Mapping UV properties throughout the cosmic horseshoe: Lessons from VLT-MUSE

Bethan L. James, Matt Auger, Max Pettini, Daniel P. Stark, V. Belokurov, Stefano Carniani

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


We present the first spatially resolved rest-frame ultraviolet (UV) study of the gravitationally lensed galaxy, the 'Cosmic Horseshoe' (J1148+1930) at z = 2.38. Our gravitational lens model shows that the system is made up of four star-forming regions, each ~4-8 kpc2 in size, from which we extract four spatially exclusive regional spectra. We study the interstellar and wind absorption lines, along with C III] doublet emission lines, in each region to investigate any variation in emission/absorption line properties. Themapped C III] emission shows distinct kinematical structure, with velocity offsets of ~±50 km s-1 between regions suggestive of a merging system, and a variation in equivalent width that indicates a change in ionization parameter and/or metallicity between the regions. Absorption line velocities reveal a range of outflow strengths, with gas outflowing in the range -200 ≲ v (km s-1) ≲ -50 relative to the systemic velocity of that region. Interestingly, the strongest gas outflow appears to emanate from the most diffuse star-forming region. The star formation rates remain relatively constant (~8-16M yr-1), mostly due to large uncertainties in reddening estimates. As such, the outflows appear to be 'global' rather than 'locally' sourced.We measure electron densities with a range of log (Ne)= 3.92-4.36 cm-3, and point out that such high densities may be common when measured using the CIII] doublet due to its large critical density. Overall, our observations demonstrate that while it is possible to trace variations in large-scale gas kinematics, detecting inhomogeneities in physical gas properties and their effects on the outflowing gas may be more difficult. This study provides important lessons for the spatially resolved rest-frame UV studies expected with future observatories, such as James Webb Space Telescope.

Original languageEnglish (US)
Pages (from-to)1726-1740
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - May 11 2018


  • Galaxies: ISM
  • Galaxies: evolution
  • Galaxies: star formation
  • Gravitational lensing: strong
  • Ultraviolet: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Mapping UV properties throughout the cosmic horseshoe: Lessons from VLT-MUSE'. Together they form a unique fingerprint.

Cite this