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Distance to the Virgo cluster galaxy M100 from Hubble Space Telescope observations of Cepheids

Illingworth, Garth D.; Kennicutt, Robert C.; Madore, Barry F. +11 more

Accurate distances to galaxies are critical for determining the present expansion rate of the Universe or Hubble constant (H₀). An important step in resolving the current uncertainty in H₀ is the measurement of the distance to the Virgo cluster of galaxies. New observations using the Hubble Space Telescope yield a distance of…

Detection of intergalactic ionized helium absorption in a high-redshift quasar

Boksenberg, A.; Deharveng, J. M.; Jakobsen, P. +3 more

Observations obtained with the recently refurbished Hubble Space Telescope reveal strong absorption arising from singly ionized helium along the line of sight to a high-redshift quasar. The strength of the absorption suggests that it may arise in a diffuse ionized intergalactic medium. The detection also confirms that substantial amounts of helium…

Evidence for a quasar in the radio galaxy Cygnus A from observation of broad-line emission

Antonucci, Robert; Hurt, Todd; Kinney, Anne

ACTIVE galaxies are thought to be powered by the accretion of surrounding dust and gas onto central black holes. The unified model^1-3 of active galaxies predicts that narrow-line radio galaxies (NLRGs), which are very luminous at radio wavelengths and have narrow optical emission lines, would appear as quasars—which have broad emission …