66 research outputs found
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: VIII. A Joint Stacking Analysis with eBOSS Quasars
We present a new upper limit on the cosmic molecular gas density at
obtained using the first year of observations from the CO Mapping
Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 282
quasars selected from the Extended Baryon Oscillation Spectroscopic Survey
(eBOSS) catalog, yielding a 95% upper limit for flux from CO(1-0) line emission
of 0.210 Jy km/s. Depending on the assumptions made, this value can be
interpreted as either an average CO line luminosity of eBOSS
quasars of K km pc s, or an average
molecular gas density in regions of the universe containing
a quasar of M cMpc. The
upper limit falls among CO line luminosities obtained from
individually-targeted quasars in the COMAP redshift range, and the
value is comparable to upper limits obtained from other
Line Intensity Mapping (LIM) surveys and their joint analyses. Further, we
forecast the values obtainable with the COMAP/eBOSS stack after the full 5-year
COMAP Pathfinder survey. We predict that a detection is probable with this
method, depending on the CO properties of the quasar sample. Based on these
achieved sensitivities, we believe that this technique of stacking LIM data on
the positions of traditional galaxy or quasar catalogs is extremely promising,
both as a technique for investigating large galaxy catalogs efficiently at high
redshift and as a technique for bolstering the sensitivity of LIM experiments,
even with a fraction of their total expected survey data.Comment: 15 pages, 8 figures. To be submitted to Ap
COMAP Early Science: VIII. A Joint Stacking Analysis with eBOSS Quasars
We present a new upper limit on the cosmic molecular gas density at z = 2.4 − 3.4 obtained using the first year of observations from the CO Mapping Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 243 quasars selected from the Extended Baryon Oscillation SpectroscopicSurvey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1-0) line emission of 0.129 Jykm/s. Depending on the balance of the emission between the quasar host and its environment, this value can be interpreted as an average CO line luminosity L′CO of eBOSS quasars of ≤ 1.26 × 1011 K km pc2s−1, or an average molecular gas density ρH2 in regions of the universe containing a quasar of ≤ 1.52 × 108 M⊙ cMpc−3. The L′ CO upper limit falls among CO line luminosities obtained fromindividually-targeted quasars in the COMAP redshift range, and the ρH2 value is comparable to upper limits obtained from other Line Intensity Mapping (LIM) surveys and their joint analyses. Further, we forecast the values obtainable with the COMAP/eBOSS stack after the full 5-year COMAP Pathfinder survey. We predict that a detection is probable with this method, depending on the CO properties of the quasar sample. Based on the achieved sensitivity, we believe that this technique of stacking LIM data on the positions of traditional galaxy or quasar catalogs is extremely promising, both asa technique for investigating large galaxy catalogs efficiently at high redshift and as a technique for bolstering the sensitivity of LIM experiments, even with a fraction of their total expected survey data
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
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Inflation and Dark Energy from spectroscopy at z > 2
The expansion of the Universe is understood to have accelerated during two
epochs: in its very first moments during a period of Inflation and much more
recently, at z < 1, when Dark Energy is hypothesized to drive cosmic
acceleration. The undiscovered mechanisms behind these two epochs represent
some of the most important open problems in fundamental physics. The large
cosmological volume at 2 < z < 5, together with the ability to efficiently
target high- galaxies with known techniques, enables large gains in the
study of Inflation and Dark Energy. A future spectroscopic survey can test the
Gaussianity of the initial conditions up to a factor of ~50 better than our
current bounds, crossing the crucial theoretical threshold of
of order unity that separates single field and
multi-field models. Simultaneously, it can measure the fraction of Dark Energy
at the percent level up to , thus serving as an unprecedented test of
the standard model and opening up a tremendous discovery space
COMAP Early Science: II. Pathfinder Instrument
Line intensity mapping (LIM) is a new technique for tracing the global
properties of galaxies over cosmic time. Detection of the very faint signals
from redshifted carbon monoxide (CO), a tracer of star formation, pushes the
limits of what is feasible with a total-power instrument. The CO Mapping
Project (COMAP) Pathfinder is a first-generation instrument aiming to prove the
concept and develop the technology for future experiments, as well as
delivering early science products. With 19 receiver channels in a hexagonal
focal plane arrangement on a 10.4 m antenna, and an instantaneous 26-34 GHz
frequency range with 2 MHz resolution, it is ideally suited to measuring
CO(=1-0) from . In this paper we discuss strategies for designing
and building the Pathfinder and the challenges that were encountered. The
design of the instrument prioritized LIM requirements over those of ancillary
science. After a couple of years of operation, the instrument is well
understood, and the first year of data is already yielding useful science
results. Experience with this Pathfinder will drive the design of the next
generations of experiments.Comment: Paper 2 of 7 in series. 27 pages, 28 figures, submitted to Ap
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: 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: IV. Power Spectrum Methodology and Results
We present the power spectrum methodology used for the first-season COMAP
analysis, and assess the quality of the current data set. The main results are
derived through the Feed-feed Pseudo-Cross-Spectrum (FPXS) method, which is a
robust estimator with respect to both noise modeling errors and experimental
systematics. We use effective transfer functions to take into account the
effects of instrumental beam smoothing and various filter operations applied
during the low-level data processing. The power spectra estimated in this way
have allowed us to identify a systematic error associated with one of our two
scanning strategies, believed to be due to residual ground or atmospheric
contamination. We omit these data from our analysis and no longer use this
scanning technique for observations. We present the power spectra from our
first season of observing and demonstrate that the uncertainties are
integrating as expected for uncorrelated noise, with any residual systematics
suppressed to a level below the noise. Using the FPXS method, and combining
data on scales we estimate , the first direct 3D
constraint on the clustering component of the CO(1-0) power spectrum in the
literature.Comment: Paper 4 of 7 in series. 18 pages, 11 figures, as accepted in Ap
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