HATLAS J142935.3-002836: Lensed Dusty Starburst

• HATLAS J142935.3-002836 is a gravitational lens system where a dusty star-forming galaxy at z=1.027 is magnified by an edge-on disk galaxy at z=0.218, enabling detailed study of merger dynamics.
• Multi-wavelength analyses reveal differential magnification and a complex source-plane morphology with multiple components, supporting vigorous merger-driven star formation and varied gas conditions.
• Recent MeerKAT observations uncovered the most distant OH megamaser and associated H I absorption, highlighting its role as a high-redshift laboratory for merger-related outflow and ISM studies.

Searching arXiv for papers on HATLAS J142935.3-002836 / H1429-0028 to ground the article in the cited literature. HATLAS J142935.3$-$002836, also referred to as HATLASJ1429-0028, H1429-0028, and G15v2.19, is a gravitational lens system in which a dusty, infrared-luminous galaxy at $z=1.027$ is magnified by a foreground edge-on disk galaxy at $z=0.218$. Across optical, infrared, millimetre, and radio studies, it has been established as a strongly lensed, dusty star-forming major merger with a nearly complete Einstein ring and a background source reconstructed as multiple components with extreme star-formation activity (Messias et al., 2014). It has become particularly important as a high-redshift laboratory for lensing, merger-driven star formation, molecular-gas excitation, and, more recently, hydroxyl megamaser phenomenology, culminating in the discovery of the most distant OH megamaser yet detected in this system (Manamela et al., 13 Feb 2026).

1. System identification and lens configuration

HATLAS J142935.3$-$002836 was identified in the Herschel-ATLAS survey in the GAMA-15 field as a bright far-IR/sub-mm source. One study reports $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$, placing it above the Herschel bright-source lens criterion $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$ (Messias et al., 2014), while another reports $S_{160\,\mu{\rm m}}=1.1\pm0.1$ Jy in the discovery context (Timmons et al., 2015). The designation itself encodes the sky position approximately as RA $=14{:}29{:}35.3$, Dec $=-00{:}28{:}36$ (Ma et al., 2018).

The foreground lens is consistently described as an edge-on disk galaxy at $z=0.218$, or more precisely $z=1.027$0 in the Gemini/GMOS-S spectroscopy reported by Messias et al. (Messias et al., 2014). The background source lies at $z=1.027$1, with more precise values from mm/sub-mm spectroscopy including $z=1.027$2 from CARMA CO(2–1), and ALMA centroids consistent with that value (Messias et al., 2014). The lensing geometry produces an almost complete Einstein ring with a diameter of about $z=1.027$3 (Messias et al., 2014). Reported Einstein-radius values differ by lens-model choice, with $z=1.027$4 in the semi-linear inversion analysis (Messias et al., 2014) and $z=1.027$5 in the Calanog et al. model quoted by later work (Manamela et al., 13 Feb 2026).

The source-plane morphology inferred from lens reconstructions is not that of a single compact galaxy. Previous near-IR and millimetre work reconstructed two or three source components, including a north-south component dominating long-wavelength emission, an east-west component prominent in the rest-frame optical/near-IR, and a tidal tail extending over tens of kpc (Messias et al., 2014). The system has therefore been interpreted as an ongoing merger, with one study quoting a mass ratio $z=1.027$6 (Messias et al., 2014), and later near-IR reconstructions requiring three source-plane components and supporting a stellar mass ratio of about 1:3 between two NIR components (Manamela et al., 13 Feb 2026).

2. Lensing, magnification, and differential amplification

Lensing is central to every physical interpretation of HATLAS J142935.3$z=1.027$7002836. In the multi-wavelength reconstruction of Messias et al., the total magnification was found to be wavelength dependent: $z=1.027$8, $z=1.027$9, $z=0.218$0, $z=0.218$1, and $z=0.218$2 (Messias et al., 2014). A separate HST/WFC3 analysis quoted a total infrared-wavelength magnification $z=0.218$3, with differential magnification of $z=0.218$4 for the compact knot-producing component and $z=0.218$5 for the larger ring-forming component (Timmons et al., 2015). The SOFIA/HAWC+ SED study adopted $z=0.218$6 from Messias et al. (Ma et al., 2018).

The source is therefore a clear case of differential magnification. In the 2014 lens model, spatially differential amplification was summarized through $z=0.218$7 and $z=0.218$8, the magnifications of the brightest source-plane regions containing 50% and 10% of the flux. For CO(4–3), $z=0.218$9 and $-$0; for 234 GHz continuum, $-$1 and $-$2; for 7 GHz, $-$3 and $-$4 (Messias et al., 2014). The authors explicitly noted that differential magnification can vary by up to a factor of $-$5.

This lensing complexity has become even more consequential in the maser context. Because MeerKAT does not resolve the OH-emitting region, the OH luminosity is quoted as an apparent, magnification-uncorrected quantity $-$6, and the authors explored plausible OH magnifications by ray-tracing hypothetical Gaussian OH components through the adopted macro-model (Manamela et al., 13 Feb 2026). That analysis found that the Eastern nucleus and a diffuse component would naturally have $-$7, similar to the near-IR magnification, whereas the Western nucleus, lying closer to the caustic, could reach $-$8 for source sizes of $-$9–$S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$0 pc (Manamela et al., 13 Feb 2026). This suggests that compact masing spots can be more strongly magnified than the dust or stellar continuum.

3. Morphology and merger structure

High-resolution imaging across HST, Keck AO, JVLA, ALMA, and ancillary facilities established that the lensed morphology varies strongly with wavelength. In the image plane, the system shows bright knots A, B, C, and D superposed on a nearly complete ring (Messias et al., 2014). The rest-frame optical/near-IR morphology differs from the radio/mm morphology: in $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$1 and F110W, knot C is relatively prominent, whereas in CO and radio/mm continuum the A+B region is brighter (Messias et al., 2014). This wavelength dependence was an early argument against interpreting the system as a simple point-like quad lens.

The source-plane reconstructions indicate a merger configuration rather than a single clumpy disk. Messias et al. reconstructed a dominant north-south component, an east-west component, and a tidal tail a few tens of kpc long, explicitly comparing the morphology to the Antennae merger as a toy model (Messias et al., 2014). Later work on the molecular gas properties referred to the two background galaxies as the NS and EW components, with the EW component dominating the rest-frame optical emission and the NS component dominating the gas and dust emission (Messias et al., 2019). The NS component half-light radius was revised from $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$2 to $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$3 (Messias et al., 2019).

The merger interpretation is physically important because it links the system to the environments in which hydroxyl megamasers are expected. The 2026 MeerKAT Letter explicitly presents H1429-0028 as a strongly lensed, dusty, star-forming major merger with a large molecular gas reservoir and very high star-formation activity, precisely the type of merger-driven environment in which OH megamasers are typically found (Manamela et al., 13 Feb 2026). The HST/WFC3 spectroscopy study was more cautious about whether the source comprised two galaxies or a compact starbursting clump embedded in one galaxy, noting that its spectroscopy lacked the velocity resolution to decide the issue (Timmons et al., 2015). Even so, the cumulative literature converges on a merger-based interpretation.

4. Stellar, dust, and star-formation properties

The intrinsic infrared luminosity places the background source in the ULIRG regime after lensing correction. The SOFIA/HAWC+ SED study, using 27-band de-blended, magnification-corrected photometry, found robust de-lensed dust luminosities of $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$4 across MAGPHYS, SED3FIT, and CIGALE configurations (Ma et al., 2018). Earlier MAGPHYS modelling gave $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$5 and $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$6 (Messias et al., 2014). Dust temperatures are consistently around $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$7 in the later SED work (Ma et al., 2018), while modified-blackbody fits in the 2014 study yielded $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$8 for an optically thin model and $S_{500\,\mu{\rm m}}=227\pm 8\,{\rm mJy}$9 for an optically thick model (Messias et al., 2014).

Star-formation-rate estimates depend on methodology. The MAGPHYS-based value from Messias et al. is $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$0, commonly rounded to $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$1 (Messias et al., 2014). The HST/WFC3 spectroscopy paper reports an extinction-corrected H$S_{500\,\mu{\rm m}}>100\,{\rm mJy}$2 SFR of $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$3, lower than the IR-derived $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$4, but explicitly states that the discrepancy is not statistically significant given the uncertainties and the known scatter among dusty IR-luminous galaxies (Timmons et al., 2015). The later SOFIA-based SED comparison found a wider model-dependent range, from $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$5 in SED3FIT to $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$6 in one CIGALE delayed-$S_{500\,\mu{\rm m}}>100\,{\rm mJy}$7 solution, with the authors emphasizing that the assumed star formation history is the dominant source of uncertainty and can shift the inferred stellar mass by as much as a factor of $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$8 (Ma et al., 2018).

Stellar-mass estimates likewise vary with SED assumptions. Messias et al. found $S_{500\,\mu{\rm m}}>100\,{\rm mJy}$9 (Messias et al., 2014), while the WFC3 study adopted $S_{160\,\mu{\rm m}}=1.1\pm0.1$0 from MAGPHYS for one line-ratio calibration (Timmons et al., 2015). The SOFIA/HAWC+ comparison showed much larger model sensitivity, spanning $S_{160\,\mu{\rm m}}=1.1\pm0.1$1 to $S_{160\,\mu{\rm m}}=1.1\pm0.1$2, and argued that this spread is driven primarily by SFH degeneracy and outshining (Ma et al., 2018).

Despite these uncertainties, several conclusions are stable. The source is heavily obscured, with $S_{160\,\mu{\rm m}}=1.1\pm0.1$3 across SED models (Ma et al., 2018), lies above the $S_{160\,\mu{\rm m}}=1.1\pm0.1$4 main sequence in the IR-based SFR–$S_{160\,\mu{\rm m}}=1.1\pm0.1$5 plane (Timmons et al., 2015), and is therefore classified as a starburst rather than an ordinary disk-like star-forming galaxy (Ma et al., 2018). The 2018 SOFIA paper also found that the AGN contribution to the total IR luminosity is negligible, with $S_{160\,\mu{\rm m}}=1.1\pm0.1$6 in SED3FIT and a conservative $S_{160\,\mu{\rm m}}=1.1\pm0.1$7 upper limit $S_{160\,\mu{\rm m}}=1.1\pm0.1$8 in the preferred CIGALE solution (Ma et al., 2018).

5. Gas reservoir, excitation, and dynamical state

The molecular interstellar medium of HATLAS J142935.3$S_{160\,\mu{\rm m}}=1.1\pm0.1$9002836 has been studied through CO and [C I] spectroscopy. Messias et al. measured total line fluxes of $=14{:}29{:}35.3$0 in CO(2–1), $=14{:}29{:}35.3$1 in CO(4–3), and $=14{:}29{:}35.3$2 in [C I]$=14{:}29{:}35.3$3, with a CO(4–3) FWHM of $=14{:}29{:}35.3$4 (Messias et al., 2014). Using dust-continuum calibration, they derived $=14{:}29{:}35.3$5, and from the ratio $=14{:}29{:}35.3$6 obtained a depletion time $=14{:}29{:}35.3$7 (Messias et al., 2014).

The 2019 re-analysis of the molecular gas properties argued that the detected gas and dust emission comes exclusively from the NS component of the merger (Messias et al., 2019). A central revision in that paper was the decomposition of the CO and [C I] profiles into three kinematic components with centroid velocities $=14{:}29{:}35.3$8, $=14{:}29{:}35.3$9, and $=-00{:}28{:}36$0 (Messias et al., 2019). Components I and II have similar magnifications, $=-00{:}28{:}36$1 and $=-00{:}28{:}36$2, whereas component III is less magnified, $=-00{:}28{:}36$3, and more compact (Messias et al., 2019).

The same study modelled the CO SLED and [C I] emission in a large velocity gradient framework using myRadex. Averaging over methods and both main components, the preferred gas conditions in the NS component are $=-00{:}28{:}36$4, $=-00{:}28{:}36$5, $=-00{:}28{:}36$6, and $=-00{:}28{:}36$7 (Messias et al., 2019). The final adopted molecular gas mass is $=-00{:}28{:}36$8 for the NS component, with $=-00{:}28{:}36$9 for the EW companion (Messias et al., 2019). A predicted CO(1–0) luminosity $z=0.218$0 then implies $z=0.218$1, which is starburst-like rather than Milky-Way-like (Messias et al., 2019).

Dynamically, Messias et al. used the isotropic virial estimator

$z=0.218$2

and, with $z=0.218$3 and $z=0.218$4, derived $z=0.218$5 for the NS component (Messias et al., 2014). The 2019 revision obtained $z=0.218$6, with a molecular-to-dynamical mass fraction $z=0.218$7 and an upper limit of 15% for the total molecular-gas fraction at $z=0.218$8 (Messias et al., 2019). The authors interpreted the gas as warm, moderately dense, compact, and associated with actively star-forming merger-driven conditions (Messias et al., 2019).

6. Optical/nebular diagnostics and AGN constraints

The HST/WFC3 slitless spectroscopy study provides the principal nebular-line constraints on the background galaxy. In the grism data, H$z=0.218$9+[NII], H$z=1.027$00, [SII], and [OIII] were detected from the background source, especially in the A+B lensed region (Timmons et al., 2015). Because of the low spectral resolution of order $z=1.027$01 Å, H$z=1.027$02 is not resolved from [NII], and the [SII] doublet is unresolved (Timmons et al., 2015). The authors therefore adopted $z=1.027$03 through indirect calibration rather than direct spectral decomposition (Timmons et al., 2015).

After correcting for [NII], they derived a Balmer decrement $z=1.027$04 and a nebular extinction $z=1.027$05, corresponding to $z=1.027$06 using the Calzetti law (Timmons et al., 2015). They estimated an O3N2 metallicity $z=1.027$07, low for a galaxy with stellar mass of order $z=1.027$08 (Timmons et al., 2015). In line-ratio space the source falls in the star-forming region and is incompatible with the AGN region in the SDSS comparison samples used in that paper (Timmons et al., 2015).

These nebular diagnostics are important because later discussions of possible AGN activity in the context of outflows and OH pumping rely on them as a baseline. The SOFIA/HAWC+ SED analysis reaffirmed that previous nebular line diagnostics indicate star-formation domination and found the AGN fraction in the IR to be negligible (Ma et al., 2018). The 2019 molecular-gas analysis likewise explicitly interpreted the object as a DSFG rather than a QSO/AGN-dominated source and noted that no strong evidence for an AGN had been found in previous studies (Messias et al., 2019).

At the same time, the 2026 OHM Letter is more cautious in the specific context of the maser and blueshifted OH line. It reports $z=1.027$09, which lies within $z=1.027$10 of the median for star-forming galaxies, and states that the radio emission could be dominated by star formation, or be a mix of star formation and AGN activity (Manamela et al., 13 Feb 2026). The authors explicitly cannot exclude contamination from the foreground lens or differential magnification between AGN and star-forming components (Manamela et al., 13 Feb 2026). Thus the broader multi-wavelength literature disfavors a dominant AGN, but it does not completely remove AGN-related ambiguity in the nuclear regions relevant to the OH emission.

7. High-redshift OH megamaser and H I absorption discovery

The most recent development in the study of HATLAS J142935.3$z=1.027$11002836 is the MeerKAT detection of both 18-cm OH emission and a previously unknown 21-cm H I absorption line, making the system the most distant OH megamaser yet detected (Manamela et al., 13 Feb 2026). MeerKAT observed the target in April 2021 with 62 antennas in the UHF band, 544–1088 MHz, using a single 6-hour track with about 4.7 h on source (Manamela et al., 13 Feb 2026). For a source at $z=1.027$12, the redshifted OH main lines at rest frequencies 1667 and 1665 MHz fall near 823 MHz according to

$z=1.027$13

If both lines arose from gas at the same velocity, the expected observed separation would be

$z=1.027$14

but the observed spectrum does not show such a simple relation (Manamela et al., 13 Feb 2026).

The OH spectrum is blended, highly complex, and unresolved spatially. A Bayesian nested-sampling analysis favored a 5-Gaussian model of the form

$z=1.027$15

with component widths ranging from $z=1.027$16 to $z=1.027$17 in the rest frame (Manamela et al., 13 Feb 2026). The five components have observed centroids between $z=1.027$18 and $z=1.027$19 MHz and line fluxes from $z=1.027$20 to $z=1.027$21, with the broad second component dominating the integrated flux (Manamela et al., 13 Feb 2026). The narrowest feature, $z=1.027$22, or $z=1.027$23, is much narrower than the broad merger-associated OH profiles usually emphasized in low-redshift OHMs and was interpreted as evidence for compact masing substructure (Manamela et al., 13 Feb 2026).

A key observational point is that the two brightest peaks are separated by only $z=1.027$24, not the expected $z=1.027$25 for a simple 1667/1665 pair sharing the same velocity (Manamela et al., 13 Feb 2026). The integrated spectrum therefore cannot be interpreted as a single kinematic component giving rise to the two main OH transitions. The authors instead infer superposed emission from multiple emitting regions and/or transitions, plausibly with different velocities and possibly different magnifications (Manamela et al., 13 Feb 2026).

The headline OH measurement is an integrated apparent luminosity

$z=1.027$26

explicitly magnification-uncorrected (Manamela et al., 13 Feb 2026). In this sense, HATLAS J142935.3$z=1.027$27002836 is the most apparently luminous OHM known. If one adopts a representative magnification $z=1.027$28, then the intrinsic value becomes approximately $z=1.027$29, which the authors state still places the source among the most luminous OH masers known and on the boundary of the gigamaser class (Manamela et al., 13 Feb 2026). The integrated detection had a signal-to-noise ratio exceeding 150 in only 4.7 h, demonstrating the capability of MeerKAT for high-redshift OHM searches (Manamela et al., 13 Feb 2026).

The same dataset yielded a newly detected H I absorption line, modelled with two Gaussians at centroid velocities $z=1.027$30 and $z=1.027$31 relative to systemic, with FWHM $z=1.027$32 and $z=1.027$33, and peak depths $z=1.027$34 and $z=1.027$35 (Manamela et al., 13 Feb 2026). Assuming $z=1.027$36 K and $z=1.027$37, the authors derived $z=1.027$38 and $z=1.027$39 (Manamela et al., 13 Feb 2026). They interpret the H I absorption as tracing gas with a mean velocity consistent with the systemic redshift but narrower than the cold molecular-gas emission, suggesting atomic gas farther out in the galaxy and/or in a smaller kinematic component than the full molecular reservoir (Manamela et al., 13 Feb 2026).

The physical interpretation of the OH profile remains unsettled. The OH emission, particularly the two brightest peaks, is blueshifted relative to the colder neutral and molecular gas, leading the authors to suggest that the OH may trace a warm molecular outflow (Manamela et al., 13 Feb 2026). An alternative, motivated by local OHMs such as Arp 220, is that at least two dominant masing regions are associated with two merging nuclei separated by about $z=1.027$40, with superposition of emission from multiple nuclei and disrupted gas mimicking a broad integrated component (Manamela et al., 13 Feb 2026). The paper concludes that both a warm molecular outflow picture and a multi-nucleus merger picture remain viable, and that strong gravitational lensing plus low angular resolution currently prevent a definitive answer. High-resolution ($z=1.027$41) OH imaging is explicitly identified as necessary to disentangle the blended 1667/1665 structure, localize the masing regions, and refine lensing corrections (Manamela et al., 13 Feb 2026).

In aggregate, HATLAS J142935.3$z=1.027$42002836 is a benchmark lensed dusty starburst whose significance has expanded over time. It began as a Herschel-selected lens candidate and became a well-studied example of a strongly lensed major merger with strong differential magnification, a large gas reservoir, high IR luminosity, and star-formation-dominated energetics (Messias et al., 2014). It has since served as a test case for the limits of SED modelling (Ma et al., 2018), for molecular-gas excitation analysis in a compact merger component (Messias et al., 2019), and for nebular-line constraints on extinction and metallicity (Timmons et al., 2015). The recent OHM discovery adds a new dimension: the system is now also the highest-redshift known hydroxyl megamaser source and, in apparent luminosity, the most luminous OHM yet reported (Manamela et al., 13 Feb 2026).