[Paper Review] Herschel-ATLAS and ALMA: HATLAS J142935.3-002836, a lensed major merger at redshift 1.027

Hugo Messias, S. Dye+30 more|Americanae (AECID Library)|Jun 18, 2014

Galaxies: Formation, Evolution, Phenomena127 references20 citations

TL;DR

This study confirms HATLAS J142935.3-002836 as a strongly lensed major merger at z = 1.027, using multi-wavelength data from Herschel-ATLAS and ALMA. The system exhibits a 10× magnification, revealing a massive, gas-rich merger with a 394 M☉ yr⁻¹ star formation rate and a 117 Myr gas depletion timescale, providing insights into high-redshift galaxy evolution through lensing magnification.

ABSTRACT

[Abridged] Aims: This work focuses on one lensed system, HATLAS J142935.3-002836 (H1429-0028), selected in the Herschel-ATLAS field. Gathering a rich, multi-wavelength dataset, we aim to confirm the lensing hypothesis and model the background source's morphology and dynamics, as well as to provide a full physical characterisation. Methods: Multi-wavelength high-resolution data is utilised to assess the nature of the system. A lensing-analysis algorithm which simultaneously fits different wavebands is adopted to characterise the lens. The background galaxy dynamical information is studied by reconstructing the 3-D source-plane of the ALMA CO(J:4-3) transition. Near-IR imaging from HST and Keck-AO allows to constrain rest-frame optical photometry independently for the foreground and background systems. Physical parameters (such as stellar and dust masses) are estimated via modelling of the spectral energy distribution taking into account source blending, foreground obscuration, and differential magnification. Results: The system comprises a foreground edge-on disk galaxy (at z_sp=0.218) with an almost complete Einstein ring around it. The background source (at z_sp=1.027) is magnified by a factor of ~8-10 depending on wavelength. It is comprised of two components and a tens of kpc long tidal tail resembling the Antennae merger. As a whole, the system is a massive stellar system (1.32[-0.41,+0.63] x1E11 Mo) forming stars at a rate of 394+-90 Mo/yr, and has a significant gas reservoir M_ISM = 4.6+-1.7 x1E10 Mo. Its depletion time due to star formation alone is thus expected to be tau_SF=M_ISM/SFR=117+-51 Myr. The dynamical mass of one of the components is estimated to be 5.8+-1.7 x1E10 Mo, and, together with the photometric total mass estimate, it implies that H1429-0028 is a major merger system (1:2.8[-1.5,+1.8]).

Motivation & Objective

• To confirm the gravitational lensing nature of HATLAS J142935.3-002836 using multi-wavelength high-resolution data.
• To model the morphology and dynamics of the high-redshift background source using ALMA CO(4→3) emission in 3D source-plane reconstruction.
• To perform a full physical characterization of the system, including stellar and dust masses, SFR, and gas reservoirs, accounting for lensing effects.
• To disentangle the photometric and dynamical contributions of the foreground lens and background source using near-IR imaging from HST and Keck-AO.
• To determine the merger mass ratio and dynamical mass of the components to assess the system as a major merger.

Proposed method

• Applied a lensing-analysis algorithm that simultaneously fits multiple wavebands to model the lensed system and derive the lens mass distribution.
• Used ALMA CO(4→3) line emission to reconstruct the 3D structure of the background source and infer its kinematics and dynamical mass.
• Employed near-IR imaging from HST and Keck-AO to obtain rest-frame optical photometry for both the foreground lens and background source, enabling separation of blended light.
• Conducted spectral energy distribution (SED) modeling with inclusion of source blending, foreground obscuration, and differential magnification to estimate physical parameters.
• Calculated magnification factors (μ ≈ 8–10) across wavelengths to correct for lensing amplification in mass and SFR estimates.
• Used dynamical mass estimates from CO kinematics and photometric mass estimates to infer the mass ratio of the merging components.

Experimental results

Research questions

• RQ1 Is HATLAS J142935.3-002836 gravitationally lensed, and what is the nature of the lensing system?
• RQ2 What is the morphology, kinematics, and dynamical mass of the high-redshift background source?
• RQ3 What are the physical properties of the system, including stellar mass, dust mass, star formation rate, and gas reservoir?
• RQ4 What is the mass ratio of the merging components, and does the system qualify as a major merger?
• RQ5 How do lensing magnification and differential amplification affect the derived physical parameters?

Key findings

• The system is a strongly lensed major merger with a foreground edge-on disk galaxy at z = 0.218 forming an almost complete Einstein ring.
• The background source at z = 1.027 is magnified by a factor of μ ≈ 8–10, depending on wavelength, enabling high-resolution study.
• The system hosts a total stellar mass of 1.32⁺⁰.⁶³₋₀.⁴¹ × 10¹¹ M☉ and a star formation rate of 394 ± 90 M☉ yr⁻¹.
• The interstellar medium (ISM) gas mass is 4.6 ± 1.7 × 10¹⁰ M☉, with a gas depletion timescale of 117 ± 51 Myr due to star formation.
• One of the merging components has a dynamical mass of 5.8 ± 1.7 × 10¹⁰ M☉, and the total mass ratio is 1:2.8⁺¹.⁸₋₁.⁵, confirming a major merger.
• The system exhibits a tens of kpc long tidal tail resembling the Antennae merger, indicating a recent or ongoing coalescence.