## Recent Postings from Cosmology and Extragalactic

### A 3.55 keV Photon Line and its Morphology from a 3.55 keV ALP Line

Galaxy clusters can efficiently convert axion-like particles (ALPs) to photons. We propose that the recently claimed detection of a 3.55–3.57 keV line in the stacked spectra of a large number of galaxy clusters and the Andromeda galaxy may originate from the decay of either a scalar or fermionic $7.1$ keV dark matter species into an axion-like particle (ALP) of mass $m_{a} \lesssim 6\cdot 10^{-11}~{\rm eV}$, which subsequently converts to a photon in the cluster magnetic field. In contrast to models in which the photon line arises directly from dark matter decay or annihilation, this can explain the anomalous line strength in the Perseus cluster. As axion-photon conversion scales as $B^2$ and cool core clusters have high central magnetic fields, this model can also explains the observed peaking of the line emission in the cool cores of the Perseus, Ophiuchus and Centaurus clusters, as opposed to the much larger dark matter halos. We describe distinctive predictions of this scenario for future observations.

### A 3.55 keV Photon Line and its Morphology from a 3.55 keV ALP Line [Cross-Listing]

Galaxy clusters can efficiently convert axion-like particles (ALPs) to photons. We propose that the recently claimed detection of a 3.55–3.57 keV line in the stacked spectra of a large number of galaxy clusters and the Andromeda galaxy may originate from the decay of either a scalar or fermionic $7.1$ keV dark matter species into an axion-like particle (ALP) of mass $m_{a} \lesssim 6\cdot 10^{-11}~{\rm eV}$, which subsequently converts to a photon in the cluster magnetic field. In contrast to models in which the photon line arises directly from dark matter decay or annihilation, this can explain the anomalous line strength in the Perseus cluster. As axion-photon conversion scales as $B^2$ and cool core clusters have high central magnetic fields, this model can also explains the observed peaking of the line emission in the cool cores of the Perseus, Ophiuchus and Centaurus clusters, as opposed to the much larger dark matter halos. We describe distinctive predictions of this scenario for future observations.

### A Measurement of the Cosmic Microwave Background B-Mode Polarization Power Spectrum at Sub-Degree Scales with POLARBEAR

We report a measurement of the B-mode polarization power spectrum in the cosmic microwave background (CMB) using the POLARBEAR experiment in Chile. The faint B-mode polarization signature carries information about the Universe’s entire history of gravitational structure formation, and the cosmic inflation that may have occurred in the very early Universe. Our measurement covers the angular multipole range 500 < l < 2100 and is based on observations of 30 square degrees with 3.5 arcmin resolution at 150 GHz. On these angular scales, gravitational lensing of the CMB by intervening structure in the Universe is expected to be the dominant source of B-mode polarization. Including both systematic and statistical uncertainties, the hypothesis of no B-mode polarization power from gravitational lensing is rejected at 97.5% confidence. The band powers are consistent with the standard cosmological model. Fitting a single lensing amplitude parameter A_BB to the measured band powers, A_BB = 1.12 +/- 0.61 (stat) +0.04/-0.10 (sys) +/- 0.07 (multi), where A_BB = 1 is the fiducial WMAP-9 LCDM value. In this expression, "stat" refers to the statistical uncertainty, "sys" to the systematic uncertainty associated with possible biases from the instrument and astrophysical foregrounds, and "multi" to the calibration uncertainties that have a multiplicative effect on the measured amplitude A_BB.

### The role of metallicity in high mass X-ray binaries in galaxy formation models

Context: Recent theoretical works claim that high-mass X-ray binaries (HMXBs) could have been important sources of energy feedback into the interstellar and intergalactic media, playing a major role in the reionization epoch. A metallicity dependence of the production rate or luminosity of the sources is a key ingredient generally assumed but not yet probed. Aims: Our goal is to explore the relation between the X-ray luminosity (Lx) and star formation rate of galaxies as a possible tracer of a metallicity dependence of the production rates and/or X-ray luminosities of HMXBs. Methods: We developed a model to estimate the Lx of star forming galaxies based on stellar evolution models which include metallicity dependences. We applied our X-ray binary models to galaxies selected from hydrodynamical cosmological simulations which include chemical evolution of the stellar populations in a self-consistent way. Results: Our models successfully reproduce the dispersion in the observed relations as an outcome of the combined effects of the mixture of stellar populations with heterogeneous chemical abundances and the metallicity dependence of the X-ray sources. We find that the evolution of the Lx as a function of SFR of galaxies could store information on possible metallicity dependences of the HMXB sources. A non-metallicity dependent model predicts a non-evolving relation while any metallicity dependence should affect the slope and the dispersion as a function of redshift. Our results suggest the characteristics of the Lx evolution can be linked to the nature of the metallicity dependence of the production rate or the Lx of the stellar sources. By confronting our models with current available observations of strong star-forming galaxies, we find that only chemistry-dependent models reproduce the observed trend for z < 4.

### Abundant molecular gas and inefficient star formation in intracluster regions: Ram pressure stripped tail of the Norma galaxy ESO137-001

For the first time, we reveal large amounts of cold molecular gas in a ram pressure stripped tail, out to a large, intracluster distance from the galaxy. With the ESO APEX telescope we have detected 12CO(2-1) emission corresponding to more than 10^9 Msun of molecular gas (assuming a Galactic value of the CO-to-H_2 conversion factor) in three Ha bright regions along the tail of the Norma cluster ram pressure stripped galaxy ESO137-001, out to a projected distance of 40 kpc from the disk. The amount of 1.5×10^8 Msun of H_2 found in the most distant region is similar to molecular masses of tidal dwarf galaxies. We speculate that a ram pressure dwarf galaxy (RPDG) could be forming in this location. Along the tail, the amount of molecular gas was found to drop, while masses of the X-ray emitting and diffuse ionized components stay roughly constant. Moreover, the amounts of hot and cold gas are large and similar, and together nearly account for the missing gas from the disk. We find a very low star formation efficiency (tau>10^10 yr) in the stripped gas in ESO~137-001 and suggest that this is due to a low average gas density in the tail, or turbulent heating of the interstellar medium that is induced by a ram pressure shock. By means of simple numerical modeling, we suggest that ESO137-001 may be at a high orbital velocity of about 3000 km/s in the Norma cluster, in order to be consistent with a first infall scenario. The corresponding strong ram pressure would then be able to strip denser gas than is usual in other known ram pressure stripped galaxies. Such a dense component in the tail is more able to quickly transform into molecular gas than stripped diffuse gas. The unprecedented bulk of observed molecular gas in the ESO137-001 tail also suggests that some stripped gas may survive ram pressure stripping in the molecular phase.

### The Hantzsche-Wendt Manifold in Cosmic Topology

The Hantzsche-Wendt space is one of the 17 multiply connected spaces of the three-dimensional Euclidean space E^3. It is a compact and orientable manifold which can serve as a model for a spatial finite universe. Since it possesses much fewer matched back-to-back circle pairs on the cosmic microwave background (CMB) sky than the other compact flat spaces, it can escape the detection by a search for matched circle pairs. The suppression of temperature correlations C(theta) on large angular scales on the CMB sky is studied. It is shown that the large-scale correlations are of the same order as for the 3-torus topology but express a much larger variability. The Hantzsche-Wendt manifold provides a topological possibility with reduced large-angle correlations that can hide from searches for matched back-to-back circle pairs.

### Constraining Warm Dark Matter with high-$z$ supernova lensing

We propose a new method to constrain the Warm Dark Matter (WDM) particle mass, $m_\chi$, based on the counts of multiply imaged, distant supernovae produced by strong lensing by intervening cosmological matter fluctuations. The counts are very sensitive to the WDM particle mass, assumed here to be $m_\chi=1, 1.5, 2$ keV. We generalize the Das & Ostriker (2006) strong lensing method to the WDM case and using the observed cosmic star formation history we compute the probability for a distant SN to undergo a strong lensing event in different cosmologies. A minimum observing time of 2 yr (5 yr) is required for a future 100 sq. degrees survey reaching $z \approx 4$ ($z \approx 3$) to disentangle at 2$\sigma$ a WDM ($m_\chi=1$ keV) model from the standard CDM scenario.

### The expansion rate of the intermediate Universe in light of Planck

We use cosmology-independent measurements of the expansion history in the redshift range 0.1 < z <1.2 and compare them with the Cosmic Microwave Background-derived expansion history predictions. The motivation is to investigate if the tension between the local (cosmology independent) Hubble constant H0 value and the Planck-derived H0 is also present at other redshifts. We conclude that there is no tension between Planck and cosmology independent-measurements of the Hubble parameter H(z) at 0.1 < z < 1.2 for the LCDM model (odds of tension are only 1:15, statistically not significant). Considering extensions of the LCDM model does not improve these odds (actually makes them worse), thus favouring the simpler model over its extensions. On the other hand the H(z) data are also not in tension with the local H0 measurements but the combination of all three data-sets shows a highly significant tension (odds ~ 1:400). Thus the new data deepen the mystery of the mismatch between Planck and local H0 measurements, and cannot univocally determine wether it is an effect localised at a particular redshift. Having said this, we find that assuming the NGC4258 maser distance as the correct anchor for H0, brings the odds to comfortable values. Further, using only the expansion history measurements we constrain, within the LCDM model, H0 = 68.5 +- 3.5 and Omega_m = 0.32 +- 0.05 without relying on any CMB prior. We also address the question of how smooth the expansion history of the universe is given the cosmology independent data and conclude that there is no evidence for deviations from smoothness on the expansion history, neither variations with time in the value of the equation of state of dark energy.

### Regularization of the big bang singularity with a time varying equation of state $w > 1$ [Cross-Listing]

We study the classical dynamics of the universe undergoing a transition from contraction to expansion through a big bang singularity. The dynamics is described by a system of differential equations for a set of physical quantities, such as the scale factor $a$, the Hubble parameter $H$, the equation of state parameter $w$, and the density parameter $\Omega$. The solutions of the dynamical system have a singularity at the big bang. We study if these solutions can be uniquely extended through the singularity. In particular, we consider the model in which the contracting universe is dominated by a scalar field with a time varying equation of state $w$, which approaches a constant value $w_c$ near the singularity. We prove that, for $w_c > 1$, the singularity is regularizable only for a discrete set of $w_c$ values that satisfy a coprime number condition. Our result implies that the evolution of a bouncing universe through the big bang singularity does not have a continuous classical limit unless the equation of state is extremely fine-tuned.

### Regularization of the big bang singularity with a time varying equation of state $w > 1$

We study the classical dynamics of the universe undergoing a transition from contraction to expansion through a big bang singularity. The dynamics is described by a system of differential equations for a set of physical quantities, such as the scale factor $a$, the Hubble parameter $H$, the equation of state parameter $w$, and the density parameter $\Omega$. The solutions of the dynamical system have a singularity at the big bang. We study if these solutions can be uniquely extended through the singularity. In particular, we consider the model in which the contracting universe is dominated by a scalar field with a time varying equation of state $w$, which approaches a constant value $w_c$ near the singularity. We prove that, for $w_c > 1$, the singularity is regularizable only for a discrete set of $w_c$ values that satisfy a coprime number condition. Our result implies that the evolution of a bouncing universe through the big bang singularity does not have a continuous classical limit unless the equation of state is extremely fine-tuned.

### Regularization of the big bang singularity with a time varying equation of state $w > 1$ [Cross-Listing]

We study the classical dynamics of the universe undergoing a transition from contraction to expansion through a big bang singularity. The dynamics is described by a system of differential equations for a set of physical quantities, such as the scale factor $a$, the Hubble parameter $H$, the equation of state parameter $w$, and the density parameter $\Omega$. The solutions of the dynamical system have a singularity at the big bang. We study if these solutions can be uniquely extended through the singularity. In particular, we consider the model in which the contracting universe is dominated by a scalar field with a time varying equation of state $w$, which approaches a constant value $w_c$ near the singularity. We prove that, for $w_c > 1$, the singularity is regularizable only for a discrete set of $w_c$ values that satisfy a coprime number condition. Our result implies that the evolution of a bouncing universe through the big bang singularity does not have a continuous classical limit unless the equation of state is extremely fine-tuned.

### A close examination of cosmic microwave background mirror-parity after Planck

Previous claims of significant evidence for mirror-parity in the large-scale cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP) experiment have been recently echoed in the first study of isotropy and statistics of CMB data from Planck. We revisit these claims with a careful analysis of the latest data available. We construct statistical estimators in both harmonic and pixel space, test them on simulated data with and without mirror-parity symmetry, apply different Galactic masks, and study the dependence of the results on arbitrary choices of free parameters. We confirm that the data exhibit evidence for odd mirror-parity at a significance which reaches as high as ~ 99 per cent C.L., under some circumstances. However, given the inherent biases in the pixel-based statistic and the dependence of both pixel and harmonic space statistics on the particular form of Galactic masking and other a-posteriori choices, we conclude that these results are not in significant tension with the predictions of the concordance cosmological model.

### Hemispherical Power Asymmetry from a Space-Dependent Component of the Adiabatic Power Spectrum

The hemispherical power asymmetry observed by Planck and WMAP can be interpreted as being due to a spatially-varying and scale-dependent component of the adiabatic power spectrum. We derive general constraints on the magnitude and scale-dependence of a component with a dipole spatial variation. The spectral index and the running of the spectral index can be shifted from their inflation model values, resulting in a smaller spectral index and a more positive running. A key prediction is a significant hemispherical asymmetry of the spectral index and of its running.

### Cosmology of the proxy theory to massive gravity [Cross-Listing]

In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in Phys. Rev. D84 (2011) 043503. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity and represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely massive gravity and Horndeski theories. We go beyond the regime which was studied in Phys. Rev. D84 (2011) 043503 and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is flat Minkowski solution, hence this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.

### Cosmology of the proxy theory to massive gravity [Cross-Listing]

In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in Phys. Rev. D84 (2011) 043503. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity and represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely massive gravity and Horndeski theories. We go beyond the regime which was studied in Phys. Rev. D84 (2011) 043503 and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is flat Minkowski solution, hence this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.

### Cosmology of the proxy theory to massive gravity

In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in Phys. Rev. D84 (2011) 043503. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity and represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely massive gravity and Horndeski theories. We go beyond the regime which was studied in Phys. Rev. D84 (2011) 043503 and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is flat Minkowski solution, hence this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.

### What could the value of the cosmological constant tell us about the future variation of the fine structure constant?

Motivated by reported claims of the measurements of a variation of the fine structure constant $\alpha$ we consider a theory where the electric charge, and consequently $\alpha$, is not a constant but depends on the Ricci scalar $R$. %We then show how this can be considered a particular case of the Bekenstein theory in which there is no need to %introduce an additional kinetic term for the scalar field associated to the electric charge, since the Einstein’s% %equations are sufficient to determine the geometry and, consequently the Ricci scalar. We then study the cosmological implications of this theory, considering in particular the effects of dark energy and of a cosmological constant on the evolution of $\alpha$. Some low-red shift expressions for the variation of $\alpha(z)$ are derived, showing the effects of the equation of state of dark energy on $\alpha$ and observing how future measurements of the variation of the fine structure constant could be used to determine indirectly the equation of state of dark energy and test this theory. In the case of a $\Lambda CDM$ Universe, according to the current estimations of the cosmological parameters, the present value of the Ricci scalar is $\approx 10%$ smaller than its future asymptotic value determined by the value of the cosmological constant, setting also a bound on the future asymptotic value of $\alpha$.

### Can the tension in the $H_0$ estimation be solved by a local overdensity?

Recent measurements of the cosmic microwave background (CMB) radiation show an apparent tension with the present value of the Hubble parameter inferred from local observations of supernovae. We examine the possibility that such a discrepancy is the consequence of the presence of a local inhomogeneity, and find that a local overdensity could in fact account for the difference or at least for part of it. While such a small inhomogeneity would not significantly affect the distance to the last scattering, and consequently the value of $H_0$ obtained from CMB observations, it can have an important effect on the local estimation of $H(z)$, since this is sensitive to the derivative of the luminosity distance. The apparent tension can in fact be solved by correctly extrapolating $H_0$ from the low redshift supernovae observations by taking into account the effects of a local inhomogeneity on the distance redshift relation. To fully explain the difference we find that we need to be located in a region about $45%$ denser than where supernovae are located. Smaller inhomogeneities can still introduce important corrections to the apparent value of $H_0^{app}$ obtained from observational data under the assumption of homogeneity, and need to be considered in the high precision cosmology era in which we are entering.

### Boltzmann Equation Solver Adapted to Emergent Chemical Non-equilibrium [Cross-Listing]

We present a novel method to solve the spatially homogeneous and isotropic relativistic Boltzmann equation. We employ a basis set of orthogonal polynomials dynamically adapted to allow emergence of chemical non-equilibrium. Two time dependent parameters characterize the set of orthogonal polynomials, the effective temperature $T(t)$ and phase space occupation factor $\Upsilon(t)$. In this first paper we address (effectively) massless fermions and derive dynamical equations for $T(t)$ and $\Upsilon(t)$ such that the zeroth order term of the basis alone captures the number density and energy density of each particle distribution. We validate our method and illustrate the reduced computational cost and the ability to represent final state chemical non-equilibrium by studying a model problem that is motivated by the physics of the neutrino freeze-out processes in the early Universe, where the essential physical characteristics include reheating from another disappearing particle component ($e^\pm$-annihilation).

### Boltzmann Equation Solver Adapted to Emergent Chemical Non-equilibrium [Cross-Listing]

We present a novel method to solve the spatially homogeneous and isotropic relativistic Boltzmann equation. We employ a basis set of orthogonal polynomials dynamically adapted to allow emergence of chemical non-equilibrium. Two time dependent parameters characterize the set of orthogonal polynomials, the effective temperature $T(t)$ and phase space occupation factor $\Upsilon(t)$. In this first paper we address (effectively) massless fermions and derive dynamical equations for $T(t)$ and $\Upsilon(t)$ such that the zeroth order term of the basis alone captures the number density and energy density of each particle distribution. We validate our method and illustrate the reduced computational cost and the ability to represent final state chemical non-equilibrium by studying a model problem that is motivated by the physics of the neutrino freeze-out processes in the early Universe, where the essential physical characteristics include reheating from another disappearing particle component ($e^\pm$-annihilation).

### Fitting the Fermi-LAT GeV excess: on the importance of including the propagation of electrons from dark matter

An excess of gamma rays at GeV energies has been pointed out in the Fermi-LAT data. This signal comes from a narrow region centred around the Galactic center and has been interpreted as possible evidence for light dark matter particles annihilating either into a mixture of leptons-anti leptons and b-bbar or into b-bbar only. Focussing on the prompt gamma-ray emission, previous works found that the best fit to the data corresponds to annihilations proceeding predominantly into b-bbar. However, here we show that omitting the diffuse photon emission originating from primary and secondary electrons produced in dark matter annihilations can actually lead to the wrong conclusion. Accounting for this emission, we find that not only are annihilations of ~ 10 GeV particles into a purely leptonic final state allowed, but such annihilations actually provide a better fit than the pure b-bbar channel. We conclude our work with a possible test of these leptophilic scenarios based on the spectral feature of the gamma-ray emission at lower energies and larger latitude.

### Fitting the Fermi-LAT GeV excess: on the importance of including the propagation of electrons from dark matter [Cross-Listing]

An excess of gamma rays at GeV energies has been pointed out in the Fermi-LAT data. This signal comes from a narrow region centred around the Galactic center and has been interpreted as possible evidence for light dark matter particles annihilating either into a mixture of leptons-anti leptons and b-bbar or into b-bbar only. Focussing on the prompt gamma-ray emission, previous works found that the best fit to the data corresponds to annihilations proceeding predominantly into b-bbar. However, here we show that omitting the diffuse photon emission originating from primary and secondary electrons produced in dark matter annihilations can actually lead to the wrong conclusion. Accounting for this emission, we find that not only are annihilations of ~ 10 GeV particles into a purely leptonic final state allowed, but such annihilations actually provide a better fit than the pure b-bbar channel. We conclude our work with a possible test of these leptophilic scenarios based on the spectral feature of the gamma-ray emission at lower energies and larger latitude.

### Phase Space of Anisotropic $R^n$ Cosmologies [Cross-Listing]

We construct general anisotropic cosmological scenarios governed by an $f(R)=R^n$ gravitational sector. Focusing then on some specific geometries, and modelling the matter content as a perfect fluid, we perform a phase-space analysis. We analyze the possibility of accelerating expansion at late times, and additionally, we determine conditions for the parameter $n$ for the existence of phantom behavior, contracting solutions as well as of cyclic cosmology. Furthermore, we analyze if the universe evolves towards the future isotropization without relying on a cosmic no-hair theorem. Our results indicate that anisotropic geometries in modified gravitational frameworks present radically different cosmological behaviors compared to the simple isotropic scenarios.

### Phase Space of Anisotropic $R^n$ Cosmologies

We construct general anisotropic cosmological scenarios governed by an $f(R)=R^n$ gravitational sector. Focusing then on some specific geometries, and modelling the matter content as a perfect fluid, we perform a phase-space analysis. We analyze the possibility of accelerating expansion at late times, and additionally, we determine conditions for the parameter $n$ for the existence of phantom behavior, contracting solutions as well as of cyclic cosmology. Furthermore, we analyze if the universe evolves towards the future isotropization without relying on a cosmic no-hair theorem. Our results indicate that anisotropic geometries in modified gravitational frameworks present radically different cosmological behaviors compared to the simple isotropic scenarios.

### Phase Space of Anisotropic $R^n$ Cosmologies [Cross-Listing]

We construct general anisotropic cosmological scenarios governed by an $f(R)=R^n$ gravitational sector. Focusing then on some specific geometries, and modelling the matter content as a perfect fluid, we perform a phase-space analysis. We analyze the possibility of accelerating expansion at late times, and additionally, we determine conditions for the parameter $n$ for the existence of phantom behavior, contracting solutions as well as of cyclic cosmology. Furthermore, we analyze if the universe evolves towards the future isotropization without relying on a cosmic no-hair theorem. Our results indicate that anisotropic geometries in modified gravitational frameworks present radically different cosmological behaviors compared to the simple isotropic scenarios.

### Damping the neutrino flavor pendulum by breaking homogeneity [Cross-Listing]

The most general case of self-induced neutrino flavor evolution is described by a set of kinetic equations for a dense neutrino gas evolving both in space and time. Solutions of these equations have been typically worked out assuming that either the time (in the core-collapse supernova environment) or space (in the early universe) homogeneity in the initial conditions is preserved through the evolution. In these cases one can gauge away the homogeneous variable and reduce the dimensionality of the problem. In this paper we investigate if small deviations from an initial postulated homogeneity can be amplified by the interacting neutrino gas, leading to a new flavor instability. To this end, we consider a simple two flavor isotropic neutrino gas evolving in time, and initially composed by only $\nu_e$ and $\bar\nu_e$ with equal densities. In the homogeneous case, this system shows a bimodal instability in the inverted mass hierarchy scheme, leading to the well studied flavor pendulum behavior. This would lead to periodic pair conversions $\nu_e \bar\nu_e \leftrightarrow \nu_x \bar\nu_x$. To break space homogeneity, we introduce small amplitude space-dependent perturbations in the matter potential. By Fourier transforming the equations of motion with respect to the space coordinate, we then numerically solve a set of coupled equations for the different Fourier modes. We find that even for arbitrarily tiny inhomogeneities, the system evolution runs away from the stable pendulum behavior: the different modes are excited and the system evolves towards flavor equilibrium. We finally comment on the role of a time decaying neutrino background density in weakening these results.

### Damping the neutrino flavor pendulum by breaking homogeneity

The most general case of self-induced neutrino flavor evolution is described by a set of kinetic equations for a dense neutrino gas evolving both in space and time. Solutions of these equations have been typically worked out assuming that either the time (in the core-collapse supernova environment) or space (in the early universe) homogeneity in the initial conditions is preserved through the evolution. In these cases one can gauge away the homogeneous variable and reduce the dimensionality of the problem. In this paper we investigate if small deviations from an initial postulated homogeneity can be amplified by the interacting neutrino gas, leading to a new flavor instability. To this end, we consider a simple two flavor isotropic neutrino gas evolving in time, and initially composed by only $\nu_e$ and $\bar\nu_e$ with equal densities. In the homogeneous case, this system shows a bimodal instability in the inverted mass hierarchy scheme, leading to the well studied flavor pendulum behavior. This would lead to periodic pair conversions $\nu_e \bar\nu_e \leftrightarrow \nu_x \bar\nu_x$. To break space homogeneity, we introduce small amplitude space-dependent perturbations in the matter potential. By Fourier transforming the equations of motion with respect to the space coordinate, we then numerically solve a set of coupled equations for the different Fourier modes. We find that even for arbitrarily tiny inhomogeneities, the system evolution runs away from the stable pendulum behavior: the different modes are excited and the system evolves towards flavor equilibrium. We finally comment on the role of a time decaying neutrino background density in weakening these results.

### Progenitor constraints on the Type-Ia supernova SN2011fe from pre-explosion Hubble Space Telescope HeII narrow-band observations

We present Hubble Space Telescope (HST) imaging observations of the site of the Type-Ia supernova SN2011fe in the nearby galaxy M101, obtained about one year prior to the event, in a narrow band centred on the HeII 4686 \AA{} emission line. In a "single-degenerate" progenitor scenario, the hard photon flux from an accreting white dwarf (WD), burning hydrogen on its surface over $\sim1$ Myr should, in principle, create a HeIII Str\"{o}mgren sphere or shell surrounding the WD. Depending on the WD luminosity, the interstellar density, and the velocity of an outflow from the WD, the HeIII region could appear unresolved, extended, or as a ring, with a range of possible surface brightnesses. We find no trace of HeII 4686 \AA{} line emission in the HST data. Using simulations, we set $2\sigma$ upper limits on the HeII 4686 \AA{} luminosity of $L_{\rm HeII} < 3.4 \times 10^{34}$ erg s$^{-1}$ for a point source, corresponding to an emission region of radius $r < 1.8$ pc. The upper limit for an extended source is $L_{\rm HeII} < 1.7 \times 10^{35}$ erg s$^{-1}$, corresponding to an extended region with $r\sim11$ pc. The largest detectable shell, given an interstellar-medium density of 1 cm$^{-3}$, has a radius of $\sim6$ pc. Our results argue against the presence, within the $\sim10^5$ yr prior to the explosion, of a supersoft X-ray source of luminosity $L_{\rm bol} \ge 3 \times 10^{37}$ erg s$^{-1}$, or of a super-Eddington accreting WD that produces an outflowing wind capable of producing cavities with radii of 2-6 pc.

### The bias of DLAs at z ~ 2.3: Evidence for very strong stellar feedback in shallow potential wells

We discuss the recent BOSS measurement of a rather high bias factor for the host galaxies/haloes of Damped Lyman-alpha Absorbers (DLAs), in the context of our previous modelling of the physical properties of DLAs within the {\Lambda}CDM paradigm. Joint modelling of the column density distribution, the velocity width distribution of associated low ionization metal absorption, and the bias parameter suggests that DLAs are hosted by galaxies with dark matter halo masses in the range 10.5 < log Mv < 13, with a rather sharp cutoff at the lower mass end, corresponding to viral velocities of ~90 km/s. The observed properties of DLAs appear to suggest very efficient (stellar) feedback in haloes with masses/virial velocities below the cutoff and a large retained baryon fraction (> 35%) in haloes above the cutoff.

### Ionizing stellar population in the disk of NGC 3310. I. The impact of a minor merger on galaxy evolution

Numerical simulations of minor mergers predict little enhancement in the global star formation activity. However, it is still unclear the impact they have on the chemical state of the whole galaxy and on the mass build-up in the galaxy bulge and disc. We present a 2-dimensional analysis of NCG 3310, currently undergoing an intense starburst likely caused by a recent minor interaction, using data from the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey (PINGS). With data from a large sample of about a hundred HII regions identified throughout the disc and spiral arms we derive, using strong-line metallicity indicators and direct derivations, a rather flat gaseous abundance gradient. Thus, metal mixing processes occurred, as in observed galaxy interactions. Spectra from PINGS data and additionalmulti-wavelength imaging were used to perform a Spectral Energy Distribution (SED) fitting to the stellar emission and a photoionization modelling of the nebulae. The ionizing stellar population is characterized by single populations with a narrow age range (2.5-5 Myr) and a broad range of masses ($10^4-6\times10^6 M_\odot$). The effect of dust grains in the nebulae is important, indicating that 25-70% of the ultraviolet photons can be absorbed by dust. The ionizing stellar population within the Hii regions represents typically a few percent of the total stellar mass. This ratio, a proxy to the specific star formation rate (sSFR), presents a flat or negative radial gradient. Therefore, minor interactions may indeed play an important role in the mass build-up of the bulge.

### Chemistry in isolation: High CCH/HCO+ line ratio in the AMIGA galaxy CIG 638

Multi-molecule observations towards an increasing variety of galaxies have been showing that the relative molecular abundances are affected by the type of activity. However, these studies are biased towards bright active galaxies, which are typically in interaction. We study the molecular composition of one of the most isolated galaxies in the local Universe where the physical and chemical properties of their molecular clouds have been determined by intrinsic mechanisms. We present 3 mm broad band observations of the galaxy CIG 638, extracted from the AMIGA sample of isolated galaxies. The emission of the J=1-0 transitions of CCH, HCN, HCO+, and HNC are detected. Integrated intensity ratios between these line are compared with similar observations from the literature towards active galaxies including starburst galaxies (SB), active galactic nuclei (AGN), luminous infrared galaxies (LIRG), and GMCs in M33. A significantly high ratio of CCH with respect to HCN, HCO+, and HNC is found towards CIG 638 when compared with all other galaxies where these species have been detected. This points to either an overabundance of CCH or to a relative lack of dense molecular gas as supported by the low HCN/CO ratio, or both. The data suggest that the CIG 638 is naturally a less perturbed galaxy where a lower fraction of dense molecular gas, as well as a more even distribution could explain the measured ratios. In this scenario the dense gas tracers would be naturally dimmer, while the UV enhanced CCH, would be overproduced in a less shielded medium.

### The 3.5 keV X-ray line signal from decaying moduli with low cutoff scale

The recent unidentified 3.5 keV X-ray line signal can be explained by decaying moduli dark matter with a cutoff scale one order of magnitude smaller than the Planck scale. We show that such modulus field with the low cutoff scale follows a time-dependent potential minimum and its abundance is reduced by the adiabatic suppression mechanism. As a result the modulus abundance can naturally be consistent with the observed dark matter abundance without any fine-tuning of the initial oscillation amplitude.

### The 3.5 keV X-ray line signal from decaying moduli with low cutoff scale [Cross-Listing]

The recent unidentified 3.5 keV X-ray line signal can be explained by decaying moduli dark matter with a cutoff scale one order of magnitude smaller than the Planck scale. We show that such modulus field with the low cutoff scale follows a time-dependent potential minimum and its abundance is reduced by the adiabatic suppression mechanism. As a result the modulus abundance can naturally be consistent with the observed dark matter abundance without any fine-tuning of the initial oscillation amplitude.

### Non-linear Chaplygin Gas Cosmologies [Cross-Listing]

We study the non-linear regime of Unified Dark Energy models, using Generalized Chaplygin Gas cosmologies as a representative example, and introduce a new parameter characterizing the level of small scale clustering in these scenarios. We show that viable Generalized Chaplygin Gas cosmologies, consistent with the most recent observational constraints, may be constructed for any value of the Generalized Chaplygin Gas parameter by considering models with a sufficiently high level of non-linear clustering.

### Non-linear Chaplygin Gas Cosmologies

We study the non-linear regime of Unified Dark Energy models, using Generalized Chaplygin Gas cosmologies as a representative example, and introduce a new parameter characterizing the level of small scale clustering in these scenarios. We show that viable Generalized Chaplygin Gas cosmologies, consistent with the most recent observational constraints, may be constructed for any value of the Generalized Chaplygin Gas parameter by considering models with a sufficiently high level of non-linear clustering.

### On the impact of correlation information on the orientation parameters between celestial reference frame realizations

In this study, we compared results of determination of the orientation angles between celestial reference frames realized by radio source position catalogues using three methods of accounting for correlation information: using the position errors only, using additionally the correlations be-tween the right ascension and declination (RA/DE correlations) reported in radio source position catalogues published in the IERS format, and using the full covariance matrix. The computations were performed with nine catalogues computed at eight analysis centres. Our analysis has shown that using the RA/DE correlations only slightly influences the computed rotational angles, whereas using the full correlation matrices leads to substantial change in the orientation parameters be-tween the compared catalogues.

### Disc heating: possible link between weak bars and superthin galaxies

The extreme flatness of stellar discs in superthin galaxies is puzzling and the apparent dearth of these objects in cosmological simulation poses challenging problem to the standard cold dark matter paradigm. Irrespective of mergers or accretion that a galaxy might be going through, stars are heated as they get older while they interact with the spirals and bars which are ubiquitous in disc galaxies — leading to a puffed up stellar disc. It remains unclear how superthin galaxies maintain their thinness through the cosmic evolution. We follow the internal evolution of a sample of 16 initially extremely thin stellar discs using collisionless N-body simulation. All of these discs eventually form a bar in their central region. Depending on the initial condition, some of these stellar discs readily form strong bars while others grow weak bars over secular evolution time scale. We show that galaxies with strong bars heat the stars very efficiently, eventually making their stellar discs thicker. On the other hand, stars are heated very slowly by weak bars — as a result galaxies hosting weak bars are able to maintain their thinness over several billion years, if left isolated. We suggest that superthin galaxies might as well be forming weak bars and thereby prevent any strong vertical heating during the course of secular evolution.

### Distribution of Slow and Fast Rotators in the Fornax Cluster

We present integral field spectroscopy of 10 early-type galaxies in the nearby, low-mass, Fornax cluster, from which we derive spatially resolved stellar kinematics. Based on the morphologies of their stellar velocity maps we classify 2/10 galaxies as slow rotators, with the remaining 8 galaxies fast rotators. Supplementing our integral field observations with morphological and kinematic data from the literature, we analyse the `kinematic’ type of all 30 galaxies in the Fornax cluster brighter than M_K = -21.5 mag (M_* ~ 6 x 10^9 M_sun). Our sample’s slow rotator fraction within one virial radius is 7(^+4_-6) per cent. 13(^+8_-6} per cent of the early-type galaxies are slow rotators, consistent with the observed fraction in other galaxy aggregates. The fraction of slow rotators in Fornax varies with cluster-centric radius, rising to 16(^+11_-8) per cent of all kinematic types within the central 0.2 virial radii, from 0 per cent in the cluster outskirts. We find that, even in mass-matched samples of slow and fast rotators, slow rotators are found preferentially at higher projected environmental density than fast rotators. This demonstrates that dynamical friction alone cannot be responsible for the differing distributions of slow and fast rotators. For dynamical friction to play a significant role, slow rotators must reside in higher mass sub-halos than fast rotators and/or form in the centres of groups before being accreted on to the cluster.

### A New Method for Measuring Extragalactic Distances

We have pioneered a new method for the measurement of extragalactic distances. This method uses the time-lag between variations in the short wavelength and long wavelength light from an active galactic nucleus (AGN), based on a quantitative physical model of dust reverberation that relates the time-lag to the absolute luminosity of the AGN. We use the large homogeneous data set from intensive monitoring observations in optical and near-infrared wavelength bands with the dedicated 2-m MAGNUM telescope to obtain the distances to 17 AGNs in the redshift range z=0.0024 to z=0.0353. These distance measurements are compared with distances measured using Cepheid variable stars, and are used to infer that H_0= 73 +- 3 (random) km/s/Mpc. The systematic error in H_0 is examined, and the uncertainty in the size distribution of dust grains is the largest source of the systematic error, which is much reduced for a sample of AGNs for which their parameter values in the model of dust reverberation are individually measured. This AGN time-lag method can be used beyond 30 Mpc, the farthest distance reached by extragalactic Cepheids, and can be extended to high-redshift quasi-stellar objects.

### The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies

We present the average rest-frame spectrum of high-redshift dusty, star-forming galaxies from 250-770GHz. This spectrum was constructed by stacking ALMA 3mm spectra of 22 such sources discovered by the South Pole Telescope and spanning z=2.0-5.7. In addition to multiple bright spectral features of 12CO, [CI], and H2O, we also detect several faint transitions of 13CO, HCN, HNC, HCO+, and CN, and use the observed line strengths to characterize the typical properties of the interstellar medium of these high-redshift starburst galaxies. We find that the 13CO brightness in these objects is comparable to that of the only other z>2 star-forming galaxy in which 13CO has been observed. We show that the emission from the high-critical density molecules HCN, HNC, HCO+, and CN is consistent with a warm, dense medium with T_kin ~ 55K and n_H2 >~ 10^5.5 cm^-3. High molecular hydrogen densities are required to reproduce the observed line ratios, and we demonstrate that alternatives to purely collisional excitation are unlikely to be significant for the bulk of these systems. We quantify the average emission from several species with no individually detected transitions, and find emission from the hydride CH and the linear molecule CCH for the first time at high redshift, indicating that these molecules may be powerful probes of interstellar chemistry in high-redshift systems. These observations represent the first constraints on many molecular species with rest-frame transitions from 0.4-1.2mm in star-forming systems at high redshift, and will be invaluable in making effective use of ALMA in full science operations.

### Origin and Evolution of Structure and Nucleosynthesis for Galaxies in the Local Group

The Milky Way is the product of a complex evolution of generations of merges, collapse, star formation, supernova and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark-matter halos, spiral density waves, and emerging dark energy. In this review we summarize observational evidence and discuss recent calculations concerning the formation, evolution nucleosynthesis in the galaxies of the Local-Group. In particular, we will briefly summarize observations and simulations for the dwarf galaxies and the two large spirals of the Local Group. We discuss how galactic halos form within the dark matter filaments that define a super-galactic plane. Gravitational interaction along this structure leads to streaming flows toward the two dominant galaxies in the cluster. These simulations and observations also suggest that a significant fraction of the Galactic halo formed as at large distances and then arrived later along these streaming flows. We also consider the insight provided by observations and simulations of nucleosynthesis both within the galactic halo and dwarf galaxies in the Local Group.

### What are we missing in elliptical galaxies ?

The scaling relation for early type galaxies in the 6dF galaxy survey does not have the velocity dispersion dependence expected from standard stellar population models. As noted in recent work with SDSS, there seems to be an additional dependence of mass to light ratio with velocity dispersion, possibly due to a bottom heavy initial mass function. Here we offer a new understanding of the 6dF galaxy survey 3D gaussian Fundamental Plane in terms of a parameterized Jeans equation, but leave mass dependence of M/L and mass dependence of structure still degenerate with just the present constraints. Hybrid models have been proposed recently. Our new analysis brings into focus promising lines of enquiry which could be pursued to lift this degeneracy, including stellar atmospheres computation, kinematic probes of ellipticals at large radius, and a large sample of one micron spectra.

### On the impact of radiation pressure on the dynamics and inner structure of dusty wind-driven shells

Massive young stellar clusters are strong sources of radiation and mechanical energy. Their powerful winds and radiation pressure sweep-up interstellar gas into thin expanding shells which trap the ionizing radiation produced by the central clusters affecting the dynamics and the distribution of their ionized gas. Here we continue our comparison of the star cluster winds and radiation pressure effects on the dynamics of shells around young massive clusters. We calculate the impact that radiation pressure has on the distribution of matter and thermal pressure within such shells as well as on the density weighted ionization parameter $U_w$ and put our results on the diagnostic diagram which allows one to discriminate between the wind-dominated and radiation-dominated regimes. We found that model predicted values of the ionization parameter agree well with typical values found in local starburst galaxies. Radiation pressure may affect the inner structure and the dynamics of wind-driven shells only at the earliest stages of evolution or if a major fraction of the star cluster mechanical luminosity is dissipated or radiated away within the star cluster volume and thus the star cluster mechanical energy output is significantly smaller than star cluster synthetic models predict. However, even in these cases radiation dominates over the wind dynamical pressure only if the exciting cluster is embedded into a high density ambient medium.

### Probing small-scale cosmological fluctuations with the 21 cm forest: effects of neutrino mass, running spectral index and warm dark matter

Although the cosmological paradigm based on cold dark matter and adiabatic, nearly scale-invariant primordial fluctuations is consistent with a wide variety of existing observations, it has yet to be sufficiently tested on scales smaller than those of massive galaxies, and various alternatives have been proposed that differ significantly in the consequent small-scale power spectrum (SSPS) of large-scale structure. Here we show that a powerful probe of the SSPS at $k\gtrsim 10$ Mpc$^{-1}$ can be provided by the 21 cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in the spectra of high-redshift background radio sources in the cosmic reionization epoch. Such features are expected to be caused predominantly by collapsed gas in starless minihalos, whose mass function can be very sensitive to the SSPS. As specific examples, we consider the effects of neutrino mass, running spectral index (RSI) and warm dark matter (WDM) on the SSPS, and evaluate the expected distribution in optical depth of 21 cm absorbers out to different redshifts. Within the current constraints on quantities such as the sum of neutrino masses $\sum m_\nu$, running of the primordial spectral index $d n_s/d \ln k$ and WDM particle mass $m_{\rm WDM}$, the statistics of the 21 cm forest manifest observationally significant differences that become larger at higher redshifts. In particular, it may be possible to probe the range of $m_{\rm WDM} \gtrsim 10$ keV that may otherwise be inaccessible. Future observations of the 21 cm forest by the Square Kilometer Array may offer a unique and valuable probe of the SSPS, as long as radio sources such as quasars or Population III gamma-ray bursts with sufficient brightness and number exist at redshifts of $z \gtrsim$ 10 – 20, and the astrophysical effects of reionization and heating can be discriminated.

### Setting new Cosmology constraints with ALMA

I make a short revision of Cosmology questions which ALMA was built to address. Without diving into much detail, I point out the ALMA specifications and strategies which are expected to provide a better handle of: the temperature evolution of the Cosmic Microwave Background (CMB) and the properties of its secondary anisotropies (such as the thermal and kinetic Sunyaev-Zel’dovich and the Ostriker-Vishniac effects); variability of dimensionless fundamental constants; Ho and galaxy initial mass function by means of strong gravitational lensing; black hole science with the greatly expected Event Horizon Telescope.

### The evolution of the star forming sequence in hierarchical galaxy formation models

It has been argued that the specific star formation rates of star forming galaxies inferred from observational data decline more rapidly below z = 2 than is predicted by hierarchical galaxy formation models. We present a detailed analysis of this problem by comparing predictions from the GALFORM semi-analytic model with an extensive compilation of data on the average star formation rates of star-forming galaxies. We also use this data to infer the form of the stellar mass assembly histories of star forming galaxies. Our analysis reveals that the currently available data favours a scenario where the stellar mass assembly histories of star forming galaxies rise at early times and then fall towards the present day. In contrast, our model predicts stellar mass assembly histories that are almost flat below z = 2 for star forming galaxies, such that the predicted star formation rates can be offset with respect to the observational data by factors of up to 2-3. This disagreement can be explained by the level of coevolution between stellar and halo mass assembly that exists in contemporary galaxy formation models. In turn, this arises because the standard implementations of star formation and supernova feedback used in the models result in the efficiencies of these process remaining approximately constant over the lifetime of a given star forming galaxy. We demonstrate how a modification to the timescale for gas ejected by feedback to be reincorporated into galaxy haloes can help to reconcile the model predictions with the data.

### Predicting Galaxy Star Formation Rates via the Co-evolution of Galaxies and Halos

In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy is determined by its dark matter halo formation history, and as such, that more quiescent galaxies reside in older halos. This simple model has been remarkably successful at predicting color-based galaxy statistics at low redshift as measured in the Sloan Digital Sky Survey (SDSS). To further test this method with observations, we present new SDSS measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star forming galaxy samples. We find that our age matching model is in excellent agreement with these new measurements. We also employ a galaxy group finder and show that our model is able to predict: (1) the relative SFRs of central and satellite galaxies, (2) the SFR-dependence of the radial distribution of satellite galaxy populations within galaxy groups, rich groups, and clusters and their surrounding larger scale environments, and (3) the interesting feature that the satellite quenched fraction as a function of projected radial distance from the central galaxy exhibits an ~r^-.15 slope, independent of environment. The accurate prediction for the spatial distribution of satellites is intriguing given the fact that we do not explicitly model satellite-specific processes after infall, and that in our model the virial radius does not mark a special transition region in the evolution of a satellite, contrary to most galaxy evolution models. The success of the model suggests that present-day galaxy SFR is strongly correlated with halo mass assembly history.

### Calculations of resonance enhancement factor in axion-search tube-experiments

It is pointed out that oscillating current density, produced due to the coupling between an external magnetic field and the cosmic axion field, can excite the TM resonant modes inside an open-ended cavity (tube). By systematically solving the field equations of axion-electrodynamics we obtain explicit expressions for the oscillating fields induced inside a cylindrical tube. We calculate the enhancement factor when a resonance condition is met. While the power obtained for TM modes replicates the previous result, we emphasize that the knowledge of explicit field configurations inside a tube opens up new ways to design axion experiments including a recent proposal to detect the induced fields using a superconducting LC circuit. In addition, as an example, we estimate the induced fields in a cylindrical tube in the presence of a static uniform magnetic field applied only to a part of its volume.

### Calculations of resonance enhancement factor in axion-search tube-experiments [Cross-Listing]

It is pointed out that oscillating current density, produced due to the coupling between an external magnetic field and the cosmic axion field, can excite the TM resonant modes inside an open-ended cavity (tube). By systematically solving the field equations of axion-electrodynamics we obtain explicit expressions for the oscillating fields induced inside a cylindrical tube. We calculate the enhancement factor when a resonance condition is met. While the power obtained for TM modes replicates the previous result, we emphasize that the knowledge of explicit field configurations inside a tube opens up new ways to design axion experiments including a recent proposal to detect the induced fields using a superconducting LC circuit. In addition, as an example, we estimate the induced fields in a cylindrical tube in the presence of a static uniform magnetic field applied only to a part of its volume.