scholarly journals Identification of an [α/Fe]—Enhanced Thick Disk Component in an Edge-on Milky Way Analog

2021 ◽  
Vol 913 (1) ◽  
pp. L11
Author(s):  
Nicholas Scott ◽  
Jesse van de Sande ◽  
Sanjib Sharma ◽  
Joss Bland-Hawthorn ◽  
Ken Freeman ◽  
...  
Keyword(s):  
2016 ◽  
Vol 771 ◽  
pp. 012032
Author(s):  
Dian Puspita Triani ◽  
M Ikbal Arifyanto
Keyword(s):  

2014 ◽  
Vol 789 (2) ◽  
pp. L30 ◽  
Author(s):  
Matthew D. Lehnert ◽  
Paola Di Matteo ◽  
Misha Haywood ◽  
Owain N. Snaith

2004 ◽  
Vol 217 ◽  
pp. 147-153
Author(s):  
B. D. Savage ◽  
B. P. Wakker ◽  
K. R. Sembach ◽  
P. Richter ◽  
M. Meade

We summarize the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study O VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo and beyond. Strong O VI absorption over the velocity range from −100 to 100 km s−1 reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T~3×105 K in the Milky Way thick disk/halo. The overall distribution of O VI can be described by a plane-parallel patchy absorbing layer with an average O VI mid-plane density of no(O VI) = 1.7×10−8 cm−3, an exponential scale height of ~2.3 kpc, and a ~0.25 dex excess of O VI in the northern Galactic polar region. Approximately 60 percent of the sky is covered by high velocity O VI with |vLSR|>100 km s−1. This high velocity O VI traces a variety of phenomena in and near the Milky Way including outflowing material from the Milky Way, tidal interactions with the Magellanic Clouds, accretion of gas onto the Milky Way, and warm/hot gas interactions in a highly extended (>70 kpc) Galactic corona or with hot intergalactic gas in the Local Group.


2014 ◽  
Vol 784 (2) ◽  
pp. L24 ◽  
Author(s):  
A. Curir ◽  
A. L. Serra ◽  
A. Spagna ◽  
M. G. Lattanzi ◽  
P. Re Fiorentin ◽  
...  

2020 ◽  
Vol 58 (1) ◽  
pp. 205-256 ◽  
Author(s):  
Amina Helmi

The advent of the second data release of the Gaia mission, in combination with data from large spectroscopic surveys, is revolutionizing our understanding of the Galaxy. Thanks to these transformational data sets and the knowledge accumulated thus far, a new, more mature picture of the evolution of the early Milky Way is currently emerging. ▪  Two of the traditional Galactic components, namely, the stellar halo and the thick disk, appear to be intimately linked: Stars with halo-like kinematics originate in similar proportions from a heated (thick) disk and from debris from a system named Gaia-Enceladus. Gaia-Enceladus was the last big merger event experienced by the Milky Way and was completed around 10 Gyr ago. The puffed-up stars now present in the halo as a consequence of the merger have thus exposed the existence of a disk component at z ∼ 1.8. This is likely related to the previously known metal-weak thick disk and may be traceable to metallicities [Fe/H] [Formula: see text] −4. As importantly, there is evidence that the merger with Gaia-Enceladus triggered star formation in the early Milky Way, plausibly leading to the appearance of the thick disk as we know it. ▪  Other merger events have been characterized better, and new ones have been uncovered. These include, for example, the Helmi streams, Sequoia, and Thamnos, which add to the list of those discovered in wide-field photometric surveys, such as the Sagittarius streams. Current knowledge of their progenitors’ properties, star formation, and chemical evolutionary histories is still incomplete. ▪  Debris from different objects shows different degrees of overlap in phase-space. This sometimes confusing situation can be improved by determining membership probabilities via quantitative statistical methods. A task for the next few years will be to use ongoing and planned spectroscopic surveys for chemical labeling and to disentangle events from one another using dimensions other than phase-space, metallicity, or [α/Fe]. ▪  These large surveys will also provide line-of-sight velocities missing for faint stars in Gaia releases and more accurate distance determinations for distant objects, which in combination with other surveys could also lead to more accurate age dating. The resulting samples of stars will cover a much wider volume of the Galaxy, allowing, for example, the linking of kinematic substructures found in the inner halo to spatial overdensities in the outer halo. ▪  All the results obtained so far are in line with the expectations of current cosmological models. Nonetheless, tailored hydrodynamical simulations to reproduce in detail the properties of the merger debris, as well as constrained cosmological simulations of the Milky Way, are needed. Such simulations will undoubtedly unravel more connections between the different Galactic components and their substructures, and will aid in pushing our knowledge of the assembly of the Milky Way to the earliest times.


1996 ◽  
Vol 169 ◽  
pp. 427-428
Author(s):  
Roland Buser ◽  
Jianxiang Rong

The metallicity-sensitive (U – G) colors from the new homogeneous catalog of photographic RGU data in seven high-latitude fields have been used to determine the larger-scale metallicity distributions of the Galactic population components. For the thick disk, preliminary analysis based on our best structural models provides a mean metallicity 〈[M/H]〉 = −0.6 ± 0.3dex and a marginal vertical metallicity gradient ≈ −0.1dex/kpc. The observed color distributions are further consistent with the (old) thin disk having mean abundance 〈[M/H]〉 = −0.3 ± 0.2dex and abundance gradient ∂[M/H]/∂z = −0.6dex/kpc.


2004 ◽  
Vol 21 (4) ◽  
pp. 371-374
Author(s):  
Geraint F. Lewis ◽  
Rodrigo A. Ibata ◽  
Michael J. Irwin ◽  
Nicolas F. Martin ◽  
Michele Bellazzini ◽  
...  

AbstractRecent observational evidence suggests that the Sagittarius dwarf galaxy represents the only major ongoing accretion event in the Galactic halo, accounting for the majority of stellar debris identified there. This paper summarises the recent discovery of another potential Milky Way accretion event, the Canis Major dwarf galaxy. This dwarf satellite galaxy is found to lie just below the Galactic plane and appears to be on an equatorial orbit. Unlike Sagittarius, which is contributing to the Galactic halo, the location and eventual demise of Canis Major suggests that it represents a building block of the thick disk.


Author(s):  
Francesca Matteucci

AbstractIn this review, I will discuss the comparison between model results and observational data for the Milky Way, the predictive power of such models as well as their limits. Such a comparison, known as Galactic archaeology, allows us to impose constraints on stellar nucleosynthesis and timescales of formation of the various Galactic components (halo, bulge, thick disk and thin disk).


2016 ◽  
Vol 11 (S321) ◽  
pp. 3-5
Author(s):  
Thomas Bensby

AbstractBased on observational data from the fourth internal data release of the Gaia-ESO Survey we probe the abundance structure in the Milky Way stellar disk as a function of galactocentric radius and height above the plane. We find that the inner and outer Galactic disks have different chemical signatures. The stars in the inner Galactic disk show abundance signatures of both the thin and thick disks, while the stars in the outer Galactic disk resemble in majority the abundances seen in the thin disk. Assuming that the Galactic thick disk can be associated with the α-enriched population, this can be interpreted as that the thick disk density drops drastically beyond a galactocentric radius of about 10 kpc. This is in agreement with recent findings that the thick disk has a short scale-length, shorter than that of the the thin disk.


2008 ◽  
Vol 4 (S255) ◽  
pp. 323-329
Author(s):  
Timothy C. Beers ◽  
Young Sun Lee ◽  
Daniela Carollo

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.


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