The Large-Scale Distribution of Neutral Hydrogen in the Galaxy

1974 ◽  
pp. 82-117 ◽  
Author(s):  
W. Butler Burton
Keyword(s):  
Large Scale ◽  
Neutral Hydrogen ◽  
The Galaxy

scholarly journals Neutral hydrogen gas within and around NGC 1316

2019 ◽  
Vol 628 ◽  
pp. A122 ◽  
Author(s):  
P. Serra ◽  
F. M. Maccagni ◽  
D. Kleiner ◽  
W. J. G. de Blok ◽  
J. H. van Gorkom ◽  
...  
Keyword(s):  
Large Scale ◽  
Molecular Form ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Neutral Gas ◽  
Tidal Forces ◽  
The Galaxy ◽  
Long Tails ◽  
Stellar Body ◽  
Fornax Cluster

We present MeerKAT observations of neutral hydrogen gas (H I) in the nearby merger remnant NGC 1316 (Fornax A), the brightest member of a galaxy group which is falling into the Fornax cluster. We find H I on a variety of scales, from the galaxy centre to its large-scale environment. For the first time we detect H I at large radii (70–150 kpc in projection), mostly distributed on two long tails associated with the galaxy. Gas in the tails dominates the H I mass of NGC 1316: 7 × 108 M⊙– 14 times more than in previous observations. The total H I mass is comparable to the amount of neutral gas found inside the stellar body, mostly in molecular form. The H I tails are associated with faint optical tidal features thought to be the remnant of a galaxy merger occurred a few billion years ago. They demonstrate that the merger was gas-rich. During the merger, tidal forces pulled some gas and stars out to large radii, where we now detect them in the form of optical tails and, thanks to our new data, H I tails; while torques caused the remaining gas to flow towards the centre of the remnant, where it was converted into molecular gas and fuelled the starburst revealed by the galaxy’s stellar populations. Several of the observed properties of NGC 1316 can be reproduced by a ∼10:1 merger between a dominant, gas-poor early-type galaxy and a smaller, gas-rich spiral occurred 1–3 Gyr ago, likely followed by subsequent accretion of satellite galaxies.

scholarly journals Quantifying EoR delay spectrum contamination from diffuse radio emission

2020 ◽  
Vol 494 (3) ◽  
pp. 3712-3727 ◽  
Author(s):  
Adam E Lanman ◽  
Jonathan C Pober ◽  
Nicholas S Kern ◽  
Eloy de Lera Acedo ◽  
David R DeBoer ◽  
...  
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
Power Spectra ◽  
Neutral Hydrogen ◽  
Spectral Structure ◽  
Wide Field ◽  
Electromagnetic Simulations ◽  
The Galaxy ◽  
Spectral Weighting ◽  
The Universe

ABSTRACT The 21 cm hyperfine transition of neutral hydrogen offers a promising probe of the large-scale structure of the universe before and during the Epoch of Reionization (EoR), when the first ionizing sources formed. Bright radio emission from foreground sources remains the biggest obstacle to detecting the faint 21 cm signal. However, the expected smoothness of foreground power leaves a clean window in Fourier space where the EoR signal can potentially be seen over thermal noise. Though the boundary of this window is well defined in principle, spectral structure in foreground sources, instrumental chromaticity, and choice of spectral weighting in analysis all affect how much foreground power spills over into the EoR window. In this paper, we run a suite of numerical simulations of wide-field visibility measurements, with a variety of diffuse foreground models and instrument configurations, and measure the extent of contaminated Fourier modes in the EoR window using a delay-transform approach to estimate power spectra. We also test these effects with a model of the Hydrogen Epoch of Reionization Array (HERA) antenna beam generated from electromagnetic simulations, to take into account further chromatic effects in the real instrument. We find that foreground power spillover is dominated by the so-called pitchfork effect, in which diffuse foreground power is brightened near the horizon due to the shortening of baselines. As a result, the extent of contaminated modes in the EoR window is largely constant over time, except when the Galaxy is near the pointing centre.

Distribution and systematic motions of neutral hydrogen

1967 ◽  
Vol 31 ◽  
pp. 143-160 ◽  
Author(s):  
P. O. Lindblad
Keyword(s):  
Recent Work ◽  
Large Scale ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Structural Features ◽  
Frequency Resolution ◽  
Narrow Strip ◽  
The Galaxy ◽  
Scale Motion ◽  
Determination Of Parameters

Recent work on the rotation curve of the Galaxy has confirmed the large-scale asymmetry of the motion of neutral hydrogen. In addition it seems that the radial velocities at the subcentral points of the lines of sight vary with longitude in a rather unsmooth manner. These irregularities of the motions may be associated with the distribution of matter in spiral arms. Large-scale systematic deviations from circular motion, ranging up to at least 30 km/sec in the outer regions of the Galaxy, are shown by observations across the anti-centre.Thus it presumably is impossible to describe the velocity field of the gas in terms of a simple general model, or to derive the force field without simultaneously solving the distribution problem. We may have to construct for each region, or for each separate feature of galactic structure, a special model that explains its radial-velocity properties. All these models must of course be in mutual agreement.The most coherent picture of the large-scale motion of the interstellar hydrogen is still given by the early Dutch and Australian surveys. A number of surveys with higher resolution are at present well on their way, although most of them are limited to a rather narrow strip along the galactic equator.In the interpretation of line profiles some method of analysis into Gaussian components is increasingly used, especially as an aid in following different structural features in diagrams giving velocity as a function of galactic longitude or latitude, and in separating these features in regions of velocity overlap. Applications of this technique and of simple model-making are demonstrated in connection with a discussion of the local and outer structure of the Galaxy.Large-scale deviations from the galactic plane as found in recent work indicate that the ‘bending’ of the plane may be a complicated phenomenon. New observations outlining the true character of this bending are necessary for a decision between the different theories about these deviations.The need for surveys with high frequency resolution and extending away from the galactic plane is emphasized. Optical identifications of members of the various structural features are highly desirable as an independent determination of parameters of structural models.

scholarly journals Extracting the Global Signal from 21-cm Fluctuations: the Multi-Tracer Approach

2019 ◽  
Author(s):  
Anastasia Fialkov ◽  
Rennan Barkana ◽  
Matt Jarvis
Keyword(s):  
Large Scale ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Neutral Hydrogen ◽  
Spectral Energy ◽  
High Redshift Galaxies ◽  
Global Signal ◽  
The Galaxy ◽  
Scale Properties ◽  
Galaxy Bias

Abstract The multi-tracer technique employs a ratio of densities of two differently biased galaxy samples that trace the same underlying matter density field, and was proposed to alleviate the cosmic variance problem. Here we propose a novel application of this approach, applying it to two different tracers one of which is the 21-cm signal of neutral hydrogen from the epochs of reionization and comic dawn. The second tracer is assumed to be a sample of high-redshift galaxies, but the approach can be generalized and applied to other high-redshift tracers. We show that the anisotropy of the ratio of the two density fields can be used to measure the sky-averaged 21-cm signal, probe the spectral energy distribution of radiative sources that drive this signal, and extract large-scale properties of the second tracer, e.g., the galaxy bias. Using simulated 21-cm maps and mock galaxy samples, we find that the method works well for an idealized galaxy survey. However, in the case of a more realistic galaxy survey which only probes highly biased luminous galaxies, the inevitable Poisson noise makes the reconstruction far more challenging. This difficulty can be mitigated with the greater sensitivity of future telescopes along with larger survey volumes.

scholarly journals Current Problems in 21 cm Line Studies of the Large-Scale Structure of the Galaxy

1974 ◽  
Vol 60 ◽  
pp. 551-572 ◽  
Author(s):  
W. B. Burton
Keyword(s):  
Shock Front ◽  
Large Scale ◽  
Spiral Structure ◽  
Density Wave ◽  
Model Fitting ◽  
Neutral Hydrogen ◽  
Wave Theory ◽  
Large Scale Structure ◽  
The Galaxy ◽  
Density Wave Theory

A number of current problems in 21 cm line studies of the Galaxy as a whole are discussed. Because of the difficulties involved with straightforward mapping, it is important to isolate integrated and other properties of the hydrogen profiles, the interpretation of which does not require accurate distance determinations. In addition, methods of analysis are necessary which either account for or exploit the sensitivity of hydrogen profiles to velocity irregularities and to geometrical configurations. The model-fitting approach to the interpretation of the hydrogen profiles is useful in this respect. Extragalactic hydrogen studies which show the relative ordering of the various components of spiral structure can inspire research in our own Galaxy. Such investigations are necessary for an understanding of the forces governing the spiral structure. It seems that the neutral hydrogen is primarily a tracer of locations where the overall distribution of stars is producing a gravitational sink. Other spiral tracers, in particular the molecules, are better considered as tracers of regions where the gas has been compressed, perhaps (at least on a large scale) by the shock front predicted by the density-wave theory.

scholarly journals On the comparison of spiral structure as delineated by gas and by stars

1964 ◽  
Vol 20 ◽  
pp. 158-160
Author(s):  
H. F. Weaver
Keyword(s):  
Large Scale ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Young Stars ◽  
Space Distribution ◽  
Galactic Rotation ◽  
Spiral Arms ◽  
Gas Concentration ◽  
The Galaxy

In an earlier article* it was pointed out that the galactic radial motions ΔE (R, l) of the very young stars did not show the uniformity of motion to be expected from a smooth regular expansion of the Galaxy. Instead, the very young stars were found to show large-scale regional peculiar motions; these regional peculiar motions are displayed in Figure 1. In addition to regional peculiar motions and the space distribution of stars, Figure 1 also shows the spiral structure delineated by neutral hydrogen gas. As is customary in such diagrams, the space distribution of gas and the space distribution of the stars are not in good agreement. As various investigators have mentioned, stars and gas appear to define different spiral arms. However, such a conclusion is not warranted by data such as those employed in construction of Figure 1. In Figure 1 (as is invariably the case in earlier published diagrams of the same sort) two distance scales have been employed in the construction of the diagram. The distances of the stars have been derived from photometric data; the distances of concentrations of neutral hydrogen gas have been derived from measured hydrogen gas radial velocities and a galactic rotation curve. It should therefore come as no surprise if there are disagreements between hydrogen spiral arms and star spiral arms. Any regional peculiar motion of a gas concentration directly becomes an error in the inferred distance of the gas concentration.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

scholarly journals Investigating the properties of a galaxy group at z = 0.6

2020 ◽  
Vol 15 (S359) ◽  
pp. 188-189
Author(s):  
Daniela Hiromi Okido ◽  
Cristina Furlanetto ◽  
Marina Trevisan ◽  
Mônica Tergolina
Keyword(s):  
Large Scale ◽  
The Other ◽  
Numerical Density ◽  
Spectroscopy Data ◽  
Stellar Kinematics ◽  
Galaxy Groups ◽  
The Galaxy ◽  
The Difference ◽  
The Impact ◽  
The Universe

AbstractGalaxy groups offer an important perspective on how the large-scale structure of the Universe has formed and evolved, being great laboratories to study the impact of the environment on the evolution of galaxies. We aim to investigate the properties of a galaxy group that is gravitationally lensing HELMS18, a submillimeter galaxy at z = 2.39. We obtained multi-object spectroscopy data using Gemini-GMOS to investigate the stellar kinematics of the central galaxies, determine its members and obtain the mass, radius and the numerical density profile of this group. Our final goal is to build a complete description of this galaxy group. In this work we present an analysis of its two central galaxies: one is an active galaxy with z = 0.59852 ± 0.00007, while the other is a passive galaxy with z = 0.6027 ± 0.0002. Furthermore, the difference between the redshifts obtained using emission and absorption lines indicates an outflow of gas with velocity v = 278.0 ± 34.3 km/s relative to the galaxy.

scholarly journals Probing the cool ISM in galaxies via 21 cm H i absorption

2012 ◽  
Vol 8 (S292) ◽  
pp. 188-188
Author(s):  
J. R. Allison ◽  
E. M. Sadler ◽  
S. J. Curran ◽  
S. N. Reeves
Keyword(s):  
Spectral Line ◽  
Active Galactic Nuclei ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Host Galaxies ◽  
The Galaxy ◽  
Early Type Galaxy ◽  
Finding Method ◽  
Compact Array ◽  
Cold Gas

AbstractRecent targeted studies of associated H i absorption in radio galaxies are starting to map out the location, and potential cosmological evolution, of the cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21 cm absorption profiles often show two distinct spectral-line components: narrow, deep lines arising from cold gas in the extended disc of the galaxy, and broad, shallow lines from cold gas close to the AGN (e.g. Morganti et al. 2011). Here, we present results from a targeted search for associated H i absorption in the youngest and most recently-triggered radio AGN in the local universe (Allison et al. 2012b). So far, by using the recently commissioned Australia Telescope Compact Array Broadband Backend (CABB; Wilson et al. 2011), we have detected two new absorbers and one previously-known system. While two of these show both a broad, shallow component and a narrow, deep component (see Fig. 1), one of the new detections has only a single broad, shallow component. Interestingly, the host galaxies of the first two detections are classified as gas-rich spirals, while the latter is an early-type galaxy. These detections were obtained using a spectral-line finding method, based on Bayesian inference, developed for future large-scale absorption surveys (Allison et al. 2012a).

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