206 research outputs found
Detection of Non-Random Galaxy Orientations in X-ray Subclusters of the Coma Cluster
This study on the Coma cluster suggests that there are deviations from a
completely random galaxy orientation on small scales. Since we found a
significant coincidence of hot-gas features identified in the latest X-ray
observations of Coma with these local anisotropies, they may indicate regions
of recent mutual interaction of member galaxies within subclusters which are
currently falling in on the main cluster.Comment: 4 pages, 4 figures, 3 tables v2: Rewritten introduction, amendments
to the 'Interpretation' sectio
Optical Spectroscopy of IRAS 02091+6333
We present a detailed spectroscopic investigation, spanning four winters, of
the asymptotic giant branch (AGB) star IRAS 02091+6333. Zijlstra & Weinberger
(2002) found a giant wall of dust around this star and modelled this unique
phenomenon. However their work suffered from the quality of the optical
investigations of the central object. Our spectroscopic investigation allowed
us to define the spectral type and the interstellar foreground extinction more
precisely. Accurate multi band photometry was carried out. This provides us
with the possibility to derive the physical parameters of the system. The
measurements presented here suggest a weak irregular photometric variability of
the target, while there is no evidence of a spectroscopic variability over the
last four years.Comment: 5 pages, Latex, 3 tables, 4 figures, Astron. & Astrophys. - in pres
Masses for the Local Group and the Milky Way
We use the very large Millennium Simulation of the concordance CDM
cosmogony to calibrate the bias and error distribution of Timing Argument
estimators of the masses of the Local Group and of the Milky Way. From a large
number of isolated spiral-spiral pairs similar to the Milky Way/Andromeda
system, we find the interquartile range of the ratio of timing mass to true
mass to be a factor of 1.8, while the 5% and 95% points of the distribution of
this ratio are separated by a factor of 5.7. Here we define true mass as the
sum of the ``virial'' masses of the two dominant galaxies. For
current best values of the distance and approach velocity of Andromeda this
leads to a median likelihood estimate of the true mass of the Local Group of
5.27\times 10^{12}\msun, or , with an
interquartile range of and a 5% to 95% range of . Thus a 95% lower confidence limit on the true mass of the Local Group
is 1.81\times 10^{12}\msun. A timing estimate of the Milky Way's mass based
on the large recession velocity observed for the distant satellite Leo I works
equally well, although with larger systematic uncertainties. It gives an
estimated virial mass for the Milky Way of 2.43 \times 10^{12}\msun with a
95% lower confidence limit of 0.80 \times 10^{12}\msun.Comment: 11 pages, 6 figures, MNRAS accepted. Added a new discussion paragraph
and a new figure regarding the relative transverse velocity but conclusions
unchange
The Cosmic Evolution Survey (COSMOS): a large-scale structure at z=0.73 and the relation of galaxy morphologies to local environment
We have identified a large-scale structure at z~0.73 in the COSMOS field,
coherently described by the distribution of galaxy photometric redshifts, an
ACS weak-lensing convergence map and the distribution of extended X-ray sources
in a mosaic of XMM observations. The main peak seen in these maps corresponds
to a rich cluster with Tx= 3.51+0.60/-0.46 keV and Lx=(1.56+/-0.04) x 10^{44}
erg/s ([0.1-2.4] keV band). We estimate an X-ray mass within
corresponding to M500~1.6 x 10^{14} Msun and a total lensing mass (extrapolated
by fitting a NFW profile) M(NFW)=(6+/-3) x 10^15 Msun. We use an automated
morphological classification of all galaxies brighter than I_AB=24 over the
structure area to measure the fraction of early-type objects as a function of
local projected density Sigma_10, based on photometric redshifts derived from
ground-based deep multi-band photometry. We recover a robust morphology-density
relation at this redshift, indicating, for comparable local densities, a
smaller fraction of early-type galaxies than today. Interestingly, this
difference is less strong at the highest densities and becomes more severe in
intermediate environments. We also find, however, local "inversions'' of the
observed global relation, possibly driven by the large-scale environment. In
particular, we find direct correspondence of a large concentration of disk
galaxies to (the colder side of) a possible shock region detected in the X-ray
temperature map and surface brightness distribution of the dominant cluster. We
interpret this as potential evidence of shock-induced star formation in
existing galaxy disks, during the ongoing merger between two sub-clusters.Comment: 15 pages (emulateapj style), 16 figs (low res.); to appear in the ApJ
Supplement COSMOS Special Issue. Low-resolution figures; full resolution
version available at:
http://www.astro.caltech.edu/~cosmos/publications/files/guzzo_0701482.pd
Conservative and disruptive modes of adolescent change in human brain functional connectivity
Adolescent changes in human brain function are not entirely understood. Here, we used multiecho functional MRI (fMRI) to measure developmental change in functional connectivity (FC) of resting-state oscillations between pairs of 330 cortical regions and 16 subcortical regions in 298 healthy adolescents scanned 520 times. Participants were aged 14 to 26 y and were scanned on 1 to 3 occasions at least 6 mo apart. We found 2 distinct modes of age-related change in FC: âconservativeâ and âdisruptive.â Conservative development was characteristic of primary cortex, which was strongly connected at 14 y and became even more connected in the period from 14 to 26 y. Disruptive development was characteristic of association cortex and subcortical regions, where connectivity was remodeled: connections that were weak at 14 y became stronger during adolescence, and connections that were strong at 14 y became weaker. These modes of development were quantified using the maturational index (MI), estimated as Spearmanâs correlation between edgewise baseline FC (at 14 y, FC14) and adolescent change in FC (ÎFC14â26), at each region. Disruptive systems (with negative MI) were activated by social cognition and autobiographical memory tasks in prior fMRI data and significantly colocated with prior maps of aerobic glycolysis (AG), AG-related gene expression, postnatal cortical surface expansion, and adolescent shrinkage of cortical thickness. The presence of these 2 modes of development was robust to numerous sensitivity analyses. We conclude that human brain organization is disrupted during adolescence by remodeling of FC between association cortical and subcortical areas
Maturation trajectories of cortical resting-state networks depend on the mediating frequency band
The functional significance of resting state networks and their abnormal manifestations in psychiatric disorders are firmly established, as is the importance of the cortical rhythms in mediating these networks. Resting state networks are known to undergo substantial reorganization from childhood to adulthood, but whether distinct cortical rhythms, which are generated by separable neural mechanisms and are often manifested abnormally in psychiatric conditions, mediate maturation differentially, remains unknown. Using magnetoencephalography (MEG) to map frequency band specific maturation of resting state networks from age 7 to 29 in 162 participants (31 independent), we found significant changes with age in networks mediated by the beta (13â30âŻHz) and gamma (31â80âŻHz) bands. More specifically, gamma band mediated networks followed an expected asymptotic trajectory, but beta band mediated networks followed a linear trajectory. Network integration increased with age in gamma band mediated networks, while local segregation increased with age in beta band mediated networks. Spatially, the hubs that changed in importance with age in the beta band mediated networks had relatively little overlap with those that showed the greatest changes in the gamma band mediated networks. These findings are relevant for our understanding of the neural mechanisms of cortical maturation, in both typical and atypical development.This work was supported by grants from the Nancy Lurie Marks Family Foundation (TK, SK, MGK), Autism Speaks (TK), The Simons Foundation (SFARI 239395, TK), The National Institute of Child Health and Development (R01HD073254, TK), National Institute for Biomedical Imaging and Bioengineering (P41EB015896, 5R01EB009048, MSH), and the Cognitive Rhythms Collaborative: A Discovery Network (NFS 1042134, MSH). (Nancy Lurie Marks Family Foundation; Autism Speaks; SFARI 239395 - Simons Foundation; R01HD073254 - National Institute of Child Health and Development; P41EB015896 - National Institute for Biomedical Imaging and Bioengineering; 5R01EB009048 - National Institute for Biomedical Imaging and Bioengineering; NFS 1042134 - Cognitive Rhythms Collaborative: A Discovery Network
The spatial clustering of mid-IR selected star forming galaxies at z ~ 1 in the GOODS fields
We present the first spatial clustering measurements of z~1, 24um-selected,
star forming galaxies in the Great Observatories Origins Deep Survey (GOODS).
The sample under investigation includes 495 objects in GOODS-South and 811
objects in GOODS-North selected down to flux densities of f_24>20 uJy and
z_AB<23.5 mag, for which spectroscopic redshifts are available. The median
redshift, IR luminosity and star formation rate (SFR) of the samples are z~0.8,
L_IR~4.4 x 10^10 L_sun, and SFR~7.6 M_sun/yr, respectively. We measure the
projected correlation function w(r_p) on scales of r_p=0.06-10 h^-1 Mpc, from
which we derive a best fit comoving correlation length of r_0 = 4.0 +- 0.4 h^-1
Mpc and slope of gamma=1.5 +- 0.1 for the whole f_24>20uJy sample after
combining the two fields. We find indications of a larger correlation length
for objects of higher luminosity, with Luminous Infrared Galaxies (LIRGs,
L_IR>10^11 L_sun) reaching r_0~5.1 h^-1 Mpc. This would imply that galaxies
with larger SFRs are hosted in progressively more massive halos, reaching
minimum halo masses of ~3 x 10^12 M_sun for LIRGs. We compare our measurements
with the predictions from semi-analytic models based on the Millennium
simulation. The variance in the models is used to estimate the errors in our
GOODS clustering measurements, which are dominated by cosmic variance. The
measurements from the two GOODS fields are found to be consistent within the
errors. On scales of the GOODS fields, the real sources appear more strongly
clustered than objects in the Millennium-simulation based catalogs, if the
selection function is applied consistently. This suggests that star formation
at z~0.5-1 is being hosted in more massive halos and denser environments than
currently predicted by galaxy formation models.[truncated]Comment: 19 pages, 15 figures. Accepted for publication in A&A. Style and
English improve
The angular correlations of galaxies in the COSMOS field
We present measurements of the two-point galaxy angular correlation function
w(\theta) in the COSMOS field. Independent determinations of w(\theta) as a
function of magnitude limit are presented for both the HST ACS catalog and also
for the ground-based data from Subaru and the CFHT. Despite having
significantly different masks, these three determinations agree well. At bright
magnitudes (IAB<22), our data generally match very well with existing
measurements and with mock catalogs based on semi-analytic galaxy formation
calculations of Kitzbichler and White from the Millennium Simulation. The
exception is that our result is at the upper end of the expected cosmic
variance scatter for \theta > 10 arcmin, which we attribute to a particularly
rich structure known to exist at z~0.8. For fainter samples, however, the level
of clustering is somewhat higher than reported by some previous studies: in all
three catalogues we find w(\theta=1')~0.014 at a median IAB magnitude of 24. At
these very faintest magnitudes, our measurements agree well with the latest
determinations from the Canada-France Legacy Survey. This level of clustering
is approximately double what is predicted by the semi-analytic catalogs (at all
angles). The semi-analytic results allow an estimate of cosmic variance, which
is too small to account for the discrepancy. We therefore conclude that the
mean amplitude of clustering at this level is higher than previously estimated.Comment: Six pages, five figures. Accepted for publication in the ApJS COSMOS
special issue, Sept. 200
Lyman Alpha Emitters at Redshift 5.7 in the COSMOS Field
We present results from a narrow-band optical survey of a contiguous area of
1.95 deg^2, covered by the Cosmic Evolution Survey (COSMOS). Both optical
narrow-band (lambda_c = 8150 AA and Delta_lambda = 120 AA) and broad-band (B,
V, g', r', i', and z') imaging observations were performed with the Subaru
prime-focus camera, Suprime-Cam on the Subaru Telescope. We provide the largest
contiguous narrow-band survey, targetting Ly alpha emitters (LAEs) at z~5.7. We
find a total of 119 LAE candidates at z~5.7. Over the wide-area covered by this
survey, we find no strong evidence for large scale clustering of LAEs. We
estimate a star formation rate (SFR) density of ~7*10^-4 M_sun yr^-1 Mpc^-3 for
LAEs at z~5.7, and compare it with previous measurements.Comment: 26 pages, 19 figures. to appear in the ApJ Supplement COSMOS Special
Issu
3D-Matched-Filter Galaxy Cluster Finder I: Selection Functions and CFHTLS Deep Clusters
We present an optimised galaxy cluster finder, 3D-Matched-Filter (3D-MF),
which utilises galaxy cluster radial profiles, luminosity functions and
redshift information to detect galaxy clusters in optical surveys. This method
is an improvement over other matched-filter methods, most notably through
implementing redshift slicing of the data to significantly reduce line-of-sight
projections and related false positives. We apply our method to the
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep fields, finding ~170
galaxy clusters per square degree in the 0.2 <= z <= 1.0 redshift range. Future
surveys such as LSST and JDEM can exploit 3D-MF's automated methodology to
produce complete and reliable galaxy cluster catalogues. We determine the
reliability and accuracy of the statistical approach of our method through a
thorough analysis of mock data from the Millennium Simulation. We detect
clusters with 100% completeness for M_200 >= 3.0x10^(14)M_sun, 88% completeness
for M_200 >= 1.0x10^(14)M_sun, and 72% completeness well into the 10^(13)M_sun
cluster mass range. We show a 36% multiple detection rate for cluster masses >=
1.5x10^(13)M_sun and a 16% false detection rate for galaxy clusters >~
5x10^(13)M_sun, reporting that for clusters with masses <~ 5x10^(13)M_sun false
detections may increase up to ~24%. Utilising these selection functions we
conclude that our galaxy cluster catalogue is the most complete CFHTLS Deep
cluster catalogue to date.Comment: 18 pages, 17 figures, 5 tables; v2: added Fig 5, minor edits to match
version published in MNRA
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