# The massive relic galaxy NGC 1277 is dark matter deficient. From dynamical models of integral-field stellar kinematics out to five effective radii

**Authors:** Sébastien Comerón, Ignacio Trujillo, Michele Cappellari, Fernando Buitrago, Luis E. Garduño, Javier Zaragoza-Cardiel, Igor A. Zinchenko, Maritza A. Lara-López, Anna Ferré-Mateu, Sami Dib  
**arXiv:** [2303.11360](https://arxiv.org/abs/2303.11360)  
**Date:** 2023-03-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.11360v3/

## Key points

- Galaxies with stellar masses greater than $10^{11} M_\odot$ are expected to contain a significant amount of dark matter within their stellar bodies
- Models suggest that in massive early-type galaxies (ETGs), dark matter should contribute around 60% of the dynamical mass within five effective radii ($5 R_e$)
- Relic galaxies are extremely rare and considered frozen remnants of the massive ETG population at redshifts greater than 2
- NGC 1277 is currently the best candidate for a relic galaxy located in the Perseus cluster
- Deep integral field GCMS data was used to study NGC 1277 out to an unprecedented radius of 6 kpc (equivalent to $5 R_e$)
- Negligible fraction of dark matter within $5 R_e$, with a two-sigma confidence level indicating $f_{DM}(5 R_e) < 0.05$
- Lack of an extended envelope in NGC 1277 would reduce dynamical friction and prevent accretion
- Proposed explanations: NGC 1277 either lost its dark matter very early or was initially deficient in dark matter; relic galaxies may have experienced dark matter stripping during their infall and interaction within galaxy clusters; NGC 1277 may have originated from a high-velocity collision between gas-rich proto-galactic fragments where the dark matter was left behind in the form of a dissipative baryon disc
- Study challenges current expectations and provides insights into formation and evolution of relic galaxies
- Further investigations needed to fully understand nature and origin of relic galaxies like NGC 1277

## Summary

According to the $\Lambda$CDM cosmology, galaxies with stellar masses greater than $10^{11} M_\odot$ are expected to contain a significant amount of dark matter within their stellar bodies. In particular, models suggest that in massive early-type galaxies (ETGs), dark matter should contribute around 60% of the dynamical mass within five effective radii ($5 R_e$). These ETGs are believed to have formed through a two-phase process: first, a compact core rapidly grows and then an extended envelope is accreted through mergers. However, there are extremely rare galaxies known as relic galaxies that have avoided the second phase and are considered frozen remnants of the massive ETG population at redshifts greater than 2. NGC 1277, located in the Perseus cluster, is currently the best candidate for a relic galaxy. To investigate this galaxy further, deep integral field GCMS data was used to study NGC 1277 out to an unprecedented radius of 6 kpc (equivalent to $5 R_e$). By employing Jeans anisotropic modeling techniques, it was found that there is a negligible fraction of dark matter within $5 R_e$, with a two-sigma confidence level indicating $f_{DM}(5 R_e) < 0.05$. This result is in tension with expectations based on current models. The lack of an extended envelope in NGC 1277 would reduce dynamical friction and prevent the accretion of such an envelope. Therefore, it is proposed that NGC 1277 either lost its dark matter very early or was initially deficient in dark matter. The implications of this discovery are discussed within the framework of recent proposals suggesting that some relic galaxies may have experienced dark matter stripping during their infall and interaction within galaxy clusters. Alternatively, it is speculated that NGC 1277 may have originated from a high-velocity collision between gas-rich proto-galactic fragments where the dark matter was left behind in the form of a dissipative baryon disc. The required relative velocities for this process to occur could have been possible in progenitors of present-day rich galaxy clusters. In summary, the study of NGC 1277 reveals its dark matter deficiency within $5 R_e$, challenging current expectations and providing insights into the formation and evolution of relic galaxies. The findings suggest that these galaxies may have lost their dark matter early on or were inherently deficient in dark matter. Further investigations are needed to fully understand the nature and origin of relic galaxies like NGC 1277.