10 research outputs found
Characteristic Functions for Cosmological Cross-Correlations
We introduce a novel unbiased, cross-correlation estimator for the one-point
statistics of cosmological random fields. One-point statistics are a useful
tool for analysis of highly non-Gaussian density fields, while
cross-correlations provide a powerful method for combining information from
pairs of fields and separating them from noise and systematics. We derive a new
Deconvolved Distribution Estimator that combines the useful properties of these
two methods into one statistic. Using two example models of a toy Gaussian
random field and a line intensity mapping survey, we demonstrate these
properties quantitatively and show that the DDE can be used for inference. This
new estimator can be applied to any pair of overlapping, non-Gaussian
cosmological observations, including large-scale structure, the
Sunyaev-Zeldovich effect, weak lensing, and many others.Comment: 13 pages, 13 figures, for submission to MNRA
Cross-correlating Carbon Monoxide Line-intensity Maps with Spectroscopic and Photometric Galaxy Surveys
Line-intensity mapping (LIM or IM) is an emerging field of observational
work, with strong potential to fit into a larger effort to probe large-scale
structure and small-scale astrophysical phenomena using multiple complementary
tracers. Taking full advantage of such complementarity means, in part,
undertaking line-intensity surveys with galaxy surveys in mind. We consider the
potential for detection of a cross-correlation signal between COMAP and blind
surveys based on photometric redshifts (as in COSMOS) or based on spectroscopic
data (as with the HETDEX survey of Lyman- emitters). We find that
obtaining accuracy in redshifts and
sources per Mpc with spectroscopic redshift determination
should enable a CO-galaxy cross spectrum detection significance at least twice
that of the CO auto spectrum. Either a future targeted spectroscopic survey or
a blind survey like HETDEX may be able to meet both of these requirements.Comment: 19 pages + appendix (31 pages total), 16 figures, 6 tables; accepted
for publication in Ap
COMAP Early Science: VII. Prospects for CO Intensity Mapping at Reionization
We introduce COMAP-EoR, the next generation of the Carbon Monoxide Mapping
Array Project aimed at extending CO intensity mapping to the Epoch of
Reionization. COMAP-EoR supplements the existing 30 GHz COMAP Pathfinder with
two additional 30 GHz instruments and a new 16 GHz receiver. This combination
of frequencies will be able to simultaneously map CO(1--0) and CO(2--1) at
reionization redshifts () in addition to providing a significant
boost to the sensitivity of the Pathfinder. We examine a set of
existing models of the EoR CO signal, and find power spectra spanning several
orders of magnitude, highlighting our extreme ignorance about this period of
cosmic history and the value of the COMAP-EoR measurement. We carry out the
most detailed forecast to date of an intensity mapping cross-correlation, and
find that five out of the six models we consider yield signal to noise ratios
(S/N) for COMAP-EoR, with the brightest reaching a S/N above 400.
We show that, for these models, COMAP-EoR can make a detailed measurement of
the cosmic molecular gas history from , as well as probe the
population of faint, star-forming galaxies predicted by these models to be
undetectable by traditional surveys. We show that, for the single model that
does not predict numerous faint emitters, a COMAP-EoR-type measurement is
required to rule out their existence. We briefly explore prospects for a
third-generation Expanded Reionization Array (COMAP-ERA) capable of detecting
the faintest models and characterizing the brightest signals in extreme detail.Comment: Paper 7 of 7 in series. 19 pages, 10 figures, to be submitted to Ap
COMAP Early Science: III. CO Data Processing
We describe the first season COMAP analysis pipeline that converts raw
detector readouts to calibrated sky maps. This pipeline implements four main
steps: gain calibration, filtering, data selection, and map-making. Absolute
gain calibration relies on a combination of instrumental and astrophysical
sources, while relative gain calibration exploits real-time total-power
variations. High efficiency filtering is achieved through spectroscopic
common-mode rejection within and across receivers, resulting in nearly
uncorrelated white noise within single-frequency channels. Consequently,
near-optimal but biased maps are produced by binning the filtered time stream
into pixelized maps; the corresponding signal bias transfer function is
estimated through simulations. Data selection is performed automatically
through a series of goodness-of-fit statistics, including and
multi-scale correlation tests. Applying this pipeline to the first-season COMAP
data, we produce a dataset with very low levels of correlated noise. We find
that one of our two scanning strategies (the Lissajous type) is sensitive to
residual instrumental systematics. As a result, we no longer use this type of
scan and exclude data taken this way from our Season 1 power spectrum
estimates. We perform a careful analysis of our data processing and observing
efficiencies and take account of planned improvements to estimate our future
performance. Power spectrum results derived from the first-season COMAP maps
are presented and discussed in companion papers.Comment: Paper 3 of 7 in series. 26 pages, 23 figures, submitted to Ap
COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
We present early results from the COMAP Galactic Plane Survey conducted
between June 2019 and April 2021, spanning in Galactic
longitude and |b|<1.\!\!^{\circ}5 in Galactic latitude with an angular
resolution of . The full survey will span -
and will be the first large-scale radio continuum survey at
GHz with sub-degree resolution. We present initial results from the first part
of the survey, including diffuse emission and spectral energy distributions
(SEDs) of HII regions and supernova remnants. Using low and high frequency
surveys to constrain free-free and thermal dust emission contributions, we find
evidence of excess flux density at GHz in six regions that we interpret
as anomalous microwave emission. Furthermore we model UCHII contributions using
data from the GHz CORNISH catalogue and reject this as the cause of the
GHz excess. Six known supernova remnants (SNR) are detected at GHz,
and we measure spectral indices consistent with the literature or show evidence
of steepening. The flux density of the SNR W44 at GHz is consistent with
a power-law extrapolation from lower frequencies with no indication of spectral
steepening in contrast with recent results from the Sardinia Radio Telescope.
We also extract five hydrogen radio recombination lines to map the warm ionized
gas, which can be used to estimate electron temperatures or to constrain
continuum free-free emission. The full COMAP Galactic plane survey, to be
released in 2023/2024, will be an invaluable resource for Galactic
astrophysics.Comment: Paper 6 of 7 in series. 28 pages, 10 figures, submitted to Ap
Cross-correlating Carbon Monoxide Line-intensity Maps with Spectroscopic and Photometric Galaxy Surveys
Line-intensity mapping is an emerging field of observational work, with strong potential to fit into a larger effort to probe large-scale structure and small-scale astrophysical phenomena using multiple complementary tracers. Taking full advantage of such complementarity means, in part, undertaking line-intensity surveys with galaxy surveys in mind. We consider the potential for detection of a cross-correlation signal between COMAP and blind surveys based on photometric redshifts (as in COSMOS) or based on spectroscopic data (as with the HETDEX survey of Lyα emitters). We find that obtaining σ_z (1+z) ≲ 0.003 accuracy in redshifts and ≳10^(−4) sources per Mpc^3 with spectroscopic redshift determination should enable a CO-galaxy cross spectrum detection significance at least twice that of the CO auto spectrum. Either a future targeted spectroscopic survey or a blind survey like HETDEX may be able to meet both of these requirements
COMAP Early Science: V. Constraints and Forecasts at
We present the current state of models for the carbon monoxide (CO)
line-intensity signal targeted by the CO Mapping Array Project (COMAP)
Pathfinder in the context of its early science results. Our fiducial model,
relating dark matter halo properties to CO luminosities, informs parameter
priors with empirical models of the galaxy-halo connection and previous CO(1-0)
observations. The Pathfinder early science data spanning wavenumbers
-Mpc represent the first direct 3D constraint on the
clustering component of the CO(1-0) power spectrum. Our 95% upper limit on the
redshift-space clustering amplitude K greatly
improves on the indirect upper limit of K reported from the CO
Power Spectrum Survey (COPSS) measurement at Mpc. The COMAP
limit excludes a subset of models from previous literature, and constrains
interpretation of the COPSS results, demonstrating the complementary nature of
COMAP and interferometric CO surveys. Using line bias expectations from our
priors, we also constrain the squared mean line intensity-bias product,
K, and the cosmic molecular gas
density, Mpc (95% upper
limits). Based on early instrument performance and our current CO signal
estimates, we forecast that the five-year Pathfinder campaign will detect the
CO power spectrum with overall signal-to-noise of 9-17. Between then and now,
we also expect to detect the CO-galaxy cross-spectrum using overlapping galaxy
survey data, enabling enhanced inferences of cosmic star-formation and
galaxy-evolution history.Comment: Paper 5 of 7 in series. 17 pages + appendix and bibliography (30
pages total); 15 figures, 6 tables; accepted for publication in ApJ; v3
reflects the accepted version with minor changes and additions to tex
COMAP Early Science: I. Overview
The CO Mapping Array Project (COMAP) aims to use line intensity mapping of
carbon monoxide (CO) to trace the distribution and global properties of
galaxies over cosmic time, back to the Epoch of Reionization (EoR). To validate
the technologies and techniques needed for this goal, a Pathfinder instrument
has been constructed and fielded. Sensitive to CO(1-0) emission from
- and a fainter contribution from CO(2-1) at -8, the
Pathfinder is surveying deg in a 5-year observing campaign to detect
the CO signal from . Using data from the first 13 months of observing,
we estimate on scales - the first direct
3D constraint on the clustering component of the CO(1-0) power spectrum. Based
on these observations alone, we obtain a constraint on the amplitude of the
clustering component (the squared mean CO line temperature-bias product) of
K - nearly an order-of-magnitude improvement
on the previous best measurement. These constraints allow us to rule out two
models from the literature. We forecast a detection of the power spectrum after
5 years with signal-to-noise ratio (S/N) 9-17. Cross-correlation with an
overlapping galaxy survey will yield a detection of the CO-galaxy power
spectrum with S/N of 19. We are also conducting a 30 GHz survey of the Galactic
plane and present a preliminary map. Looking to the future of COMAP, we examine
the prospects for future phases of the experiment to detect and characterize
the CO signal from the EoR.Comment: Paper 1 of 7 in series. 18 pages, 16 figures, submitted to Ap
A Model of Spectral Line Broadening in Signal Forecasts for Line-intensity Mapping Experiments
Line-intensity mapping observations will find fluctuations of integrated line
emission are attenuated by varying degrees at small scales due to the width of
the line emission profiles. This attenuation may significantly impact estimates
of astrophysical or cosmological quantities derived from measurements. We
consider a theoretical treatment of the effect of line broadening on both the
clustering and shot-noise components of the power spectrum of a generic
line-intensity power spectrum using a halo model. We then consider possible
simplifications to allow easier application in analysis, particularly in the
context of inferences that require numerous, repeated, fast computations of
model line-intensity signals across a large parameter space. For the CO Mapping
Array Project (COMAP) and the CO(1-0) line-intensity field at serving
as our primary case study, we expect a attenuation of the
spherically averaged power spectrum on average at relevant scales of
- Mpc, compared to for the interferometric
Millimetre-wave Intensity Mapping Experiment (mmIME) targeting shot noise from
CO lines at - at scales of Mpc. We also consider
the nature and amplitude of errors introduced by simplified treatments of line
broadening, and find that while an approximation using a single effective
velocity scale is sufficient for spherically-averaged power spectra, a more
careful treatment is necessary when considering other statistics such as higher
multipoles of the anisotropic power spectrum or the voxel intensity
distribution.Comment: 24 pages + appendix and bibliography (33 pages total), 16 figures, 2
tables; accepted for publication in Ap