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1.
We use the Least Action Principle to predict the peculiar velocities of PSC z galaxies inside cz =2000 km s−1. Linear theory is used to account for tidal effects to cz =15 000 km s−1, and we iterate galaxy positions to account for redshift distortions. As the Least Action Principle is valid beyond linear theory, we can predict reliable peculiar velocities even for very nearby galaxies (i.e., cz ≤500 km s−1). These predicted peculiar velocities are then compared with the observed velocities of 12 galaxies with Cepheid distances. The combination of the PSC z galaxy survey (with its large sky coverage and uniform selection) with the accurate Cepheid distances makes this comparison relatively free from systematic effects. We find that galaxies are good tracers of the mass, even at small (≤10  h −1 Mpc) scales; under the assumption of no biasing, 0.25≤ β ≤0.75 (at 90 per cent confidence). We use the reliable predicted peculiar velocities to estimate the Hubble constant H 0 from the local volume without 'stepping up' the distance ladder, finding a confidence range of 65–75 km s−1 Mpc−1 (at 90 per cent confidence).  相似文献   

2.
We present a comparison between the peculiar velocity fields measured from a recently completed l -band Tully–Fisher survey of field spirals (SFI) and that derived from the IRAS 1.2-Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions, and is performed using low- and high-resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 km s−1 are 1500 and 1000 km s−1 for the low- and high-resolution filters. The agreement between the high- and low-resolution SFI velocity maps is excellent. The general features in the filtered SFI and IRAS velocity fields agree remarkably well within 6000 km s−1. This good agreement between the fields allows us to determine the parameter β = Ω0.6 / b , where Ω is the cosmological density parameter, and b is the linear biasing factor. From a likelihood analysis on the SFI and IRAS modes we find that β = 0.6 ± 0.1, independently of the resolution of the modal expansion. For this value of β, the residual fields for the two filters show no systematic variations within 6000 km s−1. Most remarkable is the lack of any coherent, redshift-dependent dipole flow in the residual field.  相似文献   

3.
We present optical and near-infrared spectroscopic observations of the optical Einstein ring 0047 – 2808. We detect both [O III ] lines λλ4959, 5007 near ∼ 2.3 μm, confirming the redshift of the lensed source as z  = 3.595. The Lyα line is redshifted relative to the [O III ] line by 140 ± 20 km s−1. Similar velocity shifts have been seen in nearby starburst galaxies. The [O III ] line is very narrow, 130 km s−1 FWHM. If the ring is the image of the centre of a galaxy, the one-dimensional stellar velocity dispersion σ = 55 km s−1 is considerably smaller than the value predicted by Baugh et al. for the somewhat brighter Lyman-break galaxies. The Lyα line is significantly broader than the [O III ] line, probably due to resonant scattering. The stellar central velocity dispersion of the early-type deflector galaxy at z  = 0.485 is 250 ± 30 km s−1. This value is in good agreement both with the value predicted from the radius of the Einstein ring (and a singular isothermal sphere model for the deflector), and with the value estimated from the D n −σ relation.  相似文献   

4.
Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of     and a line-of-sight velocity dispersion σ z =599 (+230,−110) km s−1. The velocity dispersion and previously measured X-ray gas temperature of kT ≃1.9 keV are consistent with the cluster σ z kT relation, and NGC 326 is seen to be a slowly moving member of the cluster.  相似文献   

5.
A detailed dynamical analysis of the nearby rich Norma cluster (ACO 3627) is presented. From radial velocities of 296 cluster members, we find a mean velocity of 4871 ± 54 km s−1 and a velocity dispersion of 925 km s−1. The mean velocity of the E/S0 population (4979 ± 85 km s−1) is offset with respect to that of the S/Irr population (4812 ± 70 km s−1) by  Δ v = 164 km s−1  in the cluster rest frame. This offset increases towards the core of the cluster. The E/S0 population is free of any detectable substructure and appears relaxed. Its shape is clearly elongated with a position angle that is aligned along the dominant large-scale structures in this region, the so-called Norma wall. The central cD galaxy has a very large peculiar velocity of 561 km s−1 which is most probably related to an ongoing merger at the core of the cluster. The spiral/irregular galaxies reveal a large amount of substructure; two dynamically distinct subgroups within the overall spiral population have been identified, located along the Norma wall elongation. The dynamical mass of the Norma cluster within its Abell radius is  1–1.1 × 1015  h −173 M⊙  . One of the cluster members, the spiral galaxy WKK 6176 which recently was observed to have a 70 kpc X-ray tail, reveals numerous striking low-brightness filaments pointing away from the cluster centre suggesting strong interaction with the intracluster medium.  相似文献   

6.
We use updated data on distances and velocities of galaxies in the proximity of the Local Group (LG) in order to establish properties of the local Hubble flow. For 30 neighbouring galaxies with distances  0.7 < D LG < 3.0  Mpc, the local flow is characterized by the Hubble parameter   H loc= (78 ± 2) km s−1 Mpc−1  , the mean-square peculiar velocity  σv= 25 km s−1  , corrected for errors of radial velocity measurements  (∼4 km s−1)  and distance measurements  (∼10 km s−1)  , as well as the radius of the zero-velocity surface   R 0= (0.96 ± 0.03)  Mpc. The minimum value for σv is achieved when the barycentre of the LG is located at the distance   Dc = (0.55 ± 0.05) D M31  towards Andromeda galaxy (M31) corresponding to the Milky Way (MW)-to-M31 mass ratio   M MW/ M M31≃ 4/5  . In the reference frame of the 30 galaxies at 0.7–3.0 Mpc, the LG barycentre has a small peculiar velocity  ∼(24 ± 4) km s−1  towards the Sculptor constellation. The derived value of R 0 corresponds to the total mass   M T(LG) = (1.9 ± 0.2) 1012 M⊙  with  Ωm= 0.24  and a topologically flat universe, a value in good agreement with the sum of virial mass estimates for the MW and M31.  相似文献   

7.
We present a sample of 33 damped Lyman α systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts ( z abs) are within 6000 km s−1 of the quasi-stellar object's (QSO) systemic redshift ( z sys). Our sample is based on  731 2.5 < z sys < 4.5  non-broad absorption line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ≈100 per cent complete for absorbers with N (H  i )  ≥ 2 × 1020 cm−2  . The derived number density of DLAs per unit redshift, n ( z ), within  Δ v < 6000 km s−1  is higher (3.5σ significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening 'field' DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar.  相似文献   

8.
We present 13 CO J  = 1 − 0 line observations of the H  ii region complex W51B located in the high-velocity (HV) stream. These observations reveal a filamentary and clumpy structure in the molecular gas. The mean local standard of rest (LSR) velocity ∼ + 65 km s−1 of the molecular gas in this region is greater than the maximum velocities allowed by kinematic Galactic rotation curves. The size and mass of the molecular clouds are ∼ 48 × 17 pc2 and ∼ 2.4 × 105 M⊙ respectively. In a position–velocity diagram, molecular gas in the southern part comprises a redshifted ring structure with v LSR=+ 60 to +73 km s−1. The velocity gradient of this ring is ∼ 0.5 km s−1 pc−1, and the mass is ∼ 6.2 × 104 M⊙. If we assume that the ring is expanding with a uniform velocity, the expansion velocity, radius and kinetic energy are ∼ 7 km s−1, ∼ 13 pc and ∼ 3.0 × 10 49 erg respectively. The kinetic energy and mass spectrum of the ring could be explained by an expanding cylindrical cloud with a centrally condensed mass distribution. The locations of two compact H  ii regions, G49.0−0.3 and G48.9−0.3, coincide with the two molecular clumps in this ring. We discuss star formation, and the mechanism that produced the ring structure.  相似文献   

9.
We present near-infrared spectra of seven radio-loud quasars with a median redshift of 2.1, five of which were previously known to have Ly α nebulae. Extended [O  iii ] λ 5007 and H α emission are evident around six objects, at the level of a few times 10−16 erg cm−2 arcsec−2 s−1 within ≃2 arcsec of the nucleus (≡16 kpc in the adopted cosmology). Nuclear [O  ii ] λ 3727 is detected in three of the five quasars studied at this wavelength and clearly extended in one of them.
The extended [O  iii ] tends to be brighter on the side of the nucleus with the stronger, jet-like radio emission, indicating at least that the extranuclear gas is distributed anisotropically. It is also typically redshifted by several hundred km s−1 from the nuclear [O  iii ], perhaps because of the latter being blueshifted from the host galaxy's systemic velocity. Alternatively, the velocity shifts could be due to infall (which is suggested by linewidths ∼1000 km s−1 FWHM) in combination with a suitable dust geometry. Ly α /H α ratios well below the case B value suggest that some dust is present.
Photoionization modelling of the [O  iii ]/[O  ii ] ratios in the extended gas suggests that its pressure is around or less than a few times 107 cm−3 K; any confining intracluster medium is thus likely to host a strong cooling flow. A comparison with lower redshift work suggests that there has been little evolution in the nuclear emission-line properties of radio-loud quasars between redshifts 1 and 2.  相似文献   

10.
We report on a survey for narrow (full widths at half-minimum <600 km s−1) C  iv absorption lines in a sample of bright quasars at redshifts  1.8 ≤ z < 2.25  in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow C  iv absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad Mg  ii emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find that a substantial number (  ≥43 ± 6  per cent) of absorbers with   W λ15480 > 0.3  Å in the velocity range  +750 ≲ v ≲+ 12 000  km s−1 are intrinsic to the active galactic nucleus outflow. This 'outflow fraction' peaks near   v =+2000  km s−1 with a value of   f outflow≃ 0.81 ± 0.13  . At velocities below   v ≈+ 2000  km s−1, the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disc. Furthermore, we find that outflow absorbers are on average broader and stronger than cosmologically intervening systems. Finally, we find that ∼14 per cent of the quasars in our sample exhibit narrow, outflowing C  iv absorption with   W λ15480 > 0.3  Å, slightly larger than that for broad absorption line systems.  相似文献   

11.
This paper reports the results of a modest redshift survey carried out, at generally low Galactic latitudes, in the vicinity of the South Celestial Pole. Target galaxies were selected as a 'representative' sample of underlying large-scale structures. Dimensions, approximate magnitudes and radial velocity measurements, are reported for 336 galaxies. Two obvious Seyfert 1 galaxies, one probably Seyfert 1 and three Seyfert 2 galaxies have been discovered. The redshifts are used to supplement existing data and serve to map southern voids and features out to 25 000 km s−1 in the region  270° < l < 330°, 0° > b > −45°  . Three distinct superclusters and twenty apparent voids are tentatively identified. One Void, at   l = 300°, b =−20°, cz = 16 000 km s−1  , with a diameter of 6000 km s−1, is as large as any yet mapped. It appears as part of a general underdense region.  相似文献   

12.
We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of   M v =−2.5  , a half-light radius of 34 pc and a systemic velocity of  ∼−40 km s−1  . Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km s−1 and the possible stream as  ∼7 km s−1  . This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites – survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts   z > 10  and are good candidates for fossils of the reionization epoch.  相似文献   

13.
We present radial velocities for 2045 stars in the Small Magellanic Cloud (SMC), obtained from the 2dF survey by Evans et al. The great majority of these stars are of OBA type, tracing the dynamics of the young stellar population. Dividing the sample into ad hoc 'bar' and 'wing' samples (north and south, respectively, of the line:  δ=−77°50'+[4α]'  , where α is the right ascension in minutes of time) we find that the velocities in the SMC bar show a gradient of 26.3 ± 1.6 km s−1 deg−1 at a position angle of 126°± 4°. The derived gradient in the bar is robust to the adopted line of demarcation between the two samples. The largest redshifts are found in the SMC wing, in which the velocity distribution appears distinct from that in the bar, most probably a consequence of the interaction between the Magellanic Clouds that is predicted to have occurred 0.2 Gyr ago. The mean velocity for all stars in the sample is +172.0 ± 0.2 km s−1 (redshifted by ∼20 km s−1 when compared to published results for older populations), with a velocity dispersion of 30 km s−1.  相似文献   

14.
We present a catalogue of galaxies in Abell 3653 from observations made with the 2-degree field (2dF) spectrograph at the Anglo-Australian Telescope. Of the 391 objects observed, we find 111 are bona fide members of Abell 3653. We show that the cluster has a velocity of   cz = 32 214 ± 83  km s−1 ( z = 0.10 738 ± 0.00 027)  , with a velocity dispersion typical of rich, massive clusters of  σ cz = 880+66−54  . We find that the cD galaxy has a peculiar velocity of  683 ± 96  km s−1  in the cluster rest frame – some 7σ away from the mean cluster velocity, making it one of the largest and most significant peculiar velocities found for a cD galaxy to date. We investigate the cluster for signs of substructure, but do not find any significant groupings on any length scale. We consider the implications of our findings on cD formation theories.  相似文献   

15.
We have analysed the kinematical parameters of Cir X-1 to constrain the nature of its companion star, the eccentricity of the binary and the pre-supernova parameter space. We argue that the companion is most likely to be a low-mass (≲2.0 M⊙) unevolved star and that the eccentricity of the orbit is 0.94±0.04. We have evaluated the dynamical effects of the supernova explosion and we find it must have been asymmetric. On average , we find that a kick of ∼740 km s−1 is needed to account for the recently measured radial velocity of +430 km s−1 (Johnston, Fender & Wu) for this extreme system. The corresponding minimum kick velocity is ∼500 km s−1. This is the largest kick needed to explain the motion of any observed binary system. If Cir X-1 is associated with the supernova remnant G321.9-0.3 then we find a limiting minimum age of this remnant of ∼60 000 yr. Furthermore, we predict that the companion star has lost ∼10 per cent of its mass as a result of stripping and ablation from the impact of the supernova shell shortly after the explosion.  相似文献   

16.
We present extensive tests of the fast action method (FAM) for recovering the past orbits of mass tracers in an expanding universe from their redshift-space coordinates at the present epoch. The tests focus on the reconstruction of present-day peculiar velocities using mock catalogues extracted from high-resolution N -body simulations. The method allows for a self-consistent treatment of redshift-space distortions by direct minimization of a modified action for a cosmological gravitating system. When applied to ideal, volume-limited catalogues, FAM recovers unbiased peculiar velocities with a one-dimensional, 1σ error of ∼220 km  s−1  , if velocities are smoothed on a scale of  5 h −1  Mpc. Alternatively, when no smoothing is applied, FAM predicts nearly unbiased velocities for objects residing outside the highest density regions. In this second case the 1σ error decreases to a level of ∼150 km  s−1  . The correlation properties of the peculiar velocity fields are also correctly recovered on scales larger than  5 h −1  Mpc. Similar results are obtained when FAM is applied to flux-limited catalogues mimicking the IRAS PSC z survey. In this case FAM reconstructs peculiar velocities with similar intrinsic random errors, while velocity–velocity correlation properties are well reproduced beyond scales of  ∼8 h −1  Mpc. We also show that FAM provides better velocity predictions than other, competing methods based on linear theory or the Zel'dovich approximation. These results indicate that FAM can be successfully applied to presently available galaxy redshift surveys such as IRAS PSC z .  相似文献   

17.
We calculate analytically and numerically the distance–redshift equation in perfect fluid quintessence models and give an accurate fit to the numerical solutions for all the values of the density parameter and the quintessence equation of state. Then we apply our solutions to the estimation of H 0 from multiple image time delays and find that the inclusion of quintessence modifies significantly the likelihood distribution of H 0, generally reducing the best estimate with respect to a pure cosmological constant. Marginalizing over the other parameters (Ω m and the quintessence equation of state) we obtain H 0=71±6 km s−1 Mpc−1 for an empty beam and H 0=64±4 km s−1 Mpc−1 for a filled beam. These errors, however, do not take into account the uncertainty on the modelling of the lens. We also discuss the future prospects for distinguishing quintessence from a cosmological constant with time delays.  相似文献   

18.
We have studied the velocity field of the blue compact dwarf galaxy Mrk 86 (NGC 2537) using data provided by 14 long-slit optical spectra obtained in 10 different orientations and positions. This kinematical information is complemented with narrow-band ([O  iii ]5007 Å and H α ) and broad-band ( B , V , Gunn r and K ) imaging. The analysis of the galaxy global velocity field suggests that the ionized gas could be distributed in a rotating inclined disc, with projected central angular velocity of Ω=34 km s−1 kpc−1. The comparison between the stellar, H  i and modelled dark matter density profile indicates that the total mass within its optical radius is dominated by the stellar component. Peculiarities observed in its velocity field can be explained by irregularities in the ionized gas distribution or local motions induced by star formation.
Kinematical evidences for two expanding bubbles, Mrk 86–B and Mrk 86–C, are given. They show expanding velocities of 34 and 17 km s−1, H α luminosities of 3×1038 and 1.7×1039 erg s−1, and physical radii of 374 and 120 pc, respectively. The change in the [S  ii ]/H α , [N  ii ]/H α , [O  ii ]/[O  iii ] and [O  iii ]/H β line ratios with the distance to the bubble precursor suggests a diminution in the ionization parameter and, in the case of Mrk 86–B, an enhancement of the shock-excited gas emission. The optical–near-infrared colours of the bubble precursors are characteristic of low‐metallicity star‐forming regions (∼0.2 Z⊙) with burst strengths of about 1 per cent in mass.  相似文献   

19.
Using new and archival radio data, we have measured the proper motion of the black hole X-ray binary V404 Cyg to be  9.2 ± 0.3 mas yr−1  . Combined with the systemic radial velocity from the literature, we derive the full three-dimensional heliocentric space velocity of the system, which we use to calculate a peculiar velocity in the range 47–102 km s−1, with a best-fitting value of 64 km s−1. We consider possible explanations for the observed peculiar velocity and find that the black hole cannot have formed via direct collapse. A natal supernova is required, in which either significant mass  (∼11 M⊙)  was lost, giving rise to a symmetric Blaauw kick of up to ∼65 km s−1, or, more probably, asymmetries in the supernova led to an additional kick out of the orbital plane of the binary system. In the case of a purely symmetric kick, the black hole must have been formed with a mass  ∼9 M⊙  , since when it has accreted  0.5–1.5 M⊙  from its companion.  相似文献   

20.
We present radio observations of comet 9P/Tempel 1 associated with the Deep Impact spacecraft collision of 2005 July 4. Weak 18-cm OH emission was detected with the Parkes 64-m telescope, in data averaged over July 4–6, at a level of  12 ± 3 mJy km s−1  , corresponding to OH production rate  2.8 × 1028  molecules s−1 (Despois et al. inversion model, or  1.0 × 1028 s−1  for the Schleicher & A'Hearn model). We did not detect the HCN 1–0 line with the Mopra 22-m telescope over the period July 2–6. The 3σ limit of 0.06 K km s−1 for HCN on July 4 after the impact gives the limit to the HCN production rate of  <1.8 × 1025 s−1  . We did not detect the HCN 1–0 line, 6.7 GHz CH3OH line or 3.4-mm continuum with the Australia Telescope Compact Array (ATCA) on July 4, giving further limits on any small-scale structure due to an outburst. The 3σ limit on HCN emission of 2.5 K km s−1 from the ATCA around impact corresponds to limit < 4 × 1029 HCN molecules released by the impact.  相似文献   

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