Showing papers by "Joss Bland-Hawthorn published in 2018"
Heidelberg University1, Max Planck Society2, Australian National University3, University of Sydney4, Uppsala University5, York University6, Columbia University7, University of California, Berkeley8, Monash University, Clayton campus9, Australian Astronomical Observatory10, University of New South Wales11, Macquarie University12, University of Ljubljana13, University of Virginia14, INAF15, University of Canterbury16, University of Southern Queensland17, University of Stirling18, Johns Hopkins University19, Aarhus University20, Princeton University21, Carnegie Institution for Science22, Institute for Advanced Study23, Ohio State University24
TL;DR: In this paper, the authors present the GALAH second public data release (GALAH DR2) containing 342 682 stars and use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels.
Abstract: The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of theMilkyWay, designed to deliver complementary chemical information to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342 682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction, and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multistep approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T
eff
, logg, [Fe/H], [X/Fe], v
mic
, vsin i, AK
S
) for a representative training set of stars. This information is then propagated to the whole sample with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D MARCS stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.
336 citations
University of St Andrews1, University of Western Australia2, Australian National University3, Ames Research Center4, University of Sydney5, University of Edinburgh6, University of New South Wales7, University of Bristol8, University of the Western Cape9, University of Nottingham10, Cardiff University11, University of Louisville12, Australian Astronomical Observatory13, Astrophysics Research Institute14, University of Sussex15, University of Hamburg16, University of Hull17, Johns Hopkins University18, University of Central Lancashire19, Swinburne University of Technology20, Netherlands Institute for Space Research21
TL;DR: In this paper, the energy-balance code MAGPHYS was used to determine stellar and dust masses, and dust corrected star-formation rates for over 200,000 GAMA galaxies, 170, 000 G10-COSMOS galaxies and 200, 000 3D-HST galaxies.
Abstract: We use the energy-balance code MAGPHYS to determine stellar and dust masses, and dust corrected star-formation rates for over 200,000 GAMA galaxies, 170,000 G10-COSMOS galaxies and 200,000 3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous dataset spanning a broad range in stellar mass (10^8---10^12 Msol), dust mass (10^6---10^9 Msol), and star-formation rates (0.01---100 Msol per yr), and over a broad redshift range (0.0 < z < 5.0). We combine these data to measure the cosmic star-formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous dataset using consistent mass and star-formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our cosmic star-formation history we precisely reproduce the stellar-mass density with an ISM replenishment factor of 0.50 +/- 0.07, consistent with our choice of Chabrier IMF plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065---0.004 units of dust mass is also formed; (2) Over the history of the Universe approximately 90 to 95 per cent of all dust formed has been destroyed and/or ejected.
166 citations
TL;DR: The role of the cosmic web in shaping galaxy properties is investigated in the Galaxy And Mass Assembly (GAMA) spectroscopic survey in the redshift range 0.03 ≤ z ≤ 0.25 as mentioned in this paper.
Abstract: The role of the cosmic web in shaping galaxy properties is investigated in the Galaxy And Mass Assembly (GAMA) spectroscopic survey in the redshift range 0.03 ≤ z ≤ 0.25. The stellar mass, u − r dust corrected colour and specific star formation rate (sSFR) of galaxies are analysed as a function of their distances to the 3D cosmic web features, such as nodes, filaments and walls, as reconstructed by DisPerSE. Significant mass and type/colour gradients are found for the whole population, with more massive and/or passive galaxies being located closer to the filament and wall than their less massive and/or star-forming counterparts. Mass segregation persists among the star-forming population alone. The red fraction of galaxies increases when closing in on nodes, and on filaments regardless of the distance to nodes. Similarly, the star-forming population reddens (or lowers its sSFR) at fixed mass when closing in on filament, implying that some quenching takes place. These trends are also found in the state-of-the-art hydrodynamical simulation Horizon-AGN. These results suggest that on top of stellar mass and large-scale density, the traceless component of the tides from the anisotropic large-scale environment also shapes galactic properties. An extension of excursion theory accounting for filamentary tides provides a qualitative explanation in terms of anisotropic assembly bias: at a given mass, the accretion rate varies with the orientation and distance to filaments. It also explains the absence of type/colour gradients in the data on smaller, non-linear scales.
127 citations
TL;DR: Fire cosmological zoom-in simulations of three MW-mass disc galaxies are used to study the spatial distribution, chemistry, and kinematics of the oldest surviving stars in MW-like galaxies, predicting the oldest stars to be less centrally concentrated at z = 0 than stars formed at later times.
Abstract: Author(s): El-Badry, Kareem; Bland-Hawthorn, Joss; Wetzel, Andrew; Quataert, Eliot; Weisz, Daniel R; Boylan-Kolchin, Michael; Hopkins, Philip F; Faucher-Giguere, Claude-Andre; Keres, Dusan; Garrison-Kimmel, Shea | Abstract: The oldest stars in the Milky Way (MW) bear imprints of the Galaxy's early assembly history. We use FIRE cosmological zoom-in simulations of three MW-mass disc galaxies to study the spatial distribution, chemistry, and kinematics of the oldest surviving stars (z form ≳ 5) in MW-like galaxies. We predict the oldest stars to be less centrally concentrated at z = 0 than stars formed at later times as a result of two processes. First, the majority of the oldest stars are not formed in situ but are accreted during hierarchical assembly. These ex situ stars are deposited on dispersion-supported, halo-like orbits but dominate over old stars formed in situ in the solar neighbourhood, and in some simulations, even in the galactic centre. Secondly, old stars formed in situ are driven outwards by bursty star formation and energetic feedback processes that create a time-varying gravitational potential at z ≳ 2, similar to the process that creates dark matter cores and expands stellar orbits in bursty dwarf galaxies. The total fraction of stars that are ancient is more than an order of magnitude higher for sight lines away from the bulge and inner halo than for inward-looking sight lines. Although the task of identifying specific stars as ancient remains challenging, we anticipate that million-star spectral surveys and photometric surveys targeting metal-poor stars already include hundreds of stars formed before z = 5. We predict most of these targets to have higher metallicity (-3 l [Fe/H] l -2) than the most extreme metal-poor stars.
107 citations
University of Washington1, Joint Institute for Nuclear Astrophysics2, University of Notre Dame3, University of Michigan4, Massachusetts Institute of Technology5, Carnegie Institution for Science6, University of Texas at Austin7, University of Oklahoma8, University of Victoria9, Leibniz Institute for Astrophysics Potsdam10, Johns Hopkins University11, University of Sydney12, Australian National University13, University of Hull14, Heidelberg University15, Centre national de la recherche scientifique16, Saint Martin's University17, Macquarie University18, University College London19, Department of Industry20
TL;DR: In this paper, the detailed abundances and r-process classifications of 126 newly identified metal-poor stars are presented as part of an ongoing collaboration, the R-Process Alliance.
Abstract: This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance.
99 citations
Uppsala University1, Columbia University2, Monash University3, INAF4, University of New South Wales5, Macquarie University6, University of Ljubljana7, Harvard University8, University of Sydney9, University of Western Australia10, Johns Hopkins University11, Carnegie Learning12, Princeton University13
TL;DR: In this paper, the authors investigated correlations between chemical compositions, ages, and kinematics for a subset of the overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey and $Gaia$ provides a high-dimensional chemodynamical space of unprecedented size.
Abstract: The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey & $Gaia$ provides a high-dimensional chemodynamical space of unprecedented size. We present a first analysis of a subset of this overlap, of 7066 dwarf, turn-off, & sub-giant stars. [...] We investigate correlations between chemical compositions, ages, & kinematics for this sample. Stellar parameters & elemental abundances are derived from the GALAH spectra with the spectral synthesis code SME. [...] We report Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba & we note that we employ non-LTE calculations for Li, O, Al, & Fe. We show that the use of astrometric & photometric data improves the accuracy of the derived spectroscopic parameters, especially $\log g$. [...] we recover the result that stars of the high-$\alpha$ sequence are typically older than stars in the low-$\alpha$ sequence, the latter spanning $-0.7 8$ Gyr have lower angular momenta $L_z$ than the Sun, which implies that they are on eccentric orbits & originate from the inner disk. Contrary to some previous smaller scale studies we find a continuous evolution in the high-$\alpha$-sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate "high-$\alpha$ metal-rich" population. Stars in our sample that are younger than 10 Gyr, are mainly found on the low $\alpha$-sequence & show a gradient in $L_z$ from low [Fe/H] ($L_z>L_{z,\odot}$) towards higher [Fe/H] ($L_z
99 citations
California Institute of Technology1, Australian National University2, University of Western Australia3, University of Sydney4, Australian Astronomical Observatory5, Max Planck Society6, Vanderbilt University7, Swinburne University of Technology8, University of New South Wales9, University of North Carolina at Chapel Hill10, University of Queensland11, Macquarie University12, University of Melbourne13, Leibniz Institute for Astrophysics Potsdam14, University of Bonn15
TL;DR: In this paper, the authors presented the ∼800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on H'α emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1.
Abstract: We present the ∼800 star formation rate maps for the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey based on H α emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/H β, [N II]/H α, [S II]/H α, and [O I]/H α line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main-sequence population has centrally concentrated star formation similar to late-type galaxies, while galaxies >3σ below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.
95 citations
University of Sydney1, University of New South Wales2, Aarhus University3, Max Planck Society4, Heidelberg University5, Australian National University6, Uppsala University7, University of Ljubljana8, University of Western Australia9, Macquarie University10, University of Virginia11, Monash University12, Australian Astronomical Observatory13, University of Southern Queensland14
TL;DR: The Transiting Exoplanet Survey Satellite (TESS) will provide high-precision time series photometry for millions of stars with at least a half-hour cadence as mentioned in this paper.
Abstract: The Transiting Exoplanet Survey Satellite (TESS) will provide high-precision time series photometry for millions of stars with at least a half-hour cadence. Of particular interest are the circular ...
93 citations
University of Sydney1, Australian National University2, Macquarie University3, Australian Astronomical Observatory4, California Institute of Technology5, University of New South Wales6, University of Western Australia7, University of Queensland8, Leiden University9, National Autonomous University of Mexico10, University of Wisconsin-Madison11, Swinburne University of Technology12
TL;DR: The second major release of data from the Sydney - Australian Astronomical Observatory Multi-Object Integral Field Spectrograph (SAMI) Galaxy Survey as discussed by the authors was released in 2013.
Abstract: We present the second major release of data from the Sydney - Australian Astronomical Observatory Multi-Object Integral Field Spectrograph (SAMI) Galaxy Survey. Data Release Two includes data for 1559 galaxies, about 50 per cent of the full survey. Galaxies included have a redshift range 0.004 11], the velocity dispersion strongly increases towards the centre, whereas below log (M-*/M-circle dot) < 10 we find no evidence for a clear increase in the central velocity dispersion. This suggests a transition mass around log (M-*/M-circle dot) similar to 10 for galaxies with or without a dispersion-dominated bulge.
79 citations
Durham University1, European Southern Observatory2, University of Oxford3, Lancaster University4, Institute for the Physics and Mathematics of the Universe5, Leiden University6, University of Edinburgh7, University of the Western Cape8, University of Copenhagen9, University of Sydney10, University of Western Australia11, Australian National University12, Swinburne University of Technology13, Australian Astronomical Observatory14, Macquarie University15
TL;DR: In this article, velocity dispersion properties of 472 z~0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS) were analyzed.
Abstract: We analyse the velocity dispersion properties of 472 z~0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is rotationally dominated (83 +/- 5% with v_C/sigma_0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is sigma_0 = 43.2 +/- 0.8 km/s with a rotational velocity to dispersion ratio of v_C/sigma_0 = 2.6 +/- 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate and redshift we combine KROSS with data from the SAMI survey (z~0.05) and an intermediate redshift MUSE sample (z~0.5). While there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by disks that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.
76 citations
University of Western Australia1, Australian Research Council2, Australian Astronomical Observatory3, University of Sydney4, Australian National University5, Liverpool John Moores University6, Leiden University7, University of Bristol8, Monash University9, European Space Research and Technology Centre10, University of Louisville11, University of Oxford12, University of the Western Cape13, ASTRON14, Vanderbilt University15, Swinburne University of Technology16, Arizona State University17
TL;DR: The Deep Extragalactic VIsible Legacy Survey (DEVILS) as discussed by the authors is a large spectroscopic campaign at the Anglo Australian Telescope (AAT) aimed at bridging the near and distant Universe by producing the highest completeness survey of galaxies and groups at intermediate redshifts.
Abstract: The Deep Extragalactic VIsible Legacy Survey (DEVILS) is a large spectroscopic campaign at the Anglo-Australian Telescope (AAT) aimed at bridging the near and distant Universe by producing the highest completeness survey of galaxies and groups at intermediate redshifts ($0.3
Australian Astronomical Observatory1, University of Sydney2, University of Western Australia3, California Institute of Technology4, Australian National University5, Max Planck Society6, University of Queensland7, Macquarie University8, University of New South Wales9, University of North Carolina at Chapel Hill10, University of Newcastle11, University of Hamburg12, Swinburne University of Technology13, University of St Andrews14, University of Melbourne15
TL;DR: The first major release of data from the SAMI Galaxy Survey as discussed by the authors focuses on the emission-line physics of galaxies and includes data for 772 galaxies, about 20% of the full survey.
Abstract: 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 per cent of the full survey. Galaxies included have the redshift range 0.004 < z < 0.092, a large mass range (7.6 < log M*/ M⊙ < 11.6), and star formation rates of ∼10^(−4) to ∼10^1M⊙ 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 (full width at half-maximum) over the 15 arcsec diameter field of view and spectral (kinematic) resolution of R = 4263 (σ = 30 km s^(−1)) around H α. The relative flux calibration is better than 5 per cent, and absolute flux calibration has an rms of 10 per cent. The data are presented online through the Australian Astronomical Observatory's Data Central.
Johns Hopkins University1, University of St Andrews2, University of Edinburgh3, University of Bristol4, Australian Astronomical Observatory5, Leiden University6, Macquarie University7, University of Hull8, Monash University, Clayton campus9, University of Central Lancashire10, University of Groningen11, Netherlands Institute for Space Research12, Ames Research Center13, University of Sydney14, Australian National University15, University of Louisville16, Swinburne University of Technology17
TL;DR: In this paper, the authors identify potentially rapidly transitioning post-starburst (PSB) and slower transitioning green-valley galaxies, and find that the quiescent population has grown more slowly in number density at high masses than at intermediate masses.
Abstract: One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the Galaxy And Mass Assembly and VIsible MultiObject Spectrograph Public Extragalactic Redshift surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies. We identify potentially rapidly transitioning post-starburst (PSB) galaxies and slower transitioning green-valley galaxies. Over the last 8 Gyr, the quiescent population has grown more slowly in number density at high masses ({M}_\ast >10^{11}{M_{s}) than at intermediate masses ({M}_\ast >10^{10.6}{M_{s}). There is evolution in both the PSB and green-valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times. At intermediate masses ({M}_\ast >10^{10.6}{M_{s}), we find a green-valley transition time-scale of 2.6 Gyr. Alternatively, at z ~ 0.7, the entire growth rate could be explained by fast-quenching PSB galaxies, with a visibility time-scale of 0.5 Gyr. At lower redshift, the number density of PSBs is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at z 10^{11}{M_{s}), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high-mass PSB and green-valley galaxies are transitioning from star forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation.
Leibniz Institute for Astrophysics Potsdam1, University of Oxford2, University of Strasbourg3, University of Sydney4, Australian National University5, University of Cambridge6, University of Hull7, Heidelberg University8, Saint Martin's University9, Lund University10, Leibniz Institute for Neurobiology11, INAF12, University of Victoria13, University of Hong Kong14, Macquarie University15, University College London16, Australian Astronomical Observatory17, Johns Hopkins University18, University of Ljubljana19
TL;DR: In this article, the authors used data from the Radial Velocity Experiment (RAVE) and the Tycho-Gaia astrometric solution (TGAS) catalogue to compute the velocity fields yielded by the radial (VR), azimuthal (Vϕ), and vertical (Vz) components of associated Galactocentric velocity.
Abstract: We use data from the Radial Velocity Experiment (RAVE) and the Tycho-Gaia astrometric solution (TGAS) catalogue to compute the velocity fields yielded by the radial (VR), azimuthal (Vϕ),and vertical (Vz) components of associated Galactocentric velocity. We search in particular for variation in all three velocity components with distance above and below the disc midplane, as well as how each component of Vz (line-of-sight and tangential velocity projections) modifies the obtained vertical structure. To study the dependence of velocity on proper motion and distance, we use two main samples: a RAVE sample including proper motions from the Tycho-2, PPMXL, and UCAC4 catalogues, and a RAVE-TGAS sample with inferred distances and proper motions from the TGAS and UCAC5 catalogues. In both samples, we identify asymmetries in VR and Vz. Below the plane, we find the largest radial gradient to be ∂VR/∂R = -7.01 ± 0.61 km s-1 kpc-1, in agreement with recent studies. Above the plane, we find a similar gradient with ∂VR/∂R = -9.42 ± 1.77 km s-1 kpc-1. By comparing our results with previous studies, we find that the structure in Vz is strongly dependent on the adopted proper motions. Using the Galaxia Milky Way model, we demonstrate that distance uncertainties can create artificial wave-like patterns. In contrast to previous suggestions of a breathing mode seen in RAVE data, our results support a combination of bending and breathing modes, likely generated by a combination of external or internal and external mechanisms. (Less)
TL;DR: In this article, the authors present gas-phase metallicity and ionization parameter maps of 25 star-forming face-on spiral galaxies from the SAMI Galaxy Survey Data Release 1.
Abstract: We present gas-phase metallicity and ionization parameter maps of 25 star-forming face-on spiral galaxies from the SAMI Galaxy Survey Data Release 1. Self-consistent metallicity and ionization parameter maps are calculated simultaneously through an iterative process to account for the interdependence of the strong emission line diagnostics involving ([O II]+[O III])/Hβ (R_(23)) and [O III]/[O II](O32). The maps are created on a spaxel-by-spaxel basis because H II regions are not resolved at the SAMI spatial resolution. We combine the SAMI data with stellar mass, star formation rate (SFR), effective radius (R_e), ellipticity, and position angles (PA) from the GAMA survey to analyse their relation to the metallicity and ionization parameter. We find a weak trend of steepening metallicity gradient with galaxy stellar mass, with values ranging from −0.03 to −0.20 dex/R_e. Only two galaxies show radial gradients in the ionization parameter. We find that the ionization parameter has no significant correlation with either SFR, sSFR (specific SFR), or metallicity. For several individual galaxies, we find the structure in the ionization parameter maps suggestive of spiral arm features. We find a typical ionization parameter range of 7.0 < log (q) < 7.8 for our galaxy sample with no significant overall structure. An ionization parameter range of this magnitude is large enough to caution the use of metallicity diagnostics that have not considered the effects of a varying ionization parameter distribution.
TL;DR: In this paper, a new method was introduced to improve the identification of oscillation modes which exploits theoretical frequencies to guide the mode identification in the peak-bagging stage of the data analysis.
Abstract: Stellar models rely on a number of free parameters. High-quality observations of eclipsing binary stars observed by Kepler offer a great opportunity to calibrate model parameters for evolved stars. Our study focuses on six Kepler red giants with the goal of calibrating the mixing-length parameter of convection as well as the asteroseismic surface term in models. We introduce a new method to improve the identification of oscillation modes which exploits theoretical frequencies to guide the mode identification ('peak-bagging') stage of the data analysis. Our results indicate that the convective mixing-length parameter (alpha) is about 14% larger for red giants than for the Sun, in agreement with recent results from modelling the APOGEE stars. We found that the asteroseismic surface term (i.e. the frequency offset between the observed and predicted modes) correlates with stellar parameters (Teff, log g) and the mixing-length parameter. This frequency offset generally decreases as giants evolve. The two coefficients a_-1 and a_3 for the inverse and cubic terms that have been used to describe the surface term correction are found to correlate linearly. The effect of the surface term is also seen in the p-g mixed modes, however, established methods for correcting the effect are not able to properly correct the g-dominated modes in late evolved stars.
TL;DR: In this paper, a combined study of spatially resolved stellar kinematics and global stellar populations was performed using the SAMI Galaxy Survey, and the authors found a strong correlation of stellar population age with location in the (V/σ, $${\boldsymbol{\epsilon}}{{{b}e}}}$$¯¯ ϵ¯¯¯¯ e¯¯¯¯ ) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity.
Abstract: Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1–3. A galaxy’s mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy’s mass was assembled. Resolved stellar dynamics
4
trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions
5
. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI
6
and MaNGA
7
, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8
), CALIFA
9
, MASSIVE
10
), it is now feasible to connect a galaxy′s star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, $${\boldsymbol{\epsilon}}_{{\boldsymbol{e}}}$$
ϵ
e
) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.
Lund University1, Centre national de la recherche scientifique2, Leibniz Institute for Astrophysics Potsdam3, Johns Hopkins University4, University of Ljubljana5, University of Sydney6, University of Hull7, University of Cambridge8, Heidelberg University9, Kapteyn Astronomical Institute10, INAF11, University of Victoria12, University of Hong Kong13, University College London14, Australian Astronomical Observatory15
TL;DR: In this paper, the authors used data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC).
Abstract: Funding for the research in this study came from the Swedish National Space Board, the Royal Physiographic Society in Lund, and some of the computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at Lunarc under project SNIC 2016/4-17. Funding for RAVE has been provided by: the Australian Astronomical Observatory; the Leibniz-Institut fuer Astrophysik Potsdam (AIP); the Australian National University; the Australian Research Council; the French National Research Agency; the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency (research core funding No. P1-0188); the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Groningen, Heidelberg and Sydney. The RAVE web site is https://www.rave-survey.org. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
Max Planck Society1, Heidelberg University2, Uppsala University3, Harvard University4, Australian National University5, University of Sydney6, University of California, Berkeley7, Australian Astronomical Observatory8, University of New South Wales9, Macquarie University10, University of Ljubljana11, University of Virginia12, University of Southern Queensland13, University of Western Australia14, Johns Hopkins University15, Aarhus University16, Princeton University17, Institute for Advanced Study18, Carnegie Institution for Science19
TL;DR: In this paper, the authors carried out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, and Fe) in 66 stars belonging to the open cluster M67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and non-local thermodynamic equilibrium (non-LTE) radiative transfer.
Abstract: Open cluster members are coeval and share the same initial bulk chemical composition. Consequently, differences in surface abundances between members of a cluster that are at different evolutionary stages can be used to study the effects of mixing and internal chemical processing. We carry out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, and Fe) in 66 stars belonging to the open cluster M67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and non-local thermodynamic equilibrium (non-LTE) radiative transfer. From the non-LTE analysis, we find a typical star-to-star scatter in the abundance ratios of around 0.05 dex. We find trends in the abundance ratios with effective temperature, indicating systematic differences in the surface abundances between turn-off and giant stars; these trends are more pronounced when LTE is assumed. However, trends with effective temperature remain significant for Al and Si also in non-LTE. Finally, we compare the derived abundances with prediction from stellar evolution models including effects of atomic diffusion. We find overall good agreement for the abundance patterns of dwarfs and sub-giant stars, but the abundances of cool giants are lower relative to less evolved stars than predicted by the diffusion models, in particular for Mg.
TL;DR: In this article, the authors measured the vertical density and abundance profiles of the chemically and kinematically defined ''thick'' and ''thin'' discs of the Galaxy using data from the GALAH pilot survey.
Abstract: Using data from the GALAH pilot survey, we determine properties of the Galactic thin and thick discs near the solar neighbourhood. The data cover a small range of Galactocentric radius (7.9 ≲ R_GC ≲ 9.5 kpc), but extend up to 4 kpc in height from the Galactic plane, and several kpc in the direction of Galactic anti-rotation (at longitude 260° ≤ l ≤ 280°). This allows us to reliably measure the vertical density and abundance profiles of the chemically and kinematically defined `thick' and `thin' discs of the Galaxy. The thin disc (low-α population) exhibits a steep negative vertical metallicity gradient, at d[M/H]/dz = -0.18 ± 0.01 dex kpc-1, which is broadly consistent with previous studies. In contrast, its vertical α-abundance profile is almost flat, with a gradient of d[α/M]/dz = 0.008 ± 0.002 dex kpc-1. The steep vertical metallicity gradient of the low-α population is in agreement with models where radial migration has a major role in the evolution of the thin disc. The thick disc (high-α population) has a weaker vertical metallicity gradient d[M/H]/dz = -0.058 ± 0.003 dex kpc-1. The α-abundance of the thick disc is nearly constant with height, d[α/M]/dz = 0.007 ± 0.002 dex kpc-1. The negative gradient in metallicity and the small gradient in [α/M] indicate that the high-α population experienced a settling phase, but also formed prior to the onset of major Type Ia supernova enrichment. We explore the implications of the distinct α-enrichments and narrow [α/M] range of the sub- populations in the context of thick disc formation.
TL;DR: In this article, the authors present the first study of spatially-resolved stellar kinematics and global stellar populations in a large IFS galaxy survey, and find a strong correlation of stellar population age with location in the ($V / \sigma$, $\epsilon_{\rm{e}}$) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity.
Abstract: Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics trace the change in angular momentum and orbital distribution of stars due to mergers, but major mergers tend to obscure the effect of earlier interactions. With the rise of large multi-object integral field spectroscopic (IFS) surveys, such as SAMI and MaNGA, and single-object IFS surveys (e.g., ATLAS$^{\rm{3D}}$, CALIFA, MASSIVE), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, and across the full range of optical morphology and environment. Using the SAMI Galaxy Survey, here we present the first study of spatially-resolved stellar kinematics and global stellar populations in a large IFS galaxy survey. We find a strong correlation of stellar population age with location in the ($V / \sigma$, $\epsilon_{\rm{e}}$) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well. This trend is still observed when galaxies are separated into early-type and late-type samples.
University of Sydney1, Australian National University2, Max Planck Society3, University of Ljubljana4, Australian Astronomical Observatory5, Uppsala University6, University of New South Wales7, Aarhus University8, University of Virginia9, INAF10, University of Southern Queensland11, University of Western Australia12, Johns Hopkins University13
TL;DR: In this article, the authors explore t-distributed stochastic neighbor embedding (t-SNE) which identifies an optimal mapping of a high-dimensional space into fewer dimensions.
Abstract: The technique of chemical tagging uses the elemental abundances of stellar atmospheres to 'reconstruct' chemically homogeneous star clusters that have long since dispersed. The GALAH spectroscopic survey - which aims to observe one million stars using the Anglo- Australian Telescope - allows us to measure up to 30 elements or dimensions in the stellar chemical abundance space, many of which are not independent. How to find clustering reliably in a noisy high-dimensional space is a difficult problem that remains largely unsolved. Here, we explore t-distributed stochastic neighbour embedding (t-SNE) - which identifies an optimal mapping of a high-dimensional space into fewer dimensions - whilst conserving the original clustering information. Typically, the projection is made to a 2D space to aid recognition of clusters by eye. We show that this method is a reliable tool for chemical tagging because it can: (i) resolve clustering in chemical space alone, (ii) recover known open and globular clusters with high efficiency and low contamination, and (iii) relate field stars to known clusters. t-SNE also provides a useful visualization of a high-dimensional space. We demonstrate the method on a data set of 13 abundances measured in the spectra of 187 000 stars by the GALAH survey. We recover seven of the nine observed clusters (six globular and three open clusters) in chemical space with minimal contamination from field stars and low numbers of outliers. With chemical tagging, we also identify two Pleiades supercluster members (which we confirm kinematically), one as far as 6° - one tidal radius away from the cluster centre. (Less)
University of Rochester1, University of Sydney2, Australian Astronomical Observatory3, Australian Research Council4, Australian National University5, University of California, Berkeley6, Max Planck Society7, Uppsala University8, University of New South Wales9, Macquarie University10, University of Ljubljana11, University of Virginia12, University of Canterbury13, Monash University, Clayton campus14, University of Western Australia15, University of Southern Queensland16, Johns Hopkins University17, Princeton University18, Institute for Advanced Study19, Carnegie Institution for Science20
TL;DR: In this paper, the authors used GALAH (GALactic Archaeology with HERMES) survey data of nearby stars to investigate how structure in the planar (u, v) velocity distribution depends on metallicity and on viewing direction within the Galaxy.
Abstract: Using GALAH (GALactic Archaeology with HERMES) survey data of nearby stars, we look at how structure in the planar (u, v) velocity distribution depends on metallicity and on viewing direction within the Galaxy. In nearby stars with distance d ≲ 1 kpc, the Hercules stream is most strongly seen in higher metallicity stars [Fe/H] > 0.2. The Hercules stream peak v value depends on viewed galactic longitude, which we interpret as due to the gap between the stellar stream and more circular orbits being associated with a specific angular momentum value of about 1640 km s-1 kpc. The association of the gap with a particular angular momentum value supports a bar resonant model for the Hercules stream. Moving groups previously identified in Hipparcos(HIgh Precision Parallax COllecting Satellite) observations are easiest to see in stars nearer than 250 pc, and their visibility and peak velocities in the velocity distributions depends on both viewing direction (galactic longitude and hemisphere) and metallicity. We infer that there is fine structure in local velocity distributions that varies over distances of a few hundred pc in the Galaxy.
University of New South Wales1, University of Sydney2, Aarhus University3, Max Planck Society4, Australian National University5, Uppsala University6, University of Ljubljana7, University of Southern Queensland8, University of California, Riverside9, Monash University10, Australian Astronomical Observatory11, University of Padua12, Macquarie University13, University of Virginia14, University of Western Australia15, Academia Sinica16
TL;DR: The K2-HERMES project as mentioned in this paper uses the HERMES multi-object spectrograph on the Anglo-Australian Telescope to obtain R ∼ 28000 spectra of up to 360 stars in one exposure.
Abstract: Accurate and precise radius estimates of transiting exoplanets are critical for understanding their compositions and formation mechanisms. To know the planet, we must know the host star in as much detail as possible. We present first results from the K2-HERMES project, which uses the HERMES multi-object spectrograph on the Anglo-Australian Telescope to obtain R ∼ 28000 spectra of up to 360 stars in one exposure. This ongoing project aims to derive self-consistent spectroscopic parameters for about half of K2 target stars. We present complete stellar parameters and isochrone-derived masses and radii for 46 stars hosting 57 K2 candidate planets in Campaigns 1-3. Our revised host-star radii cast severe doubt on three candidate planets: EPIC 201407812.01, EPIC 203070421.01, and EPIC 202843107.01, all of which now have inferred radii well in excess of the largest known inflated Jovian planets.
TL;DR: In this paper, the authors examine the evolution of clouds in light of recent claims that they may trigger condensation of gas from the Galactic corona as they move through it, and find that 3D simulations are essential to correctly capture the condensation in all cases.
Abstract: The Galactic halo contains a complex ecosystem of multiphase intermediate-velocity and high-velocity gas clouds whose origin has defied clear explanation. They are generally believed to be involved in a Galaxy-wide recycling process, either through an accretion flow or a large-scale fountain flow, or both. We examine the evolution of these clouds in light of recent claims that they may trigger condensation of gas from the Galactic corona as they move through it. We measure condensation along a cloud's wake, with and without the presence of an ambient magnetic field, using two- (2D) and three-dimensional (3D), high-resolution simulations. We find that 3D simulations are essential to correctly capture the condensation in all cases. Magnetic fields significantly inhibit condensation in the wake of clouds at $t \gtrsim 25$ Myr, preventing the sharp upturn in cold gas mass seen in previous non-magnetic studies. The magnetic field suppresses the Kelvin-Helmholtz instability responsible for the ablation and consequent mixing of a cloud with halo gas which drives the condensation. This effect is universal across different cloud properties (density, metallicity, velocity) and magnetic field properties (strength and orientation). Simple convergence tests demonstrate that resolving the gas on progressively smaller scales leads to even less condensation. While condensation still occurs in all cases, our results show that an ambient magnetic field drastically lowers the efficiency of fountain-driven accretion and likely also accretion from condensation around high-velocity clouds. These lower specific accretion rates are in better agreement with observational constraints compared to 3D, non-magnetic simulations.
TL;DR: In this article, the authors revisited recent simulations of the stellar and dark matter components of the Sagittarius dwarf galaxy and concluded that the vast majority of the stripped gas was fully settled onto the Galaxy by ~300 Myr ago.
Abstract: The remarkable 1994 discovery of the Sagittarius dwarf galaxy (Sgr) revealed that, together with the Magellanic Clouds (MCs), there are at least three major dwarf galaxies, each with a total mass of order 10^10 - 10^11 solar masses, falling onto the Galaxy in the present epoch. Beyond a Galactic radius of 300 kpc, dwarfs tend to retain their gas. At roughly 50 kpc, the MCs have experienced substantial gas stripping as evidenced by the Magellanic Stream which extends from them. Since Sgr experienced star formation long after it fell into the Galaxy, it is interesting to explore just how and when this dwarf lost its gas. To date, there has been no definitive detection of an associated gas component. We revisit recent simulations of the stellar and dark matter components of Sgr but, for the first time, include gas that is initially bound to the infalling galaxy. We find that the gas stripping was 30 - 50 % complete at its first disc crossing ~2.7 Gyr ago, then entirely stripped at its last disc crossing ~1 Gyr ago. Our timeline is consistent with the last substantial burst of star formation in Sgr which occurred about the time of the last disc crossing. We discuss the consequences of gas stripping and conclude that the vast majority of the stripped gas was fully settled onto the Galaxy by ~300 Myr ago. It is highly unlikely that any of the high- or intermediate-velocity clouds have a direct association with the Sgr dwarf.
University of Sydney1, Macquarie University2, Max Planck Society3, Australian National University4, Uppsala University5, University of New South Wales6, University of Ljubljana7, Aarhus University8, University of Southern Queensland9, Carnegie Institution for Science10, Princeton University11, Institute for Advanced Study12
TL;DR: In this article, the authors combined spectral parameters from the GALAH survey with the Gaia DR2 catalogue to study the dynamics and chemistry of five old sparse high-latitude clusters in more detail.
Abstract: Sparse open clusters can be found at high galactic latitudes where loosely populated clusters are more easily detected against the lower stellar background. Because most star formation takes place in the thin disc, the observed population of clusters far from the Galactic plane is hard to explain. We combined spectral parameters from the GALAH survey with the Gaia DR2 catalogue to study the dynamics and chemistry of five old sparse high-latitude clusters in more detail. We find that four of them (NGC 1252, NGC 6994, NGC 7772, NGC 7826) - originally classified in 1888-are not clusters but are instead chance projections on the sky. Member stars quoted in the literature for these four clusters are unrelated in our multidimensional physical parameter space; the quoted cluster properties in the literature are therefore meaningless. We confirm the existence of visually similar NGC 1901 for which we provide a probabilistic membership analysis. An overdensity in three spatial dimensions proves to be enough to reliably detect sparse clusters, but the whole six-dimensional space must be used to identify members with high confidence, as demonstrated in the case of NGC 1901. (Less)
University of Washington1, Joint Institute for Nuclear Astrophysics2, University of Notre Dame3, University of Michigan4, Massachusetts Institute of Technology5, Carnegie Institution for Science6, University of Texas at Austin7, University of Oklahoma8, University of Victoria9, Leibniz Institute for Astrophysics Potsdam10, Johns Hopkins University11, University of Sydney12, Australian National University13, University of Hull14, Heidelberg University15, Centre national de la recherche scientifique16, Saint Martin's University17, Macquarie University18, University College London19, Department of Industry20
TL;DR: The detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance as discussed by the authors, were identified as metalpoor candidates from the RAdial Velocity Experiment (RAVE) and were followed-up at high spectral resolution with the 3.5m telescope at Apache Point Observatory.
Abstract: This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed-up at high spectral resolution (R~31,500) with the 3.5~m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from Fe I lines, taking into account non-LTE corrections and using differential abundances with respect to a set of standards. Of the 126 new stars, 124 have [Fe/H] +1.0). Nineteen stars are found to exhibit a `limited-r' signature ([Sr/Ba]>+0.5, [Ba/Eu]<0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, alpha, and Fe-peak elements match those of typical Milky Way halo stars, except for one r-I star which has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars which are consistent with membership in the Milky Way halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
TL;DR: In this paper, a novel approach is developed for measuring small losses in highly transparent Si3N4/SiO 2 waveguides on a silicon chip by measuring the transmission of an optical cavity formed by two highly reflective Bragg gratings and a uniform waveguide between the two gratings whose length can be varied to increase the loss fitting accuracy.
Abstract: A novel approach is developed for measuring small losses in highly transparent Si3N4/SiO 2 waveguides on a silicon chip. The approach is particularly applicable to waveguides written by high-resolution patterning techniques, such as e-beam lithography, whose lengths cannot be easily increased beyond several centimeters. This method is based on measuring the transmission of an optical cavity formed by two highly reflective ( R at least 0.999) simple Bragg gratings and a uniform waveguide between the two gratings whose length can be varied to increase the loss fitting accuracy. A theoretical model based on an ABCD matrix method is developed and used for the final loss value fitting. Experimentally, a cavity with extinction ratio over –70 dB and quality factor Q = 1.02×106 is realized. The fitting results show a waveguide loss of 0.24 ± 0.01 dB/cm and a grating loss of 0.31 ± 0.01 dB/cm. These results are obtained with relatively high index contrast ( Δn > 0.001) gratings with 0.1-pm wavelength scanning resolution. It is expected that with better design and wavelength scanning technique, this approach is applicable more generally to measure waveguide loss coefficients as low as 0.001 dB/cm.
TL;DR: In this paper, the authors used UV absorption-line spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to probe the southern Fermi Bubble using a sample of 17 background AGN projected behind or near the bubble.
Abstract: The Fermi Bubbles are two giant gamma-ray emitting lobes extending 55$^{\circ}$ above and below the Galactic Center. While the Northern Bubble has been extensively studied in ultraviolet (UV) absorption, little is known about the gas kinematics of the southern Bubble. We use UV absorption-line spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to probe the southern Fermi Bubble using a sample of 17 background AGN projected behind or near the Bubble. We measure the incidence of high-velocity clouds (HVC), finding that four out of six sightlines passing through the Bubble show HVC absorption, versus six out of eleven passing outside. We find strong evidence that the maximum absolute LSR velocity of the HVC components decreases as a function of galactic latitude within the Bubble, for both blueshifted and redshifted components, as expected for a decelerating outflow. We explore whether the column-density ratios SiIV/SiIII, SiIV/SiII and SiIII/SiII correlate with the absolute galactic latitude within the Bubble. These results demonstrate the use of UV absorption-line spectroscopy to characterize the kinematics and ionization conditions of embedded clouds in the Galactic Center outflow.