Image of the Week

 

Gaia reaches to the clouds – 3D kinematics of the LMC

 

Figure 1: Velocity maps of a subsample of Large Magellanic Cloud stars highlighting radial velocities on the left, residual tangential velocities in the middle and the vertical velocities on the right. The vertical velocities are a direct derivation of the freshly added line-of-sight velocities in Gaia's Data Release 3 and hence provide the new and third component to the velocities of stars in the Large Magellanic Cloud. Credits: Jiménez-Arranz, et al. A&A 2023.

 

With Gaia's Early Data Release 3 the structure and properties of the Magellanic Clouds were highlighted by the Gaia Collaboration, X. Luri, et al. A&A 2020. The paper demonstrates the quality of the Gaia data and a story discussing these results was published. Now, with the release of almost 34 million line-of-sight velocities with Gaia's full Data Release 3, the investigation continues, and for the first time, a homogeneous data set with 3D velocity information is available for a galaxy that is not our own Milky Way. For the first time, we can truly map the Large Magellanic Cloud (LMC) kinematically.

The Magellanic Clouds are two dwarf galaxies orbiting our Milky Way. Being immersed in our own galaxy, there are so many stars to see (especially near the Galactic Centre) that we cannot probe very far in the optical. This makes it hard to see the full picture and to study our own galaxy as a whole. With the Magellanic Clouds relatively nearby and the ability of Gaia to map stars across the full extent of these galaxies, they are excellent study objects on the structure and dynamics of galaxies. It is amazing to think that Gaia can not only see the individual stars in these dwarf galaxies but can also track their motions in three dimensions.

When Gaia looks at the stars in the Magellanic Clouds, it looks through a cloud of stars in the Milky Way. To distinguish which stars belong to the Milky Way and which stars are part of these dwarf galaxies is not trivial. The team from the University of Barcelona made use of a neural network and presented their improved and more efficient selection strategy in their paper "Kinematic analysis of the Large Magellanic Cloud using Gaia DR3" which has been published in A&A this January. The result is a more confident sample of stars believed to be all inside the Large Magellanic Cloud. But even with this better and more reliable method some contamination of Milky Way stars cannot be avoided.

This new and updated catalogue of LMC stars contains a few million stars and it is the first homogeneous data set containing 3-dimensional velocities for a galaxy orbiting the Milky Way! With this sample, the kinematics of this dwarf galaxy is studied in more detail. The insights we gain by studying the kinematics of other galaxies can help greatly in understanding the kinematics of our own Milky Way.

When making the selection for the stars belonging to the Large Magellanic Cloud, a choice has to be made whether to aim for a pure data set (containing stars that one is really sure that they are part of the LMC with the risk of losing some stars that might be members as well) or to aim for a complete data set (containing all stars we think might be members, with the risk of having some members that after all do not belong in the LMC). The solution shown here in the story is the optimal solution found by the team, which lies between complete purity and pure completeness.

With the use of a special mapping technique that focuses on overdensities, this optimal sample is plotted and the bar and spiral arms become distinguishable (see Figure 2). The inner disc of the Large Magellanic Cloud is mainly bar dominated. One can spot the spiral arm that starts at the end of the bar at around (-3,0) kpc in Figure 2.

 

Figure 2: A map of the Large Magellanic Clouds where the overdensities are plotted. This allows the creation of contour lines that reveal the location of the bar and the spiral arms. Credits: Jiménez-Arranz, et al. A&A 2023.

 

From the full sample of a few million Large Magellanic Cloud stars, only a subsample of about 20,000 stars has the third velocity component defined. In the top figure, Figure 1,  the velocity map is shown for the three velocity components of the subsample. It is the first time that the map on the right, showing vertical velocities, can be created. Without Gaia's Data Release 3 this would not have been possible.

The first map on the left in Figure 1 shows the radial velocities. Bear in mind that these are the radial velocities as observed from the centre of the Large Magellanic Cloud (or the location 0,0 in that map). They give an indication of the direction of the stars away or towards the centre. The velocity map in the middle of Figure 1 shows the residual tangential velocity, also with respect to the center of the Large Magellanic Cloud. We can see that the kinematics of the spiral arm is dominated by an inward motion and a rotation that is faster than that of the disc in the piece of the arm attached to the bar (the contours reflect the bar and spiral arms as explained in Figure 2).

On the right in Figure 1 the vertical velocity is shown. This is the third velocity component that so far was missing. A clear bimodality is seen here, with part of the plot bluer and the other part redder. There are many explanations possible for this bimodality. Either there is a contamination of Milky Way stars, or the inclination of the Large Magellanic Cloud with respect to our viewpoint from inside the Milky Way has been overestimated. Another explanation could be that this is caused by a warp. Also the Milky Way is warped, and similarly, the Large Magellanic Cloud could be subjected to this as well, making part of the galaxy move upwards, and the other side moves downwards.

Figure 3 shows the same velocity maps but for the full sample of the Large Magellanic Cloud stars without the third velocity component (so the few million stars as opposed to the ~20,000 stars). Evidently, the map for the third velocity component there is missing. The fact of not having the line-of-sight velocities does not bias too much the results as seen in this Figure (compare Figure 1 and Figure 3).

 

 

Figure 3: Velocity maps of the full sample of Large Magellanic Cloud stars with on the left the map of radial velocities, and on the right the map of residual tangential velocities. Credits: Jiménez-Arranz, et al. A&A 2023.

 

With Gaia's Data Release 3 we have been able to map and see the cloverleaf pattern in the center of our Milky Way caused by the stars orbiting the Galactic centre (see Gaia Collaboration, R. Drimmel et al. 2022). Similarly, now with Gaia's Data Release 3 we can see this velocity imprint also in full detail in the Large Magellanic Cloud, and add the third velocity component to its stars. Exciting times to study galaxy kinematics!

 

Further reading:

 

Credits: Story written by Tineke Roegiers and Óscar Jiménez-Arranz

[Published: 31/01/2023]

Image of the Week Archive

2023

31/01: Gaia reaches to the clouds – 3D kinematics of the LMC

25/01: Meet your neighbours: CNS5 - the fifth catalogue of nearby stars

18/01: A single-object visualisation tool for Gaia objects

2022

25/11: 100 months of Gaia data

23/11: The astonishment

09/11: Gamma-Ray Burst detection from Lagrange 2 point by Gaia

04/11: Gaia's first black hole discovery: Gaia BH1

26/10: Are Newton and Einstein in error after all?

21/10: Gaia ESA Archive goes live with third data release

06/10: Mapping the interstellar medium using the Gaia RVS spectra

26/09: Gaia on the hunt for dual quasars and gravitational lenses

23/09: Gaia's observation of relativistic deflection of light close to Jupiter

13/06: Gaia Data Release 3

10/06: MK classification of stars from BP/RP spectrophotometry across the Hertzsprung-Russell diagram

09/06: BP/RP low-resolution spectroscopy across the Hertzsprung-Russell diagram

27/05: Cepheids and their radial velocity curves

23/05: The Galaxy in your preferred colours

19/05: GaiaXPy 1.0.0 released, a tool for Gaia's BP/RP spectra users

11/05: Systemic proper motions of 73 galaxies in the Local group

28/03: Gaia query statistics

16/03: Gaia's first photo shooting of the James Webb Space Telescope

08/03: Gaia's women in science - coordination unit 8

25/02: Not only distances: what Gaia DR3 RR Lyrae stars will tell us about our Galaxy and beyond

11/02: Gaia's women in science

31/01: Astrometric orbit of the exoplanet-host star HD81040

12/01: The Local Bubble - source of our nearby stars

05/01: A Milky-Way relic of the formation of the Universe

2021

23/12: Signal-to-Noise ratio for Gaia DR3 BP/RP mean spectra

22/12: The 7 October 2021 stellar occultation by the Neptunian system

01/12: Observation of a long-predicted new type of binary star

24/09: Astrometric microlensing effect in the Gaia16aye event

22/09: the power of the third dimension - the discovery of a gigantic cavity in space

16/09: An alternative Gaia sky chart

25/08: Gaia Photometric Science Alerts and Gravitational Wave Triggers

09/07: How Gaia unveils what stars are made of

23/06: Interviews with CU3

27/04: HIP 70674 Orbital solution resulting from Gaia DR3 processing

30/03: First transiting exoplanet by Gaia

26/03: Apophis' Yarkovsky acceleration improved through stellar occultation

26/02: Matching observations to sources for Gaia DR4

2020

22/12: QSO emission lines in low-resolution BP/RP spectra

03/12: Gaia Early Data Release 3

29/10: Gaia EDR3 passbands

15/10: Star clusters are only the tip of the iceberg

04/09: Discovery of a year long superoutburst in a white dwarf binary

12/08: First calibrated XP spectra

22/07: Gaia and the size of the Solar System

16/07: Testing CDM and geometry-driven Milky Way rotation Curve Models

30/06: Gaia's impact on Solar system science

14/05: Machine-learning techniques reveal hundreds of open clusters in Gaia data

20/03: The chemical trace of Galactic stellar populations as seen by Gaia

09/01: Discovery of a new star cluster: Price-Whelan1

08/01: Largest ever seen gaseous structure in our Galaxy

2019
20/12: The lost stars of the Hyades
06/12: Do we see a dark-matter like effect in globular clusters?
12/11: Hypervelocity star ejected from a supermassive black hole
17/09: Instrument Development Award
08/08: 30th anniversary of Hipparcos
17/07: Whitehead Eclipse Avoidance Manoeuvre
28/06: Following up on Gaia Solar System Objects
19/06: News from the Gaia Archive
29/05: Spectroscopic variability of emission lines stars with Gaia
24/05: Evidence of new magnetic transitions in late-type stars
03/05: Atmospheric dynamics of AGB stars revealed by Gaia
25/04: Geographic contributions to DPAC
22/04: omega Centauri's lost stars
18/04: 53rd ESLAB symposium "the Gaia universe"
18/02: A river of stars
2018
21/12: Sonification of Gaia data
18/12: Gaia captures a rare FU Ori outburst
12/12: Changes in the DPAC Executive
26/11:New Very Low Mass dwarfs in Gaia data
19/11: Hypervelocity White Dwarfs in Gaia data
15/11: Hunting evolved carbon stars with Gaia RP spectra
13/11: Gaia catches the movement of the tiny galaxies surrounding the Milky Way
06/11: Secrets of the "wild duck" cluster revealed
12/10: 25 years since the initial GAIA proposal
09/10: 3rd Gaia DPAC Consortium Meeting
30/09: A new panoramic sky map of the Milky Way's Stellar Streams
25/09: Plausible home stars for interstellar object 'Oumuamua
11/09: Impressions from the IAU General Assembly
30/06: Asteroids in Gaia Data
14/06: Mapping and visualising Gaia DR2

25/04: In-depth stories on Gaia DR2

14/04: Gaia tops one trillion observations
16/03: Gaia DR2 Passbands
27/02: Triton observation campaign
11/02: Gaia Women In Science
29/01: Following-up on Gaia
2017
19/12: 4th launch anniversary
24/11: Gaia-GOSA service
27/10: German Gaia stamp in the making
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
04/10: 1:1 Gaia model arrives at ESAC
31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
27/08: Quest for the Sun's siblings
 
Please note: Entries from the period 2003-2010 are available in this PDF document.