A Molecular Thermometer for the Distant Universe (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 14 May 2008 20:34:32 GMT
ESO Education and Public Relations Dept.
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Text with all links and the photos are available on the ESO Website at
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http://www.eso.org/public/outreach/press-rel/pr-2008/pr-13-08.html
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Contacts:
Cédric Ledoux and Pasquier Noterdaeme
ESO, Chile
Phone: +56 2 463 30 56 or +56 55 43 53 11
Patrick Petitjean
Institut d'Astrophysique de Paris, France
Phone: +33 1 44 32 81 50
Raghunathan Srianand
Inter University Centre for Astronomy and Astrophysics
Pune, India
Phone: +91 20 569 1414 (ext 320)
Dr. Henri Boffin
ESO Press Officer
Phone: +49 89 3200 6222
Valentina Rodriguez
ESO Press Officer in Chile
Phone: +56 2 463 3123
For Immediate Release: 13 May 2008
ESO Science Release 13/08
A Molecular Thermometer for the Distant Universe
First accurate measurement of the temperature of the cosmic background at
an early epoch
Astronomers have made use of ESO's Very Large Telescope to detect for the
first time in the ultraviolet the carbon monoxide molecule in a galaxy
located almost 11 billion light-years away, a feat that had remained
elusive for 25 years. This detection allows them to obtain the most
precise measurement of the cosmic temperature at such a remote epoch.
The team of astronomers [1] aimed the UVES spectrograph on ESO's VLT for
more than 8 hours at a well-hidden galaxy whose light has taken almost 11
billion years to reach us, that is about 80% of the age of the Universe.
The only way this galaxy can be seen is through the imprint its
interstellar gas leaves on the spectrum of an even more remote quasar [2].
"Quasars are here only used as a beacon in the very distant Universe.
Interstellar clouds of gas in galaxies, located between the quasars and us
on the same line of sight, absorb parts of the light emitted by the
quasars. The resulting spectrum consequently presents dark 'valleys' that
can be attributed to well-known elements and possibly molecules," explains
Raghunathan Srianand (Pune, India), who led the team making the
observations.
Thanks to the power of the VLT and a very careful selection of the target
-- the target was selected among about ten thousands quasars -- the team
was able to discover the presence of normal and deuterated molecular
hydrogen (H2, HD) and carbon monoxide (CO) molecules in the interstellar
medium of this remote galaxy. "This is the first time that these three
molecules have been detected in absorption in front of a quasar, a
detection that has remained elusive for more than a quarter century," says
Cédric Ledoux (ESO), member of the team.
The same team had already broken the record for the most distant detection
of molecular hydrogen in a galaxy that we see as it was when the Universe
was less than 1.5 billion years old (see ESO 16/06).
The interstellar gas is the reservoir from which stars form and, as such,
is an important component of galaxies. Furthermore, because the formation
and the state of molecules are very sensitive to the physical conditions
of the gas, which in turn depend on the rate at which stars are formed,
the detailed study of the chemistry of the interstellar medium is an
important tool to understand how galaxies form.
Based on their observations, the astronomers showed that the physical
conditions prevailing in the interstellar gas in this remote galaxy are
similar to what is seen in our Galaxy, the Milky Way.
But most importantly, the team was able to measure with the best ever
precision the temperature of the cosmic background radiation in the remote
Universe [3]. "Unlike other methods, measuring the temperature of the
cosmic background using the CO molecule involves very few assumptions,"
declares co-author Pasquier Noterdaeme.
If the Universe was formed in a 'Big Bang', as most astrophysicists infer,
the glow of this primeval fireball should have been warmer in the past.
This is exactly what is found by the new measurements. "Given the current
measured temperature of 2.725 K, one would expect that the temperature 11
billion years ago was about 9.3 K," says co-author Patrick Petitjean. "Our
unique set of VLT observations allows us to deduce a temperature of 9.15
K, plus or minus 0.7 K, in excellent agreement with the theory."
"We believe our analysis pioneers interstellar chemistry studies at high
redshift and demonstrates that it is possible, together with the detection
of other molecules such as HD or CH, to use interstellar chemistry to
tackle important cosmological issues," adds Srianand.
The results described here have been presented in a Letter to the Editor
in Astronomy and Astrophysics ("First detection of CO in a high-redshift
damped Lyman-alpha system", by R. Srianand et al.).
Notes
[1]: The team is composed of Raghunathan Srianand (IUCAA, Pune, India),
Pasquier Noterdaeme and Cédric Ledoux (ESO), and Patrick Petitjean (IAP,
France). The same team already made the first measurement of the
temperature of the cosmic microwave background radiation, at a time when
the Universe was only about 2.5 billion years old, also using UVES on the
VLT (see ESO 27/00). At that time, they could only measure a temperature
in the range between 6 and 14 K.
[2]: Quasars are extraordinarily luminous objects in the distant Universe,
thought to be powered by supermassive black holes at the heart of
galaxies. A single quasar could be a thousand times brighter than an
entire galaxy of a hundred billion stars, and yet this remarkable amount
of energy originates from a volume smaller than our Solar System.
[3]: One of the fundamental predictions of the Hot Big Bang theory for the
creation of the Universe is the existence of the Cosmic Microwave
Background Radiation (CMBR). This relic radiation of the primeval fireball
was discovered in 1964 by means of radio observations by American
physicists Arno A. Penzias and Robert W. Wilson, who were rewarded with
the Nobel Prize in 1978. Precision measurements by the COBE and WMAP
satellites later showed that this ancient radiation fills the Universe,
with a present-day temperature of slightly less than 3 degrees above
absolute zero (2.725 Kelvin, or -270.4 degree Celsius). A particular
prediction of the Big Bang theory is that the Universe cools when
expanding, the temperature scaling with the dilution factor of the
Universe (1 + redshift). At the redshift of the galaxy (2.41837), one
would thus expect a temperature of 2.725 x (1 + 2.41837) = 9.315 K or
-263.835 degree Celsius.
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