Alma on the trail of galaxy death with the first quasar discovered

3C 273 is a star withinastrophysics and some cosmology. Behind this name, which initially means it’s 273e the subject of the third Cambridge catalog with the sources radio, we find the brightest quasar in the sky. It was discovered in Virgin constellation and we now know that this radio source is produced by a supermassive black hole – containing about 887 million. masses sun – observed as it was about 2.44 billion years ago.

3C 273 is the most studied quasar, with famous pictures taken telescopes Hubble and Chandra shows especially a jet of fabric about 210,000 light-years long and coming from one elliptical galaxy containing the quasar. Its discovery in the early 1960s paved the way for acceptance of the theory of big bang as the new paradigm of cosmology.

We have since known that supermassive black holes that stands behind the formidable energy of quasars shines more, by itself, than all the stars in galaxies which contains them -, comes fromgrowth large quantities of gas. That win material and the radiation produced by this growth can affect the gas content of galaxies and the rate of star formation from this gas. We also know that there is a proportionality relationship between the mass of supermassive black holes and those in the galaxies that host it in the vast majority of cases, implying that the two objects grow together.

There are therefore complex but still poorly understood relationships between the growth processes of these two objects and the fact that we observe that galaxies eventually die, that is, no longer forming a star due to their gas discharge. To see more clearly, it is necessary to be able to study more closely the galaxies that contain quasars, and a new illustration of this type of research has just been given by a team ofastrophysicists Japanese via a publication in the famous journal The Astrophysical Journal. The article in question is, as is often the case, in free access to arXiv.

850 times dynamic range to unlock the secrets of the 3C 273

The researchers performed their work usingAtacama Large Millimeter / submillimeter Array or Alma (in French: large selection of millimeter / submillimeter antennas from Atacama). Getting more details about the 3C 273 Galaxy with Alma required that they find a new image processing technique to achieve a higher dynamic range with the images. digital which makes it possible to form radio telescope.

Let us remember, to put it simply, that for these pictures, as those that can be taken with CCD sensorsis the dynamic range range of the value of brightness what the image can imagine. But in a natural environment, there are very large light amplitudes between the different ones pixels of a digital image so that one can get more information and details as the dynamic range is.

Typically, the dynamic imaging ranges frequencies available with Alma are of the order of 100 in the appropriate unit of measurement to define them. Japanese astrophysicists managed to get one contrast between the lightest and darkest tones of an Alma image of the order of 85,000, a record with Alma for extragalactic objects.

The researchers then discovered around the supermassive black hole a halo of weak radio emissions, but extending over tens of thousands of light years. Usually, these diffuse intra-galactic radio broadcasts are produced by synchrotron radiation relativistic electrons at high speeds, often in magnetic fields. But the intensity of this type of radiation is given by one spectrum which varies with frequency, which is not the case for the halo of 3C 273. In fact, the curve of the spectrum is flat.

A radiohalo of ionized hydrogen?

Astonished by this observation, astrophysicists have finally found a plausible explanation. L ‘discharge would come from the distributions ofhydrogen in the interstellar medium of the elliptical galaxy, partially ionized by the radiation specific for the substance, accumulated by the central black hole. The amount of ionized matter is far from insignificant because it is estimated at between 10 and 100 billion solar masses. The total spectrum of light emitted by the ionized gas must end with a part in the visible. But this part is clearly blocked by the dust in the galaxy, which is not the case with the radio waves in frequency bands available to Alma, which is why we are only now discovering the presence of ionized gas in the halo around 3C 273.

But, as the press release on Alma’s website explains, if stars can not normally be formed clouds of strongly ionized hydrogen gas, the amount of deionized gas in the elliptical galaxy must remain large because it does not appear that star formation has been strongly suppressed by the active core of the galaxy.

There is always that ” this discovery offers a new way of studying problems that have previously been solved using observations of visible light “, according to Shinya Komugiprofessor at Kogakuin University in Japan and lead author of the study published in Astrophysical journal. And he adds at the end of the press release that ” by applying the same technique to other quasars, we hope to understand how a galaxy evolves through its interaction with its central core “.

Françoise Combes, astrophysicist and professor at the Collège de France, explains the latest discoveries about quasars. © Area of ​​Science

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