HATLAS J142935.3-002836, a lensed major merger at z=1.027


Paper:	HATLAS J142935.3-002836, a lensed major merger at z=1.027
Volume:	499, Revolution in Astronomy with ALMA: The Third Year
Page:	41
Authors:	Messias, H.; Dye, S.; Nagar, N.; Orellana, G.; H-ATLAS team
Abstract:	This manuscript reports on the latest developments of our team's study of a gravitationally lensed system, HATLAS J142935.3-002836 (H1429-0028), selected in the Herschel-ATLAS field. Follow-up observations range from near-infrared high-resolution imaging with Hubble Space Telescope (HST) and Keck-AO (Calanog et al. 2014, Messias et al. 2014, M14), to spatially resolved spectroscopy with the Atacama Large (sub-)Millimetre Array (ALMA, M14) and HST (Timmons et al. 2015, T15). The system comprises a foreground edge-on disk galaxy (at z_sp = 0.218) and a lensed background galaxy at z_sp = 1.027. The foreground lens-properties were assessed in M14 based on the velocity-integrated CO (4to3) and 7 GHz-continuum maps as observed by ALMA and the Jansky Very Large Array, respectively. This allowed the reconstruction of the source-plane gas dynamical properties of the lensed-system and the stellar-light distribution. The background source is magnified by a factor of μ∼8–10 depending on wavelength, and it is comprised of two components and a tens-of-kpc-long tidal tail. The latest spectral energy distribution analysis by T15, considering near-infrared spatially resolved spectroscopy together with high-precision 3–4 μm photometry, point to a massive system (1.1±0.4×10¹¹ M_⊙) forming stars at a rate of 100±80 M_⊙ yr^–1. With a gas reservoir of M_ISM =4.6 ± 1.7 ×10¹⁰ M_⊙, this means a depletion time of τSF= M_ISM/SFR =460 ± 170Myr. This should be comparable to the molecular gas depletion, since we estimate a molecular gas content of 5.9±1.5×10¹⁰ M_⊙ (α=2.8±0.67 M_⊙/(K.km/s.pc²⁾) based on the metallicity estimate from T15, the CO line luminosity estimate from M14, and H₂-CO conversion-factor method from Narayanan et al. (2012). This is consistent (within 1σ) with >70% of the ISM gas being in a molecular-phase (overlapping with the range estimated by M14). Finally, the dynamical analysis by M14 point to a 1:3 merger system in the background.