arXiv subjects

Aman Khalid

Publications and source records attributed to Aman Khalid.

6 recordsLinked to original sources

arXiv2026

Comparison and verification methods to trace interaction-driven disturbances in galaxies

Low surface brightness tidal debris around galaxies, such as tails, streams, and shells, together with other interaction-driven morphological disturbances, serve as valuable indicators of past or ongoing galaxy mergers. With the growing data volume from surveys like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), automated detection methods are essential. This paper evaluates the performance of two automated methods, a Self-Supervised Learning (SSL) model and the Concentration-Asymmetry-Smoothness (CAS) parameter method, in tracing interaction-driven disturbances and merger signatures, with visual classification used as the benchmark. Visual classification yields a high-confidence disturbance fraction of 25.1 +/- 1.5% in our sample and serves as the reference standard for assessing the completeness and precision of the automated approaches. Visual classification is affected by galaxy distance and image resolution, which limit the detectability of faint low surface brightness structures. The SSL model achieves high recall (0.86 +/- 0.04) and low contamination (0.2) by retraining only its linear classifier on a small labelled dataset, making it suitable for identifying a broad set of disturbed systems, including faint tidal debris and other interaction-driven morphological disturbances, thereby providing a more complete census of merger-related features. The CAS method, using the traditional threshold A > 0.35, shows higher precision (0.77) but lower recall (0.20), indicating a conservative approach that captures cleaner but less complete samples. Visual classification and the SSL model show a significant positive correlation between stellar mass and disturbance fraction, while the CAS method exhibits a much weaker trend.

astro-ph.GA↗

arXiv2025

Investigating the imprints of tidal features on simulated galaxy outskirts in LSST-like mock observations

Tidal features provide signatures of recent galaxy mergers, offering insights into the role of mergers in galaxy evolution. The Vera C. Rubin Observatory's upcoming Legacy Survey of Space and Time (LSST) will allow for an unprecedented study of tidal features around millions of galaxies. We use mock images of galaxies at $z\sim0$ ($z\sim0.2$ for \textsc{NewHorizon}) from \textsc{NewHorizon}, \textsc{eagle}, \textsc{IllustrisTNG}, and \textsc{Magneticum Pathfinder} simulations to predict the properties of tidal features in LSST-like images. We find that tidal features are more prevalent around blue galaxies with intrinsic colours $(g-i)\leq0.5$, compared to redder ones, at fixed stellar mass. This trend correlates with elevated specific star formation rates ($\mathrm{sSFR}>10^{-10}\mathrm{\:yr}^{-1}$), suggesting that merger-induced star formation contributes to the bluer colours. Tidal feature hosts in the red sequence appear to exhibit colour profiles offset to bluer colours for galaxies with stellar masses $10^{10}<M_{\star\mathrm{,\:30\:pkpc}}/\mathrm{M}_\odot<10^{11}$, similarly blue cloud tidal feature host galaxies appear to have their colour profiles offset to bluer colours for $10^{9.5}<M_{\star\mathrm{,\:30\:pkpc}}/\mathrm{M}_\odot<10^{10.5}$. However, the differences in colour profiles in either the red sequence or the blue cloud are not statistically robust and larger samples are needed to test if these differences are real. The predictions across the simulations are quantitatively distinct; therefore, LSST observations will allow us to further constrain the differences between different subgrid physics models.

astro-ph.GA↗

arXiv2025

Tidal features around simulated groups and cluster galaxies: Enhancement and suppression of merger events through environment in LSST-like mock observations

Generally, merger likelihood increases in denser environments; however, the large relative velocities at the centres of dense clusters are expected to reduce the likelihood of mergers for satellite galaxies. Tidal features probe the recent merger histories of galaxies. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will produce an unprecedented sample of tidal features around millions of galaxies. We use LSST-like mock observations of galaxies at $z\sim0$ from the EAGLE, IllustrisTNG and Magneticum Pathfinder cosmological-hydrodynamical simulations to predict the occurrence rates of tidal features around satellite galaxies across group and cluster environments in the velocity-radius projected phase-space diagram to investigate the impact of these environments on tidal feature occurrence. We find that ancient infallers in the projected phase-space exhibit a decreasing tidal feature fraction with increasing halo mass, whereas recent infallers in the projected phase-space show unchanging tidal feature fractions with halo mass. Our results show, for the first time in cosmological simulations, a suppression of tidal feature fractions in the central regions of galaxy clusters, indicating a reduced merger rate due to higher cluster-centric velocities and lower galaxy total masses in the cluster centres. Using a toy model, we show that the presence of more tidal features in the recent infaller zone and cluster outskirts suggests that tidal features occur in interactions within infalling groups and dissipate by the time they are ancient infallers, indicating a $\lesssim3\pm2$ Gyr survival time of tidal features within clusters.

astro-ph.GA↗

arXiv2024

The MAGPI Survey: Massive slow rotator population in place by $z \sim 0.3$

We use the `Middle Ages Galaxy Properties with Integral field spectroscopy' (MAGPI) survey to investigate whether galaxies have evolved in the distribution of their stellar angular momentum in the past 3-4 Gyr, as probed by the observational proxy for spin, $λ_{R}$. We use 2D stellar kinematics to measure $λ_{R}$ along with detailed photometric models to estimate galaxy ellipticity. The combination of these measurements quantifies the kinematic classes of `fast rotators' and the rarer `slow rotators', which show no regular rotation in their line-of-sight velocity fields. We compare 51 MAGPI galaxies with $\log_{10} (M_{\star}/\mathrm{M}_\odot) > 10$ to carefully drawn samples of MaNGA galaxies in the local Universe, selected to represent possible descendants of the MAGPI progenitors. The EAGLE simulations are used to identify possible evolutionary pathways between the two samples, explicitly accounting for progenitor bias in our results and the varied evolutionary pathways a galaxy might take between the two epochs. We find that the occurrence of slow rotating galaxies is unchanged between the MAGPI ($z \sim 0.3$) and MaNGA ($z \sim 0$) samples, suggesting the massive slow rotator population was already in place $\sim 4$ Gyr ago and has not accumulated since. There is a hint of the MAGPI sample having an excess of high $λ_{R}$ galaxies compared to the MaNGA sample, corresponding to more ordered rotation, but statistically the samples are not significantly different. The large-scale stellar kinematics, as quantified through the $λ_{R}$ parameter, of galaxies at $z \sim 0.3$ have already evolved into the diversity of structures seen today in the local Universe.

astro-ph.GA↗

arXiv2024

Characterising Tidal Features Around Galaxies in Cosmological Simulations

Tidal features provide signatures of recent mergers and offer a unique insight into the assembly history of galaxies. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will enable an unprecedentedly large survey of tidal features around millions of galaxies. To decipher the contributions of mergers to galaxy evolution it will be necessary to compare the observed tidal features with theoretical predictions. Therefore, we use cosmological hydrodynamical simulations NewHorizon, EAGLE, IllustrisTNG, and Magneticum to produce LSST-like mock images of $z\sim0$ galaxies ($z\sim0.2$ for NewHorizon) with $M_{\scriptstyle\star,\text{ 30 pkpc}}\geq10^{9.5}$ M$_{\scriptstyle\odot}$. We perform a visual classification to identify tidal features and classify their morphology. We find broadly good agreement between the simulations regarding their overall tidal feature fractions: $f_{\text{NewHorizon}}=0.40\pm0.06$, $f_{\text{EAGLE}}=0.37\pm0.01$, $f_{\text{TNG}}=0.32\pm0.01$ and $f_{\text{Magneticum}}=0.32\pm0.01$, and their specific tidal feature fractions. Furthermore, we find excellent agreement regarding the trends of tidal feature fraction with stellar and halo mass. All simulations agree in predicting that the majority of central galaxies of groups and clusters exhibit at least one tidal feature, while the satellite members rarely show such features. This agreement suggests that gravity is the primary driver of the occurrence of visually-identifiable tidal features in cosmological simulations, rather than subgrid physics or hydrodynamics. All predictions can be verified directly with LSST observations.

astro-ph.GA↗

arXiv2020

Optimizing Cuckoo Filter for high burst tolerance,low latency, and high throughput

In this paper, we present an implementation of a cuckoo filter for membership testing, optimized for distributed data stores operating in high workloads. In large databases, querying becomes inefficient using traditional search methods. To achieve optimal performance it is necessary to use probabilistic data structures to test the membership of a given key, at the cost of getting false positives while querying data. The widely used bloom filters can be used for this, but they have limitations like no support for deletes. To improve upon this we use a modified version of the cuckoo filter that gives better amortized times for search, with less false positives.

cs.DC↗