NuSTAR Hard X-Ray Data and Gemini 3D Spectra Reveal Powerful AGN and Outflow Histories in Two Low-redshift Lyα Blobs

Abstract

We have shown that Ly α blobs (LABs) may still exist even at z ∼ 0.3 , about seven billion years later than most other LABs known (Shirmer et al.). Their luminous Ly α and [O iii ] emitters at z ∼ 0.3 offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at z ∼ 0.3 , SDSS J0113+0106 (J0113) and SDSS J1155−0147 (J1155), comparable in size and luminosity to “B1,” one of the best-studied LABs at z ≳ 2 . Our NuSTAR hard X-ray (3–30 keV) observations reveal powerful active galactic nuclei (AGN) with L 2 – 10 keV = ( 0.5 – 3 ) × 10 44 erg s −1 . J0113 also faded by a factor of ∼5 between 2014 and 2016, emphasizing that variable AGN may cause apparent ionization deficits in LABs. Joint spectral analyses including Chandra data constrain column densities of N H = 5.1 − 3.3 + 3.1 × 10 23 cm −2 (J0113) and N H = 6.0 − 1.1 + 1.4 × 10 22 cm −2 (J1155). J0113 is likely buried in a torus with a narrow ionization cone, but ionizing radiation is also leaking in other directions, as revealed by our Gemini/GMOS 3D spectroscopy. The latter shows a bipolar outflow over 10 kpc, with a peculiar velocity profile that is best explained by AGN flickering. X-ray analysis of J1155 reveals a weakly absorbed AGN that may ionize over a wide solid angle, consistent with our 3D spectra. Extinction-corrected [O iii ] log-luminosities are high, ∼43.6. The velocity dispersions are low, ∼100–150 km s −1 , even at the AGN positions. We argue that this is a combination of high extinction hiding the turbulent gas and previous outflows that have cleared the escape paths for their successors.