arXiv subjects

Priyanka Chakraborty

Publications and source records attributed to Priyanka Chakraborty.

At least 19 recordsLinked to original sources

arXiv2026

XRISM Reveals a Kinematically Coherent Core System of the Nearby Cool-Core Cluster Abell 2199

We present the results of a deep 251 ks XRISM/Resolve observation of the cool core of the galaxy cluster Abell 2199. From the integrated spectrum of the central $3' \times 3'$ Resolve field of view ($104 \times 104 \mathrm{~kpc}^2$), we find that the intracluster medium (ICM) redshift is consistent with that of the brightest cluster galaxy, within the optical-redshift uncertainty. This indicates that they form a kinematically coherent core system, which is offset from the mean cluster redshift by $\sim200~\mathrm{km~s^{-1}}$. The observed velocity dispersion of $\sim100~\mathrm{km~s^{-1}}$ corresponds to a three-dimensional Mach number of $M_{\mathrm{3D}}=0.16$ and a non-thermal pressure fraction of $P_{\mathrm{NT}}/P_{\mathrm{tot}}=1.4\pm0.2$%. Abell 2199 is one of the most dynamically quiescent relaxed clusters observed with XRISM, despite the presence of radio jets and a plume-like structure possibly associated with sloshing motions. Order-of-magnitude estimates suggest that turbulent dissipation could offset a non-negligible fraction of the radiative cooling losses, with $Q_{\mathrm{turb}}/Q_{\mathrm{cool}}\approx0.2$ for a large-scale driver such as sloshing and larger values for smaller AGN-feedback scales. Finally, we detect a localized enhancement of the Fe XXV He$α$ $y$ line in the southeast region, which spatially coincides with a Chandra surface brightness discontinuity.

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arXiv2026

SDSS-V LVM: Spatial Resolution Effects on Diagnostic Diagrams in the Magellanic Clouds

We investigate how spatial resolution affects emission-line diagnostics in the interstellar medium (ISM) of the Small and Large Magellanic Clouds (SMC and LMC) using SDSS Local Volume Mapper (LVM) data obtained at and degraded to 19, 42, 170 pc (for the SMC) and 17, 68, 272 pc (for the LMC), respectively. We compare the distributions of strong emission-line ratios through 1D and 2D Kolmogorov Smirnov tests. We deduced that diagnostics involving ionization and density sensitive ratios such as [OIII]λ5007/H\b{eta}, [SII]λλ6717+6731/Hα and [NII]λ6584/Hα are the most strongly impacted by resolution loss in this order. The SMC shows significant deviations even from intermediate scales (42 pc), whereas for the LMC, the coarsest resolution (272 pc) remains relatively stable, indicating that the SMC is intrinsically more affected by spatial mixing. Resolution degradation produces a marked homogenization effect: extreme values present at the finest scales are progressively diluted, causing diagnostic diagrams to converge toward their mean loci. Diffuse ionized gas is particularly sensitive to this mixing, while Hα selected ionized regions exhibit more robust behavior across resolutions. The sensitivity of diagnostic diagrams involving emission-line ratios, equivalent widths, and kinematic properties varies with both spatial resolution and galaxy, with the SMC generally showing stronger changes than the LMC. Our results demonstrate that sub-50 pc resolution is required to resolve the detailed structure of low-metallicity galaxies, and they highlight at least the need for careful interpretation of line-ratio diagnostics in extragalactic studies where coarse spatial resolution is unavoidable.

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arXiv2026

Rubin J122659.4+090236: An Extremely Low Surface Brightness Galaxy Candidate Discovered in the Rubin LSST Early Data Preview 2

We report the serendipitous discovery of an exceptionally low surface brightness galaxy (LSBG) candidate, Rubin J122659.4+090236, in Rubin Observatory imaging of the interacting NGC 4410 system, identified in the Cosmic Treasure Chest public release. 2D Sérsic modelling of the Rubin g, r, and i images reveals a nearly round system with a shallow profile (n ~ 0.4), an effective radius of R_e ~ 6'', and central surface brightnesses of $μ_{0,g}=27.52\pm0.04$, $μ_{0,r}=27.62\pm0.07$, and $μ_{0,i}=27.04\pm0.08$ mag arcsec$^{-2}$. EAZY photo-z fitting favours an intermediate-z solution at z~0.3, while a low-redshift solution at z~0.028, consistent with the NGC 4410 system, is also permitted by a restricted EAZY fit over 0<z<0.1 without imposing a redshift prior. These alternatives imply substantially different physical interpretations, ranging from a diffuse dwarf-like system to an exceptionally extended background LSBG. This discovery demonstrates Rubin's sensitivity to extremely diffuse galaxies and highlights the potential of the LSST survey to uncover large samples of such elusive systems across wide areas, enabling systematic studies of the LSBG population and its role in galaxy evolution.

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arXiv2026

The Nineteenth Data Release of the Sloan Digital Sky Survey

Mapping the local and distant Universe is key to our understanding of it. For decades, the Sloan Digital Sky Survey (SDSS) has made a concerted effort to map millions of celestial objects to constrain the physical processes that govern our Universe. The most recent and fifth generation of SDSS (SDSS-V) is organized into three scientific ``mappers". Milky Way Mapper (MWM) that aims to chart the various components of the Milky Way and constrain its formation and assembly, Black Hole Mapper (BHM), which focuses on understanding supermassive black holes in distant galaxies across the Universe, and Local Volume Mapper (LVM), which uses integral field spectroscopy to map the ionized interstellar medium in the local group. This paper describes and outlines the scope and content for the nineteenth data release (DR19) of SDSS and the most substantial to date in SDSS-V. DR19 is the first to contain data from all three mappers. Additionally, we also describe nine value added catalogs (VACs) that enhance the science that can be conducted with the SDSS-V data. Finally, we discuss how to access SDSS DR19 and provide illustrative examples and tutorials.

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arXiv2026

A Brush with Turbulence: Probing the ICM Dynamics in the Merging Toothbrush Cluster using XRISM

The Toothbrush Cluster (1RXS J0603.3+4214) is known for its northern radio relic, radio halo, and highly disturbed X-ray morphology. It shows features of both shock-driven and turbulent reacceleration, the latter of which is invoked to explain its radio halo. However, how kinetic energy from the merger is distributed into gas motions across spatial scales remains unclear. We probe the intracluster medium (ICM) dynamics in the southern, X-ray-brightest region of the cluster using a 167 ks XRISM/Resolve observation. We conduct both full-array and quadrant sub-array analyses by fitting the spectra with single and multi-component thermal models in the 3-8 keV band. The full-array spectrum favours two ICM components with a transonic line-of-sight (LOS) velocity difference of $Δv_{\mathrm{bulk}}=1635^{+165}_{-110}$ km s$^{-1}$, while the velocity dispersions are much lower, at $σ_{v,1\mathrm{D}}\sim$245-310 km s$^{-1}$. The sub-array analysis likewise reveals multiple components in at least three quadrants, with LOS bulk velocities ranging from $-2520^{+295}_{-230}$ to $+930^{+70}_{-110}$ km s$^{-1}$. The velocity dispersions remain modest at $\sim$215 km s$^{-1}$, corresponding to a turbulent pressure support of about 3-6% on scales dominating the observed line broadening. Cooler gas is detected in the NE and SW, with $kT_{\mathrm{NE}}=3.13^{+0.33}_{-0.30}$ keV and $kT_{\mathrm{SW}}=2.32^{+0.43}_{-0.37}$ keV, likely associated with a third, northern subcluster identified in weak-lensing and optical studies. Our results indicate a complex ICM kinematic structure, with evidence for at least three subclusters exhibiting supersonic bulk velocity offsets and much smaller velocity dispersions. This shows that the merger geometry has a significant line-of-sight component and may indicate that the cluster collision is relatively young, with the turbulent cascade not yet fully established.

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arXiv2026

Rubin LSST DP2 unveils almost-dark galaxies in the Virgo Cluster

Galaxies with the faintest surface brightness are currently known only in the Local Group. Similar objects should exist beyond our vicinity and are crucial for understanding galaxy evolution, structure, and dark matter content, yet surveys have not reached the depth required to detect them systematically. We present a population of seven almost-dark galaxies identified in Data Preview 2 of the Rubin Legacy Survey of Space and Time. They surround M49 in the vicinity of the Virgo Cluster, and exhibit central surface brightnesses in the range of $26.9 - 28.5 \, \mathrm{mag \, arcsec^{-2}}$ in the $g$-band, with half-light radii of $0.6 - 4.6 \, \mathrm{kpc}$ at the distance of Virgo, and stellar masses of $10^6 - 10^7 \, \mathrm{M_\odot}$. Their characteristics are analogous to those of the faintest and low-mass galaxies identified among satellite galaxies And XXI, And XXIII, and And XXV in the Local Group. This discovery demonstrates the power of the forthcoming Rubin LSST 10-year survey to uncover extremely faint galaxies at scale, promising the large statistical samples needed to constrain the faint-end luminosity function and the nature of dark matter.

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arXiv2026

The Twentieth Data Release of the Sloan Digital Sky Survey: First All-Sky BOSS Spectra, eROSITA-SDSS-V Mapper Coordinated Observations, and a Preview of the Local Volume Mapper

This paper presents the twentieth data release (DR20) from the Sloan Digital Sky Survey, the third data release of its fifth generation (SDSS-V). SDSS-V is a panoptic spectroscopy survey that is mapping the stars, gas, and galaxies through three scientific programs: the Milky Way Mapper (MWM), the Local Volume Mapper (LVM), and the Black Hole Mapper (BHM). DR20 presents the first optical (BOSS) SDSS-V spectra from southern hemisphere for the MWM and BHM surveys; new optical MWM and BHM data from the northern hemisphere are also available, for a total over 3 million spectra of 1.5 million stars and half a million galaxies and quasars, with galactic and extragalactic x-ray targets coordinate with eROSITA DR2. DR20 includes integral field spectroscopy maps from LVM of six targets and 169 tiles, spanning Galactic HII regions, planetary nebulae, and nearby galaxies. Additionally, eighteen value added catalogs are also released with DR20, based on SDSS-V MWM and BHM data, and we present a new LVM visualization tool including an RGB HiPS map as a value added product.

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arXiv2026

Metallicity Gradients in Modern Cosmological Simulations II: The Role of Bursty Versus Smooth Feedback at High-Redshift

The distribution of gas-phase metals within galaxies encodes the impact of stellar feedback on galactic evolution. At high-redshift, when galaxies are rapidly assembling, feedback-driven outflows and turbulence can strongly reshape radial metallicity gradients. In this work, we use the FIRE-2, SPICE, Thesan and Thesan Zoom cosmological simulations -- spanning a range of stellar feedback from bursty (time-variable) to smooth (steady) -- to investigate how these feedback modes shape gas-phase metallicity gradients at $3 10^{9}~{\rm M_\odot}$. These results demonstrate that bursty stellar feedback provides sufficient turbulence to prevent strong negative gradients from forming, while smooth stellar feedback does not generically allow for efficient radial redistribution of metals thereby keeping gradients steep. Finally, we compare with recent observations, finding that the majority -- but, notably, not all -- of the observed gradients may favor a bursty stellar feedback scenario. In all, these results highlight the utility of high-resolution observations of gas-phase metallicity at high-redshift as a key discriminator of these qualitatively different feedback types.

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arXiv2026

Physics of 1 keV line in X-ray binaries

X-ray binaries (XRBs) often exhibit spectral residuals in the 0.5 to 2 keV range, known as the ``1 keV residual/1 keV feature", with variable centroid and intensity across different systems. Yet a comprehensive scientific explanation of the variability of the 1 keV feature has remained largely elusive. In this paper, we explain for the first time the origin and variability of the 1 keV feature in XRBs using the spectral synthesis code \textsc{Cloudy}. We constructed line blends for the emission and absorption lines and study the variability of these blends with ionization parameters, temperature, and column density. We conducted a sample study involving five XRBs including two ultraluminous X-ray sources (ULXs): NGC 247 ULX-1, NGC 1313 X-1, a binary X-ray pulsar : Hercules X-1, and two typical low-mass X-ray binaries (LMXBs): Cygnus X-2, and Serpens X-1. Our analysis establishes a self-consistent framework explaining the variability of the 1 keV spectral feature, attributing its diversity to differences in spectral energy distribution, ionization parameter, temperature, column density, and disk reflection properties. This framework provides a comprehensive explanation for the observed 1 keV feature across these diverse XRB systems, offering insights into the underlying physical mechanisms at play.

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arXiv2026

Detection of new galaxy candidates at z > 11 in the JADES field using JWST NIRCam

We report the detection of six new galaxy candidates with photometric redshifts $z$ $>$ 11 within the JWST Advanced Deep Extragalactic Survey (JADES) GOODS-S and GOODS-N fields. These new candidates are detected through meticulous analysis of NIRCam photometry in eight filters spanning a wavelength range of 0.8-5.0 $μ$m. Photometric redshifts of these galaxy candidates are independently measured utilizing spectral energy distribution (SED) fitting techniques using \texttt{EAZY} and \texttt{BAGPIPES} codes, followed by visual scrutiny. One of these galaxy candidates is located in GOODS-S field, while the remaining five galaxies are located in GOODS-N field. Our analysis reveals that the stellar masses of these galaxies typically range from log $M_{\ast}$/$M_{\odot}$ = 7.75--8.75. Furthermore, these galaxies are typically young with their mass-weighted ages spanning from 80 to 240 Myr. Their specific star formation rates (sSFR), quantified as $\log (\text{sSFR}/\text{Gyr}$), are measured to vary between $\sim 0.95$ to 1.46. These new galaxy candidates offer a robust sample for probing the physical properties of galaxies within the first few hundred Myr of the history of the Universe. We also analyze the relationship between star formation rate (SFR) and stellar mass ($M_\ast$) within our sample.Continued investigation through spectroscopic analysis using JWST/NIRSpec is needed to spectroscopically confirm these high-redshift galaxy candidates and investigate further into their physical properties. We plan to follow up on these candidates with future NIRSpec observations.

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arXiv2026

Unveiling the Cosmic Chemistry II: "Direct" $T_e$-based metallicity of galaxies at 3 $< z <$ 10 with JWST/NIRSpec

We report the detection of the [O III] auroral line in 42 galaxies within the redshift range of $3 < z < 10$. These galaxies were selected from publicly available JWST data releases, including the JADES and PRIMALsurveys, and observed using both the low-resolution PRISM/CLEAR configuration and medium-resolution gratings. The measured electron temperatures in the high-ionization regions of these galaxies range from $T_e$([O III]) = 12,000 to 24,000 K, consistent with temperatures observed in local metal-poor galaxies and previous JWST studies. In 10 galaxies, we also detect the [O II] auroral line, allowing us to determine electron temperatures in the low-ionization regions, which range between $T_e$([O II]) = 10,830 and 20,000 K. The direct-$T_e$-based metallicities of our sample span from 12 + log(O/H) = 7.2 to 8.4, indicating these high-redshift galaxies are relatively metal-poor. By combining our sample with 25 galaxies from the literature, we expand the dataset to a total of 67 galaxies within $3 < z < 10$, effectively more than doubling the previous sample size for direct-$T_e$ based metallicity studies. This larger dataset allow us to derive empirical metallicity calibration relations based exclusively on high-redshift galaxies, using six key line ratios: R3, R2, R23, Ne3O2, O32, and O3N2. Notably, we derive a novel metallicity calibration relation for the first time using high-redshift $T_e$-based metallicities: $\hat{R}$ = 0.18log $R2$ + 0.98log $R3$. This new calibration significantly reduces the scatter in high-redshift galaxies compared to the $\hat{R}$ relation previously calibrated for low-redshift galaxies.

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arXiv2026

A Path to an All-Sky Survey with Roman

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$σ$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.

astro-ph.IM↗

arXiv2026

The Advanced X-ray Imaging Satellite (AXIS) Community Science Book

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

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arXiv2025

Double White Dwarf Binaries in SDSS-V DR19 : A catalog of DA white dwarf binaries and constraints on the binary population

The fifth-generation Sloan Digital Sky Survey (SDSS-V) includes the first large-scale spectroscopic survey of white dwarfs (WDs) in the era of Gaia parallaxes. SDSS-V collects multiple exposures per target, making it ideal for binary detection. We present a search for hydrogen atmosphere (DA) double white dwarf (DWD) binaries in this rich dataset. We quantify radial velocity variations between sub-exposures to identify binary candidates, and also measure the orbital period for a subset of DWD binary candidates. We find 63 DWD binary candidates, of which 43 are new discoveries, and we provide tentative periods for 10 binary systems. Using these measurements, we place constraints on the binary fraction of the Galactic WD population with $< 0.4$ AU separations $f_{\mathrm{bin,0.4}} = 9\%$, and the power-law index of the initial separation distribution $α= -0.62$. Using the simulated binary population, we estimate that $\leq 10$ super-Chandrasekhar binaries that merge within a Hubble time are expected in our sample. We predict that $\leq 5$ systems in our sample should be detectable via gravitational waves by LISA (Laser Interferometer Space Antenna), one of which has already been identified as a LISA verification source. We also estimate a total of about 10,000 - 20,000 LISA-detectable DWD binaries in the galaxy. Our catalog of WD+WD binary candidates in SDSS-V is now public, and promises to uncover a large number of exciting DWD systems.

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arXiv2025

Complex Ionization and Velocity Structures in GX 340+0 X-ray Binary Revealed by XRISM

We present the first high-resolution XRISM spectrum of the neutron star low-mass X-ray binary GX 340+0, revealing unprecedented detail in its emission and absorption features. The spectrum reveals a rich and complex Fe XXV He$α$ line profile and a P-Cygni profile from Ca XX. We use the state-of-the-art spectral synthesis code Cloudy to model the emission and absorption features in detail. Our analysis reveals multi-ionization and multi-velocity structures, where the combination of broad ($\sim$ 800 km/s) and narrow ($\sim$ 360 km/s) line components, along with rest-frame and blueshifted emission and absorption lines, accounts for the observed line profile complexity. We identify a modest $\sim$ 2735 km/s accretion disk wind exhibiting both absorption and emission features. We also detect a relativistic reflection feature in the spectrum, which we model using relxillNS - specifically designed to characterize X-ray reprocessing in accretion disks around neutron stars. Furthermore, we examine the detailed physics of the Fe XXV He$α$ complex, focusing on the forbidden-to-resonance line ratio under the influence of continuum pumping and optical depth effects.

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arXiv2025

The 2025 Release of Cloudy

We present the 2025 release of the spectral synthesis code Cloudy, highlighting significant enhancements to the scope and accuracy of the physics which have been made since the previous release. A major part of this development involves resolving the Lyman $α$ line into $j$-resolved fine-structure doublets, making Cloudy of use to the X-ray community. On this front, we have also updated inner-shell ionization line energies and incorporated the 1 keV feature commonly observed in X-ray binaries. Additionally, we update our in-house database, Stout, for the carbon isoelectronic sequence, improving Cloudy microphysical calculations for all wavelengths. We have also extended the molecular network by adding new silicon-bearing species, titanium-related reactions, and phosphorus-containing molecules, enhancing Cloudy's ability to model the complex chemistry relevant to rapidly growing field of exoplanet atmospheres. Finally, we outline future developments aimed at maximizing the scientific return from the current and upcoming generation of observatories, including XRISM, JWST, Roman, the Habitable Worlds Observatory (HWO) and NewAthena.

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arXiv2025

A Large Catalog of DA White Dwarf Characteristics Using SDSS and Gaia Observations

We present a catalog of 8545 and 19,257 unique DA white dwarfs observed in SDSS Data Release 19 and previous SDSS data releases, respectively. This is the largest catalog of both spectroscopic and photometric measurements of DA white dwarfs available to date, and we make this catalog and all code used to create it publicly available. We measure the apparent radial velocity, spectroscopic effective temperature and surface gravity, and photometric effective temperature and radius for all objects in our catalog. We validate our measurements against other published white dwarf catalogs. For apparent radial velocities, surface gravities, and effective temperatures measured from spectra with signal-to-noise ratios $>50$, our measurements agree with published SDSS white dwarf catalogs to within 7.5 km/s, 0.060 dex, and $2.4\%$, respectively. For radii and effective temperatures measured with Gaia photometry, our measurements agree with other published Gaia datasets to within $0.0005$ $R_\odot$ and $3\%$, respectively. We use this catalog to investigate systematic discrepancies between white dwarfs observed in SDSS-V and previous generations of SDSS. For objects observed in both SDSS-V and previous generations, we uncover systematic differences between measured spectroscopic parameters depending on which set of survey data is used. On average, the measured apparent radial velocity of a DA white dwarf is $11.5$ km/s larger and the surface gravity is $0.015$ dex smaller when a white dwarf's spectroscopic parameters are measured using SDSS-V data compared to using data from previous generations of SDSS. These differences may be due to changes in the wavelength solution across survey generations.

astro-ph.SR↗

arXiv2025

Metallicity Gradients in Modern Cosmological Simulations I: Tension Between Smooth Stellar Feedback Models and Observations

The metallicity of galaxies, and its variation with galactocentric radius, provides key insights into the formation histories of galaxies and the physical processes driving their evolution. In this work, we analyze the radial metallicity gradients of star forming galaxies in the EAGLE, Illustris, IllustrisTNG, and SIMBA cosmological simulations across a broad mass ($10^{8.0}M_\odot\leq M_\star \lesssim10^{12.0}M_\odot$) and redshift ($0\leq z\leq8$) range. We find that all simulations predict strong negative (i.e., radially decreasing) metallicity gradients at early cosmic times, likely due to their similar treatments of relatively smooth stellar feedback not providing sufficient mixing to quickly flatten gradients. The strongest redshift evolution occurs in galaxies with stellar masses of $10^{10.0}-10^{11.0}M_\odot$, while galaxies with stellar masses $< 10^{10}M_\odot$ and $>10^{11}M_\odot$ exhibit weaker redshift evolution. Our results of negative gradients at high-redshift contrast with the many positive and flat gradients in the $1 6$, the negative gradients observed with JWST and ALMA are flatter than those in simulations, albeit with closer agreement than at lower redshift. Overall, we suggest that these smooth stellar feedback galaxy simulations may not sufficiently mix their metal content radially, and that either stronger stellar feedback or additional subgrid turbulent metal diffusion models may be required to better reproduce observed metallicity gradients.

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