Daily Image
12-01-2018
The fun is starting...
| Submitter: | Raffaella Morganti |
| Description: | One of the goals of Apertif is to search for atomic neutral hydrogen located close to the central black hole of active galaxies (AGN), and to study the properties of that gas in relation to the AGN. This can be done by observing HI in absorption against the bright radio continuum emission from the active nucleus. Interestingly, in this way, it is relatively easy to detect hydrogen even in very distant sources as long as the active nucleus is bright enough at radio frequencies. Detecting such absorptions is the goal of SHARP, the HI absorption survey of Apertif. The main complication to accomplish this is the presence of radio frequency interference (RFI), meaning the radiation from e.g. airplanes, satellites etc. which can badly affect the observations. However, there is hope and the results from the Apertif commissioning shown in the figure illustrate a first success. The profile shows the HI absorption observed against a radio source (indicated with the arrow) located almost a billion light years away (redshift 0.191). Interestingly, the absorption shows a wing which, when converted in velocity, is more than 500 km/s broad and the gas is moving towards us relative to the AGN. This suggests that not only there is gas in this galaxy, but there is also gas expelled from the galaxy by the super-massive black hole at high velocities! In order to detect these type of features, a stable bandpass is essential and this seems to be the case for these Apertif observations. This is just one target chosen for the commissioning of Apertif, but illustrates exactly what we hope to see in many other cases, allowing to build much larger statistics. The fact that the flat bandpass already allows us to see the blueshifted wing is extremely encouraging. Let the fun begin! |
| Copyright: | ASTRON |
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