There is mounting evidence that supermassive black holes form and grow in bulgeless galaxies .
However , a robust determination of the fraction of AGNs in bulgeless galaxies , an important constraint to models of supermassive black hole seed formation and merger-free models of AGN fueling , is unknown , since optical studies have been shown to be incomplete for low mass AGNs .
In a recent study using the Wide-field Infrared Survey Explorer , we discovered hundreds of bulgeless galaxies that display mid-infrared signatures of extremely hot dust suggestive of powerful accreting massive black holes , despite having no signatures of black hole activity at optical wavelengths .
Here we report X-ray follow-up observations of J122434.66+555522.3 , a nearby ( z = 0.052 ) isolated bulgeless galaxy that contains an unresolved X-ray source detected at the 3 \sigma level by XMM-Newton with an observed luminosity uncorrected for intrinsic absorption of L _ { \mathrm { 2 - 10 ~ { } keV } } = ( 1.1 \pm 0.4 ) \times 10 ^ { 40 } erg s ^ { -1 } .
Ground-based near-infrared spectroscopy with the Large Binocular Telescope together with multiwavelength observations from ultraviolet to millimeter wavelengths together suggest that J1224+5555 harbors a highly absorbed AGN with an intrinsic absorption of N _ { \mathrm { H } } > 10 ^ { 24 } cm ^ { -2 } .
The hard X-ray luminosity of the putative AGN corrected for absorption is L _ { \mathrm { 2 - 10 ~ { } keV } } \sim 3 \times 10 ^ { 42 } erg s ^ { -1 } , which , depending on the bolometric correction factor , corresponds to a bolometric luminosity of the AGN of 6 \times 10 ^ { 43 } erg s ^ { -1 } \lesssim L _ { \textrm { bol . } } ~ { } \lesssim 3 \times 10 ^ { 44 } erg s ^ { -1 } , and a lower mass limit for the black hole of M _ { \textrm { BH } } \simeq 2 \times 10 ^ { 6 } ~ { } M _ { \sun } , based on the Eddington limit .
While enhanced X-ray emission and hot dust can be produced by star formation in extremely low metallicity environments typical in dwarf galaxies , J1224+5555 has a stellar mass of \sim 2.0 \times 10 ^ { 10 } ~ { } M _ { \sun } , and an above solar metallicity ( 12+ \log { \textrm { O / H } } =9.11 ) , typical of our WISE -selected bulgeless galaxies sample .
While collectively , these observations suggest the presence of an AGN , we caution that identifying obscured AGNs in the low luminosity regime is challenging , and often requires multi wavelength observations.These observations suggest that low luminosity AGNs can be heavily obscured and reside in optically quiescent galaxies , adding to the growing body of evidence that the fraction of bulgeless galaxies with accreting black holes may be significantly underestimated based on optical studies .