Formation of accretion centers in simulations of colliding uniform density H2 cores

We test here the first stage of a route of modifications to be applied to the public GADGET2 code for dynamically identifying accretion centers during the collision process of two adjacent and identical gas cores. Each colliding core has a uniform density profile and rigid body rotation; its mass and size have been chosen to represent the observed core L1544; for the thermal and rotational energy ratios with respect to the potential energy, we assume the values α = 0.3 and β = 0.1, respectively. These values favor the gravitational collapse of the core. We here study cases of both head‐on and off‐center collisions, in which the pre‐collision velocity increases the initial sound speed of the barotropic gas by up to several times. In a simulation the accretion centers are formed by the highest density particles, so we here report their location and properties in order to realize the collision effects on the collapsing and colliding cores. In one of the models, we observe a roughly spherical distribution of accretion centers located at the front wave of the collision. In a forthcoming publication we will apply the full modified GADGET code to study the collision of turbulent cores. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-resolution imaging of the cosmic mass distribution from gravitational lensing of pre-galactic H i

Low-frequency radio observations of neutral hydrogen during and before the epoch of cosmic re-ionization will provide ∼1000 quasi-independent source planes, each of precisely known redshift, if a resolution of ∼1 arcmin or better can be attained. These planes can be used to reconstruct the projected mass distribution of foreground material. Structure in these source planes is linear and Gaussian at high redshift  (30 < z < 300)  but is non-linear and non-Gaussian during re-ionization. At both epochs, significant power is expected down to subarcsecond scales. We demonstrate that this structure can, in principle, be used to make mass images with a formal signal-to-noise ratio (S/N) per pixel exceeding 10, even for pixels as small as an arcsecond. With an ideal telescope, both resolution and S/N can exceed those of even the most optimistic idealized mass maps from galaxy lensing by more than an order of magnitude. Individual dark haloes similar in mass to that of the Milky Way could be imaged with high S/N out to   z ∼ 10  . Even with a much less ambitious telescope, a wide-area survey of 21-cm lensing would provide very sensitive constraints on cosmological parameters, in particular on dark energy. These are up to 20 times tighter than the constraints obtainable from comparably sized, very deep surveys of galaxy lensing, although the best constraints come from combining data of the two types. Any radio telescope capable of mapping the 21-cm brightness temperature with good frequency resolution (∼0.05 MHz) over a band of width ≳10 MHz should be able to make mass maps of high quality. The planned Square Kilometre Array may be able to map the mass with moderate S/N down to arcminute scales, depending on the re-ionization history of the universe and the ability to subtract foreground sources.     

The Milky Way Galaxy as a strong gravitational lens

We study the gravitational lensing effects of spiral galaxies by taking a model of the Milky Way and computing its lensing properties. The model is composed of a spherical Hernquist bulge, a Miyamoto–Nagai disc and an isothermal halo. As a strong lens, a spiral galaxy like the Milky Way can give rise to four different imaging geometries. They are (i) three images on one side of the galaxy centre ('disc triplets'), (ii) three images with one close to the centre ('core triplets'), (iii) five images and (iv) seven images. Neglecting magnification bias, we show that the core triplets, disc triplets and fivefold imaging are roughly equally likely. Even though our models contain edge-on discs, their image multiplicities are not dominated by disc triplets. The halo is included for completeness, but it has a small effect on the caustic structure, the time delays and brightnesses of the images.
The Milky Way model has a maximum disc (i.e. the halo is not dynamically important in the inner parts). Strong lensing by nearly edge-on disc galaxies breaks the degeneracy between the relative contributions of the disc and halo to the overall rotation curve. If a spiral galaxy has a submaximum disc, then the astroid caustic shrinks dramatically in size, whilst the radial caustic shrinks more modestly. This causes changes in the relative likelihood of the image geometries, specifically (i) core triplets are now ∼9/2 times more likely than disc triplets, (ii) the cross-section for threefold imaging is reduced by a factor of ∼2/3, whilst (iii) the cross-section for fivefold imaging is reduced by ∼1/2. Although multiple imaging is less likely (the cross-sections are smaller), the average total magnification is greater. The time delays are smaller, as the total projected lensing mass is reduced.     

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  .     

从南极洲用微引力透镜技术探测太阳系外类地行星

太阳系外的类地行星可借助1米级望远镜用微引力透镜技术探测．基本的要求是能对银河核球进行连续观测的能力．置于南极洲冰穹A或冰穹C的望远镜特别合适．这里叙说两种可能的观测方案,一是使用一架1米的可见光望远镜(Ⅴ和Ⅰ通带),另一是用一台2米的大视场近红外望远镜．利用它们可以在数年内对类地行星在银河系内的丰度作一粗略测量,也可以对恒星大气作有用的测量．     

Oscillating Universe – An Alternative Approach in Cosmology

A new paradigm in cosmology is presented: A geometrical phase transition from the Minkowski space to an anti-deSitter space at its maximum of extension instead of a big bang with inflation. This scenario implies an open universe with a negative cosmological constant which replaces completely the cold dark matter in galaxy clusters. Baryonic matter and radiation are created from the gravitational field over a very long period of about 30 billion years. The contracting universe runs then after a further period of 13 billion years through a minimum with T _max ≃ 1.8 × 10¹² K and a particle density n _max ≃ 5 × 10³⁸ cm^-3 due to Hagedorn’s theory of a hadron gas. After the run through the minimum the universe expands like a big bang universe and reaches due to the negative cosmological constant after 44 billion years its maximal extension. Then it contracts again, and so on: An open ever-oscillating universe.     

Galaxies under the cosmic microscope: resolved spectroscopy and new constraints on the z= 1 Tully–Fisher relation

We exploit the gravitational potential of massive cluster lenses to probe the emission-line properties of six   z = 1  galaxies which appear as highly magnified luminous arcs. Using the Gemini Multi-Object Spectrograph (GMOS) integral field spectrograph together with detailed cluster lens models, we reconstruct the intrinsic morphologies and two-dimensional velocity fields in these galaxies on scales corresponds to ∼0.5 kpc (unlensed) at   z = 1  . Four of the galaxies have stable disc-like kinematics, whilst the other two resemble interacting or starburst galaxies. These galaxies lie close to the mean rest-frame I -band Tully–Fisher relation for nearby spirals suggesting a clear preference for hierarchical growth of structure. In the rest-frame B band, the observations suggest  0.5 ± 0.3 mag  of brightening, consistent with increased star-formation activity at   z = 1  . However, the galaxies with stable disc kinematics have more slowly rising rotation curves than expected from galaxies with similar surface brightness in the local Universe. We suggest that this may arise because the distant galaxies have lower bulge masses than their local counterparts. Whilst this study is based on only six galaxies, the gain in flux and in spatial resolution achieved via gravitational magnification provides a much more detailed view of the high-redshift Universe than that possible with conventional surveys.