arXiv subjects

Sukanya Mallik

Publications and source records attributed to Sukanya Mallik.

4 recordsLinked to original sources

arXiv2026

On the Origin of the Ly$α$ Damping Wing in Galaxies at $8\le z \le 10$: Explorations using the NINJA Simulations

Ly$α$ damping wing measurements of galaxies at $7\leq z\leq14$ with the JWST provide a powerful probe of the Epoch of Reionization. We combine the large-scale cosmological hydrodynamical NINJA simulations with an idealized ionized-bubble model at z=8 and 10 to quantify the contributions of the intergalactic medium (IGM), circumgalactic medium (CGM), and interstellar medium (ISM) to the observed Ly$α$ damping wing. We generate mock Ly$α$ absorption spectra, and consider three idealized scenarios: (i) galaxies embedded in a uniformly ionized IGM, (ii) galaxies surrounded by HII regions with radii of 0-400 pkpc, and (iii) the same models including Ly$α$ absorption from partially ionized gas within the virial radius. We explore IGM neutral fractions ($x_{\rm HI}$) of 0.1, 0.8, and 1.0, and compare the distribution of inferred HI column densities (NHI) with observations to constrain the sizes of HII regions and $x_{\rm HI}$ of the IGM and gas in and around galaxies. Galaxies are surrounded by over-dense gas extending to $\sim$60-100 pkpc, with its extent increasing with halo mass and showing little evolution between z=8 and 10. The inferred NHI also increases with halo and stellar mass. While the observed incidence of damped Ly$α$ absorption and the median NHI can be reproduced by different combinations of $x_{\rm HI}$ of the IGM and HII region size, models with a uniformly ionized IGM or HII regions larger than $\sim50$ pkpc fail to reproduce the strongest absorbers (NHI>$10^{22}cm^{-2}$). Including partially ionized gas within the virial radius substantially increases the incidence of these absorbers, although the predicted values remain below the observations, suggesting an additional contribution from unresolved gas in stellar birth clouds. The strongest damped Ly$α$ absorbers therefore provide a unique probe of the ionization state of the ISM, CGM, and IGM.

astro-ph.GA↗

arXiv2024

Role of ionizing background on the non-thermal broadening inferred for the aligned absorbers

Using cosmological hydrodynamical simulations at $z\sim0.5$, we measure the thermal ($b_{t}$) and non-thermal ($b_{nt}$) contribution to the line broadening for the intergalactic absorbers having \OVI\ and \HI\ absorption well aligned in the velocity space. We find that the inferred temperature based on $b_{t}$ correlates strongly with the optical depth-weighted kinetic temperature of the absorbing gas, albeit with a large scatter. We show this scatter comes from the spread in the kinetic temperature of the gas contributing to the absorption and hence depends on the feedback processes and the ionizing UV background (UVB) used in the simulations. We show the distribution of $b_{nt}$ is also affected by both feedback processes and the ionizing UVB. Therefore, $b_{nt}$ derived using aligned absorbers may not be a good probe of sub-grid turbulence. Therefore, $b_{nt}$ derived using aligned absorbers may not be a good discriminator between the effect of microscopic turbulence and UVB. Instead, the distribution of $b_{t}$ and $b_{nt}$ together with the frequency of occurrence of the aligned absorbers can be used to place additional constraints on the parameters of the simulation for a given assumed UVB.

astro-ph.GA↗

arXiv2023

Role of ionizing background and galactic feedback on the redshift space clustering of OVI absorbers in hydrodynamical simulations

We explore the effect of ionizing UV background (UVB) on the redshift space clustering of low-$\textit{z}$ ($\textit{z} \leq 0.5$) OVI absorbers using Sherwood simulations incorporating "WIND" (i.e. outflows driven by stellar feedback) only and "AGN+WIND" feedbacks. These simulations show a positive clustering signals up to a scale of 3 Mpc. We find that the effect of feedback is restricted to small scales (i.e $\leq$ 2 Mpc or 200 $\textit{kms}^{-1} $ at $\textit{z}$ ~ 0.3) and "WIND" only simulations produce stronger clustering signal compared to simulations incorporating "AGN+WIND" feedbacks. How clustering signal is affected by the assumed UVB depends on the feedback processes assumed. For the simulations considered here the effect of UVB is confined to even smaller scales (i.e <1 Mpc or $\approx 100\textit{kms}^{-1}$ at $\textit{z}$ ~ 0.3). These scales are also affected by exclusion caused by line blending. Therefore, our study suggests clustering at intermediate scales (i.e 1-2 Mpc for simulations considered here) together with the observed column density distribution can be used to constrain the effect of feedback in simulations.

astro-ph.CO↗

arXiv2023

Role of ionizing background on the statistics of metal absorbers in hydrodynamical simulations

We study the statistical properties of O VI, C IV, and Ne VIII absorbers at low-$z$ (i.e., $z<0.5$) using Sherwood simulations with "WIND" only and "WIND+AGN" feedback and Massive black simulation that incorporates both "WIND" i.e. outflows driven by stellar feedback and AGN feedbacks. For each simulation, by considering a wide range of metagalactic ionizing UV background (UVB), we show the statistical properties such as distribution functions of column density ($N$), $b$-paramerer and velocity spread ($ΔV_{90}$), the relationship between $N$ and $b$-parameter and the fraction of Lya absorbers showing detectable metal lines as a function of $N$(H I) are influenced by the UVB used. This is because UVB changes the range in density, temperature, and metallicity of gas contributing to a given absorption line. For simulations considered here, we show the difference in some of the predicted distributions between different simulations is similar to the one obtained by varying the UVB for a given simulation. Most of the observed properties of O VI absorbers are roughly matched by Sherwood simulation with "WIND+AGN" feedback when using the UVB with a lower O VI ionization rate. However, this simulation fails to produce observed distributions of C IV and fraction of H I absorbers with detectable metals. Therefore, in order to constrain different feedback processes and/or UVBs, using observed properties of H I and metal ions, it is important to perform simultaneous analysis of various observable parameters.

astro-ph.GA↗