Image of the Week

Extra-galactic Observations with GAIA

Figure 1: Combination of Gaia observations of NGC 604 with one of the sharpest images available from the Hubble Space Telescope (Image credit: ESA/Gaia/DPAC/IEEC-UB)

Today, since the start of the routine scientific operations phase on 25 July 2014, Gaia has been scanning the sky for exactly 1000 days. More than 35 TB of scientific data were gathered until now, close to 70 billion object transits through the focal plane were observed and an impressive 686 billion positional or astrometric measurements, 146 billion brightness or photometric data points, and 13.6 billion spectra were recorded until now.

The instruments onboard Gaia are measuring any object seen by its telescopes, as long as the objects appear bright and sharp enough to the autonomous source detection system. This detection system does not (and cannot) distinguish between galactic and extra-galactic stars. Hence, thanks to its excellent angular resolution and sensitivity, Gaia is not only doing the most complete and accurate census of our own Galaxy, but also it is able to observe individual stars in other, nearby galaxies.

Figure 2: M33 Galaxy, also known as the Triangulum Galaxy, as observed by Gaia. (Image credit: ESA/Gaia/DPAC/IEEC-UB)

Figure 2 shows an example of these extra-galactic capabilities of Gaia. In this case it is the M33 Galaxy, some 2.4 million light-years away. It has about 40 billion stars, but Gaia obviously just detects a tiny fraction (about 40 thousand - the brightest ones). Even for bright enough stars, sky regions like this are too dense for the excellent hardware capabilities onboard Gaia. It means that only a fraction of these extra-galactic stars can be detected or measured during a given pass, but the stars will be measured during subsequent passes throughout the mission. This is specifically relevant for stars close to the faint detection limit in crowded regions. Thus, the observed fraction of the stellar population from nearby galaxies will progressively increase, although each of those stars will obviously be measured fewer times than brighter Milky Way stars.

The figure was automatically generated by the Initial Data Treatment (IDT) monitoring system, and it focuses on the region labeled as "most unmatched" among the regions processed during a given daily run. That is, many detections in this region do not yet have any nearby entry in the accumulated and consolidated list of observed stars. The reason is the incomplete observation previously mentioned - specifically, the incomplete observations in previous passes. As the mission progresses, the fraction of observed M33 stars will progressively increase. The IDT monitoring system detected this region in two almost consecutive runs (between the 6th and 9th of December 2016), which reassures the capability of Gaia of repeatedly detecting and observing even such distant and faint objects.

To illustrate the high resolution of Gaia, a tiny and specific region of this galaxy (highlighted with a red square in Figure 2) was examined. It contains NGC 604, an HII region (an emission nebula) where many stars have just been born - basically a giant stellar nursery. Figure 3 shows the sharpest Hubble image currently available for that area, whereas Figure 4 shows the corresponding synthetic image from Gaia detections.

Figure 3: Sharpest Hubble Space Telescope image currently available for NGC 604 (Image credit: NASA/ESA/Hubble Space Telescope)

The Gaia synthetic image of NGC 604 was obtained from data covering 26 consecutive scans in a bit more than three days (four revolutions per day, two telescope scans per revolution). Past observations of that region have not been taken into account in these figures. Here we see about 150 individual stars detected in the NGC 604 region (about 0.55 square arcminutes in the figure), meaning a detected star density of about one million stars per square degree - an extremely high one. The magnitudes range from 16.2 to 20.7 (although most detections are in the 18.8 to 20.4 magnitude range).

Figure 4: Synthetic image of NGC 604 from Gaia detections. Note the very small field of view (just 50 arcseconds wide, or 0.014 degrees). Sky coordinates of objects in this plot are preliminary, determined by the daily IDT system with an accuracy of about 0.2 arcseconds. (Image credit: ESA/Gaia/DPAC/IEEC-UB)

 

In Figure 1, also serving as image of the week, we show a combination of the Hubble image with the Gaia synthetic image, where we can see that indeed many of the stars in that very distant region are detected and measured.

More information on NGC 604 can be found from the Hubble Space Telescope website, the Astronomy Picture of the Day website, and from Wikipedia. More on these extra-galactic observations by Gaia can be found here.

Credits: ESA/Gaia/DPAC/IEEC-UB, Jordi Portell, Francesca Figueras, Carme Jordi

[Published: 20/04/2017]

 

Image of the Week Archive

2017
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
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
 
Please note: Entries from the period 2003-2010 are available in this PDF document.