891 research outputs found
Reconstruction of the two-dimensional gravitational potential of galaxy clusters from X-ray and Sunyaev-Zel'dovich measurements
The mass of galaxy clusters is not a direct observable, nonetheless it is
commonly used to probe cosmological models. Based on the combination of all
main cluster observables, that is, the X-ray emission, the thermal
Sunyaev-Zel'dovich (SZ) signal, the velocity dispersion of the cluster
galaxies, and gravitational lensing, the gravitational potential of galaxy
clusters can be jointly reconstructed. We derive the two main ingredients
required for this joint reconstruction: the potentials individually
reconstructed from the observables and their covariance matrices, which act as
a weight in the joint reconstruction. We show here the method to derive these
quantities. The result of the joint reconstruction applied to a real cluster
will be discussed in a forthcoming paper. We apply the Richardson-Lucy
deprojection algorithm to data on a two-dimensional (2D) grid. We first test
the 2D deprojection algorithm on a -profile. Assuming hydrostatic
equilibrium, we further reconstruct the gravitational potential of a simulated
galaxy cluster based on synthetic SZ and X-ray data. We then reconstruct the
projected gravitational potential of the massive and dynamically active cluster
Abell 2142, based on the X-ray observations collected with XMM-Newton and the
SZ observations from the Planck satellite. Finally, we compute the covariance
matrix of the projected reconstructed potential of the cluster Abell 2142 based
on the X-ray measurements collected with XMM-Newton. The gravitational
potentials of the simulated cluster recovered from synthetic X-ray and SZ data
are consistent, even though the potential reconstructed from X-rays shows
larger deviations from the true potential. Regarding Abell 2142, the projected
gravitational cluster potentials recovered from SZ and X-ray data reproduce
well the projected potential inferred from gravitational-lensing observations.
(abridged)Comment: accepted for publication in the journal A&
Deconvolution of complex G protein-coupled receptor signaling in live cells using dynamic mass redistribution measurements
Label-free biosensor technology based on dynamic mass redistribution (DMR) of cellular constituents promises to translate GPCR signaling into complex optical 'fingerprints' in real time in living cells. Here we present a strategy to map cellular mechanisms that define label-free responses, and we compare DMR technology with traditional second-messenger assays that are currently the state of the art in GPCR drug discovery. The holistic nature of DMR measurements enabled us to (i) probe GPCR functionality along all four G-protein signaling pathways, something presently beyond reach of most other assay platforms; (ii) dissect complex GPCR signaling patterns even in primary human cells with unprecedented accuracy; (iii) define heterotrimeric G proteins as triggers for the complex optical fingerprints; and (iv) disclose previously undetected features of GPCR behavior. Our results suggest that DMR technology will have a substantial impact on systems biology and systems pharmacology as well as for the discovery of drugs with novel mechanisms
The functional significance of aberrant cervical counts in sloths: insights from automated exhaustive analysis of cervical range of motion
Besides manatees, the suspensory extant âtree slothsâ are the only mammals that deviate from a cervical count (CC) of seven vertebrae. They do so in opposite directions in the two living genera (increased versus decreased CC). Aberrant CCs seemingly reflect neck mobility in both genera, suggesting adaptive significance for their head position during suspensory locomotion and especially increased ability for neck torsion in three-toed sloths. We test two hypotheses in a comparative evolutionary framework by assessing three-dimensional intervertebral range of motion (ROM) based on exhaustive automated detection of bone collisions and joint disarticulation while accounting for interacting rotations of roll, yaw and pitch. First, we hypothesize that the increase of CC also increases overall neck mobility compared with mammals with a regular CC, and vice versa. Second, we hypothesize that the anatomy of the intervertebral articulations determines mobility of the neck. The assessment revealed that CC plays only a secondary role in defining ROM since summed torsion (roll) capacity was primarily determined by vertebral anatomy. Our results thus suggest limited neck rotational adaptive significance of the CC aberration in sloths. Further, the study demonstrates the suitability of our automated approach for the comparative assessment of osteological ROM in vertebral series.Peer Reviewe
The UHECR-FR0 Radio Galaxy Connection: A Multi-Messenger Study of Energy Spectra/Composition Emission and Intergalactic Magnetic Field Propagation
This study investigates low luminosity Fanaroff-Riley Type 0 (FR0) radio
galaxies as a potentially significant source of ultra-high energy cosmic rays
(UHECRs). Due to their much higher prevalence in the local universe compared to
more powerful radio galaxies (about five times more than FR-1s), FR0s may
provide a substantial fraction of the total UHECR energy density. To determine
the nucleon composition and energy spectrum of UHECRs emitted by FR0 sources,
simulation results from CRPropa3 are fit to Pierre Auger Observatory data. The
resulting emission spectral indices, rigidity cutoffs, and nucleon fractions
are compared to recent Auger results. The FR0 simulations include the
approximately isotropic distribution of FR0 galaxies and various intergalactic
magnetic field configurations (including random and structured fields) and
predict the fluxes of secondary photons and neutrinos produced during UHECR
propagation through cosmic photon backgrounds. This comprehensive simulation
allows for investigating the properties of the FR0 sources using observational
multi-messenger data.Comment: PoS 444 (38th ICRC) 151
Frontier fields clusters: deep Chandra observations of the complex merger MACS~J1149.6+2223
The Hubble Space Telescope Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z = 0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster
CLASH-VLT: Dissecting the Frontier Fields Galaxy Cluster MACS J0416.1-2403 with Spectra of Member Galaxies
We present VIMOS-VLT spectroscopy of the Frontier Fields cluster
MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large
spectroscopic campaign provided more than 4000 reliable redshifts, including
~800 cluster member galaxies. The unprecedented sample of cluster members at
this redshift allows us to perform a highly detailed dynamical and structural
analysis of the cluster out to ~2.2 (~4Mpc). Our analysis of
substructures reveals a complex system composed of a main massive cluster
(~0.9) presenting two major features: i) a
bimodal velocity distribution, showing two central peaks separated by ~1100 km s with comparable galaxy content and velocity
dispersion, ii) a projected elongation of the main substructures along the
NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an
isolated BCG approximately halfway between the center and the SW clump. We also
detect a low mass structure at z~0.390, ~10' S of the cluster center, projected
at ~3Mpc, with a relative line-of-sight velocity of ~-1700 km
s. The cluster mass profile that we obtain through our dynamical
analysis deviates significantly from the "universal" NFW, being best fit by a
Softened Isothermal Sphere model instead. The mass profile measured from the
galaxy dynamics is found to be in relatively good agreement with those obtained
from strong and weak lensing, as well as with that from the X-rays, despite the
clearly unrelaxed nature of the cluster. Our results reveal overall a complex
dynamical state of this massive cluster and support the hypothesis that the two
main subclusters are being observed in a pre-collisional phase, in line with
recent findings from radio and deep X-ray data. With this article we also
release the entire redshift catalog of 4386 sources in the field of this
cluster.Comment: Accepted for publication on ApJS. Revised to match the accepted
version; 21 pages, 18 figures, 9 tables. The CLASH-VLT spectroscopic catalogs
are publicly available at: http://sites.google.com/site/vltclashpublic
The discovery of lensed radio and x-ray sources behind the frontier fields cluster MACS J0717.5+3745 with the JVLA and Chandra
© 2016. The American Astronomical Society. All rights reserved.. We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster MACS J0717.5+3745. MACS J0717.5+3745 offers the largest contiguous magnified area of any known cluster, making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0-6.5 GHz JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the HST imaging. Within this sample, we find seven lensed sources with amplification factors larger than two. None of these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are likely star-forming galaxies with star-formation rates (SFRs) of 10-50 yr -1 located at . Two of the lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic nuclei, given their 2-10 keV X-ray luminosities of âŒ10 43-44 erg s -1 . From the derived radio luminosity function, we find evidence for an increase in the number density of radio sources at , compared to a sample. Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with SFRs as low as âŒ10 M o yr -1 , at the peak of cosmic star formation history
Evidence for Ubiquitous, High-EW Nebular Emission in z~7 Galaxies: Towards a Clean Measurement of the Specific Star Formation Rate using a Sample of Bright, Magnified Galaxies
Growing observational evidence now indicates that nebular line emission has a
significant impact on the rest-frame optical fluxes of z~5-7 galaxies observed
with Spitzer. This line emission makes z~5-7 galaxies appear more massive, with
lower specific star formation rates. However, corrections for this line
emission have been very difficult to perform reliably due to huge uncertainties
on the overall strength of such emission at z>~5.5. Here, we present the most
direct observational evidence yet for ubiquitous high-EW [OIII]+Hbeta line
emission in Lyman-break galaxies at z~7, while also presenting a strategy for
an improved measurement of the sSFR at z~7. We accomplish this through the
selection of bright galaxies in the narrow redshift window z~6.6-7.0 where the
IRAC 4.5 micron flux provides a clean measurement of the stellar continuum
light. Observed 4.5 micron fluxes in this window contrast with the 3.6 micron
fluxes which are contaminated by the prominent [OIII]+Hbeta lines. To ensure a
high S/N for our IRAC flux measurements, we consider only the brightest
(H_{160}<26 mag) magnified galaxies we have identified in CLASH and other
programs targeting galaxy clusters. Remarkably, the mean rest-frame optical
color for our bright seven-source sample is very blue, [3.6]-[4.5]=-0.9+/-0.3.
Such blue colors cannot be explained by the stellar continuum light and require
that the rest-frame EW of [OIII]+Hbeta be greater than 637 Angstroms for the
average source. The bluest four sources from our seven-source sample require an
even more extreme EW of 1582 Angstroms. Our derived lower limit for the mean
[OIII]+Hbeta EW could underestimate the true EW by ~2x based on a simple
modeling of the redshift distribution of our sources. We can also set a robust
lower limit of >~4 Gyr^-1 on the specific star formation rates based on the
mean SED for our seven-source sample. (abridged)Comment: 9 pages, 6 figures, 1 table, submitted to the Astrophysical Journa
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