scenario for the theoretical challenge in this field.Comment: Latex file 165 pages, 106 postscript figures. This paper is also
available at http://www.phys.uniroma1.it/DOCS/PIL/pil.html To appear in
Physics Report (Dec. 1997
The architecture of Abell 1386 and its relationship to the Sloan Great Wall
We present new radial velocities from AAOmega on the Anglo-Australian
Telescope for 307 galaxies (b_J < 19.5) in the region of the rich cluster Abell
1386. Consistent with other studies of galaxy clusters that constitute
sub-units of superstructures, we find that the velocity distribution of A1386
is very broad (21,000--42,000 kms^-1, or z=0.08--0.14) and complex. The mean
redshift of the cluster that Abell designated as number 1386 is found to be
~0.104. However, we find that it consists of various superpositions of
line-of-sight components. We investigate the reality of each component by
testing for substructure and searching for giant elliptical galaxies in each
and show that A1386 is made up of at least four significant clusters or groups
along the line of sight whose global parameters we detail. Peculiar velocities
of brightest galaxies for each of the groups are computed and found to be
different from previous works, largely due to the complexity of the sky area
and the depth of analysis performed in the present work. We also analyse A1386
in the context of its parent superclusters: Leo A, and especially the Sloan
Great Wall. Although the new clusters may be moving toward mass concentrations
in the Sloan Great Wall or beyond, many are most likely not yet physically
bound to it.Comment: 21 pages, 9 figures, includes the full appendix table. Accepted for
publication in MNRA
International Collaborative Partnership for the Study of Atrial Fibrillation (INTERAF): Rationale, Design, and Initial Descriptives.
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