8 research outputs found
Cosmology with next generation radio telescopes
Philosophiae Doctor - PhDThe next generation of radio telescopes will revolutionize cosmology by
providing large three-dimensional surveys of the universe. This work presents
forecasts using the technique 21cm intensity mapping (IM) combined with
results from the cosmic microwave background, or mock data of galaxy
surveys. First, we discuss prospects of constraining curvature independently
of the dark energy (DE) model, finding that the radio instrument HIRAX
will reach percent-level accuracy even when an arbitrary DE equation of state
is assumed. This is followed by a study of the potential of the multi-tracer
technique to surpass the cosmic variance limit, a crucial method to probe
primordial non-Gaussianity and large scale general relativistic e↵ects. Using
full sky simulations for the Square Kilometre Array phase 1 (SKA 1 MID)
and the Large Synoptic Survey Telescope (LSST), including foregrounds, we
demonstrate that the cosmic variance contaminated scenario can be beaten
even in the noise free case. Finally, we derive the signal to noise ratio for the
cosmic magnification signal from foreground HI intensity maps combined
with background galaxy count maps. Instruments like SKA1 MID and
HIRAX are highly complementary and well suited for this measurement.
Thanks to the powerful design of the planned radio instruments, all results
confirm their potential and promise an exciting future for cosmology
Simulating the Large-Scale Structure of HI Intensity Maps
Intensity mapping of neutral hydrogen (HI) is a promising observational probe
of cosmology and large-scale structure. We present wide field simulations of HI
intensity maps based on N-body simulations of a box with
particles (particle mass ).
Using a conditional mass function to populate the simulated dark matter density
field with halos below the mass resolution of the simulation (), we assign HI to
those halos according to a phenomenological halo to HI mass relation. The
simulations span a redshift range of 0.35 < z < 0.9 in redshift bins of width
and cover a quarter of the sky at an angular resolution
of about 7'. We use the simulated intensity maps to study the impact of
non-linear effects and redshift space distortions on the angular clustering of
HI. Focusing on the autocorrelations of the maps, we apply and compare several
estimators for the angular power spectrum and its covariance. We verify that
these estimators agree with analytic predictions on large scales and study the
validity of approximations based on Gaussian random fields, particularly in the
context of the covariance. We discuss how our results and the simulated maps
can be useful for planning and interpreting future HI intensity mapping
surveys.Comment: 35 pages, 19 Figures. Accepted for publication in JCA
Simulated multi-tracer analyses with HI intensity mapping
We use full sky simulations, including the effects of foreground
contamination and removal, to explore multi-tracer synergies between a SKA-like
21cm intensity mapping survey and a LSST-like photometric galaxy redshift
survey. In particular we study ratios of auto and cross-correlations between
the two tracers as estimators of the ratio of their biases, a quantity that
should benefit considerably from the cosmic variance cancellation of the
multi-tracer approach. We show how well we should be able to measure the bias
ratio on very large scales (down to ), which is crucial to measure
primordial non-Gaussianity and general relativistic effects on large scale
structure. We find that, in the absence of foregrounds but with realistic noise
levels of such surveys, the multi-tracer estimators are able to improve on the
sensitivity of a cosmic-variance contaminated measurement by a factor of .
When foregrounds are included, estimators using the 21cm auto-correlation
become biased. However, we show that cross-correlation estimators are immune to
this and do not incur in any significant penalty in terms of sensitivity from
discarding the auto-correlation data. However, the loss of long-wavelength
radial modes caused by foreground removal in combination with the low redshift
resolution of photometric surveys, reduces the sensitivity of the multi-tracer
estimator, albeit still better than the cosmic variance contaminated scenario
even in the noise free case. Finally we explore different alternative avenues
to avoid this problem.Comment: 14 pages, 11 figures, 1 tabl
MeerKLASS: MeerKAT Large Area Synoptic Survey
We discuss the ground-breaking science that will be possible with a wide area
survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area
Synoptic Survey). The current specifications of MeerKAT make it a great fit for
science applications that require large survey speeds but not necessarily high
angular resolutions. In particular, for cosmology, a large survey over for hours will potentially provide the first
ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of
dark energy. The combination with multi-wavelength data will give unique
additional information, such as exquisite constraints on primordial
non-Gaussianity using the multi-tracer technique, as well as a better handle on
foregrounds and systematics. Such a wide survey with MeerKAT is also a great
match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era
for galaxies resolved in the HI emission line beyond local structures at z >
0.01. It will also produce a large continuum galaxy sample down to a depth of
about 5\,Jy in L-band, which is quite unique over such large areas and
will allow studies of the large-scale structure of the Universe out to high
redshifts, complementing the galaxy HI survey to form a transformational
multi-wavelength approach to study galaxy dynamics and evolution. Finally, the
same survey will supply unique information for a range of other science
applications, including a large statistical investigation of galaxy clusters as
well as produce a rotation measure map across a huge swathe of the sky. The
MeerKLASS survey will be a crucial step on the road to using SKA1-MID for
cosmological applications and other commensal surveys, as described in the top
priority SKA key science projects (abridged).Comment: Larger version of the paper submitted to the Proceedings of Science,
"MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 201
A Large Sky Survey with MeerKAT
We discuss the ground-breaking science that will be possible with a wide area survey, using
the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area Synoptic Survey). The
current specifications of MeerKAT make it a great fit for cosmological applications, which require
large volumes. In particular, a large survey over ~4,000 deg^2 for ~4,000 hours will potentially
provide the first ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of dark energy. The
combination with multi-wavelength data will give unique additional information, such as the first
constraints on primordial non-Gaussianity using the multi-tracer technique, as well as a better
handle on foregrounds and systematics. The survey will also produce a large continuum galaxy
sample down to a depth of 5 µJy in L-band, unmatched by any other concurrent telescope, which
will allow to study the large-scale structure of the Universe out to high redshifts. Finally, the same
survey will supply unique information for a range of other science applications, including a large
statistical investigation of galaxy clusters, and the discovery of rare high-redshift AGN that can be
used to probe the epoch of reionization as well as produce a rotation measure map across a huge
swathe of the sky. The MeerKLASS survey will be a crucial step on the road to using SKA1-MID
for cosmological applications, as described in the top priority SKA key science projects
A Large Sky Survey with MeerKAT
We discuss the ground-breaking science that will be possible with a wide area survey, using
the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area Synoptic Survey). The
current specifications of MeerKAT make it a great fit for cosmological applications, which require
large volumes. In particular, a large survey over ~4,000 deg^2 for ~4,000 hours will potentially
provide the first ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of dark energy. The
combination with multi-wavelength data will give unique additional information, such as the first
constraints on primordial non-Gaussianity using the multi-tracer technique, as well as a better
handle on foregrounds and systematics. The survey will also produce a large continuum galaxy
sample down to a depth of 5 µJy in L-band, unmatched by any other concurrent telescope, which
will allow to study the large-scale structure of the Universe out to high redshifts. Finally, the same
survey will supply unique information for a range of other science applications, including a large
statistical investigation of galaxy clusters, and the discovery of rare high-redshift AGN that can be
used to probe the epoch of reionization as well as produce a rotation measure map across a huge
swathe of the sky. The MeerKLASS survey will be a crucial step on the road to using SKA1-MID
for cosmological applications, as described in the top priority SKA key science projects