Astrophysics

We show that the measured abundance of ultra-faint lensed galaxies at » z 6 in the Hubble Frontier Fields (HFF) provides stringent constraints on the parameter space of (i) dark matter models based onkeV sterile neutrinos; (ii) "fuzzy" wavelike dark matter models, based on Bose-Einstein condensates of ultra-light particles. For the case of sterile neutrinos, we consider two production mechanisms: resonant production through mixing with active neutrinos and the decay of scalar particles. For the former model, we derive constraints for the combination of sterile neutrino mass n m and mixing parameter q sin 2 2 ( ) which provide the tightest lower bounds on the mixing angle (and hence on the lepton asymmetry) derived so far by methods independent of baryonic physics. For the latter we compute the allowed combinations of the scalar mass, its coupling to the Higgs field, and the Yukawa coupling of scalar to sterile neutrinos. We compare our results to independent existing astrophysical bounds on sterile neutrinos in the same mass range. For the case of "fuzzy" dark matter, we show that the observed number density »1 Mpc 3 of high-redshift galaxies in the HFF sets a lower limit  y m 8 10 22 • eV (at the 3-σ confidence level) on the particle mass, a result that strongly disfavors wavelike bosonic dark matter as a viable model for structure formation. We discuss the impact on our results of uncertainties due to systematics in the selection of highly magnified, faint galaxies at high redshift.

The investigation of distant galaxy formation and evolution is a powerful tool to constrain dark matter scenarios, supporting and in some cases surpassing other astrophysical and experimental probes. The recent completion of the Hubble Frontier Field (HFF) programme combining ultra-deep Hubble Space Telescope observations and the magnification power of gravitational lensing produced by foreground galaxy clusters has enabled the detection of the faintest primordial galaxies ever studied. Here we show how the number density of such primordial galaxies allows to constrain a variety of DM models alternative to CDM. In particular, it provides stringent limits on the mass of thermal WDM candidates, on the parameter space of sterile neutrino production models, and on other DM scenarios featuring particles in the keV mass range which is also supported by recent detections of a 3.5keV X-ray line. These constraints are robust and independent of the baryonic physics modeling of galaxy formation and evolution. Fuzzy DM (ultralight DM particles) results strongly disfavored.

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We uncover the general mechanism and the nature of the today dark energy (DE). This is only based on well known quantum physics and cosmology. We show that the observed DE today originates from the cosmological quantum vacuum of light particles which provides a continuous energy distribution able to reproduce the data. Bosons give positive contributions to the DE while fermions yield negative contributions. As usual in field theory, ultraviolet divergences are subtracted from the physical quantities. The subtractions respect the symmetries of the theory and we normalize the physical quantities to be zero for the Minkowski vacuum. The resulting finite contributions to the energy density and the pressure from the quantum vacuum grow as log a(t) where a(t) is the scale factor, while the particle contributions dilute as 1/a 3 (t), as it must be for massive particles. We find the explicit today dark energy equation of state P = w(z) H: It turns to be slightly w(z) < -1 with w(z) asymptotically reaching the value -1 from below. A scalar particle can produce the observed dark energy through its quantum cosmological vacuum provided: (i) Its mass is of the order of 10 -3 eV = 1 meV, (ii) It is very weakly coupled, and (iii) it is stable on the time scale of the age of the universe. The axion vacuum thus appears as a natural candidate. The neutrino vacuum (especially the lightest mass eigenstate) can give negative contributions to the dark energy. We find that w(z = 0) is slightly below -1 by an amount ranging from (-1.5 × 10 -3 ) to (-8 × 10 -3 ) and we predict the axion mass be in the range between 4 and 5 meV . We find that the universe will expand in the future faster than the de Sitter universe, as an exponential in the square of the cosmic time. Dark energy today arises from the quantum vacuum of light particles in FRW cosmological space-time in an analogous way to the Casimir vacuum effect of quantum fields in Minkowski space-time with non-trivial boundary conditions. (+) passed away (a): Contents I. Introduction and Results 2 II. Scalar Fields in Cosmological Space-Times III. Fermion Fields in Cosmological Space-Times IV. The Cosmological Quantum Vacuum. V. Vacuum Energy Density and Pressure for Late Times VI. The Quantum Nature of the Cosmological Vacuum. VII. Dark Energy from the Cosmological Quantum Vacuum. VIII. Neutrino Mass Eigenstates IX. Light Particle Masses and the Dark Energy Density Today X. The Future Evolution of the Universe XI. Discussion XII. Conclusions A. Dimensional and Cutoff Regularization of the Vacuum Energy References I. INTRODUCTION AND RESULTS Since the discovery of the dark energy in the present universe [1], [2], an intense observational activity has improved our knowledge about it [3], [4], [5], and more activity is expected to provide new data and understanding eg. [6], [7]. Many different approachs and models have been proposed to explain the dark energy [8], [9], [10], [11], [12]. For reviews and approachs on the dark energy see for example Refs. [10], [8], [9], [11, 12].

Today, thanks in particular to the results of the ESA Planck mission, the concordance cosmological model appears to be the most robust to describe the evolution and content of the Universe from its early to late times. It summarizes the evolution of matter, made mainly of dark matter, from the primordial fluctuations generated by inflation around 10 -30 second after the Big-Bang to galaxies and clusters of galaxies, 13.8 billion years later, and the evolution of the expansion of space, with a relative slowdown in the matterdominated era and, since a few billion years, an acceleration powered by dark energy. But we are far from knowing the pillars of this model which are inflation, dark matter and dark energy. Comprehending these fundamental questions requires a detailed mapping of our observable Universe over the whole of cosmic time. The relic radiation provides the starting point and galaxies draw the cosmic web. JAXA's LiteBIRD mission will map the beginning of our Universe with a crucial test for inflation (its primordial gravity waves), and the ESA Euclid mission will map the most recent half part, crucial for dark energy. The mission concept, described in this White Paper, GAUSS, aims at being a mission to fully map the cosmic web up to the reionization era, linking early and late evolution, to tackle and disentangle the crucial degeneracies persisting after the Euclid era between dark matter and inflation properties, dark energy, structure growth and gravitation at large scale.

In order to determine as best as possible the nature of the dark matter (DM) particle (mass and decoupling temperature) we compute analytically the DM galaxy properties as the halo density profile, halo radius and surface density and compare them to their observed values. We match the theoretically computed surface density to its observed value in order to obtain: (i) the decreasing of the phasespace density since equilibration till today (ii) the mass of the dark matter particle and the decoupling temperature T d (iii) the kind of the halo density profile (core or cusp). The dark matter particle mass turns to be between 1 and 2 keV and the decoupling temperature T d turns to be above 100 GeV. keV dark matter particles necessarily produce cored density profiles while wimps (m ∼ 100 GeV, T d ∼ 5 GeV) inevitably produce cusped profiles at scales about 0.003 pc. We compute in addition the halo radius r 0 , the halo central density ρ 0 and the halo particle r. m. s. velocity v 2 1/2 halo they all reproduce the observed values within one order of magnitude. These results are independent of the particle physics model and vary very little with the statistics of the dark matter particle. The framework presented here applies to any kind of DM particles: when applied to typical CDM GeV wimps, our results are in agreement with CDM simulations. keV scale DM particles reproduce all observed galaxy magnitudes within one order of magnitude while GeV DM mass particles disagree with observations in up to eleven orders of magnitude.

In order to determine as best as possible the nature of the dark matter (DM) particle (mass and decoupling temperature) we compute analytically the DM galaxy properties as the halo density profile, halo radius and surface density and compare them to their observed values. We match the theoretically computed surface density to its observed value in order to obtain: (i) the decreasing of the phasespace density since equilibration till today (ii) the mass of the dark matter particle and the decoupling temperature T d (iii) the kind of the halo density profile (core or cusp). The dark matter particle mass turns to be between 1 and 2 keV and the decoupling temperature T d turns to be above 100 GeV. keV dark matter particles necessarily produce cored density profiles while wimps (m ∼ 100 GeV, T d ∼ 5 GeV) inevitably produce cusped profiles at scales about 0.003 pc. We compute in addition the halo radius r 0 , the halo central density ρ 0 and the halo particle r. m. s. velocity v 2 1/2 halo they all reproduce the observed values within one order of magnitude. These results are independent of the particle physics model and vary very little with the statistics of the dark matter particle. The framework presented here applies to any kind of DM particles: when applied to typical CDM GeV wimps, our results are in agreement with CDM simulations. keV scale DM particles reproduce all observed galaxy magnitudes within one order of magnitude while GeV DM mass particles disagree with observations in up to eleven orders of magnitude.

Cumulative observational evidence confirms that the surface gravity of dark matter (DM) halos μ0 D = r0ρ0, where r0 and ρ0 are the halo core radius and central density, respectively, is nearly constant and independent of galaxy luminosity for a high number of galactic systems (spirals, dwarf irregular and spheroidals, elliptics) spanning over 14 magnitudes in luminosity and of different Hubble types. Remarkably, its numerical value, μ0D ≃140M⊙/ pc 2 = (18.6 MeV )3, is approximately the same (up to a factor of 2) in all these systems. First, we present the physical consequences of the independence of μ0D from r0: the energy scales as the volume [Formula: see text], while the mass and the entropy scale as the surface [Formula: see text] and the surface times log r0, respectively. Namely, the entropy scales similarly to the black hole entropy but with a much smaller coefficient. Second, we compute the surface gravity and the density profile for small scales from first principles and th...

We numerically investigate the evolution of compact high-velocity clouds (CHVCs) passing through a hot, tenuous gas representing the highly ionized circumgalactic medium (CGM) by applying the adaptive-mesh refinement code flash. The model clouds start from both hydrostatic and thermal equilibrium and are in pressure balance with the CGM. Here, we present 14 models, divided into two mass categories and two metallicities each and different velocities. We allow for self-gravity and thermal conduction or not. All models experience mass diffusion, radiative cooling, and external heating leading to dissociation and ionization. Our main findings are (1) self-gravity stabilizes clouds against Rayleigh–Taylor instability, which is disrupted within 10 sound-crossing times without; (2) clouds can develop Jeans-instable regions internally even though they are initially below Jeans mass; (3) all clouds lose mass by ram pressure and Kelvin–Helmholtz instability; (4) thermal conduction substantial...

We present the R-band lightcurves of the Flora family asteroid (12499) 1998FR47, obtained in 2022 at two different astronomical sites: Bulgarian National Astronomical Observatory Rozhen (MPC 071) and Astronomical Station Vidojevica (MPC C89). The quadramodal lightcurves reveal a rotation period of6.172±0.003 h and an amplitude of about 0.44 mag. Using the lightcurve inversion method, with the combination of our dense lightcurves and the sparse data from DR3, we found the sidereal period, an indication of a retrograde rotation of (12499) and its low-convex resolution shape. Nonetheless, the unusual shape of the quadramodal lightcurve and its additional analysis reveals two possible periods, 3.0834±0.0085 h and 4.1245±0.0151 h, making the suspect that the asteroid might be a non-synchronised wide binary system. Spectral analysis of the asteroid using data from the GAIA DR3 shows that it is either an M- or an L-type object and maybe a piece of the first planetesimals to form in the Sol...

Context. Dusty high-z galaxies are extreme objects with high star formation rates (SFRs) and luminosities. Characterising the properties of this population and analysing their evolution over cosmic time is key to understanding galaxy evolution in the early Universe. Aims. We select a sample of high-z dusty star-forming galaxies (DSFGs) and evaluate their position on the main sequence (MS) of star-forming galaxies, the well-known correlation between stellar mass and SFR. We aim to understand the causes of their high star formation and quantify the percentage of DSFGs that lie above the MS. Methods. We adopted a multi-wavelength approach with data from optical to submillimetre wavelengths from surveys at the North Ecliptic Pole to study a submillimetre sample of high-redshift galaxies. Two submillimetre selection methods were used, including: sources selected at 850 µm with the Sub-millimetre Common-User Bolometer Array 2) SCUBA-2 instrument and Herschel-Spectral and Photometric Imaging Receiver (SPIRE) selected sources (colour-colour diagrams and 500 µm risers), finding that 185 have good multi-wavelength coverage. The resulting sample of 185 high-z candidates was further studied by spectral energy distribution fitting with the CIGALE fitting code. We derived photometric redshifts, stellar masses, SFRs, and additional physical parameters, such as the infrared luminosity and active galactic nuclei (AGN) contribution. Results. We find that the Herschel-SPIRE selected DSFGs generally have higher redshifts (z = 2.57 +0.08 -0.09 ) than sources that are selected solely by the SCUBA-2 method (z = 1.45 +0.21 -0.06 ). We find moderate SFRs (797 +108 -50 M yr -1 ), which are typically lower than those found in other studies. We find that the different results in the literature are, only in part, due to selection effects, as even in the most extreme cases, SFRs are still lower than a few thousand solar masses per year. The difference in measured SFRs affects the position of DSFGs on the MS of galaxies; most of the DSFGs lie on the MS (60%). Finally, we find that the star formation efficiency (SFE) depends on the epoch and intensity of the star formation burst in the galaxy; the later the burst, the more intense the star formation. We discuss whether the higher SFEs in DSFGs could be due to mergers.

We propose here that certain observational features of granular matter in the infrared limit, exhibiting the phenomenon of jamming, arise from an underlying effective general relativistic description. The proposal stems from the assumption (which we justify on physical grounds) that grains in granular matter move freely in an effective curved Riemannian space. The termination of their trajectories at the onset of jamming is obtained from the focussing of a converging congruence of geodesics in such a space, as a solution of the Raychaudhuri equation for such congruences. This may happen irrespective of whether or not the curvature is sourced by external stresses (via an effective Einstein equation), although the properties of the resultant jammed state solution do differ in the two cases. A definite prediction of this geometrical approach is the negative role played by those trajectories which twist about each other, in reaching the jammed state. The local symmetries of granular interaction, translational and rotational invariance (corresponding to 'force balance' and 'torque balance' in standard force-based approaches to jamming) are inherent in the effective general relativity framework. A recently-proposed effective elasticity model of the jammed state, based on a tensorial variant of standard electrostatics (Vector Charge Theory), is seen to be entirely subsumed within the linearized version of the effective general relativistic description.

The temporal characteristics of whale song are considered to be amongst the most stable elements of song production, though very few studies have looked at the timing of discrete sounds or the silences between them. This study indicates that the temporal characteristics of the song of the southeast Indian Ocean pygmy blue (SEIOPB) whale are highly variable. While the song repetition interval, or inter-song interval (ISI), appeared to remain consistent within a song event, defined as a consistent bout of singing presumed to come from an individual animal, it was found to be variable between song events. Song structure was a confounding factor in the analysis of variability in ISI with songs comprised of longer phrases naturally having a longer song repetition interval. The songs of the SEIOPB whale are characteristic of the species with only three primary song types. The three-unit song (units I, II and III) has the longest mean ISI of ~ 200 s, approximately twice that of songs composed of only two units (II and III) at a mean of ~ 100 s ISI which is approximately twice the ISI of a one-unit song (unit II only). The results of this study suggest that variability in ISI cannot be attributed to change in one element of a song but is driven by temporal changes in all elements of the song including phrase structure, unit duration and the length of the intervals between song units. Thus, the temporal characteristics of blue whale song appear to be under the control of the animal and may vary between individual whales, and within songs of an individual. It is concluded that the temporal characteristics of song potentially encode contextual information about the singer and may be influenced by audience effects, including audience composition and singer density.

The temporal characteristics of whale song are considered to be amongst the most stable elements of song production, though very few studies have looked at the timing of discrete sounds or the silences between them. This study indicates that the temporal characteristics of the song of the southeast Indian Ocean pygmy blue (SEIOPB) whale are highly variable. While the song repetition interval, or inter-song interval (ISI), appeared to remain consistent within a song event, defined as a consistent bout of singing presumed to come from an individual animal, it was found to be variable between song events. Song structure was a confounding factor in the analysis of variability in ISI with songs comprised of longer phrases naturally having a longer song repetition interval. The songs of the SEIOPB whale are characteristic of the species with only three primary song types. The three-unit song (units I, II and III) has the longest mean ISI of ~ 200 s, approximately twice that of songs composed of only two units (II and III) at a mean of ~ 100 s ISI which is approximately twice the ISI of a one-unit song (unit II only). The results of this study suggest that variability in ISI cannot be attributed to change in one element of a song but is driven by temporal changes in all elements of the song including phrase structure, unit duration and the length of the intervals between song units. Thus, the temporal characteristics of blue whale song appear to be under the control of the animal and may vary between individual whales, and within songs of an individual. It is concluded that the temporal characteristics of song potentially encode contextual information about the singer and may be influenced by audience effects, including audience composition and singer density.

EMIR, currently entering into its fabrication and AIV phase, will be one of the first common user instruments for the GTC, the 10 meter telescope under construction by GRANTECAN at the Roque de los Muchachos Observatory (Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Instituto de Astrofísica de Canarias (IAC). EMIR is designed to realize one of the central goals of 10m class telescopes, allowing observers to obtain spectra for large numbers of faint sources in an time-efficient manner. EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2.5 µm. It is equipped with two innovative subsystems: a robotic reconfigurable multislit mask and disperssive elements formed by the combination of high quality difracction grating and conventional prisms, both at the heart of the instrument. The present status of development, expected performances, schedule and plans for scientific exploitation are described and discussed. The development and fabrication of EMIR is funded by GRANTECAN and the Plan Nacional de Astronomía y Astrofísica (National Plan for Astronomy and Astrophysics, Spain).

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Space, like time, may not be fundamental. By reformulating the Hamiltonian without reference to coordinates or geometry, and replacing it with recursive structure (graph Laplacian), the paper shows that quantum dynamics unfold identically. This invites a reconsideration of space's ontological role.

We present the XMM-Newton first light image, taken in January 2000 with the EPIC pn camera during the instrument's commissioning phase, when XMM-Newton was pointing towards the Large Magellanic Cloud (LMC). The field is rich in different kinds of X-ray sources: point sources, supernova remnants (SNRs) and diffuse X-ray emission from LMC interstellar gas. The observations are of unprecedented sensitivity, reaching a few 10 32 erg/s for point sources in the LMC. We describe how these data sets were analysed and discuss some of the spectroscopic results. For the SNR N157B the power law spectrum is clearly steeper than previously determined from ROSAT and ASCA data. The existence of a significant thermal component is evident and suggests that N157B is not a Crab-like but a composite SNR. Most puzzling is the spectrum of the LMC hot interstellar medium, which indicates a significant overabundance of Ne and Mg of a few times solar.

The European Photon Imaging Camera (EPIC) consortium has provided the focal plane instruments for the three X-ray mirror systems on XMM-Newton. Two cameras with a reflecting grating spectrometer in the optical path are equipped with MOS type CCDs as focal plane detectors (Turner 2001), the telescope with the full photon flux operates the novel pn-CCD as an imaging X-ray spectrometer. The pn-CCD camera system was developed under the leadership of the Max-Planck-Institut für extraterrestrische Physik (MPE), Garching. The concept of the pn-CCD is described as well as the different operational modes of the camera system. The electrical, mechanical and thermal design of the focal plane and camera is briefly treated. The in-orbit performance is described in terms of energy resolution, quantum efficiency, time resolution, long term stability and charged particle background. Special emphasis is given to the radiation hardening of the devices and the measured and expected degradation due to radiation damage of ionizing particles in the first 9 months of in orbit operation.

The Wide-field White Light and Spectrometric Coronograph (LASCO) to be flown on SOHO in 1995 will observe the corona from just above the limb at 1.1 out to 30 solar radii (R ) . In addition to the fundamental problems of coronal physics (heating of the corona, acceleration of the solar wind, coronal transients), the scientific objectives incorporate the distribution and properties of dust particles including those released from sun-grazing comets, and interactions of coronal plasma with the dust.

We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA&#39;s unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale di...

Two muon telescopes to study solar events and climate changes are currently under construction in Campinas and Niteroi, Brazil. These telescopes are located in the South Atlantic Magnetic Anomaly and will measure muon flux. The single apparatus consists of four detectors arranged to detect vertical muons and 45 degrees inclined muons from East or West. Each detector uses a plastic scintillator slab, 150x75x5cm3, and 130 mm photomultiplier assembled into a trapezoidal container. In this paper, we illustrate the main features of the telescopes, electronics and data acquisition.

High-energy gamma rays are promising tools to constrain or reveal the nature of dark matter, in particular Weakly Interacting Massive Particles. Being well into its pre-construction phase, the Cherenkov Telescope Array (CTA) will soon probe the sky in the 20 GeV -300 TeV energy range. Thanks to its improved energy and angular resolutions as well as significantly larger effective area when compared to the current generation of Cherenkov telescopes, CTA is expected to probe heavier dark matter, with unprecedented sensitivity, reaching the thermal annihilation cross-section at 1 TeV. This talk will summarise the planned dark matter search strategies with CTA, focusing on the signal from the Galactic centre. As observed with the Fermi LAT at lower energies, this region is rather complex and CTA will be the first ground-based observatory sensitive to the large scale diffuse astrophysical emission from that region. We report on the collaboration effort to study the impact of such extended astrophysical backgrounds on the dark matter search, based on Fermi-LAT data in order to guide our observational strategies, taking into account various sources of systematic uncertainty.

We analyze the conditions that enable acceleration of particles to ultra-high energies, ∼ 10 20 eV (UHECRs). We show that broad band photon data recently provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the ability of active galactic nuclei (AGN) to produce UHECRs. The high energy (MeV -GeV) photons are produced by Compton scattering of the emitted low energy photons and the cosmic microwave background or extra-galactic background light. The ratio of the luminosities at high and low photon energies can therefore be used as a probe of the physical conditions in the acceleration site. We find that existing data excludes core regions of nearby radio-loud AGN as possible acceleration sites of UHECR protons. However, we show that giant radio lobes are not excluded. We apply our method to Cen A, and show that acceleration of protons to ∼ 10 20 eV can only occur at distances 100 kpc from the core.

Astrophysical sources emit gravitational waves in a large variety of processes occurred since the beginning of star and galaxy formation. These waves permeate our high redshift Universe, and form a background which is the result of the superposition of different components, each associated to a specific astrophysical process. Each component has different spectral properties and features that it is important to investigate in view of a possible, future detection. In this contribution, we will review recent theoretical predictions for backgrounds produced by extragalactic sources and discuss their detectability with current and future gravitational wave observatories.

Light bosonic fields are ubiquitous in extensions of the Standard Model. Even when minimally coupled to gravity, these fields might evade the assumptions of the black-hole no-hair theorems and give rise to spinning black holes which can be drastically different from the Kerr metric. Furthermore, they allow for self-gravitating compact solitons, known as (scalar or Proca) boson stars. The quasi-periodic oscillations (QPOs) observed in the X-ray flux emitted by accreting compact objects carry information about the strong-field region, thus providing a powerful tool to constrain deviations from Kerr's geometry and to search for exotic compact objects. By using the relativistic precession model as a proxy to interpret the QPOs in terms of geodesic frequencies, we investigate how the QPO frequencies could be used to test the no-hair theorem and the existence of light bosonic fields near accreting compact objects. We show that a detection of two QPO triplets with current sensitivity can already constrain these models, and that the future eXTP mission or a LOFT-like mission can set very stringent constraints on black holes with bosonic hair and on (scalar or Proca) boson stars. The peculiar geodesic structure of compact scalar/Proca boson stars implies that these objects can easily be ruled out as alternative models for X-ray source GRO J1655-40.

Non radial oscillations of neutron stars are associated with the emission of gravitational waves. The characteristic frequencies of these oscillations can be computed using the theory of stellar perturbations, and they are shown to carry detailed information on the internal structure of the emitting source. Moreover, they appear to be encoded in various radiative processes, as for instance in the tail of the giant flares of Soft Gamma Repeaters. Thus, their determination is central to the theory of stellar perturbation. A viable approach to the problem consists in formulating this theory as a problem of resonant scattering of gravitational waves incident on the potential barrier generated by the spacetime curvature. This approach discloses some unexpected correspondences between the theory of stellar perturbations and the theory of quantum mechanics, and allows us to predict new relativistic effects.

We develop a new method to measure neutron star parameters and derive constraints on the equation of state of dense matter by fitting the frequencies of simultaneous Quasi Periodic Oscillation modes observed in the X-ray flux of accreting neutron stars in low mass X-ray binaries. To this aim we calculate the fundamental frequencies of geodesic motion around rotating neutron stars based on an accurate general-relativistic approximation for their external spacetime. Once the fundamental frequencies are related to the observed frequencies through a QPO model, they can be fit to the data to obtain estimates of the three parameters describing the spacetime, namely the neutron star mass, angular momentum and quadrupole moment. From these parameters we derive information on the neutron star structure and equation of state. We present a proof of principle of our method applied to pairs of kHz QPO frequencies observed from three systems (4U1608-52, 4U0614+09 and 4U1728-34). We identify the kHz QPOs with the azimuthal and the periastron precession frequencies of matter orbiting the neutron star, and via our Bayesian inference technique we derive constraints on the neutrons stars' masses and radii. This method is applicable to other geodesic-frequency-based QPO models.

We study the tidal effects of a Kerr black hole on a neutron star in black hole-neutron star binary systems using a semi-analytical approach which describes the neutron star as a deformable ellipsoid. Relativistic effects on the neutron star selfgravity are taken into account by employing a scalar potential resulting from relativistic stellar structure equations. We calculate quasi-equilibrium sequences of black holeneutron star binaries, and the critical orbital separation at which the star is disrupted by the black hole tidal field: the latter quantity is of particular interest because when it is greater than the radius of the innermost stable circular orbit, a short gamma-ray burst scenario may develop.

We develop a new method to measure neutron star parameters and derive constraints on the equation of state of dense matter by fitting the frequencies of simultaneous Quasi Periodic Oscillation modes observed in the X-ray flux of accreting neutron stars in low mass X-ray binaries. To this aim we calculate the fundamental frequencies of geodesic motion around rotating neutron stars based on an accurate general-relativistic approximation for their external spacetime. Once the fundamental frequencies are related to the observed frequencies through a QPO model, they can be fit to the data to obtain estimates of the three parameters describing the spacetime, namely the neutron star mass, angular momentum and quadrupole moment. From these parameters we derive information on the neutron star structure and equation of state. We present a proof of principle of our method applied to pairs of kHz QPO frequencies observed from three systems (4U1608-52, 4U0614+09 and 4U1728-34). We identify the kHz QPOs with the azimuthal and the periastron precession frequencies of matter orbiting the neutron star, and via our Bayesian inference technique we derive constraints on the neutrons stars' masses and radii. This method is applicable to other geodesic-frequency-based QPO models.

We compute the energy spectra of the gravitational signals emitted when a mass m 0 is scattered by the gravitational field of a star of mass M >> m 0 . We show that, unlike black holes in similar processes, the quasi-normal modes of the star are excited, and that the amount of energy emitted in these modes depends on how close the exciting mass can get to the star.

In this paper we consider the Extrasolar Planetary Systems recently discovered in our Galaxy as potential sources of gravitational waves. We estimate the frequency and characteristic amplitude of the radiation they emit due to the orbital motion, using the quadrupole formalism. In addition, we check whether the conditions needed for the resonant excitation of the f- and g-modes of the central star can be fulfilled. By a Roche-lobe analysis, we show that there could exist systems in which the low-order g-modes could be excited, although this does not happen in the systems discovered up to now.

In open clusters the scatter about the single-star main sequence is usually negligible. However, unresolved binary systems are brighter and redder than single stars, and thus some 'stars' appear shifted away from the main sequence. We make very simple models of the Praesepe cluster, and find evidence that low-mass systems prefer independent component masses, whereas systems of higher mass than the sun appear to favour some correlation towards equal-mass components.

According to the standard model of cosmology the visible, baryonic matter of galaxies is embedded in dark matter haloes, thus extending the mass and the size of galaxies by one to two orders of magnitude. Taking into account dynamical friction between the dark matter haloes, the nearby located M81 group of galaxies as well as the Hickson compact groups of galaxies are here investigated with regard to their dynamical behaviour. The results of the employment of the Markov Chain Monte Carlo method and the genetic algorithm show statistically substantial merger rates between galaxies, and long living constellations without merging galaxies comprise -apart from very few instances -initially unbound systems only. This result is derived based on three-and four-body calculations for a model of rigid Navarro-Frenk-White profiles for the dark matter haloes, but verified by the comparison to randomly chosen individual solutions for the M81 galaxy group with high-resolution simulations of live self-consistent systems (N -body calculations). In consequence, the observed compact configurations of major galaxies are a very unlikely occurence if dark matter haloes exist.

Context. We introduce the Dwarf Galaxy Survey with Amateur Telescopes (DGSAT) project and report the discovery of eleven low surface brightness (LSB) galaxies in the fields of the nearby galaxies NGC 2683, NGC 3628, NGC 4594 (M 104), NGC 4631, NGC 5457 (M 101), and NGC 7814. Aims. The DGSAT project aims to use the potential of small-sized telescopes to probe LSB features around large galaxies and to increase the sample size of the dwarf satellite galaxies in the Local Volume. Methods. Using long exposure images, fields of the target spiral galaxies are explored for extended LSB objects. After identifying dwarf galaxy candidates, their observed properties are extracted by fitting models to their light profiles. Results. We find three, one, three, one, one, and two new LSB galaxies in the fields of NGC 2683, 3628, 4594, 4631, 5457, and 7814, respectively. In addition to the newly found galaxies, we analyse the structural properties of nine already known galaxies. All of these 20 dwarf galaxy candidates have effective surface brightnesses in the range 25.3 < ∼ µ e < ∼ 28.8 mag arcsec -2 and are fit with Sersic profiles with indices n < ∼ 1. Assuming that they are in the vicinity of the above mentioned massive galaxies, their r-band absolute magnitudes, their effective radii, and their luminosities are in the ranges -15.6 < ∼ M r < ∼ -7.8, 160 pc < ∼ R e < ∼ 4.1 kpc, and 0.1 × 10 6 < ∼ L L r < ∼ 127 × 10 6 , respectively. To determine whether these LSB galaxies are indeed satellites of the above mentioned massive galaxies, their distances need to be determined via further observations. Conclusions. Using small telescopes, we are readily able to detect LSB galaxies with similar properties to the known dwarf galaxies of the Local Group.

We investigate, for the first time, the formation and evolution of the tidal tail released from a young Pleiades-like star cluster due to expulsion of primordial gas in a realistic gravitational field of the Galaxy. The tidal tails (as well as clusters) are integrated by nbody6 from their embedded phase for more than 300 Myr. We vary the star formation efficiency (SFE) from 33% to 100% and the timescales of gas expulsion as free parameters, and provide predictions for the morphology and kinematics of the evolved tail for each of the models. The resulting tail properties are intended for comparison with Gaia measurements, where an inverse analysis of our findings might constrain some of the poorly understood conditions and processes in embedded star clusters during the gas phase and gas expulsion.

This is an erratum to the paper 'The ultra-diffuse dwarf galaxies NGC 1052-DF2 and 1052-DF4 are in conflict with standard cosmology' published in MNRAS 489 (2), 2634-2651 (2019). Sentence number five in the abstract has been corrected for a small linguistic error which, if uncorrected, may lead to misunderstanding. The complete abstract with the corrected sentence reads as follows: 'Recently van Dokkum et al. reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at 20 Mpc from Earth. In contrast, DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much shorter distance near 10 Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of 886 km s -1 , which differs from that of the Local Group (LG) velocity vector by 1298 km s -1 with an angle of 117 • . Taking into account the dynamical M/L ratio, the stellar mass, half-light radius, peculiar

Ultra-compact dwarf galaxies (UCDs) share many properties with globular clusters (GCs) and are found in similar environments. Here, a large sample of UCDs and GCs around NGC 1399, the central giant elliptical of the Fornax galaxy cluster, is used to infer their formation history and also to shed light on the formation of NGC 1399 itself. We assumed that all GCs and UCDs in our sample are the result of star cluster (SC) formation processes and used them as tracers of past star formation activities. After correcting our GC/UCD sample for mass loss, we interpreted their overall mass function to be a superposition of SC populations that formed coevally during different formation epochs. The SC masses of each population were distributed according to the embedded cluster mass function (ECMF), a pure power law with the slope -β. Each ECMF was characterized by a stellar upper mass limit, M max , which depended on the star formation rate (SFR). We decomposed the observed GC/UCD mass function into individual SC populations and converted M max of each SC population to an SFR. The overall distribution of SFRs reveals under which conditions the GC/UCD sample around NGC 1399 formed. Considering the constraints set by the age of the GCs/UCDs and the present stellar mass of NGC 1399, we found that the formation of the GCs/UCDs can be well explained within our framework with values for β below 2.3. This finding agrees very well with the observation of young SCs where β ≈ 2.0 is usually found. Even though we took into account that some of the most massive objects might not be genuine SCs and applied different corrections for the mass loss, we found that these considerations do not influence much the outcome. We derived the peak SFRs to be between approximately 300 and 3000 M yr -1 , which matches the SFRs observed in massive high-redshift sub-millimeter galaxies and an SFR estimate inferred from NGC 1399 based on the so-called downsizing picture, meaning that more massive galaxies must have formed over shorter periods of time. Our findings give rise to the interpretation that NGC 1399 and its GC/UCD system formed in a relatively short, intense starburst early on.

The observed mass-to-light (M/L) ratios of a large sample of GCs in M31 show an inverse trend with metallicity compared to what is expected from Simple Stellar Population (SSP) models with an invariant canonical stellar IMF, in the sense that the observed M/L ratios decrease with increasing metallicity. We show that incorporating the effect of dynamical evolution the SSP models with a canonical IMF can not explain the decreasing M/L ratios with increasing metallicity for the M31 GCs. The recently derived top-heavy IMF as a function of metallicity and embedded cluster density is proposed to explain the lower than expected M/L ratios of metal-rich GCs. We find that the SSP models with a top-heavy IMF, retaining a metallicity-and cluster mass-dependent fraction of the remnants within the clusters, and taking standard dynamical evolution into account can successfully explain the observed M/L -[F e/H] relation of M31 GCs. Thus we propose that the kinematical data of GCs can be used to constrain the top-heaviness of the IMF in GCs.

The stellar initial mass function (IMF) is commonly interpreted to be a scale-invariant probability density distribution function (PDF) such that many small clusters yield the same IMF as one massive cluster of the same combined number of stars. Observations of the galaxy-wide IMF challenge this as dwarf galaxies do not form as many massive stars as expected. This indicates a highly self-regulated star formation process in which stellar masses are not stochastically sampled from the IMF and are instead related to the environment of star formation. Here, the nature of star formation is studied using the relation between the most massive star born in a star cluster and its parental stellar cluster mass (the m max -M ecl relation). This relation has been argued to be a statistical effect if stars are sampled randomly from the IMF. The tightness of the relation, given a set of young clusters compiled from the literature, probes this scenario. By comparing the observed m max -M ecl distribution with synthetic star clusters with stochastically sampled stellar masses, we find that the expected dispersion of the mock observations is much larger than the observed dispersion. This conclusion depends on the accuracy of the mass uncertainties. Assuming that the uncertainties from the literature are correct, our test rejects the hypothesis that the IMF is a PDF at a more than 4.5σ confidence level. Alternatively, we provide a deterministic stellar mass sampling tool which reproduces the observed m max -M ecl distribution and compares well with the luminosities of star-forming molecular clumps. In addition, we find that there is a significant flattening of the m max -M ecl relation near m max = 13 M . This may suggest strong feedback of stars more massive than about 13 M and/or the ejections of the most massive stars from young clusters in the mass range 63 to 400 M to be likely important physical processes in forming clusters.

We present a method to test the isotropy of the magnitude-redshift relation of Type Ia Supernovae (SNe Ia) and single out the most discrepant direction (in terms of the signal-to-noise ratio) with respect to the all-sky data. Our technique accounts for possible directional variations of the corrections for SNe Ia and yields all-sky maps of the best-fit cosmological parameters with arbitrary angular resolution. To show its potential, we apply our method to the recent Union2.1 compilation, building maps with three different angular resolutions. We use a Monte Carlo method to estimate the statistical significance with which we could reject the null hypothesis that the magnitude-redshift relation is isotropic based on the properties of the observed most discrepant directions. We find that, based on pure signal-tonoise arguments, the null hypothesis cannot be rejected at any meaningful confidence level. However, if we also consider that the strongest deviations in the Union2.1 sample closely align with the dipole temperature anisotropy of the cosmic microwave background, we find that the null hypothesis should be rejected at the 95 -99 per cent confidence level, slightly depending on the angular resolution of the study. If this result is not due to a statistical fluke, it might either indicate that the SN data have not been cleaned from all possible systematics or even point towards new physics. We finally discuss future perspectives in the field for achieving larger and more uniform data sets that will vastly improve the quality of the results and optimally exploit our method.

We study the correlation of orbital poles of the 11 classical satellite galaxies of the Milky Way, comparing results from previous proper motions with the independent data by Gaia DR2. Previous results on the degree of correlation and its significance are confirmed by the new data. A majority of the satellites co-orbit along the Vast Polar Structure, the plane (or disk) of satellite galaxies defined by their positions. The orbital planes of eight satellites align to < 20 • with a common direction, seven even orbit in the same sense. Most also share similar specific angular momenta, though their wide distribution on the sky does not support a recent group infall or satellitesof-satellites origin. The orbital pole concentration has continuously increased as more precise proper motions were measured, as expected if the underlying distribution shows true correlation that is washed out by observational uncertainties. The orbital poles of the up to seven most correlated satellites are in fact almost as concentrated as expected for the best-possible orbital alignment achievable given the satellite positions. Combining the best-available proper motions substantially increases the tension with ΛCDM cosmological expectations: < 0.1 per cent of simulated satellite systems in IllustrisTNG contain seven orbital poles as closely aligned as observed. Simulated systems that simultaneously reproduce the concentration of orbital poles and the flattening of the satellite distribution have a frequency of < 0.1 per cent for any number of k > 3 combined orbital poles, indicating that these results are not affected by a look-elsewhere effect. This compounds the Planes of Satellite Galaxies Problem.

Observations show that galaxies follow a mass-metallicity relation over a wide range of masses. One currently favoured explanation is that less massive galaxies are less able to retain the gas and stellar ejecta and thus may lose the freshly produced metals in the form of galactic outflows. Galaxies with a low current star formation rate have been found to contain star clusters up to a lower mass limit. Since stars are predominately born in clusters, and less massive clusters have been found to be less likely to contain very massive stars, this implies that in environments or at times of low star formation, the stellar initial mass function does not extend to as high masses as during high star formation epochs. It is found that the oxygen yield is reduced by a factor of thirty when the star formation rate is decreased by 3 to 4 orders of magnitude. With this concept, chemical evolution models for galaxies of a range of masses are computed and shown to provide an excellent fit to the mass-metallicity relation derived recently by . Furthermore, the models match the relation between galaxy mass and effective yield. Thus, the scenario of a variable integrated stellar initial mass function, which is based on the concept of formation of stars in clusters, may offer an attractive alternative or partial explanation of the mass-metallicity relation in galaxies.

Tidal streams of globular clusters are ideal tracers of the Galactic gravitational potential. Compared to the few known, complex and diffuse dwarf-galaxy streams, they are kinematically cold, have thin morphologies and are abundant in the halo of the Milky Way. Their coldness and thinness in combination with potential epicyclic substructure in the vicinity of the stream progenitor turns them into high-precision scales. With the example of Palomar 5, we demonstrate how modeling of a globular cluster stream allows us to simultaneously measure the properties of the disrupting globular cluster, its orbital motion, and the gravitational potential of the Milky Way.