scholarly journals The total stellar halo mass of the Milky Way

2019 ◽  
Vol 490 (3) ◽  
pp. 3426-3439 ◽  
Author(s):  
Alis J Deason ◽  
Vasily Belokurov ◽  
Jason L Sanders
Keyword(s):  
Density Profile ◽  
Galactic Halo ◽  
Mass Function ◽  
Initial Mass Function ◽  
Total Luminosity ◽  
Stellar Halo ◽  
Merger Event ◽  
Red Giant ◽  
Number Counts ◽  
Good Agreement

ABSTRACT We measure the total stellar halo luminosity using red giant branch (RGB) stars selected from Gaia data release 2. Using slices in magnitude, colour, and location on the sky, we decompose RGB stars belonging to the disc and halo by fitting two-dimensional Gaussians to the Galactic proper motion distributions. The number counts of RGB stars are converted to total stellar halo luminosity using a suite of isochrones weighted by age and metallicity, and by applying a volume correction based on the stellar halo density profile. Our method is tested and calibrated using Galaxia and N-body models. We find a total luminosity (out to 100 kpc) of $L_{\rm halo} = 7.9 \pm 2.0 \times 10^8\, \mathrm{L}_\odot$ excluding Sgr, and $L_{\rm halo} = 9.4 \pm 2.4 \times 10^8\, \mathrm{L}_\odot$ including Sgr. These values are appropriate for our adopted stellar halo density profile and metallicity distribution, but additional systematics related to these assumptions are quantified and discussed. Assuming a stellar mass-to-light ratio appropriate for a Kroupa initial mass function (M⋆/L = 1.5), we estimate a stellar halo mass of $M^\star _{\rm halo} = 1.4 \pm 0.4\times 10^9 \, \mathrm{M}_\odot$. This mass is larger than previous estimates in the literature, but is in good agreement with the emerging picture that the (inner) stellar halo is dominated by one massive dwarf progenitor. Finally, we argue that the combination of a ${\sim}10^9\, \mathrm{M}_\odot$ mass and an average metallicity of 〈[Fe/H]〉 ∼ −1.5 for the Galactic halo points to an ancient (∼10 Gyr) merger event.

scholarly journals Is a top-heavy initial mass function needed to reproduce the submillimetre galaxy number counts?

2017 ◽  
Vol 472 (2) ◽  
pp. 2462-2467 ◽  
Author(s):  
Mohammadtaher Safarzadeh ◽  
Yu Lu ◽  
Christopher C. Hayward
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Number Counts

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 < [Fe/H] < −1 and 0.0 < [Mg/Fe] < 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 > 0.7 is M*,accreted, e > 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.

scholarly journals Galactic structure from infrared studies

1979 ◽  
Vol 84 ◽  
pp. 105-111 ◽  
Author(s):  
J. L. Puget ◽  
G. Serra ◽  
C. Ryter
Keyword(s):  
Galactic Center ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Far Infrared ◽  
Mass Function ◽  
Infrared Emission ◽  
Initial Mass Function ◽  
Young Stars ◽  
Infrared Studies ◽  
Red Giant

Star densities on a galactic scale are traced by far infrared emission of dust heated by young stars and by the 2.4 μm radiation of stars in the red giant phase. Coherent results are obtained, pointing to a very strong star formation rate during the last ∼200 My in a ring 5 kpc from the galactic center. A steepening of the initial mass function compared to that observed in the solar vicinity is also suggested.

scholarly journals A search for red giant solar-like oscillations in all Kepler data

2019 ◽  
Vol 485 (4) ◽  
pp. 5616-5630 ◽  
Author(s):  
Marc Hon ◽  
Dennis Stello ◽  
Rafael A García ◽  
Savita Mathur ◽  
Sanjib Sharma ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Red Giants ◽  
Simulated Model ◽  
Processing Pipeline ◽  
Kepler Mission ◽  
Data Release ◽  
Red Giant ◽  
Subgiant Stars ◽  
Good Agreement

ABSTRACT The recently published Kepler mission Data Release 25 (DR25) reported on ∼197 000 targets observed during the mission. Despite this, no wide search for red giants showing solar-like oscillations have been made across all stars observed in Kepler’s long-cadence mode. In this work, we perform this task using custom apertures on the Kepler pixel files and detect oscillations in 21 914 stars, representing the largest sample of solar-like oscillating stars to date. We measure their frequency at maximum power, νmax, down to $\nu _{\mathrm{max}}\simeq 4\, \mu$Hz and obtain log (g) estimates with a typical uncertainty below 0.05 dex, which is superior to typical measurements from spectroscopy. Additionally, the νmax distribution of our detections show good agreement with results from a simulated model of the Milky Way, with a ratio of observed to predicted stars of 0.992 for stars with $10 \lt \nu _{\mathrm{max}}\lt 270\, \mu$Hz. Among our red giant detections, we find 909 to be dwarf/subgiant stars whose flux signal is polluted by a neighbouring giant as a result of using larger photometric apertures than those used by the NASA Kepler science processing pipeline. We further find that only 293 of the polluting giants are known Kepler targets. The remainder comprises over 600 newly identified oscillating red giants, with many expected to belong to the Galactic halo, serendipitously falling within the Kepler pixel files of targeted stars.

scholarly journals Type-Ia Supernova Rates and the Progenitor Problem: A Review

2012 ◽  
Vol 29 (4) ◽  
pp. 447-465 ◽  
Author(s):  
D. Maoz ◽  
F. Mannucci
Keyword(s):  
Theoretical Models ◽  
Mass Function ◽  
Initial Mass Function ◽  
Rate Measurement ◽  
Short Delay ◽  
Rate Versus ◽  
Type Ia ◽  
Red Giant ◽  
Merger Rate ◽  
Ia Supernovae

AbstractThe identity of the progenitor systems of type-Ia supernovae (SNe Ia) is a major unsolved problem in astrophysics. SN Ia rates are providing some striking clues. We review the basics of SN rate measurement, preach about some sins of SN rate measurement and analysis, and illustrate one of these sins with an analogy about Martian scientists. We review the recent progress in measuring SN Ia rates in various environments and redshifts, and their use to reconstruct the SN Ia delay-time distribution (DTD)—the SN rate versus time that would follow a hypothetical brief burst of star formation. A good number of DTD measurements, using a variety of methods, appear to be converging. At delays 1 <t<10 Gyr, these measurements show a similar, ∼t−1, power-law shape. The DTD peaks at the shortest delays probed. This result supports the idea of a double-degenerate progenitor origin for SNe Ia. Single-degenerate progenitors may still play a role in producing short-delay SNe Ia, or perhaps all SNe Ia, if the red-giant donor channel is more efficient than is found by most theoretical models. The DTD normalization enjoys fairly good agreement (though perhaps some tension), among the various measurements, with a Hubble time–integrated DTD value of about 2 ± 1 SNe Ia per 1000M⊙ (stellar mass formed with a low–mass turnover initial mass function). The local WD binary population suggests that the WD merger rate can explain the Galactic SN Ia rate, but only if sub-Chandra mergers lead to SN Ia events. We point to some future directions that should lead to progress in the field, including measurement of the bivariate (delay and stretch) SN Ia response function.

scholarly journals EMP stars with high mass IMF and hierarchical galaxy formation

2009 ◽  
Vol 5 (S265) ◽  
pp. 128-129
Author(s):  
Yutaka Komiya ◽  
Takuma Suda ◽  
Asao Habe ◽  
Masayuki Y. Fujimoto
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Galactic Halo ◽  
Early Stage ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Halo Stars ◽  
The Galaxy ◽  
Metallicity Distribution

AbstractExtremely metal-poor (EMP) stars in the Galactic halo are stars formed in the very early stage of the chemical evolution of the Galaxy. In previous study, we proposed that typical mass of EMP stars are massive, based on observations of carbon-enhanced EMP stars. In this study, we build a merger tree of the Galaxy semi-analytically and follow the chemical evolution along the merger tree. We also consider the effect of binary and high-mass initial mass function(IMF). Resultant theoretical metallicity distribution function (MDF) and abundance distribution are compared with observed metal-poor halo stars.

Lifting the Veil on Ultra Metal-Poor Stars in the Outermost Halo

2017 ◽  
Vol 13 (S334) ◽  
pp. 389-390
Author(s):  
Jinmi Yoon ◽  
Devin D. Whitten ◽  
Timothy C. Beers ◽  
Vinicius M. Placco ◽  
Young Sun Lee ◽  
...  
Keyword(s):  
Early Universe ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Mass Function ◽  
Initial Mass Function ◽  
Theoretical Studies ◽  
The Past ◽  
Large Numbers ◽  
The Galaxy ◽  
The Veil

AbstractThe study of extremely metal-poor (EMP; [Fe/H] &lt;−3.0) and ultra metal-poor (UMP; [Fe/H] &lt;−4.0) stars is crucial for better understanding first-star nucleosynthesis and constraining the initial mass function in the early Universe. However, UMP stars discovered in the past 25 years only number ~25. A few recent theoretical studies have pointed out that there is likely to exist large numbers of EMP and UMP stars in the periphery of the Galactic halo, at distances exceeding 30-50 kpc. We present identifications of several new EMP/UMP stars and introduce a survey to expedite discovering hundreds to thousands of EMP/UMP stars in the outermost halo (as well as in the local volume) over the next few years, which could revolutionize chemical-evolution studies of the Galaxy.

scholarly journals Carbon-enhanced metal-poor stars as probes of early Galactic nucleosynthesis

2009 ◽  
Vol 5 (S265) ◽  
pp. 117-117
Author(s):  
O. R. Pols ◽  
R. G. Izzard ◽  
E. Glebbeek ◽  
R. J. Stancliffe
Keyword(s):  
Binary Systems ◽  
Galactic Halo ◽  
Large Fraction ◽  
Mass Function ◽  
Initial Mass Function ◽  
Asymptotic Giant Branch ◽  
Mass Star ◽  
Low Mass ◽  
Process Elements ◽  
Early Galaxy

A large fraction, between 10 and 25%, of very metal-poor stars in the Galactic halo are carbon-rich objects, with enhancements of carbon relative to iron exceeding a factor 10. The majority of these carbon-enhanced metal-poor (CEMP) stars show enhancements of heavy s-process elements and have been found to be spectroscopic binary systems. Many of their properties are well explained by the binary mass transfer scenario, in which a former asymptotic giant branch (AGB) companion star has polluted the low-mass star with its nucleosynthesis products. The same scenario predicts the existence of nitrogen-rich metal-poor (NEMP) stars, with [N/C] > 0.5, from AGB companions more massive than about 3 solar masses. In contrast to CEMP stars, however, such NEMP stars are very rare. Recent studies suggest that the high frequency of CEMP stars requires a modified initial mass function (IMF) in the early Galaxy, weighted towards intermediate-mass stars. Such models also implicitly predict a large number of NEMP stars which is not seen.

scholarly journals VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy

2019 ◽  
Vol 626 ◽  
pp. A15 ◽  
Author(s):  
V. Hill ◽  
Á. Skúladóttir ◽  
E. Tolstoy ◽  
K. A. Venn ◽  
M. D. Shetrone ◽  
...  
Keyword(s):  
High Resolution ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Automated Analysis ◽  
Mass Function ◽  
Initial Mass Function ◽  
Core Collapse ◽  
Chemical Abundances ◽  
Type Ia ◽  
Supernovae Type Ia

We present detailed chemical abundances for 99 red-giant branch stars in the centre of the Sculptor dwarf spheroidal galaxy, which have been obtained from high-resolution VLT/FLAMES spectroscopy. The abundances of Li, Na, α-elements (O, Mg, Si, Ca Ti), iron-peak elements (Sc, Cr, Fe, Co, Ni, Zn), and r- and s-process elements (Ba, La, Nd, Eu) were all derived using stellar atmosphere models and semi-automated analysis techniques. The iron abundances populate the whole metallicity distribution of the galaxy with the exception of the very low metallicity tail, −2.3 ≤ [Fe/H] ≤ −0.9. There is a marked decrease in [α/Fe] over our sample, from the Galactic halo plateau value at low [Fe/H] and then, after a “knee”, a decrease to sub-solar [α/Fe] at high [Fe/H]. This is consistent with products of core-collapse supernovae dominating at early times, followed by the onset of supernovae type Ia as early as ∼12 Gyr ago. The s-process products from low-mass AGB stars also participate in the chemical evolution of Sculptor on a timescale comparable to that of supernovae type Ia. However, the r-process is consistent with having no time delay relative to core-collapse supernovae, at least at the later stages of the chemical evolution in Sculptor. Using the simple and well-behaved chemical evolution of Sculptor, we further derive empirical constraints on the relative importance of massive stars and supernovae type Ia to the nucleosynthesis of individual iron-peak and α-elements. The most important contribution of supernovae type Ia is to the iron-peak elements: Fe, Cr, and Mn. There is, however, also a modest but non-negligible contribution to both the heavier α-elements: S, Ca and Ti, and some of the iron-peak elements: Sc and Co. We see only a very small or no contribution to O, Mg, Ni, and Zn from supernovae type Ia in Sculptor. The observed chemical abundances in Sculptor show no evidence of a significantly different initial mass function, compared to that of the Milky Way. With the exception of neutron-capture elements at low [Fe/H], the scatter around mean trends in Sculptor for [Fe/H] >  −2.3 is extremely low, and compatible with observational errors. Combined with the small scatter in the age-elemental abundances relation, this calls for an efficient mixing of metals in the gas in the centre of Sculptor since ∼12 Gyr ago.

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