On the Sr I 4607 A Hanle depolarization signals in the quiet Sun

The Hanle depolarization signals of Sr 4607 A have been used to estimate the unsigned magnetic flux and magnetic energy existing in the quiet Sun photosphere. However, the Sr 4607 A Hanle signals are not sensitive to the unsigned flux and energy. They only bear information on the fraction of photosphere occupied by magnetic field strengths smaller than the Hanle saturation, which do not contribute to the unsigned flux and energy. We deduce an approximate expression for the relationship between magnetic fill factor and Hanle signal. When applied to existing Hanle depolarization measurements, it indicates that only 40% of the quiet Sun is filled by magnetic fields with a strength smaller than 60 G. The remaining 60% of the surface has field strengths above this limit. Such constraint will be needed to determine the distribution of magnetic field strengths existing in the quiet Sun.Comment: To appear in A&

Supermassive black hole wake or bulgeless edge-on galaxy? II: Order-of-magnitude analysis of the two physical scenarios

-- Context. A recently discovered thin long object aligned with a nearby galaxy could be the stellar wake induced by the passage of a supermassive black hole (SMBH) kicked out from the nearby galaxy by the slingshot effect of a three-body encounter of SMBHs. Alternatively, the object could be a bulgeless edge-on galaxy coincidentally aligned with a second nearby companion. In contrast with the latter, the SMBH interpretation requires a number of unlikely events to happen simultaneously. -- 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) simeq 11.4 pm 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 x 10**-17 and Pgalax > 1.4 x 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 10**6 and 2 x 10**12 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.Comment: Accepted for publication in A&A. Follow up of SA+23, A&A, 673, L