Path integrals in quadratic gravity Belokurov, Vladimir V.; Shavgulidze, Evgeniy T.
The journal of high energy physics,
02/2022, Letnik:
2022, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A
bstract
Using the invariance of Quadratic Gravity in FLRW metric under the group of diffeomorphisms of the time coordinate, we rewrite the action
A
of the theory in terms of the invariant dynamical ...variable
g
(
τ
)
.
We propose to consider the path integrals ∫
F
(
g
) exp {−
A
}
dg
as the integrals over the functional measure
μ
(
g
) = exp {−
A
2
}
dg,
where
A
2
is the part of the action
A
quadratic in
R.
The rest part of the action in the exponent stands in the integrand as the “interaction” term. We prove the measure
μ
(
g
) to be equivalent to the Wiener measure, and, as an example, calculate the averaged scale factor in the first nontrivial perturbative order.
ABSTRACT
The Gaia Radial Velocity Spectrometer (RVS) provides a sample of 7224 631 stars with full six-dimensional phase space information. Bayesian distances of these stars are available from the ...catalogue of Schönrich, McMillan & Eyer. We exploit this to map out the behaviour of the velocity ellipsoid within 5 kpc of the Sun. We find that the tilt of the disc-dominated RVS sample is accurately described by the relation $\alpha = (0.952 \pm 0.007)\arctan (|z|/R)$, where (R, z) are cylindrical polar coordinates. This corresponds to velocity ellipsoids close to spherical alignment (for which the normalizing constant would be unity) and pointing towards the Galactic Centre. Flattening of the tilt of the velocity ellipsoids is enhanced close to the plane and Galactic Centre, whilst at high elevations far from the Galactic Centre the population is consistent with exact spherical alignment. Using the LAMOST catalogue cross-matched with Gaia DR2, we construct thin disc and halo samples of reasonable purity based on metallicity. We find that the tilt of thin disc stars straddles $\alpha = (0.909{\!-\!}1.038)\arctan (|z|/R)$, and of halo stars straddles $\alpha = (0.927{\!-\!}1.063)\arctan (|z|/R)$. We caution against the use of reciprocal parallax for distances in studies of the tilt, as this can lead to serious artefacts.
We announce the discovery of a new Galactic companion found in data from the ESO VST ATLAS survey, and followed up with deep imaging on the 4-m William Herschel Telescope. The satellite is located in ...the constellation of Crater (the Cup) at a distance of ∼170 kpc. Its half-light radius is r
h = 30 pc and its luminosity is M
V
= −5.5. The bulk of its stellar population is old and metal poor. We would probably have classified the newly discovered satellite as an extended globular cluster were it not for the presence of a handful of blue loop stars and a sparsely populated red clump. The existence of the core helium burning population implies that star formation occurred in Crater perhaps as recently as 400 Myr ago. No globular cluster has ever accomplished the feat of prolonging its star formation by several Gyr. Therefore, if our hypothesis that the blue bright stars in Crater are blue loop giants is correct, the new satellite should be classified as a dwarf galaxy with unusual properties. Note that only 10°to the north of Crater, two ultrafaint galaxies Leo IV and Leo V orbit the Galaxy at approximately the same distance. This hints that all three satellites may once have been closely associated before falling together into the Milky Way halo.
ABSTRACT
The highly-substructured outskirts of the Magellanic Clouds provide ideal locations for studying the complex interaction history between both Clouds and the Milky Way (MW). In this paper, we ...investigate the origin of a >20° long arm-like feature in the northern outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. We find that the arm has a similar geometry and metallicity to the nearby outer LMC disc, indicating that it is comprised of perturbed disc material. Whilst the azimuthal velocity and velocity dispersions along the arm are consistent with those in the outer LMC, the in-plane radial velocity and out-of-plane vertical velocity are significantly perturbed from equilibrium disc kinematics. We compare these observations to a new suite of dynamical models of the Magellanic/MW system, which describe the LMC as a collection of tracer particles within a rigid potential, and the SMC as a rigid Hernquist potential. Our models indicate the tidal force of the MW during the LMC’s infall is likely responsible for the observed increasing out-of-plane velocity along the arm. Our models also suggest close LMC/SMC interactions within the past Gyr, particularly the SMC’s pericentric passage ∼150 Myr ago and a possible SMC crossing of the LMC disc plane ∼400 Myr ago, likely do not perturb stars that today comprise the arm. Historical interactions with the SMC prior to ∼1 Gyr ago may be required to explain some of the observed kinematic properties of the arm, in particular its strongly negative in-plane radial velocity.
We report the discovery of tidal tails around the Galactic globular cluster NGC 7492, based on the Data Release 1 of the Pan-STARRS1 survey. The tails were detected using a version of the matched ...filter technique applied to the (g − r, r) and (g − i, i) color-magnitude diagrams. Tidal tails emerging from the cluster extend at least ∼3 5 in the north-east to south-east direction, equivalent to ∼1.5 kpc in projected length.
Abstract
We present the first spatially resolved rest-frame ultraviolet (UV) study of the gravitationally lensed galaxy, the ‘Cosmic Horseshoe’ (J1148+1930) at z = 2.38. Our gravitational lens model ...shows that the system is made up of four star-forming regions, each ∼4–8 kpc2 in size, from which we extract four spatially exclusive regional spectra. We study the interstellar and wind absorption lines, along with C iii doublet emission lines, in each region to investigate any variation in emission/absorption line properties. The mapped C iii emission shows distinct kinematical structure, with velocity offsets of ∼±50 km s−1 between regions suggestive of a merging system, and a variation in equivalent width that indicates a change in ionization parameter and/or metallicity between the regions. Absorption line velocities reveal a range of outflow strengths, with gas outflowing in the range −200 ≲ v (km s−1) ≲ −50 relative to the systemic velocity of that region. Interestingly, the strongest gas outflow appears to emanate from the most diffuse star-forming region. The star formation rates remain relatively constant (∼8–16 M⊙ yr−1), mostly due to large uncertainties in reddening estimates. As such, the outflows appear to be ‘global’ rather than ‘locally’ sourced. We measure electron densities with a range of log (Ne) = 3.92–4.36 cm−3, and point out that such high densities may be common when measured using the C iii doublet due to its large critical density. Overall, our observations demonstrate that while it is possible to trace variations in large-scale gas kinematics, detecting inhomogeneities in physical gas properties and their effects on the outflowing gas may be more difficult. This study provides important lessons for the spatially resolved rest-frame UV studies expected with future observatories, such as James Webb Space Telescope.
A
bstract
A regular approach to evaluate the functional integrals over the quasi-invariant measure on the group of diffeomorphisms is presented. As an important example of the application of this ...technique, we explicitly evaluate the correlation functions in the Schwarzian theory.
We cross-match high-precision astrometric data from Gaia DR2 with accurate multiband photometry from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar streams in ...the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra. We determine low-confidence proper-motion measurements for four additional stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment between stream tracks and the systemic proper motion of streams that may suggest a systematic gravitational influence from the Large Magellanic Cloud (LMC). These proper motions, when combined with radial velocity measurements, will allow for detailed orbit modeling that can be used to constrain properties of the LMC and its effect on nearby streams, as well as global properties of the Milky Way's gravitational potential.
Balancing mass and momentum in the Local Group Diaz, J. D.; Koposov, S. E.; Irwin, M. ...
Monthly Notices of the Royal Astronomical Society,
09/2014, Letnik:
443, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In the rest frame of the Local Group (LG), the total momentum of the Milky Way (MW) and Andromeda (M31) should balance to zero. We use this fact to constrain new solutions for the solar motion with ...respect to the LG centre of mass, the total mass of the LG, and the individual masses of M31 and the MW. Using the set of remote LG galaxies at >350 kpc from the MW and M31, we find that the solar motion has amplitude V
⊙ = 299 ± 15 km s−1 in a direction pointing towards galactic longitude l
⊙ = 98
$_{.}^{\circ}$
4 ± 3
$_{.}^{\circ}$
6 and galactic latitude b
⊙ = −5
$_{.}^{\circ}$
9 ± 3
$_{.}^{\circ}$
0. The velocities of M31 and the MW in this rest frame give a direct measurement of their mass ratio, for which we find log10(M
M31/M
MW) = 0.36 ± 0.29. We combine these measurements with the virial theorem to estimate the total mass within the LG as M
LG = (2.5 ± 0.4) × 1012 M⊙. Our value for M
LG is consistent with the sum of literature values for M
MW and M
M31. This suggests that the mass of the LG is almost entirely located within the two largest galaxies rather than being dispersed on larger scales or in a background medium. The outskirts of the LG are seemingly rather empty. Combining our measurement for M
LG and the mass ratio, we estimate the individual masses of the MW and M31 to be M
MW = (0.8 ± 0.5) × 1012 M⊙ and M
M31 = (1.7 ± 0.3) × 1012 M⊙, respectively. Our analysis favours M31 being more massive than the MW by a factor of ∼2.3, and the uncertainties allow only a small probability (9.8 per cent) that the MW is more massive. This is consistent with other properties such as the maximum rotational velocities, total stellar content, and numbers of globular clusters and dwarf satellites, which all suggest that M
M31/M
MW > 1.
AbstractWe present the first detailed study of the behaviour of the stellar proper motion across the entire Galactic anticentre area visible in the Sloan Digital Sky Survey (SDSS) data. We use ...recalibrated SDSS astrometry in combination with positions from Gaia DR1 to provide tangential motion measurements with a systematic uncertainty <5 km s-1 for the Main Sequence stars at the distance of the Monoceros Ring. We demonstrate that Monoceros members rotate around the Galaxy with azimuthal speeds of ∼230 km s-1 , only slightly lower than that of the Sun. Additionally, both vertical and azimuthal components of their motion are shown to vary considerably but gradually as a function of Galactic longitude and latitude. The stellar overdensity in the anti-centre region can be split into two components, the narrow, stream-like ACS and the smooth Ring. According to our analysis, these two structures show very similar but clearly distinct kinematic trends, which can be summarized as follows: the amplitude of the velocity variation in vπ and vz in the ACS is higher compared to the Ring, whose velocity gradients appear to be flatter. Currently, no model available can explain the entirety of the data in this area of the sky. However, the new accurate kinematic map introduced here should provide strong constraints on the genesis of the Monoceros Ring and the associated substructure.
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