scholarly journals The mass and light distribution of the galaxy: a three-component model

1979 ◽  
Vol 84 ◽  
pp. 441-450 ◽  
Author(s):  
J. P. Ostriker ◽  
J. A. R. Caldwell
Keyword(s):  
Least Square ◽  
Component Model ◽  
Dark Halo ◽  
Escape Velocity ◽  
Circular Velocity ◽  
The Galaxy ◽  
Minimization Technique ◽  
Imperfect Knowledge ◽  
The Masses ◽  
Best Fit

The galaxy is represented schematically by a three-component model: a disc having the form of a modified exponential distribution, a spheroidal (bulge + nucleus) component and a dark halo component which, following the nomenclature of Einasto, we call the corona. The shapes of these components, chosen on the basis of observations of other galaxies, are consistent with imperfect knowledge of the Galaxy; values of the adjustable parameters are chosen by a least square minimization technique to best fit the most accurate kinematical and dynamical galactic observations. The local radius, circular velocity and escape velocity are found to be (R⊙, V⊙, Vesc) = (9.05 ± 0.33 kpc, 247 ± 13 km/s, 550 ± 24) quite close to the values determined from observations directly. The masses in the three components are (MD, MSp, MC) = (0.78 ± 0.13, 0.81 ± 0.09, 20.3) × 1011 M⊙ for a model with coronal radius of 335 kpc. If the quite uncertain coronal radius is reduced to 100 kpc the model is essentially unchanged except that then MC = 6.65 × 1011 M⊙. The disc and spheroidal components have in either case luminosities (in the visual band of (LD, LSp) = (2.0, 0.2) × 1010 L⊙. The galaxy is a normal giant spiral of type Sb-Sc similar to NGC 4565.

scholarly journals Probing the Tides in Interacting Galaxy Pairs

1990 ◽  
Vol 124 ◽  
pp. 537-542
Author(s):  
Kirk D. Borne
Keyword(s):  
Gravitational Field ◽  
Binary System ◽  
Driving Forces ◽  
Elliptical Galaxies ◽  
Physical Parameters ◽  
Tidal Interactions ◽  
The Galaxy ◽  
Merger Rate ◽  
The Masses ◽  
Best Fit

AbstractDetailed spectroscopic and imaging observations of colliding elliptical galaxies have revealed unmistakable diagnostic signatures of the tidal interactions. It is possible to compare both the distorted luminosity distributions and the disturbed internal rotation profiles with numerical simulations in order to model the strength of the tidal gravitational field acting within a given pair of galaxies. Using the best-fit numerical model, one can then measure directly the mass of a specific interacting binary system. This technique applies to individual pairs and therefore complements the classical methods of measuring the masses of galaxy pairs in well-defined statistical samples. The “personalized” modeling of galaxy pairs also permits the derivation of each binary’s orbit, spatial orientation, and interaction timescale. Similarly, one can probe the tides in less-detailed observations of disturbed galaxies in order to estimate some of the physical parameters for larger samples of interacting galaxy pairs. These parameters are useful inputs to the more universal problems of (1) the galaxy merger rate, (2) the strength and duration of the driving forces behind tidally-stimulated phenomena (e.g., starbursts and maybe QSOs), and (3) the identification of long-lived signatures of interaction/merger events.

scholarly journals The RAVE Survey: Constraining the Local Galactic Escape Speed

2006 ◽  
Vol 2 (S235) ◽  
pp. 137-137 ◽  
Author(s):  
Martin C. Smith ◽  
G. R. Ruchti ◽  
A. Helmi ◽  
R. F. G. Wyse ◽  
Keyword(s):  
Galaxy Formation ◽  
Precise Measurement ◽  
Dark Halo ◽  
Escape Velocity ◽  
Radial Extent ◽  
The Galaxy ◽  
Virial Mass ◽  
Halo Masses ◽  
Escape Speed ◽  
Good Agreement

AbstractWe report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high velocity stars from the RAVE survey and two previously published datasets (the Geneva-Copenhagen survey and the Beers et al. catalogue of metal-poor stars). We use cosmological simulations of disk galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 492 km s−1 < vesc <594 kms (90% confidence), with a median likelihood of 536 kms. The fact that v2esc is significantly greater than 2v2circ implies that there must be a significant amount of mass exterior to the Solar circle, i.e. this convincingly demonstrates the presence of a dark halo in the Galaxy. For a simple isothermal halo, one can calculate that the minimum radial extent is ~54 kpc. We use our constraints on vesc to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of 1.31+0.97−0.49 × 1012M⊙ and virial radius of 297+60−44 kpc (90% confidence). For this model the circular velocity at the virial radius is 141+27−19kms. Although our halo masses are model dependent, we find that they are in good agreement with each other.

scholarly journals Head-to-Toe Measurement of El Gordo: Improved Analysis of the Galaxy Cluster ACT-CL J0102–4915 with New Wide-field Hubble Space Telescope Imaging Data

2021 ◽  
Vol 923 (1) ◽  
pp. 101
Author(s):  
Jinhyub Kim ◽  
M. James Jee ◽  
John P. Hughes ◽  
Mijin Yoon ◽  
Kim HyeongHan ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
Galaxy Cluster ◽  
Wide Field ◽  
Mass Ratio ◽  
Imaging Data ◽  
Space Telescope ◽  
Strong Lensing ◽  
The Galaxy ◽  
The Masses ◽  
Best Fit

Abstract We present an improved weak-lensing (WL) study of the high-z (z = 0.87) merging galaxy cluster ACT-CL J0102–4915 (“El Gordo”) based on new wide-field Hubble Space Telescope imaging data. The new imaging data cover the ∼3.5 × ∼3.5 Mpc region centered on the cluster and enable us to detect WL signals beyond the virial radius, which was not possible in previous studies. We confirm the binary mass structure consisting of the northwestern (NW) and southeastern (SE) subclusters and the ∼2σ dissociation between the SE mass peak and the X-ray cool core. We obtain the mass estimates of the subclusters by simultaneously fitting two Navarro–Frenk–White (NFW) halos without employing mass–concentration relations. The masses are M 200 c NW = 9.9 − 2.2 + 2.1 × 1014 and M 200 c SE = 6.5 − 1.4 + 1.9 × 1014 M ⊙ for the NW and SE subclusters, respectively. The mass ratio is consistent with our previous WL study but significantly different from the previous strong-lensing results. This discrepancy is attributed to the use of extrapolation in strong-lensing studies because the SE component possesses a higher concentration. By superposing the two best-fit NFW halos, we determine the total mass of El Gordo to be M 200 c = 2.13 − 0.23 + 0.25 × 1015 M ⊙, which is ∼23% lower than our previous WL result [M 200c = (2.76 ± 0.51) × 1015 M ⊙]. Our updated mass is a more direct measurement, since we are not extrapolating to R 200c as in all previous studies. The new mass is compatible with the current ΛCDM cosmology.

scholarly journals The black hole-dark matter halo connection

2007 ◽  
Vol 3 (S245) ◽  
pp. 257-258 ◽  
Author(s):  
Bassem M. Sabra ◽  
Maya Abi Akl ◽  
Gilbert Chahine
Keyword(s):  
Dark Matter ◽  
Velocity Dispersion ◽  
Dark Matter Halo ◽  
Host Galaxies ◽  
Circular Velocity ◽  
Direct Measurements ◽  
The Galaxy ◽  
Stellar Velocity ◽  
The Masses ◽  
The Relationship

AbstractWe explore the connection between the central supermassive blackholes (SMBH) in galaxies and the dark matter halo through the relation between the masses of the SMBHs and the maximum circular velocities of their host galaxies, as well as the relationship between stellar velocity dispersion of the spheroidal component and the circular velocity. We rely on a heterogeneous sample containing galaxies of all types. The only requirement is that the galaxy has direct measurements of its SMBH mass, MBH, circular velocity, vc, and velocity dispersion, σ. We present a direct observational MBH − vc relation.

Direct Assessment of Effective Renal Plasma Flow from Renoscintigraphy with a Gamma Camera and an On-Line Computer

1981 ◽  
Vol 20 (06) ◽  
pp. 274-278
Author(s):  
J. Liniecki ◽  
J. Bialobrzeski ◽  
Ewa Mlodkowska ◽  
M. J. Surma
Keyword(s):  
Count Rate ◽  
Renal Plasma Flow ◽  
Early Period ◽  
Least Square Method ◽  
Least Square ◽  
Uptake Coefficient ◽  
Positive Linear Correlation ◽  
On Line ◽  
Best Fit ◽  
Plasma Activity

A concept of a kidney uptake coefficient (UC) of 131I-o-hippurate was developed by analogy from the corresponding kidney clearance of blood plasma in the early period after injection of the hippurate. The UC for each kidney was defined as the count-rate over its ROI at a time shorter than the peak in the renoscintigraphic curve divided by the integral of the count-rate curve over the "blood"-ROI. A procedure for normalization of both curves against each other was also developed. The total kidney clearance of the hippurate was determined from the function of plasma activity concentration vs. time after a single injection; the determinations were made at 5, 10, 15, 20, 30, 45, 60, 75 and 90 min after intravenous administration of 131I-o-hippurate and the best-fit curve was obtained by means of the least-square method. When the UC was related to the absolute value of the clearance a positive linear correlation was found (r = 0.922, ρ > 0.99). Using this regression equation the clearance could be estimated in reverse from the uptake coefficient calculated solely on the basis of the renoscintigraphic curves without blood sampling. The errors of the estimate are compatible with the requirement of a fast appraisal of renal function for purposes of clinical diagknosis.

scholarly journals Estimation of Galactic Model Parameters by Interval Method

1996 ◽  
Vol 169 ◽  
pp. 713-714
Author(s):  
S. A. Kutuzov
Keyword(s):  
Mutual Interaction ◽  
Component Model ◽  
Model Parameters ◽  
Interval Method ◽  
Two Component ◽  
The Galaxy ◽  
Galactic Model

The interval method of estimating model parameters (MPs) for the Galaxy was suggested earlier (Kutuzov 1988). Intervals are proposed to be used both for observational estimates of galactic parameters (GPs) and for the values of MPs. In this work we consider a model as a tool for studying mutual interaction of GPs. Two-component model is considered (Kutuzov, Ossipkov 1989). We have to estimate the array P of eight MPs.

Fitting Weibull Strength Data and Applying It to Stochastic Mechanical Design

1992 ◽  
Vol 114 (1) ◽  
pp. 35-41 ◽  
Author(s):  
C. R. Mischke
Keyword(s):  
Mechanical Design ◽  
Least Square ◽  
Stochastic Methods ◽  
Coordinate Transformations ◽  
Strength Data ◽  
The Third ◽  
Tension Tests ◽  
Property Data ◽  
Simple Tension ◽  
Best Fit

This is the second paper in a series relating to stochastic methods in mechanical design. The first is entitled, “Some Property Data and Corresponding Weibull Parameters for Stochastic Mechanical Design,” and the third, “Some Stochastic Mechanical Design Applications.” When data are sparse, many investigators prefer employing coordinate transformations to rectify the data string, and a least-square regression to seek the best fit. Such an approach introduces some bias, which the method presented here is intended to reduce. With mass-produced products, extensive testing can be carried out and prototypes built and evaluated. When production is small, material testing may be limited to simple tension tests or perhaps none at all. How should a designer proceed in order to achieve a reliability goal or to assess a design to see if the goal has been realized? The purpose of this paper is to show how sparse strength data can be reduced to distributional parameters with less bias and how such information can be used when designing to a reliability goal.

scholarly journals Big Three Dragons: A [N ii] 122 μm Constraint and New Dust-continuum Detection of a z = 7.15 Bright Lyman-break Galaxy with ALMA

2021 ◽  
Vol 923 (1) ◽  
pp. 5
Author(s):  
Yuma Sugahara ◽  
Akio K. Inoue ◽  
Takuya Hashimoto ◽  
Satoshi Yamanaka ◽  
Seiji Fujimoto ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Far Infrared ◽  
Abundance Ratio ◽  
Continuum Emission ◽  
Spectral Energy ◽  
High Ionization ◽  
The Galaxy ◽  
Infrared Spectral ◽  
Best Fit ◽  
Redshift Galaxies

Abstract We present new Atacama Large Millimeter/submillimeter Array Band 7 observational results of a Lyman-break galaxy at z = 7.15, B14-65666 (“Big Three Dragons”), which is an object detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum emission during the epoch of reionization. Our targets are the [N ii] 122 μm fine-structure emission line and the underlying 120 μm dust continuum. The dust continuum is detected with a ∼19σ significance. From far-infrared spectral energy distribution sampled at 90, 120, and 160 μm, we obtain a best-fit dust temperature of 40 K (79 K) and an infrared luminosity of log 10 ( L IR / L ⊙ ) = 11.6 (12.1) at the emissivity index β = 2.0 (1.0). The [N ii] 122 μm line is not detected. The 3σ upper limit of the [N ii] luminosity is 8.1 × 107 L ⊙. From the [N ii], [O iii], and [C ii] line luminosities, we use the Cloudy photoionization code to estimate nebular parameters as functions of metallicity. If the metallicity of the galaxy is high (Z > 0.4 Z ⊙), the ionization parameter and hydrogen density are log 10 U ≃ − 2.7 ± 0.1 and n H ≃ 50–250 cm−3, respectively, which are comparable to those measured in low-redshift galaxies. The nitrogen-to-oxygen abundance ratio, N/O, is constrained to be subsolar. At Z < 0.4 Z ⊙, the allowed U drastically increases as the assumed metallicity decreases. For high ionization parameters, the N/O constraint becomes weak. Finally, our Cloudy models predict the location of B14-65666 on the BPT diagram, thereby allowing a comparison with low-redshift galaxies.

scholarly journals Biopolymer Drill-in Fluid Performance for Different Rheological Models using Statistical Characterisation

2019 ◽  
Vol 19 (1) ◽  
pp. 86-92
Author(s):  
M. Owusu ◽  
H. Osei
Keyword(s):  
Rheological Model ◽  
Rheological Behaviour ◽  
Primary Objective ◽  
Least Square ◽  
Model Parameters ◽  
Drilling Fluids ◽  
Cleaning Efficiency ◽  
Rheological Models ◽  
Least Square Regression ◽  
Best Fit

Appropriate selection of rheological models is important for hydraulic calculations of pressure loss prediction and hole cleaning efficiency of drilling fluids. Power law, Bingham-Plastic and Herschel-Bulkley models are the conventional fluid models used in the oilfield. However, there are other models that have been proposed in literature which are under/or not utilized in the petroleum industry. The primary objective of this paper is to recommend a rheological model that best-fits the rheological behaviour of xanthan gum-based biopolymer drill-in fluids for hydraulic evaluations. Ten rheological models were evaluated in this study. These rheological models have been posed deterministically and due to the unrealistic nature have been replaced by statistical models, by adding an error (disturbance) term and making suitable assumptions about them. Rheological model parameters were estimated by least-square regression method. Models like Sisko and modified Sisko which are not conventional models in oil industry gave a good fit. Modified Sisko model which is a four parameter rheological model was selected as the best-fit model since it produced the least residual mean square of 0.61 Ibf2/100ft4. There is 95% certainty that the true best-fit curve lies within the confidence band of this function of interest. Keywords: Biopolymer; Least-Square Regression; Residual Mean Squares; Rheologram

scholarly journals Movement Studies on a Hanging Glacier in Relation with an Ice Avalanche

1977 ◽  
Vol 19 (81) ◽  
pp. 671-672 ◽  
Author(s):  
André Flotron
Keyword(s):  
Flow Pattern ◽  
The State ◽  
Least Square ◽  
Velocity Versus ◽  
Surface Part ◽  
Different Types ◽  
Best Fit ◽  
Ice Avalanche

AbstractIn 1972 the state of a hanging glacier on the Weisshorn gave cause for alarm, as part of it seemed to be accelerating and a repetition of an earlier avalanche of ice seemed possible (see Röthlisberger, previous abstract). For this reason movement surveys were undertaken. The various surveying methods applied on the Weisshorn are outlined and the accuracy of the measurements is given. By least-square analysis different types of curves have been fitted to the data for velocity versus time. The best fit obtained so-far has been with hyperbolae. The confidence of extrapolations from such curves is discussed in relation to forecasts. By evaluating repeated photographs taken by an automatic camera from a single position, using a stereo plotter, the flow pattern has been established at the surface, part of the front, and one of the lateral faces of the ice mass. Changes with time caused by the deformation of the ice mass, the formation of crevasses and the crumbling away of the ice at the edge have been observed.

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