Project B

Searching for intermediate mass black holes

Marianne Heida & George Lansbury

(email advisors)

We know of many stellar mass (5-100 Msun) and supermassive (>100,000 Msun) black holes, but none in between. A class of very bright X-ray sources may be the key to finding these elusive intermediate mass black holes.

Supermassive black holes inhabit the center of every galaxy and they are already seen in the very early Universe. To form them so quickly probably requires 'seed' black holes with intermediate masses - not yet supermassive, but significantly more massive than the stellar mass black holes that are the remnants of the most massive stars. These intermediate mass black holes, or IMBHs, have been extremely difficult to find: we still only know of a handful of promising candidates.

One place to look for IMBHs is a class of X-ray sources called hyperluminous X-ray sources or HLXs. These are too bright in X-rays to host stellar mass black holes, but they are located outside of the nucleus of their host galaxy and so cannot be supermassive black holes either. An observational challenge to overcome is that many apparent HLXs actually turn out to be background active galactic nuclei (AGN): distant galaxies with X-ray-bright supermassive black holes at their centres, which just happen to be positioned behind the closer foreground galaxy. The only way to tell the difference is to analyze an optical spectrum of the candidate HLX and measure its redshift.

We observed a large sample of candidate HLXs with the Double Spectrograph on the 200'' Hale Telescope on Palomar Observatory. The student will analyze these broadband optical spectra, identify the visible emission lines, and use these to determine the redshifts of the HLX candidates. By comparing these with the redshifts of the nearby galaxies we will then be able to classify the source as either a bona fide HLX - possibly hosting an IMBH - or as a foreground or background source. Any background AGN discovered are interesting in their own right, and the student will also learn to use multiwavelength archival data to characterize these sources.

#IMBHs #AGN #spectroscopy #redshifts #multiwavelength

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