Recession Velocity Research Articles

The globular cluster kinematics and galaxy dark matter content of NGC 3923

This paper presents further results from our spectroscopic study of the globular cluster (GC) system of the group elliptical NGC 3923. From observations made with the GMOS instrument on the Gemini South Telescope, an additional 50 GC and ultra-compact dwarf (UCD) candidates have been spectroscopically confirmed as members of the NGC 3923 system. When the recessional velocities of these GCs are combined with the 29 GC velocities reported previously, a total sample of 79 GC/UCD velocities is produced. This sample extends to over 6 arcmin (> 6 Re∼ 30 kpc) from the centre of NGC 3923 and is used to study the dynamics of the GC system and the dark matter content of NGC 3923. It is found that the GC system of NGC 3923 displays no appreciable rotation, and that the projected velocity dispersion is constant with radius within the uncertainties. The velocity dispersion profiles of the integrated light and GC system of NGC 3923 are indistinguishable over the region in which they overlap. We find some evidence that the diffuse light and GCs of NGC 3923 have radially biased orbits within ∼130 arcsec. The application of axisymmetric orbit-based models to the GC and integrated light velocity dispersion profiles demonstrates that a significant increase in the mass-to-light ratio (from M/LV= 8 to 26) at large galactocentric radii is required to explain this observation. We therefore confirm the presence of a dark matter halo in NGC 3923. We find that dark matter comprises 17.5 per cent of the mass within 1 Re, 41.2 per cent within 2 Re and 75.6 per cent within the radius of our last kinematic tracer at 6.9 Re. The total dynamical mass within this radius is found to be M⊙. In common with other studies of large ellipticals, we find that our derived dynamical mass profile is consistently higher than that derived by X-ray observations, by a factor of around 2.

Consequences from conservation of the total density of the universe during the expansion

The recent Cosmic Microwave Background (CMB) experiments have shown that the average density of the universe is close to the critical one and the universe is asymptotically flat (Euclidean). Taking into account that the universe remains flat and the total density of the universe Ω0 is conserved equal to a unit during the cosmological expansion, the Schwarzschild radius of the observable universe has been determined equal to the Hubble distance 1 2 ~ 2    cH R c GM Rs , where M is the mass of the observable universe, R is the Hubble distance and H is the Hubble constant. Besides, it has been shown that the speed of the light c appears the parabolic velocity for the observable universe p v R GM c   2 and the recessional velocity Hr vr  of an arbitrary galaxy at a distance r > 100 Mps from the observer, is equal to the parabolic velocity for the sphere, having radius r and a centre, coinciding with the observer. The requirement for conservation of 1 0   during the expansion enables to derive the Hoyle-Carvalho formula for the mass of the observable universe kg GH c M 53 3 10 ~ 2  by a new approach.

Inverse Determination of Interfacial Wear Temperatures with a Receding Boundary and the Implications for Tribotesting

Frictionally generated interfacial temperatures are of great interest during tribotesting and candidate materials evaluations, as well as from actual components in service. Unfortunately, it is very difficult, if not impossible, to directly interrogate the interacting surfaces for these temperatures, especially when the wear surface is receding. Though remote measurements of temperature or strain are usually obtainable, they can only hint at the frictional temperatures unless they are just below the surface and, thus, quickly vulnerable to wear damage. In order to overcome these inherent difficulties, a least-squares enforcement of remote temperature data was used with a direct analytical solution for a cylindrical specimen with a receding surface to determine the interfacial temperatures as a function of time. Comparisons between the direct and inverse analytical solutions, as well as resulting interfacial predictions, based on existing data showed excellent agreement and verified the ability of the method to determine temperatures based on remote data. As expected, stray transfer from the lateral surface of the pin, specimen dimensions, as well as the recession velocity of the surface clearly influenced the interfacial temperature history and will therefore have important ramifications for tribotesting and the evaluation of the results.

THE ARECIBO LEGACY FAST ALFA SURVEY: THE α.40 H I SOURCE CATALOG, ITS CHARACTERISTICS AND THEIR IMPACT ON THE DERIVATION OF THE H I MASS FUNCTION

We present a current catalog of 21 cm HI line sources extracted from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey over ~2800 square degrees of sky: the alpha.40 catalog. Covering 40% of the final survey area, the alpha.40 catalog contains 15855 sources in the regions 07h30m < R.A. < 16h30m, +04 deg < Dec. < +16 deg and +24 deg < Dec. < +28 deg and 22h < R.A. < 03h, +14 deg < Dec. < +16 deg and +24 deg < Dec. < +32 deg. Of those, 15041 are certainly extragalactic, yielding a source density of 5.3 galaxies per square degree, a factor of 29 improvement over the catalog extracted from the HI Parkes All Sky Survey. In addition to the source centroid positions, HI line flux densities, recessional velocities and line widths, the catalog includes the coordinates of the most probable optical counterpart of each HI line detection, and a separate compilation provides a crossmatch to identifications given in the photometric and spectroscopic catalogs associated with the Sloan Digital Sky Survey Data Release 7. Fewer than 2% of the extragalactic HI line sources cannot be identified with a feasible optical counterpart; some of those may be rare OH megamasers at 0.16 < z < 0.25. A detailed analysis is presented of the completeness, width dependent sensitivity function and bias inherent in the current alpha.40 catalog. The impact of survey selection, distance errors, current volume coverage and local large scale structure on the derivation of the HI mass function is assessed. While alpha.40 does not yet provide a completely representative sampling of cosmological volume, derivations of the HI mass function using future data releases from ALFALFA will further improve both statistical and systematic uncertainties.

DISCOVERY AND FOLLOW-UP OF A NEARBY GALAXY FROM THE ARECIBO ZONE OF AVOIDANCE SURVEY

The Arecibo L-Band Feed Array Zone of Avoidance (ALFA ZOA) Survey has discovered a nearby galaxy, ALFA ZOA J1952+1428, at a heliocentric velocity of +279 km s-1. The galaxy was discovered at low Galactic latitude by 21-cm emission from neutral hydrogen (Hi). We have obtained follow-up observations with the EVLA and the 0.9-m SARA optical telescope. The Hi distribution overlaps an uncataloged, potential optical counterpart. The Hi linear size is 1.4 kpc at our adopted distance of D = 7 Mpc, but the distance estimate is uncertain as Hubble's law is unreliable at low recessional velocities. The optical counterpart has mB = 16.9 mag and B - R = 0.1 mag. These characteristics, including MHI = 107.0 M\odot and LB = 107.5 L\odot, if at 7 Mpc, indicate that this galaxy is a blue compact dwarf, but this remains uncertain until further follow-up observations are complete. Optical follow-up observations are ongoing and near infrared follow-up observations have been scheduled.

Narrow-line Seyfert 1 galaxies: an amasing class of AGN

[Abridged] Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that have all the properties of type 1 Seyfert galaxies but show peculiar characteristics, including the narrowest Balmer lines, strongest Fe II emission, and extreme properties in the X-rays. Line and continuum radio observations provide an optimal tool to access the (often) optically obscured innermost regions of AGN and reveal the kinematics of the gas around their central engines. We investigate the interplay between the peculiar NLS1 class of AGN and the maser phenomenon, to help us understand the nature of the maser emission in some NLS1s where water maser emission has been detected. We observed a sample of NLS1 galaxies with the Green Bank Telescope in a search for water maser emission at 22 GHz. We also reduced and analysed archival Green Bank Telescope and Very Large Array data and produced 22-GHz spectra for the five NLS1 galaxies with detected maser emission. In particular, we imaged the maser and nuclear radio continuum of NGC5506 at subarcsec scales with the Very Large Array. We discovered maser emission in two NLS1 galaxies: IGRJ16385-2057, and IRAS03450+0055. In addition to the three previously known maser detections in the NLS1s Mrk766, NGC4051, and NGC5506, this yields a water maser detection rate in NLS1 galaxies of ~7% (5/71). This value rises significantly to ~21% (5/24) when considering only NLS1 galaxies at recessional velocities less than 10000 km/s. For NGC4051 and NGC5506, we find that the water maser emission is located within 5 and 12 pc, respectively, of nuclear radio continuum knots, which are interpreted as core-jet structures.

Pulse dynamics upon three-wave parametric interaction in the presence of cubic and quadratic nonlinearities

The features of the three-wave parametric interaction in a medium with quadratic and cubic nonlinearities upon low-frequency pumping and nonzero detuning from the phase matching were studied. It has been shown that the common wave packet formed by the signal and idle waves is decayed into partial pulses, whose dynamics is determined by effective dispersion parameters. The presence of two types of nonlinearities extends the possibilities of controlling the dynamics of the forming partial pulses due to the variation of the pump wave power. The velocity of recession of partial pulses can reach large values and even exceed the speed of light in the vacuum.

FRW universe models in conformally flat-spacetime coordinates I: General formalism

The 3-space of a universe model is defined at a certain simultaneity. Hence space depends on which time is used. We find a general formula generating all known and also some new transformations to conformally flat spacetime coordinates. A general formula for the recession velocity is deduced.

Fermi Coordinates, Simultaneity, and Expanding Space in Robertson–Walker Cosmologies

Explicit Fermi coordinates are given for geodesic observers comoving with the Hubble flow in expanding Robertson–Walker space–times, along with exact expressions for the metric tensors in Fermi coordinates. For the case of non-inflationary cosmologies, it is shown that Fermi coordinate charts are global, and space–time is foliated by space slices of constant Fermi (proper) time that have finite extent. A universal upper bound for the proper radius of any leaf of the foliation, i.e., for the proper radius of the spatial universe at any fixed time of the geodesic observer, is given. A general expression is derived for the geometrically defined Fermi relative velocity of a test particle (e.g., a galaxy cluster) comoving with the Hubble flow away from the observer. Least upper bounds of superluminal recessional Fermi velocities are given for space–times whose scale factors follow power laws, including matter-dominated and radiation-dominated cosmologies. Exact expressions for the proper radius of any leaf of the foliation for this same class of space–times are given. It is shown that the radii increase linearly with proper time of the observer moving with the Hubble flow. These results are applied to particular cosmological models.

SPATIALLY RESOLVED SPECTROSCOPIC OBSERVATIONS OF A POSSIBLE E+A PROGENITOR: SDSS J160241.00+521426.9

In order to investigate the evolution of E+A galaxies, we observed a galaxy SDSS J160241.00+521426.9, a possible E+A progenitor which shows both emission and strong Balmer absorptions, and its neighbor galaxy. We used the integral field spectroscopic mode of the Kyoto Tridimensional Spectrograph (Kyoto3DII), mounted on the University of Hawaii 88-inch telescope located on Mauna Kea, and the slit-spectroscopic mode of the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope. We found a strong Balmer absorption region in the center of the galaxy and an emission-line region located 2 kpc from the center, in the direction of its neighbor galaxy. The recession velocities of the galaxy and its neighbor galaxy differ only by 100 km s^-1, which suggests that they are a physical pair and would have been interacting. Comparing observed Lick indices of Balmer lines and color indices with those predicted from stellar population synthesis models, we find that a suddenly quenched star-formation scenario is plausible for the star-formation history of the central region. We consider that star formation started in the galaxy due to galaxy interactions and was quenched in the central region, whereas star formation in a region offset from the center still continues or has begun recently. This work is the first study of a possible E+A progenitor using spatially resolved spectroscopy.

The kinematic component of the cosmological redshift

It is widely believed that the cosmological redshift is not a Doppler shift. However, Bunn & Hogg have recently pointed out that to settle properly this problem, one has to transport parallelly the velocity four-vector of a distant galaxy to the observer's position. Performing such a transport along the null geodesic of photons arriving from the galaxy, they found that the cosmological redshift is purely kinematic. Here we argue that one should rather transport the velocity four-vector along the geodesic connecting the points of intersection of the world-lines of the galaxy and the observer with the hypersurface of constant cosmic time. We find that the resulting relation between the transported velocity and the redshift of arriving photons is not given by a relativistic Doppler formula. Instead, for small redshifts it coincides with the well known non-relativistic decomposition of the redshift into a Doppler (kinematic) component and a gravitational one. We perform such a decomposition for arbitrary large redshifts and derive a formula for the kinematic component of the cosmological redshift, valid for any FLRW cosmology. In particular, in a universe with Omega_m = 0.24 and Omega_Lambda = 0.76, a quasar at a redshift 6, at the time of emission of photons reaching us today had the recession velocity v = 0.997c. This can be contrasted with v = 0.96c, had the redshift been entirely kinematic. Thus, for recession velocities of such high-redshift sources, the effect of deceleration of the early Universe clearly prevails over the effect of its relatively recent acceleration. Last but not least, we show that the so-called proper recession velocities of galaxies, commonly used in cosmology, are in fact radial components of the galaxies' four-velocity vectors. As such, they can indeed attain superluminal values, but should not be regarded as real velocities.

The galaxy population of Abell 1367: photometric and spectroscopic data

Photometric and spectroscopic observations of the galaxy population of the galaxy cluster Abell 1367 have been obtained, over a field of 34 by 90 arcmin, covering the cluster centre out to a radius of about 2.2 Mpc. U, B and R broad-band and H alpha narrow-band imaging observations were carried out using the Wide Field Camera (WFC) on the 2.5m INT. J and K near-infrared imaging was obtained using the Wide Field Camera (WFCAM) on the 3.8 m UKIRT, covering a somewhat smaller field of 0.75 square degrees on the cluster centre. The spectroscopic observations were carried out using a multifibre spectrograph (WYFFOS) on the 4.2 m WHT, over the same field as the optical imaging observations. Our photometric data give optical and near-infrared magnitudes for 303 galaxies in our survey regions, down to stated diameter and B-band magnitude limits, determined within R24 isophotal diameters. Our spectroscopic data of 328 objects provide 84 galaxies with detections of emission and/or absorption lines. Combining these with published spectroscopic data gives 126 galaxies within our sample for which recession velocities are known. Of these, 72 galaxies are confirmed as cluster members of Abell 1367, 11 of which are identified in this study. (abridged)

Spectroscopic confirmation of Hα-selected satellite galaxies

We present a spectroscopic test confirming the potential of narrow-band optical imaging as a method for detecting star-forming satellites around nearby galaxies. To date the efficiency of such methods, and particularly the fraction of false detections resulting from its use, has not been tested. In this paper we use optical spectroscopy to verify the nature of objects that are apparently emission-line satellites, taken from imaging presented elsewhere. Observations of 12 probable satellites around 11 host galaxies are presented and used to compare the recession velocities of the host and satellite. This test confirms, in all cases, that there is genuine line emission, that the detected line is hydrogen alpha, and that the satellites have similar recession velocities to their hosts with a maximum difference of ~ 250 km/s, consistent with their being gravitationally bound companions. We conclude that the spectroscopy has confirmed that narrow-band imaging through H alpha filters is a reliable method for detecting genuine, star-forming satellites with low contamination from galaxies seen in projection along the line-of-sight.

Does gravity operate between galaxies? Observational evidence re-examined

The redshifts and luminosities of type 1A supernovae are conventionally fitted with the current paradigm, which holds that the galaxies are locally stationary in an expanding metric. The fit fails unless the expansion is accelerating; driven perhaps by ‘dark energy’. Is the recession of the galaxies slowed down by gravity or speeded up by some repulsive force? To shed light on this question the redshifts and apparent magnitudes of type 1A supernovae are re-analysed in a cartesian frame of reference omitting gravitational effects. The redshift is ascribed to the relativistic Doppler effect which gives the recession velocity when the light was emitted; if this has not changed, the distance reached and the luminosity follow immediately. This simple concept fits the observations surprisingly well with the Hubble constant H 0 =62.9±0.3 km s −1 Mpc −1 . It appears that the galaxies recede at unchanging velocities, so on the largest scale there is no significant intergalactic force. Reasons for the apparent absence of an intergalactic force are discussed.

Distance to the SNR CTB109/AXP 1E 2259+586 by Hiabsorption and self-absorption

AbstractWe suggest a revised distance to the supernova remnant G109.1−1.0 (CTB109) and its associated anomalous X-ray pulsar (AXP)1E2259+586 by analysing 21-cm Hi-line and 12CO-line spectra of CTB109, Hii region Sh152 and the adjacent molecular cloud complex. CTB109 has been established to be interacting with a large molecular cloud (recession velocity at v=−55kms−1). The highest radial velocities of absorption features towards CTB109 (−56kms−1) and Sh152 (−65kms−1) are larger than the recombination line velocity (−50kms−1) of Sh152 demonstrating the velocity reversal within the Perseus Arm. The molecular cloud has cold Hi column density large enough to produce Hi self-absorption (HISA) and Hi narrow self-absorption (HINSA) if it was at the near side of the velocity reversal. Absence of both HISA and HINSA indicates that the cloud is at the far side of the velocity reversal within the Perseus Arm, so we obtain a distance for CTB109 of 4 ± 0.8kpc. The new distance still leads to a normal explosion energy for CTB 109/AXP 1E 2259+586.

A RADIAL VELOCITY AND CALCIUM TRIPLET ABUNDANCE SURVEY OF FIELD SMALL MAGELLANIC CLOUD GIANTS

We present the results of a pilot wide-field radial velocity and metal abundance survey of red giants in 10 fields in the Small Magellanic Cloud (SMC). The targets lie at projected distances of 0.9 and 1.9 kpc from the SMC center (m − M = 18.79) to the north, east, south, and west. Two more fields are to the east at distances of 3.9 and 5.1 kpc. In this last field, we find only a few to no SMC giants, suggesting that the edge of the SMC in this direction lies approximately at 6 kpc from its center. In all eastern fields, we observe a double peak in the radial velocities of stars, with a component at the classical SMC recession velocity of ∼160 km s−1 and a high-velocity component at about 200 km s−1, similar to observations in H i. In the most distant field (3.9 kpc), the low-velocity component is at 106 km s−1. The metal abundance distribution in all fields is broad and centered at about [Fe/H] ∼−1.25, reaching to solar and possibly slightly supersolar values and down to [Fe/H] of about −2.5. In the two innermost (0.9 kpc) northern and southern fields, we observe a secondary peak at metallicities of about ∼−0.6. This may be evidence of a second episode of star formation in the center, possibly triggered by the interactions that created the Stream and Bridge.

The kinematic origin of the cosmological redshift

A common belief about big-bang cosmology is that the cosmological redshift cannot be properly viewed as a Doppler shift (that is, as evidence for a recession velocity) but must be viewed in terms of the stretching of space. We argue that, contrary to this view, the most natural interpretation of the redshift is as a Doppler shift, or rather as the accumulation of many infinitesimal Doppler shifts. The stretching-of-space interpretation obscures a central idea of relativity, namely that it is always valid to choose a coordinate system that is locally Minkowskian. We show that an observed frequency shift in any spacetime can be interpreted either as a kinematic (Doppler) shift or a gravitational shift by imagining a suitable family of observers along the photon’s path. In the context of the expanding universe, the kinematic interpretation corresponds to a family of comoving observers and hence is more natural.

THE PHOTOMETRIC AND KINEMATIC STRUCTURE OF FACE-ON DISK GALAXIES. II. INTEGRATED LINE PROFILE CHARACTERIZATION AND THE ORIGIN OF LINE PROFILE ASYMMETRY

We perform a moments analysis of H I and H II global line profiles for 33 nearly face-on disk galaxies for the threefold purpose of rationalizing and interpreting line profile indices in the literature, presenting robust moment definitions with analytic error functions calibrated against Monte Carlo simulation, and probing the physical origin of line profile asymmetries. The first four profile moments serve as viable surrogates for the recession velocity, line width, asymmetry, and profile shape, respectively. The first three moments are superior, by a factor of ~2 in precision, to related quantities defined in the literature. First and third profile moments are related; skew can be used to calculate more accurate recession velocities from global profiles. Second and fourth profile moments are linked, corresponding to the known trend that narrow (but well resolved) line widths tend to be more Gaussian. Hα kurtosis also appears correlated with the spatially resolved line width of the ionized gas. No systematics appear between various measures of line width and true rotation speed other than the wide range of normalizations, which we calibrate. This conclusion and calibration, however, is highly sample dependent. The ratio of H II to H I widths is consistent with unity, even at low projected line width. There may be a trend toward a decrease in the ratio of H II to H I widths consistent with previous studies, but we also observe greater scatter. While there is good agreement between H I and H II first, second, and fourth moments, we find no positive correlation between skew measured from H I and H II profiles. Detailed analysis of the spatially resolved Hα distribution demonstrates that H II global profile asymmetries are dominated by differences in the gas distribution, not kinematic asymmetries.

The outer halo globular clusters of M31

Abstract We present Keck/HIRES spectra of three globular clusters in the outer halo of M31, at projected distances beyond ≈80 kpc from M31. The measured recession velocities for all three globular clusters confirm their association with the globular cluster system of M31. We find evidence for a declining velocity dispersion with radius for the globular cluster system. Their measured internal velocity dispersions, derived virial masses and mass-to-light ratios are consistent with those for the bulk of the M31 globular cluster system. We derive old ages and metallicities which indicate that all three belong to the metal-poor halo globular cluster subpopulation. We find indications that the radial gradient of the mean metallicity of the globular cluster system interior to 50 kpc flattens in the outer regions, however it is still more metal-poor than the corresponding field stars at the same (projected) radius.

The X-ray view of giga-hertz peaked spectrum radio galaxies

This paper presents the X-ray properties of a flux- and volume-limited complete sample of 16 Giga-Hertz Peaked Spectrum (GPS) galaxies. This study addresses three basic questions in our understanding of the nature and evolution of GPS sources: a) What is the physical origin of the X-ray emission in GPS galaxies? b) What physical system is associated with the X-ray obscuration? c) What is the "endpoint" of the evolution of compact radio sources? We obtain a 100% (94%) detection fraction in the 0.5-2 keV (0.5-10 keV) energy band. GPS galaxy X-ray spectra are typically highly obscured. The X-ray column density is higher than the HI column density measured in the radio by a factor of 10 to 100. GPS galaxies lie well on the extrapolation to high radio powers of the correlation between radio and X-ray luminosity known in low-luminosity FRI radio galaxies. On the other hand, GPS galaxies exhibit a comparable X-ray luminosity to FRII radio galaxies, notwithstanding their much higher radio luminosity. The X-ray to radio luminosity ratio distribution in our sample is consistent with the bulk of the high-energy emission being produced by the accretion disk, as well as with dynamical models of GPS evolution where X-rays are produced by Compton upscattering of ambient photons. Further support for the former scenario comes from the location of GPS galaxies in the X-ray to O[III] luminosity ratio versus column density plane. We propose that GPS galaxies are young radio sources, which would reach their full maturity as classical FRII radio galaxies. However, column densities ~10^{22} atoms/cm/cm could lead to a significant underestimate of dynamical age determinations based on the hotspot recession velocity measurements. (abridged)