scholarly journals The Distribution of Faint Galaxies

1987 ◽  
Vol 124 ◽  
pp. 367-381 ◽  
Author(s):  
Richard Ellis
Keyword(s):  
Large Scale ◽  
Spectral Signatures ◽  
Number Magnitude ◽  
Redshift Surveys ◽  
Faint Galaxy ◽  
Faint Object ◽  
Luminous Galaxies ◽  
Blue Galaxies ◽  
Nearby Galaxies ◽  
Galaxy Populations

Faint galaxy data are reviewed in the context of standard evolutionary models and our understanding of the statistical properties of galaxy populations. The differences in number magnitude counts from group to group can largely be understood via fluctuations induced by large scale clustering. However count slopes still present convincing arguments for an extra component of faint blue galaxies beyond B ∼21. Colours provide an useful tool in estimating redshift distributions but the uncertainties are large for the bluest galaxies of interest. However, new faint object redshift surveys are now underway and promise to determine definitively the nature of this extra component. We discuss preliminary results from one of these surveys. Neither distant luminous galaxies nor intrinsically faint nearby galaxies appear to be very numerous to B = 21.5. Many of the galaxies with 0.2 < z < 0.4 show spectral signatures of prominent star-formation. If such objects are somehow related to the excess counts, the traditional redshift-dependent evolutionary theory may require revision.

scholarly journals An Emission-Line Galaxy Survey with the UK Schmidt Telescope

1987 ◽  
Vol 121 ◽  
pp. 53-55
Author(s):  
M. Kalafi ◽  
A. Savage ◽  
A.R. Good ◽  
R.D. Cannon ◽  
M.G. Yates
Keyword(s):  
Emission Line ◽  
Large Scale ◽  
Preliminary Investigation ◽  
Schmidt Telescope ◽  
Large Area ◽  
Number Magnitude ◽  
Emission Line Galaxies ◽  
Galaxy Populations ◽  
The Uk ◽  
Line Galaxy

The use of objective prisms in conjunction with the large area coverage afforded by Schmidt telescopes provides a very powerful means of detecting large numbers of emission-line galaxies, and allows one to study their large scale distribution. An important question that has yet to be fully addressed is the relationship between the number-magnitude distributions of the normal field galaxy and emission-line galaxy populations. A comparison such as this would effectively probe the evolution with time of these active objects. For example, study of the distant (z = 0.458) cluster of galaxies associated with 3C 295 (Dressler & Gunn 1983) indicates that emission-line objects may have been far more numerous in the past than at present. As a preliminary investigation in advance of a larger project, we report here on a search for emission-line galaxies in four United Kingdom 1.2m Schmidt Telescope (UKST) objective prism fields.

scholarly journals Isophotal Effects in Faint Galaxy Samples

1996 ◽  
Vol 171 ◽  
pp. 347-347
Author(s):  
P. Bristow ◽  
S. Philllipps
Keyword(s):  
Monte Carlo ◽  
Number Magnitude ◽  
Faint Galaxy ◽  
Total Luminosity ◽  
Galaxy Populations ◽  
Galaxy Population ◽  
Observational Techniques

Using Monte Carlo style simulations of galaxy populations we create artificial faint galaxy samples which mimic those obtained by actual observational techniques. By comparison of samples selected according to total luminosity or luminosity within an isophote we are able to estimate the extent to which isophotal effects could cause number magnitude counts of faint galaxies to appear artificially steep (cf. McGaugh 1994, Phillipps 1993). We find that, if we assume a ‘standard’ non-evolving galaxy population (essentially that used by Broadhurst, Ellis & Shanks 1988 amongst others) then isophotal effects alone cannot account for the discrepancy between the observed steepness and no-evolution models, though they could significantly reduce the amount of evolution required and alter the median redshifts. Modifying the underlying galaxy population by the addition of a bivariate brightness dwarf component as observed in clusters (e.g. Irwin et al 1990) increases the significance of the isophotal effects, though only fractionally, despite the fact that such effects would be highly important for such a population considered on its own.

scholarly journals Large-Scale Flows in the Local Universe

1996 ◽  
Vol 168 ◽  
pp. 175-182 ◽  
Author(s):  
D.S. Mathewson ◽  
V.L. Ford
Keyword(s):  
Large Scale ◽  
Velocity Measurements ◽  
Local Universe ◽  
Peculiar Velocities ◽  
Redshift Surveys ◽  
Density Maps ◽  
The Universe ◽  
Great Wall ◽  
Great Attractor ◽  
Streaming Flow

Peculiar velocity measurements of 2500 southern spiral galaxies show large-scale flows in the direction of the Hydra-Centaurus clusters which fully participate in the flow themselves. The flow is not uniform over this region and seems to be associated with the denser regions which participate in the flow of amplitude about 400km/s. In the less dense regions the flow is small or non-existent. This makes the flow quite asymmetric and inconsistent with that expected from large-scale, parallel streaming flow that includes all galaxies out to 6000km/s as previously thought. The flow cannot be modelled by a Great Attractor at 4300km/s or the Centaurus clusters at 3500km/s. Indeed, from the density maps derived from the redshift surveys of “optical” and IRAS galaxies, it is difficult to see how the mass concentrations can be responsible particularly as they themselves participate in the flow. These results bring into question the generally accepted reason for the peculiar velocities of galaxies that they arise solely as a consequence of infall into the dense regions of the universe. To the N. of the Great Attractor region, the flow increases and shows no sign of diminishing out to the redshift limit of 8000km/s in this direction. We may have detected flow in the nearest section of the Great Wall.

scholarly journals The Environment of OJ 287: Nearby Galaxies and a Long Optical Jet?

1996 ◽  
Vol 175 ◽  
pp. 47-48
Author(s):  
A. Sillanpää ◽  
L. Takalo ◽  
K. Nilsson ◽  
T. Pursimo ◽  
P. Teerikorpi ◽  
...  
Keyword(s):  
Large Scale ◽  
Radio Galaxies ◽  
Trigger Mechanism ◽  
Galaxy Clustering ◽  
Bl Lac Objects ◽  
Close Interaction ◽  
Relativistic Jet ◽  
Bl Lac ◽  
Nearby Galaxies ◽  
Bl Lacs

A widely accepted model for BL Lac objects is that they are radio galaxies with a relativistic jet pointing almost directly towards us. But we need a clear trigger mechanism for these jets. One possibility is the close interaction between the BL Lac host and the closeby galaxies (e.g. Heckman et al. 1986). This interaction has been seen many times in the case of quasars (Hutchings et al. 1989) but not so much is known about the close surroundings of the BL Lac objects although there has been some pioneer work like Stickel et al. (1993). The problem has usually been that the images are not deep enough and that the seeing has not been so good. To clarify the situation we have started an observing program to get very deep images in the sub-arcsecond seeing conditions from the whole 1 Jy sample (Stickel et al. 1991) of BL Lac objects. The aims of this study are: 1. to search for very close companions to the BL Lacs, 2. to study the large scale galaxy clustering around the BL Lacs and 3. to study the BL Lac hosts themselves.

The large-scale structure of homogeneous turbulence

1967 ◽  
Vol 27 (3) ◽  
pp. 581-593 ◽  
Author(s):  
P. G. Saffman
Keyword(s):  
Large Scale ◽  
Isotropic Turbulence ◽  
Homogeneous Turbulence ◽  
Wave Number ◽  
Initial Instant ◽  
Force System ◽  
Correlation Tensor ◽  
Number Magnitude ◽  
Small Wave Number ◽  
Conservation Of Momentum

A field of homogeneous turbulence generated at an initial instant by a distribution of random impulsive forces is considered. The statistical properties of the forces are assumed to be such that the integral moments of the cumulants of the force system all exist. The motion generated has the property that at the initial instant\[ E(\kappa) = C\kappa^2 + o(\kappa^2), \]whereE(k) is the energy spectrum function,kis the wave-number magnitude, andCis a positive number which is not in general zero. The corresponding forms of the velocity covariance spectral tensor and correlation tensor are determined. It is found that the terms in the velocity covarianceRij(r) areO(r−3) for large values of the separation magnituder.An argument based on the conservation of momentum is used to show thatCis a dynamical invariant and that the forms of the velocity covariance at large separation and the spectral tensor at small wave number are likewise invariant. For isotropic turbulence, the Loitsianski integral diverges but the integral\[ \int_0^{\infty} r^2R(r)dr = \frac{1}{2}\pi C \]exists and is invariant.

scholarly journals Improvement of Clay and Sand Quantification Based on a Novel Approach with a Focus on Multispectral Satellite Images

2018 ◽  
Vol 10 (10) ◽  
pp. 1555 ◽  
Author(s):  
Caio Fongaro ◽  
José Demattê ◽  
Rodnei Rizzo ◽  
José Lucas Safanelli ◽  
Wanderson Mendes ◽  
...  
Keyword(s):  
Model Calibration ◽  
Large Scale ◽  
Satellite Images ◽  
Satellite Image ◽  
Soil Mapping ◽  
Spectral Signatures ◽  
Novel Approach ◽  
Multispectral Satellite Images ◽  
Reduced Costs ◽  
Multispectral Satellite Image

Soil mapping demands large-scale surveys that are costly and time consuming. It is necessary to identify strategies with reduced costs to obtain detailed information for soil mapping. We aimed to compare multispectral satellite image and relief parameters for the quantification and mapping of clay and sand contents. The Temporal Synthetic Spectral (TESS) reflectance and Synthetic Soil Image (SYSI) approaches were used to identify and characterize texture spectral signatures at the image level. Soil samples were collected (0–20 cm depth, 919 points) from an area of 14,614 km2 in Brazil for reference and model calibration. We compared different prediction approaches: (a) TESS and SYSI; (b) Relief-Derived Covariates (RDC); and (c) SYSI plus RDC. The TESS method produced highly similar behavior to the laboratory convolved data. The sandy textural class showed a greater increase in average spectral reflectance from Band 1 to 7 compared with the clayey class. The prediction using SYSI produced a better result for clay (R2 = 0.83; RMSE = 65.0 g kg−1) and sand (R2 = 0.86; RMSE = 79.9 g kg−1). Multispectral satellite images were more stable for the identification of soil properties than relief parameters.

scholarly journals Faint Galaxy Number-Counts

1996 ◽  
Vol 171 ◽  
pp. 225-228
Author(s):  
N. Metcalfe ◽  
T. Shanks ◽  
R. Fong ◽  
J. Gardner ◽  
N. Roche
Keyword(s):  
Wavelength Range ◽  
Evolutionary History ◽  
Statistical Properties ◽  
Normal Galaxies ◽  
Number Magnitude ◽  
Faint Galaxy ◽  
Wide Wavelength Range ◽  
History Of ◽  
Number Counts ◽  
Additional Constraints

Observers studying the cosmology and evolutionary history of our Universe through the statistical properties of ‘normal’ galaxies have four main tools at their disposal. (1) The number-redshift relation. Although a very powerful diagnostic, spectroscopic surveys are currently limited to B < 24m and significantly incomplete in the range, 23m< B < 24m. (2) Galaxy number-magnitude counts. Although by themselves, they cannot constrain models as tightly as spectroscopy, they can be measured ∼ 4m fainter, where cosmological effects are expected to be significant. (3) Galaxy colours over a wide wavelength range, which provide additional constraints. (4) The dependence of galaxy clustering with magnitude. ω(θ) can be measured to the limit of the counts.Here we report on the latest Durham count and clustering work.

scholarly journals Persistence of the colour–density relation and efficient environmental quenching to z ∼ 1.4

2019 ◽  
Vol 490 (1) ◽  
pp. 1231-1254 ◽  
Author(s):  
B C Lemaux ◽  
A R Tomczak ◽  
L M Lubin ◽  
R R Gal ◽  
L Shen ◽  
...  
Keyword(s):  
Star Formation ◽  
Time Scales ◽  
Large Scale ◽  
Formation Rate ◽  
Cosmic Time ◽  
Stellar Mass ◽  
Cluster Galaxies ◽  
Quenching Efficiency ◽  
Density Relation ◽  
Galaxy Populations

ABSTRACT Using ∼5000 spectroscopically confirmed galaxies drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey we investigate the relationship between colour and galaxy density for galaxy populations of various stellar masses in the redshift range 0.55 ≤ z ≤ 1.4. The fraction of galaxies with colours consistent with no ongoing star formation (fq) is broadly observed to increase with increasing stellar mass, increasing galaxy density, and decreasing redshift, with clear differences observed in fq between field and group/cluster galaxies at the highest redshifts studied. We use a semi-empirical model to generate a suite of mock group/cluster galaxies unaffected by environmentally specific processes and compare these galaxies at fixed stellar mass and redshift to observed populations to constrain the efficiency of environmentally driven quenching (Ψconvert). High-density environments from 0.55 ≤ z ≤ 1.4 appear capable of efficiently quenching galaxies with $\log (\mathcal {M}_{\ast }/\mathcal {M}_{\odot })\gt 10.45$. Lower stellar mass galaxies also appear efficiently quenched at the lowest redshifts studied here, but this quenching efficiency is seen to drop precipitously with increasing redshift. Quenching efficiencies, combined with simulated group/cluster accretion histories and results on the star formation rate-density relation from a companion ORELSE study, are used to constrain the average time from group/cluster accretion to quiescence and the elapsed time between accretion and the inception of the quenching event. These time-scales were constrained to be 〈tconvert〉 = 2.4 ± 0.3 and 〈tdelay〉 = 1.3 ± 0.4 Gyr, respectively, for galaxies with $\log (\mathcal {M}_{\ast }/\mathcal {M}_{\odot })\gt 10.45$ and 〈tconvert〉 = 3.3 ± 0.3 and 〈tdelay〉 = 2.2 ± 0.4 Gyr for lower stellar mass galaxies. These quenching efficiencies and associated time-scales are used to rule out certain environmental mechanisms as being the primary processes responsible for transforming the star formation properties of galaxies over this 4 Gyr window in cosmic time.

Visual and Near-Infrared Photometry of Nearby Dwarf Spheroidals

1999 ◽  
Vol 192 ◽  
pp. 455-458 ◽  
Author(s):  
F. Kerschbaum ◽  
W. Nowotny ◽  
J. Hron ◽  
M. Schultheis
Keyword(s):  
Near Infrared ◽  
Broad Band ◽  
Feasibility Studies ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Faint Object ◽  
Nearby Galaxies ◽  
Dwarf Spheroidals ◽  
Faint Object Spectrograph ◽  
Infrared Survey

This paper is based on photometry from two different observational approaches. Both are of an explorative character and act as feasibility studies. For the future we plan to use these methods to study Asymptotic Giant Branch (AGB) stars in nearby galaxies.First, we present results on broad-band photometry in Bessell V and I, as well as narrow-band measurements in the Wing 778 nm and 812 nm filters of a galactic globular cluster using the new Austrian Oe-FOSC (Oesterreich Faint Object Spectrograph and Camera), a copy of the ESO Instrument EFOSC mounted on our 1.5 m-telescope.The second part of the contribution deals with the possibilities of using Gunn I, J and KS measurements originating from the DENIS (DEep Near Infrared Survey of the Southern Sky) project on similar objects. A few southern dwarf spheroidals already observed within DENIS (covering now some 40% of the southern hemisphere) are selected.

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