A new upper limit on the density of generally distributed intergalactic neutral hydrogen

1987 ◽  
Vol 318 ◽  
pp. L11 ◽  
Author(s):  
Charles C. Steidel ◽  
Wallace L. W. Sargent
Keyword(s):  
Neutral Hydrogen ◽  
Upper Limit

scholarly journals Sensitive Search for HI in E and SO galaxies

1983 ◽  
Vol 100 ◽  
pp. 305-306
Author(s):  
Norbert Thonnard
Keyword(s):  
Neutral Hydrogen ◽  
Optical Image ◽  
Type I ◽  
Hydrogen Line ◽  
Upper Limit

Do elliptical and SO galaxies in which type I supernovae (SNI) were detected contain more gas than those without SNI detections? Thirteen E and SO galaxies in the Virgo and Pegasus I clusters, seven with SNI detections and six without, were mapped well beyond the optical image at the 21-cm neutral hydrogen line. No HI was detected. In Virgo, the upper limit to MMI/LB is between 0.0005 and 0.0024.

scholarly journals Measuring the distance to the black hole candidate X-ray binary MAXI J1348–630 using H i absorption

2020 ◽  
Vol 501 (1) ◽  
pp. L60-L64
Author(s):  
J Chauhan ◽  
J C A Miller-Jones ◽  
W Raja ◽  
J R Allison ◽  
P F L Jacob ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutral Hydrogen ◽  
Tangent Point ◽  
X Ray ◽  
Black Hole Candidate ◽  
Upper Limit ◽  
Local Standard ◽  
Point Distance ◽  
Spectral State ◽  
Local Standard Of Rest

ABSTRACT We present neutral hydrogen (H i) absorption spectra of the black hole candidate X-ray binary (XRB) MAXI J1348–630 using the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. The ASKAP H i spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of −31 ± 4 km s−1 for MAXI J1348–630, as compared to −50 ± 4 km s−1 for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of $2.2^{+0.5}_{-0.6}$ kpc for MAXI J1348–630, and a strong upper limit of the tangent point distance at 5.3 ± 0.1 kpc. Our preferred distance implies that MAXI J1348–630 reached 17 ± 10  per cent of the Eddington luminosity at the peak of its outburst, and that the source transited from the soft to the hard X-ray spectral state at 2.5 ± 1.5  per cent of the Eddington luminosity. The MeerKAT H i spectrum of MAXI J1348–630 (obtained from the older, low-resolution 4k mode) is consistent with the re-binned ASKAP spectrum, highlighting the potential of the eventual capabilities of MeerKAT for XRB spectral line studies.

scholarly journals Comparing foreground removal techniques for recovery of the LOFAR-EoR 21 cm power spectrum

2020 ◽  
Vol 500 (2) ◽  
pp. 2264-2277 ◽  
Author(s):  
Ian Hothi ◽  
Emma Chapman ◽  
Jonathan R Pritchard ◽  
F G Mertens ◽  
L V E Koopmans ◽  
...  
Keyword(s):  
Neutral Hydrogen ◽  
Instrumental Effects ◽  
Independent Components ◽  
Upper Limit ◽  
Current Usage ◽  
Noise Limit ◽  
Instrumental Effect ◽  
Removal Technique ◽  
Foreground Removal ◽  
Mode Mixing

ABSTRACT We compare various foreground removal techniques that are being utilized to remove bright foregrounds in various experiments aiming to detect the redshifted 21 cm signal of neutral hydrogen from the epoch of reionization. In this work, we test the performance of removal techniques (FastICA, GMCA, and GPR) on 10 nights of LOFAR data and investigate the possibility of recovering the latest upper limit on the 21 cm signal. Interestingly, we find that GMCA and FastICA reproduce the most recent 2σ upper limit of $\Delta ^2_{21} \lt $ (73)2 mK2 at k = 0.075 hcMpc−1, which resulted from the application of GPR. We also find that FastICA and GMCA begin to deviate from the noise-limit at k-scales larger than ∼0.1 hcMpc−1. We then replicate the data via simulations to see the source of FastICA and GMCA’s limitations, by testing them against various instrumental effects. We find that no single instrumental effect, such as primary beam effects or mode-mixing, can explain the poorer recovery by FastICA and GMCA at larger k-scales. We then test scale-independence of FastICA and GMCA, and find that lower k-scales can be modelled by a smaller number of independent components. For larger scales (k ≳ 0.1 hcMpc−1), more independent components are needed to fit the foregrounds. We conclude that, the current usage of GPR by the LOFAR collaboration is the appropriate removal technique. It is both robust and less prone to overfitting, with future improvements to GPR’s fitting optimization to yield deeper limits.

scholarly journals SILVERRUSH. XI. Constraints on the Lyα Luminosity Function and Cosmic Reionization at z = 7.3 with Subaru/Hyper Suprime-Cam

2021 ◽  
Vol 923 (2) ◽  
pp. 229
Author(s):  
Hinako Goto ◽  
Kazuhiro Shimasaku ◽  
Satoshi Yamanaka ◽  
Rieko Momose ◽  
Makoto Ando ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Intergalactic Medium ◽  
Neutral Hydrogen ◽  
Neutral Fraction ◽  
Estimation Methods ◽  
Large Area ◽  
Upper Limit ◽  
Narrowband Imaging ◽  
First Time

Abstract The Lyα luminosity function (LF) of Lyα emitters (LAEs) has been used to constrain the neutral hydrogen fraction in the intergalactic medium (IGM) and thus the timeline of cosmic reionization. Here we present the results of a new narrowband imaging survey for z = 7.3 LAEs in a large area of ∼3 deg2 with Subaru/Hyper Suprime-Cam. No LAEs are detected down to L Lyα ≃ 1043.2 erg s−1 in an effective cosmic volume of ∼2 × 106 Mpc3, placing an upper limit on the bright part of the z = 7.3 Lyα LF for the first time and confirming a decrease in bright LAEs from z = 7.0. By comparing this upper limit with the Lyα LF in the case of fully ionized IGM, which is predicted using an observed z = 5.7 Lyα LF on the assumption that the intrinsic Lyα LF evolves in the same way as the UV LF, we obtain the relative IGM transmission T Ly α IGM ( 7.3 ) / T Ly α IGM ( 5.7 ) < 0.77 and then the volume-averaged neutral fraction x H I(7.3) > 0.28. Cosmic reionization is thus still ongoing at z = 7.3, consistent with results from other x H I estimation methods. A similar analysis using literature Lyα LFs finds that at z = 6.6 and 7.0, the observed Lyα LF agrees with the predicted one, consistent with full ionization.

scholarly journals Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

2020 ◽  
Vol 493 (2) ◽  
pp. 1662-1685 ◽  
Author(s):  
F G Mertens ◽  
M Mevius ◽  
L V E Koopmans ◽  
A R Offringa ◽  
G Mellema ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Gaussian Process Regression ◽  
Spectral Structure ◽  
Signal Power ◽  
Spectral Correlation ◽  
Upper Limit ◽  
Upper Limits ◽  
Excess Power

ABSTRACT A new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted power spectrum inference. Previously seen ‘excess power’ due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25–0.45 MHz and is partially correlated between nights, especially in the foreground wedge region. The correlation is stronger between nights covering similar local sidereal times. A best 2-σ upper limit of $\Delta ^2_{21} \lt (73)^2\, \mathrm{mK^2}$ at $k = 0.075\, \mathrm{h\, cMpc^{-1}}$ is found, an improvement by a factor ≈8 in power compared to the previously reported upper limit. The remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radiofrequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.

scholarly journals Radio Images of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 17-28 ◽  
Author(s):  
Yervant Terzian
Keyword(s):  
Magnetic Field ◽  
Neutral Hydrogen ◽  
Planetary Nebulae ◽  
Aperture Synthesis ◽  
Large Array ◽  
Very Large Array ◽  
Upper Limit ◽  
Neutral Material ◽  
Continuum Radio ◽  
The Continuum

The continuum radio spectra of planetary nebulae are discussed, and the structure of these objects is examined from the observed aperture synthesis brightness distributions determined with the Very Large Array. The use of radio observations in determining distances to planetary nebulae is examined. The detection of atomic neutral hydrogen at λ21 cm associated with planetary nebulae, as well as the associated CO and OH components are discussed. An upper limit, of the nebular magnetic field associated with the neutral material, of 1mG is reported for NGC 6302.

scholarly journals The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6

2011 ◽  
Vol 413 (2) ◽  
pp. 1174-1183 ◽  
Author(s):  
Gregory Paciga ◽  
Tzu-Ching Chang ◽  
Yashwant Gupta ◽  
Rajaram Nityanada ◽  
Julia Odegova ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Neutral Hydrogen ◽  
Upper Limit

Motions of neutral hydrogen at high latitudes

1967 ◽  
Vol 31 ◽  
pp. 265-278 ◽  
Author(s):  
A. Blaauw ◽  
I. Fejes ◽  
C. R. Tolbert ◽  
A. N. M. Hulsbosch ◽  
E. Raimond
Keyword(s):  
Surface Density ◽  
Velocity Dispersion ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
High Latitudes ◽  
Low Velocity

Earlier investigations have shown that there is a preponderance of negative velocities in the hydrogen gas at high latitudes, and that in certain areas very little low-velocity gas occurs. In the region 100° &lt;l&lt; 250°, + 40° &lt;b&lt; + 85°, there appears to be a disturbance, with velocities between - 30 and - 80 km/sec. This ‘streaming’ involves about 3000 (r/100)2solar masses (rin pc). In the same region there is a low surface density at low velocities (|V| &lt; 30 km/sec). About 40% of the gas in the disturbance is in the form of separate concentrations superimposed on a relatively smooth background. The number of these concentrations as a function of velocity remains constant from - 30 to - 60 km/sec but drops rapidly at higher negative velocities. The velocity dispersion in the concentrations varies little about 6·2 km/sec. Concentrations at positive velocities are much less abundant.

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