44 research outputs found
Gravitational Wave Detection with Relative Astrometry using Roman's Galactic Bulge Time Domain Survey
Gravitational waves (GWs) are a new avenue of observing our Universe. So far,
we have seen them in the ~10-100 Hz range, and there are hints that we might
soon detect them in the nanohertz regime. Multiple efforts are underway to
access GWs across the frequency spectrum; however, parts of the frequency space
are currently not covered by any planned or future observatories. Photometric
surveys can bridge the microhertz gap in the spectrum between LISA and Pulsar
Timing Arrays (PTAs) through relative astrometric measurements. Similar to PTA
measurements, these astrometric measurements rely on the correlated spacetime
distortions produced by gravitational waves at Earth, which induce coherent,
apparent stellar position changes on the sky. To detect microhertz GWs with an
imaging survey, a combination of high relative astrometric precision, a large
number of observed stars, and a high cadence of exposures are needed. Roman's
proposed core community survey, the Galactic Bulge Time Domain Survey (RGBTDS),
would have all of these components. RGBTDS would be sensitive to GWs with
frequencies ranging from Hz to Hz,
which opens up a unique GW observing window for supermassive black hole
binaries and their waveform evolution. We note that small changes to the survey
could enhance Roman's sensitivity to GWs, making it possible to observe the GW
background signal that PTAs have recently hinted at with an SNR 70.Comment: White paper. 9 pages, 2 figures. Submitted to the Roman Core
Community Surveys white paper cal
Effective Field Theory for Dark Matter Absorption on Single Phonons
Single phonon excitations, with energies in the range,
are a powerful probe of light dark matter (DM). Utilizing effective field
theory, we derive a framework to compute DM absorption rates into single
phonons starting from general DM-electron, proton, and neutron interactions. We
apply the framework to a variety of DM models: Yukawa coupled scalars,
axionlike particles (ALPs) with derivative interactions, and vector DM coupling
via gauge interactions or Standard Model electric and magnetic dipole moments.
We find that GaAs or targets can set powerful
constraints on a model, and targets with electronic spin ordering
are similarly sensitive to DM coupling to the electron magnetic dipole moment.
Lastly, we make the code, \textsf{PhonoDark-abs} (an extension of the existing
\textsf{PhonoDark} code which computes general DM-single phonon scattering
rates), publicly available.Comment: 36 pages, 5 figure
Modified Gravity and Dark Energy models Beyond CDM Testable by LSST
One of the main science goals of the Large Synoptic Survey Telescope (LSST)
is to uncover the nature of cosmic acceleration. In the base analysis, possible
deviations from the Lambda-Cold-Dark-Matter (CDM) background evolution
will be probed by fitting a CDM model, which allows for a
redshift-dependent dark energy equation of state with , within general
relativity (GR). A rich array of other phenomena can arise due to deviations
from the standard CDM+GR model though, including modifications to the
growth rate of structure and lensing, and novel screening effects on non-linear
scales. Concrete physical models are needed to provide consistent predictions
for these (potentially small) effects, to give us the best chance of detecting
them and separating them from astrophysical systematics. A complex plethora of
possible models has been constructed over the past few decades, with none
emerging as a particular favorite. This document prioritizes a subset of these
models along with rationales for further study and inclusion into the LSST Dark
Energy Science Collaboration (DESC) data analysis pipelines, based on their
observational viability, theoretical plausibility, and level of theoretical
development. We provide references and theoretical expressions to aid the
integration of these models into DESC software and simulations, and give
justifications for why other models were not prioritized. While DESC efforts
are free to pursue other models, we provide here guidelines on which theories
appear to have higher priority for collaboration efforts due to their perceived
promise and greater instructional value.Comment: 61 pages. Some acknowledgments and references added. This is
version-1.1 of an internal collaboration document of LSST-DESC that is being
made public and is not planned for submission to a journa
Gravitational wave detection with photometric surveys
Gravitational wave (GW) detections have considerably enriched our understanding of the universe. To date, all GW events from individual sources have been found by interferometer-type detectors. In this paper, we study a GW detection technique based on astrometric solutions from photometric surveys and demonstrate that it offers a highly flexible frequency range that can uniquely complement existing detection methods. From repeated point-source astrometric measurements, periodic GW-induced deflections can be extracted and wave parameters inferred. We emphasize that this method can be applied widely to any photometric surveys relying on relative astrometric measurements, in addition to surveys designed to measure absolute astrometry, such as Gaia. We illustrate how high-cadence observations of the galactic bulge, such as offered by the Roman Space Telescope’s Exoplanet MicroLensing (EML) survey, have the potential to be a potent GW probe with a complementary frequency range to Gaia, pulsar timing arrays, and the Laser Interferometer Space Antenna. We calculate that the Roman EML survey is sensitive to GWs with frequencies ranging from 7.7×10⁻⁸ Hz to 5.6×10⁻⁴ Hz, which opens up a unique GW observing window for supermassive black hole binaries and their waveform evolution. While the detection threshold assuming the currently expected performance proves too high for detecting individual GWs in light of the expected supermassive black hole binary population distribution, we show that binaries with chirp mass M_c > 10^(8.3) M_⊙ out to 100 Mpc can be detected if the telescope is able to achieve an astrometric accuracy of 0.11 mas. To confidently detect binaries with M_c > 10⁷ M_⊙ out to 50 Mpc, a factor of 100 sensitivity improvement is required. We propose several improvement strategies, including recovering the mean astrometric deflection and increasing astrometric accuracy, number of observed stars, field-of-view size, and observational cadence. We also discuss how other existing and planned photometric surveys could contribute to detecting GWs via astrometry
Discovery of a close-separation binary quasar at the heart of a z~0.2 merging galaxy and its implications for low-frequency gravitational waves
Supermassive black hole (SMBH) binaries with masses of ~10^8--10^9 Msun are
expected to dominate the contribution to the as-yet undetected gravitational
wave background (GWB) signal at the nanohertz frequencies accessible to Pulsar
Timing Arrays (PTA). We currently lack firm empirical constraints on the
amplitude of the GWB due to the dearth of confirmed SMBH binaries in the
required mass range. Using HST/WFC3 images, we have discovered a z~0.2 quasar
hosted in a merger remnant with two closely separated (0.13'' or ~430pc)
continuum cores at the heart of the galaxy SDSSJ1010+1413. The two cores are
spatially coincident with two powerful [OIII]-emitting point sources with
quasar-like luminosities (L_AGN ~ 5x10^46 erg/s, suggesting the presence of a
bound SMBH system, each with M_BH > 4x10^8 Msun. We place an upper limit on the
merging timescale of the SMBH pair of 2.5 billion years, roughly the Universe
lookback time at z~0.2. There is likely a population of quasar binaries similar
to SDSSJ1010+1413 that contribute to a stochastic GWB that should be detected
in the next several years. If the GWB is not detected this could indicate that
SMBHs merge only over extremely long timescales, remaining as close separation
binaries for many Hubble times, the so-called `final-parsec problem'.Comment: Accepted to ApJL (in press), 9 pages, 5 figure
<scp>ReSurveyEurope</scp>: A database of resurveyed vegetation plots in Europe
AbstractAimsWe introduce ReSurveyEurope — a new data source of resurveyed vegetation plots in Europe, compiled by a collaborative network of vegetation scientists. We describe the scope of this initiative, provide an overview of currently available data, governance, data contribution rules, and accessibility. In addition, we outline further steps, including potential research questions.ResultsReSurveyEurope includes resurveyed vegetation plots from all habitats. Version 1.0 of ReSurveyEurope contains 283,135 observations (i.e., individual surveys of each plot) from 79,190 plots sampled in 449 independent resurvey projects. Of these, 62,139 (78%) are permanent plots, that is, marked in situ, or located with GPS, which allow for high spatial accuracy in resurvey. The remaining 17,051 (22%) plots are from studies in which plots from the initial survey could not be exactly relocated. Four data sets, which together account for 28,470 (36%) plots, provide only presence/absence information on plant species, while the remaining 50,720 (64%) plots contain abundance information (e.g., percentage cover or cover–abundance classes such as variants of the Braun‐Blanquet scale). The oldest plots were sampled in 1911 in the Swiss Alps, while most plots were sampled between 1950 and 2020.ConclusionsReSurveyEurope is a new resource to address a wide range of research questions on fine‐scale changes in European vegetation. The initiative is devoted to an inclusive and transparent governance and data usage approach, based on slightly adapted rules of the well‐established European Vegetation Archive (EVA). ReSurveyEurope data are ready for use, and proposals for analyses of the data set can be submitted at any time to the coordinators. Still, further data contributions are highly welcome.</jats:sec