The Five‐hundred‐meter Aperture Spherical Radio Telescope project

Li, Di; Pan, Zhichen

doi:10.1002/2015rs005877

Cited by 98 publications

(91 citation statements)

References 16 publications

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“…The large-scale distribution of 18-cm OH emission in the galaxy could shed light on the features of the galactic molecular ISM not revealed by conventional CO mapping observations. Future observations by the 500m FAST telescope (Li & Pan 2016), and the SKA (Dickey et al 2012) may help to reveal a portion of this dark molecular ISM content through OH absorption studies; however, the low excitation temperature of the 18-cm OH lines (Engelke & Allen 2018) remains an impediment to the straightforward interpretation of OH observations in the inner Galaxy in the presence of substantial ambient nonthermal continuum emission. An all-sky survey for OH emission in the outer Galaxy would not be hindered by the much weaker continuum of the galactic background there; however, an effective OH emission survey may be presently out of reach of current instruments owing to the long integration times required to obtain the necessary sensitivity.…”

Section: Discussionmentioning

confidence: 99%

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

Busch

Allen

Engelke

et al. 2019

ApJ

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We report the results from a new, highly sensitive (∆T mb ∼ 3mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 x 9-pixel grid covering a 1 • × 1 • patch of sky in the direction of l = 105. • 00, b = +2. • 50 towards the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope (GBT) 1667 MHz OH results with archival 12 CO(1-0) observations from the Five College Radio Astronomy Observatory (FCRAO) Outer Galaxy Survey within the velocity range of the Perseus Arm at these galactic coordinates. Out of the 81 statistically-independent pointings in our survey area, 86% show detectable OH emission at 1667 MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits below an A v of 0.2, but the CO emission does not appear until the volume density exceeds 100-200 cm −3 . These results demonstrate that a combination of low column density A v and low volume density n H can explain the lack of CO emission along sight lines exhibiting OH emission. The 18-cm OH main lines, with their low critical density of n * ∼ 1 cm −3 , are collisionally excited over a large fraction of the quiescent galactic environment and, for observations of sufficient sensitivity, provide an optically-thin radio tracer for diffuse H 2 .

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Section: Discussionmentioning

confidence: 99%

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

Busch

Allen

Engelke

et al. 2019

ApJ

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“…Being able to analyse a large sky area is crucial in increasing the statistics of the galaxy pairs, and in enhancing a possible filament signal; besides, being able to explore different sky regions would lead to more sensible conclusions, mitigating the effects of local sample variance. Surveys conducted using next-generation facilities like the Square Kilometer Array (Braun et al 2015) and the FAST telescope (Li & Pan 2016) are expected to provide improved maps over a larger sky area thanks to the higher sensitivity and survey speed. A proper foreground removal clearly remains the critical point for delivering final maps with sufficient sensitivity to enable a detection of the filament HI signal.…”

Section: Discussionmentioning

confidence: 99%

Searching for H i imprints in cosmic web filaments with 21-cm intensity mapping

Tramonte

2019

Monthly Notices of the Royal Astronomical Society

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We investigate the possible presence of neutral hydrogen (HI) in intergalactic filaments at very low redshift (z ∼ 0.08), by stacking a set of 274,712 2dFGRS galaxy pairs over 21-cm maps obtained with dedicated observations conducted with the Parkes radio telescope, over a total sky area of approximately 1,300 square degrees covering two patches in the northern and in the southern Galactic hemispheres. The stacking is performed by combining local maps in which each pair is brought to a common reference frame; the resulting signal from the edge galaxies is then removed to extract the filament residual emission. We repeat the analysis on maps cleaned removing either 10 or 20 foreground modes in a principal component analysis. Our study does not reveal any clear HI excess in the considered filaments in either case; we determine upper limits on the total filament HI brightness temperature at T b 10.3 µK for the 10-mode and at T b 4.8 µK for the 20-mode removed maps at the 95% confidence level. These estimates translate into upper limits for the local filament HI density parameter, Ω (f) HI 7.0 × 10 −5 and Ω (f) HI 3.2 × 10 −5 respectively, and for the HI column density, N HI 4.6 × 10 15 cm −2 and N HI 2.1 × 10 15 cm −2 respectively. These column density constraints are consistent with previous detections of HI in the warm-hot intergalactic medium obtained observing broad Ly α absorption systems. The present work shows for the first time how such constraints can be achieved using the stacking of galaxy pairs on 21-cm maps.

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“…b. FAST FAST is the largest single-dish telescope, which also has the multibeam system of 19 feed-horns array [35,36]. The multibeam system is proposed to work at frequencies from 1.05 to 1.45GHz with system temperature of 25K.…”

Section: Experiments Parametersmentioning

confidence: 99%

Constraints on primordial non-Gaussianity from future Hi intensity mapping experiments

2017

Phys. Rev. D

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The primordial non-Gaussianity induces scale-dependent bias of the HI with respect to the underlying dark matter, which exhibits features on the very large scales of the 21-cm power spectrum potentially observable with HI intensity mapping observations. We forecast the prospective constraints on the four fundamental shapes of primordial non-Gaussianity (local, equilateral, orthogonal, and enfolded), with the current and future HI intensity mapping experiments, BINGO, FAST, and SKA-I. With the current configuration of the experiments and assumed one-year observation time, we find that the SKA-I will provide tighter constraints on the local shape of primoridal non-Gaussianity than Planck. The results are (σ f local NL

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The Five‐hundred‐meter Aperture Spherical Radio Telescope project

Cited by 98 publications

References 16 publications

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

Searching for H i imprints in cosmic web filaments with 21-cm intensity mapping

Constraints on primordial non-Gaussianity from future Hi intensity mapping experiments

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