The kinematics and zero-point of the log P–〈MK〉 relation for Galactic RR Lyrae variables via statistical parallax

We use accurate absolute proper motions and Two-Micron All-Sky Survey   K_s   -band apparent magnitudes for 364 Galactic RR Lyrae variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-point of the   K_s   -band period–luminosity relation for these stars via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be  [ U ₀(Halo), V ₀(Halo), W ₀(Halo)]= (−12 ± 10, −217 ± 9, −6 ± 6) km s⁻¹  and  [ U ₀(Disc), V ₀(Disc), W ₀(Disc)]= (−15 ± 7, −44 ± 7, −25 ± 5) km s⁻¹  , respectively, and the corresponding components of the velocity-dispersion ellipsoids,  [σ V_R (Halo), σ V _θ(Halo), σ W (Halo)]= (167 ± 9, 86 ± 6, 78 ± 5) km s⁻¹  and  [σ V_R (Disc), σ V _θ(Disc), σ W (Disc)]= (55 ± 7, 44 ± 6, 30 ± 4) km s⁻¹  , respectively. The fraction of thick-disc stars is estimated at  0.25 ± 0.03  . The corrected infrared period–luminosity relation is     , implying a Large Magellanic Cloud (LMC) distance modulus of  18.27 ± 0.08  and a solar Galactocentric distance of  7.58 ± 0.40 kpc  . Our results suggest no or slightly prograde rotation for the population of halo RR Lyraes in the Milky Way.     

Spectroscopic solution of the star QX Cas

High-resolution spectroscopic observations around the Hα line of the binary star QX Cas covering the whole orbital period are presented. Our radial velocity solution, the first ever determined, requires an eccentric orbit with the following orbital parameters: eccentricity,   e = 0.22 ± 0.01  ; longitude of periastron,  ω= 45°± 5°  ; semi-amplitudes of the radial velocity curves of the primary and secondary stars,   K ₁ sin  i = 125.8 ± 0.9 km s⁻¹  and   K ₂ sin  i = 144.8 ± 1.1 km s⁻¹  ; gamma velocity,   V ₀= 65.1 ± 0.5 km s⁻¹  ; and mass ratio,   q = 0.869 ± 0.013  . The corresponding lower limits of the masses of the components and their separation are         , and   a sin  i = 31.34 ± 0.48 R_⊙  .     

The pattern speed of the OH/IR stars in the Milky Way

We show how the continuity equation can be used to determine pattern speeds in the Milky Way Galaxy (MWG). This method, first discussed by Tremaine & Weinberg in the context of external galaxies, requires projected positions, ( l , b ), and line-of-sight velocities for a spatially complete sample of relaxed tracers. If the local standard of rest (LSR) has a zero velocity in the radial direction ( u _LSR), then the quantity that is measured is  Δ V ≡Ω_p R ₀- V _LSR  , where Ω_p is the pattern speed of the non-axisymmetric feature, R ₀ is the distance of the Sun from the Galactic centre and V _LSR is the tangential motion of the LSR, including the circular velocity. We use simple models to assess the reliability of the method for measuring a single, constant pattern speed of either a bar or spiral in the inner MWG. We then apply the method to the OH/IR stars in the ATCA/VLA OH 1612-MHz survey of Sevenster et al., finding  Δ V =252±41 km s^-1,  if   u _LSR=0  . Assuming further that   R ₀=8 kpc  and   V _LSR=220 km s^-1,  this gives  Ω_p=59±5 km s^-1 kpc^-1  with a possible systematic error of perhaps 10 km s⁻¹ kpc⁻¹. The non-axisymmetric feature for which we measure this pattern speed must be in the disc of the MWG.     

The orbits of open clusters in the Galaxy

We present and analyse the kinematics and orbits for a sample of 488 open clusters (OCs) in the Galaxy. The velocity ellipsoid for our present sample is derived as  (σ _U , σ _V , σ _W ) = (28.7, 15.8, 11.0) km s⁻¹  which represents a young thin-disc population. We also confirm that the velocity dispersions increase with the age of a cluster subsample. The orbits of OCs are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of   b =−0.070 ± 0.011   dex kpc⁻¹. The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of   b =−0.082 ± 0.014   dex kpc⁻¹. The distribution of derived orbital eccentricities for OCs is very similar to that derived for the field population of dwarfs and giants in the thin disc.     

The Hubble flow around the Local Group

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  σ_v= 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 σ_v is achieved when the barycentre of the LG is located at the distance   D_c = (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  Ω_m= 0.24  and a topologically flat universe, a value in good agreement with the sum of virial mass estimates for the MW and M31.     

Kinematics of O-B5 giants

To study the kinematics of O-B5 giant stars (luminosity class III), 290 non-Gould belt stars with proper motions taken from the Hipparcos catalogue are used, of which 107 have radial velocities taken from other sources. Semidefinite programming solves for the kinematical parameters and the coefficients of the velocity ellipsoid. The condition that both solutions must yield the same solar velocity is enforced. The results obtained are reasonable: solar velocity of 13.83 ± 0.17 km s⁻¹; Oort's constants, in units of km s⁻¹ kpc⁻¹, A = 16.08 ± 0.72 and   B =−10.74 ± 0.65,  implying a rotational velocity of 228.0 ± 21.4 km s⁻¹ if we take the distance to the Galactic Centre as 8.5 ± 1.1 kpc; velocity dispersions, in units of km s⁻¹, of  σ _x = 32.44 ± 5.04, σ _y = 26.16 ± 2.75, σ _z = 18.71 ± 2.39  with a vertex deviation of         

Redshift and velocity dispersion of the cluster of galaxies around NGC 326

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.     

Could the Galactic disc heating be due to globular cluster impacts?

So far, six mechanisms have been proposed to account for the Galactic disc heating. Of these, the most important appear to be a combination of scattering of stars by molecular clouds and by spiral arms. We study a further mechanism, namely the repeated disc impact of the original Galactic globular cluster population up to the present. We find that globular clusters could have contributed at most a small fraction of the current vertical energy of the disc, as they could heat the whole disc to  σ _z = 5.5 km s⁻¹  (c.f. the observed 18 and 39 km s⁻¹ for the thick and thin discs, respectively). We find that the rate of rise of disc heat (  α= 0.22  in  σ _z ∼ t ^α  with t being time) is close to that found for scattering by molecular clouds.     

The large peculiar velocity of the cD galaxy in Abell 3653

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.     

Measurement of the epicycle frequency in the Galactic disc and initial velocities of open clusters

A new method to measure the epicycle frequency κ in the Galactic disc is presented. We make use of the large data base on open clusters completed by our group to derive the observed velocity vector (amplitude and direction) of the clusters in the Galactic plane. In the epicycle approximation, this velocity is equal to the circular velocity given by the rotation curve, plus a residual or perturbation velocity, of which the direction rotates as a function of time with the frequency κ. Due to the non-random direction of the perturbation velocity at the birth time of the clusters, a plot of the present-day direction angle of this velocity as a function of the age of the clusters reveals systematic trends from which the epicycle frequency can be obtained. Our analysis considers that the Galactic potential is mainly axis-symmetric, or in other words, that the effect of the spiral arms on the Galactic orbits is small; in this sense, our results do not depend on any specific model of the spiral structure. The values of κ that we obtain provide constraints on the rotation velocity of the disc; in particular, V ₀ is found to be  230 ± 15 km s⁻¹  even if the short scale  ( R ₀= 7.5 kpc)  of the Galaxy is adopted. The measured κ at the solar radius is  43 ± 5 km s⁻¹ kpc ⁻¹  . The distribution of initial velocities of open clusters is discussed.     

Non-circular motion evidence in the circumnuclear region of M100 (NGC 4321)

We analyse new integral-field spectroscopy of the inner region (central 2.5 kpc) of the spiral galaxy NGC 4321 to study the peculiar kinematics of this region. Fourier analysis of the velocity residuals obtained by subtracting an axisymmetric rotation model from the Hα velocity field indicates that the distortions are global features generated by an   m = 2  perturbation of the gravitational potential which can be explained by the nuclear bar. This bar has been previously observed in the near-infrared but not in the optical continuum dominated by star formation. We detect the optical counterpart of this bar in the 2D distribution of the old stellar population (inferred from the equivalent width map of the stellar absorption lines). We apply the Tremaine–Weinberg method to the stellar velocity field to calculate the pattern speed of the inner bar, obtaining a value of  Ω_b= 160 ± 70 km s⁻¹ kpc⁻¹  . This value is considerably larger than the one obtained when a simple bar model is considered. However, the uncertainties in the pattern speed determination prevent us from giving support to alternative scenarios.     

Spectroscopy of the optical Einstein ring 0047 – 2808

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.     

An excess of damped Lyman α galaxies near quasi-stellar objects

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.     

New constraints on a triaxial model of the Galaxy

We determine the most likely values of the free parameters of an N -body model for the Galaxy developed by Fux via a discrete–discrete comparison with the positions on the sky and line-of-sight velocities of an unbiased, homogeneous sample of OH/IR stars. Via Monte Carlo simulation, we find the plausibility of the best-fitting models, as well as the errors on the determined values. The parameters that are constrained best by these projected data are the total mass of the model and the viewing angle of the central bar, although the distribution of the latter has multiple maxima. The other two free parameters, the size of the bar and the (azimuthal) velocity of the Sun, are less well-constrained. The best model has a viewing angle of ∼ 44°, a semimajor axis of 2.5 kpc (corotation radius 4.5 kpc, pattern speed 46 km s⁻¹ kpc⁻¹), a bar mass of 1.7×10¹⁰ M_⊙ and a tangential velocity of the local standard of rest of 171 km s⁻¹. We argue that the lower values that are commonly found from stellar data for the viewing angle (∼25°) arise when too few coordinates are available, when the longitude range is too narrow or when low latitudes are excluded from the fit. The new constraints on the viewing angle of the Galactic bar from stellar line-of-sight velocities decrease further the ability of the distribution of the bar to account for the observed microlensing optical depth toward Baade's window: our model reproduces only half the observed value. The signal of triaxiality diminishes quickly with increasing latitude, fading within approximately 1 scaleheight (≲3°). This suggests that Baade's window is not a very appropriate region in which to sample bar properties.     

Distant field blue horizontal branch stars – III. Identification of a probable outer halo stream at Galactocentric distance r= 70 kpc

We present FOcal Reducer/low dispersion Spectrograph-1 spectra (from the European Southern Observatory's Very Large Telescope) of a sample of 34 faint  20.0 < g * < 21.1  A-type stars selected from the Sloan Digital Sky Survey Early Data Release, with the goal of measuring the velocity dispersion of blue horizontal branch (BHB) stars in the remote Galactic halo,   R ∼ 80 kpc  . We show that colour selection with  1.08 < u *− g * < 1.40  and  −0.2 < g *− r * < −0.04  minimizes contamination of the sample by less luminous blue stragglers. In classifying the stars we confine our attention to the 20 stars with spectra of signal-to-noise ratio >15 Å⁻¹. Classification produces a sample of eight BHB stars at distances  65–102 kpc  from the Sun (mean 80 kpc), which represents the most distant sample of Galactic stars with measured radial velocities. The dispersion of the measured radial component of the velocity with respect to the centre of the Galaxy is  58 ± 15 km s⁻¹  . This value is anomalously low in comparison with measured values for stars at smaller distances, as well as for satellites at similar distances. Seeking an explanation for the low measured velocity dispersion, further analysis reveals that six of the eight remote BHB stars are plausibly associated with a single orbit. Three previously known outer halo carbon stars also appear to belong to this stream. The velocity dispersion of all nine stars relative to the orbit is only  15 ± 4 km s⁻¹  . Further observations along the orbit are required to trace the full extent of this structure on the sky.     

Clustering of luminous red galaxies – II. Small-scale redshift-space distortions

This is the second paper of a series where we study the clustering of luminous red galaxies (LRG) in the recent spectroscopic Sloan Digital Sky Survey (SDSS) data release, DR6, which has 75 000 LRG covering over  1 Gpc³  h ⁻³  for  0.15 < z < 0.47  . Here, we focus on modelling redshift-space distortions in  ξ(σ, π)  , the two-point correlation in separate line-of-sight and perpendicular directions, at small scales and in the line-of-sight. We show that a simple Kaiser model for the anisotropic two-point correlation function in redshift space, convolved with a distribution of random peculiar velocities with an exponential form, can describe well the correlation of LRG on all scales. We show that to describe with accuracy the so-called 'fingers-of-God' (FOG) elongations in the radial direction, it is necessary to model the scale dependence of both bias b and the pairwise rms peculiar velocity σ₁₂ with the distance. We show how both quantities can be inferred from the  ξ(σ, π)  data. From   r ≃ 10 Mpc  h ⁻¹  to   r ≃ 1 Mpc  h ⁻¹  , both the bias and σ₁₂ are shown to increase by a factor of 2: from   b = 2  to 4 and from  σ₁₂= 400  to  800 km s⁻¹  . The latter is in good agreement, within a 5 per cent accuracy in the recovered velocities, with direct velocity measurements in dark matter simulations with  Ω_m= 0.25  and  σ₈= 0.85  .     

The interstellar medium in the Upper Cepheus-Cassiopeia region

We have studied the kinematics and spatial distribution of the interstellar gas in the sky region  110°≤ l ≤ 135°, 10°≤ b ≤ 20°  , using the extensive Leiden–Dwingeloo Survey of H  i emission and the Columbia Survey of CO emission. The spectra show two main velocity components, namely feature A that has a mean local standard of rest (LSR) velocity of  ∼0  km s⁻¹  and is due to the Lindblad ring of the Gould belt, and feature C that has a mean LSR velocity of  ∼−11  km s⁻¹  and is associated to the local arm or Orion arm. The H  i and CO distributions of feature A in the region trace a large complex of gas and dust known as the Cepheus Flare, which lies at a distance of 300 pc. The spectral line profiles of feature A, which are rather broad and often double-peaked, reveal that the Cepheus Flare forms part of a big expanding shell of interstellar matter that encloses an old supernova remnant associated with a void inside the Cepheus Flare. On the other hand, by analysing the distribution and velocity structure of feature C, we have detected a second large expanding shell in the region, located at a distance of 800 pc in the local arm. This shell surrounds the stellar association Cepheus OB4 and was probably generated by stellar winds and supernovae of Cepheus OB4. The radii, expansion velocities and H  i masses of the two shells are approximately 50 pc, 4  km s⁻¹ and  1.3 × 10⁴ M_⊙  for the Cepheus Flare shell and 100 pc, 4 km s⁻¹ and  9.9 × 10⁴ M_⊙  for the Cepheus OB4 shell. Both shells have similar ages of the order of a few 10⁶ yr.     

Radio observations of comet 9P/Tempel 1 with the Australia Telescope facilities during the Deep Impact encounter

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.