Image of the Week

A new Panoramic Sky map of the Milky Way's Stellar streams

 

Stellar stream structures in the northern Galactic sky, as obtained by the STREAMFINDER algorithm after processing the Gaia data. Every point on this map is a star, where the associated color represents their flow speeds. A rich network of criss-crossing streams can be seen. In addition of detecting previously known streams, for example the so called "GD-1" stream, the researchers also reported several streams as new discoveries, suffixed here with "*". Image credit: Khyati Malhan, Rodrigo A. Ibata, Nicolas F. Martin

 

A group of researchers from the Observatoire Astronomique de Strasbourg created an all-sky structural and kinematic map of the stellar stream substructures of the Milky Way halo. This was accomplished using Gaia Data Release 2 and was possible due to the unprecedented quality of the data.

This initial mapping of the stellar substructures in the galactic halo starts to unravel the complex formation history of our Galaxy. The formation and evolution of galaxies is one of the great outstanding problems of astrophysics. One of the prevailing frameworks that attempts to explain the structure and the composition of the Milky Way galaxy, known as the hierarchical structure formation framework, suggests that the Milky Way halo was built up over an extended period through the aggregation and accretion of smaller mass systems (such as satellite galaxies).

Numerical simulations based on this cosmological paradigm have shown that when low mass stellar systems orbiting the host galaxy come too close to the host’s centre, they undergo disruption and distortion due to the action of tidal forces. This process rips out stars from the progenitor and leads to the formation of stellar residues that are called "tidal debris’". A series of such merging and accretion events in the environment of the galaxy, collectively, gives rise to an inhomogeneous distribution of stars in the galactic halo. If this theoretically-motivated hierarchical cosmological model is indeed correct, then it is expected to see some fossil residues of these past or on-going accretion events.

With the arrival of Gaia DR2, Khyati Malhan along with his PhD supervisor Dr. Rodrigo A. Ibata (CNRS, DR2) and researcher Dr. Nicolas F. Martin (CNRS, CR), built a state-of-the-art algorithm to analyse the Gaia data. STREAMFINDER is a new powerful algorithm that was designed to detect stellar streams in the Milky Way halo. Stellar streams are a class of stellar debris that are formed when the tidal disruption acts slowly. These structures are of extreme astrophysical importance, as they serve as sensitive seismographs allowing us to probe the underlying dark matter distribution of the Milky Way galaxy, and are also crucial as tracers of the galaxy formation process. The algorithm was constructed to hunt for groups of stars in the dataset that resembled such streams, sharing similar orbits and also containing particular types of stellar populations.

Potential streams of stars identified by STREAMFINDER in the Milky Way's inner halo, from 5 to 15 kpc. Results for a metal-rich selection are shown in the top panels, while results for intermediate metallicity are shown in the lower panels. Some of the previously known stream structures can be seen in these maps, for example the so called "GD-1" stream, Indus and Jhelum. All stream points displayed here have detection significance of more than 5 σ. Image credit: Khyati Malhan, Rodrigo A. Ibata, Nicolas F. Martin

 

 

On the very day of the data release, 25th April 2018, these researchers launched STREAMFINDER on the Gaia data. This study reveals, for the first time, an all-sky structural and kinematic map of the stellar streams of the Milky Way halo. They found a rich network of criss-crossing streams, often with striking kinematic coherence. Several of these structures, which can be seen in the above figures named Gaia -1, 2, 3, 4 and 5, were reported as discoveries. The lumpiness in these maps strongly supports the picture in which the Milky Way accumulated stars by undergoing a significant number of merging and accretion events. While the results that they obtained are but a first step in the comprehensive mapping of the Milky Way’s stellar halo, they already show the promise of the Gaia mission, borne out by the rich view of the heavens it has unveiled.

This story is based on the article "Ghostly Tributaries to the Milky Way: Charting the Halo's Stellar Streams with the Gaia DR2 catalogue." by Khyati Malhan, Rodrigo A. Ibata and Nicolas F. Martin which was published on 12 September 2018 in Monthly Notices of Royal Astronomical Society.

 

 

Stellar stream structures in the southern Galactic sky, as obtained by the STREAMFINDER algorithm after processing the Gaia data. Every point on this map is a star, where the associated color represents their flow speeds. A rich network of criss-crossing streams can be seen. In addition of detecting previously known streams, for example the "Sagittarius" stream, the researchers also reported several streams as new discoveries, suffixed here with "*". Gaia-2, for example, is a newly discovered stream that can be seen to be lying right at the southern Galactic cap. Image credit: Khyati Malhan, Rodrigo A. Ibata, Nicolas F. Martin

Credits: ESA/Gaia/DPAC, Khyati Malhan from the Observatoire Astronomique de Strasbourg, Rodrigo A. Ibata from CNRS, Nicolas F. Martin from CNRS

[Published: 30/09/2018]

 

Image of the Week Archive

2018
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.