[Paper Review] An anomalous concentration of QSOs around NGC 3079

E. M. Burbidge, G. R. Burbidge+2 more|arXiv (Cornell University)|Oct 28, 2005

History and Developments in Astronomy1 references3 citations

TL;DR

The paper presents strong evidence for a physical association between NGC 3079 and at least 21 QSOs within 1°, with a surface density of bright QSOs 100× higher than the field average. The probability of this concentration being accidental is <10⁻⁶, and gravitational lensing or microlensing cannot explain the anomaly, suggesting the QSOs are physically ejected from NGC 3079 rather than cosmologically distant objects.

ABSTRACT

It is shown that there are at least 21 QSOs within 1 degree of the nearby active spiral galaxy NGC3079. Many of them are bright (mag&lt;18) so that the surface density of those closer than 15 arc minutes to the galaxy centre is close to 100 times the average in the field. The probability that this is an accidental configuration is shown to be less or equal to one in a million. Discovery selection effects and microlensing fail by a large factor to explain the phenomenon, suggesting that the QSOs may lie in the same physical space as NGC3079. However, two of them make up the apparently lensed pair 0957+561A, B whose lensing galaxy lies at z=0.355. This problem is discussed in the concluding section.

Motivation & Objective

• To investigate the statistical significance of a high concentration of QSOs near the active spiral galaxy NGC 3079.
• To test whether selection effects or gravitational lensing (microlensing or strong lensing) can explain the observed QSO clustering.
• To assess whether the QSOs are physically associated with NGC 3079, challenging the standard cosmological interpretation of their redshifts.
• To examine the anomalous proximity of a group of QSOs near the well-known lensed pair 0957+561A,B and its implications.

Proposed method

• Compiled a list of 21 QSOs within 1° of NGC 3079 from multiple surveys (optical, radio, X-ray, and catalogues), including redshifts and magnitudes.
• Calculated angular distances and surface densities of QSOs within 15′ and 35′ of NGC 3079’s nucleus, comparing them to the average field density of ~0.3 QSOs per square degree for m < 18.
• Assessed the probability of accidental clustering using statistical methods, yielding a significance level of <10⁻⁶ for the overall concentration.
• Evaluated the lensing hypothesis by computing microlensing optical depth and expected number of lensed QSOs in the field, finding it insufficient to explain the observed excess.
• Analyzed X-ray QSOs with Fx > 50×10⁻¹⁴ erg cm⁻² s⁻¹, finding four such sources within 36′ of NGC 3079, far exceeding the expected 0.12 in that area.
• Examined the spatial clustering of QSOs near the 0957+561 lens system, noting their angular proximity and low chance of being coincidental (≈10⁻⁵).

Experimental results

Research questions

• RQ1 Is the observed concentration of QSOs around NGC 3079 statistically significant, or could it be due to chance?
• RQ2 Can standard gravitational lensing mechanisms—microlensing or strong lensing—explain the high density of bright QSOs near NGC 3079?
• RQ3 Why are four highly X-ray-luminous QSOs aligned along NGC 3079’s major axis, and is this alignment coincidental?
• RQ4 What explains the anomalous clustering of QSOs near the 0957+561 lensed pair, which is already known to be gravitationally lensed?
• RQ5 Could the QSOs be physically associated with NGC 3079, implying non-cosmological redshifts?

Key findings

• There are at least 21 QSOs within 1° of NGC 3079, with seven having magnitudes brighter than 18.0, resulting in a surface density of bright QSOs approximately 100 times higher than the average field density.
• The probability of this QSO concentration occurring by chance is less than 10⁻⁶, indicating a highly significant non-accidental clustering.
• Microlensing and strong lensing models fail to account for the observed QSO excess, as the expected number of lensed QSOs in the region is far too low (e.g., only ~0.3 expected for b < 22 in the 0.355 redshift cluster).
• Four X-ray-bright QSOs (Fx > 50×10⁻¹⁴ erg cm⁻² s⁻¹) lie within 36′ of NGC 3079, while only ~0.12 are expected in that area, indicating a significant overdensity.
• A group of four QSOs (ASV23, ASV24, ASV31, MARK132) lie within 1.35–2.36 arcminutes of the 0957+561 lensed pair, with a chance coincidence probability of ~10⁻⁵, suggesting a physical or structural anomaly.
• The presence of a second anomalous QSO concentration near 0957+561, combined with the main cluster near NGC 3079, suggests a possible common origin, possibly linked to physical ejection processes.