arXiv subjects

Mikhail Denissenya

Publications and source records attributed to Mikhail Denissenya.

13 recordsLinked to original sources

arXiv2024

Model independent approach for calculating galaxy rotation curves for low $S/N$ MaNGA galaxies

Internal kinematics of galaxies, traced through the stellar rotation curve or two dimensional velocity map, carry important information on galactic structure and dark matter. With upcoming surveys, the velocity map may play a key role in the development of kinematic lensing as an astrophysical probe. We improve techniques for extracting velocity information from integral field spectroscopy at low signal-to-noise ($S/N$), without a template, and demonstrate substantial advantages over the standard Penalized PiXel-Fitting method (pPXF) approach. Robust rotation curves can be derived down to $S/N\approx 2$ using our method.

astro-ph.GA↗

arXiv2023

Model Independent Dark Matter Properties from Cosmic Growth

Dark matter dominates the matter budget of the universe but its nature is unknown. Deviations from the standard model, where dark matter clusters with the same gravitational strength as baryons, and has the same pressureless equation of state as baryons, can be tested by cosmic growth measurements. We take a model independent approach, allowing deviations in bins of redshift, and compute the constraints enabled by ongoing cosmic structure surveys through redshift space distortions and peculiar velocities. These can produce constraints at the $3-14\%$ level in four independent redshift bins over $z=[0,4]$.

astro-ph.CO↗

arXiv2023

Model Independent Reconstruction of Galaxy Stellar Velocity Map

We develop a model independent, robust method for determining galaxy rotation velocities across a 2D array of spaxels from an integral field spectrograph. Simulations demonstrate the method is accurate down to lower spectral signal-to-noise than standard methods: 99\% accurate when median $S/N=4$. We apply it to MaNGA data to construct the galaxy velocity map and galaxy rotation curve. We also develop a highly efficient cubic smoothing approach that is $25\times$ faster computationally and only slightly less accurate. Such model independent methods could be useful in studying dark matter properties without assuming a galaxy model.

astro-ph.CO↗

arXiv2023

Connecting Primordial Gravitational Waves and Dark Energy

Cosmic acceleration manifested in the early universe as inflation, generating primordial gravitational waves detectable in the cosmic microwave background (CMB) radiation. Cosmic acceleration is occurring again at present as dark energy, detectable in cosmic distance and structure surveys. We explore the intriguing idea of connecting the two occurrences through quintessential inflation by an $α$-attractor potential without a cosmological constant. For this model we demonstrate robustness of the connection $1+w_0\approx 4/(3N^2r)$ between the present day dark energy equation of state parameter $w_0$ and the primordial tensor to scalar ratio $r$ for a wide range of initial conditions. Analytics and numerical solutions produce current thawing behavior, resulting in a tight relation $w_a\approx-1.53(1+w_0)\approx -0.2\,(4\times 10^{-3}/r)$. Upcoming CMB and galaxy redshift surveys can test this consistency condition. Within this model, lack of detection of a dark energy deviation from $Λ$ predicts a higher $r$, and lack of detection of $r$ predicts greater dark energy dynamics.

astro-ph.CO↗

arXiv2022

Constraining Scale Dependent Growth with Redshift Surveys

Ongoing and future redshift surveys have the capability to measure the growth rate of large scale structure at the percent level over a broad range of redshifts, tightly constraining cosmological parameters. Beyond general relativity, however, the growth rate in the linear density perturbation regime can be not only redshift dependent but scale dependent, revealing important clues to modified gravity. We demonstrate that a fully model independent approach of binning the gravitational strength $G_{\rm eff}(k,z)$ matches scalar-tensor results for the growth rate $fσ_8(k,z)$ to $0.02\%$-$0.27\%$ rms accuracy. For data of the quality of the Dark Energy Spectroscopic Instrument (DESI) we find the bin values can be constrained to 1.4\%-28\%. We also explore the general scalar-tensor form, constraining the amplitude and past and future scalaron mass/shape parameters. Perhaps most interesting is the strong complementarity of low redshift peculiar velocity data with DESI-like redshift space distortion measurements, enabling improvements up to a factor 6-7 on 2D joint confidence contour areas. Finally, we quantify some issues with gravity parametrizations that do not include all the key physics.

astro-ph.CO↗

arXiv2022

Deep Learning Unresolved Lensed Lightcurves

Gravitationally lensed sources may have unresolved or blended multiple images, and for time varying sources the lightcurves from individual images can overlap. We use convolutional neural nets to both classify the lightcurves as due to unlensed, double, or quad lensed sources and fit for the time delays. Focusing on lensed supernova systems with time delays $Δt\gtrsim6$ days, we achieve 100\% precision and recall in identifying the number of images and then estimating the time delays to $σ_{Δt}\approx1$ day, with a $1000\times$ speedup relative to our previous Monte Carlo technique. This also succeeds for flux noise levels $\sim10\%$. For $Δt\in[2,6]$ days we obtain 94--98\% accuracy, depending on image configuration. We also explore using partial lightcurves where observations only start near maximum light, without the rise time data, and quantify the success.

astro-ph.IM↗

arXiv2022

Out of One, Many: Distinguishing Time Delays from Lensed Supernovae

Gravitationally lensed Type Ia supernovae are an emerging probe with great potential for constraining dark energy, spatial curvature, and the Hubble constant. The multiple images and their time delayed and magnified fluxes may be unresolved, however, blended into a single lightcurve. We demonstrate methods without a fixed source template matching for extracting the individual images, determining whether there are one (no lensing) or two or four (lensed) images, and measuring the time delays between them that are valuable cosmological probes. We find 100% success for determining the number of images for time delays greater than $\sim10$ days.

astro-ph.CO↗

arXiv2021

Ultra Fast Astronomy: Optimized Detection of Multimessenger Transients

Ultra Fast Astronomy is a new frontier becoming enabled by improved detector technology allowing discovery of optical transients on millisecond to nanosecond time scales. These may reveal counterparts of energetic processes such as fast radio bursts, gamma ray bursts, gravitational wave events, or play a role in the optical search for extraterrestrial intelligence (oSETI). We explore some example science cases and their optimization under constrained resources, basically how to distribute observations along the spectrum of short duration searches of many targets or long searches over fewer targets. As a demonstration of the method we present some analytic and some numerical optimizations, of both raw detections and science characterization such as an information matrix analysis of constraining a burst delay -- flash duration relation.

astro-ph.IM↗

arXiv2021

Distinguishing Time Clustering of Astrophysical Bursts

Many astrophysical bursts can recur, and their time series structure or pattern could be closely tied to the emission and system physics. While analysis of periodic events is well established, some sources, e.g. some fast radio bursts and soft gamma-ray emitters, are suspected of more subtle and less explored periodic windowed behavior: the bursts themselves are not periodic, but the activity only occurs during periodic windows. We focus here on distinguishing periodic windowed behavior from merely clustered events through time clustering analysis, using techniques analogous to spatial clustering, demonstrating methods for identifying and characterizing the behavior. An important aspect is accounting for the ``curious incident of the dog in the night time'' - lack of bursts carries information. As a worked example, we analyze six years of data from the soft gamma repeater SGR1935+2154, deriving a window period of 231 days and 55% duty cycle; this has now successfully predicted both active and inactive periods.

astro-ph.IM↗

arXiv2018

Gravity's Islands: Parametrizing Horndeski Stability

Cosmic acceleration may be due to modified gravity, with effective field theory or property functions describing the theory. Connection to cosmological observations through practical parametrization of these functions is difficult and also faces the issue that not all assumed time dependence or parts of parameter space give a stable theory. We investigate the relation between parametrization and stability in Horndeski gravity, showing that the results are highly dependent on the function parametrization. This can cause misinterpretations of cosmological observations, hiding and even ruling out key theoretical signatures. We discuss approaches and constraints that can be placed on the property functions and scalar sound speed to preserve some observational properties, but find that parametrizations closest to the observations, e.g. in terms of the gravitational strengths, offer more robust physical interpretations. In addition we present an example of how future observations of the B-mode polarization of the cosmic microwave background from primordial gravitational waves can probe different aspects of gravity.

astro-ph.CO↗

arXiv2018

Cosmic Curvature Tested Directly from Observations

Cosmic spatial curvature is a fundamental geometric quantity of the Universe. We investigate a model independent, geometric approach to measure spatial curvature directly from observations, without any derivatives of data. This employs strong lensing time delays and supernova distance measurements to measure the curvature itself, rather than just testing consistency with flatness. We define two curvature estimators, with differing error propagation characteristics, that can crosscheck each other, and also show how they can be used to map the curvature in redshift slices, to test constancy of curvature as required by the Robertson-Walker metric. Simulating realizations of redshift distributions and distance measurements of lenses and sources, we estimate uncertainties on the curvature enabled by next generation measurements. The results indicate that the model independent methods, using only geometry without assuming forms for the energy density constituents, can determine the curvature at the $\sim6\times10^{-3}$ level.

astro-ph.CO↗

arXiv2017

Subpercent Accurate Fitting of Modified Gravity Growth

Adding to our previous method for dealing with gravitational modifications at redshift $z\gtrsim3$ through a single parameter, we investigate treatment of lower redshift modifications to linear growth observables. We establish subpercent accurate fits to the redshift space distortion observable $fσ_8(a)$ using two parameters binned in redshift, testing the results for modifications with time dependence that rises, falls, is nonmonotonic, is multipeaked, and corresponds to $f(R)$ and braneworld gravity. The residuals are then propagated to cosmological parameter biases for DESI observations, and found to cause a shift in the dark energy joint confidence contour by less than the equivalent of $\sim0.1σ$. The proposed 2--3 parameter modified gravity description also can reveal physical characteristics of the underlying theory.

astro-ph.CO↗

arXiv2017

Cosmic Growth Signatures of Modified Gravitational Strength

Cosmic growth of large scale structure probes the entire history of cosmic expansion and gravitational coupling. To get a clear picture of the effects of modification of gravity we consider a deviation in the coupling strength (effective Newton's constant) at different redshifts, with different durations and amplitudes. We derive, analytically and numerically, the impact on the growth rate and growth amplitude. Galaxy redshift surveys can measure a product of these through redshift space distortions and we connect the modified gravity to the observable in a way that may provide a useful parametrization of the ability of future surveys to test gravity. In particular, modifications during the matter dominated era can be treated by a single parameter, the "area" of the modification, to an accuracy of $\sim0.3\%$ in the observables. We project constraints on both early and late time gravity for the Dark Energy Spectroscopic Instrument and discuss what is needed for tightening tests of gravity to better than 5% uncertainty.

astro-ph.CO↗