Halo stars orbit within the potential of the Milky Way, and hence their kinematics can be used to understand the underlying mass distribution. In this paper, we decompose the Galaxy into three major ...components-a bulge, a Miyamoto-Nagai disk, and a Navarro-Frenk-White dark matter halo - and then model the kinematic data of the halo blue horizontal branch and K-giant stars from the Sloan Extension for Galactic Understanding and Exploration. Additionally, we use the gas terminal velocity curve and the Sgr A super(*) proper motion. With the distance of the Sun from the center of the Galaxy R sub(middot in circle) = 8.5 kpc, our kinematic analysis reveals that the density of the stellar halo has a break at 17.2 super(+1.1) sub(-1.0) kpc and an exponential cutoff in the outer parts starting at 97.7 super(+15.6) sub(-15.8) kpc. Some of the above estimates, in particular M sub(vir), are dependent on the adopted value of R sub(middot in circle) and also on the choice of the outer power-law index of the tracer number density.
ABSTRACT
Creating a data base of 21 cm brightness temperature signals from the Epoch of Reionization (EoR) for an array of reionization histories is a complex and computationally expensive task, ...given the range of astrophysical processes involved and the possibly high-dimensional parameter space that is to be probed. We utilize a specific type of neural network, a progressively growing generative adversarial network (PGGAN), to produce realistic tomography images of the 21 cm brightness temperature during the EoR, covering a continuous three-dimensional parameter space that models varying X-ray emissivity, Lyman band emissivity, and ratio between hard and soft X-rays. The GPU-trained network generates new samples at a resolution of ∼3 arcmin in a second (on a laptop CPU), and the resulting global 21 cm signal, power spectrum, and pixel distribution function agree well with those of the training data, taken from the 21SSD catalogue (Semelin et al.). Finally, we showcase how a trained PGGAN can be leveraged for the converse task of inferring parameters from 21 cm tomography samples via Approximate Bayesian Computation.
ABSTRACT
The Cosmological Principle, that the Universe is homogeneous and isotropic on sufficiently large scales, underpins the standard model of cosmology. However, a recent analysis of 1.36 million ...infrared-selected quasars has identified a significant tension in the amplitude of the number-count dipole compared to that derived from the cosmic microwave background (CMB), thus challenging the Cosmological Principle. Here, we present a Bayesian analysis of the same quasar sample, testing various hypotheses using the Bayesian evidence. We find unambiguous evidence for the presence of a dipole in the distribution of quasars with a direction that is consistent with the dipole identified in the CMB. However, the amplitude of the dipole is found to be 2.7 times larger than that expected from the conventional kinematic explanation of the CMB dipole, with a statistical significance of 5.7σ. To compare these results with theoretical expectations, we sharpen the ΛCDM predictions for the probability distribution of the amplitude, taking into account a number of observational and theoretical systematics. In particular, we show that the presence of the Galactic plane mask causes a considerable loss of dipole signal due to a leakage of power into higher multipoles, exacerbating the discrepancy in the amplitude. By contrast, we show using probabilistic arguments that the source evolution of quasars improves the discrepancy, but only mildly so. These results support the original findings of an anomalously large quasar dipole, independent of the statistical methodology used.
We present an analysis of wide-field photometric surveys of the Palomar 5 globular cluster and its stellar stream, based on g- and r-band measures together with narrow-band DDO 51 photometry. In this ...first study, we use the deep (g, r) data to measure the incidence of gaps and peaks along the stream. Examining the star-counts profile of the stream plus contaminating populations, we find no evidence for significant underdensities, and find only a single significant overdensity. This is at odds with earlier studies based on matched-filter maps derived from shallower SDSS data if the contaminating population possesses plausible spatial properties. The lack of substantial substructure along the stream may be used in future dynamical simulations to examine the incidence of dark matter sub-halos in the Galactic halo. We also present a measurement of the relative distances along the stream, which we use to create the deepest wide-field map of this system to date.
ABSTRACT
Due to differing gravitational potentials and path lengths, gravitational lensing induces time delays between multiple images of a source that, for solar mass objects, are of the order of ...∼10−5 s. If an astrophysically compact source, such as a fast radio burst (FRB), is observed through a region with a high optical depth of such microlensing masses, this gravitational lensing time delay can be imprinted on short time-scale transient signals. In this paper, we consider the impact of the parity of the macroimage on the resultant microlensing time delays. It is found that this parity is directly imprinted on the microlensing signal, with macroimages formed at minima of the time arrival surface beginning with the most highly magnified microimages and then progressing to the fainter microimages. For macroimages at the maxima of the time arrival surface, this situation is reversed, with fainter images observed first and finishing with the brightest microimages. For macroimages at saddle points, the signal again begins with fainter images, followed by brighter images before again fading through the fainter microimages. The growing populations of cosmologically distant bursty transient sources will undoubtedly result in the discovery of strong lensed, multiply imaged FRBs, which will be susceptible to microlensing by compact masses. With the temporal resolution being offered by modern and future facilities, the detection of microlensing-induced time delays will reveal the parities of the gravitational lens macroimages, providing additional constraints on macrolensing mass models and improving the efficacy of these transient sources as cosmological probes.
ABSTRACT
The exploration of the redshift drift, a direct measurement of cosmological expansion, is expected to take several decades of observation with stable, sensitive instruments. We introduced a ...new method to probe cosmology that bypasses the long-period observation by observing the redshift difference, an accumulation of the redshift drift, in multiple-image gravitational lens systems. With this, the photons observed in each image will have traversed through different paths between the source and the observer, and so the lensed images will show different redshifts when observed at the same instance. Here, we consider the impact of the underlying cosmology on the observed redshift difference in gravitational lens systems, generating synthetic data for realistic lens models and exploring the accuracy of determined cosmological parameters. We show that, while the redshift difference is sensitive to the densities of matter and dark energy within a universe, it is independent of the Hubble constant. Finally, we determine the observational considerations for using the redshift difference as a cosmological probe, finding that one thousand lensed sources are enough to make robust determinations of the underlying cosmological parameters. Upcoming cluster lens surveys, such as the Euclid, are expected to detect a sufficient number of such systems.
Abstract
Due to the expansion of our universe, the redshift of distant objects changes with time. Although the amplitude of this redshift drift is small, it will be measurable with decade-long ...campaigns by the next generation of telescopes. Here we present an alternative view of the redshift drift which captures the expansion of the universe in single-epoch observations of the multiple images of gravitationally lensed sources. Considering a sufficiently massive lens, with an associated time delay of order decades, simultaneous photons arriving at a detector would have been emitted decades earlier in one image compared to another, leading to an instantaneous
redshift difference
between the images. We also investigated the peculiar velocity which may influence the redshift difference in observation. While still requiring the observational power of the next generation of telescopes and instruments, the advantage of such a single-epoch detection over other redshift drift measurements is that it will be less susceptible to systematic effects that result from requiring instrument stability over decade-long campaigns.
Here, we present a kinematic study of the Galactic halo out to a radius of ~60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. ...Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates (sigma sub(r), sigma sub(theta), sigma sub(phi)) and the anisotropy profile (beta). The radial velocity dispersion profile (sigma sub(r)) is measured out to a galactocentric radius of r ~ 60 kpc, but due to the lack of proper-motion information, sigma sub(theta), sigma sub(phi), and beta could only be derived directly out to r ~ 25 kpc. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of beta approximately 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (upsilon sub(circ)) of the Galaxy out to r ~ 25 kpc.
As the remnants of stars with initial masses 8 M , white dwarfs contain valuable information on the formation histories of stellar populations. In this paper, we use deep, high-quality, u-band ...photometry from the Canada-France Imaging Survey, griz photometry from Pan-STARRS1, as well as proper motions from Gaia DR2, to select 25,156 white dwarf candidates over ∼4500 deg2 using a reduced proper motion diagram. We develop a new white dwarf population synthesis code that returns mock observations of the Galactic field white dwarf population for a given star formation history, while simultaneously taking into account the geometry of the Milky Way (MW), survey parameters, and selection effects. We use this model to derive the star formation histories of the thin disk, thick disk, and stellar halo. Our results show that the MW disk began forming stars (11.3 0.5) Gyr ago, with a peak rate of (8.8 1.4) M yr −1 at (9.8 0.4) Gyr, before a slow decline to a constant rate until the present day-consistent with recent results suggesting a merging event with a satellite galaxy. Studying the residuals between the data and best-fit model shows evidence for a slight increase in star formation over the past 3 Gyr. We fit the local fraction of helium-atmosphere white dwarfs to be (21 3)%. Incorporating this methodology with data from future wide-field surveys such as the Large Synoptic Survey Telescope, Euclid, The Cosmological Advanced Survey Telescope for Optical and ultraviolet Research, and the Wide Field Infrared Survey Telescope should provide an unprecedented view into the formation of the MW at its earliest epoch through its white dwarfs.
ABSTRACT
We present the first SkyMapper stellar population analysis of the Large Magellanic Cloud (hereafter LMC), including the identification of 3578 candidate Carbon Stars through their extremely ...red g − r colours. Coupled with Gaia astrometry, we analyse the distribution and kinematics of this Carbon Star population, finding the LMC to be centred at (RA, Dec.) = (80.90° ± 0.29, −68.74° ± 0.12), with a bulk proper motion of $(\mu _{\alpha },\mu _{\delta }) = (1.878\pm 0.007,0.293\pm 0.018) \, \mathrm{mas \, yr^{-1}}$ and a disc inclination of i = 25.6° ± 1.1 at position angle θ = 135.6° ± 3.3°. We complement this study with the identification and analysis of additional stellar populations, finding that the dynamical centre for red giant branch stars is similar to that seen for the Carbon Stars, whereas for young stars the dynamical centre is significantly offset from the older populations. This potentially indicates that the young stars were formed as a consequence of a strong tidal interaction, probably with the Small Magellanic Cloud. In terms of internal dynamics, the tangential velocity profile increases linearly within $\sim \!3\ \, \mathrm{kpc}$, after which it maintains an approximately constant value of $V_{\mathrm{ rot}} = 83.6\pm 1.7 \, \mathrm{km \, s^{-1}}$ until $\sim \!7 \, \mathrm{kpc}$. With an asymmetric drift correction, we estimate the mass within $7\, \mathrm{kpc}$ to be $M_{\rm LMC}(\lt 7\, \mathrm{kpc}) = (2.5\pm 0.1)\times 10^{10}{\rm \, {\rm M}_{\odot }}$ and within the tidal radius ($\sim\! 30\ \, \mathrm{kpc}$) to be $M_{\rm LMC}(\lt 30\, \mathrm{kpc}) = (1.06 \pm 0.32)\times 10^{11}\ {\rm \, {\rm M}_{\odot }}$, consistent with other recent measurements.
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