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

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.

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The last breath of the Sagittarius dSph

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2114 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4162-4182 ◽

Cited By ~ 3

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.

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Using ground based data as a precursor for Gaia in getting proper motions of satellites

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005750 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 210-213

Author(s):

Tobias K. Fritz ◽

Sean T. Linden ◽

Paul Zivick ◽

Nitya Kallivayalil ◽

Jo Bovy

Keyword(s):

Adaptive Optics ◽

Globular Cluster ◽

Proper Motion ◽

Milky Way ◽

Dwarf Galaxy ◽

Optical Data ◽

Line Of Sight ◽

Wide Field ◽

Proper Motions ◽

Tidal Stream

AbstractWe present our effort to measure the proper motions of satellites in the halo of the Milky Way with mainly ground based telescopes as a precursor on what is possible with Gaia. For our first study, we used wide field optical data from the LBT combined with a first epoch of SDSS observations, on the globular cluster Palomar 5 (Pal 5). Since Pal 5 is associated with a tidal stream it is very useful to constrain the shape of the potential of the Milky Way. The motion and other properties of the Pal 5 system constrain the inner halo of the Milky Way to be rather spherical. Further, we combined adaptive optics and HST to get an absolute proper motion of the globular cluster Pyxis. Using the proper motion and the line-of-sight velocity we find that the orbit of Pyxis is rather eccentric with its apocenter at more than 100 kpc and its pericenter at about 30 kpc. The dynamics excludes an association with the ATLAS stream, the Magellanic clouds, and all satellites of the Milky Way at least down to the mass of Leo II. However, the properties of Pyxis, like metallicity and age, point to an origin from a dwarf of at least the mass of Leo II. We therefore propose that Pyxis originated from an unknown relatively massive dwarf galaxy, which is likely today fully disrupted. Assuming that Pyxis is bound to the Milky Way we derive a 68% lower limit on the mass of the Milky Way of 9.5 × 1011 M⊙.

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A New Absolute Proper Motion Determination of Leo I Using HST/WFPC2 Images and Gaia EDR3

The Astronomical Journal ◽

10.3847/1538-3881/ac30dc ◽

2021 ◽

Vol 163 (1) ◽

pp. 1

Author(s):

Dana I. Casetti-Dinescu ◽

Caitlin K. Hansen ◽

Terrence M. Girard ◽

Vera Kozhurina-Platais ◽

Imants Platais ◽

...

Keyword(s):

Proper Motion ◽

Milky Way ◽

Proper Motions ◽

Large Area ◽

Field Of Study ◽

Data Set ◽

Polar Structure ◽

The Galaxy ◽

The Absolute

Abstract We measure the absolute proper motion of Leo I using a WFPC2/HST data set that spans up to 10 yr to date the longest time baseline utilized for this satellite. The measurement relies on ∼2300 Leo I stars located near the center of light of the galaxy; the correction to absolute proper motion is based on 174 Gaia EDR3 stars and 10 galaxies. Having generated highly precise, relative proper motions for all Gaia EDR3 stars in our WFPC2 field of study, our correction to the absolute EDR3 system does not rely on these Gaia stars being Leo I members. This new determination also benefits from a recently improved astrometric calibration of WFPC2. The resulting proper-motion value, (μ α , μ δ ) = (−0.007 ± 0.035, − 0.119 ± 0.026) mas yr−1 is in agreement with recent, large-area, Gaia EDR3-based determinations. We discuss all the recent measurements of Leo I’s proper motion and adopt a combined, multistudy average of ( μ α 3 meas , μ δ 3 meas ) = ( − 0.036 ± 0.016 , − 0.130 ± 0.010 ) mas yr−1. This value of absolute proper motion for Leo I indicates its orbital pole is well aligned with that of the vast polar structure, defined by the majority of the brightest dwarf spheroidal satellites of the Milky Way.

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The accreted nuclear clusters of the Milky Way

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3407 ◽

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.

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The VMC survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833144 ◽

2018 ◽

Vol 613 ◽

pp. L8 ◽

Cited By ~ 7

Author(s):

F. Niederhofer ◽

M.-R. L. Cioni ◽

S. Rubele ◽

T. Schmidt ◽

K. Bekki ◽

...

Keyword(s):

Near Infrared ◽

Two Dimensions ◽

Magellanic Clouds ◽

Line Of Sight ◽

Main Body ◽

Proper Motions ◽

Velocity Pattern ◽

Spatially Resolved ◽

Magnitude Diagram ◽

Over Time

We present the first spatially resolved map of stellar proper motions within the central (~3.1 × 2.4 kpc) regions of the Small Magellanic Cloud (SMC). The data used for this study encompasses four tiles from the ongoing near-infrared VISTA survey of the Magellanic Clouds system and covers a total contiguous area on the sky of ~6.81 deg2. Proper motions have been calculated independently in two dimensions from the spatial offsets in the Ks filter over time baselines between 22 and 27 months. The reflex motions of approximately 33 000 background galaxies are used to calibrate the stellar motions to an absolute scale. The resulting catalog is composed of more than 690 000 stars which have been selected based on their position in the (J − Ks, Ks) color-magnitude diagram. For the median absolute proper motion of the SMC, we find (μαcos(δ), μδ) = (1.087 ± 0.192 (sys.) ± 0.003 (stat.), −1.187 ± 0.008 (sys.) ± 0.003 (stat.)) mas yr−1, consistent with previous studies. Mapping the proper motions as a function of position within the SMC reveals a nonuniform velocity pattern indicative of a tidal feature behind the main body of the SMC and a flow of stars in the south-east moving predominantly along the line-of-sight.

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THE EARLY GREAT DEBATE: A COMMENT ON IBN AL-HAYTHAM‘S WORK ON THE LOCATION OF THE MILKY WAY WITH RESPECT TO THE EARTH

Arabic Sciences and Philosophy ◽

10.1017/s0957423917000078 ◽

2018 ◽

Vol 28 (1) ◽

pp. 1-30 ◽

Cited By ~ 1

Author(s):

Andreas Eckart

Keyword(s):

Milky Way ◽

Last Millennium ◽

The Moon ◽

Proper Motions ◽

Stellar Proper Motions ◽

The Earth ◽

Great Debate ◽

The Galaxy ◽

Early Translation ◽

Critical Translation

AbstractAt the very beginning of the last millennium Ibn al-Haytham greatly contributed to the investigation of the Milky Way. Here, the only three currently known versions of his work on the location of the Milky Way are compared to each other and discussed. A comparison of the texts and an early translation into German by E. Wiedemann in 1906 reveals several differences that triggered a new critical translation of the passed down text. We give detailed comments on the work and check the validity of Ibn al-Haytham's arguments. We also discuss his work in the framework of the ‘Great Debate’ on the Milky Way that took place around 1920, more than a decade after Wiedemann's translation. We find that Ibn al-Haytham's work is certainly at the peak of the unaided-eye era of the Milky Way's discovery. Through his own argumentation and in comparison to Ptolemy's observations Ibn al-Haytham clearly identifies the Galaxy as an extraterrestrial body that is not part of the atmosphere but much further away than the Moon. With some of his statements on the stellar positions passed down by Ptolemy, Ibn al-Haytham also anticipates the concept of stellar proper motions.

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10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

Symposium - International Astronomical Union ◽

10.1017/s0074180900085478 ◽

1998 ◽

Vol 184 ◽

pp. 433-434

Author(s):

A. M. Ghez ◽

B. L. Klein ◽

C. McCabe ◽

M. Morris ◽

E. E. Becklin

Keyword(s):

Black Hole ◽

Milky Way ◽

Galactic Center ◽

Robust Method ◽

Proper Motions ◽

Central Black Hole ◽

Milky Way Galaxy ◽

The Galaxy ◽

Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

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VMC proper motions of the Magellanic Bridge

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006762 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 130-133 ◽

Cited By ~ 1

Author(s):

Thomas Schmidt ◽

Maria-Rosa Cioni ◽

Florian Niederhofer ◽

Jonathan Diaz ◽

Gal Matijevic

Keyword(s):

Galaxy Evolution ◽

Milky Way ◽

Dwarf Galaxy ◽

Large Mass ◽

Proper Motions ◽

Dynamical Simulation ◽

Open Questions ◽

The Hierarchical Structure ◽

The Universe ◽

Good Agreement

AbstractDwarf galaxies enable us to study early phases of galaxy evolution and are key to many open questions about the hierarchical structure of the Universe. The Large and Small Magellanic Cloud (LMC and SMC) are the most luminous dwarf galaxy satellites of the Milky Way (MW). They are most likely gravitationally bound to each other, and their last interaction occurred about 200 Myr ago. Also, they are in an early phase of minor merging with the MW and will impact the Galactic structure in the future because of their relatively large mass. However, there are still major uncertainties regarding their origin and their interactions with one another and with the Milky Way. We cross-correlated the VMC and Gaia DR2 data to select a sample of stars that likely belong to the Magellanic Bridge, a feature formed of gas and stars which is connecting the LMC and the SMC. We removed potential MW foregound stars using a combination of parallax and colour-magnitude criteria and calculated the proper motions of the Bridge member stars. Our analysis supports a motion of star towards the LMC, which was found to be in good agreement with a dynamical simulation, of the SMC being stripped by the LMC.

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Stellar Populations of the Outer Milky-Way Halo

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317009279 ◽

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).

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Can we detect Galactic spiral arms? 3D dust distribution in the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005695 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 189-192 ◽

Cited By ~ 1

Author(s):

Sara Rezaei Kh. ◽

Coryn A. L. Bailer-Jones ◽

Morgan Fouesneau ◽

Richard Hanson

Keyword(s):

Spatial Correlation ◽

High Precision ◽

Milky Way ◽

Precision Measurements ◽

Line Of Sight ◽

Spiral Arms ◽

Dust Extinction ◽

The Galaxy ◽

Galactic Spiral ◽

Dust Distribution

AbstractWe present a model to map the 3D distribution of dust in the Milky Way. Although dust is just a tiny fraction of what comprises the Galaxy, it plays an important role in various processes. In recent years various maps of dust extinction have been produced, but we still lack a good knowledge of the dust distribution. Our presented approach leverages line-of-sight extinctions towards stars in the Galaxy at measured distances. Since extinction is proportional to the integral of the dust density towards a given star, it is possible to reconstruct the 3D distribution of dust by combining many lines-of-sight in a model accounting for the spatial correlation of the dust. Such a technique can be used to infer the most probable 3D distribution of dust in the Galaxy even in regions which have not been observed. This contribution provides one of the first maps which does not show the “fingers of God” effect. Furthermore, we show that expected high precision measurements of distances and extinctions offer the possibility of mapping the spiral arms in the Galaxy.

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