Author ORCID Identifier

Belén Alcalde Pampliega: 0000-0002-4140-0428

Kevin C. Harrington: 0000-0001-5429-5762

Aristeidis Amvrosiadis: 0000-0002-4465-1564

Manuel Aravena: 0000-0002-6290-3198

Min S.Yun: 0000-0001-7095-7543

Hugo Messias: 0000-0002-2985-7994

Antonio Hernán-Caballero: 0000-0002-4237-5500

Leindert Boogaard: 0000-0002-3952-8588

Axel Weiß: 0000-0003-4678-3939

Benjamin Beauchesne: 0000-0002-0443-6018

Alejandro Santamaría-Miranda: 0000-0001-6267-2820

Eric Jiménez-Andrade: 0000-0002-2640-5917

Manuel Solimano: 0000-0001-6629-0379

James Lowenthal: 0000-0001-9969-3115

Patrick Kamieneski: 0000-0001-9394-6732

Q. Daniel Wang: 0009-0002-9714-1928

Chentao Yang: 0000-0002-8117-9991

Amit Vishwas: 0000-0002-4444-8929

Brenda Frye: 0000-0003-1625-8009

Yiqing Song: 0000-0002-3139-3041

Meghana Killi: 0000-0001-5289-3291

Document Type

Article

Publication Date

2-10-2026

Publication Title

Astronomy & Astrophysics

Abstract

We present a detailed analysis of J154506, a strongly lensed submillimetre galaxy (SMG) behind the Lupus-I molecular cloud, and a characterisation of its physical properties using a combination of new and archival data, including VLT/MUSE and FORS2 optical data. We identify two high-significance (S/N >5) emission lines at 97.0 and 145.5 GHz, corresponding to CO(4-3) and CO(6-5), respectively, in spectral scans from the Atacama Compact Array (ACA) and the Large Millimetre Telescope (LMT), as well as the [CII] 158 µm fine-structure line at 400 GHz observed with the Atacama Pathfinder Experiment (APEX). These detections yield a spectroscopic redshift of zspec = 3.7515 ±0.0005. We also report the detection of [CI], HCN(4-3), and two H2O+ transitions, further confirming the redshift and providing insights into the physical properties of J154506. By modelling sub-arcsecond resolution (0.75′′) ALMA Band 6 and 7 continuum data in the uv-plane, we derive an average magnification factor of 6.0 ±0.4, and our analysis reveals a relatively cold dust (38 K) in a starburst galaxy (∼900 M⊙yr−1) with a high intrinsic dust mass (∼2.5 ×109 M⊙) and infrared (IR) luminosity (∼6 ×1012 L⊙). Non-local thermodynamic equilibrium radiative transfer modelling of the joint dust spectral energy distribution (SED) and CO line excitation suggests the dust continuum emission is primarily associated with relatively diffuse regions with molecular gas densities of 102−104cm−3, rather than compact, high-pressure environments typical of extreme starbursts or active galactic nuclei (AGNs). This interpretation is supported by the close-to-unity ratio between the dust and gas kinetic temperatures, which argues against highly energetic heating mechanisms. The CO excitation ladder peaks close to CO(5-4) and is dominated by slightly denser molecular gas. Our results underscore the unique power of far-IR and submillimetre observations to both uncover and characterise scarce, strongly lensed, high-redshift galaxies, even when they are obscured by foreground molecular clouds.

Keywords

galaxies: starburst, galaxies: high-redshift, submillimetre: galaxies, gravitational lensing: strong

Volume

706

First Page

A174

Rights

Licensed to Smith College and distributed CC-BY 4.0 under the Smith College Faculty Open Access Policy.

Version

Author's Accepted Manuscript

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