Paurush Punyasheel

Visted the Cosmic Dawn Center housed at Technical University of Denmark, while working on my Masters' thesis. Actively took part in workshops, guest lectures and daily activities of the DAWN DTU team.

PhD student in computational astrophysics, working on creating galaxy simulations and forward modelling them.

We use the First Light And Reionisation Epoch Simulations (FLARES) to study the evolution of the rest-frame ultraviolet (UV) and far-infrared (FIR) sizes for a statistical sample of massive (≳ 10^9M⊙) high redshift galaxies (z ∈ [5, 10]). Galaxies are post-processed using the skirt radiative transfer code, to self-consistently obtain the full spectral energy distribution and surface brightness distribution. We create mock observations of the galaxies for the Near Infrared Camera (NIRCam) to study the rest-frame UV (1500 Å) morphology. We also generate mock rest-frame FIR (50 μm) photometry and mock ALMA 158 μm (0.01′′ − 0.03′′ and ≈0.3′′ angular resolution) observations to study the dust-continuum sizes. We find the effect of dust on observed sizes reduces with increasing wavelength fromthe UV to optical (∼ 0.6 times the UV at 0.4μm), with no evolution in FIR sizes. Observed sizes vary within 0.4−1.2 times the intrinsicsizes at different signal to noise ratios (SNR = 5-20) across redshifts. The effect of PSF and noise makes bright structures prominent, whereas fainter regions blend with noise, leading to an underestimation (factor of 0.4 − 0.8) of sizes at SNR=5. At SNR=15-20, the underestimation reduces (factor of 0.6 − 0.9) at z = 5 − 8 but due to PSF, at z = 9 − 10, bright cores are dominant, resulting inan overestimation (factor of 1.0-1.2) of sizes. For ALMA, low (≈0.3′′) resolution sizes are effected by noise which acts as extended emission. The size evolution in UV broadly agrees with current observational samples and other simulations. This work is one of the first to analyse the panchromatic sizes of a statistically significant sample of simulated high-redshift galaxies, complementing agrowing body of research highlighting the importance of conducting an equivalent comparison between observed galaxies and their simulated counterparts in the early Universe.

Recent observations have revealed intriguing offsets between the UV and FIR emission in high redshift galaxies. In this study, we use the First Light And Reionisation Epoch Simulations (FLARES) to compute the spatial offset of ultraviolet (UV) and far-infrared (FIR) centres for a statistical sample (6890) of massive (M*>10^9) high redshift galaxies (z>5). The galaxies are post-processed with the SKIRT radiative transfer code, to obtain the full spectral energy distribution and surface brightness profile. We simulate \textit{James Webb Space Telescope (JWST)} Near Infrared Camera (NIRCam; rest-frame 1500 Å) and ALMA rest-frame 158 \um\ observations of the galaxies and then calculate the distance between the UV-FIR centres to analyse which physical processes drive the observed UV - FIR spatial offset. We find that nearly 16% of galaxies exhibit spatial offsets greater than 2.5 kpc between their UV and FIR emission peaks. We establish that the spatial offsets do not correlate with stellar mass, UV/FIR luminosity, and size. Offsets also do not correlate with AGN feedback or with large-scale environment or merger history. Galaxies with significant offsets preferentially have bluer UV slopes [-2.5,-1.5], consistent with recent star formation and dust-attenuated cores displacing the observed UV centroid. They show an accelerated star formation history, forming half their z=5 stellar mass ~0.1 Gyr earlier than galaxies without offsets. These galaxies are enriched earlier than galaxies without an offset and show enhanced stellar metallicities, indicating a transition to an outward growth at higher redshifts (z>6).

Worked on my thesis at the Cosmic Dawn Center housed at Technical University of Denmark, using forward modeled ultra high redshift galaxies in hydrodynamical simulation (FLARES). Post processed the galaxies using SKIRT radiative transfer code to mock NIRCAM \& ALMA observations. Studied the size and structure evolution of galaxies in a high redshift universe with cosmic time. Observational Sizes have a substantial inaccuracy compared to actual sizes. Further studied the nature and abundances of dust by comparing the IR and UV continuum. Also investigated the environmental effects on the morphological and spatial properties of the galaxies.

Worked on image analysis on the data provided by PanSTARRS Observatory at University of Hawaii in a citizen scientist effort. Used Astrometrica, a scientific grade astrometric data reduction tool for CCD images, to analyze moving objects in the observations, and identify possible asteroids with one successful preliminary discovery.

Worked on a CubeSat (EINSAT) at my university, which aims to be deployed to low-earth orbit and monitor stars to detect exoplanet transits by precision photometry. Focused on developing and simulating photometric reduction procedures, and computing standards to cope with low downlink rates.