scholarly journals Resolved Stellar Halos of M87 and NGC 5128: Metallicities from the Red-Giant Branch

2015 ◽  
Vol 11 (S317) ◽  
pp. 276-277
Author(s):  
Sarah A. Bird
Keyword(s):  
Distribution Function ◽  
Galactic Center ◽  
Elliptical Galaxies ◽  
Stellar Halo ◽  
Red Giant ◽  
Metallicity Distribution

AbstractWe have searched halo fields of two giant elliptical galaxies: M87, using HST images at 10 kpc from the galactic center, and NGC 5128 (Cen A), using VIMOS VLT images at 65 kpc from the center and archival HST data from 8 to 38 kpc from the center. We have resolved thousands of red-giant-branch (RGB) stars in these stellar halo fields using V and I filters, and, in addition, measured the metallicity using stellar isochrones. The metallicity distribution function (MDF) of the inner stellar halo of M87 is similar to that of NGC 5128's stellar halo.

scholarly journals Deriving the Metallicity Distribution Function of Galactic Systems

2003 ◽  
Vol 20 (2) ◽  
pp. 189-195 ◽  
Author(s):  
Yeshe Fenner ◽  
Brad K. Gibson
Keyword(s):  
Distribution Function ◽  
Star Formation ◽  
Chemical Evolution ◽  
Thin Disk ◽  
Star Formation History ◽  
Dual Phase ◽  
Formation History ◽  
Stellar Halo ◽  
Star Formation Histories ◽  
Metallicity Distribution

AbstractThe chemical evolution of the Milky Way is investigated using a dual-phase metal-enriched infall model in which primordial gas fuels the earliest epoch of star formation, followed by the ongoing formation of stars from newly accreted gas. The latest metallicity distribution of local K-dwarfs is reproduced by this model, which allows the Galactic thin disk to form from slightly metal-enriched gas with α-element enhancement. Our model predicts ages for the stellar halo and thin disk of 12.5 and 7.4 Gyr respectively, in agreement with empirically determined values. The model presented in this paper is compared with a similar dual-phase infall model from Chiappini et al. (2001). We discuss a degeneracy that enables both models to recover the K-dwarf metallicity distribution while yielding different star formation histories.The metallicity distribution function (MDF) of K-dwarfs is proposed to be more directly comparable to chemical evolution model results than the G-dwarf distribution because lower mass K-dwarfs are less susceptible to stellar evolutionary effects. The K-dwarf MDF should consequently be a better probe of star formation history and provide a stronger constraint to chemical evolution models than the widely used G-dwarf MDF. The corrections that should be applied to a G-dwarf MDF are quantified for the case of the outer halo of NGC 5128.

scholarly journals Cool stars in the Galactic center as seen by APOGEE

2020 ◽  
Vol 642 ◽  
pp. A81
Author(s):  
M. Schultheis ◽  
A. Rojas-Arriagada ◽  
K. Cunha ◽  
M. Zoccali ◽  
C. Chiappini ◽  
...  
Keyword(s):  
Distribution Function ◽  
Galactic Center ◽  
Rotation Velocity ◽  
Interstellar Extinction ◽  
Asymptotic Giant Branch ◽  
Stellar Disk ◽  
Agb Stars ◽  
Cool Star ◽  
Center Region ◽  
Metallicity Distribution

The Galactic center region, including the nuclear disk, has until recently been largely avoided in chemical census studies because of extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), allow the measurement of metallicities in the inner region of our Galaxy. Making use of the latest APOGEE data release (DR16), we are able for the first time to study cool Asymptotic Giant branch (AGB) stars and supergiants in this region. The stellar parameters of five known AGB stars and one supergiant star (VR 5-7) show that their location is well above the tip of the red giant branch. We studied metallicities of 157 M giants situated within 150 pc of the Galactic center from observations obtained by the APOGEE survey with reliable stellar parameters from the APOGEE pipeline making use of the cool star grid down to 3200 K. Distances, interstellar extinction values, and radial velocities were checked to confirm that these stars are indeed situated in the Galactic center region. We detect a clear bimodal structure in the metallicity distribution function, with a dominant metal-rich peak of [Fe/H] ∼ +0.3 dex and a metal-poor peak around {Fe/H] = −0.5 dex, which is 0.2 dex poorer than Baade’s Window. The α-elements Mg, Si, Ca, and O show a similar trend to the Galactic bulge. The metal-poor component is enhanced in the α-elements, suggesting that this population could be associated with the classical bulge and a fast formation scenario. We find a clear signature of a rotating nuclear stellar disk and a significant fraction of high-velocity stars with vgal >  300 km s−1; the metal-rich stars show a much higher rotation velocity (∼200 km s−1) with respect to the metal-poor stars (∼140 km s−1). The chemical abundances as well as the metallicity distribution function suggest that the nuclear stellar disk and the nuclear star cluster show distinct chemical signatures and might be formed differently.

scholarly journals The Metallicity Distribution of the Milky Way Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
M. Ness ◽  
K. Freeman
Keyword(s):  
Distribution Function ◽  
Milky Way ◽  
Vertical Gradient ◽  
The Galaxy ◽  
Stellar Halo ◽  
Different Populations ◽  
Formation And Evolution ◽  
The Mean ◽  
Inner Region ◽  
Metallicity Distribution

AbstractThe Galactic bulge of the Milky Way is made up of stars with a broad range of metallicity, –3.0 < [Fe/H] < 1 dex. The mean of the metallicity distribution function decreases as a function of height z from the plane and, more weakly, with galactic radius RGC. The most metal-rich stars in the inner Galaxy are concentrated to the plane and the more metal-poor stars are found predominantly further from the plane, with an overall vertical gradient in the mean of the metallicity distribution function of about − 0.45 dex kpc−1. This vertical gradient is believed to reflect the changing contribution with height of different populations in the innermost region of the Galaxy. The more metal-rich stars of the bulge are part of the boxy/peanut structure and comprise stars in orbits which trace out the underlying X-shape. There is still a lack of consensus on the origin of the metal-poor stars ([Fe/H] < −0.5) in the region of the bulge. Some studies attribute the more metal-poor stars of the bulge to the thick disk and stellar halo that are present in the inner region, and other studies propose that the metal-poor stars are a distinct ‘old spheroid’ bulge population. Understanding the origin of the populations that make up the metallicity distribution function of the bulge, and identifying if there is a unique bulge population which has formed separately from the disk and halo, has important consequences for identifying the relevant processes in the formation and evolution of the Milky Way.

A New Mass Modelling Trick

2006 ◽  
Vol 2 (S235) ◽  
pp. 88-89
Author(s):  
Dalia Chakrabarty
Keyword(s):  
Distribution Function ◽  
Velocity Dispersion ◽  
Type Systems ◽  
Elliptical Galaxies ◽  
Space Distribution ◽  
Early Type ◽  
Phase Space Distribution ◽  
Mass Distributions ◽  
Kinematic Information ◽  
System Geometry

The estimation of the distribution of the total (luminous and dark) mass in early type systems is hard! Even for the lucky few systems for which kinematic information is available, its implementation is mired in problems, given uncertainties about the assumptions that enter the calculations; the most critical of such assumptions involve considerations of the system geometry and the shape of its velocity ellipsoid. This work offers an independent means of getting to the mass distributions of early type galaxies, without relying directly on the phase space distribution function. The methodology is based upon the well established idea that in elliptical galaxies, the largest variations in normalised velocity dispersion profiles occur typically at R < 0.5Re (Re≡ half-light radius) and at R ≥ 2Re.

scholarly journals Weighing the stellar constituents of the galactic halo with APOGEE red giant stars

2020 ◽  
Vol 492 (3) ◽  
pp. 3631-3646 ◽  
Author(s):  
J Ted Mackereth ◽  
Jo Bovy
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Power Laws ◽  
Stellar Mass ◽  
Giant Star ◽  
Giant Stars ◽  
Stellar Halo ◽  
Tentative Evidence ◽  
History Of ◽  
Red Giant

ABSTRACT The stellar mass in the halo of the Milky Way is notoriously difficult to determine, owing to the paucity of its stars in the solar neighbourhood. With tentative evidence from Gaia that the nearby stellar halo is dominated by a massive accretion event – referred to as Gaia-Enceladus or Sausage – these constraints are now increasingly urgent. We measure the mass in kinematically selected mono-abundance populations (MAPs) of the stellar halo between −3 &lt; [Fe/H] &lt; −1 and 0.0 &lt; [Mg/Fe] &lt; 0.4 using red giant star counts from APOGEE DR14. We find that MAPs are well fit by single power laws on triaxial ellipsoidal surfaces, and we show that that the power-law slope α changes such that high [Mg/Fe] populations have α ∼ 4, whereas low [Mg/Fe] MAPs are more extended with shallow slopes, α ∼ 2. We estimate the total stellar mass to be $M_{*,\mathrm{tot}} = 1.3^{+0.3}_{-0.2}\times 10^{9}\ \mathrm{M_{\odot}}$, of which we estimate ${\sim}0.9^{+0.2}_{-0.1} \times 10^{9}\ \mathrm{M_{\odot}}$ to be accreted. We estimate that the mass of accreted stars with e &gt; 0.7 is M*,accreted, e &gt; 0.7 = 3 ± 1 (stat.) ± 1 (syst.) × 108 M⊙, or ${\sim}30{-}50{{\ \rm per\ cent}}$ of the accreted halo mass. If the majority of these stars are the progeny of a massive accreted dwarf, this places an upper limit on its stellar mass, and implies a halo mass for the progenitor of ∼1010.2 ± 0.2 M⊙. This constraint not only shows that the Gaia-Enceladus/Sausage progenitor may not be as massive as originally suggested, but that the majority of the Milky Way stellar halo was accreted. These measurements are an important step towards fully reconstructing the assembly history of the Milky Way.

Detect the density profile with LAMOST K giants

2017 ◽  
Vol 13 (S334) ◽  
pp. 387-388
Author(s):  
Yan Xu ◽  
Chao Liu
Keyword(s):  
Density Distribution ◽  
Power Law ◽  
Density Profile ◽  
Milky Way ◽  
Galactic Center ◽  
Fitting Method ◽  
Stellar Halo ◽  
Model Independent ◽  
Power Law Index ◽  
K Giants

AbstractThe density distribution of the Milky Way halo is detected with 5351 LAMOST DR3 metal poor K giants using a nonparametric method. The nonparametric fitting method is a model independent way to estimate the halo density distribution while to a large extent avoiding the influence of the halo substucture. We show that the K giants density profile can be fitted well by single power law. We found no indication of a break in the power law index. The powerlaw index n = 5.0−0.64+0.64. The data show that the stellar halo is flattened at smaller radii, and becomes more spherical farther from the Galactic center. The flattening q(r=15Kpc)is about0.64, q(20Kpc) is about 0.8, q(30Kpc) is about 0.96.

The Metallicity Distribution Function of Halo Dwarfs and Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 517-518
Author(s):  
J. B. Laird ◽  
M. P. Rupin ◽  
B. W. Carney ◽  
D. W. Latham ◽  
R. L. Kurucz
Keyword(s):  
Distribution Function ◽  
Simple Model ◽  
Chemical Evolution ◽  
Globular Clusters ◽  
Dwarf Stars ◽  
Metallicity Distribution

Metallicities have been determined for a chemically unbiased sample of field halo dwarf stars. Their metallicity distribution function is similar to the predictions of a simple model of chemical evolution, but somewhat different from that of globular clusters.

scholarly journals Distance to the nearby dwarf galaxy [TT2009] 25 in the NGC 891 group using the tip of the red giant branch

2019 ◽  
Vol 629 ◽  
pp. L2 ◽  
Author(s):  
Oliver Müller ◽  
Rodrigo Ibata ◽  
Marina Rejkuba ◽  
Lorenzo Posti
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Small Scale ◽  
Accurate Information ◽  
Standard Candle ◽  
Stellar Halo ◽  
Red Giant ◽  
Small Field Of View

Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.

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