The Hubble Constant from Strongly Lensed Supernovae with Standardizable Magnifications

The dominant uncertainty in the current measurement of the Hubble constant (H 0) with strong gravitational lensing time delays is attributed to uncertainties in the mass profiles of the main deflector galaxies. Strongly lensed supernovae (glSNe) can provide, in addition to measurable time delays, lensing magnification constraints when knowledge about the unlensed apparent brightness of the explosion is imposed. We present a hierarchical Bayesian framework to combine a data set of SNe that are not strongly lensed and a data set of strongly lensed SNe with measured time delays. We jointly constrain (i) H 0 using the time delays as an absolute distance indicator, (ii) the lens model profiles using the magnification ratio of lensed and unlensed fluxes on the population level, and (iii) the unlensed apparent magnitude distribution of the SN population and the redshift–luminosity relation of the relative expansion history of the universe. We apply our joint inference framework on a future expected data set of glSNe and forecast that a sample of 144 glSNe of Type Ia with well-measured time series and imaging data will measure H 0 to 1.5%. We discuss strategies to mitigate systematics associated with using absolute flux measurements of glSNe to constrain the mass density profiles. Using the magnification of SN images is a promising and complementary alternative to using stellar kinematics. Future surveys, such as the Rubin and Roman observatories, will be able to discover the necessary number of glSNe, and with additional follow-up observations, this methodology will provide precise constraints on mass profiles and H 0.

ANTAGONISM OF SAXITOXIN AND TETRODOTOXIN BLOCK BY INTERNAL MONOVALENT CATIONS IN SQUID AXON

The block of voltage-dependent sodium channels by saxitoxin (STX) and tetrodotoxin (TTX) was investigated in voltage-clamped squid giant axons internally perfused with a variety of permeant monovalent cations. Substitution of internal Na+ by either NH4+ or N2H5+ resulted in a reduction of outward current through sodium channels under control conditions. In contrast, anomalous increases in both inward and outward currents were seen for the same ions if some of the channels were blocked by STX or TTX, suggesting a relief of block by these internal cations. External NH4+ was without effect on the apparent magnitude of toxin block. Likewise, internal inorganic monovalent cations were without effect, suggesting that proton donation by NH4+ might be involved in reducing toxin block. Consistent with this hypothesis, decreases in internal pH mimicked internal perfusion with NH4+ in reducing toxin block. The interaction between internally applied protons and externally applied toxin molecules appears to be competitive, as transient increases in sodium channel current were observed during step increases in intracellular pH in the presence of a fixed STX concentration. In addition to these effects on toxin block, low internal pH produced a voltage-dependent block of sodium channels and enhanced steady-state inactivation. Elevation of external buffer capacity only marginally diminished the modulation of STX block by internal NH4+, suggesting that alkalinization of the periaxonal space and a resultant decrease in the cationic STX concentration during NH4+ perfusion may play only a minor role in the effect. These observations indicate that internal monovalent cations can exert trans-channel influences on external toxin binding sites on sodium channels.

ONGOING FOLLOW-UP NEA OBSERVATIONS IN UKRAINE AND CHINA USING RDS CCD TECHNIQUE

The current state of near-Earth asteroids (NEAs) observations shows an annual increase in the number of newly discovered objects However, the frequency distribution of NEAs by size shows a sharp decrease in the number of objects with size less than 300 m, which contradicts the results of theoretical modeling of the NEA population. Considering definition of potentially hazardous asteroids (PHA), only objects with diameters more than 140 m could pose catastrophic consequences to the Earth and mankind in general. But in the same time, impacts of smaller size objects could lead to significant consequences on local level and their large predicted number increases this probability. Due to their small size which results in faint apparent magnitude, such NEAs are discovered in a short interval of their close approach (CA) to the Earth, when their apparent magnitude are tending to be as bright as possible for a given size. This is not only facilitates the detection of such new objects but also increases their observability by small ground-based telescopes. However, apparent rate of motion during this time might exceed 10 deg d −1 making the observations challenging. The used Rotating-drift-scan CCD (RDS CCD) technique allows to get images of fast-moving objects as a point, that in turn to determine the coordinates of their image centers with sufficient astrometric precision. Obtained in current research project positions show errors in the range ± (0.2″ − 0.3″) in both coordinates with comparison both to JPL's HORIZONS 1 system and NEODyS-2 2 service. The part of observations was obtained around time moment of minimal distance to the Earth during current CA for newly discovered NEAs. Such observations are important to extend observed orbital arc for reliable improvement of their orbit determinations and reducing orbital uncertainty, so it will be possible to recover them in next apparitions.

The Far-away Blues: Exploring the Furthest Extents of the Boötes I Ultra-faint Dwarf Galaxy

Establishing the spatial extents and the nature of the outer stellar populations of dwarf galaxies is necessary for the determination of their total masses, current dynamical states, and past evolution. We here describe our investigation of the outer stellar content of the Boötes I ultra-faint dwarf galaxy, a satellite of the the Milky Way. We identify candidate member blue horizontal branch and blue straggler stars of Boötes I, both tracers of the underlying ancient stellar population, using a combination of multiband Pan-STARRS photometry and Gaia astrometry. We find a total of twenty-four candidate blue horizontal branch member stars with apparent magnitudes and proper motions consistent with membership of Boötes I, nine of which reside at projected distances beyond the nominal King profile tidal radius derived from earlier fits to photometry. We also identify four blue straggler stars of appropriate apparent magnitude to be at the distance of Boötes I, but all four are too faint to have high-quality astrometry from Gaia. The outer blue horizontal branch stars that we have identified confirm that the spatial distribution of the stellar population of Boötes I is quite extended. The morphology on the sky of these outer envelope candidate member stars is evocative of tidal interactions, a possibility that we explore further with simple dynamical models.

Identification of Single Spectral Lines in Large Spectroscopic Surveys Using UMLAUT: an Unsupervised Machine-learning Algorithm Based on Unbiased Topology

The identification of an emission line is unambiguous when multiple spectral features are clearly visible in the same spectrum. However, in many cases, only one line is detected, making it difficult to correctly determine the redshift. We developed a freely available unsupervised machine-learning algorithm based on unbiased topology (UMLAUT) that can be used in a very wide variety of contexts, including the identification of single emission lines. To this purpose, the algorithm combines different sources of information, such as the apparent magnitude, size and color of the emitting source, and the equivalent width and wavelength of the detected line. In each specific case, the algorithm automatically identifies the most relevant ones (i.e., those able to minimize the dispersion associated with the output parameter). The outputs can be easily integrated into different algorithms, allowing us to combine supervised and unsupervised techniques and increasing the overall accuracy. We tested our software on WISP (WFC3 IR Spectroscopic Parallel) survey data. WISP represents one of the closest existing analogs to the near-IR spectroscopic surveys that are going to be performed by the future Euclid and Roman missions. These missions will investigate the large-scale structure of the universe by surveying a large portion of the extragalactic sky in near-IR slitless spectroscopy, detecting a relevant fraction of single emission lines. In our tests, UMLAUT correctly identifies real lines in 83.2% of the cases. The accuracy is slightly higher (84.4%) when combining our unsupervised approach with a supervised approach we previously developed.

ENVIRONMENTAL DEPENDENCE OF AGE, STELLAR MASS, STAR FORMATION RATE AND STELLAR VELOCITY DISPERSION OF ACTIVE GALACTIC NUCLEUS HOST GALAXIES

Using the apparent-magnitude limited active galactic nucleus (AGN) host galaxy sample of the Sloan Digital Sky Survey Data Release 12 (SDSS DR12), we investigate the environmental dependence of age, stellar mass, the star formation rate (SFR) and stellar velocity dispersion of AGN host galaxies. We divide the whole apparent-magnitude limited AGN sample into many subsamples with a redshift binning size of Δz = 0.01, and analyse the environmental dependence of these galaxy properties of subsamples in each redshift bin. It turns out that these parameters of AGN host galaxies seemingly only have a weak environmental dependence.

FRW cosmological models with cosmological constant in f (R,T) theory of gravity

In the present paper, we have generalized the behaviors of {\color{blue}transit-decelerating to accelerating} FRW cosmological model in f (R, T) gravity theory, where R, T are Ricci scalar and trace of energy-momentum tensor respectively. The solution of the corresponding field equations is obtained by assuming a linear function of the Hubble parameter H, i.e., q = c₁ + c₂H which gives a time-dependent DP (deceleration parameter) q(t)=-1+\frac{c_2}{\sqrt{2c_2 t +c_3}}, where c₃ and c₂ are arbitrary integrating constants [Tiwari et al., Eur. Phys. J. Plus: 131, 447 (2016); 132, 126 (2017)]. There are two scenarios in which we explain the particular form of scale factor thus obtained (i) By using the recent constraints from OHD and JLA data which shows a cosmic deceleration to acceleration and (ii) By using new constraints from supernovae type la union data which shows accelerating expansion universe (q<0) throughout the evolution. We have observed that the EoS parameter, energy density parameters, and important cosmological planes yield the results compatible with the modern observational data. For the derived models, we have calculated various physical parameters as Luminosity distance, Distance modulus, and Apparent magnitude versus redshift for both supporting current observations.

The double quasar Q2138-431: detection of a lensing galaxy

ABSTRACT This paper reviews the question of whether the wide separation double quasar Q2138-431 is a gravitational lens. From early work, the two quasar images are known to have almost identical spectra and redshifts, but no lensing galaxy has so far been detected. In this paper, we used recent deep surveys in infrared and optical bands to search for the presence of a galaxy with the expected properties of a gravitational lens. The search revealed a 5σ detection of a faint galaxy between the two quasar images on a deep J-band frame from the VISTA Science Archive, with apparent magnitude J = 20.68. Non-detection in the I-band implied a redshift z &gt; 0.6, and mass modelling of the quasar system gave a mass of $1.31 \times 10^{12} \, \mathrm{M}_\odot$ for the lensing galaxy, with mass-to-light ratio M⊙/L⊙ = 9.0. Archival photographic data from the UK 1.2m Schmidt telescope covering 25 yr were used to construct light curves for the two quasar images, which were then cross-correlated to measure any time lag. This showed image B to lead image A by around a year, consistent with 410 d from the mass model. Although the similarity of the spectra and the detection of the lensing galaxy are the most compelling arguments for the classification of Q2138-431 as a gravitational lens, the time delay and mass-to-light ratio provide a consistent picture to support this conclusion. The wide separation of the quasar images and the simplicity of the mass model make Q2138-431 an excellent system for the measurement of the Hubble constant.

Design and performance of the flash satellite “Ladybeetle-1”

The first satellite which can flash Morse code on orbit is introduced in this paper. The design of the system includes light energy estimation, attitude mode design, elevation angle analysis and flash time design. It is a 100 kg satellite with two LED arrays on 547 km. When it flashes, the satellite points to the observation location. The LED rays flash as the rule of Morse code. The satellite was sent to the orbit in Dec 2018 and the test of flash was completed within one month after then. The photo taken by star sensor can compare the apparent magnitude by the gray level. The results of the analysis show that the satellite can achieve 0 apparent magnitude, which is consistent with the design of the system. As a meaningful scientific experiment, “Ladybeetle-1” links space technology with popular science education and also provides a reference for space applications.

Completeness of the Gaia-verse – IV. The astrometry spread function of Gaia DR2

ABSTRACT Gaia Data Release 2 (DR2) published positions, parallaxes, and proper motions for an unprecedented 1331 909 727 sources, revolutionizing the field of Galactic dynamics. We complement this data with the astrometry spread function (ASF), the expected uncertainty in the measured positions, proper motions, and parallax for a non-accelerating point source. The ASF is a Gaussian function for which we construct the 5D astrometric covariance matrix as a function of position on the sky and apparent magnitude using the Gaia DR2 scanning law and demonstrate excellent agreement with the observed data. This can be used to answer the question ‘What astrometric covariance would Gaia have published if my star was a non-accelerating point source?’. The ASF will enable characterization of binary systems, exoplanet orbits, astrometric microlensing events, and extended sources that add an excess astrometric noise to the expected astrometry uncertainty. By using the ASF to estimate the unit weight error of Gaia DR2 sources, we demonstrate that the ASF indeed provides a direct probe of the excess source noise. We use the ASF to estimate the contribution to the selection function of the Gaia astrometric sample from a cut on astrometric_sigma5d_max showing high completeness for G &lt; 20 dropping to ${\lt} 1{{\ \rm per\ cent}}$ in underscanned regions of the sky for G = 21. We have added an ASF module to the python package scanninglaw (https://github.com/gaiaverse/scanninglaw) through which users can access the ASF.