84 research outputs found
LISA Galactic Binaries in the Roman Galactic Bulge Time-Domain Survey
Short-period Galactic white dwarf binaries detectable by LISA are the only
guaranteed persistent sources for multi-messenger gravitational-wave astronomy.
Large-scale surveys in the 2020s present an opportunity to conduct preparatory
science campaigns to maximize the science yield from future multi-messenger
targets. The Nancy Grace Roman Space Telescope Galactic Bulge Time Domain
Survey will (in its Reference Survey design) image seven fields in the Galactic
Bulge approximately 40,000 times each. Although the Reference Survey cadence is
optimized for detecting exoplanets via microlensing, it is also capable of
detecting short-period white dwarf binaries. In this paper, we present
forecasts for the number of detached short-period binaries the Roman Galactic
Bulge Time Domain Survey will discover and the implications for the design of
electromagnetic surveys. Although population models are highly uncertain, we
find a high probability that the baseline survey will detect of order ~5
detached white dwarf binaries. The Reference Survey would also have a
chance of detecting several known benchmark white dwarf binaries
at the distance of the Galactic Bulge.Comment: 9 pages, 4 figure, 1 tabl
Dust-polarization Maps and Interstellar Turbulence
Perhaps the most intriguing result of Planck\u27s dust-polarization measurements is the observation that the power in the E-mode polarization is twice that in the B mode, as opposed to pre-Planck expectations of roughly equal dust powers in the E and B modes. Here we show how the E- and B-mode powers depend on the detailed properties of the fluctuations in the magnetized interstellar medium (ISM). These fluctuations can be decomposed into slow, fast, and AlfvĂ©n magnetohydrodynamic (MHD) waves, which comprise a complete basis that can be used to describe linear fluctuations of a magnetized fluid. They can alternatively be decomposed in terms of one longitudinal and two transverse components of a fluid-displacement field. The intensity (T) and E- and B-mode amplitudes induced by each of the three types of waves, in both decompositions, are then calculated. To illustrate how these tools can be applied, we consider a toy model of the ISM in which dust traces a single component of plasma, and obtain the EE/BB ratio and TE correlation for several ansatzes for the power in slow/fast/AlfvĂ©n waves and in longitudinal/transverse waves. Although our model may be too simplistic to properly describe the nonlinear structure of interstellar magnetic fields, we find that the observed EE/BB ratio (and its scale invariance) and positive TEcorrelationâas well as the observed power-law index for the angular spectrum of these fluctuationsâare not easily accommodated in terms of simple MHD turbulence prescriptions for the expected powers in slow, fast, and AlfvĂ©n waves. We speculate that the ~0.1â30 pc length scales probed by these dust-polarization measurements are not described by MHD turbulence, but rather probe the large-scale physics that drives ISM turbulence. We find that a slightly anisotropic spectrum of random fluid displacements produces EE/BB 2 and a positive TE cross-correlation. Furthermore, we find that large EE/BB and positive TE are due primarily to longitudinal, rather than transverse, modes in the random-displacement field, providing, perhaps, some clue to the mechanism that stirs the ISM. Future investigations involving the spatial dependence of the EE/BB ratio, TE correlation, and local departures from statistical isotropy in dust-polarization maps, as well as further tests of some of the assumptions in this analysis, are outlined. This work may also aid in the improvement of foreground-separation techniques for studies of cosmic microwave background polarization
Dust-polarization Maps and Interstellar Turbulence
Perhaps the most intriguing result of Planck\u27s dust-polarization measurements is the observation that the power in the E-mode polarization is twice that in the B mode, as opposed to pre-Planck expectations of roughly equal dust powers in the E and B modes. Here we show how the E- and B-mode powers depend on the detailed properties of the fluctuations in the magnetized interstellar medium (ISM). These fluctuations can be decomposed into slow, fast, and AlfvĂ©n magnetohydrodynamic (MHD) waves, which comprise a complete basis that can be used to describe linear fluctuations of a magnetized fluid. They can alternatively be decomposed in terms of one longitudinal and two transverse components of a fluid-displacement field. The intensity (T) and E- and B-mode amplitudes induced by each of the three types of waves, in both decompositions, are then calculated. To illustrate how these tools can be applied, we consider a toy model of the ISM in which dust traces a single component of plasma, and obtain the EE/BB ratio and TE correlation for several ansatzes for the power in slow/fast/AlfvĂ©n waves and in longitudinal/transverse waves. Although our model may be too simplistic to properly describe the nonlinear structure of interstellar magnetic fields, we find that the observed EE/BB ratio (and its scale invariance) and positive TEcorrelationâas well as the observed power-law index for the angular spectrum of these fluctuationsâare not easily accommodated in terms of simple MHD turbulence prescriptions for the expected powers in slow, fast, and AlfvĂ©n waves. We speculate that the ~0.1â30 pc length scales probed by these dust-polarization measurements are not described by MHD turbulence, but rather probe the large-scale physics that drives ISM turbulence. We find that a slightly anisotropic spectrum of random fluid displacements produces EE/BB 2 and a positive TE cross-correlation. Furthermore, we find that large EE/BB and positive TE are due primarily to longitudinal, rather than transverse, modes in the random-displacement field, providing, perhaps, some clue to the mechanism that stirs the ISM. Future investigations involving the spatial dependence of the EE/BB ratio, TE correlation, and local departures from statistical isotropy in dust-polarization maps, as well as further tests of some of the assumptions in this analysis, are outlined. This work may also aid in the improvement of foreground-separation techniques for studies of cosmic microwave background polarization
Weak Lensing of the CMB by Large-Scale Structure
Several recent papers have studied lensing of the CMB by large-scale
structures, which probes the projected matter distribution from to
. This interest is motivated in part by upcoming high resolution,
high sensitivity CMB experiments, such as APEX/SZ, ACT, SPT or Planck, which
should be sensitive to lensing. In this paper we examine the reconstruction of
the large-scale dark matter distribution from lensed CMB temperature
anisotropies. We go beyond previous work in using numerical simulations to
include higher order, non-Gaussian effects and study how well the quadratic
estimator of \cite{Hu01a} is able to recover the input field. We also study
contamination by kinetic Sunyaev-Zel'dovich signals, which is spectrally
indistinguishable from lensed CMB anisotropies. We finish by estimating the
sensitivity of the previously cited experiments.Comment: 26 pages, 13 figures, replaced to match the minor revisions of the
accepted versio
Optical-to-virial velocity ratios of local disk galaxies from combined kinematics and galaxy-galaxy lensing
In this paper, we measure the optical-to-virial velocity ratios Vopt/V200c of
disk galaxies in the Sloan Digital Sky Survey (SDSS) at a mean redshift of
= 0.07 and with stellar masses 10^9 M_sun < M_* < 10^11 M_sun. Vopt/V200c, the
ratio of the circular velocity measured at the virial radius of the dark matter
halo (\sim150 kpc) to that at the optical radius of the disk (\sim10 kpc), is a
powerful observational constraint on disk galaxy formation. It links galaxies
to their dark matter haloes dynamically and constrains the total mass profile
of disk galaxies over an order of magnitude in length scale. For this
measurement, we combine Vopt derived from the Tully-Fisher relation (TFR) from
Reyes et al. with V200c derived from halo masses measured with galaxy-galaxy
lensing. In anticipation of this combination, we use similarly-selected galaxy
samples for both the lensing and TFR analysis. For three M_* bins with
lensing-weighted mean stellar masses of 0.6, 2.7, and 6.5 x 10^10 M_sun, we
find halo-to-stellar mass ratios M_vir/M_* = 41, 23, and 26, with 1-sigma
statistical uncertainties of around 0.1 dex, and Vopt/V200c = 1.27\pm0.08,
1.39\pm0.06, 1.27\pm0.08 (1{\sigma}). Our results suggest that the dark matter
and baryonic contributions to the mass within the optical radius are
comparable, if the dark matter halo profile has not been significantly modified
by baryons. The results obtained in this work will serve as inputs to and
constraints on disk galaxy formation models, which will be explored in future
work. Finally, we note that this paper presents a new and improved galaxy shape
catalogue for weak lensing that covers the full SDSS DR7 footprint.Comment: Matches accepted version in MNRAS; added subsection on Sec. 6.3 and
expanded Table 4; 38 pages, 19 figure
The WiggleZ Dark Energy Survey: Direct constraints on blue galaxy intrinsic alignments at intermediate redshifts
Correlations between the intrinsic shapes of galaxy pairs, and between the
intrinsic shapes of galaxies and the large-scale density field, may be induced
by tidal fields. These correlations, which have been detected at low redshifts
(z<0.35) for bright red galaxies in the Sloan Digital Sky Survey (SDSS), and
for which upper limits exist for blue galaxies at z~0.1, provide a window into
galaxy formation and evolution, and are also an important contaminant for
current and future weak lensing surveys. Measurements of these alignments at
intermediate redshifts (z~0.6) that are more relevant for cosmic shear
observations are very important for understanding the origin and redshift
evolution of these alignments, and for minimising their impact on weak lensing
measurements. We present the first such intermediate-redshift measurement for
blue galaxies, using galaxy shape measurements from SDSS and spectroscopic
redshifts from the WiggleZ Dark Energy Survey. Our null detection allows us to
place upper limits on the contamination of weak lensing measurements by blue
galaxy intrinsic alignments that, for the first time, do not require
significant model-dependent extrapolation from the z~0.1 SDSS observations.
Also, combining the SDSS and WiggleZ constraints gives us a long redshift
baseline with which to constrain intrinsic alignment models and contamination
of the cosmic shear power spectrum. Assuming that the alignments can be
explained by linear alignment with the smoothed local density field, we find
that a measurement of \sigma_8 in a blue-galaxy dominated, CFHTLS-like survey
would be contaminated by at most +/-0.02 (95% confidence level, SDSS and
WiggleZ) or +/-0.03 (WiggleZ alone) due to intrinsic alignments. [Abridged]Comment: 18 pages, 12 figures, accepted to MNRAS; v2 has correction to one
author's name, NO other changes; v3 has minor changes in explanation and
calculations, no significant difference in results or conclusions; v4 has an
additional footnote about model interpretation, no changes to
data/calculations/result
CMBPol Mission Concept Study: Gravitational Lensing
Gravitational lensing of the cosmic microwave background by large-scale
structure in the late universe is both a source of cosmological information and
a potential contaminant of primordial gravity waves. Because lensing imprints
growth of structure in the late universe on the CMB, measurements of CMB
lensing will constrain parameters to which the CMB would not otherwise be
sensitive, such as neutrino mass.
If the instrumental noise is sufficiently small (<~ 5 uK-arcmin), the
gravitational lensing contribution to the large-scale B-mode will be the
limiting source of contamination when constraining a stochastic background of
gravity waves in the early universe, one of the most exciting prospects for
future CMB polarization experiments. High-sensitivity measurements of
small-scale B-modes can reduce this contamination through a lens reconstruction
technique that separates the lensing and primordial contributions to the B-mode
on large scales.
A fundamental design decision for a future CMB polarization experiment such
as CMBpol is whether to have coarse angular resolution so that only the
large-scale B-mode (and the large-scale E-mode from reionization) is measured,
or high resolution to additionally measure CMB lensing. The purpose of this
white paper is to evaluate the science case for CMB lensing in polarization:
constraints on cosmological parameters, increased sensitivity to the gravity
wave B-mode via lens reconstruction, expected level of contamination from
non-CMB foregrounds, and required control of beam systematics
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