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| Format: | Preprint |
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2024
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| Online Access: | https://arxiv.org/abs/2412.08605 |
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| _version_ | 1866917951962087424 |
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| author | Darling, Jeremy |
| author_facet | Darling, Jeremy |
| contents | We present new astrometric constraints on the stochastic gravitational wave background and construct the first astrometric Hellings-Downs curve using quasar proper motions. From quadrupolar vector spherical harmonic fits to the Gaia proper motions of 1,108,858 quasars, we obtain a frequency-integrated upper limit on the gravitational wave energy density, $h_{70}^2Ω_{GW} \leq 0.023$ (95% confidence limit), for frequencies between 11.2 nHz and $3.1\times10^{-9}$ nHz ($1.33/t_0$). However, from the astrometric Hellings-Downs curve that describes the correlated proper motions between 2,104,609,881 quasar pairs as a function of their angular separation, we find a stronger constraint: a characteristic strain of $h_{c} \leq 2.7 \times 10^{-12}$ for $f_{\rm ref} = 1$ yr$^{-1}$ and $h_{70}^2Ω_{\rm GW} \leq 0.0096$ at 95% confidence. We probe down to $\pm$0.005 $μ$as$^2$ yr$^{-2}$ in correlated power and obtain the lowest astrometric limit to date. This is also the first time that optical wavelength astrometry surpasses limits from radio-frequency interferometry. This astrometric analysis does not yet reach the sensitivity needed to detect the pulsar timing-based red gravitational wave spectrum extrapolated to the quasar gravitational wave sensitivity window, assuming that the turnover in the spectrum occurs at $\sim$1 nHz for massive black hole binaries. The limits presented here may exclude some exotic interpretations of the stochastic gravitational wave background. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2412_08605 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | A New Approach to the Low Frequency Stochastic Gravitational Wave Background: Constraints from Quasars and the Astrometric Hellings-Downs Curve Darling, Jeremy Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology We present new astrometric constraints on the stochastic gravitational wave background and construct the first astrometric Hellings-Downs curve using quasar proper motions. From quadrupolar vector spherical harmonic fits to the Gaia proper motions of 1,108,858 quasars, we obtain a frequency-integrated upper limit on the gravitational wave energy density, $h_{70}^2Ω_{GW} \leq 0.023$ (95% confidence limit), for frequencies between 11.2 nHz and $3.1\times10^{-9}$ nHz ($1.33/t_0$). However, from the astrometric Hellings-Downs curve that describes the correlated proper motions between 2,104,609,881 quasar pairs as a function of their angular separation, we find a stronger constraint: a characteristic strain of $h_{c} \leq 2.7 \times 10^{-12}$ for $f_{\rm ref} = 1$ yr$^{-1}$ and $h_{70}^2Ω_{\rm GW} \leq 0.0096$ at 95% confidence. We probe down to $\pm$0.005 $μ$as$^2$ yr$^{-2}$ in correlated power and obtain the lowest astrometric limit to date. This is also the first time that optical wavelength astrometry surpasses limits from radio-frequency interferometry. This astrometric analysis does not yet reach the sensitivity needed to detect the pulsar timing-based red gravitational wave spectrum extrapolated to the quasar gravitational wave sensitivity window, assuming that the turnover in the spectrum occurs at $\sim$1 nHz for massive black hole binaries. The limits presented here may exclude some exotic interpretations of the stochastic gravitational wave background. |
| title | A New Approach to the Low Frequency Stochastic Gravitational Wave Background: Constraints from Quasars and the Astrometric Hellings-Downs Curve |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2412.08605 |