scholarly journals The last breath of the Sagittarius dSph

2020 ◽  
Vol 497 (4) ◽  
pp. 4162-4182 ◽  
Author(s):  
Eugene Vasiliev ◽  
Vasily Belokurov
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Final State ◽  
Tidal Forces ◽  
The Galaxy ◽  
The Mean ◽  
Red Clump ◽  
Astrometric Data

ABSTRACT We use the astrometric and photometric data from Gaia Data Release 2 and line-of-sight velocities from various other surveys to study the 3D structure and kinematics of the Sagittarius dwarf galaxy. The combination of photometric and astrometric data makes it possible to obtain a very clean separation of Sgr member stars from the Milky Way foreground; our final catalogue contains 2.6 × 105 candidate members with magnitudes G < 18, more than half of them being red clump stars. We construct and analyse maps of the mean proper motion and its dispersion over the region ∼30 × 12 deg, which show a number of interesting features. The intrinsic 3D density distribution (orientation, thickness) is strongly constrained by kinematics; we find that the remnant is a prolate structure with the major axis pointing at ∼45° from the orbital velocity and extending up to ∼5 kpc, where it transitions into the stream. We perform a large suite of N-body simulations of a disrupting Sgr galaxy as it orbits the Milky Way over the past 2.5 Gyr, which are tailored to reproduce the observed properties of the remnant (not the stream). The richness of available constraints means that only a narrow range of parameters produce a final state consistent with observations. The total mass of the remnant is $\sim \!4\times 10^8\, \mathrm{M}_\odot$, of which roughly a quarter resides in stars. The galaxy is significantly out of equilibrium, and even its central density is below the limit required to withstand tidal forces. We conclude that the Sgr galaxy will likely be disrupted over the next Gyr.

scholarly journals New constraints on the structure of the nuclear stellar cluster of the Milky Way from star counts and MIR imaging

2020 ◽  
Vol 634 ◽  
pp. A71 ◽  
Author(s):  
E. Gallego-Cano ◽  
R. Schödel ◽  
F. Nogueras-Lara ◽  
H. Dong ◽  
B. Shahzamanian ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
3D Structure ◽  
Major Axis ◽  
Stellar Disk ◽  
Axis Ratio ◽  
Stellar Cluster ◽  
Red Clump

Context. The Milky Way nuclear star cluster (MWNSC) is a crucial laboratory for studying the galactic nuclei of other galaxies, but its properties have not been determined unambiguously until now. Aims. We aim to study the size and spatial structure of the MWNSC. Methods. This study uses data and methods that address potential shortcomings of previous studies on the topic. We use 0.2″ angular resolution Ks data to create a stellar density map in the central 86.4 pc × 21 pc at the Galactic center. We include data from selected adaptive-optics-assisted images obtained for the inner parsecs. In addition, we use Spitzer/IRAC mid-infrared (MIR) images. We model the Galactic bulge and the nuclear stellar disk in order to subtract them from the MWNSC. Finally, we fit a Sérsic model to the MWNSC and investigate its symmetry. Results. Our results are consistent with previous work. The MWNSC is flattened with an axis ratio of q = 0.71 ± 0.10, an effective radius of Re = (5.1 ± 1.0) pc, and a Sérsic index of n = 2.2 ± 0.7. Its major axis may be tilted out of the Galactic plane by up to −10°. The distribution of the giants brighter than the Red Clump (RC) is found to be significantly flatter than the distribution of the faint stars. We investigate the 3D structure of the central stellar cusp using our results on the MWNSC structure on large scales to constrain the deprojection of the measured stellar surface number density, obtaining a value of the 3D inner power law of γ = 1.38 ± 0.06sys ± 0.01stat. Conclusions. The MWNSC shares its main properties with other extragalactic NSCs found in spiral galaxies. The differences in the structure between bright giants and RC stars might be related to the existence of not completely mixed populations of different ages. This may hint at recent growth of the MWNSC through star formation or cluster accretion.

scholarly journals A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars

2020 ◽  
Vol 501 (2) ◽  
pp. 1690-1700
Author(s):  
Julio A Carballo-Bello ◽  
David Martínez-Delgado ◽  
Jesús M Corral-Santana ◽  
Emilio J Alfaro ◽  
Camila Navarrete ◽  
...  
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
Line Of Sight ◽  
Proper Motions ◽  
Large Area ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Pollution Area ◽  
New Evidence ◽  
Astrometric Data

ABSTRACT We present the Dark Energy Camera (DECam) imaging combined with Gaia Data Release 2 (DR2) data to study the Canis Major overdensity. The presence of the so-called Blue Plume stars in a low-pollution area of the colour–magnitude diagram allows us to derive the distance and proper motions of this stellar feature along the line of sight of its hypothetical core. The stellar overdensity extends on a large area of the sky at low Galactic latitudes, below the plane, and in the range 230° < ℓ < 255°. According to the orbit derived for Canis Major, it presents an on-plane rotation around the Milky Way. Moreover, additional overdensities of Blue Plume stars are found around the plane and across the Galaxy, proving that these objects are not only associated with that structure. The spatial distribution of these stars, derived using Gaia astrometric data, confirms that the detection of the Canis Major overdensity results more from the warped structure of the Milky Way disc than from the accretion of a dwarf galaxy.

scholarly journals A new near-IR window of low extinction in the Galactic plane

2018 ◽  
Vol 616 ◽  
pp. A26 ◽  
Author(s):  
Dante Minniti ◽  
Roberto K. Saito ◽  
Oscar A. Gonzalez ◽  
Javier Alonso-García ◽  
Marina Rejkuba ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Galactic Plane ◽  
Structural Constraints ◽  
Magnitude Distribution ◽  
Near Ir ◽  
Disk Structure ◽  
The Galaxy ◽  
The Mean ◽  
Red Clump

Aims. The windows of low extinction in the Milky Way (MW) plane are rare but important because they enable us to place structural constraints on the opposite side of the Galaxy, which has hither to been done rarely. Methods. We use the near-infrared (near-IR) images of the VISTA Variables in the Vía Láctea (VVV) Survey to build extinction maps and to identify low extinction windows towards the Southern Galactic plane. Here we report the discovery of VVV WIN 1713−3939, a very interesting window with relatively uniform and low extinction conveniently placed very close to the Galactic plane. Results. The new window of roughly 30 arcmin diameter is located at Galactic coordinates (l, b) = (347.4, −0.4) deg. We analyse the VVV near-IR colour-magnitude diagrams in this window. The mean total near-IR extinction and reddening values measured for this window are AKs = 0.46 and E(J − Ks) = 0.95. The red clump giants within the window show a bimodal magnitude distribution in the Ks band, with peaks at Ks = 14.1 and 14.8 mag, corresponding to mean distances of D = 11.0 ± 2.4 and 14.8 ± 3.6 kpc, respectively. We discuss the origin of these red clump overdensities within the context of the MW disk structure.

scholarly journals The accreted nuclear clusters of the Milky Way

2020 ◽  
Vol 500 (2) ◽  
pp. 2514-2524
Author(s):  
Joel Pfeffer ◽  
Carmela Lardo ◽  
Nate Bastian ◽  
Sara Saracino ◽  
Sebastian Kamann
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Star Clusters ◽  
Host Galaxy ◽  
The Galaxy ◽  
Nuclear Clusters ◽  
The Common ◽  
Massive Clusters ◽  
Peculiar Case

ABSTRACT A number of the massive clusters in the halo, bulge, and disc of the Galaxy are not genuine globular clusters (GCs) but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs and can be readily traced back to their host galaxy (e.g. M54 and the Sagittarius Dwarf galaxy), others have proven more elusive. Here, we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, ω Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken, and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate-mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster–cluster merger.

scholarly journals Nonlinear Dynamo in a Disk Galaxy

1993 ◽  
Vol 157 ◽  
pp. 349-353
Author(s):  
A. Poezd ◽  
A. Shukurov ◽  
D.D. Sokoloff
Keyword(s):  
Magnetic Field ◽  
Milky Way ◽  
Dynamo Model ◽  
The Galaxy ◽  
Seed Field ◽  
Andromeda Nebula ◽  
The Mean ◽  
Dynamo Equation ◽  
The Magnetic Field

A nonlinear thin-disk galactic dynamo model based on α-quenching is proposed. Assuming that the mean helicity depends on the magnetic field strength averaged across the disk, we derive a universal form of nonlinearity in the radial dynamo equation. We discuss the evolution of the regular magnetic field in the Milky Way and the Andromeda Nebula. It is argued that the reversals of the regular magnetic field in the Galaxy are a relic inherited from the structure of the seed field. We also briefly discuss the role of the turbulent diamagnetism and the effects of galactic evolution on the dynamo.

scholarly journals The dwarf galaxy satellite system of Centaurus A

2019 ◽  
Vol 629 ◽  
pp. A18 ◽  
Author(s):  
Oliver Müller ◽  
Marina Rejkuba ◽  
Marcel S. Pawlowski ◽  
Rodrigo Ibata ◽  
Federico Lelli ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Asymptotic Giant Branch ◽  
Semi Major Axis ◽  
Distance Measurements ◽  
Red Giant

Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.

Stellar Populations of the Outer Milky-Way Halo

2017 ◽  
Vol 13 (S334) ◽  
pp. 29-33
Author(s):  
Baslio Santiago ◽  
Elmer Luque ◽  
Adriano Pieres ◽  
Anna Bárbara Queiroz
Keyword(s):  
Galaxy Evolution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Building Blocks ◽  
Early Stages ◽  
Dark Energy Survey ◽  
Stellar Streams ◽  
The Galaxy

AbstractThe stellar spheroidal components of the Milky-Way contain the oldest and most metal poor of its stars. Inevitably the processes governing the early stages of Galaxy evolution are imprinted upon them. According to the currently favoured hierarchical bottom-up scenario of galaxy formation, these components, specially the Galactic halo, are the repository of most of the mass built up from accretion events in those early stages. These events are still going on today, as attested by the long stellar streams associated to the Sagittarius dwarf galaxy and several other observed tidal substructure, whose geometry, extent, and kinematics are important constraints to reconstruct the MW gravitational potential and infer its total (visible + dark) mass. In addition, the remaining system of MW satellites is expected to be a fossil record of the much larger population of Galactic building blocks that once existed and got accreted. For all these reasons, it is crucial to unravel as much of this remaining population as possible, as well as the current stellar streams that orbit within the halo. The best bet to achieve this task is to carry out wide, deep, and multi-band photometric surveys that provide homogeneous stellar samples. In this contribution, we summarize the results of several years of work towards detecting and characterizing distant MW stellar systems, star clusters and dwarf spheroidals alike, with an emphasis on the analysis of data from the Dark Energy Survey (DES). We argue that most of the volume in distance, size and luminosity space, both in the Galaxy and in the Clouds, is still unprobed. We then discuss the perspectives of exploring this outer MW volume using the current surveys, as well as other current and future surveys, such as the Large Synoptic Survey Telescope (LSST).

scholarly journals Mapping the Hidden Universe: The Galaxy Distribution in the Zone of Avoidance

2000 ◽  
Vol 17 (1) ◽  
pp. 6-12 ◽  
Author(s):  
Renée C. Kraan-Korteweg ◽  
Sebastian Juraszek
Keyword(s):  
Milky Way ◽  
Current Status ◽  
Microwave Background ◽  
Galaxy Distribution ◽  
Velocity Flow ◽  
The Galaxy ◽  
The Mean ◽  
Zone Of Avoidance ◽  
Mean Time ◽  
Great Attractor

AbstractDue to the foreground extinction of the Milky Way, galaxies become increasingly faint as they approach the Galactic Equator creating a ‘zone of avoidance’ (ZOA) in the distribution of optically visible galaxies of about 25%. A ‘whole-sky’ map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor (GA) region. The current status of deep optical galaxy searches behind the Milky Way and their completeness as a function of foreground extinction will be reviewed. It has been shown that these surveys—which in the mean time cover the whole ZOA (Figure 2)—result in a considerable reduction of the ZOA from extinction levels of AB =1m.0 (Figure 1) to AB =3m.0 (Figure 3). In the remaining, optically opaque ZOA, systematic HI surveys are powerful in uncovering galaxies, as is demonstrated for the GA region with data from the full sensitivity Parkes Multibeam HI survey (300°≤l≤332°, ∣b∣≤5°.5, Figure 4).

scholarly journals Reconstructing the Last Major Merger of the Milky Way with the H3 Survey

2021 ◽  
Vol 923 (1) ◽  
pp. 92
Author(s):  
Rohan P. Naidu ◽  
Charlie Conroy ◽  
Ana Bonaca ◽  
Dennis Zaritsky ◽  
Rainer Weinberger ◽  
...  
Keyword(s):  
Milky Way ◽  
Age Distribution ◽  
Major Axis ◽  
Angular Momenta ◽  
Outer Disk ◽  
The Galaxy ◽  
Stellar Halo ◽  
Major Merger ◽  
Triaxial Shape

Abstract Several lines of evidence suggest that the Milky Way underwent a major merger at z ∼ 2 with the Gaia-Sausage-Enceladus (GSE) galaxy. Here we use H3 Survey data to argue that GSE entered the Galaxy on a retrograde orbit based on a population of highly retrograde stars with chemistry similar to the largely radial GSE debris. We present the first tailored N-body simulations of the merger. From a grid of ≈500 simulations we find that a GSE with M ⋆ = 5 × 108 M ⊙, M DM = 2 × 1011 M ⊙ best matches the H3 data. This simulation shows that the retrograde stars are stripped from GSE’s outer disk early in the merger. Despite being selected purely on angular momenta and radial distributions, this simulation reproduces and explains the following phenomena: (i) the triaxial shape of the inner halo, whose major axis is at ≈35° to the plane and connects GSE’s apocenters; (ii) the Hercules-Aquila Cloud and the Virgo Overdensity, which arise due to apocenter pileup; and (iii) the 2 Gyr lag between the quenching of GSE and the truncation of the age distribution of the in situ halo, which tracks the lag between the first and final GSE pericenters. We make the following predictions: (i) the inner halo has a “double-break” density profile with breaks at both ≈15–18 kpc and 30 kpc, coincident with the GSE apocenters; and (ii) the outer halo has retrograde streams awaiting discovery at >30 kpc that contain ≈10% of GSE’s stars. The retrograde (radial) GSE debris originates from its outer (inner) disk—exploiting this trend, we reconstruct the stellar metallicity gradient of GSE (−0.04 ± 0.01 dex r 50 − 1 ). These simulations imply that GSE delivered ≈20% of the Milky Way’s present-day dark matter and ≈50% of its stellar halo.

scholarly journals The Sheet of Giants: Unusual properties of the Milky Way’s immediate neighbourhood

2020 ◽  
Vol 494 (2) ◽  
pp. 2600-2617 ◽  
Author(s):  
Maria K Neuzil ◽  
Philip Mansfield ◽  
Andrey V Kravtsov
Keyword(s):  
Milky Way ◽  
Number Density ◽  
Local Volume ◽  
Oblate Ellipsoid ◽  
Galaxy Distribution ◽  
Λcdm Model ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
The Mean ◽  
The Impact

ABSTRACT We quantify the shape and overdensity of the galaxy distribution in the ‘Local Sheet’ within a sphere of R = 8 Mpc and compare these properties with the expectations of the ΛCDM model. We measure ellipsoidal axis ratios of c/a ≈ 0.16 and b/a ≈ 0.79, indicating that the distribution of galaxies in the Local Volume can be approximated by a flattened oblate ellipsoid, consistent with the ‘sheet’-like configuration noted in previous studies. In contrast with previous estimates that the Local Sheet has a density close to average, we find that the number density of faint and bright galaxies in the Local Volume is ≈1.7 and ≈5.2 times denser, respectively, than the mean number density of galaxies of the same luminosity. Comparison with simulations shows that the number density contrasts of bright and faint galaxies within 8 Mpc alone make the Local Volume a ≈2.5 σ outlier in the ΛCDM cosmology. Our results indicate that the cosmic neighbourhood of the Milky Way may be unusual for galaxies of similar luminosity. The impact of the peculiar properties of our neighbourhood on the properties of the Milky Way and other nearby galaxies is not yet understood and warrants further study.

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