arXiv subjects

Derek Sikorski

Publications and source records attributed to Derek Sikorski.

8 recordsLinked to original sources

arXiv2026

Emergence and Detection of Electron-Scale Current Sheets in Turbulence with MMS Observations and fully kinetic 3D simulations

The solar wind is characterized by turbulence, where a cascade produces intermittent current structures called current sheets (CS) that efficiently dissipate energy into the plasma. These have been studied with in situ spacecraft observations, but single-spacecraft techniques such as the partial variance of increments (PVI) are inherently limited since they lack spatial context. A combined analysis of in situ observations and numerical simulations can provide significant insight into the properties of intermittent structures forming in heliospheric turbulence. Understanding the size and distribution of these structures is crucial in tracing the pathways of energy dissipation and particle energization in space plasma. Using 3D fully kinetic simulations of magnetized turbulence, we identify CS via machine learning and find a complex broken-power-law distribution for the CS widths, where the power-law breaks separate ion-scale CS from electron-scale CS. Electron-scale CS dominate, with widths peaking near $2d_e$. Comparing simulations with MMS data, we test PVI as a CS detector and show it can infer CS scale, though oblique crossings inflate inferred sizes. The prevalence of electron-scale sheets suggests they may contribute to plasma heating in aggregate.

physics.plasm-ph↗

arXiv2026

Quantifying the Impact of Incompleteness on Identifying and Interpreting Galaxy Protocluster Populations with the TNG-Cluster Simulation

We use the TNG-Cluster simulation to investigate how stellar mass and star formation rate (SFR) incompleteness affect the identification of density peaks within galaxy protoclusters at different redshifts. Our analysis focuses on a sample of $352$ protoclusters, defined as the progenitor populations of galaxies that reside within the virialized region of $z=0$ clusters with $M_{\rm{200}}^{z=0}\sim10^{14.3-15.5}~{\rm M}_{\odot}$. For comparison, we define our "baseline" protocluster population as galaxies with ${M}_{\star}> 10^{8.5}~{\rm M}_{\odot}$ at any redshift. We find that ${M}_{\star}$-limited (${M}_{\star} > 10^{9.5}~{\rm M}_{\odot}$) and SFR-limited ($\rm{SFR} > 10~{\rm M}_{\odot} \mathrm{yr}^{-1}$) subpopulations recover the baseline highest galaxy density peak in roughly $\sim60\%$ of cases within an accuracy of $1.0$ pMpc (corresponding to an angular scale of $\sim 2-2.5$ arcmin) at $z > 2$. This recovery fraction drops to $\sim40-50\%$ when restricting to galaxies with ${M}_{\star} > 10^{10.0}~{\rm M}_{\odot}$. We find that the baseline highest galaxy density peaks typically coincide with the highest dark matter and stellar mass density peaks, with separations less than $0.5$ pMpc in $\sim60-75\%$ of cases at $z>2$. This agreement drops to $\sim45-50\%$ when restricting to galaxies with ${M}_{\star} > 10^{10.0}~{\rm M}_{\odot}$. These results indicate that identifying the densest regions of protoclusters -- i.e., the core -- is highly sensitive to stellar mass and SFR completeness limits. Nevertheless, at $z>2$ we find that the baseline highest galaxy density peaks are generally sites of enhanced star formation and accelerated mass growth relative to the remainder of the protocluster, consistent with some observational studies.

astro-ph.GA↗

arXiv2026

Elemental Abundances in the Binary Star V505 Per

We present a detailed chemical abundance analysis of the eclipsing binary system V505 Per. High resolution spectra were analyzed using the MOOG spectrum analysis code, and we determined abundances not only for iron and lithium but also for Si, Na, Ca, Mn, and Ni, elements that have not previously been analyzed in detail for this system. Abundances were computed across 15 temperature points using model atmospheres, with stellar parameters refined by minimizing abundance trends with excitation potential. We determined effective temperatures of T_eff = 6650 +/- 50 K for the primary and T_eff = 6550 +/- 50 K for the secondary, with iron abundances of [Fe/H] = -0.10 +/- 0.06 and [Fe/H] = -0.19 +/- 0.07, respectively. Most [X/Fe] ratios are consistent with solar values, though manganese is deficient. Our analysis of the effective temperatures shows that both stars lie on the hot edge of the lithium dip, consistent with Koenigsberger et al. (2025), which may help resolve the inconsistency noted of the stars lithium abundance within the dip by Baugh et al. (2013).

astro-ph.SR↗

arXiv2026

The HST-Hyperion Survey: Environmental Imprints on the Stellar-Mass Function at z~2.5

Not all galaxies at Cosmic Noon evolve in the same way. It remains unclear how the local environment -- especially the extreme overdensities of protoclusters -- affects stellar mass assembly at high redshift. The stellar mass function (SMF) encodes these processes; comparing SMFs across environments reveals differences in evolutionary history. We present the SMF of the Hyperion proto-supercluster at $z\sim2.5$, one of the largest and most massive protostructures known. This dataset provides the most statistically robust SMF of a single protostructure at $z>2$. By comparing the SMF of overdense peaks within Hyperion to the coeval field, we ask: how early, and how strongly, does a dense environment favor massive galaxies? Using COSMOS2020 photometry with ground-based and new HST grism spectroscopy, we construct a 3D overdensity map that assigns galaxies to peaks, outskirts, or the field. We perform 100 Monte Carlo realizations to propagate redshift and mass uncertainties, and derive SMFs normalized to the field. The peaks show a clear excess of massive galaxies: number densities at $\log(M_*/M_\odot)\sim 11$ are ~10x higher than the field, while those at $\log(M_*/M_\odot)\sim 9.5$ are enhanced by only ~3.5x. By contrast, the outskirts and Hyperion as a whole mirror the field. Environmental effects on stellar mass growth are thus evident by $z\sim 2.5$. The densest regions already host galaxies with accelerated growth, while the global SMF masks this signal. Protostructures therefore begin shaping the high-mass end of the SMF well before cluster quenching, and may drive the elevated star formation at Cosmic Noon.

astro-ph.GA↗

arXiv2025

The Enhancement of Ion Heating in Kinetic, Anti-Parallel Reconnection in the Presence of a Flow Shear

We investigate the kinetic effects of upstream, magnetic field-aligned, flow shear on anti-parallel magnetic reconnection using 2.5D Particle-In-Cell simulations. Our results demonstrate that flow shear significantly alters the reconnection process, leading to enhanced ion heating, reduced outflow speeds, and a modified reconnection geometry. In contrast to previous Hall Magnetohydrodynaic (MHD) studies, we find that reconnection becomes a more efficient plasma heating mechanism in the presence of sub-Alfvénic flow shear, with ion heating increasing by as much as 300\%. This enhanced heating is achieved by efficiently converting the incoming flow shear energy into thermal energy through istropization in the exhaust. The enhanced heating leads to a pressure gradient away form the x-line exerting a force that reduces the outflow jet speed and slows down the reconnection process. This conversion is due to beam selection effects, mixing and scattering in the exhaust. A theoretical model is developed which predicts well the exhaust heating and outflow speed reduction. These results offer a potential explanation for recent Parker Solar Probe observations of suppressed reconnection in the presence of flow shear and carry significant implications for energy dissipation in turbulent plasmas.

physics.plasm-ph↗

arXiv2025

The HST-Hyperion Survey: Grism Observations of a $z\sim2.5$ Proto-Supercluster

We present first results and catalogs from the HST-Hyperion survey. This survey has collected 50 orbits of WFC3/F160W imaging and WFC3/G141 grism spectroscopy in the most overdense regions of the Hyperion proto-supercluster at $z\sim2.45$, which are analyzed in conjunction with the adjacent 56 orbits of WFC3/F140W imaging and WFC3/G141 grism spectroscopy from the 3D-HST survey. Sources were identified and spectra extracted using GRIZLI, which subsequently fit the combined grism data with object-matched photometric data from the COSMOS2020 catalog to obtain a redshift and best-fit spectral model. Each source was then visually inspected by multiple team members and quality flags were assigned. A total of 12814 objects with $m_{HST} \leq 25.0$ were inspected, of which 5629 (44%) have reliable redshifts from the grism data, which are sensitive to emission lines at a level of $\sim8.8 \times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ ($1σ$). Comparison to high-quality ground-based spectroscopic redshifts yields a scatter of $σ_{\rm NMAD} = 0.0016$. The resulting catalogs contain 125 confirmed members of the Hyperion structure within $2.40<z<2.53$, with an additional 71 confirmed galaxies in projection within $2.35<z<2.65$. The redshift, stellar population, and line flux catalogs, as well as all grism spectra, are publicly available.

astro-ph.GA↗

arXiv2025

Discovering Large-Scale Structure at $2<z<5$ in the C3VO Survey

The Charting Cluster Construction with VUDS and ORELSE (C3VO) survey is an ongoing imaging and spectroscopic campaign aiming to map out the growth of structure up to $z\sim5$ and was born from the combination of the Visible Multi-Object Spectrograph Ultra Deep Survey and the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. As we previously accomplished with the ORELSE survey, we apply our technique known as Voronoi tessellation Monte Carlo (VMC) mapping to search for serendipitous galaxy overdensities at $2 14$ and $2 14.5$. In the C3VO fields, we were able to recover many of the previously known structures in the literature as well as find hundreds of new overdensity candidates, once again demonstrating the powerful capabilities of VMC mapping when applied to wide-field optical and infrared galaxy evolution surveys at ever higher redshifts.

astro-ph.GA↗

arXiv2024

Enhanced AGN Activity in Overdense Galactic Environments at $2 < z < 4$

We conduct a study on the relationship between galaxy environments and their active galactic nuclei (AGN) activity at high redshifts ($2.0 10^{12.8}M_\odot$) overdense ($σ_δ>5.0$) peak, normalized with respect to the size of the peak. These findings indicate that the prevalence of AGN activity is highly dependent on the environment in which a host galaxy resides, even at early times in the formation history of the Universe.

astro-ph.GA↗