Search

We present H i spectral line and radio-continuum Very Large Array (VLA) data of the galaxy NGC 765, complemented by optical and Chandra X-ray maps. NGC 765 has the largest H i-to-optical ratio known to date of any spiral galaxy and one of the largest known H i discs in absolute size with a diameter of 240 kpc measured at a surface density of atom cm−2. We derive a total H i mass of , a dynamical mass of and an H i mass-to-luminosity ratio of , making it the nearest and largest ‘crouching giant’. Optical images reveal evidence of a central bar with tightly wound low surface brightness spiral arms extending from it. Radio-continuum ( W Hz−1) and X-ray ( ) emission is found to coincide with the optical core of the galaxy, compatible with nuclear activity powered by a low-luminosity active galactic nucleus. We may be dealing with a galaxy that has retained in its current morphology traces of its formation history. In fact, it may still be undergoing some accretion, as evidenced by the presence of H i clumps the size (<10 kpc) and mass ( ) of small (dIrr) galaxies in the outskirts of its H i disc and by the presence of two similarly sized companions. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet spectra of highly-charged hafnium, tantalum and gold were produced with an electron beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) and recorded with a flat-field grazing-incidence spectrometer in the wavelength range 4-20 nm. The beam energy was varied between 1.84 and 5.15 keV to selectively enhance spectra from specific ionization stages. Identifications of strong n = 4-n = 4 transitions from Rb-like hafnium (35+) to Co-like gold (52+) were determined with the aid of collisional-radiative modelling of the EBIT plasma. Good quantitative agreement between simulated and measured spectra was achieved. Over 150 spectral lines were identified, 115 of which are new. [ABSTRACT FROM AUTHOR]