651 research outputs found
Understanding joint action: Current theoretical and empirical approaches
Joint actions are omnipresent, ranging from a handshake between two people to the coordination of groups of people playing in an orchestra. We are highly skilled at coordinating our actions with those of others to reach common goals and rely on this ability throughout our daily lives. What are the social, cognitive and neural processes underlying this ability? How do others around us influence our task representations? How does joint action influence interpersonal interactions? How do language and gesture support joint action? What differentiates joint action from individual action? This article forms an introductory editorial to the field of joint action. It accompanies contributions to the special issue entitled "Current Issues in Joint Action Research". The issue brings together conceptual and empirical approaches on different topics, ranging from lower-level issues such as the link between perception and joint action, to higher-level issues such as language as a form of joint action
The Evolution of Rest-Frame K-band Properties of Early-Type Galaxies from z=1 to the Present
We measure the evolution of the rest-frame K-band Fundamental Plane from z=1
to the present by using IRAC imaging of a sample of early-type galaxies in the
Chandra Deep Field-South at z~1 with accurately measured dynamical masses. We
find that evolves as , which is
slower than in the B-band (). In the B-band
the evolution has been demonstrated to be strongly mass dependent. In the
K-band we find a weaker trend: galaxies more massive than
evolve as ;
less massive galaxies evolve as . As
expected from stellar population models the evolution in is slower than
the evolution in . However, when we make a quantitative comparison, we
find that the single burst Bruzual-Charlot models do not fit the results well,
unless large dust opacities are allowed at z=1. Models with a flat IMF fit
better, Maraston models with a different treatment of AGB stars fit best. These
results show that the interpretation of rest-frame near-IR photometry is
severely hampered by model uncertainties and therefore that the determination
of galaxy masses from rest-frame near-IR photometry may be harder than was
thought before.Comment: 5 pages, 3 figures, Accepted for publication in ApJ
The Evolution of the Field and Cluster Morphology-Density Relation for Mass-Selected Samples of Galaxies
The Sloan Digital Sky Survey (SDSS) and photometric/spectroscopic surveys in
the GOODS-South field (the Chandra Deep Field-South, CDFS) are used to
construct volume-limited, stellar mass-selected samples of galaxies at
redshifts 0<z<1. The CDFS sample at 0.6<z<1.0 contains 207 galaxies complete
down to M=4x10^10 Msol (for a ``diet'' Salpeter IMF), corresponding to a
luminosity limit for red galaxies of M_B=-20.1. The SDSS sample at
0.020<z<0.045 contains 2003 galaxies down to the same mass limit, which
corresponds to M_B=-19.3 for red galaxies. Morphologies are determined with an
automated method, using the Sersic parameter n and a measure of the residual
from the model fits, called ``bumpiness'', to distinguish different
morphologies. These classifications are verified with visual classifications.
In agreement with previous studies, 65-70% of the galaxies are located on the
red sequence, both at z~0.03 and at z~0.8. Similarly, 65-70% of the galaxies
have n>2.5. The fraction of E+S0 galaxies is 43+/-3%$ at z~0.03 and 48+/-7% at
z~0.8, i.e., it has not changed significantly since z~0.8. When combined with
recent results for cluster galaxies in the same redshift range, we find that
the morphology-density relation for galaxies more massive than 0.5M* has
remained constant since at least z~0.8. This implies that galaxies evolve in
mass, morphology and density such that the morphology-density relation does not
change. In particular, the decline of star formation activity and the
accompanying increase in the stellar mass density of red galaxies since z~1
must happen without large changes in the early-type galaxy fraction in a given
environment.Comment: 16 pages, 13 figures, 2 tables. Updated to match journal version.
Will appear in ApJ (vol. 670, p. 206
Mass-Selection and the Evolution of the Morphology-Density Relation from z=0.8 to z=0
We examined the morphology-density relations for galaxy samples selected by
luminosity and by mass in each of five massive X-ray clusters from z=0.023 to
0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and
visual morphologies were obtained primarily from Hubble Space Telescope images.
Morphology-density relations (MDR) are derived in each cluster from a complete,
luminosity-selected sample of 452 galaxies with a magnitude limit M_V <
M^{*}_{V} + 1. The change in the early-type fraction with redshift matches
previous work for massive clusters of galaxies. We performed a similar
analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies
with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects,
the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and
encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the
mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar
to those in the luminosity-selected sample but show larger early-type
fractions. However, the trend with redshift in the fraction of elliptical and
S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the
mass- and luminosity-selected samples. The clear trend seen in the early-type
fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The
early-type galaxy fraction changes much less, and is consistent with being
constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 <
\Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than
> 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type
fraction in luminosity-selected samples. (Abstract abridged)Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to
ApJ. Version updated to reflect published version, includes new references
and a correction to table
Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
We present a comprehensive mass reconstruction of the rich galaxy cluster Cl
0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing
constraints. The weak-lensing signal from a dense distribution of background
galaxies (~120 per square arcmin) across the cluster enables the derivation of
a high-resolution parameter-free mass map. The strongly-lensed objects tightly
constrain the mass structure of the cluster inner region on an absolute scale,
breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17
obtained in such a way is remarkable. It reveals a ringlike dark matter
substructure at r~75" surrounding a soft, dense core at r~50". We interpret
this peculiar sub-structure as the result of a high-speed line-of-sight
collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated
by the cluster velocity distribution. Our numerical simulation with purely
collisionless particles demonstrates that such density ripples can arise by
radially expanding, decelerating particles that originally comprised the
pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56,
but viewed the collision axis at a much later epoch. In addition, we
show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and
lensing can be resolved by treating the cluster X-ray emission as coming from a
superposition of two X-ray systems. The cluster's unusual X-ray surface
brightness profile that requires a two isothermal sphere description supports
this hypothesis.Comment: To appear in the June 1 issue of The Astrophysical Journa
Comparing Dynamical and Photometric Mass Estimates of Low- and High-Redshift Galaxies: Random and Systematic Uncertainties
We determine the importance of redshift-dependent systematic effects in the
determination of stellar masses from broad band spectral energy distributions
(SEDs), using high quality kinematic and photometric data of early-type
galaxies at z~1 and z~0. We find that photometric masses of z~1 galaxies can be
systematically different, by up to a factor of 2, from photometric masses of
z~0 galaxies with the same dynamical mass. The magnitude of this bias depends
on the choice of stellar population synthesis model and the rest-frame
wavelength range used in the fits. The best result, i.e., without significant
bias, is obtained when rest-frame optical SEDs are fitted with models from
Bruzual&Charlot (2003). When the SEDs are extended to the rest-frame near-IR, a
bias is introduced: photometric masses of the z~1 galaxies increase by a factor
of 2 relative to the photometric masses of the z~0 galaxies. When we use the
Maraston (2005) models, the photometric masses of the z~1 galaxies are low
relative to the photometric masses of the z~0 galaxies by a factor of ~1.8.
This offset occurs both for fits based on rest-frame optical SEDs, and fits
based on rest-frame optical+near-IR SEDs. The results indicate that model
uncertainties produce uncertainties as high as a factor of 2.5 in mass
estimates from rest-frame near-IR photometry, independent of uncertainties due
to unknown star formation histories.Comment: Accepted for publication in ApJ (12 pages, 11 figures
Магнитный контроль параметров ферромагнитных объектов методом высших гармоник
В данной работе объектом исследования являются контрольные образцы тороидальной формы из ферромагнитных сталей различных марок, изготовленные согласно ГОСТ 8.377-80, магнитные параметры которых исследуются с помощью разработанной многопараметровой установки для измерения магнитных характеристик MS-1.In this work, the object of the study is the control samples of toroidal shape of ferromagnetic steels of different brands, made according to GOST 8.377-80, the magnetic parameters of which are investigated using the developed multiparameter installation for measuring the magnetic characteristics of MS-1
Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z2: High velocity dispersions in progenitors of compact quiescent galaxies
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13
compact star-forming galaxies (SFGs) at redshift with star
formation rates of SFR100M y and masses of
log(M/M). Their high integrated gas velocity dispersions of
=230 km s, as measured from emission
lines of H and [OIII], and the resultant
M relation and MM all
match well to those of compact quiescent galaxies at , as measured from
stellar absorption lines. Since log(M/M)
dex, these compact SFGs appear to be dynamically relaxed and more evolved,
i.e., more depleted in gas and dark matter (13\%) than their
non-compact SFG counterparts at the same epoch. Without infusion of external
gas, depletion timescales are short, less than 300 Myr. This discovery
adds another link to our new dynamical chain of evidence that compact SFGs at
are already losing gas to become the immediate progenitors of
compact quiescent galaxies by .Comment: 12 pages, 7 figures, submitted to Ap
The Ellipticities of Cluster Early-type Galaxies from z~1 to z~0: No Evolution in the Overall Distribution of Bulge-to-Disk Ratios
We have compiled a sample of early-type cluster galaxies from 0 < z < 1.3 and
measured the evolution of their ellipticity distributions. Our sample contains
487 galaxies in 17 z>0.3 clusters with high quality space-based imaging and a
comparable sample of 210 galaxies in 10 clusters at z<0.05. We select
early-type galaxies (elliptical and S0 galaxies) that fall within the cluster
R_{200}, and which lie on the red-sequence in the magnitude range -19.3 > M_B >
-21, after correcting for luminosity evolution. Our ellipticity measurements
are made in a consistent manner over our whole sample. We perform extensive
simulations to quantify the systematic and statistical errors, and find that it
is crucial to use PSF-corrected model fits. We find that neither the median
ellipticity, nor the shape of the ellipticity distribution of cluster
early-type galaxies evolves with redshift from z ~ 0 to z > 1. These results
are strongly suggestive of an unchanging overall bulge-to-disk ratio
distribution for cluster early-type galaxies over the last ~8Gyr. This result
contrasts with that from visual classifications which show that the fraction of
morphologically-selected disk-dominated early-type galaxies, or S0s, is
significantly lower at z>0.4 than at z~0. Taking the ellipticity measurements
and assuming, as in all previous studies, that the intrinsic ellipticity
distribution of both elliptical and S0 galaxies remains constant, then we
conclude from the lack of evolution in the observed early-type ellipticity
distribution that the relative fractions of ellipticals and S0s do not evolve
from z~1 to z=0 for a red-sequence selected samples of galaxies in the cores of
clusters of galaxies.Comment: 21 pages, 15 color figures, revised to match final ApJ version.
Corrected discussion of Andreon et al 1996 from previous versio
HST/WFC3 grism observations of z ∼ 1 clusters : the cluster versus field stellar mass-size relation and evidence for size growth of quiescent galaxies from minor mergers
Minor mergers are thought to be responsible for the size growth of quiescent field galaxies with decreasing redshift. We test this hypothesis using the cluster environment as a laboratory. Satellite galaxies in clusters move at high velocities, making mergers between them rare. The stellar mass-size relation in 10 clusters and in the field is measured and compared at z similar to 1. Our cluster sample contains 344 spectroscopically confirmed cluster members with Gemini/Gemini Multi-Object Spectrographs and 182 confirmed with Hubble Space Telescope/Wide Field Camera 3 G141 grism spectroscopy. On average, quiescent and star-forming cluster galaxies are smaller than their field counterparts by (0.08 +/- 0.04) and (0.07 +/- 0.01) dex, respectively. These size offsets are consistent with the average sizes of quiescent and star-forming field galaxies between 1.2 <= z <= 1.5, implying the cluster environment has inhibited size growth between this period and z similar to 1. The negligible differences measured between the z similar to 0 field and cluster quiescent mass-size relations in other works imply that the average size of quiescent cluster galaxies must rise with decreasing redshift. Using a toy model, we show that the disappearance of the compact cluster galaxies might be explained if, on average, similar to 40 per cent of them merge with their brightest cluster galaxies (BCGs) and similar to 60 per cent are tidally destroyed into the intracluster light (ICL) between 0 <= z <= 1. This is in agreement with the observed stellar mass growth of BCGs between 0 <= z <= 1 and the observed ICL stellar mass fraction at z similar to 0. Our results support minor mergers as the cause for the size growth in quiescent field galaxies, with cluster-specific processes responsible for the similarity between the field and cluster quiescent mass-size relations at low redshift
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