Astronomy and Astrophysics
Aims: We aim to assign a probability of occurrence to the two competing scenarios.
Methods: The probability that the SMBH passage leaves a trace of stars is factorized as the product of the probabilities of all the independent events required for this to happen (PSMBH). Then, each factor is estimated individually. The same exercise is repeated with the edge-on galaxy interpretation (Pgalax).
Results: Our estimate yields log(Pgalax/PSMBH)≃11.4 ± 1.6, where the error is evaluated considering that both Pgalax and PSMBH are products of a large number of random independent variables. Based on the estimated probabilities, PSMBH < 6 × 10−17 and Pgalax > 1.4 × 10−5, we determined the number of objects to be expected in various existing, ongoing, and forthcoming surveys, as well as among all observable galaxies (i.e., when observing between 106 and 2 × 1012 galaxies). In the edge-on galaxy scenario, there are always objects to be detected, whereas in the SMBH scenario, the expectation is always compatible with zero.
Conclusions: Despite the appeal of the runaway SMBH explanation, arguments based on the Occam's razor clearly favor the bulgeless edge-on galaxy interpretation. Our work does not rule out the existence of runaway SMBHs leaving stellar trails. It tells that the vD23 object is more likely to be a bulgeless edge-on galaxy.
Starsbursts play a key role in the cosmic evolution of galaxies, and thus in the star formation (SF) history of the universe, the production of metals, and the feedback coupling galaxies with the cosmic web. Extreme SF conditions prevail early on during the formation of the first stars and galaxies, therefore, the starburst phenomenon constitutes a