Separation of the visible and dark matter in the Einstein ring LBG J213512.73−010143

We model the mass distribution in the recently discovered Einstein ring LBG J213512.73−010143 (the 'Cosmic Eye') using archival Hubble Space Telescope imaging. We reconstruct the mass density profile of the z = 0.73 lens and the surface brightness distribution of the z = 3.07 source and find that the observed ring is best fitted with a dual-component lens model consisting of a baryonic Sersic component nested within a dark matter halo. The dark matter halo has an inner slope of 1.42^+0.24_−0.22, consistent with cold dark matter simulations after allowing for baryon contraction. The baryonic component has a mass-to-light ratio of  1.71^+0.28_−0.38 M_⊙/L _{B ⊙}  which when evolved to the present day is in agreement with local ellipticals. Within the Einstein radius of 0.77 arcsec (5.6 kpc), the baryons account for 46 ± 11 per cent of the projected lens mass. External shear from a nearby foreground cluster is accurately predicted by the model. The reconstructed surface brightness distribution in the source plane clearly shows two peaks. Through a generalization of our lens inversion method, we conclude that the redshifts of both peaks are consistent with each other, suggesting that we are seeing structure within a single galaxy.     

The bending of light and lensing in modified gravity

Our modified gravity theory (MOG) was used successfully in the past to explain a range of astronomical and cosmological observations, including galaxy rotation curves, the cosmic microwave background acoustic peaks, and the galaxy mass power spectrum. MOG was also used successfully to explain the unusual features of the Bullet Cluster  1E0657−558  without exotic dark matter. In the present work, we derive the relativistic equations of motion in the spherically symmetric field of a point source in MOG and, in particular, we derive equations for light bending and lensing. Our results also have broader applications in the case of extended distributions of matter, and they can be used to validate the Bullet Cluster results and provide a possible explanation for the merging clusters in Abell 520.     

The growth of supermassive black holes in pseudo-bulges, classical bulges and elliptical galaxies

Using results from structural analysis of a sample of nearly 1000 local galaxies from the Sloan Digital Sky Survey, we estimate how the mass in central black holes is distributed amongst elliptical galaxies, classical bulges and pseudo-bulges, and investigate the relation between their stellar masses and central stellar velocity dispersion σ. Assuming a single relation between elliptical galaxy/bulge mass, M _Bulge, and central black hole mass, M _BH, we find that  55⁺⁸₋₄  per cent of the mass in black holes in the local universe is in the centres of elliptical galaxies,  41⁺⁴₋₂  per cent in classical bulges and  4^+0.9_−0.4  per cent in pseudo-bulges. We find that ellipticals, classical bulges and pseudo-bulges follow different relations between their stellar masses and σ, and the most significant offset occurs for pseudo-bulges in barred galaxies. This structural dissimilarity leads to discrepant black hole masses if single   M _BH– M _Bulge  and   M _BH–σ  relations are used. Adopting relations from the literature, we find that the   M _BH–σ  relation yields an estimate of the total mass density in black holes that is roughly 55 per cent larger than if the   M _BH– M _Bulge  relation is used.     

Constraints on decaying dark matter from XMM–Newton observations of M31

We derive constraints on the parameters of the radiatively decaying dark matter (DM) particle, using the XMM–Newton EPIC spectra of the Andromeda galaxy (M31). Using the observations of the outer (5–13 arcmin) parts of M31, we improve the existing constraints. For the case of sterile neutrino DM, combining our constraints with the latest computation of abundances of sterile neutrinos in the Dodelson–Widrow (DW) scenario, we obtain the lower mass limit   m _s < 4 keV  , which is stronger than the previous one   m _s < 6 keV  , obtained recently by Asaka, Laine & Shaposhnikov. Comparing this limit with the most recent results on Lyman α forest analysis of Viel et al.  ( m _s > 5.6 keV  ), we argue that the scenario in which all the DM is produced via the DW mechanism is ruled out. We discuss, however, other production mechanisms and note that the sterile neutrino remains a viable candidate for DM, either warm or cold.     

An iterative filter to reconstruct planetary transit signals in the presence of stellar variability

We report the identification, from a photometric, astrometric and spectroscopic study, of a massive white dwarf member of the nearby, approximately solar metallicity, Coma Berenices open star cluster (Melotte 111). We find the optical to near-infrared energy distribution of WD 1216+260 to be entirely consistent with that of an isolated DA and determine the effective temperature and surface gravity of this object to be   T _eff= 15 739⁺¹⁹⁷₋₁₉₆ K  and  log  g = 8.46^+0.03_−0.02  . We set tight limits on the mass of a putative cool companion,   M ≳ 0.036 M_⊙  (spatially unresolved) and   M ≳ 0.034 M_⊙  (spatially resolved and   a ≲ 2500 au  ). Based on the predictions of CO core, thick H layer evolutionary models we determine the mass and cooling time of WD 1216+260 to be   M _WD= 0.90 ± 0.04 M_⊙  and  τ_cool= 363⁺⁴⁶₋₄₁ Myr  , respectively. For an adopted cluster age of  τ= 500 ± 100 Myr  we infer the mass of its progenitor star to be   M _init= 4.77^+5.37_−0.97 M_⊙  . We briefly discuss this result in the context of the form of the stellar initial mass–final mass relation.     

H 0 from an orientation-unbiased sample of Sunyaev–Zel'dovich and X-ray clusters

We have observed the Sunyaev–Zel'dovich (SZ) effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the Bright Cluster Sample and the Northern ROSAT All-Sky Survey (RASS) cluster catalogues to be well above the surface brightness limit of the RASS, and hence to be unbiased with respect to the orientation of the cluster. This controls a major potential systematic effect in the SZ/X-ray method of measuring H ₀. Taking the weighted geometric mean of the results and including the main sources of error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity and substructure of the clusters, we find   H ₀= 59⁺¹⁰₋₉ (random)⁺⁸₋₇(systematic) km s⁻¹ Mpc⁻¹  assuming a standard cold dark matter model with  Ω_M= 1.0, Ω_Λ= 0.0  or   H ₀= 66⁺¹¹₋₁₀ ⁺⁹₋₈ km  s⁻¹ Mpc⁻¹  if  Ω_M= 0.3, Ω_Λ= 0.7  .     

Baryonic conversion tree: the global assembly of stars and dark matter in galaxies from the Sloan Digital Sky Survey

Using the spectroscopic sample of the Sloan Digital Sky Survey Data Release 1 (SDSS DR1), we measure how gas was transformed into stars as a function of time and stellar mass: the baryonic conversion tree (BCT). There is a clear correlation between early star formation activity and present-day stellar mass: the more massive galaxies have formed approximately 80 per cent of their stars at   z > 1  , while for the less massive ones the value is only approximately 20 per cent. By comparing the BCT with the dark matter merger tree, we find indications that star formation efficiency at   z > 1  had to be approximately a factor of two higher than today (∼10 per cent) in galaxies with present-day stellar mass larger than  2 × 10¹¹ M_⊙  , if this early star formation occurred in the main progenitor. Therefore, the λ cold dark matter (LCDM) paradigm can accommodate a large number of red objects. On the other hand, in galaxies with present-day stellar mass less than  10¹¹ M_⊙  , efficient star formation seems to have been triggered at   z ∼ 0.2  . We show that there is a characteristic mass  ( M _*∼ 10¹⁰ M_⊙)  for feedback efficiency (or lack of star formation). For galaxies with masses lower than this, feedback (or star formation suppression) is very efficient while for higher masses it is not. The BCT, determined here for the first time, should be an important observable with which to confront theoretical models of galaxy formation.     

ROSAT PSPC observations of the outer regions of the Perseus cluster of galaxies

We present an analysis of four off-axis ROSAT Position Sensitive Proportional Counter (PSPC) observations of the Perseus cluster of galaxies (Abell 426). We detect the surface brightness profile to a radius of 80 arcmin (∼2.4 h⁻¹₅₀ Mpc) from the X-ray peak. The profile is measured in various sectors and in three different energy bands. First, a colour analysis highlights a slight variation of N _H over the region, and cool components in the core and in the eastern sector. We apply the β-model to the profiles from different sectors and present a solution to the, so-called, β-problem. The residuals from an azimuthally-averaged profile highlight extended emission both in the east and in the west, with estimated luminosities of about 8 and 1 ×10⁴³ erg s⁻¹, respectively. We fit several models to the surface brightness profile, including the one obtained from the Navarro, Frenk &38; White potential. We obtain the best fit with the gas distribution described by a power law in the inner, cooling region and a β-model for the extended emission. Through the best-fitting results and the constraints from the deprojection of the surface brightness profiles, we define the radius where the overdensity inside the cluster is 200 times the critical value, r ₂₀₀, at 2.7 h⁻¹₅₀ Mpc. Within 2.3  h⁻¹₅₀ Mpc (0.85 r ₂₀₀), the total mass in the Perseus cluster is 1.2 × 10¹⁵ M_⊙ and its gas fraction is about 30 per cent.     

Dark matter haloes within clusters

We examine the properties of dark matter haloes within a rich galaxy cluster using a high-resolution simulation that captures the cosmological context of a cold dark matter universe. The mass and force resolution permit the resolution of 150 haloes with circular velocities larger than 80 km s⁻¹ within the cluster virial radius of 2 Mpc (with Hubble constant H ₀ = 50 km s⁻¹ Mpc⁻¹). This enables an unprecedented study of the statistical properties of a large sample of dark matter haloes evolving in a dense environment. The cumulative fraction of mass attached to these haloes varies from close to zero per cent at 200 kpc to 13 per cent at the virial radius. Even at this resolution the overmerging problem persists; haloes that pass within 100–200 kpc of the cluster centre are tidally disrupted. Additional substructure is lost at earlier epochs within the massive progenitor haloes. The median ratio of apocentric to pericentric radii is 6:1, so that the orbital distribution is close to isotropic, circular orbits are rare and radial orbits are common. The orbits of haloes are unbiased with respect to both position within the cluster and the orbits of the smooth dark matter background, and no velocity bias is detected. The tidal radii of surviving haloes are generally well-fitted using the simple analytic prediction applied to their orbital pericentres. Haloes within clusters have higher concentrations than those in the field. Within the cluster, halo density profiles can be modified by tidal forces and individual encounters with other haloes that cause significant mass loss —'galaxy harassment'. Mergers between haloes do not occur inside the cluster virial radius.     

The environmental dependence of the chemical properties of star-forming galaxies

We use a  0.040 < z < 0.085  sample of 37 866 star-forming galaxies from the Fourth Data Release of the Sloan Digital Sky Survey to investigate the dependence of gas-phase chemical properties on stellar mass and environment. The local density, determined from the projected distances to the fourth and fifth nearest neighbours, is used as an environment indicator. Considering environments ranging from voids, i.e.  log Σ≲−0.8  , to the periphery of galaxy clusters, i.e.  log Σ≈ 0.8  , we find no dependence of the relationship between galaxy stellar mass and gas-phase oxygen abundance, along with its associated scatter, on local galaxy density. However, the star-forming gas in galaxies shows a marginal increase in the chemical enrichment level at a fixed stellar mass in denser environments. Compared with galaxies of similar stellar mass in low-density environments, they are enhanced by a few per cent for massive galaxies to about 20 per cent for galaxies with stellar masses  ≲10^9.5 M_⊙  . These results imply that the evolution of star-forming galaxies is driven primarily by their intrinsic properties and is largely independent of their environment over a large range of local galaxy density.     

Revisiting the baryon fractions of galaxy clusters: a comparison with WMAP 3-yr results

The universal baryonic mass fraction  (Ω_b/Ω_m)  can be sensitively constrained using X-ray observations of galaxy clusters. In this paper, we compare the baryonic mass fraction inferred from measurements of the cosmic microwave background with the gas mass fractions ( f _gas) of a large sample of clusters taken from the recent literature. In systems cooler than 4 keV, f _gas declines as the system temperature decreases. However, in higher temperature systems, f _gas( r ₅₀₀) converges to  ≈(0.12 ± 0.02)( h /0.72)^−1.5  , where the uncertainty reflects the systematic variations between clusters at r ₅₀₀. This is significantly lower than the maximum-likelihood value of the baryon fraction from the recently released Wilkinson Microwave Anisotropy Probe ( WMAP ) 3-yr results. We investigate possible reasons for this discrepancy, including the effects of radiative cooling and non-gravitational heating, and conclude that the most likely solution is that Ω_m is higher than the best-fitting WMAP value (we find  Ω_m= 0.36^+0.11_−0.08  ), but consistent at the 2σ level. Degeneracies within the WMAP data require that σ₈ must also be greater than the maximum likelihood value for consistency between the data sets.     

Microlensing in dark matter haloes

Using eight dark matter haloes extracted from fully self-consistent cosmological N -body simulations, we perform microlensing experiments. A hypothetical observer is placed at a distance of 8.5 kpc from the centre of the halo measuring optical depths, event durations and event rates towards the direction of the Large Magellanic Cloud. We simulate 1600 microlensing experiments for each halo. Assuming that the whole halo consists of massive astronomical compact halo objects (MACHOs),   f = 1.0  , and a single MACHO mass is   m _M= 1.0 M_⊙  , the simulations yield mean values of  τ= 4.7^+5.0_−2.2× 10⁻⁷  and  Γ= 1.6^+1.3_−0.6× 10⁻⁶  events star⁻¹ yr⁻¹. We find that triaxiality and substructure can have major effects on the measured values so that τ and Γ values of up to three times the mean can be found. If we fit our values of τ and Γ to the MACHO collaboration observations, we find   f = 0.23^+0.15_−0.13  and   m _M= 0.44^+0.24_−0.16  . Five out of the eight haloes under investigation produce f and m _M values mainly concentrated within these bounds.     

Line emission in the brightest cluster galaxies of the NOAO Fundamental Plane and Sloan Digital Sky Surveys

We examine the optical emission-line properties of brightest cluster galaxies (BCGs) selected from two large, homogeneous data sets. The first is the X-ray selected National Optical Astronomy Observatory Fundamental Plane Survey (NFPS), and the second is the C4 catalogue of optically selected clusters built from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Our goal is to better understand the optical line emission in BCGs with respect to properties of the galaxy and the host cluster. Throughout the analysis we compare the line emission of the BCGs to that of a control sample made of the other bright galaxies near the cluster centre. Overall, both the NFPS and SDSS show a modest fraction of BCGs with emission lines (∼15 per cent). No trend in the fraction of emitting BCGs as a function of galaxy mass or cluster velocity dispersion is found. However, we find that, for those BCGs found in cooling flow clusters,  71⁺⁹₋₁₄  have optical emission. Furthermore, if we consider only BCGs within 50 kpc of the X-ray centre of a cooling flow cluster, the emission-line fraction rises further to  100⁺⁰₋₁₅  per cent. Excluding the cooling flow clusters, only ∼10 per cent of BCGs are line emitting, comparable to the control sample of galaxies. We show that the physical origin of the emission-line activity varies: in some cases it has LINER-like line ratios, whereas in others it is a composite of star-formation and LINER-like activity. We conclude that the presence of emission lines in BCGs is directly related to the cooling of X-ray gas at the cluster centre.     

The lens and source of the optical Einstein ring gravitational lens ER 0047–2808

We perform a detailed analysis of the optical gravitational lens ER 0047–2808 imaged with the Wide Field Planetary Camera 2 on the Hubble Space Telescope . Using software specifically designed for the analysis of resolved gravitational lens systems, we focus on how the image alone can constrain the mass distribution in the lens galaxy. We find that the data are of sufficient quality to strongly constrain the lens model with no a priori assumptions about the source. Using a variety of mass models, we find statistically acceptable results for elliptical isothermal-like models with an Einstein radius of 1.17 arcsec. An elliptical power-law model  (Σ∝ R ^−β)  for the surface mass density favours a slope slightly steeper than isothermal with  β= 1.08 ± 0.03  . Other models including a constant mass-to-light ratio (M/L), pure Navarro, Frenk & White halo and (surprisingly) an isothermal sphere with external shear are ruled out by the data. We find the galaxy light profile can only be fit with a Sérsic plus point-source model. The resulting total  M/L _B   contained within the images is  4.7  h ₆₅± 0.3  . In addition, we find the luminous matter is aligned with the total mass distribution within a few degrees. This is the first time a resolved optical gravitational lens image has been quantitatively reproduced using a non-parametric source.
The source, reconstructed by the software, is revealed to have two bright regions, with an unresolved component inside the caustic and a resolved component straddling a fold caustic. The angular size of the entire source is ∼0.1 arcsec and its (unlensed) Lyα flux is  3 × 10⁻¹⁷ erg s⁻¹ cm⁻²  .     

A Bayesian periodogram finds evidence for three planets in HD 11964

A Bayesian multiplanet Kepler periodogram has been developed for the analysis of precision radial velocity data. The periodogram employs a parallel tempering Markov chain Monte Carlo algorithm. The HD 11964 data have been re-analysed using 1, 2, 3 and 4 planet models. Assuming that all the models are equally probable a priori, the three planet model is found to be ≥600 times more probable than the next most probable model which is a two planet model. The most probable model exhibits three periods of  38.02^+0.06_−0.05, 360⁺⁴₋₄ and 1924⁺⁴⁴₋₄₃ d  , and eccentricities of  0.22^+0.11_−0.22, 0.63^+0.34_−0.17 and 0.05^+0.03_−0.05  , respectively. Assuming the three signals (each one consistent with a Keplerian orbit) are caused by planets, the corresponding limits on planetary mass ( M sin  i ) and semimajor axis are     respectively. The small difference (1.3σ) between the 360-d period and one year suggests that it might be worth investigating the barycentric correction for the HD 11964 data.     

A Bayesian Kepler periodogram detects a second planet in HD 208487

An automatic Bayesian Kepler periodogram has been developed for identifying and characterizing multiple planetary orbits in precision radial velocity data. The periodogram is powered by a parallel tempering Markov chain Monte Carlo (MCMC) algorithm which is capable of efficiently exploring a multiplanet model parameter space. The periodogram employs an alternative method for converting the time of an observation to true anomaly that enables it to handle much larger data sets without a significant increase in computation time. Improvements in the periodogram and further tests using data from HD 208487 have resulted in the detection of a second planet with a period of 909⁸²₋₉₂ d, an eccentricity of 0.37^0.26_−0.20, a semimajor axis of 1.87^0.13_−0.14 au and an M sin  i = 0.45^+0.11_−0.13 M _J. The revised parameters of the first planet are period = 129.8 ± 0.4 d, eccentricity = 0.20 ± 0.09, semimajor axis = 0.51 ± 0.02 au and M sin  i = 0.41 ± 0.05  M _J. Particular attention is paid to several methods for calculating the model marginal likelihood which is used to compare the probabilities of models with different numbers of planets.     

A survey for planetary transits in the field of NGC 7789

We present results from 30 nights of observations of the open cluster NGC 7789 with the Wide Field Camera on the Isaac Newton Telescope, La Palma. From ∼900 epochs, we obtained light curves and Sloan   r '− i '  colours for ∼33 000 stars, with ∼2400 stars having better than 1 per cent precision. We expected to detect ∼2 transiting hot Jupiter planets if 1 per cent of stars host such a companion and a typical hot Jupiter radius is  ∼1.2  R _J  . We find 24 transit candidates, 14 of which we can assign a period. We rule out the transiting planet model for 21 of these candidates using various robust arguments. For two candidates, we are unable to decide on their nature, although it seems most likely that they are eclipsing binaries as well. We have one candidate exhibiting a single eclipse, for which we derive a radius of  1.81^+0.09_−0.00  R _J  . Three candidates remain that require follow-up observations in order to determine their nature.     

Gas in simulations of high-redshift galaxies and minihaloes

We study the gas content of haloes in the early universe using high-resolution hydrodynamical simulations. We extract from the simulations and also predict, based on linear theory, the halo mass for which the enclosed baryon fraction equals half of the mean cosmic fraction. We find a rough agreement between the simulations and the predictions, which suggests that during the high-redshift era before stellar heating, the minimum mass needed for a minihalo to keep most of its baryons throughout its formation was  ∼3 × 10⁴ M_⊙  . We also carry out a detailed resolution analysis and show that in order to determine a halo's gas fraction even to 20 per cent accuracy, the halo must be resolved into at least 500 dark matter particles.     

Dynamical parallax of σ Ori AB: mass, distance and age

The massive OB-type binary σ Ori AB is in the centre of the very young σ Orionis cluster. I have computed the most probable distances and masses of the binary for several ages using a dynamical parallax-like method. It incorporates the BVRIH -band apparent magnitudes of both components, precise orbital parameters, interstellar extinction and a widely used grid of stellar models from the literature, Kepler's third law and a  χ²  minimization. The derived distance is  334⁺²⁵₋₂₂ pc  for an age of 3 ± 2 Ma; larger ages and distances are unlikely. The masses of the primary and the secondary lie on the approximate intervals  16–20 and 10–12 M_⊙  , respectively. I also discuss the possibility of σ Ori AB being a triple system at ∼ 385 pc. These results will help to constrain the properties of young stars and substellar objects in the σ Orionis cluster.     

On the galaxy stellar mass function, the mass–metallicity relation and the implied baryonic mass function

A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4–8 per cent of the baryon density (assuming  Ω_b= 0.045  ). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the   z < 0.05  GSMF using the New York University Value-Added Galaxy Catalog sample of 49 968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has  α₂≃−1.6  . At masses below  ∼10^8.5 M_⊙  , the GSMF may be significantly incomplete because of missing low-surface-brightness galaxies. One interpretation of the stellar mass–metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principle, we determine a simple relationship between baryonic mass and stellar mass and present an 'implied baryonic mass function'. This function has a faint-end slope,  α₂≃−1.9  . Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function → galaxy baryonic mass function → GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses  ∼10¹¹ M_⊙  corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses.