Chemodynamical evolution of the Milky Way disk - I. The solar vicinity
TL;DR: In this paper, the authors present a new approach for studying the chemo-dynamical evolution in disk galaxies, which consists of fusing disk chemical evolution models with compatible numerical simulations of galactic disks.
Abstract: In the first paper of this series, we present a new approach for studying the chemo-dynamical evolution in disk galaxies, which consists of fusing disk chemical evolution models with compatible numerical simulations of galactic disks. This method avoids known star formation and chemical enrichment problems encountered in simulations. Here we focus on the Milky Way, by using a detailed thin-disk chemical evolution model (matching local observables, which are weakly affected by radial migration) and a simulation in the cosmological context, with dynamical properties close to those of our Galaxy. We examine in detail the interplay between in situ chemical enrichment and radial migration and their impact on key observables in the solar neighborhood, e.g., the age-metallicity-velocity relation, the metallicity distribution, and gradients in the radial and vertical directions. We show that, due to radial migration from mergers at high redshift and the central bar at later times, a sizable fraction of old metal-poor high-[α /Fe] stars can reach the solar vicinity. This naturally accounts for a number of recent observations related to both the thin and thick disks, despite the fact that we use thin-disk chemistry only. Although significant radial mixing is present, the slope in the age-metallicity relation is only weakly affected, with a scatter compatible with recent observational work. While we find a smooth density distribution in the [O/Fe]–[Fe/H] plane, we can recover the observed discontinuity by selecting particles according to kinematic criteria used in high-resolution samples to define the thin and thick disks. We outline a new method for estimating the birth place of the Sun and predict that the most likely radius lies in the range 4.4 = 8 kpc). A new, unifying model for the Milky Way thick disk is offered, where both mergers and radial migration play a role at different stages of the disk evolution. We show that in the absence of early-on massive mergers the vertical velocity dispersion of the oldest stars is underestimated by a factor of ~2 compared with observations. We can, therefore, argue that the Milky Way thick disk is unlikely to have been formed through a quiescent disk evolution. An observational test involving both chemical and kinematic information must be devised to ascertain this possibility.
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University of Virginia1, Liverpool John Moores University2, Texas Christian University3, University of La Laguna4, Spanish National Research Council5, Johns Hopkins University6, Sternberg Astronomical Institute7, New Mexico State University8, University of Arizona9, Ohio State University10, Pennsylvania State University11, University of Wisconsin-Madison12, Eötvös Loránd University13, University of Toronto14, University of Michigan15, University of Texas at Austin16, Leibniz Institute for Astrophysics Potsdam17, Yale University18, University of Colorado Boulder19, New York University20, Princeton University21, University of Utah22, Goddard Space Flight Center23, University of Birmingham24, Aarhus University25, Harvard University26, Space Telescope Science Institute27, Computer Sciences Corporation28, Paris Diderot University29, INAF30, Max Planck Society31, Space Science Institute32, Pierre-and-Marie-Curie University33, University of Franche-Comté34, Federal University of Rio de Janeiro35, University of Nice Sophia Antipolis36
TL;DR: In this article, the Hungarian National Research, Development and Innovation Office (K-119517) and Hungarian National Science Foundation (KNFI) have proposed a method to detect the presence of asteroids in Earth's magnetic field.
Abstract: National Science Foundation [AST-1109178, AST-1616636]; Gemini Observatory; Spanish Ministry of Economy and Competitiveness [AYA-2011-27754]; NASA [NNX12AE17G]; Hungarian Academy of Sciences; Hungarian NKFI of the Hungarian National Research, Development and Innovation Office [K-119517]; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science
1,193 citations
University of Sydney1, Australian Astronomical Observatory2, Australian National University3, University of New South Wales4, Macquarie University5, University of Ljubljana6, University of Southern Queensland7, Max Planck Society8, Monash University9, University of Cambridge10, INAF11, Joint Institute for Nuclear Astrophysics12, University of Minnesota13, University of Western Australia14, Uppsala University15, Harvard University16
TL;DR: The Galactic Archaeology with HERMES (GALAH) survey is a large high-resolution spectroscopic survey using the newly commissioned High Efficiency and Resolution Multi-element Spectrograph (HERMES) on the Anglo-Australian Telescope as discussed by the authors.
Abstract: The Galactic Archaeology with HERMES (GALAH) survey is a large high-resolution spectroscopic survey using the newly commissioned High Efficiency and Resolution Multi-Element Spectrograph (HERMES) on the Anglo-Australian Telescope. The HERMES spectrograph provides high-resolution (R ~ 28 000) spectra in four passbands for 392 stars simultaneously over a 2 deg field of view. The goal of the survey is to unravel the formation and evolutionary history of the Milky Way, using fossil remnants of ancient star formation events which have been disrupted and are now dispersed throughout the Galaxy. Chemical tagging seeks to identify such dispersed remnants solely from their common and unique chemical signatures; these groups are unidentifiable from their spatial, photometric or kinematic properties. To carry out chemical tagging, the GALAH survey will acquire spectra for a million stars down to V ~ 14. The HERMES spectra of FGK stars contain absorption lines from 29 elements including light proton-capture elements, α-elements, odd-Z elements, iron-peak elements and n-capture elements from the light and heavy s-process and the r-process. This paper describes the motivation and planned execution of the GALAH survey, and presents some results on the first-light performance of HERMES.
630 citations
New Mexico State University1, Princeton University2, University of Michigan3, Vanderbilt University4, Ohio State University5, University of Pittsburgh6, University of Virginia7, Spanish National Research Council8, University of La Laguna9, Joint Institute for Nuclear Astrophysics10, Leibniz Institute for Astrophysics Potsdam11, Texas Christian University12, INAF13, Case Western Reserve University14, Pennsylvania State University15, Eötvös Loránd University16, University of Franche-Comté17, Liverpool John Moores University18, University of Nice Sophia Antipolis19, University of Texas at Austin20, Johns Hopkins University21
TL;DR: In this paper, the authors measured the distribution of stars in the [/Fe] versus [Fe/H] plane and the metallicity distribution functions (MDFs) across an unprecedented volume of the Milky Way disk, with radius 3 < R < 15 kpc and height kpc.
Abstract: Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [/Fe] versus [Fe/H] plane and the metallicity distribution functions (MDFs) across an unprecedented volume of the Milky Way disk, with radius 3 < R < 15 kpc and height kpc. Stars in the inner disk (R < 5 kpc) lie along a single track in [/Fe] versus [Fe/H], starting with -enhanced, metal-poor stars and ending at [/Fe] ∼ 0 and [Fe/H] ∼ +0.4. At larger radii we find two distinct sequences in [/Fe] versus [Fe/H] space, with a roughly solar- sequence that spans a decade in metallicity and a high- sequence that merges with the low- sequence at super-solar [Fe/H]. The location of the high- sequence is nearly constant across the disk.
573 citations
Cites background from "Chemodynamical evolution of the Mil..."
...In the future, we plan to do a more detailed comparison between APOGEE observations and the simulation from 11 Minchev et al. (2013), in which the selection function is taken into account....
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...The fraction of stars that undergo radial migration is difficult to predict from first principles because it depends in detail on spiral structure, bar perturbations, and perturbations by and mergers with satellites (e.g., Roškar et al. (2008); Bird et al. (2012, 2013); Minchev et al. (2013))....
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...…models of the chemical and kinematical evolution of the Milky Way have become increasingly sophisticated (e.g., Hou et al. 2000; Chiappini et al. 2001; Schönrich & Binney 2009; Kubryk et al. 2013; Minchev et al. 2013) and attempt to explain both the chemical and dynamical history of the Galaxy....
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...…Minchev et al. (2013) match many observed properties of the disk, such as the stellar distribution in the [α/Fe] vs. [Fe/H] plane (see Figure 12 of Minchev et al. 2013), and the flattening of the radial gradient with height (e.g., Anders et al. 2014; Hayden et al. 2014, see Figure 10 of Minchev…...
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...Recent simulations by Minchev et al. (2013) match many observed properties of the disk, such as the stellar distribution in the [α/Fe] vs. [Fe/H] plane (see Figure 12 of Minchev et al. 2013), and the flattening of the radial gradient with height (e.g., Anders et al. 2014; Hayden et al. 2014, see…...
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TL;DR: In this article, the authors analyzed a sample of solar neighborhood stars that have high-quality abundance determinations and showed that there are two distinct regimes of [α/Fe] versus age, which they identify as the epochs of the thick and thin disk formation.
Abstract: We analyze a sample of solar neighborhood stars that have high-quality abundance determinations and show that there are two distinct regimes of [α/Fe] versus age, which we identify as the epochs of the thick and thin disk formation. A tight correlation between metallicity and [α/Fe] versus age is clearly identifiable for thick disk stars, implying that this population formed from a well mixed interstellar medium, probably initially in starburst and then more quiescently, over a time scale of 4−5 Gyr. Thick disk stars have vertical velocity dispersions which correlate with age, with the youngest objects of this population having small scale heights similar to those of thin disk stars. A natural consequence of these two results is that a vertical metallicity gradient is expected in this population. We suggest that the youngest thick disk set the initial conditions from which the inner thin disk started to form about 8 Gyr ago, at [Fe/H] in the range of (−0.1, +0.1) dex and [α/Fe] ∼ 0.1 dex. This also provides an explanation for the apparent coincidence between the existence of a step in metallicity at 7−10 kpc in the thin disk and the confinement of the thick disk within R < 10 kpc. We suggest that the outer thin disk developed outside the influence of the thick disk, giving rise to a separate structure, but also that the high alphaenrichment of those regions may originate from a primordial pollution of the outer regions by the gas expelled from the forming thick disk. Metal-poor thin disk stars ([Fe/H] < −0.4 dex) in the solar vicinity, whose properties are best explained by them originating in the outer disk, are shown to be as old as the youngest thick disk (9−10 Gyr). This implies that the outer thin disk started to form while the thick disk was still forming stars in the inner parts of the Galaxy. Hence, while the overall inner (thick+thin) disk is comprised of two structures with different scale lengths and whose combination may give the impression of an inside-out formation process, the thin disk itself probably formed its first stars in its outskirts. Moreover, we point out that, given the tight age−metallicity and age–[α/Fe] relations that exist in the thick disk, an inside-out process would give rise to a radial gradient in metallicity and α-elements in this population, which is not observed. Finally, we argue that our results leave little room for radial migration (in the sense of churning) either to have contaminated the solar vicinity, or, on a larger scale, to have redistributed stars in significant proportion across the solar annulus.
511 citations
Cites background from "Chemodynamical evolution of the Mil..."
...…have often claimed that radial migration is a fundamental mechanism in driving the evolution of a thick disk because, in these models, thick disk stars within the solar neighborhood are found with a variety of formation radii, frequently smaller than 4 kpc (Brook et al. 2012; Minchev et al. 2013)....
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...Moreover, if the α-enriched population had an initial gradient that was subsequently erased, we should find a significant increase of the metallicity dispersion with age (Minchev et al. 2013), especially at ages greater than 8 Gyr, which is not observed....
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...The possibility that the thick disk is the result of secular processes instead of more violent ones has been extensively debated in the last couple of years (Schönrich & Binney 2009b; Loebman et al. 2011; Minchev et al. 2013)....
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TL;DR: In this paper, the authors measured the distribution of stars in the [$α$/Fe] vs [Fe/H] plane and the metallicity distribution functions (MDF) across an unprecedented volume of the Milky Way disk, with radius $3 11$ kpc.
Abstract: Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [$\alpha$/Fe] vs [Fe/H] plane and the metallicity distribution functions (MDF) across an unprecedented volume of the Milky Way disk, with radius $3 11$ kpc The peak of the midplane MDF shifts to lower metallicity at larger $R$, reflecting the Galactic metallicity gradient Most strikingly, the shape of the midplane MDF changes systematically with radius, with a negatively skewed distribution at $3 1$ kpc or [$\alpha$/Fe]$>018$, the MDF shows little dependence on $R$ The positive skewness of the outer disk MDF may be a signature of radial migration; we show that blurring of stellar populations by orbital eccentricities is not enough to explain the reversal of MDF shape but a simple model of radial migration can do so
503 citations
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TL;DR: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System as discussed by the authors, and it is an essential refer...
Abstract: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...
8,605 citations
31 Dec 2008
4,447 citations
"Chemodynamical evolution of the Mil..." refers methods in this paper
...1, where we have corrected for asymmetric drift as described in, e.g., Binney and Tremaine (2008)....
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TL;DR: In this paper, the nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 M{sub {circle_dot}} and metals Z = 0, 10{sup {minus}4}, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for non-solar metallicities).
Abstract: The nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 M{sub {circle_dot}} and metallicities Z = 0, 10{sup {minus}4}, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for non-solar metallicities). Altogether 78 different model supernova explosions are calculated. In each case nucleosynthesis has already been determined for 200 isotopes in each of 600 to 1200 zones of the presupernova star, including the effects of time dependent convection. Here each star is exploded using a piston to give a specified final kinetic energy at infinity (typically 1.2 {times} 10{sup 51} erg), and the explosive modifications to the nucleosynthesis, including the effects of neutrino irradiation, determined. A single value of the critical {sup 12}C({sub {alpha},{gamma}}){sup 16}O reaction rate corresponding to S(300 keV) = 170 keV barns is used in all calculations. The synthesis of each isotope is discussed along with its sensitivity to model parameters. In each case, the final mass of the collapsed remnant is also determined and often found not to correspond to the location of the pistonmore » (typically the edge of the iron core), but to a ``mass cut`` farther out. This mass cut is sensitive not only to the explosion energy, but also to the presupernova structure, stellar mass, and the metallicity. Unless the explosion mechanism, for unknown reasons, provides a much larger characteristic energy in more massive stars, it appears likely that stars larger than about 30 M{sub {center_dot}} will experience considerable reimplosion of heavy elements following the initial launch of a successful shock. While such explosions will produce a viable, bright Type II supernova light curve, lacking the radioactive tail, they will have dramatically reduced yields of heavy elements and may leave black hole remnants of up to 10 and more solar masses.« less
3,649 citations
TL;DR: GALFIT as mentioned in this paper is a two-dimensional fitting algorithm designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope.
Abstract: We present a two-dimensional fitting algorithm (GALFIT) designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope. Our algorithm improves on previous techniques in two areas: by being able to simultaneously fit a galaxy with an arbitrary number of components and with optimization in computation speed, suited for working on large galaxy images. We use two-dimensional models such as the "Nuker" law, the Sersic (de Vaucouleurs) profile, an exponential disk, and Gaussian or Moffat functions. The azimuthal shapes are generalized ellipses that can fit disky and boxy components. Some potential applications of our program include: standard modeling of global galaxy profiles; extracting bars, stellar disks, double nuclei, and compact nuclear sources; and measuring absolute dust extinction or surface brightness fluctuations after removing the galaxy model. When examined in detail, we find that even simple looking galaxies generally require at least three components to be modeled accurately, rather than the one or two components more often employed. Many galaxies with complex isophotes, ellipticity changes, and position angle twists can be modeled accurately in two dimensions. We illustrate this by way of 11 case studies, which include regular and barred spiral galaxies, highly disky lenticular galaxies, and elliptical galaxies displaying various levels of complexities. A useful extension of this algorithm is to accurately extract nuclear point sources in galaxies. We compare two-dimensional and one-dimensional extraction techniques on simulated images of galaxies having nuclear slopes with different degrees of cuspiness, and we then illustrate the application of the program to several examples of nearby galaxies with weak nuclei.
2,670 citations
TL;DR: GALFIT as mentioned in this paper is a 2D fitting algorithm to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope.
Abstract: We present a two-dimensional (2-D) fitting algorithm (GALFIT) designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope. Our algorithm improves on previous techniques in two areas, by being able to simultaneously fit a galaxy with an arbitrary number of components, and with optimization in computation speed, suited for working on large galaxy images. We use 2-D models such as the ``Nuker'' law, the Sersic (de Vaucouleurs) profile, an exponential disk, and Gaussian or Moffat functions. The azimuthal shapes are generalized ellipses that can fit disky and boxy components. Many galaxies with complex isophotes, ellipticity changes, and position-angle twists can be modeled accurately in 2-D. When examined in detail, we find that even simple-looking galaxies generally require at least three components to be modeled accurately, rather than the one or two components more often employed. We illustrate this by way of 7 case studies, which include regular and barred spiral galaxies, highly disky lenticular galaxies, and elliptical galaxies displaying various levels of complexities. A useful extension of this algorithm is to accurately extract nuclear point sources in galaxies. We compare 2-D and 1-D extraction techniques on simulated images of galaxies having nuclear slopes with different degrees of cuspiness, and we then illustrate the application of the program to several examples of nearby galaxies with weak nuclei.
1,726 citations
"Chemodynamical evolution of the Mil..." refers methods in this paper
...(ii) the bulge is relatively small, with a bulge-to-total ratio of ∼1/5 (as measured with GALFIT – Peng et al. 2002 – on a mock i-band image, see bottom panel of Fig....
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