Image of the Week

 

Mapping the interstellar medium using the Gaia RVS spectra

 

Figure 1. Upper left panel: the animation shows how the intensity, or strength, of the DIB at 862 nm gets stronger at increasing stellar distance along a given line of sight. The distance of each star is indicated in the plot, while the black line shows the best model description. Lower left panel: here we show a measure of the strength of the DIB, by measuring its equivalent width, or EW), at changing distance, and we can see a clear correlation between the strength and the distance from Earth. The uncertainty on the measured EW is shown as well: as the distance increases, so does the noise on the spectrum and the EWs become more difficult to measure precisely. Right panel: we move from a single line-of sight to all the possible line-of-sights explored by Gaia spectra. We show a face-on view of the Galaxy (sketch created by R. Benjamin, in Churchwell et al. 2009) superimposing the spatial distribution of the DIB EWs. Credits: ESA/Gaia/DPAC - CC BY-SA 3.0 IGO, based on images published in Gaia Collaboration, Schultheis, et al. 2022.

 

The spectrum of a star is a gold mine of information, not only on the star itself but also on the dusty interstellar medium that is between us and the star. Both the star and the interstellar medium absorb the light that is emitted from the stellar surface, and the result is the presence of absorption features in the spectrum.

Having different origins, the 2 types of features (from star and for the medium) behave in a different way. The position of the stellar features changes according to the radial velocity of the star as seen from the observer (the well known Doppler effect) while the interstellar medium features are at a fixed position in the spectrum, i.e. their wavelength does not change. The features originating from stars have long been identified and are quite well understood, while there are still many things that remain unknown concerning the interstellar features.

The most famous interstellar feature is due to sodium (its atomic name is Na) but there are many, more subtle, features that have since been found. The interstellar medium is everywhere in space, and its properties, density and chemical composition can vary a lot in different regions of the Galaxy. But the farther we look, the stronger is its signature on the spectra. This is because the light of the star statistically crosses a larger amount of interstellar medium.

Diffuse interstellar bands (DIBs) are weak and have very broad absorption features, found at specific wavelengths, that originate from the interstellar medium. One example is shown in the left panel in the above figure, where the same feature with different intensities (or strengths) is shown as an animated image. They were first detected more than 100 years ago in 1919 by Mary L. Heger at Lick Observatory when she studied the interstellar sodium lines. She noticed that the absorption features remained stationary in the spectrum, while the lines originating from the star moved over time. These were later identified as Na lines.

So far, astronomers have found more than 600 DIBs but only one DIB has been successfully reproduced by laboratory measurements, tracing its origin to absorption by a complex molecule Buckminsterfullerene (C60+). However we still don’t know the origin of all the other DIBs, including the DIB observed at 862 nm in Gaia RVS spectra. This is what we call the longest mystery in stellar spectroscopy.

In the Gaia RVS wavelength range, DIBs are present and can be measured. Gaia Data Release 3 provides the first homogeneous all-sky survey of the DIB at 862 nm containing nearly half a million sources. This is so far the largest catalogue of DIBs.

The animation provided above shows in different ways how the strength of the DIB depends on the distance of the star. To build the plot on the left panels, we selected a specific line of sight, i.e. a direction in the sky, and extracted a sequence of Gaia RVS spectra from stars in this direction having measurable DIBs. Of course, Gaia also provides a solid determination of the distance.

On the upper left panel, we show an animated sequence of Gaia spectra zoomed in on the DIB region at 862 nm. We can clearly see how the DIB at 862 nm gets stronger at increasing stellar distance, which is also reported on the plot.

The lower left panel shows this correlation more clearly, by plotting the equivalent width (EW) of this feature, i.e. a measure of the strength of this feature, versus the distance of the star. The uncertainty of the equivalent width (EW) measurement is also shown in the plot: we receive less light from a more distant star, and therefore the noise on the Gaia spectra becomes stronger and the measure of the equivalent width gets more uncertain.

The animation in the right panel extends this concept to the entire Galactic plane visible by Gaia, using all the DIB EWs available in Gaia DR3, i.e. all the lines of sight. The animation represents (a projection of) the first 3-D map of DIB absorptions. Thanks to the homogeneity, high quality and uniformity of the Gaia DIB database, for the first time detailed spatial structures of the DIB distribution are revealed.

To build the animation shown above, we have selected only the high quality sample of DIBs (see additional information below) provided in the Gaia Data Release 3, as discussed and presented in Gaia Collaboration, Schultheis et al. (2022).

In Gaia Collaboration, Schultheis et al. (2022) we go further in the analysis. We have demonstrated a tight relation with the amount of interstellar dust, i.e. the interstellar reddening, showing the similarities between the DIB 862nm carrier, whose origin is still unknown, and the dust distribution in the Milky Way. This is possible due to the independent measures of interstellar reddening available for these stars, as measured from Gaia XP spectra and available in Gaia DR3. We also show that the picture is still quite complex, since there are important differences with the dust distribution, such as the presence of the DIBs in the so-called Local Bubble (a zone devoid of dust).

Due to the large number of high quality DIB measures, we could assess the rest-frame central wavelength of the DIB with an unprecedented precision. This is a fundamental step to try to reproduce these DIB features with detailed laboratory measurements to unveil the origin of the still unknown carrier of the DIB at 862 nm.

 

Additional information

  • The high-quality sample consists of DIB measurements with a quality flag QFlag <= 2 and where the uncertainty of the DIB strength is better than 50%. In total this sample consists of 141 103 stars. The details on the flagging system are presented in Recio-Blanco et al. (2022).
  • An introduction on the nature of the DIBs will be published in the Gaia Pills of Science
  • A related article on the interstellar medium was published on the Gaia Data Release 3 publication day.

 

Credits: ESA/Gaia/DPAC, article written by Mathias Schultheis, Rosanna Sordo, and Orlagh Creevey

[Published: 06/10/2022] ​​​​​​

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.