arXiv subjects

Hanna Parul

Publications and source records attributed to Hanna Parul.

11 recordsLinked to original sources

arXiv2026

Unveiling the Milky Way with a Gaia DR3 census of OB-type stars within 2 kpc. I. Tracing local Galactic structure, massive star-forming regions and core-collapse supernova progenitors

O- and B-type stars are young and hot, thereby serving as vital tracers of the star formation and spiral arm structure of the Milky Way. At the dusk of the \textit{Gaia} DR3 era, a high-confidence and accurate catalogue appears timely. Here we have characterized a population of 105,971 OB-type stars (T$_{\rm eff} >$ 10,000 K; hereafter OB stars) within 2 kpc from the Sun, using an astro-photometric Bayesian inference tool. Our resulting map unveils a complex view of the young stellar populations across the thin disk, with prominent large-scale features such as the Cepheus Spur, the Giant Oval Cavity, and a segment of the Sagittarius-Carina spiral arm all visible. Their inhomogeneous spatial distribution implies that massive star formation has taken place clustered across a few highly concentrated regions. We find a correlation between the overdensities of OB stars and young open clusters ($<$20 Myr), although OB stars can be better detected in high-extinction regions. We identify over 4200 OB stars as core-collapse supernova (ccSN) or direct-collapse black hole (BH) progenitor candidates, and therefore targets of interest for spectroscopic follow-up. Furthermore, we find no OB-type star ccSN progenitor to explode within the next 1 Myr within 100 pc, at which such an event could be harmful to Earth's biosphere. Finally, we identify more BH progenitors to collapse within the next 1 Myr than ccSN to explode, despite the former's much scarcer number - which could be indicative of a recent massive star formation burst in the local Milky Way.

astro-ph.GA↗

arXiv2026

Bar-induced deflection of open cluster tidal tails

We present a systematic study of how the Galactic bar affects the orientation of tidal tails of open clusters and assess the power of tail morphology to constrain the bar's pattern speed. Using test-particle simulations, we follow the evolution of $\sim 1450$ observed open clusters from the Hunt & Reffert (2024) catalogue in an axisymmetric reference potential and in eight barred potentials with pattern speeds ranging from $\Omega_b = 20$ km/s/kpc to $\Omega_b = 55$ km/s/kpc. We quantify the bar effect through the deflection angle -- the rotation of the tail orientation in the barred model relative to the axisymmetric case. The deflection angle varies systematically with bar pattern speed and cluster guiding radius. The largest deflections occur for clusters near the outer Lindblad resonance (OLR), with the sign of the angle set by the orientation of the orbit's pericentre relative to the bar's major axis. For each cluster we measure the distance from the centre beyond which different bar models produce distinguishable tail orientations, and classify each cluster as bar-sensitive or bar-insensitive based on its maximum absolute deflection across the bar models. Comparing with observed tidal tails from the literature, we find that the extended tails of NGC 2632 and the Hyades disfavour moderate pattern speeds. We provide a catalogue of deflection angles, minimal tail extents, and bar-sensitivity flags to guide future observational searches and the re-assessment of existing tidal tail catalogues.

astro-ph.GA↗

arXiv2026

The origin of strong $\alpha$-element bimodalities in FIRE simulations of Milky Way-mass galaxies

One of the Milky Way's characteristic features is a strongly bimodal distribution of $\alpha$-process elements, such as Mg, at fixed [Fe/H] in stellar abundances. We examine patterns in [Mg/Fe] versus [Fe/H] in FIRE-2 simulations of Milky Way-mass galaxies. Out of 16 galaxies, 4 are capable of producing a strongly bimodal distribution. In all four galaxies, the high-$\alpha$ population corresponds to an older, radially-compact, thick disk, and the low-$\alpha$ population corresponds to a younger, radially-extended, thin disk, similar to the MW.The transition from high- to low-$\alpha$ took $0.3-1.2\Gyr$ and began $5.5-6.5\Gyr$ ago. [Mg/Fe] decreased at relatively fixed [Fe/H], both in the galaxy overall and at fixed radii: Fe enrichment nearly balanced gas accretion (and therefore dilution), but Mg enrichment was weaker. Importantly, this transition occurred during a period of relatively low gas fraction ($5-15\%$), immediately after a rapid decline in star formation (halving within a few hundred Myr), which caused an increase in Fe-producing white-dwarf supernovae relative to Mg-producing core-collapse supernovae. Only one case coincided with a major merger coalescence. We find similar trends in measuring stars by their current radius and by their birth radius, therefore, radial redistribution did not play a dominant role in the formation of a bimodality or its spatial dependence today. Overall, in FIRE-2, strong $\alpha$-element bimodalities are relatively uncommon ($\sim25\%$), often not associated with a major merger, and arise primarily from a rapid decline in star formation during relatively low gas fraction.

astro-ph.GA↗

arXiv2025

Understanding the Origin and Dynamical Evolution of the Unique Open Star Cluster Berkeley 20 using FIRE Simulations

Open clusters (OCs) act as key probes that can be leveraged to constrain the formation and evolution of the Milky Way (MW)'s disk, as each has a unique chemical fingerprint and well-constrained age. Significant Galactic dynamic interactions can leave imprints on the orbital properties of OCs, allowing us to use the present day properties of long-lived OCs to reconstruct the MW's dynamic history. To explore these changes, we identify OC analogs in FIRE-2 simulations of MW-mass galaxies. For this work, we focus on one particular FIRE-2 OC, which we identify as an analog to the old, subsolar, distant, and high Galactic latitude MW OC, Berkeley 20. Our simulated OC resides ~6 kpc from the galactic center and ultimately reaches a height $|Z_{\mathrm{max}}|>2$ kpc from the galactic disk, similar to Berkeley 20. We trace the simulated cluster's orbital and environmental history, identifying key perturbative episodes, including: (1) an interaction with a gas overdensity in a spiral arm that prompts an outward migration event and (2) a substantial interaction with a Sagittarius Dwarf Spheroidal Galaxy-mass satellite that causes significant orbital modification. Our simulated OC shows significant resilience to disruption during both its outward migration and the satellite-driven heating event that causes subsequent inward migration. Ultimately, we find these two key processes -- migration and satellite heating -- are essential to include when assessing OC orbital dynamics in the era of Gaia.

astro-ph.GA↗

arXiv2025

How many stars form in compact clusters in the local Milky Way?

Two main models coexist for the environment in which stars form. The clustered model stipulates that the bulk of star formation occurs within dense embedded clusters, but only a minority of them survive the residual gas expulsion phase caused by massive stellar feedback unbinding the clusters. On the other hand, the hierarchical model predicts that star formation happens at a range of scales and densities, where open clusters (OCs) only emerge from the densest regions. We aim to exploit a recent catalog of compact OCs, corrected for completeness, to obtain an updated estimation of the surface density star formation rate within OCs ($\sum_{\rm SFR,OC}$), which we compare with recent estimates of $\sum_{\rm SFR}$ to determine which model is more likely. We have applied two methods. The first one consisted of integrating over the power law that was fit for the mass function of the youngest OCs using a MC sampling. The second one consisted of counting the total compact mass within these youngest OCs within 1 kpc, so that the result could be directly compared with local values of $\sum_{\rm SFR}$. We estimated new $\sum_{\rm SFR,OC}$ values between $736^{+159}_{-176}$ and $875^{+34}_{-35}$ M$_{\odot}$ Myr$^{-1}$ kpc$^{-2}$, depending on the methodology. These results are significantly higher than previous $\sum_{\rm SFR,OC}$ estimates, which we attribute to the incompleteness of past catalogs, and are consistent with the majority ($\geq$ 50 \%) or even the vast majority ($\geq$ 80 \%) of the star formation occurring in initially compact clusters, through comparisons with $\sum_{\rm SFR}$ from the recent literature. Our new $\sum_{\rm SFR,OC}$ values are consistent with clustered formation being the most dominant mode of star formation.

astro-ph.GA↗

arXiv2025

Effect of gas accretion on $\alpha$-element bimodality in Milky Way-mass galaxies in the FIRE-2 simulations

We analyse the stellar distributions on the [Fe/H]-[Mg/Fe] plane for 11 Milky Way-mass galaxies from the FIRE-2 cosmological baryonic zoom-in simulations. Alpha-element bimodality, in the form of two separate sequences on the [Fe/H]-[Mg/Fe] plane, is not a universal feature of disk galaxies. Five galaxies demonstrate double sequences with the $\alpha$-enriched one being older and kinematically hotter, in qualitative agreement with the high-$\alpha$ and low-$\alpha$ populations in the Milky Way disk; three galaxies have unimodal distribution, two show weakly-bimodal features where low-$\alpha$ sequence is visible only over a short range of metallicities, and one show strong bimodality with a different slope of high-$\alpha$ population. We examine the galaxies' gas accretion history over the last 8 Gyr, when bimodal sequences emerge, and demonstrate that the presence of the low-$\alpha$ sequence in the bimodal galaxies is related to the recent infall of metal-poor gas from the circumgalactic medium that joins the galaxy in the outskirts and induces significant growth of the gas disks compared to their non-bimodal counterparts. We also analyse the sources of the accreted gas and illustrate that both gas-rich mergers and smooth accretion of ambient gas can be the source of the accreted gas, and create slightly different bimodal patterns.

astro-ph.GA↗

arXiv2024

Domain adaptation in application to gravitational lens finding

The next decade is expected to see a tenfold increase in the number of strong gravitational lenses, driven by new wide-field imaging surveys. To discover these rare objects, efficient automated detection methods need to be developed. In this work, we assess the performance of three domain adaptation techniques -- Adversarial Discriminative Domain Adaptation (ADDA), Wasserstein Distance Guided Representation Learning (WDGRL), and Supervised Domain Adaptation (SDA) -- in enhancing lens-finding algorithms trained on simulated data when applied to observations from the Hyper Suprime-Cam Subaru Strategic Program. We find that WDGRL combined with an ENN-based encoder provides the best performance in an unsupervised setting and that supervised domain adaptation is able to enhance the model's ability to distinguish between lenses and common similar-looking false positives, such as spiral galaxies, which is crucial for future lens surveys.

astro-ph.IM↗

arXiv2024

Strong Chemical Tagging in FIRE: Intra and Inter-Cluster Chemical Homogeneity in Open Clusters in Milky Way-like Galaxy Simulations

Open star clusters are the essential building blocks of the Galactic disk; "strong chemical tagging" - the premise that all star clusters can be reconstructed given chemistry information alone - is a driving force behind many current and upcoming large Galactic spectroscopic surveys. In this work, we characterize abundance patterns for 9 elements (C, N, O, Ne, Mg, Si, S, Ca, and Fe) in open clusters (OCs) in three galaxies (m12i, m12f, and m12m) from the Latte suite of FIRE-2 simulations to investigate if strong chemical tagging is possible in these simulations. We select young massive (>=10^(4.6) Msun) OCs formed in the last ~100 Myr and calculate the intra- and inter-cluster abundance scatter for these clusters. We compare these results with analogous calculations drawn from observations of OCs in the Milky Way. We find the intra-cluster scatter of the observations and simulations to be comparable. While the abundance scatter within each cluster is minimal (<0.020 dex), the mean abundance patterns of different clusters are not unique. We also calculate the chemical difference in intra- and inter-cluster star pairs and find it, in general, to be so small that it is difficult to distinguish between stars drawn from the same OC or from different OCs. Despite tracing three distinct nucleosynthetic families (core-collapse supernovae, white dwarf supernovae, and stellar winds), we conclude that these elemental abundances do not provide enough discriminating information to use strong chemical tagging for reliable OC membership.

astro-ph.GA↗

arXiv2024

$\texttt{DiffLense}$: A Conditional Diffusion Model for Super-Resolution of Gravitational Lensing Data

Gravitational lensing data is frequently collected at low resolution due to instrumental limitations and observing conditions. Machine learning-based super-resolution techniques offer a method to enhance the resolution of these images, enabling more precise measurements of lensing effects and a better understanding of the matter distribution in the lensing system. This enhancement can significantly improve our knowledge of the distribution of mass within the lensing galaxy and its environment, as well as the properties of the background source being lensed. Traditional super-resolution techniques typically learn a mapping function from lower-resolution to higher-resolution samples. However, these methods are often constrained by their dependence on optimizing a fixed distance function, which can result in the loss of intricate details crucial for astrophysical analysis. In this work, we introduce $\texttt{DiffLense}$, a novel super-resolution pipeline based on a conditional diffusion model specifically designed to enhance the resolution of gravitational lensing images obtained from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Our approach adopts a generative model, leveraging the detailed structural information present in Hubble Space Telescope (HST) counterparts. The diffusion model, trained to generate HST data, is conditioned on HSC data pre-processed with denoising techniques and thresholding to significantly reduce noise and background interference. This process leads to a more distinct and less overlapping conditional distribution during the model's training phase. We demonstrate that $\texttt{DiffLense}$ outperforms existing state-of-the-art single-image super-resolution techniques, particularly in retaining the fine details necessary for astrophysical analyses.

astro-ph.IM↗

arXiv2023

The imprint of bursty star formation on alpha-element abundance patterns in Milky Way-like galaxies

Milky Way-mass galaxies in the FIRE-2 simulations demonstrate two main modes of star formation. At high redshifts star formation occurs in a series of short and intense bursts, while at low redshifts star formation proceeds at a steady rate with a transition from one mode to another at times ranging from 3 to 7 Gyr ago for different galaxies. We analyse how the mode of star formation affects iron and alpha-element abundance. We find that the early bursty regime imprints a measurable pattern in stellar elemental abundances in the form of a "sideways chevron" shape on the [Fe/H] - [O/Fe] plane and the scatter in [O/Fe] at a given stellar age is higher than when a galaxy is in the steady regime. That suggests that the evolution of [O/Fe] scatter with age provides an estimate of the end of the bursty phase. We investigate the feasibility of observing of this effect by adding mock observational errors to a simulated stellar survey and find that the transition between the bursty and steady phase should be detectable in the Milky Way, although larger observational uncertainties make the transition shallower. We apply our method to observations of the Milky Way from the Second APOKASC Catalog and estimate that the transition to steady star formation in the Milky Way happened 7-8 Gyrs ago, earlier than transition times measured in the simulations.

astro-ph.GA↗

arXiv2021

Decoding Dark Matter Substructure without Supervision

The identity of dark matter remains one of the most pressing questions in physics today. While many promising dark matter candidates have been put forth over the last half-century, to date the true identity of dark matter remains elusive. While it is possible that one of the many proposed candidates may turn out to be dark matter, it is at least equally likely that the correct physical description has yet to be proposed. To address this challenge, novel applications of machine learning can help physicists gain insight into the dark sector from a theory agnostic perspective. In this work we demonstrate the use of unsupervised machine learning techniques to infer the presence of substructure in dark matter halos using galaxy-galaxy strong lensing simulations.

astro-ph.CO↗