ID-MAGE II: The Star Forming Satellites of Low-Mass Hosts

arXiv:2603.18973 · astro-ph.GA · Submitted 2026-03-19 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "ID-MAGE II: The Star Forming Satellites of Low-Mass Hosts".

Jocelyn: The gist The authors present results from their ongoing campaign to follow up satellite candidates from the Identifying Dwarfs of MC Analog Galaxies (ID-MAGE) survey,

Vera: First, who's behind it and why it matters.

Paper summary: Vera: So to wrap up this section, we’re talking about ID-MAGE II: The Star Forming Satellites of Low-Mass Hosts. The core claim is that spectroscopic follow-up was effective at filtering the initial three hundred fifty-five unresolved candidates into a much cleaner sample.

Jocelyn: They’re essentially using their velocity measurements to confidently identify six probable satellite galaxies and clearing out seventy-seven background galaxies, which is a solid way to improve the data quality for these low-mass hosts around LMC and SMC masses.

Subrahmanyan: The paper focuses on updating our previous estimates for the average number of satellites per host, finding that this new sample gives us one point seven plus or minus zero point seven satellites per LMC-mass or SMC-mass host, based on their refined selection criteria.

Vera: And they've looked at star formation and gas content too; they used GALEX data to check the probable and confirmed satellites and found that only two appear likely to be quenched in this mass range.

Jocelyn: They also noted that among those nine probable or confirmed satellites in that mass range, six of them are H i-rich, meaning they still have gas, and two of them are H i-deficient.

Subrahmanyan: That’s significant because it points toward different quenching pathways happening at the low-mass scale compared to what we see in higher mass systems.

Vera: And they found that the higher quenched fraction relative to isolated dwarfs, combined with that nearly fifty percent H i deficiency rate, shows that these low-mass hosts really do impact the evolution of their satellites.

Jocelyn: The paper also highlights how the lower quenched fraction compared to satellites orbiting Milky Way-mass hosts illustrates why understanding how these low-mass hosts specifically quench their satellites is so important for our models.

Subrahmanyan: It reinforces that we shouldn't just over-tailor our models using only MW-mass host satellites, because the environmental influence around dwarf galaxies can be quite different.

Conclusion: Vera: So looking at the ID-MAGE II results, it seems the environment around low-mass hosts is indeed driving the evolution of their satellites, and interestingly, that impact is weaker than you might expect compared to those around more massive hosts.

Jocelyn: That’s what it suggests; we're seeing a different kind of environmental influence at this scale because the paper found that these low-mass systems have a lower quenched fraction for their satellites when compared to MW-mass hosts.

Subrahmanyan: This means that the mechanisms by which low-mass hosts quench their satellites might be less efficient than those in larger systems, perhaps favoring processes like starvation over rapid stripping.

Vera: That’s the implication—we need to focus our research on understanding what exactly is happening at this lower mass scale where these specific environmental effects are playing out.

Jocelyn: And for anyone just listening, it means that the way a small galaxy interacts with its surroundings shapes the fate of its satellites in a way that’s distinct from what we observe in larger systems like our own Milky Way.

Subrahmanyan: It puts constraints on the theoretical models because if low-mass hosts are less efficient drivers, then those models need to account for that reduced environmental influence.

Vera: We're still working on the unconfirmed galaxies—the one hundred ninety-eight from ID-MAGE—but this paper gives us a very solid foundation for understanding how these low-mass environments shape satellite evolution.

Department of Physics and Astronomy, Dartmouth College · Steward Observatory, University of Arizona · Space Telescope Science Institute · AURA/Rubin Observatory Department of Physics & Astronomy, University of Tampa Department of Physics, University of Surrey Department of Astronomy, University Washington Department of Physics and Engineering Physics and Astronomy, Queen’s University

astro-ph.GA

Submitted: 2026-03-19

Updated: 2026-10-09

Comments: 18 pages, 6 page appendix, accepted for publication

License: http://creativecommons.org/licenses/by-nc-sa/4.0/

Importance score: 71/100

The gist: The gist The authors present results from their ongoing campaign to follow up satellite candidates from the Identifying Dwarfs of MC Analog Galaxies (ID-MAGE) survey, identifying six probable

Key concepts

ID-MAGE survey: This survey initially identified hundreds of unresolved satellite candidates around nearby LMC- and SMC-mass hosts (36 Mpc away). The goal was to find these faint galaxies that orbit larger host galaxies, providing a sample for studying galaxy evolution.
Spectroscopic follow-up: Using telescopes like the Green Bank Telescope and SALT, researchers obtained velocities from candidates. This allowed them to distinguish true satellite galaxies from unrelated background objects by measuring their motion relative to the host galaxy's gravitational influence.
Quenched fraction: This refers to the percentage of satellites that have stopped forming new stars. The study found that low-mass hosts have a higher quenched fraction for their satellites compared to isolated dwarfs, suggesting their environment strongly influences how these small galaxies evolve.

Terminology

Calibration — 9× in this paper · explained in 7 episodes
Dark Energy Survey — 5× in this paper
Green Bank Telescope — 5× in this paper
Dark Energy Survey Instrument — 3× in this paper
Accuracy — 1× in this paper · explained in 1 episode
Adam — 1× in this paper · explained in 2 episodes
Cooperation — 1× in this paper · explained in 2 episodes
Milky Way — 1× in this paper
NOIRLab and the Lawrence Berkeley National Laboratory — 1× in this paper
Near-Earth Object Wide-field Infrared Survey Explorer — 1× in this paper

Summary

The gist The authors present results from their ongoing campaign to follow up satellite candidates from the Identifying Dwarfs of MC Analog Galaxies (ID-MAGE) survey, identifying six probable satellite galaxies and 77 background galaxies based on spectroscopic follow-up; this underscores the ability of spectroscopic follow-up to effectively separate satellites from background galaxies<ref:2603.18973#pg2>

Satellite Identification and Sample Refinement

The initial ID-MAGE survey identified 355 unresolved satellite candidates around 36 nearby LMC- and SMC-mass hosts (D=4−10 Mpc)<ref:2603.18973#pg3>. Based on velocities, the authors identify six candidates as probable satellite galaxies with stellar masses between 6.5 × 105 ≤ M⋆/M⊙ ≤ 1.5 × 107 and seventy-seven as background galaxies<ref:2603.18973#pg4>. The results underscore the ability of spectroscopic follow-up to effectively separate satellites from background galaxies<ref:2603.18973#pg5>. Using the refined sample, they update their previously derived estimates for the average satellite population per host and find 1.7±0.7 (1.0±0.3) satellites per LMC-mass (SMC-mass) host<ref:2603.18973#pg5>. Their current satellite sample includes 25 galaxies confirmed by distances or velocities, including the complete satellite populations of three hosts (UGC 04422: zero satellites, UGC 08201: zero satellites, NGC 3432: four satellites)<ref:2603.18973#pg5>.

Satellite Population Estimates and Environmental Impact

The authors derive an upper bound of 3.1±1.2 (1.7±0.6) satellites per LMC-mass (SMC-mass) host with MV ≲ −9, which is consistent with previous searches such as ELVES-Dwarf, MADCASH, and DELVE-DEEP<ref:2603.18973#pg5>. The decrease in the upper bounds compared to bounds for LMC-mass (4.0±1.4) and SMC-mass (2.1±0.6) hosts in Paper I is due to the removal of background contaminants<ref:2603.18973#pg6>. They find that 77 candidates are background galaxies, including all 47 full sample candidates and 30 high likelihood candidates<ref:2603.18973#pg6>. The lower bound estimate of 1.7±0.7 (1.0±0.3) satellites per LMC-mass (SMC-mass) host is in excellent agreement with their estimates from Paper I of 1.7±0.7(1.2±0.4) satellites per LMC-mass (SMC-mass) host<ref:2603.18973#pg6>. The number of satellites NGC 3432 hosts is in good agreement with predictions from G. A. Dooley et al. (2017a) and I. M. E. Santos-Santos et al. (2022) for a 1.5×109M⊙ host<ref:2603.18973#pg7>.

Star Formation and Gas Content Analysis

The authors used archival GALEX data to determine their star formation rates (SFRs) for the probable and confirmed satellites, finding that only two appear likely to be quenched<ref:2603.18973#pg8>. Among the nine probable and confirmed satellites in this mass range, six of nine (≃67%) are H irich and two of nine (≃22%) are H i-deficient<ref:2603.18973#pg9>. MAGE J0006-2456 has an H i-mass fraction of 0.2 and clear evidence of ongoing star formation in the UV data<ref:2603.18973#pg9>. The other plausible quenched satellite is MAGE J1245+6158, which has a very weak NUV detection and no FUV<ref:2603.18973#pg10>.

Quenching Mechanisms in Low-Mass Hosts

The authors find that the higher quenched fraction relative to isolated dwarfs, together with the nearly 50% H i deficiency rate, demonstrates that low-mass hosts do significantly impact the evolution of their satellites. The higher quenched fraction relative to isolated dwarfs, together with the nearly 50% H i deficiency rate, demonstrates that low-mass hosts do significantly impact the evolution of their satellites. The lower quenched fraction compared to satellites of MW-mass hosts illustrates the importance of understanding how low-mass hosts specifically quench their satellites.

Conclusion and Future Work

The completed ID-MAGE survey will include a diverse sample of satellites around low-mass hosts, providing key insights into how this environment impacts a galaxy’s properties. The authors conclude that the environment around low-mass hosts is driving the evolution of their satellites, and unsurprisingly, the impact is weaker than that of high-mass hosts. They are working to follow-up the 198 unconfirmed galaxies in ID-MAGE.

How it works

The authors present 110 velocity measurements for 83 candidates from new MDM 2.4 m, SALT, and GBT observations, and archival DESI DR1 data. They find that 77 candidates are background galaxies, and six are probable satellites. The authors derive estimates for the satellite populations of LMC- and SMC-mass host galaxies using the same methods as in Paper I.

Observations and Confirmation Methods

The authors used the Green Bank Telescope (GBT), the South African Large Telescope (SALT), and the MDM Observatory 2.4 m Hiltner telescope on Kitt Peak for spectroscopic follow-up<ref:2603.18973#pg6>. They assume the C. B. Brook et al. (2014) model virial masses of the LMC and SMC as central point masses to set their velocity range for satellite confirmation. Velocity-confirmation effectively removes background contaminants and provides a mostly pure satellite sample.

Data Sources and Analysis Tools

The research utilizes data from the Dark Energy Survey Instrument Data Release 1 (DESI DR-10) imaging, Green Bank Telescope (GBT), MDM Observatory 2.4 m, Robert Stobie Spectrograph (RSS) on SALT, and archival DESI DR-1 data<ref:2603.18973#pg6>. They also cross-matched the IDMAGE candidate list with the public DESI DR-1 data to check the DESI archive.

Key Findings Summary

The paper finds 77 candidates are background galaxies, and six are probable satellites. The authors find 1.7±0.7(1.2±0.4) satellites per LMC-mass (SMC-mass) host with MV ≲ −9, consistent with previous searches such as ELVES-Dwarf, MADCASH, and DELVE-DEEP. The authors have completed follow-up observations of the candidates for three of their 36 hosts. Two SMC-mass hosts (UGC 04426 and UGC 08291) have no identified satellites. The third host with completed follow-up observations is NGC 3432, an LMC-mass host with four probable satellites based on their velocities.

Appendix Details

The appendix presents spectra used to determine the velocities of the six newly velocity-confirmed candidates. The appendix also includes H i measurements for 108 ID-MAGE candidates including 20 new detections, 13 archival measurements, and 75 non-detections which can be used to determine H i-mass limits. The analysis of the satellite mass function for the LMC-mass host NGC 3432 is 3σ outlier above the G. A. Dooley et al. (2017a) predictions and 1.5σ above I. M. E.

Improvements for AI systems

A system can now accurately estimate satellite populations using refined velocity data, as we derive an upper and lower estimate of the satellite population using the probable and confirmed satellites and the remaining candidates from the high-likelihood sample in Paper I. This allows for a more robust comparison with existing constraints, such as predictions from G. A. Dooley et al. (2017a) and in excellent agreement with Paper I.
The system can perform environmental impact assessments on galaxy evolution by analyzing quenching fractions, as the quenched fraction of 10% to 25% falls roughly between isolated galaxies and satellites of MW-mass hosts. This enables researchers to conclude that low-mass hosts impact the quenching of their satellites, while also noting, the lower quenched fraction compared to satellites of MW-mass hosts illustrates the importance of understanding how low-mass hosts specifically quench their satellites.
The system can differentiate between gas-rich and gas-poor satellite populations based on spectroscopic data, as it can identify "14 probable or confirmed satellites are gas-rich (MHI/M⋆ > 1), and six are H i deficient (MHI < M⋆)," allowing for a more nuanced understanding of environmental effects.
The system can evaluate the top-heavy satellite mass function in specific hosts, as it notes that NGC 3432’s satellite system is unusual compared to simulation predictions due to the satellites’ masses, and can compare these findings with literature like DDO 161 (M⋆ = 108.3M⊙).
The system can predict the expected outcome of future follow-up campaigns by identifying biases, as it states, "Our follow-up of the most massive satellites (M⋆ > 107 M⊙) in our sample is nearly complete and is not biased towards star-forming satellites. This informs future observational strategies by noting that velocity confirmation is most efficient for star-forming and gas-rich satellites but struggles with quenched galaxies."

Abstract

We present results from our ongoing campaign to follow up the satellite candidates from the Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE) survey. Previously, we published a list of 355 unresolved satellite candidates identified around 36 nearby LMC- and SMC-mass hosts (D = 4 - 10 Mpc). We present the velocities of 83 satellite candidates from new Green Bank Telescope HI observations, optical long-slit spectra, and the Dark Energy Survey Instrument Data Release 1. Based on their velocities, we identify six candidates as probable satellite galaxies (6.5 times10 5 at most M/M at most1.5 times10 7) and 77 as background galaxies. Our results underscore the ability of spectroscopic follow-up to effectively separate satellites from background galaxies. Using the refined sample, we update our previously derived estimates for the average satellite population per host and find 1.7 plus or minus 0.7 (1.0 plus or minus 0.3) satellites per LMC-mass (SMC-mass) host. Our current satellite sample includes 25 galaxies confirmed by distances or velocities. This set includes the complete satellite populations of three hosts (UGC 04422: zero satellites, UGC 08201: zero satellites, NGC 3432: four satellites), which we compare to simulations and known satellite systems from the literature. Our sample is nearly complete for the most massive satellites (M > 10 7 M). We find these massive satellites have a quenched fraction of 10--25%, placing them between the < 5% quenched fraction of isolated galaxies and the 40--70% quenched fraction of MW-analog satellites with 10 7 M < M < 10 8 M. This demonstrates the impact that low-mass galaxies have on the evolution of their satellites.