SDSS IV MaNGA: Discovery of an Ha Blob Associated with a Dry Galaxy Pair-Ejected Gas or a ``Dark'' Galaxy Candidate?

We report the discovery of a mysterious giant Ha. blob that is similar to 8 kpc away from the main MaNGA target 1-24145, one component of a dry galaxy merger, and has been identified in the first-year SDSS-IV MaNGA data. The size of the Ha. blob is similar to 3-4 kpc in radius, and the Ha. distribution is centrally concentrated. However, there is no optical continuum counterpart in the deep broadband images reaching similar to 26.9 mag arcsec(-2) in surface brightness. We estimate that the masses of the ionized and cold gases are 3.3 x 10(5) M-circle dot and < 1.3 x 10(9) M-circle dot respectively. The emission-line ratios indicate that the Ha. blob is photoionized by a combination of massive young stars and AGNs. Furthermore, the ionization line ratio decreases from MaNGA 1-24145 to the H alpha blob, suggesting that the primary ionizing source may come from MaNGA 1-24145, likely a low-activity AGN. Possible explanations for this Ha. blob include the AGN outflow, the gas remnant being tidally or ram-pressure stripped from MaNGA 1-24145, or an extremely low surface brightness galaxy. However, the stripping scenario is less favored according to galaxy merger simulations and the morphology of the H alpha blob. With the current data, we cannot distinguish whether this Ha. blob is ejected gas due to a past AGN outburst, or a special category of ``ultra-diffuse galaxy'' interacting with MaNGA 1-24145 that further induces the gas inflow to fuel the AGN in MaNGA 1-24145.