Abstract
Light curves produced by wide-field exoplanet transit surveys such as CoRoT, Kepler, and the Transiting Exoplanet Survey Satellite are affected by sensor-wide systematic noise, which is ...correlated both spatiotemporally and with other instrumental parameters such as the photometric magnitude. Robust and effective systematics mitigation is necessary to achieve the level of photometric accuracy required to detect exoplanet transits and to faithfully recover other forms of intrinsic astrophysical variability. We demonstrate the feasibility of a new exploratory algorithm to remove spatially correlated systematic noise and detrend light curves obtained from wide-field transit surveys. This spatial systematics algorithm is data-driven and fits a low-rank linear model for the systematics conditioned on a total-variation spatial constraint. The total-variation constraint models spatial systematic structure across the sensor on a foundational level. The fit is performed using gradient descent applied to, a variable reduced least-squares penalty and a modified form of total-variation prior; both the systematics basis vectors and their weighting coefficients are iteratively varied. The algorithm was numerically evaluated against a reference principal component analysis, using both signal injection on a selected Kepler dataset, as well as full simulations within the same Kepler coordinate framework. We develop our algorithm to reduce the overfitting of astrophysical variability over longer signal timescales (days) while performing comparably relative to the reference method for exoplanet transit timescales. The algorithm performance and application are assessed, and future development is outlined.
ABSTRACT We study the abundance of substructure in the matter density near galaxies using ALMA Science Verification observations of the strong lensing system SDP.81. We present a method to measure ...the abundance of subhalos around galaxies using interferometric observations of gravitational lenses. Using simulated ALMA observations we explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. We apply our formalism to ALMA observations of SDP.81. We find evidence for the presence of a M = 108.96 0.12M subhalo near one of the images, with a significance of 6.9 in a joint fit to data from bands 6 and 7; the effect of the subhalo is also detected in both bands individually. We also derive constraints on the abundance of dark matter (DM) subhalos down to M ∼ 2 × 107M , pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted DM subhalos. We find hints of additional substructure, warranting further study using the full SDP.81 data set (including, for example, the spectroscopic imaging of the lensed carbon monoxide emission). We compare the results of this search to the predictions of ΛCDM halos, and find that given current uncertainties in the host halo properties of SDP.81, our measurements of substructure are consistent with theoretical expectations. Observations of larger samples of gravitational lenses with ALMA should be able to improve the constraints on the abundance of galactic substructure.
We examine the counts-in-cells (CiC) probability distribution functions (PDFs) that describe dark matter halos in the Dark Energy Universe Simulations (DEUS). We describe the measurements between ...redshifts z = 0 to z = 4 on both linear and nonlinear scales. The best fits of the gravitational quasi-equilibrium distribution (GQED), the negative binomial distribution (NBD), the Poisson-Lognormal distribution (PLN), and the Poisson-Lognormal distribution with a bias parameter (PLNB) are compared to simulations. The fits agree reasonably consistently over a range of redshifts and scales. To distinguish quintessence (RPCDM) and phantom (wCDM) dark energy from Λ dark energy, we present a new method that compares the model parameters of the CiC PDFs. We find that the mean and variance of the halo CiC on 2-25h−1 Mpc scales between redshifts 0.65 < z < 4 show significant percentage differences for different dark energy cosmologies. On 15-25 h−1 Mpc scales, the g parameter in NBD, parameter in PLN, and b and Cb parameters in PLNB show larger percentage differences for different dark energy cosmologies than on smaller scales. On 2-6 h−1 Mpc scales, the kurtosis and the b parameter in the GQED show larger percentage differences for different dark energy cosmologies than on larger scales. For cosmologies explored in the DEUS, the percentage differences between these statistics for the RPCDM and wCDM dark energy cosmologies relative to ΛCDM generally increases with redshift from a few percent to significantly larger percentages at z = 4. Applying our method to simulations and galaxy surveys can provide a useful way to distinguish among dark energy models and cosmologies in general.
The treatment of systematic noise is a significant aspect of transit exoplanet data processing due to the signal strength of systematic noise relative to a transit signal. Typically, the standard ...approach to transit detection is to estimate and remove systematic noise independently of and prior to a transit detection test. If a transit signal is present in a light curve, the process of systematic noise removal may distort the transit signal by overfitting and thereby reduce detection efficiency. We present a Bayesian framework for joint detection of transit signals and systematic noise characterization and describe the implementation of these detectors as optimal Neyman-Pearson likelihood ratio tests. The joint detectors reduce to closed form as matched filters under the assumption of a Gaussian Bayesian prior for the systematic noise. The performance of the exploratory detectors was evaluated in injection tests and show ∼2% improvement in overall detection efficiency relative to the standard approach. We find that joint detection efficiency is specifically improved for short-period, low transit-depth exoplanet transits, providing evidence in support of the hypothesis that joint detection may indeed help to mitigate overfitting. In addition, an initial feasibility test to detect known exoplanets in Kepler data using the joint detectors produced encouraging preliminary results.
We examine the flux density ratio anomaly in the quadruply imaged strong gravitational lens, B1422+231, and consider the contribution of 10–103M⊙ primordial black holes (PBHs) as a potential dark ...matter constituent. We describe the first flux density ratio measurement of B1422+231 in the millimeter-wave band using the Atacama Large Millimeter Array (ALMA). The flux density of the quasar at 233 GHz is dominated by synchrotron emission and the source size is estimated to be less than 66.9 pc. The observed flux density ratios at 233 GHz are similar to those measured in other wave bands, which cannot be explained by a simple smooth mass model of the lens galaxy. We examine the probability of the flux density ratio anomaly arising from PBH microlensing using ray tracing simulations. The simulations consider the cases where 10% and 50% of dark matter are 10–103M⊙ PBHs with a power law mass function. The simulated scenarios are consistent with the ALMA observations, so PBH dark matter cannot be ruled out as a cause of flux density ratio anomalies. Our analysis shows that the anomalous flux density ratio for B1422+231 can be explained by a lens model with a significant fraction of dark matter being PBHs. This study demonstrates the potential for new constraints on PBH dark matter using ALMA observations of multiply imaged strong gravitational lenses.
The Zeeman effect is the only observational technique available to measure directly the strength of magnetic fields in regions of star formation. This chapter reviews the physics of the Zeeman effect ...and its practical use in both extended gas and in masers. We discuss observational results for the five species for which the Zeeman effect has been detected in the interstellar medium—H I, OH, and CN in extended gas and OH, CH3OH, and H2O in masers. These species cover a wide range in density, from ~10 cm−3 to ~1010 cm−3, which allows magnetic fields to be measured over the full range of cloud densities. However, there are significant limitations, including that only the line-of-sight component of the magnetic field strength can usually be measured and that there are often significant uncertainties about the physical conditions being sampled, particularly for masers. We discuss statistical methods to partially overcome these limitations. The results of Zeeman observations are that the mass to magnetic flux ratio, which measures the relative importance of gravity to magnetic support, is subcritical (gravity dominates magnetic support) at lower densities but supercritical for NH≳1022 cm−2. Above nH ~ 300 cm−3, which is roughly the density at which clouds typically become self-gravitating, the strength of magnetic fields increases approximately as B ∝ n2/3, which suggest that magnetic fields do not provide significant support at high densities. This is consistent with high-density clouds being supercritical. However, magnetic fields have a large range in strengths at any given density, so the role of magnetic fields should differ significantly from one cloud to another. And for maser regions the dependence of field strength on density may have a slightly lower slope. Turbulent reconnection theory seems to best match the Zeeman observational results.
Mapping magnetic fields is the key to resolving the unclear physical picture of circumstellar magnetic fields in late-type evolved stars. Observations of linearly polarized emission from thermal ...molecular line transitions due to the Goldreich-Kylafis (G-K) effect provide valuable insights into the magnetic field geometry in these sources that are complementary to other key studies. In this paper, we present the detection of spectral-line polarization from both the thermal J = 2−1 CO line and the v = 1, J = 5−4 SiO maser line toward two thermal-pulsating asymptotic giant branch stars, R Crt and R Leo. The observed fractional linear polarization in the CO emission is measured as ml ∼ 3.1% and ml ∼ 9.7% for R Crt and R Leo, respectively. A circumstellar envelope (CSE) model profile and the associated parameters are estimated and used as input to a more detailed modeling of the predicted linear polarization expected from the G-K effect. The observed thermal line polarization level is consistent with the predicted results from the G-K model for R Crt; additional effects need to be considered for R Leo.
We present dust opacity spectral indexes (b) of the youngest protostellar systems (so-called Class 0 sources), L1448 IRS 2, L1448 IRS 3, and L1157, obtained between the l = 1.3 mm and 2.7 mm ...continua, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The unprecedented compact configuration and image fidelity of CARMA allow a better detection of the dust continuum emission from Class 0 sources, with a less serious missing flux problem normally associated with interferometry. Through visibility modeling at both l = 1.3 mm and 2.7 mm simultaneously, as well as image and visibility comparison, we show that b of the three Class 0 sources are around or smaller than 1, indicating that dust grains have already significantly grown at the Class 0 stage. In addition, we find a radial dependence of b, which implies faster grain growth in the denser central regions and/or dust segregation. Density distributions of the Class 0 sources are also addressed by visibility modeling.
We have conducted Combined Array for Research in Millimeter-wave Astronomy observations of LiH, in absorption, toward three quasars. These quasars, B0218+357, PKS1830--211, and PKS0201+113, have ...redshifts of z = 0.685 -- 3.387, and shift the LiH J = 1-0 transition to the 1 mm and 3 mm wavelength bands, where atmospheric absorption is sharply reduced from that predominating near the rest frequency of 443 GHz. We report a 3 Delta *s detection of LiH toward B0218+357 with a column density of 1.4 X 1012 cm--2 and place an upper limit on the 6Li/7Li ratio of <0.16. LiH was not detected toward any other source.
We present a time series of synoptic images of the linearly polarized v = 1, J = 1-0 SiO maser emission toward the Mira variable, TX Cam. These data comprise 43 individual epochs at an approximate ...biweekly sampling over an optical pulsation phase range of = 0.68 to = 1.82. The images have an angular resolution of ~500 is a subset of as and were obtained using the Very Long Baseline Array (VLBA), operating in the 43 GHz band in spectral-line, polarization mode. We have previously published the total intensity time series for this pulsation phase range; this paper serves to present the linearly polarized image sequence and an associated animation representing the evolution of the linear polarization morphology over time. We find a predominantly tangential polarization morphology, a high degree of persistence in linear polarization properties over individual component lifetimes, and stronger linear polarization in the inner projected shell than at larger projected shell radii. We present an initial polarization proper motion analysis examining the possible dynamical influence of magnetic fields in component motions in the extended atmospheres of late-type, evolved stars.
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