Dying Young: Massive Dead Disk Galaxy Challenges the Picture of How Galaxies Evolve

Stsci_2017-26_1024

stsci_2017-26 June 21st, 2017

Credit: NASA, ESA, and S. Toft (University of Copenhagen)

By combining the power of a natural lens in space with the capability of NASAs Hubble Space Telescope, astronomers made a surprising discoverythe first example of very compact yet massive disk-shaped and rotating galaxy that stopped making stars only a few billion years after the big bang. Finding a galaxy that is pancake-shapedmuch like our own Milky Wayso early in the history of the universe challenges the current understanding of how massive galaxies form and evolve, say researchers.

The galaxy, called MACS 2129-1, is considered dead because it is no longer making stars. The existence of dead galaxies so earlywhen the universe was just one-quarter its current agehas long been a puzzle, as the Universe at that time was full of gas and at the peak of the cosmic star formation history. The leading theory has been that they formed in galaxy collisions that efficiently drove all the gas into the center of the collision and turned it into stars.

Perhaps we have been blind to the fact that early dead galaxies could in fact be disks, simply because we havent been able to resolve them, said study leader Sune Toft of the Dark Cosmology Centre at the Niels Bohr Institute, University of Copenhagen. This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies.

When the universe was just 3 billion years old, half of the most massive galaxies were extremely compact and had already completed their star formation. Astronomers believe that they ultimately grew into the most massive elliptical galaxies seen in the nearby universe today. Scientists theorize they did this through mergers with small companion galaxies, which added to the stars on the galaxys outskirts.

Confirming this scenario requires more powerful telescopes than are currently available, whether on Earth or in space. However, through the phenomenon known as gravitational lensing, a massive, foreground cluster of galaxies functions as a natural telescope, magnifying and stretching images of far more distant background galaxies. By joining this natural lens with the resolving power of Hubble, scientists were able to see into the center of the dead galaxy.

The astronomers expected to see a chaotic ball of stars formed through mergers. Instead, they found a pancake-shaped stellar distribution, meaning that the stars must have been born in a disk. The remote galaxy is three times as massive as the Milky Way but only half the size. Rotational velocity measurements made with the European Southern Observatorys Very Large Telescope (VLT) showed that the disk galaxy is spinning more than twice as fast as the Milky Way.

This is observational evidence that at least some of the earliest dead galaxies must have gone through major makeovers, changing not just their structure, but also the motions of their stars, to evolve into the giant elliptical galaxies we see today.

Using archival data from the Cluster Lensing And Supernova survey with Hubble (CLASH), Toft and his team were able to determine the stellar mass, star formation rate, and the ages of the stars.

We can see that the star formation stopped first in the center of the galaxy and then moved outwards through the galaxy, Toft said. In other words, it died inside out. Until now it had been impossible to resolve them, so we didnt know if star formation stopped all at once in the whole galaxy, or if it stopped first in the center, or if it stopped first in the outskirts.

Why this galaxy stopped forming stars is still unknown. It may be the result of an active galactic nucleus, where energy is gushing from a supermassive black hole. This energy inhibits star formation. Or it may be the result of halo quenching, where, when cold gas tries to stream into the galaxys center, its rapidly heated. This prevents it from reaching the center and cooling down into star-forming clouds.

But how do these young, massive, compact disks evolve into the elliptical galaxies we see in the present-day universe? Probably through mergers, Toft said. If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies. You could also imagine major mergers. This would definitely also destroy the ordered motion of the stars.

The findings are published in the June 22 issue of the journal Nature. Toft and his team hope to use NASAs upcoming James Webb Space Telescope to look for a larger sample of such galaxies.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASAs Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. The Very Large Telescope is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of Northern Chile.

Provider: Hubble Space Telescope | STScI

Image Source: http://hubblesite.org/news_release/news/2017-26

Curator: STScI, Baltimore, MD, USA

Image Use Policy: http://hubblesite.org/copyright/

Image Details

Image Type
Observation
Object Name
MACS J2129-0741 MACS2129-1
Subject - Local Universe
Galaxy > Grouping > Cluster

Distance

Universescale3
5,700,000,000 light years
Stsci_2017-26_128
 

Position Details

Position (ICRS)
RA = 21h 29m 26.1s
DEC = -7° 41’ 28.8”
Orientation
North is 60.1° CCW
Field of View
1.8 x 1.4 arcminutes
Constellation
Aquarius

Color Mapping

  Telescope Spectral Band Wavelength
Blue Hubble (ACS/WFC) Optical (B) 435.0 nm
Blue Hubble (ACS/WFC) Optical (g) 475.0 nm
Blue Hubble (ACS/WFC) Optical (V) 606.0 nm
Blue Hubble (ACS/WFC) Optical (r) 625.0 nm
Green Hubble (ACS/WFC) Optical (i) 775.0 nm
Green Hubble (ACS/WFC) Optical (I) 814.0 nm
Green Hubble (ACS/WFC) Optical (z) 850.0 nm
Red Hubble (WFC3/IR) Near-IR (Y) 1.1 µm
Red Hubble (WFC3/IR) Near-IR (YJ) 1.1 µm
Red Hubble (WFC3/IR) Near-IR (J) 1.3 µm
Red Hubble (WFC3/IR) Near-IR (JH) 1.4 µm
Red Hubble (WFC3/IR) Near-IR (H) 1.6 µm
Spectrum_base
Blue
Blue
Blue
Blue
Green
Green
Green
Red
Red
Red
Red
Red
Stsci_2017-26_1280
×
ID
2017-26
Subject Category
C.5.5.3  
Subject Name
MACS J2129-0741, MACS2129-1
Credits
NASA, ESA, and S. Toft (University of Copenhagen)
Release Date
2017-06-21T00:00:00
Lightyears
5,700,000,000
Redshift
0.588
Reference Url
http://hubblesite.org/news_release/news/2017-26
Type
Observation
Image Quality
Good
Distance Notes
Facility
Hubble, Hubble, Hubble, Hubble, Hubble, Hubble, Hubble, Hubble, Hubble, Hubble, Hubble, Hubble
Instrument
ACS/WFC, ACS/WFC, ACS/WFC, ACS/WFC, ACS/WFC, ACS/WFC, ACS/WFC, WFC3/IR, WFC3/IR, WFC3/IR, WFC3/IR, WFC3/IR
Color Assignment
Blue, Blue, Blue, Blue, Green, Green, Green, Red, Red, Red, Red, Red
Band
Optical, Optical, Optical, Optical, Optical, Optical, Optical, Near-IR, Near-IR, Near-IR, Near-IR, Near-IR
Bandpass
B, g, V, r, i, I, z, Y, YJ, J, JH, H
Central Wavelength
435, 475, 606, 625, 775, 814, 850, 1050, 1100, 1250, 1400, 1600
Start Time
Integration Time
Dataset ID
Notes
Coordinate Frame
ICRS
Equinox
2000.0
Reference Value
322.35858333300, -7.69133333333
Reference Dimension
3528.00, 2822.00
Reference Pixel
1573.92156037572, 807.10214978829
Scale
-0.00000831090, 0.00000831090
Rotation
60.14907799088
Coordinate System Projection:
TAN
Quality
Full
FITS Header
Notes
World Coordinate System resolved using PinpointWCS 0.9.2 revision 218+ by the Chandra X-ray Center
Creator (Curator)
STScI
URL
http://hubblesite.org
Name
Space Telescope Science Institute Office of Public Outreach
Email
outreach@stsci.edu
Telephone
410-338-4444
Address
3700 San Martin Drive
City
Baltimore
State/Province
MD
Postal Code
21218
Country
USA
Rights
http://hubblesite.org/copyright/
Publisher
STScI
Publisher ID
stsci
Resource ID
STSCI-H-p1726a-f-3528x2822.tif
Metadata Date
2018-04-10T16:29:52-04:00
Metadata Version
1.2
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Detailed color mapping information coming soon...

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Universescalefull
5,700,000,000 light years