An Observation and Analysis by Julian Caruana Abela
ASM Vice President describes the surprise acquisition of distant galaxies using modest equipment!
ARP 188 – Tadpole Galaxy
Arp 188, the Tadpole Galaxy, is a strongly perturbed barred spiral galaxy located in the constellation Draco at a distance of approximately 420 million light-years. It has an apparent magnitude of 14.4-14.8, making it a relatively faint target that requires long integration and careful processing to reveal its full structure.
Its most distinctive feature is a 280,000-light-year tidal tail, formed during a past gravitational interaction with a smaller companion galaxy. This interaction defines its morphology and makes it a prominent example of an interacting system.
Imaging and Reprocessing
This dataset was originally acquired in June 2024 and later reprocessed using improved calibration and processing techniques in PixInsight.
Arp 188 is currently the second most distant extragalactic object in my imaging collection, with Hoag’s Object remaining the most distant once further data is acquired and processed. At these scales, the observed light has travelled for hundreds of millions of years, placing the observation firmly within a cosmological context.
Background Field: Red-Shifted Sources
Initial Observation
During reprocessing, a subtle concentration of faint, unresolved sources became visible to the left of Arp 188. These features were not apparent in the original reduction and remained consistent across multiple processing stages, suggesting they are real astrophysical sources rather than artefacts.
Following this, the field was investigated further in collaboration with Connor Sant Fournier (President of the Astronomical Society of Malta), using:
- SDSS SkyServer
- SIMBAD
- Cross-matching catalogued coordinates and identifications
Identified Sources in the Field
The region contains multiple catalogued extragalactic and high-energy sources, including:
- SDSS J160502.06+553750.3 – photometric extragalactic candidate
- SDSS J160456.83+553659.2 – galaxy/extragalactic candidate
- HSCS J160500.53+553743.0 – Hyper Suprime-Cam galaxy candidate
- HSCS J160458.55+553921.2 – extragalactic source candidate
- NSC J160459+553700 – cluster candidate (photometric overdensity)
- [KMA2007] 241.26104+55.63254 – galaxy cluster candidate
- [SPD2011] 6708 – cluster candidate
- 1RXS J160456.9+553727 – ROSAT X-ray source
- NVSS J160511+553857 – NVSS radio source
Spectroscopic Confirmation
At least one source in the field has spectroscopic data confirming it as a galaxy with a redshift of:
z = 0.25121 ± 0.00003
The spectrum includes clearly identified emission and absorption features:
Hβ, OIII, Hα, NII, SII, He I, Ca H & K, Mg, and Na D – all consistently redshifted relative to rest-frame wavelengths.
This confirms the presence of a background galaxy at a cosmological distance. However, this classification applies only to the spectroscopically measured object and should not be extended to nearby sources without additional data.
Interpretation
Overall, the field contains a mix of:
- Photometric galaxy candidates
- Spectroscopically confirmed extragalactic sources
- Cluster candidates
- Radio detections
- X-ray sources
These objects appear projected behind Arp 188, but their physical association cannot be determined from imaging and catalogue data alone.
Conclusion
Revisiting this dataset not only improved the structural detail within Arp 188 itself but also revealed a richer and more complex background field than initially apparent. However, accurately identifying these redshifted galaxies and extracting the scientific context required for this analysis would not have been possible without external catalog cross-referencing and expert guidance.
I am especially grateful to Connor Sant Fournier, President of the Astronomical Society of Malta (ASM) and a PhD researcher specialising in redshift galaxies, for his time, expertise, and valuable assistance throughout the investigation of this field. His support was essential in helping interpret and validate the background sources, and it significantly strengthened the scientific reliability of this work.
Location: Żejtun, Malta (Bortle 6)
Telescope: Sky-Watcher 130 PDS
Camera: ZWO ASI 533 MC Pro (colour)
Total Integration Time: 10 hours 5 minutes
Acquisition Dates: 27–28 May 2024