Abstract
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 and the CO(1–0) line-intensity field at
z
∼ 3 serving as our primary case study, we expect a ∼10% attenuation of the spherically averaged power spectrum on average at relevant scales of
k
≈ 0.2–0.3 Mpc
−1
compared to ∼25% for the interferometric Millimetre-wave Intensity Mapping Experiment targeting shot noise from CO lines at
z
∼ 1–5 at scales of
k
≳ 1 Mpc
−1
. 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.
Abstract 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 Spectroscopic Survey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1–0) line emission of 0.129 Jy km s −1 . 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 × 10 11 K km pc 2 s −1 , or an average molecular gas density ρ H 2 in regions of the Universe containing a quasar of ≤1.52 × 10 8 M ⊙ cMpc −3 . The L CO ′ upper limit falls among CO line luminosities obtained from individually targeted quasars in the COMAP redshift range, and the ρ H 2 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 yr 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 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.
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 Ly emitters). We find that obtaining accuracy in redshifts and 10−4 sources per Mpc3 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.
Abstract
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 (
z
∼ 5–8) in addition to providing a significant boost to the
z
∼ 3 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/Ns) ≳ 20 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
z
∼ 2–8, 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.
Abstract We report observations of the ground state transitions of 12 CO, 13 CO, C 18 O, HCN, and HCO + at 88–115 GHz in the inner region of the nearby galaxy IC 342. These data were obtained with ...the 16 pixel spectroscopic focal plane array Argus on the 100 m Robert C. Byrd Green Bank Telescope (GBT) at 6″–9″ resolution. In the nuclear bar region, the intensity distributions of 12 CO(1–0) and 13 CO(1–0) emission trace moderate densities, and differ from the dense gas distributions sampled in C 18 O(1–0), HCN(1–0), and HCO + (1–0). We observe a constant HCN(1–0)-to-HCO + (1–0) ratio of 1.2 ± 0.1 across the whole ∼1 kpc bar. This indicates that the HCN(1–0) and HCO + (1–0) lines have intermediate optical depth, and that the corresponding n H 2 of the gas producing the emission is of order 10 4.5−6 cm −3 . We show that HCO + (1–0) is thermalized and HCN(1–0) is close to thermalization. The very tight correlation between the HCN(1–0) and HCO + (1–0) intensities across the 1 kpc bar suggests that this ratio is more sensitive to the relative abundance of the two species than to the gas density. We confirm an angular offset (∼10″) between the spatial distribution of molecular gas and the star formation sites. Finally, we find a breakdown of the L IR – L HCN correlation at high spatial resolution due to the effect of incomplete sampling of star-forming regions by HCN emission in IC 342. The scatter of the L IR – L HCN relation decreases as the spatial scale increases from 10″ to 30″ (170–510 pc), and is comparable to the scatter of the global relation at a scale of 340 pc.
Abstract
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
k
= 0.051–0.62 Mpc
−1
, we estimate
P
CO
(k) = −2. 7 ± 1.7 × 10
4
μ
K
2
Mpc
3
, the first direct 3D constraint on the clustering component of the CO(1–0) power spectrum in the literature.
Abstract
We present early results from the CO Mapping Array Project (COMAP) Galactic Plane Survey conducted between 2019 June and 2021 April, spanning 20° <
ℓ
< 40° in Galactic longitude and ∣
b
∣ < ...1.°5 in Galactic latitude with an angular resolution of 4.′5. We present initial results from the first part of the survey, including the diffuse emission and spectral energy distributions of H
ii
regions and supernova remnants (SNRs). Using low- and high-frequency surveys to constrain free–free and thermal dust emission contributions, we find evidence of excess flux density at 30 GHz in six regions, which we interpret as anomalous microwave emission. Furthermore we model ultracompact H
ii
contributions using data from the 5 GHz CORNISH catalog and reject these as the cause of the 30 GHz excess. Six known SNRs are detected at 30 GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at 30 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 (RRLs) 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 span
ℓ
∼ 20°–220° and will be the first large-scale radio continuum and RRL survey at 30 GHz with 4.′5 resolution.
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