Mapping UV properties throughout the Cosmic Horseshoe: lessons from VLT-MUSE. Issue 2 (6th February 2018)

• Record Type: Journal Article
• Authors: James, Bethan L; Auger, Matt; Pettini, Max; Stark, Daniel P; Belokurov, V; Carniani, Stefano
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 476:Issue 2(2018)
• Page Start: 1726
• Page End: 1740
• Publication Date: 2018-02-06
• Subjects: gravitational lensing: strong -- galaxies: evolution -- galaxies: ISM -- galaxies: star formation -- ultraviolet: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty315
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: 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 kpc 2 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. The mapped 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 (∼8–16 M⊙ 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 ( N e ) = 3.92–4.36 cm −3, and point out that such high densities may be common when measured using the C iii ] 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 .