scholarly journals Optical Galaxy Selection

1999 ◽  
Vol 171 ◽  
pp. 19-26
Author(s):  
Stacy McGaugh
Keyword(s):  
Surface Brightness ◽  
Brightness Distribution ◽  
Selection Effects ◽  
Considerable Uncertainty ◽  
The Way

AbstractOur view of the properties of galaxies is strongly affected by the way in which we survey for them. I discuss some aspects of selection effects and methods to compensate for them. One result is an estimate of the surface brightness distribution. I believe this is progress, but considerable uncertainty remains.

scholarly journals Finding the Bivariate Brightness Distribution of Galaxies from an HI Selected Sample

1999 ◽  
Vol 16 (1) ◽  
pp. 12-17 ◽  
Author(s):  
R. F. Minchin
Keyword(s):  
Surface Brightness ◽  
Brightness Distribution ◽  
Selection Effects ◽  
Data Cubes ◽  
Real Noise ◽  
Sky Survey ◽  
Uniform Sample ◽  
Deep Survey ◽  
Survey Results ◽  
Optical Wavelengths

AbstractA method is presented that will enable the bivariate luminosity/surface brightness distribution of galaxies to be determined from a relatively small HI selected sample. This will be taken from the HI Parkes All Sky Survey (HIPASS). The advantages of using an HI sample in order to avoid the selection effects that are present at optical wavelengths are discussed. We are developing an algorithm to automatically extract a uniform sample of galaxies from the HIPASS data cubes and to determine the parameters of these galaxies. We have so far conducted tests involving both simulated sources injected into cubes with real noise and data from the Multibeam Deep survey. Results from these tests are encouraging.

scholarly journals When Darwin Met Einstein: Gravitational Lens Inversion with Genetic Algorithms

2005 ◽  
Vol 22 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Brendon J. Brewer ◽  
Geraint F. Lewis
Keyword(s):  
Genetic Algorithms ◽  
Gravitational Lensing ◽  
Surface Brightness ◽  
Initial Study ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Atmospheric Effects ◽  
Lens Model ◽  
New Approach ◽  
Genetic Algorithm Approach

AbstractGravitational lensing can magnify a distant source, revealing structural detail which is normally unresolvable. Recovering this detail through an inversion of the influence of gravitational lensing, however, requires optimisation of not only lens parameters, but also of the surface brightness distribution of the source. This paper outlines a new approach to this inversion, utilising genetic algorithms to reconstruct the source profile. In this initial study, the effects of image degradation due to instrumental and atmospheric effects are neglected and it is assumed that the lens model is accurately known, but the genetic algorithm approach can be incorporated into more general optimisation techniques, allowing the optimisation of both the parameters for a lensing model and the surface brightness of the source.

scholarly journals CO line and radio continuum study of elephant trunks: the Pillars of Creation in M16

2020 ◽  
Vol 492 (4) ◽  
pp. 5966-5979 ◽  
Author(s):  
Yoshiaki Sofue
Keyword(s):  
Surface Brightness ◽  
Galactic Plane ◽  
Brightness Distribution ◽  
Radio Continuum ◽  
Very Large Array ◽  
Heating Source ◽  
Velocity Gradients ◽  
Magnetic Oscillation ◽  
H Ii Region ◽  
Line Survey

ABSTRACT Molecular line and radio continuum properties of the elephant trunks (ET, Pillars of Creation) in M16 are investigated by analysing 12CO(J = 1−0) , 13CO(J = 1−0) and C18O(J = 1−0) line survey data from the Nobeyama 45-m telescope and the Galactic plane radio survey at 20 and 90 cm with the Very Large Array. The head clump of Pillar West I is found to be the brightest radio source in M16, showing a thermal spectrum and the properties of a compact H ii region, with the nearest O5 star in NGC 6611 being the heating source. The radio pillars have a cometary structure concave to the molecular trunk head, and the surface brightness distribution obeys a simple illumination law from a remote excitation source. The molecular density in the pillar head is estimated to be several 104 H2 cm−3 and the molecular mass is $\sim 13\!-\!40 \, \mathrm{M}_\odot$. CO-line kinematics reveals random rotation of the clumps in the pillar tail at ∼1–2 km s−1, comparable with the velocity dispersion and estimated Alfvén velocity. It is suggested that the random directions of the velocity gradients would manifest as torsional magnetic oscillation of the clumps around the pillar axis.

scholarly journals The mergers in Abell 2256: displaced gas and its connection to the radio-emitting plasma

2020 ◽  
Vol 495 (4) ◽  
pp. 5014-5026 ◽  
Author(s):  
J P Breuer ◽  
N Werner ◽  
F Mernier ◽  
T Mroczkowski ◽  
A Simionescu ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Large Scale ◽  
Cold Front ◽  
Low Frequency ◽  
Brightness Distribution ◽  
Analytical Models ◽  
Line Of Sight ◽  
Cluster Galaxy ◽  
X Ray ◽  
Low Entropy

ABSTRACT We present the results of deep Chandra and XMM–Newton X-ray imaging and spatially resolved spectroscopy of Abell 2256, a nearby (z = 0.058) galaxy cluster experiencing multiple mergers and displaying a rich radio morphology dominated by a large relic. The X-ray data reveal three subclusters: (i) the ‘main cluster’; (ii) the remnant of an older merger in the east of the cluster with an ∼600 kpc-long tail; (iii) a bright, bullet-like, low-entropy infalling system, with a large line-of-sight velocity component. The low-entropy system displays a 250 kpc-long cold front with a break and an intriguing surface brightness decrement. Interestingly, the infalling gas is not co-spatial with bright galaxies and the radio-loud brightest cluster galaxy of the infalling group appears dissociated from the low-entropy plasma by ∼50 kpc in projection, to the south of the eastern edge of the cold front. Assuming that the dark matter follows the galaxy distribution, we predict that it is also significantly offset from the low-entropy gas. Part of the low-frequency radio emission near the cold front might be revived by magnetic field amplification due to differential gas motions. Using analytical models and numerical simulations, we investigate the possibility that the supersonic infall of the subcluster generates a large-scale shock along our line of sight, which can be detected in the X-ray temperature map but is not associated with any clear features in the surface brightness distribution.

Variation in the near-infrared surface brightness distribution of the bipolar nebula OH 231.8 + 4.2

1992 ◽  
Vol 398 ◽  
pp. 552 ◽  
Author(s):  
Joel H. Kastner ◽  
David A. Weintraub ◽  
B. Zuckerman ◽  
E. E. Becklin ◽  
I. McLean ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Near Infrared ◽  
Brightness Distribution

scholarly journals Opaque Spiral Disks: Some Empirical Facts and Consequences

1991 ◽  
Vol 144 ◽  
pp. 245-256
Author(s):  
Edwin A. Valentijn
Keyword(s):  
Surface Brightness ◽  
Axial Ratio ◽  
Recent Analysis ◽  
Line Of Sight ◽  
Selection Effects ◽  
Complete Sample ◽  
Large Samples ◽  
The Galaxy ◽  
Absorbing Material ◽  
Image Position

A recent analysis of the surface brightness profiles of a complete sample of 9381 spiral galaxies extracted from ESO-LV (Lauberts and Valentijn, 1989) showed that many galaxy disks of especially Sb–Sc galaxies are opaque (Valentijn, 1990). This paper studied how the observed surface brightness μobs varies as a function of the observed axial ratio a/b, by fitting the data of samples of spirals with (1) assuming the a/b to give the inclination angle of the disks to the line of sight. A sample of galaxies that were fully transparent at the particular radius used for the test would have C ≃ 1, while C <~ 0.25 signifies opaque conditions, the transition value being heavily dependent on the spatial distribution of the absorbing material and the effect of multiple scatterings (Bruzual et al. 1988). The most frequently-used C values range from 0.5–0.9 (Holmberg 1975, de Vaucouleurs et al. 1976, Sandage and Tammann 1981). However, Valentijn (1990) derived C values well below 0.25 for large samples of spirals throughout the galaxy disks; this result is not significantly affected by selection effects in either magnitude, angular diameter or axial ratio, nor by the presence of bulges (at least for types Sb and later).

scholarly journals The way we measure: comparison of methods to derive radial surface brightness profiles

2016 ◽  
Vol 464 (2) ◽  
pp. 1591-1606 ◽  
Author(s):  
S. P. C. Peters ◽  
P. C. van der Kruit ◽  
R. S. de Jong
Keyword(s):  
Surface Brightness ◽  
Comparison Of Methods ◽  
Measure Comparison ◽  
The Way

scholarly journals The Size-Luminosity Relation of Disk Galaxies in EDisCS Clusters

2006 ◽  
Vol 2 (S235) ◽  
pp. 201-201
Author(s):  
Stephanie M. Gogarten ◽  
Julianne J. Dalcanton ◽  
Luc Simard ◽  
Gregory Rudnick ◽  
Vandana Desai ◽  
...  
Keyword(s):  
Surface Brightness ◽  
High Redshift ◽  
Disk Galaxies ◽  
Selection Effects ◽  
Distant Cluster ◽  
Cluster Survey ◽  
Low Surface Brightness ◽  
Advanced Camera For Surveys ◽  
Low Surface Brightness Galaxies

AbstractWe present the size-luminosity relation (SLR) for disk galaxies observed in eight clusters from the ESO Distant Cluster Survey (EDisCS). These clusters, at redshifts 0.4 < z < 0.8, were observed with the Hubble Space Telescope's Advanced Camera for Surveys. While we observe a change in the SLR with redshift, namely that there is an absence of low surface brightness galaxies at high redshift, we demonstrate that this could be a product of selection effects and thus is not a confirmation of evolution. We also compare the SLR for cluster and field galaxies in each redshift bin and see no significant effects of environment on the SLR.

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