The Formation Times and Building Blocks of Milky Way-mass Galaxies in the FIRE Simulations

Surveys of the Milky Way (MW) and M31 enable detailed studies of stellar populations across ages and metallicities, with the goal of reconstructing formation histories across cosmic time. These surveys motivate key questions for galactic archaeology in a cosmological context: when did the main progenitor of a MW/M31-mass galaxy form, and what were the galactic building blocks that formed it? We investigate the formation times and progenitor galaxies of MW/M31-mass galaxies using the FIRE-2 cosmological simulations, including 6 isolated MW/M31-mass galaxies and 6 galaxies in Local Group (LG)-like pairs at z = 0. We examine main progenitor "formation" based on two metrics: (1) transition from primarily ex-situ to in-situ stellar mass growth and (2) mass dominance compared to other progenitors. We find that the main progenitor of a MW/M31-mass galaxy emerged typically at z ~ 3-4 (11.6-12.2 Gyr ago), while stars in the bulge region (inner 2 kpc) at z = 0 formed primarily in a single main progenitor at z < 5 (< 12.6 Gyr ago). Compared with isolated hosts, the main progenitors of LG-like paired hosts emerged significantly earlier (\Delta z ~ 2, \Delta t ~ 1.6 Gyr), with ~ 4x higher stellar mass at all z > 4 (> 12.2 Gyr ago). This highlights the importance of environment in MW/M31-mass galaxy formation, especially at early times. Overall, about 100 galaxies with M_star > 10^5 M_sun formed a typical MW/M31-mass system. Thus, surviving satellites represent a highly incomplete census (by ~ 5x) of the progenitor population.Comment: 20 pages, 8 figures, accepted for publication in MNRA

On the origin of anomalous velocity clouds in the Milky Way

We report that neutral hydrogen (HI) gas clouds, resembling High Velocity Clouds (HVCs) observed in the Milky Way (MW), appear in MW-sized disk galaxies formed in high-resolution Lambda Cold Dark Matter (LCDM) cosmological simulations which include gas-dynamics, radiative cooling, star formation, supernova feedback, and metal enrichment. Two such disk galaxies are analyzed, and HI column density and velocity distributions in all-sky Aitoff projections are constructed. The simulations demonstrate that LCDM is able to create galaxies with sufficient numbers of anomalous velocity gas clouds consistent with the HVCs observed within the MW, and that they are found within a galactocentric radius of 150 kpc. We also find that one of the galaxies has a polar gas ring, with radius 30 kpc, which appears as a large structure of HVCs in the Aitoff projection. Such large structures may share an origin similar to extended HVCs observed in the MW, such as Complex C.Comment: Accepted by ApJL, 08 Jun 2006. 5 pages, 5 figures, 1 table. LaTeX (emulateapj.cls). File with high resolution images available at http://astronomy.swin.edu.au/~tconnors/publications/ . References added; discussion added to, but conclusions unchange

The SAMI Galaxy Survey: Cubism and covariance, putting round pegs into square holes

We present a methodology for the regularization and combination of sparse sampled and irregularly gridded observations from fibre-optic multiobject integral field spectroscopy. The approach minimizes interpolation and retains image resolution on combining subpixel dithered data. We discuss the methodology in the context of the Sydney-AAO multiobject integral field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral field spectroscopy across a 1° diameter field of view. The SAMI Galaxy Survey is targeting ~3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral field bundles results in only a 10 per cent degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting data cubes which retains 90 per cent of the covariance information while incurring only a modest increase in the survey data volume

Overview of the SDSS-IV MaNGA survey: mapping nearby galaxies at Apache Point Observatory

We present an overview of a new integral field spectroscopic survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) that began on 2014 July 1. MaNGA will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. We summarize essential characteristics of the instrument and survey design in the context of MaNGA's key science goals and present prototype observations to demonstrate MaNGA's scientific potential. MaNGA employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12'' (19 fibers) to 32'' (127 fibers). Two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 Å at R ~ 2000. With a typical integration time of 3 hr, MaNGA reaches a target r-band signal-to-noise ratio of 4-8 (Å–1 per 2'' fiber) at 23 AB mag arcsec–2, which is typical for the outskirts of MaNGA galaxies. Targets are selected with M * 109 M ☉ using SDSS-I redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. Analysis of our prototype observations demonstrates MaNGA's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. MaNGA's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr

Correlation between infectivity and disease associated prion protein in the nervous system and selected edible tissues of naturally affected scrapie sheep

<div><p>The transmissible spongiform encephalopathies (TSEs) or prion diseases are a group of fatal neurodegenerative disorders characterised by the accumulation of a pathological form of a host protein known as prion protein (PrP). The validation of abnormal PrP detection techniques is fundamental to allow the use of high-throughput laboratory based tests, avoiding the limitations of bioassays. We used scrapie, a prototype TSE, to examine the relationship between infectivity and laboratory based diagnostic tools. The data may help to optimise strategies to prevent exposure of humans to small ruminant TSE material via the food chain. Abnormal PrP distribution/accumulation was assessed by immunohistochemistry (IHC), Western blot (WB) and ELISA in samples from four animals. In addition, infectivity was detected using a sensitive bank vole bioassay with selected samples from two of the four sheep and protein misfolding cyclic amplification using bank vole brain as substrate (vPMCA) was also carried out in selected samples from one animal. Lymph nodes, oculomotor muscles, sciatic nerve and kidney were positive by IHC, WB and ELISA, although at levels 100–1000 fold lower than the brain, and contained detectable infectivity by bioassay. Tissues not infectious by bioassay were also negative by all laboratory tests including PMCA. Although discrepancies were observed in tissues with very low levels of abnormal PrP, there was an overall good correlation between IHC, WB, ELISA and bioassay results. Most importantly, there was a good correlation between the detection of abnormal PrP in tissues using laboratory tests and the levels of infectivity even when the titre was low. These findings provide useful information for risk modellers and represent a first step toward the validation of laboratory tests used to quantify prion infectivity, which would greatly aid TSE risk assessment policies.</p></div

The SAMI Galaxy Survey : data release one with emission-line physics value-added products

SAMI DR1 data products available from http://datacentral.aao.gov.au/asvo/surveys/sami/We present the first major release of data from the SAMI Galaxy Survey. This data release focuses on the emission-line physics of galaxies. Data Release One includes data for 772 galaxies, about 20% of the full survey. Galaxies included have the redshift range 0.004 <  z < 0.092, a large massrange (7.6 < log M∗/M⊙ < 11.6), and star-formation rates of ∼10−4 to ∼101 M⊙yr−1. For each galaxy, we include two spectral cubes and a set of spatially resolved 2D maps: single- and multi-component emission-line fits (with dust extinction corrections for strong lines), local dust extinction and star-formation rate. Calibration of the fibre throughputs, fluxes and differential-atmospheric-refraction has been improved over the Early Data Release. The data have average spatial resolution of 2.16 arcsec (FWHM) over the 15 arcsec diameter field of view and spectral (kinematic) resolution R= 4263 (σ= 30 km s−1) around Hα. The relative flux calibration is better than 5% and absolute flux calibration better than ±0.22 mag, with the latter estimate limited by galaxy photometry. The data are presented online through the Australian Astronomical Observatory’s Data Central.Publisher PDFPeer reviewe

Real-world generalizations in Conrad's third-person narratives

And Captain MacWhirr wrote home from the coast of China twelve times every year, desiring quaintly to be “remembered to the children,” and subscribing himself “your loving husband,” as calmly as if the words so long used by so many men were, apart from their shape, worn-out things, and of a faded meaning. The China seas north and south are narrow seas. They are seas full of every-day, eloquent facts, such as islands, sand-banks, reefs, swift and changeable currents – tangled facts that nevertheless speak to a seaman in clear and definite language. Their speech appealed to Captain MacWhirr’s sense of realities so forcibly that he had given up his state-room below and practically lived all his days on the bridge of his ship, often having his meals sent up, and sleeping at night in the chart-room. (Conrad 1950, 15)submittedVersion© 2018. This is the authors' manuscript to the article