Περίληψη :
In 2010 the Wide-field Infrared Survey Explorer(WISE) discovered a new population of Hyper-Luminous Infrared Galaxies, the so called Hot Dust-Obscured-Galaxies(Hot DOGs), with infrared luminosities reaching LIR > 1014L⊙. Amongst them J224607.56-052634.9, hereafter W2246-0526, which lies at a redshift z = 4.601 is the most luminous. These objects are heavily dust obscured quasars and are considered an important step in galaxy evolution, assumed to be a transitional phase between heavily obscured and unobscured quasars, in which Active Galactic Nuclei activity is the driving force responsible for the clearing of the surrounding dust.
Hot DOGs have been found to exist in overdensities and are part of merger systems, which can often be viewed as the dominant mechanism driving their extreme luminosities. Understanding the true nature of companion galaxies of Hot DOGs is therefore essential in understanding the evolution of the merger system and constraining the mechanism that drives the extreme luminosity. Most companion galaxies discovered in such systems thus far have been identified as star-forming. This may be biased since observations at high redshifts with telescopes like the Atacama Large Millimeter Array(ALMA) can become limited as they can only probe dust and cold gas, traced through species like [C ii]158μm or CO transitions. With the launch of the James Webb Space Telescope(JWST) scientists have gained access to emission lines, which at these redshifts would have otherwise been redshifted to unobservable wavelengths, that can act as accurate AGN diagnostics.
In this study a 3D JWST/NIRSpec IFU image was used in order to first detect the companions of W2246-0526, and then inspect their emission line spectra for AGN activity, making the study one of the first of its kind. Initially, the continuum emission was subtracted using a running median subtraction filter (RMSF). The analysis focused on the emission lines Hα λ6565, Hβ λ4862, the [O ii] λλ3727, 3730 doublet and the [O iii] λλ4960, 5008 doublet. Moment-0 maps were created for each line, followed by source detection. The resulting catalogues were examined further in order to remove any duplicate detections, and a similar procedure was carried out across lines to identify sources detected in at least two emission lines. Spectra were then extracted for each source and fitted across twelve emission lines, [O ii] λλ3727, 3730, Hβ, [O iii] λλ4960, 5008, [O i] λλ6302, 6365, [N ii] λλ6549, 6585, Hα and [S ii] λλ6718, 6733, with two models: the first assumed individual Gaussian profiles, while the second added broad Gaussian components to the Balmer lines Hβ and Hα, which are used as an indicator of an AGN. Finally, a Baldwin, Phillips & Terlevich (BPT) diagram was constructed as a second diagnostic.
The entire analysis resulted in the detection of nine secure companions to W2246-0526, with another eight sources fitting the criteria, but requiring caution. Overall three companion galaxies favoured the broad component addition. In the BPT diagram one companion shows strong signs of AGN activity, while three more are characterised as composite, lying in the grey area separating star forming from AGN in the diagram.
