LOFAR discovers new giant galaxy in all-sky survey

A team of astronomers led by ASTRON astronomer Dr. George Heald has discovered a previously unknown gigantic radio galaxy, using initial images from a new, ongoing all-sky radio survey. The galaxy was found using the powerful International LOFAR Telescope (ILT), built and designed by ASTRON. The team is currently performing LOFAR's first all-sky imaging survey, the Multi-frequency Snapshot Sky Survey (MSSS). While browsing the first set of MSSS images, Dr. Heald identified a new source the size of the full moon projected on the sky. The radio emission is associated with material ejected from one member of an interacting galaxy triplet system tens to hundreds of millions of years ago. The physical extent of the material is much larger than the galaxy system itself, extending millions of light years across intergalactic space. The MSSS survey is still ongoing, and is poised to discover many new sources like this one.

Overlay of the new GRG (blue-white colors) on an optical image from the
Digitized Sky survey. The inset shows the central galaxy triplet (image
from Sloan Digital Sky Survey). The image is about 2 Mpc across.

The new galaxy is a member of a class of objects called Giant Radio Galaxies (GRGs). GRGs are a type of radio galaxy with extremely large physical size, suggesting that they are either very powerful or very old. LOFAR is an effective tool to find new GRGs like this one because of its extreme sensitivity to such large objects, combined with its operation at low frequencies that are well suited to observing old sources.

The center of the new GRG is associated with one member of a galaxy triplet known as UGC 09555. The central galaxy is located at a redshift of z=0.054536, or 750 million light years from Earth. The central radio source was previously known and has a flat radio spectrum, typical of giant radio galaxies.

LOFAR's MSSS survey is a concerted effort to image the entire northern sky at very low radio frequencies, between 30 and 160 MHz (wavelengths from 2m to 10m). The primary aim of the survey is to perform an initial shallow scan of the sky, in order to create an all-sky model that will support the calibration of much deeper observations. It is comparable in sensitivity and angular resolution to previous surveys with ‘classical' radio telescopes like the Very Large Array (VLA) in the USA, ASTRON's Westerbork Synthesis Radio Telescope (WSRT), and the Giant Metrewave Radio Telescope (GMRT) in India. MSSS is unique in that it operates at substantially lower frequencies, and is therefore poised to uncover new sources that were missed by previous surveys. Its broad bandwidth coverage is also novel in all-sky radio surveys, and will be used to provide additional information about the detected objects.

The international team of astronomers that is performing the MSSS survey is made up of about fifty members from various institutes, mostly in the Netherlands, Germany, the UK, Poland, France and Italy.

End of press release

For more information please contact:

Femke Boekhorst, PR & Communication. E-mail: boekhorst@astron.nl. Phone: +31 521 595 204.

Dr. George Heald, astronomer. E-mail: heald@astron.nl. Phone: +31 521 595 100.

More information about MSSS can be found on the ASTRON website: http://www.astron.nl/radio-observatory/lofar-msss/lofar-msss

A LOFAR View of M87

A paper appears on the arxiv today with new images of the centre of nearby elliptical galaxy M87, taken with the Dutch LOFAR stations.

M87 at Metre Wavelenghts: the LOFAR Picture, by de Gasperin et al. (A&A in press).

M87 (also known at Virgo-A) is one of the two massive elliptical galaxies found at the centre of our nearest cluster of galaxies (the Virgo cluster).

In the centre of M87 is a well know actively accreting supermassive black hole, which is emitting jets of energetic particles which emit significant amounts of radio. These jets are even (just) visible in optical images of M87 (the blue line below).

Optical image of M87 taken with Hubble Space Telescope. Scale 3x3 arcmins.  More details. 

M87 has often been a poster child for radio astronomy images. These images of the jet taken by the NRAO's VLA can be seen in many talks about radio galaxies and AGN.

M87 imaged at 90cm (300 Mhz) with the VLA. Scale 15x15 arcmin. More details. 

And especially this series of images zooming into the central regions.

For more details see the APOD entry for this image. 

The paper on the arxiv today used observations of M87 with both the HBA and LBA arrays of LOFAR. The Dutch stations only were used in this observation - adding in international stations like Chilbolton will be able to increase the resolution even further, and I will look forward to seeing that in the future.

I have extracted two of the images from the paper. This first was taken with the HBA at 140 MHz (2.1 m) and shows an area 15x15 arcmin in size (same as the VLA image above, but at wavelengths more than twice as large).

And this shows one of the many LBA images made - this one at 25 Mhz (12m) of a slightly larger sky area (21x21 arcmin). 

These new observations at lower frequencies than ever before allow scientists to better constrain the spectral shape of the radio emission from the jets, which in turn can be used to constrain the details of how the supermassive black hole in the centre of M87 is able to power these extremely extended emission regions.