An article to be published in the journal “Astronomy & Astrophysics” describes the first detailed X-ray observation of a galaxy cataloged as W1835+4355 of a rare type because at its center there’s a quasar of the Hot DOG (Hot Dust-Obscured Galaxies) type. A team led by Luca Zappacosta of INAF in Rome, Italy, used data collected by ESA’s XMM-Newton and NASA’s NuSTAR space telescopes to obtain the most accurate X-ray emission detections from a Hot DOG galaxy. This will be useful to better understand the nature of this type of galaxies and the activity of the supermassive black hole at their center.
Quasars and in general active galactic nuclei are now well known but Hot DOG galaxies are hot and full of dust that absorb most of the electromagnetic radiation. The supermassive black hole at their center is very active so around it there are huge amounts of materials that are heated to the point of becoming so bright that they’re considered hyperluminous quasars but paradoxically in the Hot DOGs materials are also those that obscure them.
The galaxy W1835+4355, or simply W1835, was discovered thanks to the WISE space telescope, in fact its complete “name” is WISE J183533.71+435549.1. Its emissions at the infrared frequencies can pass through gas and dust and it’s thanks to them that many Hot DOG galaxies have been identified.
The image (courtesy Luca Zappacosta et al. All rights reserved) shows a view of the NuSTAR space telescope in equatorial coordinates where the galaxy W1835+4355 is marked by a blue circle. The red circles indicate sources identified by the XMM-Newton space telescope.
Luca Zappacosta and his colleagues have been working for some time to try to study the emissions from W1835+4355 at other detectable frequencies, those at X-rays that in some areas are not absorbed. This is the first analysis of the X radiation spectrum from 1 to 70 keV (kilo-electronvolts), emitted by a Hot DOG. The researchers combined the data collected by the XMM-Newton space telescope for energies below 10 keV and by the NuSTAR space telescope, inaugurated in June 2012, for energies of several tens of keV.
Luca Zappacosta stressed the importance of this result in the research on Hot DOG galaxies and on active galactic nuclei in general. The hot DOGs discovered are very far away and as a result we see them as they were when the universe was between 2 and 3 billion years old. In these young galaxies the central supermassive black hole could be extremely active because there was an enormous amount of gas and dust inside the galaxies and therefore around it as well.
Understanding the processes underway in Hot DOG galaxies could help to understand a moment of evolution of the most massive galaxies and the influence of the active galactic nucleus on star formation. Those supermassive black holes can have masses billions of times the Sun’s and their influence could also extend to other galaxies within galactic clusters.