scholarly journals Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

2020 ◽  
Vol 500 (1) ◽  
pp. 1385-1403 ◽  
Author(s):  
Danny Horta ◽  
Ricardo P Schiavon ◽  
J Ted Mackereth ◽  
Joel Pfeffer ◽  
Andrew C Mason ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Numerical Simulations ◽  
Early Life ◽  
Milky Way ◽  
Stellar Structure ◽  
Galactic Centre ◽  
Galaxy Structure ◽  
Elemental Abundances ◽  
Low Mass ◽  
The Mean

ABSTRACT We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within ∼4 kpc of the Galactic Centre. Characterized by a chemical composition resembling those of low-mass satellites of the Milky Way, this new inner Galaxy structure (IGS) seems to be chemically and dynamically detached from more metal-rich populations in the inner Galaxy. We conjecture that this structure is associated with an accretion event that likely occurred in the early life of the Milky Way. Comparing the mean elemental abundances of this structure with predictions from cosmological numerical simulations, we estimate that the progenitor system had a stellar mass of ∼5 × 108 M⊙, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:in situ ratio within our metal-poor ([Fe/H] < –0.8) bulge sample is somewhere between 1:3 and 1:2, confirming predictions of cosmological numerical simulations by various groups.

The direct and residual effects of the plane of nutrition of calves in early life on physical performance and gains in chemical composition

1990 ◽  
Vol 1990 ◽  
pp. 110-110
Author(s):  
D C Patterson ◽  
R H J Steen
Keyword(s):  
Chemical Composition ◽  
Early Life ◽  
Crude Protein ◽  
Live Weight ◽  
Residual Effects ◽  
Period 2 ◽  
Milk Substitute ◽  
The Mean ◽  
Ad Libitum ◽  
Representative Samples

The direct, residual and overall effects of the plane of nutrition of calves in early life were investigated with a factorial arrangement of high, medium and low planes of nutrition (H, M and L respectively) imposed from 2 to 14 weeks of age (Period 1) and high and low planes of nutrition (H and L respectively) from 14 to 26 weeks (Period 2). A common high plane of nutrition was offered from 26 weeks of age until the mean slaughter live weight of 527 kg. The planes of nutrition were based on appropriate fixed allowances of concentrates and good quality silage offered ad libitum apart from the first half of Period 1 where appropriate allowances of milk substitute were offered and the roughage was hay. In addition to the final slaughter point, representative samples of three calves per treatment were also slaughtered at the start of the experiment and at the end of Periods 1 and 2 and crude protein, total lipid and ash were determined. Energy contents of the tissues were also estimated from protein and lipid analyses.

scholarly journals Galaxy simulations in the Gaia era

2017 ◽  
Vol 12 (S330) ◽  
pp. 127-135
Author(s):  
Ivan Minchev
Keyword(s):  
Chemical Composition ◽  
Numerical Simulations ◽  
Spectroscopic Data ◽  
Milky Way ◽  
Disk Galaxies ◽  
Physical Processes ◽  
Radial Migration ◽  
Cosmological Context ◽  
Enormous Amount ◽  
Formation And Evolution

AbstractWe live in an age where an enormous amount of astrometric, photometric, asteroseismic, and spectroscopic data of Milky Way stars are being acquired, many orders of magnitude larger than about a decade ago. Thanks to the Gaia astrometric mission and followup ground-based spectroscopic surveys in the next 5-10 years about 10-20 Million stars will have accurate 6D kinematics and chemical composition measurements. KEPLER-2, PLATO, and TESS will provide asteroseismic ages for a good fraction of those. In this article we outline some outstanding problems concerning the formation and evolution of the Milky Way and argue that, due to the complexity of physical processes involved in the formation of disk galaxies, numerical simulations in the cosmological context are needed for the interpretation of Milky Way observations. We also discuss in some detail the formation of the Milky Way thick disk, chemodynamical models, and the effects of radial migration.

scholarly journals A universality of dark-halo surface density for the Milky Way and Andromeda dwarf satellites as a probe of the coldness of dark matter

2015 ◽  
Vol 11 (S317) ◽  
pp. 306-307
Author(s):  
Kohei Hayashi ◽  
Masashi Chiba
Keyword(s):  
Dark Matter ◽  
Surface Density ◽  
Milky Way ◽  
Mass Range ◽  
Dark Halo ◽  
Density Profiles ◽  
Dwarf Spheroidal Galaxies ◽  
Galaxy Sample ◽  
Low Mass ◽  
The Mean

AbstractWe propose a new astrophysical test on the nature of dark matter based on the properties of dark halos associated with dwarf spheroidal galaxies. The method adopts a mean surface density of a dark halo defined within a radius of maximum circular velocity, which is derivable for a wide variety of galaxies with any dark-matter density profiles. We find that even though dark halo density profiles are derived based on the different assumptions for each galaxy sample, this surface density is generally constant across a wide mass range of galaxy. We find that at higher halo-mass scales, this constancy for real galaxies can be naturally reproduced by both cold and warm dark matter (CDM and WDM) models. However, at low-mass scales, for which we have estimated from the Milky Way and Andromeda dwarf satellites, the mean surface density derived from WDM models largely deviates from the observed constancy, whereas CDM models are in reasonable agreement with observations.

scholarly journals Abundance matching with the mean star formation rate: there is no missing satellites problem in the Milky Way above M200 ∼ 109 M⊙

2019 ◽  
Vol 487 (4) ◽  
pp. 5799-5812 ◽  
Author(s):  
J I Read ◽  
D Erkal
Keyword(s):  
Star Formation ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Mass Function ◽  
Accurate Estimate ◽  
Empirical Method ◽  
Galactic Centre ◽  
The Mean

ABSTRACT We introduce a novel abundance matching technique that produces a more accurate estimate of the pre-infall halo mass, M200, for satellite galaxies. To achieve this, we abundance match with the mean star formation rate, averaged over the time when a galaxy was forming stars, 〈SFR〉, instead of the stellar mass, M∗. Using data from the Sloan Digital Sky Survey, the GAMA survey and the Bolshoi simulation, we obtain a statistical 〈SFR〉−M200 relation in Λ cold dark matter. We then compare the pre-infall halo mass, $M^{\rm abund}_{200}$, derived from this relation with the pre-infall dynamical mass, $M^{\rm dyn}_{200}$, for 21 nearby dSph and dIrr galaxies, finding a good agreement between the two. As a first application, we use our new 〈SFR〉−M200 relation to empirically measure the cumulative mass function of a volume-complete sample of bright Milky Way satellites within 280 kpc of the Galactic centre. Comparing this with a suite of cosmological ‘zoom’ simulations of Milky Way-mass haloes that account for subhalo depletion by the Milky Way disc, we find no missing satellites problem above M200 ∼ 109 M⊙ in the Milky Way. We discuss how this empirical method can be applied to a larger sample of nearby spiral galaxies.

scholarly journals The K2-HERMES Survey: age and metallicity of the thick disc

2019 ◽  
Vol 490 (4) ◽  
pp. 5335-5352 ◽  
Author(s):  
Sanjib Sharma ◽  
Dennis Stello ◽  
Joss Bland-Hawthorn ◽  
Michael R Hayden ◽  
Joel C Zinn ◽  
...  
Keyword(s):  
Selection Function ◽  
Population Synthesis ◽  
Low Mass Stars ◽  
Mass Scaling ◽  
Elemental Abundances ◽  
Thick Disc ◽  
Promising Tool ◽  
Low Mass ◽  
The Mean ◽  
First Time

ABSTRACT Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-sampling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z⊙) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.

scholarly journals Simultaneous calibration of spectro-photometric distances and the Gaia DR2 parallax zero-point offset with deep learning

2019 ◽  
Vol 489 (2) ◽  
pp. 2079-2096 ◽  
Author(s):  
Henry W Leung ◽  
Jo Bovy
Keyword(s):  
Milky Way ◽  
Zero Point ◽  
Galactic Centre ◽  
Dynamical Structure ◽  
The Sun ◽  
Large Area ◽  
Data Set ◽  
The Mean ◽  
Gaia Dr2 ◽  
Flexible Model

ABSTRACT Gaia measures the five astrometric parameters for stars in the Milky Way, but only four of them (positions and proper motion, but not distance) are well measured beyond a few kpc from the Sun. Modern spectroscopic surveys such as APOGEE cover a large area of the Milky Way disc and we can use the relation between spectra and luminosity to determine distances to stars beyond Gaia’s parallax reach. Here, we design a deep neural network trained on stars in common between Gaia and APOGEE that determines spectro-photometric distances to APOGEE stars, while including a flexible model to calibrate parallax zero-point biases in Gaia DR2. We determine the zero-point offset to be $-52.3 \pm 2.0\, \mu \mathrm{as}$ when modelling it as a global constant, but also train a multivariate zero-point offset model that depends on G, GBP − GRP colour, and Teff and that can be applied to all ≈58 million stars in Gaia DR2 within APOGEE’s colour–magnitude range and within APOGEE’s sky footprint. Our spectro-photometric distances are more precise than Gaia at distances ${\gtrsim} 2\, \mathrm{kpc}$ from the Sun. We release a catalogue of spectro-photometric distances for the entire APOGEE DR14 data set which covers Galactocentric radii $2\, \mathrm{kpc} \lesssim R \lesssim 19\, \mathrm{kpc}$; ${\approx} 150\, 000$ stars have ${\lt} 10{{\ \rm per\ cent}}$ uncertainty, making this a powerful sample to study the chemo-dynamical structure of the disc. We use this sample to map the mean [Fe/H] and 15 abundance ratios [X/Fe] from the Galactic Centre to the edge of the disc. Among many interesting trends, we find that the bulge and bar region at $R \lesssim 5\, \mathrm{kpc}$ clearly stands out in [Fe/H] and most abundance ratios.

Incubation Temperature Influences the Duration of Egg Hatching and Early Development in the Boreal Digging Frog, Kaloula Borealis

2020 ◽  
Vol 3 (1) ◽  
pp. ACCEPTED
Author(s):  
Rho-Jeong Rae
Keyword(s):  
Water Temperature ◽  
Early Life ◽  
Rainy Season ◽  
Incubation Temperature ◽  
Life Stages ◽  
Early Life Stages ◽  
Egg Hatching ◽  
Significant Difference ◽  
The Mean ◽  
Hatching Rates

This study investigated the boreal digging frog, Kaloula borealis, to determine the egg hatching period and whether the hatching period is affected by incubation temperature. The results of this study showed that all the eggs hatched within 48 h after spawning, with 28.1% (±10.8, n=52) hatching within 24 h and 99.9% (±0.23, n=49) within 48 h after spawning. A significant difference was noted in the mean hatching proportion of tadpoles at different water temperatures. The mean hatching rates between 15 and 24 h after spawning was higher at a water temperature of 21.1 (±0.2) °C than at 24.1 (±0.2) °C. These results suggest that incubation temperature affected the early life stages of the boreal digging frog, since they spawn in ponds or puddles that form during the rainy season.

scholarly journals Spectra of M Dwarfs - Dimmed by Dust

1998 ◽  
Vol 11 (1) ◽  
pp. 439-440
Author(s):  
T. Tsuji ◽  
K. Ohnaka ◽  
W. Aoki ◽  
H.R.A. Jones
Keyword(s):  
Chemical Composition ◽  
Brown Dwarfs ◽  
Surface Chemical ◽  
Basic Information ◽  
M Dwarfs ◽  
Surface Chemical Composition ◽  
Molecular Lines ◽  
Low Mass

Spectra of M dwarfs are rich in atomic and molecular lines. These spectra provide such basic information as Teff (or radius), log g (or mass), surface chemical composition, and something more (e.g. activity) if properly interpreted. It is recognized, however, that spectra of M dwarfs are already dimmed by the dust formed in their photospheres (Tsuji et al. 1996a) and this effect, which has been overlooked until recently, should be taken into account in any interpretation and analysis of the spectra of very low mass objects (VLMOs) including late M dwarfs and brown dwarfs.

scholarly journals On the origin of the helium-rich population in the peculiar globular cluster Omega Centauri

2009 ◽  
Vol 5 (S268) ◽  
pp. 187-188
Author(s):  
Donatella Romano ◽  
M. Tosi ◽  
M. Cignoni ◽  
F. Matteucci ◽  
E. Pancino ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Globular Cluster ◽  
Main Sequence ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Potential Well ◽  
Galactic Winds ◽  
Supernova Explosions

AbstractIn this contribution we discuss the origin of the extreme helium-rich stars which inhabit the blue main sequence (bMS) of the Galactic globular cluster Omega Centauri. In a scenario where the cluster is the surviving remnant of a dwarf galaxy ingested by the Milky Way many Gyr ago, the peculiar chemical composition of the bMS stars can be naturally explained by considering the effects of strong differential galactic winds, which develop owing to multiple supernova explosions in a shallow potential well.

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