scholarly journals Absorption by Neutral Hydrogen in the Irregular Galaxy M82

1972 ◽  
Vol 44 ◽  
pp. 74-74
Author(s):  
M. Guélin ◽  
L. Weliachew
Keyword(s):  
Radio Source ◽  
Velocity Gradient ◽  
Neutral Hydrogen ◽  
Major Axis ◽  
Velocity Spread ◽  
Absorption Profile ◽  
Irregular Galaxy ◽  
Negative Temperatures ◽  
The Galaxy ◽  
Right Ascension

A neutral hydrogen survey of the irregular galaxy M82 has been carried out with the transit radio telescope at Nançay, France. The resolving power was 4′ in right ascension and 34′ in declination. The velocity resolution was 59 km s−1.Drift scans covering 58′ in right ascension were taken across the center of the galaxy where the radio source is located; fourteen scans were averaged.Line profiles were derived every 2′ in right ascension. The profiles at ±4′ from the radio source are similar within the measurement errors. In particular, they do not show any rotation effect within ±15 km s−1. They were averaged in order to provide an estimate of the expected emission profile at the radio source position.Subtraction of this average from the line profile measured in front of the radio source yielded significant negative temperatures at all velocities from 180 to 360 km s−1 and no positive temperatures at other velocities.These negative temperatures were assigned to absorption of the radiation from the radio source by neutral hydrogen in M82.Absorption is running from 3 to 6% in depth. The average velocity of the absorption profile is lying between the central emission velocity and the optically-determined velocity which are known to show a large disagreement.The width of the absorption profile shows a velocity gradient of 200 km s−1 across the 35′ × 20′ radio source. Such a large velocity spread across this angular extent is only shown by the excited gas showing emission lines at optical wavelengths (Burbidge et al., 1964).Since then, the absorption in M82 at the neutral hydrogen wavelength has been confirmed by measurements done with the Owens Valley Radio interferometer at 2 spacings where any emission is completely resolved (interfringes were 3′ and 1′.5).In addition to the conclusions of the single dish observations done at Nançay, the interferometer data have shown that the steeper velocity gradient occurs along the major axis of the galaxy which coincides with the major axis of the radio source.

scholarly journals Measurement of the solar system acceleration using the Earth scale factor

2018 ◽  
Vol 610 ◽  
pp. A36 ◽  
Author(s):  
O. Titov ◽  
H. Krásná
Keyword(s):  
Solar System ◽  
Radio Source ◽  
Scale Factor ◽  
Intrinsic Structure ◽  
Structure Variation ◽  
Long Baseline ◽  
The Galaxy ◽  
Vlbi Data ◽  
The Individual ◽  
Right Ascension

Aim. We propose an alternative method to detect the secular aberration drift induced by the solar system acceleration due to the attraction to the Galaxy centre. This method is free of the individual radio source proper motion caused by intrinsic structure variation. Methods. We developed a procedure to estimate the scale factor directly from very long baseline interferometry (VLBI) data analysis in a source-wise mode within a global solution. The scale factor is estimated for each reference radio source individually as a function of astrometric coordinates (right ascension and declination). This approach splits the systematic dipole effect and uncorrelated motions on the level of observational parameters. Results. We processed VLBI observations from 1979.7 to 2016.5 to obtain the scale factor estimates for more than 4000 reference radio sources. We show that the estimates highlight a dipole systematics aligned with the direction to the centre of the Galaxy. With this method we obtained a Galactocentric acceleration vector with an amplitude of 5.2 ± 0.2 μas/yr and direction αG = 281∘± 3∘ and δG = −35∘± 3∘.

scholarly journals The Dark Massive Halo in the Elliptical Galaxy NGC 5266

1995 ◽  
Vol 164 ◽  
pp. 446-446
Author(s):  
A. Pizzella ◽  
R. Morganti ◽  
M.E. Sadler ◽  
F. Bertola
Keyword(s):  
Spiral Galaxies ◽  
Elliptical Galaxy ◽  
Neutral Hydrogen ◽  
Major Axis ◽  
Minor Axis ◽  
Representative Point ◽  
Dust Lane ◽  
The Galaxy ◽  
Central Regions ◽  
Parallel Behaviour

Recent observations with the Australia Telescope reveal that the elliptical galaxy NGC 5266 has a disk like structure of neutral hydrogen extending as far as almost 10 Re which approximatively lies along the galaxy's major axis, at 65° apart from the inner minor–axis dust lane (Varnas et al 1987). From the present data is not clear whether the HI structure and the dust lane are two distinct disks or a single warped structure. The regularity of the velocity field of the HI structure allow us to use it as a probe of the potential of NGC 5266. The velocity curve along the major axis is flat till the last measured point (rmax ~ 10′) at Vrot = 200km/s. Assuming that the gas in moving in circular orbits, we can derive the mass of the galaxy inside to this radius. The mass–to–light ratio M/LB rises from about 3 in the central regions to 12 at 9 Re (D = 57.6 Mpc), thus indicating that NGC 5266 is embedded in a dark massive halo. Moreover the representative point (cumulative M/LB within the last measured point) of NGC 5266 in the diagram log(M/LB) – log(Re) falls well within the region characteristic of spiral galaxies (Figure 2, Bertola et al. 1993), as do ellipticals previously studied in HI, thus reinforcing the suggestion (Bertola et al. 1993) of a parallel behaviour of the dark matter in elliptical and spiral galaxies.

scholarly journals Determining the accuracy of VLBI radio source catalogs

2018 ◽  
Vol 620 ◽  
pp. A160 ◽  
Author(s):  
N. Liu ◽  
S. B. Lambert ◽  
Z. Zhu
Keyword(s):  
Radio Source ◽  
Major Axis ◽  
Scale Factor ◽  
Noise Floor ◽  
Long Baseline ◽  
Formal Error ◽  
Standard Solution ◽  
The Difference ◽  
Improved Accuracy ◽  
Right Ascension

Aims. We propose to estimate the accuracy of current very long baseline interferometry (VLBI) catalogs. Methods. The difference of source position estimated from two decimation solutions was analyzed to estimate the scale factor and noise floor for the formal error of radio source positions by two different methods. In one method, we investigated the weighted root-square-mean (wrms) scatter of source positional differences versus the number of observed sessions; for the other one, we compared the wrms difference versus the formal error. Based on the estimated noise floor and scale factor, we determined the realistic error of radio source positions in the standard solution and compared it with that of Gaia DR2 and ICRF2 catalogs. Results. The estimated scale factors from two methods are rather consistent, which is of ∼1.3 in both coordinates. As for the noise floor, it is estimated to be 20–25 μas for sources observed in at least ten sessions, and it could reduce down to ∼10 μas for sources which have been observed more than 1000 times. The inflated median formal error of our solution is of the same order as the Gaia DR2 catalog in declination and the direction of major axis of the error ellipse, but smaller by a factor of two in right ascension. With respect to the ICRF2 catalog, our solution yields an improved accuracy by a factor of about three. Conclusions. Currently, the VLBI radio source catalog still provides source positions with the best accuracy which is about 20–25 μas. Moreover, the noise floor of VLBI catalogs could potentially reach 10 μas with more observations in the future.

scholarly journals Neutral Hydrogen In The Irregular Galaxy Ngc 3Lo9

1966 ◽  
Vol 19 (5) ◽  
pp. 687 ◽  
Keyword(s):  
Radio Telescope ◽  
Total Mass ◽  
Rotation Curve ◽  
Neutral Hydrogen ◽  
Irregular Galaxy ◽  
The Galaxy

The galaxy NGC 3109 was investigated at 21 cm wavelength with the 210 ft radio telescope at Parkes. For a distance d = 2�2 Mpc the total mass of neutral hydrogen is MH = 2�2 X 109 M0 (corrected for self-absorption). The rotation curve has been determined

The hydrogen distribution in galaxies

1967 ◽  
Vol 31 ◽  
pp. 189-197 ◽  
Author(s):  
Morton S. Roberts
Keyword(s):  
Ring Width ◽  
Neutral Hydrogen ◽  
Major Axis ◽  
Ring Structure ◽  
Hydrogen Distribution ◽  
Ring Radius ◽  
Systemic Velocity ◽  
Irregular Galaxies ◽  
The Galaxy ◽  
Ring Structures

Results of 21-cm line observations with the 300-foot telescope are summarized. Along the major axis of M 31, the peaks in the distribution of neutral hydrogen correlate closely (but do not exactly coincide) with the optical spiral arms. The distribution of hydrogen over the galaxy shows a ring pattern; the same is true in M 33.Resolution of such ring structures may be facilitated by consideration of profile integrals over a restricted velocity range around the systemic velocity. Out of nine spiral systems studied, with minor axis > 10′ (arc), only NGC 628 exhibits no ring. The ratios ring radius to ring width and optical radius to ring radius vary little about averages 2·5 and 1·7. In two irregular galaxies, no ring structure was observed.Neutral-hydrogen haloes, if present, can only be studied in large edge-on systems. In NGC 4244 and 7640, the upper limit to the density of neutral hydrogen in the halo is 0·001 cm-3. Qualitative considerations indicate that a similar value may apply in the Galaxy.

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 Rotation of the Galaxy NGC 1316 associated with the Radio Source Fornax A

Nature ◽  
1965 ◽  
Vol 207 (5003) ◽  
pp. 1282-1282 ◽  
Author(s):  
LEONARD SEARLE
Keyword(s):  
Radio Source ◽  
The Galaxy

scholarly journals Radio and X-ray Observations of the Restarted Radio Galaxy in the Galaxy Cluster CL 0838+1948

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 108
Author(s):  
Simona Giacintucci ◽  
Tracy Clarke ◽  
Namir E. Kassim ◽  
Wendy Peters ◽  
Emil Polisensky
Keyword(s):  
Radio Source ◽  
Survey Data ◽  
Radio Galaxy ◽  
Galaxy Cluster ◽  
Gas Emission ◽  
Low Frequencies ◽  
Nuclear Activity ◽  
X Ray ◽  
Hot Gas ◽  
The Galaxy

We present VLA Low-band Ionosphere and Transient Experiment (VLITE) 338 MHz observations of the galaxy cluster CL 0838+1948. We combine the VLITE data with Giant Metrewave Radio Telescope 610 MHz observations and survey data. The central galaxy hosts a 250 kpc source whose emission is dominated by two large lobes at low frequencies. At higher frequencies, a pair of smaller lobes (∼30 kpc) is detected within the galaxy optical envelope. The observed morphology is consistent with a restarted radio galaxy. The outer lobes have a spectral index αout=1.6, indicating that they are old, whereas the inner lobes have αinn=0.6, typical for an active source. Spectral modeling confirms that the outer emission is a dying source whose nuclear activity switched off not more than 110 Myr ago. Using archival Chandra X-ray data, we compare the radio and hot gas emission. We find that the active radio source is contained within the innermost and X-ray brightest region, possibly a galactic corona. Alternatively, it could be the remnant of a larger cool core whose outer layers have been heated by the former epoch of activity that has generated the outer lobes.

scholarly journals Can intrinsic alignments of elongated low-mass galaxies be used to map the cosmic web at high redshift?

2019 ◽  
Vol 488 (4) ◽  
pp. 5580-5593 ◽  
Author(s):  
Viraj Pandya ◽  
Joel Primack ◽  
Peter Behroozi ◽  
Avishai Dekel ◽  
Haowen Zhang ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
High Redshift ◽  
Major Axis ◽  
Real Space ◽  
Significant Alignment ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Future Work

ABSTRACT Hubble Space Telescope observations show that low-mass ($M_*=10^9\!-\!10^{10}\, \mathrm{M}_{\odot }$) galaxies at high redshift (z = 1.0–2.5) tend to be elongated (prolate) rather than disky (oblate) or spheroidal. This is explained in zoom-in cosmological hydrodynamical simulations by the fact that these galaxies are forming in cosmic web filaments where accretion happens preferentially along the direction of elongation. We ask whether the elongated morphology of these galaxies allows them to be used as effective tracers of cosmic web filaments at high redshift via their intrinsic alignments. Using mock light cones and spectroscopically confirmed galaxy pairs from the Cosmic Assembly Near-infared Deep Extragalactic Legacy Survey (CANDELS), we test two types of alignments: (1) between the galaxy major axis and the direction to nearby galaxies of any mass and (2) between the major axes of nearby pairs of low-mass, likely prolate, galaxies. The mock light cones predict strong signals in 3D real space, 3D redshift space, and 2D projected redshift space for both types of alignments (assuming prolate galaxy orientations are the same as those of their host prolate haloes), but we do not detect significant alignment signals in CANDELS observations. However, we show that spectroscopic redshifts have been obtained for only a small fraction of highly elongated galaxies, and accounting for spectroscopic incompleteness and redshift errors significantly degrades the 2D mock signal. This may partly explain the alignment discrepancy and highlights one of several avenues for future work.

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