5,455 research outputs found
The rates and time-delay distribution of multiply imaged supernovae behind lensing clusters
Time delays of gravitationally lensed sources can be used to constrain the
mass model of a deflector and determine cosmological parameters. We here
present an analysis of the time-delay distribution of multiply imaged sources
behind 17 strong lensing galaxy clusters with well-calibrated mass models. We
find that for time delays less than 1000 days, at z=3.0, their logarithmic
probability distribution functions are well represented by P (log \Delta t)=5.3
x 10^-4 \Delta t^\beta M_250^-2\beta, with \beta=0.77, where M_250 is the
projected cluster mass inside 250 kpc (in 10^14 M_sun), and \beta is the
power-law slope of the distribution. The resultant probability distribution
function enables us to estimate the time-delay distribution in a lensing
cluster of known mass. For a cluster with M_250=2 x 10^14 M_sun, the fraction
of time delays less than 1000 days is approximately 3%. Taking Abell 1689 as an
example, its dark halo and brightest galaxies, with central velocity
dispersions larger than 500 km/s, mainly produce large time delays, while
galaxy-scale mass clumps are responsible for generating smaller time delays. We
estimate the probability of observing multiple images of a supernova in the
known images of Abell 1689. A two-component model of estimating the supernova
rate is applied in this work. For a magnitude threshold of m_AB=26.5, the
yearly rate of Type Ia (core-collapse) supernovae with time delays less than
1000 days is 0.004 +- 0.002 (0.029 +- 0.001). If the magnitude threshold is
lowered to m_AB ~ 27.0, the rate of core-collapse supernovae suitable for time
delay observation is 0.044 +- 0.015 per year.Comment: 23 pages, 7 figures, JCAP in pres
An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger
We investigate the physical properties, geometry and dynamics of the massive
cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics.
Featuring two galaxy overdensities separated by about 250 kpc in projection on
the sky, and a single peak in the X-ray surface brightness distribution located
between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of
a binary, post-collision merger. Our spectral analysis of the X-ray emission,
as measured by our Chandra ACIS-I observation of the system, finds the
intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs
of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field
of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s
(n_z=66) and no significant evidence of bimodality or substructure along the
line of sight. In addition, the difference in radial velocity between the
brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small
compared to typical collision velocities of several 1000 km/s. A strongly
lensed background galaxy at z=0.873 (which features variable X-ray emission
from an active nucleus) provides the main constraint on the mass distribution
of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the
north-western cluster component and a much less certain estimate of
(1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good
agreement with our X-ray mass estimates which yield a total mass of MACS
J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......Comment: 11 pages, 8 figures, and 2 tables. Accepted for publication in MNRA
VLT/X-Shooter Near-Infrared Spectroscopy and HST Imaging of Gravitationally-Lensed z~2 Compact Quiescent Galaxies
Quiescent massive galaxies at z~2 are thought to be the progenitors of
present-day massive ellipticals. Observations revealed them to be
extraordinarily compact. The determination of stellar ages, star formation
rates and dust properties via spectroscopic measurements has up to now only
been feasible for the most luminous and massive specimens (~3x M*). Here we
present a spectroscopic study of two near-infrared selected galaxies which are
close to the characteristic stellar mass M* (~0.9x M* and ~1.3x M*) and whose
observed brightness has been boosted by the gravitational lensing effect. We
measure the redshifts of the two galaxies to be z=1.71\pm0.02 and
z=2.15\pm0.01. By fitting stellar population synthesis models to their
spectro-photometric SEDs we determine their ages to be 2.4^{+0.8}_{-0.6} Gyr
and 1.7\pm0.3 Gyr, respectively, which implies that the two galaxies have
higher mass-to-light ratios than most quiescent z~2 galaxies in other studies.
We find no direct evidence for active star-formation or AGN activity in either
of the two galaxies, based on the non-detection of emission lines. Based on the
derived redshifts and stellar ages we estimate the formation redshifts to be
z=4.3^{+3.4}_{-1.2} and z=4.3^{+1.0}_{-0.6}, respectively. We use the increased
spatial resolution due to the gravitational lensing to derive constraints on
the morphology. Fitting Sersic profiles to the de-lensed images of the two
galaxies confirms their compactness, with one of them being spheroid-like, and
the other providing the first confirmation of a passive lenticular galaxy at a
spectroscopically derived redshift z~2.Comment: accepted for publication in Ap
The Abundance of Low-luminosity Lyman alpha Emitters at High Redshift
We derive the luminosity function of high-redshift Lyman alpha emitting
sources from a deep, blind, spectroscopic survey that utilized strong-lensing
magnification by intermediate-redshift clusters of galaxies. We observed
carefully selected regions near 9 clusters, consistent with magnification
factors generally greater than 10 for the redshift range 4.5<z<6.7. Eleven
emission-line candidates were located in the range 2.2<z<5.6 whose
identification we justify as Lyman alpha, in most cases via further
spectroscopic observations. The selection function we constructed for our
survey takes into account our varying intrinsic Lyman alpha line sensitivity as
a function of wavelength and sky position. By virtue of the strong
magnification factor, we provide constraints on the Lyman alpha luminosity
function to unprecedented limits of 10^40 erg/s, corresponding to a
star-formation rate of 0.01 Msun/yr. Our cumulative z=5 Lyman alpha luminosity
function is consistent with a power law form, n(>L) proportional to L^-1 over
10^41 to 10^42.5 erg/s. When combined with the results of other surveys,
limited at higher luminosities, our results suggest evidence for the
suppression of star formation in low-mass halos, as predicted in popular models
of galaxy formation.Comment: 22 pages, 14 figures, submitted to Ap
Privatization, Investment and Ownership Efficiency
We provide a model that explains the following empirical observations: i) private ownership is more efficient than public ownership, ii) privatizations are associated with increases in efficiency and iii) the increase in efficiency predates the privatization. The two key mechanisms explaining the results are: (i) a government owner keeping control takes into account the negative effect on employment of investment and (ii) a privatizing government has a stronger incentive to invest than an acquiring firm: the government exploits the fact that investments increase the sales price not only due to the increase in the acquirer's profit, but also due to a reduced profit for the non-acquirer.Privatization; Asset Ownership; Restructuring; Oligopoly
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