‘Invisible’ galaxies, distorted arcs and galactic rings revealed by first images from INGRID

Contact: Dr. Chris Packham

cp@ing.iac.es

34-922-425431

Isaac Newton Group of Telescopes

The Isaac Newton Group Red Imaging Device (INGRID) saw its first light on
the William Herschel Telescope on March 16. INGRID provides astronomers with
the opportunity to make large field of view, deep near-infrared observations
of the universe, as demonstrated by the images achieved on the first night
of scientific use.

First light observations from INGRID reveal the central regions of the
massive cluster of galaxies, Abell 2218, at a distance of approximately 2
thousand million light years from Earth. Several arc like features are
clearly visible around the brightest galaxies at the cluster center. These
represent the distorted and gravitationally magnified images of very distant
galaxies behind the cluster. The huge concentration of dark matter in the
core of the cluster acts as a gravitational lens, bending the paths of light
rays from the background galaxies and in the process magnifying their
images, in accordance with Einstein’s theory of relativity.

This image is being used to study the properties of a rare class of galaxies
which are bright at near-infrared wavelengths but invisible in the optical,
and a possibly related family of very luminous galaxies which emit most of
their energy in infrared light. By exploiting the magnification by the
cluster lens, astronomers can investigate the properties of these faint
galaxies in much greater detail than would otherwise be possible. The new
infrared camera, INGRID, facilitates the study of these very distant and
faint galaxies.

INGRID was also used to image the spiral galaxy Messier 95 (NGC 3351), a
galaxy at a distance of some 30 million light years from Earth. The image
shows a combination of near-infrared INGRID images in the J and K_s bands
tracing the location of old stars, and an optical image, obtained with the
1m Jacobus Kapteyn Telescope, which primarily traces young stars.

Messier 95 is noteworthy because it has a prominent bar, and a number of
rings outlined mainly by relatively young stars. The most obvious of these
rings is the so-called inner ring, formed by a pair of tightly-wound spiral
arms connecting to the end of the bar. A bright but small nuclear ring,
outlined by very intense regions of star formation, can be seen surrounding
the nucleus . In the outer parts of the galaxy, a third ring is present,
although very faint and barely visible on the images. Rings and bars are
common features of spiral galaxies, thought to be directly related to the
overall dynamics of the galaxy. As such, they are powerful probes of the
physical mechanisms that organise star formation in the disk, in spiral
arms, and in and just around the nucleus.

INGRID saw her first light on the William Herschel Telescope (WHT), the
telescope named after Sir William Herschel, a little after the 200th
anniversary of the discovery of infrared radiation by this famous
astronomer. INGRID makes use of a single array enabling observations between
the wavelengths of 0.9 to 2.4 micrometers. Observations at these wavelengths
are particularly important for a variety of reasons:

• infrared light penetrates dust which commonly surrounds galaxies and young
  stars far better than optical light and therefore INGRID can see into
  otherwise obscured regions of the universe.
  

  
  

• maps of our own Galaxy are most easily made at infrared wavelengths due to
  clouds of dust hiding the optical light.
  

  
  

• light from the distant galaxies is redshifted, moving the galaxy’s optical
  light to infrared wavelengths where optical detectors no longer detect
  light.
  

  
  

• some of the key elements of the universe are best detected at infrared
  wavelengths, allowing astronomers new insights into the building blocks of
  stars, planets and even life itself.
  

  
  

• planets and brown dwarfs (‘failed stars’) shine brightest at infrared
  wavelengths.
  

  
  

• stars and galaxies used to map the universe in order to understand the
  big-bang model are best observed at infrared wavelengths.

Dr. Chris Packham, INGRID project scientist commented “The moment of first
light was very special for all those involved with INGRID as it constituted
the climax of three years of hard work. I was delighted as the first images
showed the wide field capabilities of INGRID and revealed the arms of a
beautiful spiral galaxy, confirming the high quality of the optics. I was
particularly satisfied as INGRID made some of these images only 45 minutes
after sunset on the first night of commissioning!”. In fact commissioning
went so smoothly that second night images from INGRID were displayed live
via the internet to London during a lecture to the Royal Institution.

While it is clear that infrared observations are key to many aspects of
astronomy, constructing infrared instruments is far from easy, as all the
components of INGRID must be kept at less than 190 degrees C below zero and
in a vacuum! The volume of INGRID is some 70 litres and holds the
all-important optical components steady at temperatures between 30 degrees C
(ambient) to -190 degrees C (operating) at all orientations to better than
20 micrometers, half the width of a human hair! INGRID is the first
instrument developed, assembled and commissioned by the Isaac Newton Group
on La Palma, with assistance from the Royal Greenwich Observatory, Cambridge
and the Astronomy Technology Centre, Edinburgh, and the Spanish Instituto de
Astrofisica de Canarias on the neighbouring island of Tenerife.

INGRID is now available for observations to the UK, Dutch and Spanish
astronomical communities. For UK astronomers it represents an especially
interesting addition to their astronomical facilities when combined with the
instruments available at UKIRT, the UK’s dedicated infrared telescope in
Hawaii, as the instruments available fully compliment each other.

The WHT has now enhanced its capabilities with INGRID, as with the touch of
a button astronomers can image the cosmos at wavelengths from ultraviolet to
infrared by using INGRID and an optical camera already on the WHT. Later
this year, INGRID will be used with the WHT’s new adaptive optics instrument
NAOMI. This will allow the finest details possible with the WHT to be seen
with INGRID by the use of special optics which can change its shape to
remove the ‘twinkling’ from the stars.

The Isaac Newton Group of Telescopes is an establishment of the Particle
Physics and Astronomy Research Council of the United Kingdom and the
Nederlandse Organisatie voor Wetenschappelijk Onderzoek of the Netherlands
The Isaac Newton Group of Telescopes (ING) consists of the 4.2 metre William
Herschel Telescope, the 2.5 metre Isaac Newton Telescope and the 1.0 metre
Jacobus Kapteyn Telescope. The telescopes are owned and operated jointly by
the Particle Physics and Astronomy Research Council (PPARC) of the United
Kingdom and the Nederlandse Organisatie voor Wetenschappelijk Onderzoek
(NWO) of the Netherlands. The telescopes are located in the Spanish
Observatorio del Roque de Los Muchachos on La Palma which is operated on
behalf of Spain by the Instituto de Astrofisica de Canarias (IAC).

PICTURES

Gravitational Arcs in Abell 2218

Location: http://www.ing.iac.es/PR/press/ing100.html

Picture credit: Ian Smail (University of Durham) and Chris Packham (ING).

Caption: The image is a combination of a B-band frame acquired using a CCD
on the WHT Cassegrain focus with two near-infrared exposures in the J- and
K-bands obtained with INGRID with the B (0.4 micrometres), J (1.2
micrometres), and K (2.2 micrometres) images coded as blue, green and red.
The field of view of this image is 3 arcminutes, corresponding to 2 million
light years across at the distance of the cluster. The INGRID exposure times
totalled 4 hours in J and 2.5 hours in K under good sky conditions (better
than 0.8 arcsecond seeing).

Rings and Bars in Messier 95

Location: http://www.ing.iac.es/PR/press/ing100.html

Picture credit: Johan Knapen (ING and University of Hertfordshire)

Caption: False colour image showing the morphology of the barred spiral
galaxy Messier 95. Young stars and sites of current star formation show up
as blue regions, whereas the red light, measured with INGRID, traces
dustlanes in the galaxy, and the older stellar populations. The dust lanes,
lacking blue emission, are seen as brownish red in the image; the bar is
made up of old stars and shows up as white.

INGRID on the William Herschel Telescope

Location: http://www.ing.iac.es/PR/press/ing100.html

Picture credit: Isaac Newton Group of Telescopes.

Caption: INGRID mounted on the Acquisition and Guidance box of the 4.2m
William Herschel Telescope (folded Cassegrain focus). It is held in
alignment by the purpose built support bracket (coloured gold in the
picture). The array’s controller and the instrument’s closed cycle cooler
can also be seen mounted directly onto the main vacuum jacket. The
collimating optics assembly is just visible through the spaces in the
support bracket.

4.2m William Herschel Telescope

Location: http://www.ing.iac.es/PR/press/ing100.html

Picture credit: Isaac Newton Group of Telescopes.

Caption: The 4.2m William Herschel Telescope.

FOR FURTHER INFORMATION PLEASE CONTACT:

Dr. Ian Smail
Royal Society Research Fellow
Department of Physics, University of Durham
E-mail: Ian.Smail@durham.ac.uk
Phone: 44-191-3747463
Fax: 44-191-3747465

Dr. Johan Knapen
Research Fellow
Isaac Newton Group of Telescopes and University of Hertfordshire
E-mail: knapen@ing.iac.es

Mr. Javier Mendez
ING Public Relations Officer
Isaac Newton Group of Telescopes
E-mail: jma@ing.iac.es
Phone: 34-922-425464, 34-616-464111
Fax: 34-922-425401

More information on the 200th anniversary of the discovery of infrared rays
by Sir William Herschel can be found in this Royal Astronomical Society
press release:
http://www.ras.org.uk/press/pn00-02.htm

INGRID home page:
http://www.ing.iac.es/Astronomy/IR/INGRID

http://www.ast.cam.ac.uk/ING/Astronomy/IR/INGRID (UK mirror)

More information on ING:
http://www.ing.iac.es/PR/

http://www.ast.cam.ac.uk/ING/PR/

Other web sites:
PPARC: http://www.pparc.ac.uk

NWO: http://www.nwo.nl