Galactic googly : the rotation-metallicity bias in the inner stellar halo of the Milky Way

The first and second moments of stellar velocities encode important information about the formation history of the Galactic halo. However, due to the lack of tangential motion and inaccurate distances of the halo stars, the velocity moments in the Galactic halo have largely remained ‘known unknowns’. Fortunately, our off-centric position within the Galaxy allows us to estimate these moments in the galactocentric frame using the observed radial velocities of the stars alone. We use these velocities coupled with the hierarchical Bayesian scheme, which allows easy marginalization over the missing data (the proper motion, and uncertainty-free distance and line-of-sight velocity), to measure the velocity dispersions, orbital anisotropy (β) and streaming motion (vrot) of the halo main-sequence turn-off (MSTO) and K-giant (KG) stars in the inner stellar halo (r ≲ 15 kpc). We study the metallicity bias in kinematics of the halo stars and observe that the comparatively metal-rich ([Fe/H] > −1.4) and the metal-poor ([Fe/H] ≤ −1.4) MSTO samples show a clear systematic difference in vrot ∼ 20-40 km s−1, depending on how restrictive the spatial cuts to cull the disc contamination are. The bias is also detected in KG samples but with less certainty. Both MSTO and KG populations suggest that the inner stellar halo of the Galaxy is radially biased i.e. σr > σθ or σϕ and β ≃ 0.5. The apparent metallicity contrariety in the rotation velocity among the halo sub-populations supports the co-existence of multiple populations in the galactic halo that may have formed through distinct formation scenarios, i.e. in situ versus accretion.Publisher PDFPeer reviewe

A SkyMapper view of the large magellanic cloud: The dynamics of stellar populations

We present the first SkyMapper stellar population analysis of the Large Magellanic Cloud (hereafter LMC), including the identification of 3578 candidate Carbon Stars through their extremely red g − r colours. Coupled with Gaia astrometry, we analyse the distribution and kinematics of this Carbon Star population, finding the LMC to be centred at (RA, Dec.) = (80.90 ◦ ± 0.29, −68.74 ◦ ± 0.12), with a bulk proper motion of (μ α , μ δ ) = (1.878 ± 0.007, 0.293 ± 0.018) mas yr −1 and a disc inclination of i = 25.6 ◦ ± 1.1 at position angle θ = 135.6 ◦ ± 3.3 ◦ . We complement this study with the identification and analysis of additional stellar populations, finding that the dynamical centre for red giant branch stars is similar to that seen for the Carbon Stars, whereas for young stars the dynamical centre is significantly offset from the older populations. This potentially indicates that the young stars were formed as a consequence of a strong tidal interaction, probably with the Small Magellanic Cloud. In terms of internal dynamics, the tangential velocity profile increases linearly within ∼3 kpc, after which it maintains an approximately constant value of V rot = 83.6 ± 1.7 km s−1 until ∼7 kpc. With an asymmetric drift correction, we estimate the mass within 7 kpc to be M LMC (< 7 kpc) = (2.5 ± 0.1) × 10 10 M ⊙ and within the tidal radius (∼30 kpc) to be M LMC (< 30 kpc) = (1.06 ± 0.32) × 10 11 M ⊙ , consistent with other recent measurements.ZW gratefully acknowledges financial support through a the Dean’s International Postgraduate Research Scholarship from the Physics School of the University of Sydney. DM holds an Australian Research Council (ARC) Future Fellowship (FT160100206). We thank the anonymous reviewer for their constructive suggestions. The national facility capability for SkyMapper has been funded through ARC LIEF grant LE130100104 from the Australian Research Council, awarded to the University of Sydney, the Australian National University, Swinburne University of Technology, the University of Queensland, the University of Western Australia, the University of Melbourne, Curtin University of Technology, Monash University and the Australian Astronomical Observator

The large-scale ionization cones in the Galaxy

There is compelling evidence for a highly energetic Seyfert explosion (10^{56-57} erg) that occurred in the Galactic Centre a few million years ago. The clearest indications are the x-ray/gamma-ray "10 kpc bubbles" identified by the Rosat and Fermi satellites. In an earlier paper, we suggested another manifestation of this nuclear activity, i.e. elevated H-alpha emission along a section of the Magellanic Stream due to a burst (or flare) of ionizing radiation from Sgr A*. We now provide further evidence for a powerful flare event: UV absorption line ratios (in particular CIV/CII, SiIV/SiII) observed by the Hubble Space Telescope reveal that some Stream clouds towards both galactic poles are highly ionized by a source capable of producing ionization energies up to at least 50 eV. We show how these are clouds caught in a beam of bipolar, radiative "ionization cones" from a Seyfert nucleus associated with Sgr A*. In our model, the biconic axis is tilted by about 15 deg from the South Galactic Pole with an opening angle of roughly 60 deg. For the Stream at such large Galactic distances (D > 75 kpc), nuclear activity is a plausible explanation for all of the observed signatures: elevated H-alpha emission and H ionization fraction (X_e > 0.5), enhanced CIV/CII and SiIV/SiII ratios, and high CIV and SiIV column densities. Wind-driven "shock cones" are ruled out because the Fermi bubbles lose their momentum and energy to the Galactic corona long before reaching the Stream. The nuclear flare event must have had a radiative UV luminosity close to the Eddington limit (f_E ~ 0.1-1). Our time-dependent Seyfert flare models adequately explain the observations and indicate the Seyfert flare event took place T_o = 3.5 +/- 1 Myr ago. The timing estimates are consistent with the mechanical timescales needed to explain the x-ray/gamma-ray bubbles in leptonic jet/wind models (2-8 Myr).Comment: 21 pages; 15 figures; 2 movies (this version matches published version

On the origin of the Monoceros Ring - I. Kinematics, proper motions, and the nature of the progenitor

TheMonoceros Ring (MRi) structure is an apparent stellar overdensity that has been postulated to entirely encircle the Galactic plane and has been variously described as being due to lineof- sight effects of the Galactic warp and flare or of extragalactic origin (via accretion). Despite being intensely scrutinized in the literature for more than a decade, no studies to date have been able to definitively uncover its origins. Here we use N-body simulations and a genetic algorithm to explore the parameter space for the initial position, orbital parameters, and, for the first time, the final location of a satellite progenitor. We fit our models to the latest Pan-STARRS data to determine whether an accretion scenario is capable of producing an inplane ring-like structure matching the known parameters of the MRi. Our simulations produce streams that closely match the location, proper motion, and kinematics of the MRi structure. However, we are not able to reproduce the mass estimates from earlier studies based on Pan- STARRS data. Furthermore, in contrast to earlier studies, our best-fitting models are those for progenitors on retrograde orbits. If the MRi was produced by satellite accretion, we find that its progenitor has an initial mass upper limit of ~ 1010M⊙ and the remnant is likely located behind the Galactic bulge, making it difficult to locate observationally. While our models produce realistic MRi-like structures, we cannot definitively conclude that the MRi was produced by the accretion of a satellite galaxy.RRL acknowledges support by the Chilean Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics (MAS). RRL also acknowledges support from the STFC/Newton Fund ST/M007995/1 and the CONICYT/Newton Fund DPI20140114. BCC acknowledges the support of the Australian Research Council through Discovery project DP150100862. AYQH was supported by a National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144469. The authors acknowledge the University of Sydney HPC service at the University of Sydney for providing HPC resources that have contributed to the research results reported within this paper

Report on trends in the Italian productive system

In the last decade the Italian economy has underperformed compared both with the previous decades and with the main European countries. It is widely acknowledged that this evolution reflects unresolved structural problems, which have become more urgent in view of the major changes in the world economy (the new technological paradigm, globalization, European economic integration). The goal of the Report is to make a critical survey of all the empirical analyses on the Italian economy and to derive policy suggestions. The evolution of Italy’s productive system is examined from a long-run perspective, highlighting weaknesses and possible signs of recovery and elaborating on the systemic features that may have negatively affected growth performance directly or indirectly through the above exogenous shocks. The focus, mostly but not exclusively microeconomic, emphasizes the considerable heterogeneity of firms, a crucial element for identifying the factors that affect economic growth.growth, productivity, market structure, firm heterogeneity

HumMeth27QCReport: an R package for quality control and primary analysis of Illumina Infinium methylation data

<p>Abstract</p> <p>Background</p> <p>The study of the human DNA methylome has gained particular interest in the last few years. Researchers can nowadays investigate the potential role of DNA methylation in common disorders by taking advantage of new high-throughput technologies. Among these, Illumina Infinium assays can interrogate the methylation levels of hundreds of thousands of CpG sites, offering an ideal solution for genome-wide methylation profiling. However, like for other high-throughput technologies, the main bottleneck remains at the stage of data analysis rather than data production.</p> <p>Findings</p> <p>We have developed <it>HumMeth27QCReport</it>, an R package devoted to researchers wanting to quickly analyse their Illumina Infinium methylation arrays. This package automates quality control steps by generating a report including sample-independent and sample-dependent quality plots, and performs primary analysis of raw methylation calls by computing data normalization, statistics, and sample similarities. This package is available at CRAN repository, and can be integrated in any Galaxy instance through the implementation of ad-hoc scripts accessible at Galaxy Tool Shed.</p> <p>Conclusions</p> <p>Our package provides users of the Illumina Infinium Methylation assays with a simplified, automated, open-source quality control and primary analysis of their methylation data. Moreover, to enhance its use by experimental researchers, the tool is being distributed along with the scripts necessary for its implementation in the Galaxy workbench. Finally, although it was originally developed for HumanMethylation27, we proved its compatibility with data generated with the HumanMethylation450 Bead Chip.</p

NGC 147, NGC 185 and CassII: a genetic approach to orbital properties, star formation and tidal debris

NGC147, NGC185 and CassiopeiaII (CassII) have similar positions in the sky, distances and measured line of sight velocities. This proximity in phase space suggests that these three satellites of M31 form a subgroup within the Local Group. Nevertheless, the differences in their star formation history and interstellar medium, and the recent discovery of a stellar stream in NGC~147, combined with the lack of tidal features in the other two satellites, are all indications of complex and diverse interactions between M31 and these three satellites. We use a genetic algorithm to explore the different orbits that these satellites can have and select six sets of orbits that could best explain the observational features of the NGC147, NGC185 and CassII satellites. The parameters of these orbits are then used as a starting point for N-body simulations. We present models for which NGC147, NGC185 and CassII are a bound group for a total time of at least one Gyr but still undergo different interactions with M31 and as a result NGC147 has a clear stellar stream whereas the other two satellites have no significant tidal features. This result shows that it is possible to find solutions that reproduce the contrasting properties of the satellites and for which NGC147-NGC185-CassII have been gravitationally bound.Comment: Accepted for publication on MNRAS. 12 pages, 9 figure

A genetic approach to galaxy interactions

Interactions between galaxies play an important role in galaxy evolution. They can trigger bursts of star formation and change the galaxy morphology, leading to the formation of stellar and gaseous tails. The dynamical processes involved in the interaction between two galaxies can only be understood in full by reconstructing their orbital history. The drawback of this approach is the large number of parameters that influence the orbits, such as the masses, velocities and positions of the galaxies. This thesis studies interacting galaxies by analyzing different orbital scenarios and selecting those configurations which lead to a better description of the observed properties of the system. The combination of a genetic algorithm with N-Body simulations allows for an automatic comparison between observations and simulations, in order to select those orbits able to reproduce observed tidal structures. In particular, two systems of galaxies are objects of study: the nearby Magellanic System and three of M31 satellites, NGC 147, NGC 185 and the newly discovered Cass II. The Large Magellanic Cloud and its smaller companion offer the unique laboratory to study galaxy interactions. The presence of a bridge of gas connecting the two Clouds and an elongated tail of gas, the Magellanic Stream, suggests that these satellites are interacting between each other and the Milky Way. The combination of the genetic algorithm with the N-Body simulations allows for a better selection of the orbits of these galaxies, entirely based on the ability to reproduce the observational constraints. Our simulations show that the only interactions between the Large and the Small Magellanic Clouds for a period of 3 Gyr are able to reproduce the key observed features. The two elliptical galaxies, NGC 147 and NGC 185, and the recently discovery spheroidal Cass II show evidence of being part of small subgroup of satellites, orbiting their host. We explore this scenario, overcoming the lack of the kinematic information by considering the tangential velocities as free parameters. Using the recent discovery of a stellar stream in NGC 147 by the Pan-Andromeda Archaeological Survey (PAndAS) team as a constraint on the orbit, this method provides a set of orbital scenarios able to explain the star formation history and morphology of these satellites

A SkyMapper view of the Large Magellanic Cloud: the dynamics of stellar populations

International audienc