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New Measurements of Distances to Galaxies in the NGC 1052 Field with the Hubble and James Webb Space Telescopes: Testing the Bullet-Dwarf Origin of the Trail

Using Hubble and James Webb Space Telescope data, this study confirms that the ultra-diffuse galaxies in the NGC 1052 field, including the dark-matter-deficient DF2 and DF4, are located at approximately 17–20 Mpc and are not associated with the foreground NGC 1035 group, though it reveals a significant distance discrepancy for DF2 between previous HST measurements and new JWST/SBF results that warrants further uniform JWST observations.

Original authors: Yimeng Tang, Gagandeep S. Anand, Aaron J. Romanowsky, Pieter G. van Dokkum, Kevin A. Bundy

Published 2026-06-04

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CC BY 4.0

Original authors: Yimeng Tang, Gagandeep S. Anand, Aaron J. Romanowsky, Pieter G. van Dokkum, Kevin A. Bundy

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Cosmic Mystery: A Missing Link in the Universe

Imagine you are looking at a long, straight line of cars parked on a highway. You notice something strange: three of these cars are made entirely of lightweight foam (they lack the heavy metal "dark matter" that usually holds galaxies together). You also notice that these foam cars are all lined up perfectly, as if they were flung out of a cannon in a single, high-speed crash.

This is the story of the NGC 1052 field. Astronomers have found a "trail" of tiny, faint galaxies (dwarfs) that seem to be the debris from a violent collision between two gas-rich galaxies. This theory is called the "Bullet-Dwarf" scenario.

However, there is a problem. The highway (the sky) is crowded. There is another group of galaxies (the NGC 1035 group) that sits much closer to us, like a row of houses in the foreground. Skeptics argued that the "trail" of foam cars might just be an optical illusion—a trick of perspective where the distant foam cars and the closer houses happen to line up perfectly from our point of view.

The Goal: The authors of this paper wanted to measure the exact distance to these galaxies to see if they are really a 3D line in space (the "Bullet-Dwarf" theory) or just a 2D coincidence (the "Optical Illusion" theory).

The Tools: Two Different Rulers

To measure the distance to these galaxies, the team used two different "rulers" (methods):

The "Flicker" Ruler (SBF): They used the Hubble Space Telescope (HST). Imagine looking at a wall covered in tiny, unlit lightbulbs from far away. From a distance, the wall looks smooth. But if you get closer, you see the individual bulbs, and the wall looks "flickery" or grainy. The graininess (Surface Brightness Fluctuation) tells you how far away you are. The grainier it looks, the closer it is.
The "Standard Candle" Ruler (TRGB): They used the James Webb Space Telescope (JWST). This telescope is so powerful it can see individual stars. They looked for a specific type of dying star (a Red Giant) that always shines with the exact same brightness. By measuring how dim that star looks, they can calculate the distance with extreme precision.

The Findings: What the Rulers Said

1. The Trail is Real (It's not an Illusion)

The team measured the distances to eight different dwarf galaxies in the trail using the Hubble "Flicker" ruler.

The Result: All the dwarf galaxies were found to be about 20 million light-years away.
The Comparison: The nearby "foreground" group (NGC 1035) is only about 13 million light-years away.
The Conclusion: Since the trail galaxies are much farther away than the foreground group, they are not an optical illusion. They are physically located in the same neighborhood as the giant galaxy NGC 1052. The trail is a real, 3D structure.

2. The "Bullet" Problem: A Discrepancy in Distance

Here is where things get tricky. The team focused on one specific galaxy in the trail, DF2.

Old Measurement (HST): Previous studies using Hubble said DF2 was 21.7 million light-years away.
New Measurement (JWST): The new, super-sharp JWST data said DF2 is actually 17.6 million light-years away.
The Conflict: The new JWST measurement agrees with the team's own "Flicker" measurement (17.7 million light-years), but it disagrees with the old HST measurement.

Why does this matter?
In the "Bullet-Dwarf" story, the timing and distance of the crash are crucial. If DF2 is closer than we thought, it changes the math of how the collision happened. It might mean the galaxies were further apart in the past, which challenges the current theory of how they crashed.

3. The "Ghost" in the Data

The authors suspect the old HST measurement might be slightly wrong because it was trying to measure very faint stars in a crowded field. The JWST telescope is like having a better pair of glasses; it can separate the stars from the background noise much better. The authors believe the 17.6 million light-year distance is the correct one.

The Bottom Line

The Trail is Real: The line of dwarf galaxies is not a coincidence caused by a foreground group. They are all neighbors of NGC 1052, located about 20 million light-years away.
The Distance is Shifting: The most famous galaxy in the trail, DF2, is likely closer (17.6 million light-years) than previously thought.
The Mystery Remains: While we know the trail is real, the exact distance to DF2 creates a puzzle for the "Bullet-Dwarf" collision theory. The authors suggest we need more high-quality data from JWST for the other galaxies in the trail to solve this final piece of the puzzle.

In short: The "trail" isn't a mirage, but the map of exactly where the crash happened needs to be redrawn with more precise tools.

Technical Summary: New Measurements of Distances to Galaxies in the NGC 1052 Field

Problem Statement
The origin of ultra-diffuse galaxies (UDGs) lacking dark matter (DM), specifically NGC 1052-DF2 and DF4, remains a critical puzzle in near-field cosmology. These galaxies, along with a linear trail of dwarf galaxies in the NGC 1052 field, are hypothesized to be the remnants of a high-velocity "bullet-dwarf" collision between two gas-rich progenitors. However, the physical reality of this linear trail is contested. The trail overlaps in projection with the foreground NGC 1035 group at $\sim13$ Mpc, raising the possibility that the alignment is a chance superposition of unrelated galaxies rather than a coherent 3D structure. While distances to DF2 and DF4 have been measured via the Tip of the Red Giant Branch (TRGB) method using deep Hubble Space Telescope (HST) imaging ( $21.7 \pm 1.2$ and $20.0 \pm 1.6$ Mpc, respectively), distances to the other trail dwarfs remained unknown, preventing a definitive test of the "bullet-dwarf" scenario versus the projection artifact hypothesis.

Methodology
The authors employed two primary distance measurement techniques to resolve these uncertainties:

Surface Brightness Fluctuation (SBF) with HST:
- Data: Utilized HST/ACS imaging (F606W and F814W bands) from programs GO 14644 and 16912 for eight candidate trail dwarfs, as well as the giant galaxies NGC 1052 and NGC 1035.
- Analysis: Applied a specialized flat-fielding procedure and drizzling with a lanczos3 kernel. The SBF signal was measured from F814W images, which offer stronger amplitude dominated by red giant stars.
- Calibration: Converted SBF signals to distances using the empirical calibration by Y. J. Kim & M. G. (2021) for dwarfs and J. P. Blakeslee et al. (2010) for NGC 1052. For NGC 1035, a hybrid approach was used due to its color falling outside standard ranges.
- Robustness: Uncertainties were derived from 1000 Monte Carlo realizations, accounting for background source contributions, photometric errors, and calibration systematics.
TRGB with James Webb Space Telescope (JWST):
- Data: Analyzed serendipitous JWST/NIRCam observations of DF2 (F090W and F150W filters) from a pure parallel survey.
- Analysis: Performed PSF photometry using DOLPHOT with strict quality cuts. Constructed Color-Magnitude Diagrams (CMDs) and measured the TRGB magnitude using a Sobel edge-detection algorithm and a maximum-likelihood technique.
- Calibration: Applied the absolute TRGB calibration ( $M_{TRGB} = -4.36 \pm 0.056$ mag) derived from the megamaser host NGC 4258, ensuring high precision.

Key Results

Trail Dwarf Distances: The SBF analysis places all eight measured trail dwarfs at distances of $\sim20$ Mpc. This is consistent with the distance of NGC 1052 and significantly distinct from the foreground NGC 1035 group ( $\sim13.8 \pm 1.1$ Mpc). This result strongly disfavors the hypothesis that the trail is an artifact of overlapping galaxy groups.
DF2 Distance Discrepancy:
- HST SBF: The authors derive an SBF distance for DF2 of $17.7 \pm 1.4$ Mpc.
- JWST TRGB: The new JWST-based TRGB distance for DF2 is $17.6 \pm 0.6$ Mpc.
- Conflict: Both new measurements are inconsistent with the previously published HST TRGB distance of $21.7 \pm 1.2$ Mpc (Z. Shen et al. 2023). The authors note that the JWST data shows a TRGB magnitude ( $m_{TRGB,0} = 26.87 \pm 0.02$ ) that is significantly brighter than the value implied by the older HST distance.
Kinematics and Structure: While the SBF distances confirm the dwarfs are not foreground objects, the uncertainties are too large to definitively confirm a linear 3D structure or a specific slope in distance versus Right Ascension. However, the results are consistent with the "bullet-dwarf" scenario where the trail members are physically associated with NGC 1052.

Significance and Claims
The paper claims to provide critical evidence against the "projection artifact" hypothesis, confirming that the trail dwarfs are likely members of the NGC 1052 system rather than the foreground NGC 1035 group.

However, the authors exercise significant caution regarding the absolute distances. The convergence of the HST SBF and JWST TRGB results at $\sim17.6-17.7$ Mpc for DF2 suggests the previous HST TRGB distance of $\sim22$ Mpc may be overestimated, potentially due to issues with photometric zeropoints or image alignment in the deeper HST data. The authors state that the true distance of DF2 is likely $\sim18$ Mpc rather than $\sim22$ Mpc.

The paper concludes that while the "bullet-dwarf" scenario remains the best model explaining the unique properties of these galaxies (DM deficiency, overluminous globular clusters, and kinematic alignment), the current distance uncertainties prevent a definitive confirmation of the trail's 3D linearity. The authors emphasize that obtaining uniform JWST imaging for the remaining trail dwarfs is critically needed to resolve the distance discrepancy and test the formation scenario rigorously. They note that if DF2 is indeed closer than previously thought, it may challenge the standard interpretation of the collision dynamics unless orbital modifications occurred post-collision.