Akaxia Cruz
Physics PhD candidate, NSF Graduate Research Fellow,
University of Washington
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Research
Astrophysical implications of non-standard dark matter
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Curriculum Vitae
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Contact
admcruz [at] uw.edu
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- "Astrophysical Plasma Instabilities induced by Long-Range Interacting Dark Matter", A. Cruz and M. McQuinn (Submitted). 2022 Available from arXiv.
- "Dark Matter, Black Holes, and Cold Clumps in the Circumgalactic Medium", A.Cruz, J. Werk, T. R. Quinn, B. Shih, I. Butsky, N. N. Sanchez, A. Pontzen (in prep) 2022.
- "The Impact of Cosmic Rays on the Kinematics of the Circumgalactic Medium", I. S. Butsky, J. K. Werk, K. Tchernyshyov, D. B. Fielding, J. Breneman, D. R. Piacitelli, T. R. Quinn, N. N. Sanchez, A.Cruz, C. B. Hummels ApJ 2022. Available from ApJ.
- "Self-Interacting Dark Matter and the Delay of Super-Massive Black Hole Growth", A. Cruz, A. Pontzen, M. Volonteri, T. R. Quinn, M. Tremmel, A. M. Brooks, N. N. Sanchez, F. Munshi, A. DiCintio, MNRAS 2021. Available from MNRAS.
- "One-Two Quench: A Double Minor Merger Scenario", N. N. Sanchez, M. Tremmel, J. Werk, A. Pontzen, C. Christensen, T. Quinn, S. Loebman, A. Cruz
ApJ (Submitted) 2020 Available from arXiv. - "Not So Heavy Metals: Black Hole Feedback Enriches the Circumgalactic Medium", N. N. Sanchez, J. Werk, M. Tremmel, A. Pontzen, C. Christensen, T. Quinn, A. Cruz, ApJ 2019, Available from arXiv.
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- In Cruz et al. 2020 I used fully cosmological galaxy simulations in cold DM (CDM) and self-interacting DM (SIDM) with a constant cross-section of 1 cm^2/g to examine how the co-evolution of SMBHs and their MW-mass host galaxies (Mvir ~ 7 x 10^11 Msol at z = 0) is influenced by different DM models. To do this I used physically motivated models of SMBH formation and growth and simulated a MW-mass galaxy with quenched star formation in CDM and SIDM to maximize the effects of SMBH growth on galaxy evolution. I then ran a Genetically Modified version of these galaxies to check for result dependent sensitivity to small changes. I determined that:
1. SMBH formation is consistently suppressed in SIDM relative to a LCDM cosmology. My CDM simulations produced ~ 2 or 3 times more SMBHs than my SIDM simulations.
2. SIDM delays SMBH growth through mergers by billions of years compared to CDM, as can be seen in the left panel of Figure 1.
3. SIDM SMBHs generate less SMBH feedback compared to CDM SMBHs during the first 5 Gyrs of their evolution as can be seen in the right panel of Figure 1. Nonetheless, by z = 0.8 their SMBH masses differ only by around 0.2 dex , so that both CDM and SIDM runs remain compatible with the MBH-M* relation.
4. SIDM galaxies have a larger central reservoir of gas available for star formation.
5. SIDM galaxies form about 3 or 4 times more stars than CDM galaxies over their lifetimes. - This work suggests that upcoming multi-messanger SMBH observations will allow us to probe the microscopic nature of DM in an emerging new way.
- In Cruz et al. 2020 I used fully cosmological galaxy simulations in cold DM (CDM) and self-interacting DM (SIDM) with a constant cross-section of 1 cm^2/g to examine how the co-evolution of SMBHs and their MW-mass host galaxies (Mvir ~ 7 x 10^11 Msol at z = 0) is influenced by different DM models. To do this I used physically motivated models of SMBH formation and growth and simulated a MW-mass galaxy with quenched star formation in CDM and SIDM to maximize the effects of SMBH growth on galaxy evolution. I then ran a Genetically Modified version of these galaxies to check for result dependent sensitivity to small changes. I determined that:
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- Every simulation study of the CGM to date has used a CDM backdrop. However, interestingly, I have found that O VI column densities are significantly altered by the backdrop DM model used in simulations. A set of GM MW-mass galaxies simulations with baryons and SMBHs in CDM and SIDM have found that the evolution of the galaxies' SMBHs is delayed by billions of years in SIDM models compared to their CDM counterparts, due to SIDM coring in the high-z universe. This is a natural prediction of a DM model which lowers DM densities at high-z, as it naturally lowers SMBH halo occupation fractions and increases dynamical friction time scales. The delayed SMBH growth in SIDM has a plethora of physical implications, including enhanced O VI column densities and distinct absorption spectra. Thus, DM indirectly imprints itself onto feedback processes which may be detected using the CGM.
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- The existence of dark matter (DM) has been made robust through multiple orthogonal astrophysical probes, yet the microscopic properties of DM remain unknown. In particular, it is unclear whether DM interacts with itself and/or with the standard model (SM) non-gravitationally. Cold DM, a single, collision-less particle species with negligible primordial thermal dispersion is largely considered the “concordance” DM model in the astrophysical community. Yet, observations on dwarf scales suggest that DM might be self-interacting. Milli-charged DM (mDM) can couple non-gravitationally with itself and with the SM. I do analytic calculations which show streaming mDM can cause transverse EM Weibel plasma instabilities in galactic systems, such as DM falling onto Milky-Way like galaxies and in merging galaxies clusters.
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- Publications
- SIDM and SMBH Growth
- SIDM and Kinematics of the CGM
- Milli-Charged DM
