Discovery of an exceptionally bright giant arc atz= 2.369, gravitationally lensed by thePlanckcluster PSZ1 G311.65−18.48

Abstract

As part of an all-sky follow-up of the Planck catalogue of Sunyaev-Zeldovich (SZ) cluster candidates detected in the first 14 months of data, we are observing cluster candidates in the southern sky in the optical imaging and spectroscopy through an ESO Large Programme. Inspection of ESO New Technology Telescope (NTT) R-and z-band imaging data from our programme has revealed an unusually large and bright arc in the field of PSZ1 G311.65−18.48. We establish the basic photometric and morphological properties of the arc and provide conclusive evidence for the gravitational lensing nature of this object. Guided by the NTT images, we have obtained a long-slit spectrum with IMACS on the Magellan-I Baade Telescope, covering a part of the arc and the brightest cluster galaxy of PSZ1 G311.65−18.48. Our imaging data confirm the presence of a galaxy cluster coinciding (within 0 .6) with the position of the Planck SZ source. The arc is separated by ∼30 from the brightest cluster galaxy, which closely coincides with the center of curvature of the arc. A photometric analysis yields integrated (Vega) magnitudes of (R, z, J, K s ) = (17. 82, 17.38, 16.75, 15.43) for the arc, more than one magnitude brighter than any previously known lensed arc at z ∼ 2-3. The arc is a vigorously star-forming galaxy at z = 2.369, while the Planck SZ cluster lens is at z = 0.443. Even when allowing for lensing magnifications as high as µ = 100 still leads to the conclusion that the source galaxy is among the intrinsically most luminous normal (i.e., non-AGN) galaxies known at z ∼ 2-3.

The Sunburst Arc: Direct Lyman α escape observed in the brightest known lensed galaxy

“…We find that it contains strong evidence for direct escape of Lyman α photons through a perforated optically thick medium. The galaxy was serendipitously discovered in follow-up imaging of its lensing cluster, which was discovered through its Sunyaev-Zel'dovich effect in the Planck data (Planck Collaboration XXIX 2014) and was first reported and described by Dahle et al (2016). This is to our knowledge the first unambiguous detection of this type of spectral signature, and it bears remarkable resemblance to theoretical predictions of, for instance, Behrens et al (2014).…”

Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy

“…The galaxy is designated PSZ1-ARC G311.6602-18.4624 as in the discovery paper (19). The arc segments referred to in the discovery paper (19) as S1, S2 and S3 are here referred to as Arc 1, Arc 2 and Arc 3, respectively. The counterarc was not yet confirmed as part of the lensed system in the discovery paper.…”

“…The Lyman-α profile indicated that it was a prime candidate for strong LyC escape through a narrow channel oriented towards Earth (13). Such a LyC channel should appear as a multiply-imaged, compact source coincident with some of the brightest regions seen in the extended, non-ionizing stellar continuum (19) when observed using telescopes with sufficient resolution and ultraviolet capabilities.…”

The Strong Gravitationally Lensed Herschel Galaxy HLock01: Optical Spectroscopy Reveals a Close Galaxy Merger with Evidence of Inflowing Gas

“…In the optical, it is one of the brightest gravitationally lensed high-z star-forming galaxies known so far (e.g., Yee et al 1996;Allam et al 2007;Belokurov et al 2007;Smail et al 2007;Lin et al 2009;Wuyts et al 2010;Bayliss et al 2011;Dahle et al 2016;Marques-Chaves et al 2017), with an apparent total magnitude of R=19.73±0.01. Even after accounting for the magnification produced by the lensing group of galaxies (μ HST =8.5±0.5), it is still very luminous in the rest-frame UV with an absolute magnitude M UV =−23.4, two-and-a-half magnitudes more luminous than typical LBGs (L UV * ) at a similar redshift (Reddy & Steidel 2009).…”