scholarly journals High reddening patches in Gaia DR2

2020 ◽  
Vol 634 ◽  
pp. A33
Author(s):  
Leire Beitia-Antero ◽  
Ana Inés Gómez de Castro ◽  
Raúl de la Fuente Marcos
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Spectroscopic Analysis ◽  
Galactic Halo ◽  
Spiral Galaxies ◽  
Monte Carlo Sampling ◽  
The Other ◽  
Host Galaxies ◽  
Galactic Model ◽  
Gaia Dr2

Context. Deep GALEX UV data show that the extreme outskirts of some spiral galaxies are teeming with star formation. Such young stellar populations evolving so far away from the bulk of their host galaxies challenge our overall understanding of how star formation proceeds at galactic scales. It is at present unclear whether our own Milky Way may also exhibit ongoing and recent star formation beyond the conventional edge of the disk (∼15 kpc). Aims. Using Gaia DR2 data, we aim to determine if such a population is present in the Galactic halo, beyond the nominal radius of the Milky Way disk. Methods. We studied the kinematics of Gaia DR2 sources with parallax values between 1/60 and 1/30 milliarcseconds towards two regions that show abnormally high values of extinction and reddening; the results are compared with predictions from GALAXIA Galactic model. We also plotted the color–magnitude (CM) diagrams with heliocentric distances computed inverting the parallaxes, and studied the effects of the large parallax errors by Monte Carlo sampling. Results. The kinematics point towards a Galactic origin for one of the regions, while the provenance of the stars in the other is not clear. A spectroscopic analysis of some of the sources in the first region confirms that they are located in the halo. The CM diagram of the sources suggests that some of them are young.

scholarly journals A Comparison of Chemical Evolution between the Milky Way and M31 Galaxy

2006 ◽  
Vol 2 (S235) ◽  
pp. 313-313
Author(s):  
J. Yin ◽  
J.L. Hou ◽  
R.X. Chang ◽  
S. Boissier ◽  
N. Prantzos
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Milky Way ◽  
Local Group ◽  
Spiral Galaxies ◽  
Star Formation History ◽  
Milky Way Galaxy ◽  
Andromeda Galaxy ◽  
Formation History ◽  
Formation And Evolution

Andromeda galaxy (M31,NGC224) is the biggest spiral in the Local Group. By studying the star formation history(SFH) and chemical evolution of M31, and comparing with the Milky Way Galaxy, we are able to understand more about the formation and evolution of spiral galaxies.

scholarly journals Magnetic fields in our Milky Way Galaxy and nearby galaxies

2012 ◽  
Vol 8 (S294) ◽  
pp. 213-224 ◽  
Author(s):  
JinLin Han
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Large Scale ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Measure Data ◽  
Submillimeter Wavelength ◽  
Nearby Galaxies

AbstractMagnetic fields in our Galaxy and nearby galaxies have been revealed by starlight polarization, polarized emission from dust grains and clouds at millimeter and submillimeter wavelength, the Zeeman effect of spectral lines or maser lines from clouds or clumps, diffuse radio synchrotron emission from relativistic electrons in interstellar magnetic fields, and the Faraday rotation of background radio sources as well as pulsars for our Milky Way. It is easy to get a global structure for magnetic fields in nearby galaxies, while we have observed many details of magnetic fields in our Milky Way, especially by using pulsar rotation measure data. In general, magnetic fields in spiral galaxies probably have a large-scale structure. The fields follow the spiral arms with or without the field direction reversals. In the halo of spiral galaxies magnetic fields exist and probably also have a large-scale structure as toroidal and poloidal fields, but seem to be slightly weaker than those in the disk. In the central region of some galaxies, poloidal fields have been detected as vertical components. Magnetic field directions in galaxies seem to have been preserved during cloud formation and star formation, from large-scale diffuse interstellar medium to molecular clouds and then to the cloud cores in star formation regions or clumps for the maser spots. Magnetic fields in galaxies are passive to dynamics.

scholarly journals Synthetic catalog of black holes in the Milky Way

2020 ◽  
Vol 638 ◽  
pp. A94 ◽  
Author(s):  
A. Olejak ◽  
K. Belczynski ◽  
T. Bulik ◽  
M. Sobolewska
Keyword(s):  
Black Holes ◽  
Star Formation ◽  
Binary Systems ◽  
Milky Way ◽  
Galactic Halo ◽  
Galactic Disk ◽  
Compact Objects ◽  
Star Formation History ◽  
Average Mass ◽  
Synthetic Catalog

Aims. We present an open-access database that includes a synthetic catalog of black holes (BHs) in the Milky Way, divided by the components disk, bulge, and halo. Methods. To calculate the evolution of single and binary stars, we used the updated population synthesis code StarTrack. We applied a new model of the star formation history and chemical evolution of Galactic disk, bulge, and halo that was synthesized from observational and theoretical data. This model can be easily employed for other studies of population evolution. Results. We find that at the current Milky Way (disk+bulge+halo) contains about 1.2 × 108 single BHs with an average mass of about 14 M⊙, and 9.3 × 106 BHs in binary systems with an average mass of 19 M⊙. We present basic statistical properties of the BH population in three Galactic components such as the distributions of BH masses, velocities, or the numbers of BH binary systems in different evolutionary configurations. Conclusions. The metallicity of a stellar population has a significant effect on the final BH mass through the stellar winds. The most massive single BH in our simulation of 113 M⊙ originates from a merger of a BH and a helium star in a low-metallicity stellar environment in the Galactic halo. We constrain that only ∼0.006% of the total Galactic halo mass (including dark matter) can be hidden in the form of stellar origin BHs. These BHs cannot be detected by current observational surveys. We calculated the merger rates for current Galactic double compact objects (DCOs) for two considered common-envelope models: ∼3–81 Myr−1 for BH-BH, ∼1–9 Myr−1 for BH-neutron star (NS), and ∼14–59 Myr−1 for NS-NS systems. We show the evolution of the merger rates of DCOs since the formation of the Milky Way until the current moment with the new star formation model of the Galaxy.

scholarly journals Properties of Wolf-Rayet Stars

2007 ◽  
Vol 3 (S250) ◽  
pp. 47-62 ◽  
Author(s):  
Paul A. Crowther
Keyword(s):  
Star Formation ◽  
Empirical Evidence ◽  
Recent Progress ◽  
Milky Way ◽  
Spectroscopic Analysis ◽  
Evolutionary Models ◽  
Chemical Abundances ◽  
Near Ir ◽  
Stellar Temperatures

AbstractA review of recent progress relating to Wolf-Rayet (WR) stars is presented. Topics include improved Milky Way statistics from near-IR surveys, different flavours of hydrogen-rich and hydrogen-poor WN stars, WR masses from binary orbits, plus spectroscopic analysis of WR stars resulting in stellar temperatures, luminosities, ionizing fluxes, plus wind properties accounting for clumping. Chemical abundances of WN and WC stars are presented, including a discussion of neon abundances in WC and WO stars fromSpitzerobservations. Empirical evidence supporting metallicity-dependent winds is also presented, including its effect on subtype distributions in different environments. Finally, difficulties in comparisons between evolutionary models and observations are highlighted, plus outstanding issues with predictions from continuous star formation and instantaneous bursts in the Milky Way,

scholarly journals Tango for three: Sagittarius, LMC, and the Milky Way

2020 ◽  
Vol 501 (2) ◽  
pp. 2279-2304
Author(s):  
Eugene Vasiliev ◽  
Vasily Belokurov ◽  
Denis Erkal
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Large Magellanic Cloud ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Tentative Evidence ◽  
Virial Mass ◽  
Lyrae Stars ◽  
Astrometric Data ◽  
Gaia Dr2

ABSTRACT We assemble a catalogue of candidate Sagittarius stream members with 5D and 6D phase-space information, using astrometric data from Gaia DR2, distances estimated from RR Lyrae stars, and line-of-sight velocities from various spectroscopic surveys. We find a clear misalignment between the stream track and the direction of the reflex-corrected proper motions in the leading arm of the stream, which we interpret as a signature of a time-dependent perturbation of the gravitational potential. A likely cause of this perturbation is the recent passage of the most massive Milky Way satellite – the Large Magellanic Cloud (LMC). We develop novel methods for simulating the Sagittarius stream in the presence of the LMC, using specially tailored N-body simulations and a flexible parametrization of the Milky Way halo density profile. We find that while models without the LMC can fit most stream features rather well, they fail to reproduce the misalignment and overestimate the distance to the leading arm apocentre. On the other hand, models with an LMC mass in the range $(1.3\pm 0.3)\times 10^{11}\, \mathrm{M}_\odot$ rectify these deficiencies. We demonstrate that the stream can not be modelled adequately in a static Milky Way. Instead, our Galaxy is required to lurch toward the massive in-falling Cloud, giving the Sgr stream its peculiar shape and kinematics. By exploring the parameter space of Milky Way potentials, we determine the enclosed mass within 100 kpc to be $(5.6\pm 0.4)\times 10^{11}\, \mathrm{M}_\odot$, and the virial mass to be $(9.0\pm 1.3)\times 10^{11}\, \mathrm{M}_\odot$, and find tentative evidence for a radially-varying shape and orientation of the Galactic halo.

scholarly journals Stars and Gas in the Large Interacting Galaxy NGC 6872

2004 ◽  
Vol 217 ◽  
pp. 422-423 ◽  
Author(s):  
Cathy Horellou ◽  
Bärbel Koribalski
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Spiral Galaxies ◽  
The Other ◽  
Dark Matter Halo ◽  
Stellar Clusters ◽  
Test Models ◽  
The Galaxy ◽  
Tidal Perturbations ◽  
Tidal Tails

The luminous barred galaxy NGC 6872 is one of the largest spiral galaxies known. Star formation occurs all along the arms, which extend over more than 100 kpc. The galaxy experiences tidal perturbations from the nearby companion IC 4970 passing by on a low-inclination, prograde orbit. We have mapped the large-scale distribution and kinematics of the atomic gas (HI) in the NGC 6872/IC 4970 system and carried out N-body simulations with stars and gas. HI is absent from the central region; on the other hand, large gas concentrations are found at the tip of the tidal arms, spatially coincident with the blue stellar clusters and with the peaks of the Hα distribution. We use that remarkable system to investigate the evolution of gas and stars in a close prograde encounter, examine the influence of a dark matter halo on the length of the tidal tails, and test models of collisionally induced star formation.

scholarly journals The mass fraction of halo stars contributed by the disruption of globular clusters in the E-MOSAICS simulations

2020 ◽  
Vol 493 (3) ◽  
pp. 3422-3428 ◽  
Author(s):  
Marta Reina-Campos ◽  
Meghan E Hughes ◽  
J M Diederik Kruijssen ◽  
Joel L Pfeffer ◽  
Nate Bastian ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Light Element ◽  
Element Abundance ◽  
Host Galaxies ◽  
Stellar Cluster ◽  
Halo Stars ◽  
Stellar Halo

ABSTRACT Globular clusters (GCs) have been posited, alongside dwarf galaxies, as significant contributors to the field stellar population of the Galactic halo. In order to quantify their contribution, we examine the fraction of halo stars formed in stellar clusters in the suite of 25 present-day Milky Way-mass cosmological zoom simulations from the E-MOSAICS project. We find that a median of 2.3 and 0.3 per cent of the mass in halo field stars formed in clusters and GCs, defined as clusters more massive than 5 × 103 and 105 M⊙, respectively, with the 25–75th percentiles spanning 1.9–3.0 and 0.2–0.5 per cent being caused by differences in the assembly histories of the host galaxies. Under the extreme assumption that no stellar cluster survives to the present day, the mass fractions increase to a median of 5.9 and 1.8 per cent. These small fractions indicate that the disruption of GCs plays a subdominant role in the build-up of the stellar halo. We also determine the contributed halo mass fraction that would present signatures of light-element abundance variations considered to be unique to GCs, and find that clusters and GCs would contribute a median of 1.1 and 0.2 per cent, respectively. We estimate the contributed fraction of GC stars to the Milky Way halo, based on recent surveys, and find upper limits of 2–5 per cent (significantly lower than previous estimates), suggesting that models other than those invoking strong mass loss are required to describe the formation of chemically enriched stellar populations in GCs.

scholarly journals Lithium and beryllium in the Gaia-Enceladus galaxy

2020 ◽  
Vol 496 (3) ◽  
pp. 2902-2909
Author(s):  
P Molaro ◽  
G Cescutti ◽  
X Fu
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Chemical Abundances ◽  
Dwarf Stars ◽  
Evolution Experiment ◽  
External Galaxies ◽  
Low Metallicity ◽  
Gaia Dr2

ABSTRACT Data from Gaia DR2 and The Apache Point Observatory Galactic Evolution Experiment surveys revealed a relatively new component in the inner Galactic halo, which is likely the dynamical remnant of a disrupted dwarf galaxy named Gaia-Enceladus that collided with the Milky Way about 10 Gyr ago. This merging event offers an extraordinary opportunity to study chemical abundances of elements in a dwarf galaxy, since they are generally hampered in external galaxies. Here, we focus on 7Li and 9Be in dwarf stars that are out of reach even in Local Group galaxies. Searching in GALAH, Gaia-ESO survey and in literature, we found several existing 7Li abundance determinations of stars belonging to the Gaia-Enceladus galaxy. The 7Li abundances of stars at the low metallicity end overlap with those of the Galactic halo. These are effective extragalactic 7Li measurements, which suggest that the 7Li Spite plateau is universal, as is the cosmological 7Li problem. We found a 7Li-rich giant out of 101 stars, which suggests a small percentage similar to that of the Milky Way. We also collect 9Be abundance for a subsample of 25 Gaia-Enceladus stars from literature. Their abundances share the Galactic [Be/H] values at the low metallicity end but grow slower with [Fe/H] and show a reduced dispersion. This suggests that the scatter observed in the Milky Way could reflect the different 9Be evolution patterns of different stellar components that are mixed-up in the Galactic halo.

scholarly journals Cosmological simulations of the same spiral galaxy: the impact of baryonic physics

2020 ◽  
Vol 501 (1) ◽  
pp. 62-77
Author(s):  
A Nuñez-Castiñeyra ◽  
E Nezri ◽  
J Devriendt ◽  
R Teyssier
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Galaxy Formation ◽  
Spiral Galaxy ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Cosmological Simulations ◽  
Star Forming ◽  
Small Scales ◽  
The Impact

ABSTRACT The interplay of star formation (SF) and supernova (SN) feedback in galaxy formation is a key element for understanding galaxy evolution. Since these processes occur at small scales, it is necessary to have sub-grid models that recover their evolution and environmental effects at the scales reached by cosmological simulations. In this work, we present the results of the Mochima simulation, where we simulate the same spiral galaxy inhabiting a Milky Way (MW) size halo in a cosmological environment changing the sub-grid models for SN feedback and SF. We test combinations of the Schmidt law and a multifreefall based SF with delayed cooling feedback or mechanical feedback. We reach a resolution of 35 pc in a zoom-in box of 36 Mpc. For this, we use the code $\rm{\small RAMSES}$ with the implementation of gas turbulence in time and trace the local hydrodynamical features of the star-forming gas. Finally, we compare the galaxies at redshift 0 with global and interstellar medium observations in the MW and local spiral galaxies. The simulations show successful comparisons with observations. Nevertheless, diverse galactic morphologies are obtained from different numerical implementations. We highlight the importance of detailed modelling of the SF and feedback processes, especially for simulations with a resolution that start to reach scales relevant for molecular cloud physics. Future improvements could alleviate the degeneracies exhibited in our simulated galaxies under different sub-grid models.

scholarly journals Origin of the Galactic Halo: accretion vs. in situ formation

2017 ◽  
Vol 13 (S334) ◽  
pp. 34-37
Author(s):  
Emanuele Spitoni ◽  
Fiorenzo Vincenzo ◽  
Francesca Matteucci ◽  
Donatella Romano
Keyword(s):  
Star Formation ◽  
Neutron Capture ◽  
Time Scale ◽  
Galactic Halo ◽  
Building Blocks ◽  
The Other ◽  
Chemical Abundances ◽  
Halo Stars ◽  
In Situ Formation

AbstractWe test the hypothesis that the classical and ultra-faint dwarf spheroidal satellites of the our Galaxy have been the building blocks of the Galactic halo by comparing their [O/Fe] and [Ba/Fe] vs. [Fe/H] patterns with the ones observed in Galactic halo stars. The [O/Fe] ratio deviates substantially from the observed abundance ratios in the Galactic halo stars for [Fe/H] > -2 dex, while they overlap for lower metallicities. On the other hand, for the neutron capture elements, the discrepancy is extended at all the metallicities, suggesting that the majority of stars in the halo are likely to have been formed in situ. We present the results for a model considering the effects of an enriched gas stripped from dwarf satellites on the chemical evolution of the Galactic halo. We find that the resulting chemical abundances of the halo stars depend on the adopted infall time-scale, and the presence of a threshold in the gas for star formation.

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