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GAIA Cepheid parallaxes and Local Hole relieve $H_0$ tension

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 نشر من قبل Tom Shanks
 تاريخ النشر 2018
  مجال البحث فيزياء
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There is an $approx9pm2.5$% tension between the value of Hubbles Constant, $H_0=67.4pm0.5$km,s$^{-1}$Mpc$^{-1}$, implied by the {it Planck} microwave background power spectrum and that given by the distance scale of $H_0=73.4pm1.7$km,s$^{-1}$Mpc$^{-1}$. But with a plausible assumption about a {it Gaia} DR2 parallax systematic offset, we find that {it Gaia} parallax distances of Milky Way Cepheid calibrators are $approx12-15$% longer than previously estimated. Similarly, {it Gaia} also implies $approx4.7pm1.7$% longer distances for 46 Cepheids than previous distances on the scale of Riess et al. Then we show that the existence of an $approx150$h$^{-1}$Mpc `Local Hole in the galaxy distribution implies an outflow of $approx500$km,s$^{-1}$. Accounting for this in the recession velocities of SNIa standard candles out to $zapprox0.15$ reduces $H_0$ by a further $approx1.8$%. Combining the above two results would reduce the distance scale $H_0$ estimate by $approx7$% from $H_0approx73.4pm1.7$ to $approx68.9pm1.6$ km,s$^{-1}$Mpc$^{-1}$, in reasonable agreement with the {it Planck} value. We conclude that the discrepancy between distance scale and {it Planck} $H_0$ measurements remains unconfirmed due to uncertainties caused by {it Gaia} systematics and an unexpectedly inhomogeneous local galaxy distribution.



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