Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs and the Discordance Seen with the Cosmological Principle

Abstract

According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would appear in some of the observed properties of the Cosmos a dipole anisotropy, which could in turn be exploited to determine the peculiar motion of the solar system. The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has given a peculiar velocity vector 370 km s−1 along l=264∘,b=48∘. However, some other dipoles, for instance, from the number counts, sky brightness or redshift distributions in large samples of distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar velocity many times larger than that from the CMBR, though surprisingly, in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of 0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. From this, we find a peculiar velocity, which is more than four times the CMBR value, although the direction seems to be within ∼2σ of the CMBR dipole. A genuine value of the solar peculiar velocity should be the same irrespective of the data or the technique employed to estimate it. Therefore, such discordant dipole amplitudes might mean that the explanation for these dipoles, including that of the CMBR, might in fact be something else. The observed fact that the direction in all cases is the same, though obtained from completely independent surveys using different instruments and techniques, by different sets of people employing different computing routines, might nonetheless indicate that these dipoles are not merely due to some systematics, otherwise why would they all be pointing along the same direction. It might instead suggest a preferred direction in the Universe, implying a genuine anisotropy, which would violate the Cosmological Principle, the core of the modern cosmology.

Peculiar motion of Solar system from the Hubble diagram of supernovae Ia and its implications for cosmology

“…Though the uncertainty in the pole position for the SNe Ia dipole direction is large, but it agrees, within ∼ 1σ, with the CMBR dipole direction, RA= 168 • , Dec= −7 • . However the amplitude of the velocity, 1.6±0.4×10 3 km s −1 , is > ∼ 4 times the CMBR value, our derived motion though seems to be in excellent agreement with the value [19][20][21][22] derived from the NRAO VLA Sky Survey [31] data as well as that derived recently [27,28] from the number counts of mid infra red AGNs [32], but is smaller than [23,24] that derived from the TIFR GMRT Sky Survey data [33,34] or the DR12Q data [25] from the Sloan Digital Sky Survey III [35].…”

“…The values we obtained for the peculiar velocity for the two sub-samples respectively were p = 5.1 ± 1. A factor of > ∼ 4 in the peculiar velocity derived here from SNe IA as compared to the CMBR value, as well as the earlier derived large factors of two to ten in the dipole amplitudes from various AGN datasets [19][20][21][22][23][24][25][26][27][28] may perhaps be pointers to the need for some rethinking on the conventional interpretation of these dipoles, especially, whether these dipoles do pertain to the peculiar motion of the Solar system. At the same time, an alignment of dipole directions in all cases cannot be fortuitous and is perhaps an indication of a preferred direction in the cosmos, which would imply a breakdown of the cosmological principle, the basic foundation over which the edifice of the modern cosmology has been erected.…”

“…ing > ∼ 10 5 sources [19][20][21][22][23][24][25][26][27][28], can yield statistically significant results from much smaller number ( < ∼ 10 3 ) of SNe. Moreover, the completeness of the survey, an absolute requirement in other methods where all sources above a certain observed flux density limit are part of the sample, is not a prerequisite.…”

“…However, an unexpected, substantially bigger dipole anisotropy, observed in a large sample of distant radio sources, yielded a peculiar motion ∼ 4 times [19] the CMBR value, though in the same direction as the CMBR dipole. Subsequent confirmations of the peculiar velocity with respect to AGN reference frames being much larger than the CMBR value [20][21][22][23][24][25][26][27][28], cast doubts on the CMBR dipole being the ultimate representatives of the solar peculiar motion. It might be desirable to determine the peculiar velocity with respect to a different reference frame, and if possible using an independent method, to examine whether the derived peculiar motion is indeed significantly larger than that inferred from the CMBR dipole.…”

The deceleration parameter in ‘tilted’ universes: generalising the Friedmann background

“…As a result, an increasing number of cosmologists are reconsidering the current cosmological paradigm and even question the FRW models and the Cosmological Principle itself [28][29][30][31][32][33]. Persistent reports of anomalous dipolar anisotropies in the number counts of distant radio-sources have added to this debate [34][35][36][37][38][39][40][41][42][43][44][45][46][47]. In summary, it is conceivable that the time may have come to review some of our long-standing views and perceptions regarding the universe we live in.…”