A precise extragalactic test of General Relativity

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Abstract

Einstein's theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens, ESO 325-G004, provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, \(\gamma\). By reconstructing the observed light profile of the lensed arcs and the observed spatially resolved stellar kinematics with a single self-consistent model, we conclude that \(\gamma = 0.97 \pm 0.09\) at 68% confidence. Our result is consistent with the prediction of 1 from General Relativity and provides a strong extragalactic constraint on the weak-field metric of gravity.

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The Structure of Cold Dark Matter Halos

Simon D. M. White, Julio Navarro, Carlos Frenk (1995)

We use N-body simulations to investigate the structure of dark halos in the standard Cold Dark Matter cosmogony. Halos are excised from simulations of cosmologically representative regions and are resimulated individually at high resolution. We study objects with masses ranging from those of dwarf galaxy halos to those of rich galaxy clusters. The spherically averaged density profiles of all our halos can be fit over two decades in radius by scaling a simple ``universal'' profile. The characteristic overdensity of a halo, or equivalently its concentration, correlates strongly with halo mass in a way which reflects the mass dependence of the epoch of halo formation. Halo profiles are approximately isothermal over a large range in radii, but are significantly shallower than \(r^{-2}\) near the center and steeper than \(r^{-2}\) near the virial radius. Matching the observed rotation curves of disk galaxies requires disk mass-to-light ratios to increase systematically with luminosity. Further, it suggests that the halos of bright galaxies depend only weakly on galaxy luminosity and have circular velocities significantly lower than the disk rotation speed. This may explain why luminosity and dynamics are uncorrelated in observed samples of binary galaxies and of satellite/spiral systems. For galaxy clusters, our halo models are consistent both with the presence of giant arcs and with the observed structure of the intracluster medium, and they suggest a simple explanation for the disparate estimates of cluster core radii found by previous authors. Our results also highlight two shortcomings of the CDM model. CDM halos are too concentrated to be consistent with the halo parameters inferred for dwarf irregulars, and the predicted abundance of galaxy halos is larger than the observed abundance of galaxies.

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Revisiting the Scaling Relations of Black Hole Masses and Host Galaxy Properties

Chung-Pei Ma, Nicholas McConnell (2012)

New kinematic data and modeling efforts in the past few years have substantially expanded and revised dynamical measurements of black hole masses (Mbh) at the centers of nearby galaxies. Here we compile an updated sample of 72 black holes and their host galaxies, and present revised scaling relations between Mbh and stellar velocity dispersion (sigma), V-band luminosity (L), and bulge stellar mass (Mbulge), for different galaxy subsamples. Our best-fitting power law relations for the full galaxy sample are log(Mbh) = 8.32 + 5.64*log(sigma/200 kms), log(Mbh) = 9.23 + 1.11*log(L/10^{11} Lsun), and log(Mbh) = 8.46 + 1.05*log(Mbulge/10^{11} Msun). A log-quadratic fit to the Mbh-sigma relation with an additional term of beta_2*[log(sigma/200 kms)]^2 gives beta_2 = 1.68 +/- 1.82 and does not decrease the intrinsic scatter in Mbh. When the early- and late-type galaxies are fit separately, we obtain similar slopes of 5.20 and 5.06 for the Mbh-sigma relation but significantly different intercepts -- Mbh in early-type galaxies are about 2 times higher than in late types at a given sigma. Within early-type galaxies, our fits to Mbh(sigma) give Mbh that is about 2 times higher in galaxies with central core profiles than those with central power-law profiles. Our Mbh-L and Mbh-Mbulge relations for early-type galaxies are similar to those from earlier compilations. When the conventional quadrature method is used to determine the intrinsic scatter in Mbh, our dataset shows weak evidence for increased scatter at Mbulge < 10^{11} Msun or L_V < 10^{10.3} Lsun, while the scatter stays constant for 10^{11} < Mbulge < 10^{12.3} Msun and 10^{10.3} < L_V < 10^{11.5} Lsun. A Bayesian analysis indicates a larger sample of Mbh measurements would be needed to detect any statistically significant trend in the scatter with galaxy properties.

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A systematic variation of the stellar initial mass function in early-type galaxies

Katherine Alatalo, Richard McDermid, P. de Zeeuw … (2012)

Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars. It depends on the stellar initial mass function (IMF) describing the distribution of stellar masses when the population formed. Consequently knowledge of the IMF is critical to virtually every aspect of galaxy evolution. More than half a century after the first IMF determination, no consensus has emerged on whether it is universal in different galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot be both universal, but they could not break the degeneracy between the two effects. Only recently indications were found that massive elliptical galaxies may not have the same IMF as our Milky Way. Here we report unambiguous evidence for a strong systematic variation of the IMF in early-type galaxies as a function of their stellar mass-to-light ratio, producing differences up to a factor of three in mass. This was inferred from detailed dynamical models of the two-dimensional stellar kinematics for the large Atlas3D representative sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass. Our finding indicates that the IMF depends intimately on a galaxy's formation history.

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Publication date Created: 21 June 2018

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ArXiV ID: 1806.08300

SO-VID: dc6859a7-72f8-4b10-8917-d2463f2c9ae2

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http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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Comments Published in Science. 42 pages, 10 figures including supplementary text and figures

Categories astro-ph.CO astro-ph.GA gr-qc

ScienceOpen disciplines: Cosmology & Extragalactic astrophysics,General relativity & Quantum cosmology,Galaxy astrophysics

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ScienceOpen disciplines: Cosmology & Extragalactic astrophysics, General relativity & Quantum cosmology, Galaxy astrophysics

A precise extragalactic test of General Relativity

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Gravitational Waves

Most cited references 10

The Structure of Cold Dark Matter Halos

Revisiting the Scaling Relations of Black Hole Masses and Host Galaxy Properties

A systematic variation of the stellar initial mass function in early-type galaxies

Author and article information

Journal

Article

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