Oswaldo Vazquez

The Dark Matter Properties of the Most Extreme Galaxies in the Early Universe

Recent observations have revealed an interesting kind of "extreme" galaxy: one that forms very early in the Universe’s history (within a couple billion years after the Big Bang) and has a stellar mass at least ten times that of the Milky Way. As the Universe expands and gravitational-instability collapses bodies which later merge to yield more massive systems, galaxies are formed in dark matter haloes. Some dark matter halo properties are: halo mass, halo growth rate, concentration, spin, environment, etc. This work attempts to understand which halo properties determine the properties of the extreme galaxies that form within them using IllustrisTNG, a cosmological and hydrodynamical galaxy formation simulation.

We studied the full population of central galaxies with \(M_\star>10^9\:\mathrm{M}_\odot\) at \(z=3\). The stellar mass and halo mass functions of this population are shown in panel (a) of the figure below. We selected the 20 galaxies with the highest stellar mass as these would be considered "extreme" (shaded in blue). The resulting sample all have \(M_\star>10^{11.23}\:\mathrm{M}_\odot\). Also, we examine a “complementary” sample of galaxies with comparable halo mass but lower stellar mass than the top 20 sample (shaded in red). The top 20 stellar mass sample is plotted on the stellar-halo mass relation and colored by their specific star formation rates (sSFR) (see panel (b)). From the stellar-halo mass relation, we see that the most massive galaxies do not always live in the most massive haloes. Thus, halo mass is not sufficient to determine where the extreme galaxies will live. Additionally, the sSFR of the high mass sample do not follow a clear trend, i.e. the star formation activity does not depend on stellar or halo mass. By looking at \(M_\star(z)\) and \(M_\mathrm{DM}(z)\) of all systems in both samples, we see that galaxy population and masses grow with time.

Another halo property we evaluated was concentration, which is a measure of how densely the halo’s matter is distributed through space. We assume the NFW dark matter density profile and from it we calculate the mass profile within the sphere with boundary at \(r = R_{500}\) (which is the radius in which the mean density is 500 times the critical density of the Universe) and set the virial radius \(R_\mathrm{vir}\) to \(R_{200}\). We can relate these halo properties to the concentration \(c_\mathrm{NFW}\) as \[\tilde{m}\left(\ln(1+c_\mathrm{NFW})+\frac{c_\mathrm{NFW}}{1+c_\mathrm{NFW}}\right)=\ln(1+\tilde{r}c_\mathrm{NFW})+\frac{\tilde{r}c_\mathrm{NFW}}{1+\tilde{r}c_\mathrm{NFW}}\] where \(\tilde{m}\equiv M_{500}/M_{200}\) and \(\tilde{r}\equiv R_{500}/R_{200}\). The next step was to numerically solve for \(c_\mathrm{NFW}\) for all systems at redshift 3 and relate it to halo mass in a density map shown at the bottom of panel (b). The time evolution of concentration for both high and low mass samples is given at the bottom of panel (c) and we see that \(c_\mathrm{NFW}\) remains relatively unchanged over cosmic time for both samples and thus appears surprisingly to not be a halo parameter that plays a role in early galaxy formation.

In summary, we studied halo mass, star activity, and concentration with the objective to learn about the essence of early-forming massive galaxies but found that none of the mentioned properties fully determine where these extreme galaxies form. This is incredibly important as the link between a galaxy and its home halo is so fundamental that, in principle, studying some halo properties should give a lot of information to describe the nature of a galaxy. However, extreme galaxies appear to be much more complex. Perhaps by studying other halo properties such as growth rate, spin, and environment we can unveil whether they are significant for describing early galaxy formation. The role of baryons may also be a nontrivial contribution to examine in further studies.

This material is based upon work supported by the National Science Foundation under grant No. AST-1757792.

References

[1] Marinacci, F., Vogelsberger, M., Pakmor, R., et al. 2018, MNRAS, 480, 5113

[2] Naiman, J. P., Pillepich, A., Springel, V., et al. 2018, MNRAS, 477, 1206

[3] Navarro, J. F., Frenk, C. S., & White, S. D. M. 1996, ApJ, 462, 563.

[4] Nelson, D., Pillepich, A., Springel, V., et al. 2018, MNRAS, 475, 624

[5] Peebles, P. J. E. 1969, ApJ, 155, 393

[6] Pillepich, A., Springel, V., Nelson, D., et al. 2018a, MNRAS, 473, 4077

[7] Pillepich, A., Nelson, D., Hernquist, L., et al. 2018b, MNRAS, 475, 648

[8] Springel, V., Pakmor, R., Pillepich, A., et al. 2018, MNRAS, 475, 676

[9] Valentino, F., Tanaka, M., Davidzon, I., et al. 2020, ApJ, 889, 93

[10] Weinberger, R., Springel, V., Hernquist, L., et al. 2017, MNRAS, 465, 3291

TauRunner: A Monte Carlo for Very-High-Energy Tau Neutrino Propagation

Neutrinos are a unique fundamental particle that only interact via gravity and the weak force. Since they have no electric charge, they do not participate in electromagnetic interactions. Thus neutrinos are not visible and have miniscule chances of interacting with matter, which makes them difficult to detect. The Standard Model of particle physics contains three flavors (types) of neutrinos: electron, muon, and tau neutrinos (each related to their respective charged particle). Of these three neutrino flavors, so far the least studied one is the tau neutrino; this is because tau neutrinos are harder to identify and produce.

Neutrinos with a wide range of energies have been detected through the years and their fluxes are shown below, those in the GZK region are extremely rare and the subject of an exhaustive search that goes back more than half a century. These neutrinos are expected to be produced by cosmic-ray interactions with the cosmic microwave background (CMB). During travel, they morph from one flavor to another yielding, in the standard scenario, a democratic flavor composition at their arrival on Earth.

The hunt for cosmogenic neutrinos is a target of next generation observatories: IceCube-Gen2, RNO, GRAND, POEMMA, and CHANT. A novel detection strategy for these neutrinos has been put forward. This new technique relies on the observation of Earth-throughgoing tau neutrinos at PeV energies. By measuring the flux at this energy, we can indirectly observe the flux at EeV energies since these two are related by the cascading down of the neutrinos. However, such a link demands an accurate simulation of the VHE tau neutrino transport. TauRunner is a Python Monte Carlo (MC) package developed in 2019 that was intended for such effort, but contained some limitations. My contribution to the MC has been to add antineutrino secondaries produced in some tau decay channels. I used the Inversion method to sample the energies, ensured the secondaries were appropriately propagated, and conducted unit tests to confirm the simulation gets results that agree with our present empirical knowledge. The emerging neutrino spectrum for a monochromatic flux of tau neutrinos is shown below.

Other features added to TauRunner include the ability for the user to propagate particles through any medium with spherical symmetry (originally the Earth was the only option). The code is still undergoing improvements centered around optimization, legibility of the code, and easier installation. With this new version of TauRunner, it is expected to have a more precise simulation of the Very-High-Energy tau neutrino signal which should be of great aid for the search of the GZK flux. It is essential to continue developing quality software to facilitate this effort. Access TauRunner here: https://github.com/icecube/TauRunner. Check out my Proceeding Of Science pre-publication for the 37th International Cosmic Ray Conference (ICRC2021) at https://pos.sissa.it/395/1030/.

References

[1] IceCube collaboration, IceCube-Gen2: A Vision for the Future of Neutrino Astronomy in Antarctica, 1412.5106.

[2] J.A. Aguilar et al., The Next-Generation Radio Neutrino Observatory – Multi-Messenger Neutrino Astrophysics at Extreme Energies, 1907.12526.

[3] K. Fang et al., The Giant Radio Array for Neutrino Detection (GRAND): Present and Perspectives, PoS ICRC2017 (2018) 996 [1708.05128].

[4] POEMMA collaboration, POEMMA: Probe Of Extreme Multi-Messenger Astrophysics, EPJ Web Conf. 210 (2019) 06008.

[5] A. Neronov, D.V. Semikoz, L.A. Anchordoqui, J. Adams and A.V. Olinto, Sensitivity of a proposed space-based Cherenkov astrophysical-neutrino telescope, Phys. Rev. D95 (2017) 023004 [1606.03629].

[6] ARA collaboration, Constraints on the diffuse flux of ultrahigh energy neutrinos from four years of Askaryan Radio Array data in two stations, Phys. Rev. D 102 (2020) 043021 [1912.00987].

[7] A. Anker et al., A search for cosmogenic neutrinos with the ARIANNA test bed using 4.5 years of data, JCAP 03 (2020) 053 [1909.00840].

[8] ANITA collaboration, Constraints on the ultra-high energy cosmic neutrino flux from the fourth flight of ANITA, 1902.04005.

[9] Pierre Auger collaboration, Probing the origin of ultra-high-energy cosmic rays with neutrinos in the EeV energy range using the Pierre Auger Observatory, 1906.07422.

[10] IceCube collaboration, The first search for extremely-high energy cosmogenic neutrinos with the IceCube Neutrino Observatory, Phys. Rev. D82 (2010) 072003 [1009.1442].

[11] ARIANNA collaboration, A First Search for Cosmogenic Neutrinos with the ARIANNA Hexagonal Radio Array, Astropart. Phys. 70 (2015) 12 [1410.7352].

[12] Pierre Auger collaboration, Improved limit to the diffuse flux of ultrahigh energy neutrinos from the Pierre Auger Observatory, Phys. Rev. D91 (2015) 092008 [1504.05397].

[13] IceCube collaboration, Constraints on Ultrahigh-Energy Cosmic-Ray Sources from a Search for Neutrinos above 10 PeV with IceCube, Phys. Rev. Lett. 117 (2016) 241101 [1607.05886].

[14] ARA collaboration, Performance of two Askaryan Radio Array stations and first results in the search for ultrahigh energy neutrinos, Phys. Rev. D93 (2016) 082003 [1507.08991].

[15] ANITA collaboration, Constraints on the diffuse high-energy neutrino flux from the third flight of ANITA, Phys. Rev. D98 (2018) 022001 [1803.02719].