Search

The dearth of dwarf galaxies in the local universe is hard to reconcile with the large number of low mass haloes expected within the concordance $\Lambda$CDM paradigm. In this paper we perform a systematic evaluation of the uncertainties affecting the measurement of DM halo abundance using galaxy kinematics. Using a large sample of dwarf galaxies with spatially resolved kinematic data we derive a correction to obtain the observed abundance of galaxies as a function of their halo maximum circular velocity from the line-of-sight velocity function in the Local Volume. This estimate provides a direct means of comparing the predictions of theoretical models and simulations (including nonstandard cosmologies and novel galaxy formation physics) to the observational constraints. The new "galactic $V_{max}$" function is steeper than the line-of-sight velocity function but still shallower than the theoretical CDM expectation, showing that some unaccounted physical process is necessary to reduce the abundance of galaxies and/or drastically modify their density profiles compared to CDM haloes. Using this new galactic $V_{max}$ function, we investigate the viability of baryonic solutions such as feedback-powered outflows and photoevaporation of gas from an ionising radiation background. At the 3-$\sigma$ confidence level neither energetic feedback nor photoevaporation are effective enough to reconcile the disagreement. In the case of maximum baryonic effects, the theoretical estimate still deviates significantly from the observations for $V_{max} < 60$ km/s. CDM predicts at least 1.8 times more galaxies with $V_{max} = 50$ km/s and 2.5 times more than observed at $30$ km/s. Recent hydrodynamic simulations seem to resolve the discrepancy but disagree with the properties of observed galaxies with resolved kinematics. (abridged), Comment: 17 pages, 22 figures; major revisions include clarification of the method, expanded comparison with simulations with a new figure, analysis of uncertainties in model as well as pressure support corrections, and a new table with nomenclature

The observed number of dwarf galaxies as a function of rotation velocity is significantly smaller than predicted by the standard model of cosmology. This discrepancy cannot be simply solved by assuming strong baryonic feedback processes, since they would violate the observed relation between maximum circular velocity (vmax) and baryon mass of galaxies. A speculative but tantalizing possibility is that the mismatch between observation and theory points towards the existence of non-cold or non-collisionless dark matter (DM). In this paper, we investigate the effects of warm (WDM), mixed (MDM, i.e. warm plus cold), and self-interacting DM (SIDM) scenarios on the abundance of dwarf galaxies and the relation between observed H I line width and maximum circular velocity. Both effects have the potential to alleviate the apparent mismatch between the observed and theoretical abundance of galaxies as a function of vmax. For the case of WDM and MDM, we show that the discrepancy disappears, even for lukewarm models that evade stringent bounds from the Lyman-α forest. SIDM scenarios can also provide a solution as long as they lead to extended (≳1.5 kpc) DM cores in the density profiles of dwarf galaxies. Only models with velocity-dependent cross-sections can yield such cores without violating other observational constraints at larger scales., Monthly Notices of the Royal Astronomical Society, 470 (2), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

We describe a general Godunov-type splitting for numerical simulations of the Fisher–Kolmogorov–Petrovski–Piskunov growth and diffusion equation on a world map with Neumann boundary conditions. The procedure is semi-implicit, hence quite stable. Our principal application for this solver is modeling human population dispersal over geographical maps with changing paleovegetation and paleoclimate in the late Pleistocene. As a proxy for carrying capacity we use Net Primary Productivity (NPP) to predict times for human arrival in the Americas., PLoS ONE, 12 (1), ISSN:1932-6203

Individual-based models (IBMs) of human populations capture spatio-temporal dynamics using rules that govern the birth, behavior, and death of individuals. We explore a stochastic IBM of logistic growth-diffusion with constant time steps and independent, simultaneous actions of birth, death, and movement that approaches the Fisher-Kolmogorov model in the continuum limit. This model is well-suited to parallelization on high-performance computers. We explore its emergent properties with analytical approximations and numerical simulations in parameter ranges relevant to human population dynamics and ecology, and reproduce continuous-time results in the limit of small transition probabilities. Our model prediction indicates that the population density and dispersal speed are affected by fluctuations in the number of individuals. The discrete-time model displays novel properties owing to the binomial character of the fluctuations: in certain regimes of the growth model, a decrease in time step size drives the system away from the continuum limit. These effects are especially important at local population sizes of, PLoS ONE, 12 (4), ISSN:1932-6203

Merging has been proposed to explain multiple populations in globular clusters (GCs) where there is a spread in iron abundance (hereafter, iron-complex GCs). By means of N-body simulations, we investigate if merging is consistent with the observations of sub-populations and rotation in iron-complex GCs. The key parameters are the initial mass and density ratios of the progenitors. When densities are similar, the more massive progenitor dominates the central part of the merger remnant and the less massive progenitor forms an extended rotating population. The low-mass progenitor can become the majority population in the central regions of the merger remnant only if its initial density is higher by roughly the mass ratio. To match the radial distribution of multiple populations in two iron-complex GCs ({\omega} Cen and NGC 1851), the less massive progenitor needs to be four times as dense as the larger one. Our merger remnants show solid-body rotation in the inner parts, becoming differential in the outer parts. Rotation velocity V and ellipticity {\epsilon} are in agreement with models for oblate rotators with isotropic dispersion. We discuss several kinematic signatures of a merger with a denser lower mass progenitor that can be tested with future observations., Comment: 13 pages, 11 figures, accepted for publication in MNRAS

The theoretical studies about galaxy formation and evolution are the subject of this Chapter. They started with the recognition that the Hubble sequence is not a simple morphological description of galaxies, but a possible scheme separating and characterizing the physical processes that bring galaxies to their present form. When the Hubble tuning fork reached its actual shape—around 1936 with the discovery of the S0 galaxies—, the Hertzsprung-Russell diagram that revealed the existence of the main sequence of stellar structures was already in place, but its explanation in terms of nuclear reactions was still to come (the p-p chain of Bethe appeared in 1939). Just before the end of the WWII the time was mature for the concept of stellar populations formulated by Baade, but only 􏰃 20 years later appeared the first monolithic collapse model of galaxies formation by Eggen et al. (1962). In 1964 Arno Penzias and Robert Woodrow Wilson measured the CMB radiation opening the way toward the current cosmological model. With the 1970s the idea that merging events have produced many of the actual galaxy structures appeared in the literature with the Toomre’ works. Leonard Searle and Robert Zinn proposed that galaxies form by the coalescence of smaller progenitors. At the same time the discovery of the existence of dark matter (DM) rapidly changed our idea of galaxies and how structures form in the Universe. White & Rees and Fall & Efstathiou developed the actual view of galaxy formation, in which baryons fall into the potential wells of hierarchically growing dark matter structures. The two decades 1980s–1990s have seen the development of Semi-Analytic Models (SAM) of galaxy formation and evolution and of numerical hydrodynamical simulations of increasing resolution and complexity. With the new century, the Universe was discovered to accelerate its expansion and thanks to the big redshift galaxy surveys the idea of the cosmic web started to be accepted. Today the dominating paradigm is that provided by the 􏰋CDM cosmology, a framework in which the Universe is believed to be composed of 􏰃 70% of dark energy (DE), 􏰃 26% of cold and hot DM, and 􏰃 4% of baryons. Within this model the values of the cosmological parameters, such as the Hubble expansion rate H0, are known with great accuracy. This is the precision cosmology era, a very awkward situation in which the cosmological parameters are known very well, but we do not know what the Universe is composed of. The following interviews go over some theoretical investigations that, along this century of extra-galactic research, tried to shed some light on the galaxy formation and evolution. Section 8.2 deals with the first attempts to simulate the Hubble tuning fork from basic physical principles. Then, in Sect.8.3 we better define the differences between the monolithic scenario of galaxy formation and the hierarchical scheme, introducing some hybrid versions of the two frameworks. In Sects. 8.4 and 8.5 we provide a much clear view of the star formation history, i.e. of the convolution of the Initial Mass Function (IMF) and the Star Formation Rate (SFR). The role of feedback is analyzed in Sect. 8.6, that of chemical enrichment in Sect. 8.7, and that of Magnetic Fields in Sect. 8.8. We finally propose a panoramic view of the comparisons between observations and models in Sect. 8.9.

The beauty and the charm of the Milky May (MW) have been celebrated by countless poets and writers of many Countries along the centuries (see e.g. the beautiful anthology of Piero Boitani [46]). The stellar nature of the MW was firstly observed by Galileo. In 1610 in the Sidereus Nuncius [126] Galileo wrote that the MW is “nient’altro che una congerie di innumerevoli Stelle, disseminate a mucchi; ch`e in qualunque regione di essa si diriga il cannocchiale, subito una ingente folla di Stelle si presenta alla vista, delle quali parecchi si vedono abbastanza grandi e molto distinte; ma la moltitudine delle piccole `e del tutto inesplorabile”. In the same paragraph, Galileo remarked that observations with his telescope, for the first time, wipe out centuries of philosophical discussions about the nature of the MW. Three more centuries have been necessary to complete a second radical Copernican Revolution that displaces the solar system from being roughly at the center of the MW and project this latter in the vast Universe populated by billions of similar spiral galaxies (see Chapter1). The first part of this Chapter is dedicated to the crescendo of studies that have progressively contributed to our understanding of the MW. Section 2.2, by James Lattis, reviews the fundamental step in recognizing the Galaxy as a “normal” spiral, before the WWII. Piet van der Kruit in Section 2.3, goes into the evolution of our knowledge of the MW structure and of kinematics. This Section, starting from the achievements of Jaan Ort in the 1920s about the Galaxy differential rotation, brings us to the modern view of theMWand how this reverberates in general on the understanding of spiral galaxies. The Galaxy is made by stars of different families. The fundamental concepts of stellar populations is introduced in Section 2.4 by Antonella Vallenari with an historical evolution up to the use of stars in the definition of MW structure and the clock they provide to understand the MW evolutionary path. The dust properties in the MW are discussed in Section 2.5 by Daniela Calzetti. The second part of the Chapter is dedicated to the problem of the extragalactic distance scale. As mentioned in Chapter 1 there was a long term debate on this issue that has seen two different schools of thought on opposite positions. Barry Madore introduces the debate about the determination of the distance scale and the use of adequate primary and secondary indicators for the purpose. The third part of the Chapter is dedicated to the nearby galaxies of theMWand to the exploration from inside of a gravitationally bound group of galaxies in an evolving environment. It is worth to mention that the MW and the companions in the socalled Local Group (LG) are basically the only galaxies we can study resolving their stellar components. In this sense, the MW and the LG galaxies are a sort of Rosetta stone for understanding extragalactic objects. They are of overwhelming importance even for understanding distant galaxies since among the recently discovered ultra faint dwarfs (UFD) might lurk the debris of first galaxies (see the contribution of Volker Bromm in Chapter 6. In Section 2.7 Valentina Karachentseva describes the population of galaxies members of the LG, their discovery along this century of research and their properties. A zoom on the Andromeda galaxy M31 is provided by Rodrigo Ibata in Section 2.7.1, while the dwarf galaxy populations, with the widest number of members in the LG is presented by Carme Gallart in Section 2.7.2. An overall view of the co-evolution of the galaxies members of the LG is presented in Section 2.8 by Rodrigo Ibata and Goerge Lake. In Section 2.9 Brent Tully brings us just outside the LG discussing the present view of the structure and motions in the nearby Universe. The Chapter closes with what we call the “lessons for the future” in Section 2.10. The road toward a modern vision of The Galaxy and a precise calibration of the galaxy distances was and remains hard.

BackgroundExcess loads of nutrients finding their way into waterbodies can cause rapid and excessive growth of phytoplankton species and lead to the formation of cyanobacterial harmful algal blooms (cyano-HABs). Toxic cyanobacteria produce a broad range of bioactive metabolites, some of which are known as cyanotoxins. These metabolites can negatively impact the ecosystem, and human and animal health, thus their presence needs to be closely monitored and mitigated. This study aimed to monitor St. George Lake (Athalassa National Forest Park, Cyprus) for its water quality characteristics, and initiate a new methodology to control the bloom that occurred in the lake during summer 2019, by comparing hydrogen peroxide treatment with novel metallic peroxide granules as source of hydrogen peroxide.ResultsLake monitoring showed that pH, salinity, total dissolved solids and conductivity varied throughout the year, and nutrients concentration was high, indicating a eutrophic lake. The cyanobacteriumMerismopediasp. bloomed in the lake between June and September 2019, comprising up to 99% of the phytoplankton biovolume. The presence of microcystin synthase encoding gene (mcyB, mcyE) was documented, however microcystins were not detected by tandem mass spectroscopy. Treatment with liquid hydrogen peroxide in concentrations 1 to 5 mg L−1had no effect on the phycocyanin fluorescence (Ft) and quantum yield of PSII (Fv/Fm) indicating an ineffective treatment for the denseMerismopediabloom (1 million cells mL−1 ± 20%). Metallic peroxide granules tested for their H2O2releasing capacity in St. George Lake water, showing that CaO2released higher H2O2concentration and therefore have better mitigation efficiency than MgO2granules.ConclusionThe present study highlights the importance of monitoring several water parameters to conclude on the different actions to be taken to limit eutrophication in the catchment area. The findings demonstrated that testing for the presence of genes involved in cyanotoxin production may not be sufficient to follow cyanotoxins in the water, therefore it should be accompanied with analytical confirmation. Treatment experiments indicated that slow release of H2O2from peroxide granules may be an alternative to liquid hydrogen peroxide when applied in appropriate doses, but further investigation is needed before it is applied at the field.Graphic Abstract