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arXiv2008

Correlation Lengths of Red and Blue Galaxies: A New Cosmic Ruler

A comparison of the correlation lengths of red galaxies with blue can provide a new cosmic ruler. Using 269,000 galaxies from the SDSS DR6 survey, I show that the 3D correlation length averaged over many clusters remains very nearly constant at Lo=4.797+/-0.024 Mpc/h from small redshifts out to redshifts of 0.5. This serves as a new measure of cosmic length scales as well as a means of testing the standard cosmological model that is almost free of selection biases. The cluster number density also appears to remain constant over this redshift range.

astro-ph↗

arXiv2008

Interferometric and seismic constraints on the roAp star alpha Cir

We present new constraints on the rapidly oscillating Ap star alpha Cir, derived from a combination of interferometric and photometric data obtained with the Sydney University Stellar Interferometer (SUSI) and the WIRE satellite. The highlights of our study are: 1. The first determination of the angular diameter of an roAp star. 2. A nearly model-independent determination of the effective temperature of alpha Cir, which is found to be lower than previously estimated values. 3. Detection of two new oscillation frequencies allowing a determination of the large separation of alpha Cir. Based on this new information, we have computed non-magnetic and magnetic models for alpha Cir. We show that the value of the observed large separation found from the new data agrees well with that derived from theoretical models. Moreover, we also show how the magnetic field may explain some of the anomalies seen in the oscillation spectrum and how these in turn provide constraints on the magnitude and topology of the magnetic field.

astro-ph↗

arXiv2008

Overview of the lithium problem in metal-poor stars and new results on 6Li

Two problems are discussed here. The first one is the 0.4 dex discrepancy between the 7Li abundance derived from the spectra of metal-poor halo stars on the one hand, and from Big Bang nucleosynthesis, based on the cosmological parameters constrained by the WMAP measurements, on the other hand. Lithium, indeed, can be depleted in the convection zone of unevolved stars. The understanding of the hydrodynamics of the crucial zone near the bottom of the convective envelope in dwarfs or turn-off stars of solar metallicity has recently made enormous progress with the inclusion of internal gravity waves. However, similar work for metal-poor stars is still lacking. Therefore it is not yet clear whether the depletion occurring in the metal-poor stars themselves is adequate to produce a 7Li plateau. The second problem pertains to the large amount of 6Li recently found in metal-poor halo stars. The convection-related asymmetry of the 7Li line could mimic the signal attributed so far to the weak blend of 6Li in the red wing of the 7Li line. Theoretical computations show that the signal generated by the asymmetry of 7Li is 2.0, 2.1, and 3.7 per cent for [Fe/H]= -3.0, -2.0, -1.0, respectively (Teff =6250 K and log g=4.0 [cgs]). In addition we re-investigate the statistical properties of the 6Li plateau and show that previous analyses were biased. Our conclusion is that the 6Li plateau can be reinterpreted in terms of intrinsic line asymmetry, without the need to invoke a contribution of 6Li. (abridged)

astro-ph↗

arXiv2008

X-ray spectral states of microquasars

We discuss the origin of the dramatically different X-ray spectral shapes observed in the Low Hard State (LHS: dominated by thermal comptonisation) and the High Soft State (HSS: dominated by the accretion disc thermal emission and non-thermal comptonisation in the corona). We present numerical simulations using a new code accounting for the so-called synchrotron boiler effect. These numerical simulations when compared to the data allow us to constrain the magnetic field and temperature of the hot protons in the corona. For the hard state of Cygnus X-1 we find a magnetic field below equipartition with radiation, suggesting that the corona is not powered through magnetic field dissipation (as assumed in most accretion disc corona models). On the other hand, our results also point toward proton temperatures that are substantially lower than typical temperatures of the ADAF models. Finally, we show that in both spectral states Comptonising plasma could be powered essentially through power-law acceleration of non-thermal electrons, which are then partly thermalised by the synchrotron and Coulomb boiler. This suggests that, contrary to current beliefs, the corona of the HSS and that of the LHS could be of very similar nature. The differences between the LHS and HSS coronal spectra would then be predominantly caused by the strong disc soft cooling emission which is present in the HSS and absent in the LHS.

astro-ph↗

arXiv2009

A theoretical framework for the detection of point-sources in Cosmic Microwave Background maps

The detection of point-sources in microwave maps is a critical step in the analysis of the Cosmic Microwave Background (CMB) data. If not properly removed, these sources have adverse effects on the estimation of the power-spectrum and/or the test of Gaussianity of the CMB component. The techniques to extract point sources from an observed image used up to now do not show a general consensus about their real performance and properties. Their characteristics have been studied essentially through numerical simulations based on semi-empirical models of the CMB and the Galactic foreground. Such models often have different levels of sophistication and/or are based on different physical assumptions (e.g. the number of Galactic components and level of the noise). Moreover, the application of a given technique to a set of data (either simulated or experimental) requires the tuning of one or more parameters that unavoidably is a subjective operation. Hence, a reliable comparison is difficult. What is missing is a statistical analysis of the properties of the proposed methodologies. This is the aim of the present paper. The statistical properties of the detection techniques in the context of two different criteria, i.e. the Neyman-Pearson criterion and the maximization of the signal-to-noise ratio, are analyzed through an analytical approach. Various examples, techniques and the conditions under which they work satisfactorily are shown together with their limits and implementation details. Exploiting some a priori information, it is possible to develop simple algorithms with performances similar to those of more sophisticated but complex techniques. In this respect, a detection algorithm, useful in future ground-based experiments as, for example the Atacama Large Millimeter/submillimeter Array, is presented.

astro-ph↗

arXiv2008

A close look at compact triple radio sources

We show an archival 1.4-GHz Very Large Array (VLA) image of the core-dominated triple (CDT) radio source J1628+3906, along with a recent high-resolution 5-GHz Very Long Baseline Interferometry (VLBI) image of its core. This core is resolved into two nearly symmetric components at ~10 milli-arcsecond (mas) angular scale. The inner structure is markedly misaligned with respect to the large-scale structure. This morphology can be interpreted as a possible signature of once ceased and then restarted activity of the galactic nucleus, coupled with a rapid repositioning of the central radio jet axis. In a search for compact (<5"), optically identified, and highly redshifted (z>3) quasars in the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) and the Sloan Digital Sky Survey (SDSS) catalogues, we have also found two quasars associated with weaker two-sided radio lobes at ~10" scale. We present archival 1.4-GHz VLA images of these quasars (J1036+1326 and J1353+5725). The compact cores of both of these CDT sources are likely to be detectable at mas scales. Future VLBI observations at the highest resolution could reveal if their inner radio structure is similar to that of the Compact Symmetric Objects (CSOs). The characteristic directions of their arcsecond-scale and mas-scale structures are probably misaligned which could also support the "restarting and rapid repositioning" scenario.

astro-ph↗

arXiv2009

Supersymmetry, General Relativity and Unity of Nature

The basic idea and some physical implications of nonlinear supersymmetric general relativity (NLSUSY GR) are presented. NLSUSY GR may give new insights into the origin of mass and the mysterious relations between the cosmology and the low energy particle physics, e.g. the spontaneous SUSY breaking scale, the cosmological constant, the (dark) energy density of the universe and the neutrino mass.

hep-th↗

arXiv2010

Nearby Spiral Galaxy Globular Cluster Systems II: Globular Cluster Abundances in NGC 300

We present new metallicity estimates for globular cluster (GC) candidates in the Sd spiral NGC 300, one of the nearest spiral galaxies outside the Local Group. We have obtained optical spectroscopy for 44 Sculptor Group GC candidates with the Boller and Chivens (B&C) spectrograph on the Baade Telescope at Las Campanas Observatory. There are 2 GCs in NGC 253 and 12 objects in NGC 300 with globular-cluster-like spectral features, 9 of which have radial velocities above 0 km/s. The remaining three, due to their radial velocities being below the expected 95% confidence limit for velocities of NGC 300 halo objects, are flagged as possible foreground stars. The non-clusterlike candidates included 13 stars, 15 galaxies, and an HII region. One GC, four galaxies, two stars, and the HII region from our sample were identified in archival Hubble Space Telescope images. For the GCs, we measure spectral indices and estimate metallicities using an empirical calibration based on Milky Way GCs. The GCs of NGC 300 appear similar to those of the Milky Way. Excluding possible stars and including clusters from the literature, the GC system (GCS) has a velocity dispersion of 68 km/s, and has no clear evidence of rotation. The mean metallicity for our full cluster sample plus one literature object is [Fe/H] = -0.94, lying above the relationship between mean GC metallicity and overall galaxy luminosity. Excluding the three low-velocity candidates, we obtain a mean [Fe/H] = -0.98, still higher than expected, raising the possibility of significant foreground star contamination even in this sample. Visual confirmation of genuine GCs using high-resolution space-based imagery could greatly reduce the potential problem of interlopers in small samples of GCSs in low-radial-velocity galaxies.

astro-ph↗

arXiv2008

The contribution of INTEGRAL to blazar science

We review 6 years of INTEGRAL observations of blazars, from Target-Of-Opportunity (TOO) to normal observations to coordinated campaigns, from the new and unexpected discoveries to the improvements in this research field. We also shortly review what is expected from INTEGRAL for the forthcoming years.

astro-ph↗

arXiv2010

Modell zur Entstehung eines Rings aus Dunkler Materie in der Milchstraßenebene

Both the distribution of hydrogen and the rotation curve of the Milky Way indicate the existence of a ring of Cold Dark Matter in the galactic plane with a radius of 14 kiloparsecs around the galactic centre. Using a semianalytical model, the formation of such a structure by the accretion of dwarf galaxies is simulated. The formation of the ring can be explained by the infall of a single dwarf galaxy, as well as by the infall of several dwarf galaxies under the condition that the eccentricity of the orbits is not larger than 0.2 and the inclination of the orbits is small. Also exclusion limits for the mass of dwarf galaxies, which contributed to the formation of the ring, are determined. ----- Die Verteilung von Wasserstoffgas sowie die Rotationskurve der Milchstraße deuten auf die Existenz eines Rings aus kalter Dunkler Materie innerhalb der Milchstraßenebene in einem Abstand von rund 14 Kiloparsec um das galaktische Zentrum. Es wird mit Hilfe eines semianalytischen Modells die Entstehung eines solchen Rings durch den Einfall von Zwerggalaxien in die Milchstraße simuliert. Die Entstehung des Rings kann sowohl durch einen Einzeleinfall als auch durch den Einfall mehrerer Zwerggalaxien erklärt werden, solange die numerische Exzentrizität der Orbits nicht 0.2 übersteigt und die Inklination der Orbits klein ist. Auch ein die Mindestmasse einer an der Ringentstehung beteiligten Zwerggalaxie beschreibender Zusammenhang ist ermittelt worden.

astro-ph↗

arXiv2008

Dark Matter Annihilation Signals: The Importance of Radiative Corrections

Being able to safely distinguish astrophysical from potential dark matter (DM) annihilation signals is of utmost importance for indirect DM searches. To this end, one has to rely on distinctive -- and unique -- spectral signatures to look for. Internal bremsstrahlung (IB), unavoidable in the presence of charged annihilation products, provides such a signature. In fact, as it generically dominates the gamma-ray spectrum expected from DM annihilations, at high energies, it may well turn out to be more important for indirect DM searches than the traditionally looked-for line signals. As illustrated in some detail, the observation of IB signatures would even allow to distinguish between different DM candidates or to constrain significantly the parameter space of, e.g., neutralino DM. The gamma-ray contributions reported here are therefore of great interest for the already launched Fermi/GLAST satellite and the upcoming new generation of Air Cherenkov Telescope systems like CTA -- which are most sensitive at the high energies where these effects are particularly important. Finally, radiative corrections may even significantly alter the positron spectrum from DM annihilations; an intriguing positron excess recently found by the PAMELA satellite might turn out to be an indication of the peculiar spectral signature expected in that case.

hep-ph↗

arXiv2008

Dark Matter Related to Axion and Axino

I discuss the essential features of the QCD axion: the strong CP solution and hence its theoretical necessity. I also review the axion and axino effects on astrophysics and cosmology, in particular with emphasis on their role in the dark matter component in the universe.

hep-ph↗

arXiv2008

Are AGN the Best Factories for High Energy Particles and Photons?

The main properties of AGN are reviewed, focussing on the accretion process and on the question of whether AGN are the best factories of ultra high energy particles and photons. I recall the large differences between the accretion/ejection flows in strong and weak accretors, and I conclude that, since low luminosity AGN and even "dormant" massive black holes in nuclei of galaxies are powering strong confined magnetized jets able to accelerate high energy particles, and are present in a large proportion of galaxies, they might be better potential sources of high energy particles and photons than luminous AGN and powerful radio galaxies.

astro-ph↗

arXiv2008

The Gaia Era: synergy between space missions and ground based surveys

The Gaia mission is expected to provide highly accurate astrometric, photometric, and spectroscopic measurements for about $10^9$ objects. Automated classification of detected sources is a key part of the data processing. Here a few aspects of the Gaia classification process are presented. Information from other surveys at longer wavelengths, and from follow-up ground based observations will be complementary to Gaia data especially at faint magnitudes, and will offer a great opportunity to understand our Galaxy.

astro-ph↗

arXiv2013

Radial distance on a stationary frame in a homogeneous and isotropic universe

This paper presents a physical distance to all radial events in a homogeneous and isotropic universe as a transform from Friedman-Lemaitre-Robertson-Walker (FLRW) coordinates, the model that solves the Einstein Field equation for an ideal fluid. Any well behaved transform is also a solution. The problem is relating the coordinates of the transform to observables. In the present case the objective is to find T,R on a stationary frame that has the R be a physical observable for all distances. We do this by working backwards, assuming the form of the metric that we desire, with some undetermined coefficients. These coefficients are then related to the partial derivatives of the transform. The transformed coordinates T,R are found by the integration of partial differential equations in the FLRW variables. We show that dR has the same units as the radial differential of the FLRW metric, which makes it observable. We develop a criterion for how close the transformed T comes to an observable time. Close to the space origin at the present time, T also becomes physical, so that the stationary acceleration becomes Newtonian. We show that a galactic point on a R,T plot starts close to the space origin at the beginning, moves out to a physical distance and finite time where it can release light that will be seen at the origin at the present time. Lastly, because the observable R has a finite limit at a finite T for t = 0 where the galactic velocity approaches the light speed, we see that the universe filled with an ideal fluid as seen on clocks and rulers on the stationary frame has a finite extent like that of an expanding empty universe, beyond which are no galaxies and no space.

astro-ph↗

arXiv2013

Scenario of Accelerating Universe from the Phenomenological Λ- Models

Dark matter, the major component of the matter content of the Universe, played a significant role at early stages during structure formation. But at present the Universe is dark energy dominated as well as accelerating. Here, the presence of dark energy has been established by including a time-dependent $Λ$ term in the Einstein's field equations. This model is compatible with the idea of an accelerating Universe so far as the value of the deceleration parameter is concerned. Possibility of a change in sign of the deceleration parameter is also discussed. The impact of considering the speed of light as variable in the field equations has also been investigated by using a well known time-dependent $Λ$ model.

astro-ph↗

arXiv2012

Analytic calculations of the spectra of ultra-high energy cosmic ray nuclei. I. The case of CMB radiation

We present a systematic study of different methods for the analytic calculation of ultra-high energy nuclei diffuse spectra. Nuclei propagating in the intergalactic space are photo-disintegrated and decrease their Lorentz factor due to the interaction with cosmic microwave background and extragalactic background light. We calculate the evolution trajectories in the backward time, that describe how atomic mass number $A$ and Lorentz factor $Γ$ change with redshift $z$. Three methods of spectra calculations are investigated and compared: {\it (i)} trajectory method, {\it(ii)} kinetic equation combined with trajectory calculations and {\it (iii)} coupled kinetic equations. We believe that these three methods exhaust at least the principal possibilities for any analytic solution of the problem. In the most straightforward method {\it(i)} only trajectory calculations are used to connect the observed nuclei flux with the production rate of primary (accelerated) nuclei $A_0$. In the second method {\it (ii)} the flux (space density) of primary nuclei, and secondary nuclei and protons are calculated with the help of kinetic equation and trajectories are used only to determine the generation rates of these nuclei. The third method {\it (iii)} consists in solving the complete set of coupled kinetic equations, written starting with primary nuclei $A_0$, then for $A_0-1$ etc down to the $A$ of interest. The solution of the preceding equation gives the generation rate for the one which follows. An important element of the calculations for all methods is the systematic use of Lorentz factor instead of energy. We consider here the interaction of nuclei only with the cosmic microwave background, this case is particularly suitable for understanding the physical results.

astro-ph↗

arXiv2008

Prospects for measuring the moment of inertia of pulsar PSR J0737-3039A

Here we consider the possibility of measuring at 10% or better the moment of inertia I of the J0737-3039A via the gravitomagnetic spin-orbit periastron precession. It turns out that the prospect of measuring the moment of inertia of PSR J0737-3039A at 10% accuracy or better seems unlikely given the limitations to the precision with which the system's basic binary and post-Keplerian parameters can be measured via radio timing.

gr-qc↗