scholarly journals Studies of the Milky Way 1850–1930: some highlights

1985 ◽  
Vol 106 ◽  
pp. 43-58
Author(s):  
Robert W. Smith
Keyword(s):  
Milky Way ◽  
History Of Astronomy ◽  
Galactic System ◽  
Widespread Acceptance ◽  
The Galaxy ◽  
History Of ◽  
Entire History ◽  
Short Time ◽  
Time Form ◽  
Size And Structure

“The Copernicus of the sidereal system is not to be expected for many generations”. So wrote R.A. Proctor1 in his Essays in Astronomy in 1872. Indeed things did look bleak at this time for those who hoped for a good understanding of the size and structure of the Galaxy. Why was this so, and why was there to be such an astonishing transformation of this situation between 1918 and 1930? Certainly these twelve years saw the widespread acceptance of no less than six fundamentally new ways of viewing the Galactic System. These profound shifts, occurring in such a short time, form, I would suggest, one of the most exciting chapters in the entire history of astronomy. And in this paper I shall attempt to describe and analyze what these changes were, what led up to them, as well as to examine the events surrounding them.

scholarly journals Kinematical & Chemical Characteristics of the Thin and Thick Disks

2008 ◽  
Vol 4 (S254) ◽  
pp. 179-190 ◽  
Author(s):  
Rosemary F. G. Wyse
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Observational Evidence ◽  
Chemical Characteristics ◽  
Chemical Abundance ◽  
The Galaxy ◽  
History Of ◽  
Thin And Thick Disks ◽  
Thick Disks

AbstractI discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.

scholarly journals Relics of Primordial Star Formation: The Milky Way and Local Dwarfs

2008 ◽  
Vol 4 (S255) ◽  
pp. 323-329
Author(s):  
Timothy C. Beers ◽  
Young Sun Lee ◽  
Daniela Carollo
Keyword(s):  
Milky Way ◽  
Thick Disk ◽  
Structural Components ◽  
Halo Structure ◽  
Orbital Parameters ◽  
The Past ◽  
Element Ratios ◽  
Test Models ◽  
The Galaxy ◽  
History Of

AbstractMassive spectroscopic surveys of stars in the thick disk and halo populations of the Galaxy hold the potential to provide strong constraints on the processes involved in (and the timing of) the assembly history of the primary structural components of the Galaxy. In this talk, we explore what has been learned from one of the first such dedicated surveys, SDSS/SEGUE. Over the course of the past three years, SEGUE has obtained spectra for over 200,000 stars, while another hundred thousand stars been added from the calibration star observations of the (primarily extragalactic) SDSS, and other directed programs. A total of well over 10,000 stars with [Fe/H] < −2.0 have been discovered, including several hundred with [Fe/H] < −3.0. Their kinematics have revealed a inner/outer halo structure of the Galaxy.New determinations of the alpha element ratios for tens of thousands of these stars are reported. Correlations of the alpha-element ratios with kinematics and orbital parameters can be used to test models of the likely formation of the thick-disk and halo components. These new data will (eventually) be considered in connection with possible associations with the present dwarf satellite galaxies of the Milky Way.

scholarly journals The early merger that made the galaxy’s stellar halo

2019 ◽  
Vol 14 (S353) ◽  
pp. 113-120
Author(s):  
N. Wyn Evans
Keyword(s):  
Milky Way ◽  
Current Understanding ◽  
Proper Motions ◽  
Widespread Acceptance ◽  
Stellar Halo ◽  
History Of ◽  
Milky Way Halo

AbstractThe last two years have seen widespread acceptance of the idea that the Milky Way halo was largely created in an early (8-10 Gyr ago) and massive (>1010Mȯ) merger. The roots of this idea pre-date the Gaia mission, but the exquisite proper motions available from Gaia have made the hypothesis irresistible. We trace the history of this idea, reviewing the series of papers that led to our current understanding.

scholarly journals The Evolutionary History of the Milky Way

1996 ◽  
Vol 171 ◽  
pp. 3-10
Author(s):  
K.C. Freeman
Keyword(s):  
Evolutionary History ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Galactic Disk ◽  
Small Satellite ◽  
Galactic Bulge ◽  
The Galaxy ◽  
History Of ◽  
Satellite Galaxies

The accretion of small satellite galaxies appears to have been important in the formation of the metal-poor halo of the Galaxy. The disrupting Sgr dwarf galaxy and the recent discovery of a young, metal-poor component of the halo indicate that this is a continuing process. The evolution of the galactic disk, and some consequences of the bar-like nature of the galactic bulge are briefly discussed.

scholarly journals The tale of the Milky Way globular cluster NGC 6362 – I. The orbit and its possible extended star debris features as revealed by Gaia DR2

2019 ◽  
Vol 489 (4) ◽  
pp. 4565-4573
Author(s):  
Richa Kundu ◽  
José G Fernández-Trincado ◽  
Dante Minniti ◽  
Harinder P Singh ◽  
Edmundo Moreno ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Vertical Component ◽  
Galactic Disc ◽  
Corotation Radius ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
History Of ◽  
Event Based ◽  
Gaia Dr2

ABSTRACTWe report the identification of possible extended star debris candidates beyond the cluster tidal radius of NGC 6362 based on the second Gaia data release (Gaia DR2). We found 259 objects possibly associated with the cluster lying in the vicinity of the giant branch and 1–2 magnitudes fainter/brighter than the main-sequence turn-off in the cluster colour–magnitude diagram and which cover an area on the sky of ∼4.1 deg2 centred on the cluster. We traced back the orbit of NGC 6362 in a realistic Milky Way potential, using the gravpot16 package, for 3 Gyr. The orbit shows that the cluster shares similar orbital properties as the inner disc, having peri-/apogalactic distances, and maximum vertical excursion from the Galactic plane inside the corotation radius (CR), moving inwards from CR radius to visit the inner regions of the Milky Way. The dynamical history of the cluster reveals that it has crossed the Galactic disc several times in its lifetime and has recently undergone a gravitational shock, ∼15.9 Myr ago, suggesting that less than 0.1 per cent of its mass has been lost during the current disc-shocking event. Based on the cluster’s orbit and position in the Galaxy, we conclude that the possible extended star debris candidates are a combined effect of the shocks from the Galactic disc and evaporation from the cluster. Lastly, the evolution of the vertical component of the angular momentum shows that the cluster is strongly affected dynamically by the Galactic bar potential.

NIHAO-UHD: High-resolution Simulations of MW mass galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 209-212
Author(s):  
Tobias Buck ◽  
Andrea Macciò ◽  
Melissa Ness ◽  
Aura Obreja ◽  
Aaron Dutton
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Satellite System ◽  
The Galaxy ◽  
First Results ◽  
History Of ◽  
Galaxy Center ◽  
Hydrodynamical Simulations ◽  
Very High ◽  
Disc Galaxies

AbstractHigh resolution cosmological and hydrodynamical simulations have reached a resolution able to resolve in a self consistent way the disc of our galaxy, the galaxy center and the satellites orbiting around it. We present first results from the NIHAO-UHD project, a set of very high-resolution baryonic zoom-in simulations of Milky Way mass disc galaxies. These simulations model the full cosmological assembly history of the galaxies and their satellite system using the same, well tested physics as the NIHAO project. We show that these simulations can self-consistently reproduce the observed kinematical and morphological features of the X-shaped bulge observed in our own Milky Way.

scholarly journals Surveys for Metal-Poor Stars in the Galaxy: A New Window on the Low-Abundance Universe

1998 ◽  
Vol 11 (1) ◽  
pp. 58-61
Author(s):  
T.C. Beers
Keyword(s):  
Milky Way ◽  
High Signal ◽  
Signal To Noise ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
History Of ◽  
Chemical History ◽  
Low Metallicity ◽  
New Generation ◽  
The Universe

Measurement of the abundances of the light and heavy elements in stars of the Milky Way galaxy is the cornerstone for the study of numerous aspects of chemical evolution in galaxies and the Universe. We stand poised to enter an era of rapid understanding, as new-generation telescopes with apertures in the 8m-10m class enable astronomers to obtain high-resolution, high-signal-to-noise near-UV, optical, and IR spectra of the stars which have locked up the chemical history of our Galaxy in their outer atmospheres. It is thus appropriate to review present surveys for the low-metallicity stars of our Galaxy, as the stars we uncover today will be studied so intensively in the coming decades.

scholarly journals SDSS-IV MaNGA: the ‘G-dwarf problem’ revisited

2021 ◽  
Vol 502 (1) ◽  
pp. L95-L98
Author(s):  
Michael J Greener ◽  
Michael Merrifield ◽  
Alfonso Aragón-Salamanca ◽  
Thomas Peterken ◽  
Brett Andrews ◽  
...  
Keyword(s):  
Milky Way ◽  
High Mass ◽  
Dwarf Stars ◽  
The Galaxy ◽  
Star Formation In Galaxies ◽  
History Of ◽  
Low Metallicity ◽  
Low Mass ◽  
Gas Accretion ◽  
Made In

ABSTRACT The levels of heavy elements in stars are the product of enhancement by previous stellar generations, and the distribution of this metallicity among the population contains clues to the process by which a galaxy formed. Most famously, the ‘G-dwarf problem’ highlighted the small number of low-metallicity G-dwarf stars in the Milky Way, which is inconsistent with the simplest picture of a galaxy formed from a ‘closed box’ of gas. It can be resolved by treating the Galaxy as an open system that accretes gas throughout its life. This observation has classically only been made in the Milky Way, but the availability of high-quality spectral data from SDSS-IV MaNGA and the development of new analysis techniques mean that we can now make equivalent measurements for a large sample of spiral galaxies. Our analysis shows that high-mass spirals generically show a similar deficit of low-metallicity stars, implying that the Milky Way’s history of gas accretion is common. By contrast, low-mass spirals show little sign of a G-dwarf problem, presenting the metallicity distribution that would be expected if such systems evolved as pretty much closed boxes. This distinction can be understood from the differing timescales for star formation in galaxies of differing masses.

scholarly journals Chemodynamical properties of the Anticentre Stream: a surviving disc fossil from a past satellite interaction

2019 ◽  
Vol 492 (1) ◽  
pp. L61-L65 ◽  
Author(s):  
Chervin F P Laporte ◽  
Vasily Belokurov ◽  
Sergey E Koposov ◽  
Martin C Smith ◽  
Vanessa Hill
Keyword(s):  
Milky Way ◽  
Stellar Populations ◽  
Galactic Disc ◽  
Chemical Enrichment ◽  
Tidal Tail ◽  
Data Release ◽  
The Galaxy ◽  
History Of

ABSTRACT Using Gaia second data release (DR2), we trace the Anticentre Stream (ACS) in various stellar populations across the sky and find that it is kinematically and spatially decoupled from the Monoceros Ring. Using stars from lamost and segue, we show that the ACS is systematically more metal-poor than Monoceros by 0.1 dex with indications of a narrower metallicity spread. Furthermore, the ACS is predominantly populated of old stars ($\sim 10\, \rm {Gyr}$), whereas Monoceros has a pronounced tail of younger stars ($6-10\, \rm {Gyr}$) as revealed by their cumulative age distributions. Put together, all of this evidence support predictions from simulations of the interaction of the Sagittarius dwarf with the Milky Way, which argue that the ACS is the remains of a tidal tail of the Galaxy excited during Sgr’s first pericentric passage after it crossed the virial radius, whereas Monoceros consists of the composite stellar populations excited during the more extended phases of the interaction. Importantly, the ACS can be viewed as a stand-alone fossil of the chemical enrichment history of the Galactic disc.

Monitoring a methanol maser flare associated with the massive star-forming region G358.93–0.03

2020 ◽  
Vol 494 (1) ◽  
pp. L59-L63
Author(s):  
A E Volvach ◽  
L N Volvach ◽  
M G Larionov ◽  
G C MacLeod ◽  
S P van den Heever ◽  
...  
Keyword(s):  
Massive Star ◽  
Star Forming ◽  
Methanol Maser ◽  
The Galaxy ◽  
History Of ◽  
Entire History ◽  
Methanol Masers

ABSTRACT We report the earliest detection of the 19.967-GHz [transition 21–30E (t = 0)] methanol maser associated with the massive star-forming region G358.93–0.03. The flare was detectable from 2019 January 23 to March 5, for only 44 d. It turned out to be the most powerful 19.967-GHz maser in the Galaxy in the entire history of observations, taking into account the 104-Jy flux from it on the Earth’s surface and the distance to the source, 6.75 kpc. The 19.967-GHz maser flared contemporaneously with the first of two flares detected in associated 20.971-GHz methanol masers. We estimated that the ratio of flux densities between these two transitions is F20.971/F19.967 = 14 ± 4, increasing to &gt;520 in the second flare. We discuss the differences between the two flares in the 20.971-GHz methanol masers and the consequence thereof.

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