arXiv subjects

John Herbert Marr

Publications and source records attributed to John Herbert Marr.

5 recordsLinked to original sources

arXiv2023

Faint Galaxy Number Counts in the Durhamand SDSS Catalogues

Galaxy number counts in the $K$-, $H$-, $I$-, $R$-, $B$- and $U$-bands from the Durham Extragalactic Astronomy and Cosmology catalogue could be well-fitted over their whole range using luminosity function (LF) parameters derived from the SDSS at the bright region and required only modest luminosity evolution with the steepening of the LF slope ($α$), except for a sudden steep increase in the $B$-band and a less steep increase in the $U$-band at faint magnitudes that required a starburst evolutionary model to account for the excess faint number counts. A cosmological model treating Hubble expansion as an Einstein curvature required less correction at faint magnitudes than a standard $Λ$CDM model, without requiring dark matter or dark energy. Data from DR17 of the SDSS in the $g$, $i$, $r$, $u$ and $z$ bands over two areas of the sky centred on the North Galactic Cap (NGC) and above the South Galactic Cap (SGC), with areas of 5954 and 859 sq. deg., respectively, and a combined count of 622,121 galaxies, were used to construct bright galaxy number counts and galaxy redshift/density plots within the limits of redshift $\leq0.4$ and mag $\leq20$. Their comparative densities confirmed an extensive void in the Southern sky with a deficit of 26\% out to a redshift $z$$\leq$0.15. Although not included in the number count data set because of its incompleteness at fainter magnitudes, extending the SDSS redshift-number count survey to fainter and more distant galaxies with redshift $\leq1.20$ showed a secondary peak in the number counts with many QSOs, bright X-ray and radio sources, and evolving irregular galaxies with rapid star formation rates. This sub-population at redshifts of 0.45--0.65 may account for the excess counts observed in the $B$-band.

astro-ph.GA↗

arXiv2022

Stability and Damping in the Disks of Massive Galaxies

After their initial formation, disk galaxies are observed to be rotationally stable over periods of >6 Gyr, implying that any large velocity disturbances of stars and gas clouds are damped rapidly on the timescale of their rotation. However, it is also known that despite this damping, there must be a degree of random local motion to stabilize the orbits against degenerate collapse. A mechanism for such damping is proposed by a combination of inter-stellar gravitational interactions, and interactions with the Oort clouds and exo-Oort objects associated with each star. Analysis of the gravitational interactions between two stars is a three-body problem, because the stars are also in orbit round the large virtual mass of the galaxy. These mechanisms may produce rapid damping of large perturbations within a time period that is short on the scale of observational look-back time, but long on the scale of the disk rotational period for stars with small perturbations. This mechanism may also account for the locally observed mean perturbations in the Milky Way of 8-15~km/s for younger stars and 20-30~km/s for older stars.

astro-ph.GA↗

arXiv2022

Hubble Expansion as an Einstein Curvature

Extending the spacetime manifold of general relativity (GR) to incorporate the Hubble expansion of space as a specific curvature, generates a modified solution with three additional non-zero Christoffel symbols and a reformulated Ricci tensor and curvature. The observational consequences of this reformulation are compared with the $Λ$CDM model for luminosity distance using the extensive type~Ia supernovae (SNe~1a) data with redshift corrected to the CMB, and for angular diameter distance using the recent baryonic acoustic oscillation (BAO) data. For the SNe~1a data, the modified GR and $Λ$CDM models differ by $^{+0.11}_{-0.15}~μ_B$~mag. over $z_{cmb}=0.01-1.3$, with overall weighted RMS errors of $\pm0.136$ $μ_B$~mag for modified GR and $\pm0.151$ $μ_B$~mag for $Λ$CDM respectively. The BAO measures span a range $z=0.106-2.36$, with weighted RMS errors of $\pm0.034$~Mpc with $H_0=67.6\pm0.25$ for the modified GR model, and $\pm0.085$~Mpc with $H_0=70.0\pm0.25$ for the $Λ$CDM model. The derived GR metric for this new solution describes both the SNe~1a and the BAO observations with comparable accuracy to the $w'Λ$CDM model. By incorporating the Hubble expansion of space within general relativity as a specific curvature term, these observations may be described without requiring additional parameters for either dark matter or accelerating dark energy.

physics.gen-ph↗

arXiv2020

Entropy and Mass Distribution in Disc Galaxies

The relaxed motion of stars and gas in galactic discs is well approximated by a rotational velocity that is a function of radial position only, implying that individual components have lost any information about their prior states. Thermodynamically, such an equilibrium state is a microcanonical ensemble with maximum entropy, characterised by a lognormal probability distribution. Assuming this for the surface density distribution yields rotation curves that closely match observational data across a wide range of disc masses and galaxy types, and provides a useful tool for modelling the theoretical density distribution in the disc. A universal disc spin parameter emerges from the model, giving a tight virial mass estimator with strong correlation between angular momentum and disc mass, suggesting a mechanism by which the proto-disc developed by dumping excess mass to the core, or excess angular momentum to a satellite galaxy. The baryonic-to-dynamic mass ratio for the model approaches unity for high mass galaxies, but is generally $<1$ for low mass discs, and this discrepancy appears to follow a similar relationship to that shown in recent work on the radial acceleration relation (RAR). Although this may support Modified Newtonian Dynamics (MOND) in preference to a dark matter (DM) halo, it does not exclude undetected baryonic mass or a gravitational DM component in the disc.

astro-ph.GA↗

arXiv2015

Angular momentum of disc galaxies with a lognormal density distribution

By postulating that the majority of the mass and angular momentum of a disc galaxy is confined to the disc with a lognormal surface density distribution, and that galactic discs are substantially, if not fully, self-gravitating, it may be shown that the resultant rotation curves (RCs) display a good overall fit to observational data for a wide range of galaxy types. With this hypothesis, the total angular momentum $J$, and total energy |$E$| of 38 disc galaxies was computed and plotted against the derived disc masses, with best fit slopes for $J$ of $1.683\pm0.018$ and |$E$| of $1.643\pm0.038$, and a universal disc spin parameter $λ=0.423\pm0.014$. Using the disc parameters $V_{max}$ and $R_{max}$ as surrogates for the virial velocity and radius, a virial mass estimator $M_{disc}\propto{}R_{max}V_{max}^2$ was generated, with a log-log slope of $1.024\pm0.014$ for the 38 galaxies, and a proportionality constant $λ^*=1.47\pm0.20\times10^5M_\odot{}kpc^{-1}km^{-2}s^2$. This relationship has less scatter than $M_\odot\propto{}V^α$, and may provide an alternative to the Tully-Fisher relation in determining virial disc masses.

astro-ph.GA↗