NuSTAR hard X-ray data and Gemini 3D spectra reveal powerful AGN and outflow histories in two low-redshift Lyman-α blobs

Abstract

We have shown that Lyα 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 Lyα 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) x 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^(+3.1)_(-3.3) x 10^(23) cm^(−2) (J0113) and N_H = 6.0^(+1.4)_(-1.1) x 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.

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