ORCID Profile
0000-0002-7714-2379
Current Organisations
Australian National University
,
Raman Research Institute
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Publisher: Oxford University Press (OUP)
Date: 26-11-2021
Abstract: The hot component of the circumgalactic medium (CGM) around star-forming galaxies is detected as diffuse X-ray emission. The X-ray spectra from the CGM depend on the temperature and metallicity of the emitting plasma, providing important information about the feeding and feedback of the galaxy. The observed spectra are commonly fitted using simple one-temperature (1-T) or two-temperature (2-T) models. However, the actual temperature distribution of the gas can be complex because of the interaction between galactic outflows and halo gas. Here, we demonstrate this by analysing 3D hydrodynamical simulations of the CGM with a realistic outflow model. We investigate the physical properties of the simulated hot CGM, which shows a broad distribution in density, temperature, and metallicity. By constructing and fitting the simulated spectra, we show that, while the 1-T and 2-T models are able to fit the synthesized spectra reasonably well, the inferred temperature(s) does not bear much physical meaning. Instead, we propose a lognormal distribution as a more physical model. The lognormal model better fits the simulated spectra while reproducing the gas temperature distribution. We also show that when the star formation rate is high, the spectra inside the biconical outflows are distinct from those outside, as outflows are generally hotter and more metal enriched. Finally, we produce mock spectra for future missions with the eV-level spectral resolution, such as Athena, Lynx, the Hot Universe Baryon Surveyor, and theX-ray Imaging and Spectroscopy Mission.
Publisher: American Astronomical Society
Date: 30-04-2020
Publisher: Oxford University Press (OUP)
Date: 23-12-2020
Abstract: We study the synchrotron radio emission from extra-planar regions of star-forming galaxies. We use ideal magnetohydrodynamic simulations of a rotating Milky Way-type disc galaxy with distributed star formation sites for three star formation rates (0.3, 3, 30 M⊙ yr−1). From our simulations, we see emergence of galactic-scale magnetized outflows, carrying gas from the disc. We compare the morphology of the outflowing gas with hydrodynamic simulations. We look at the spatial distribution of magnetic field in the outflows. Assuming that a certain fraction of gas energy density is converted into cosmic ray energy density, and using information about the magnetic field, we obtain synchrotron emissivity throughout the simulation domain. We generate the surface brightness maps at 1.4 GHz. The outflows are more extended in the vertical direction than radial and hence have an oblate shape. We further find that the matter right behind the outer shock shines brighter in these maps than that above or below. To understand whether this feature can be observed, we produce vertical intensity profiles. We convolve the vertical intensity profile with the typical beam sizes of radio telescopes, for a galaxy located at 10 Mpc to estimate the radio scale height and compare with observations. The radio scale height is ∼300–1200 pc, depending on the resolution of the telescope. We relate the advection speed of the outer shock with the surface density of star formation as ${\\rm v}_{\\rm adv} \\propto \\Sigma _{\\rm SFR}^{0.3}$, which is consistent with earlier observations and analytical estimates.
Publisher: Oxford University Press (OUP)
Date: 29-01-2018
DOI: 10.1093/MNRAS/STY198
Publisher: Oxford University Press (OUP)
Date: 14-07-2023
Abstract: Interstellar medium (ISM) and circumgalactic medium (CGM) around galaxies are linked to several physical processes that drive galaxy evolution. For ex le, the X-ray emission from the CGM gas around ellipticals has been linked to the active galactic nucleus (AGN) feedback occurring in the host. Upcoming telescopes, such as Hot Universe Baryon Survey (HUBS) with ∼2 eV resolution, can provide us with deep insights about the hot gas properties of such galaxies that constrain these processes. In this project, we discuss X-ray emission of the ISM and CGM of elliptical galaxies simulated using macer code. We generate X-ray emission data from the macer simulations with various feedback models and produce mock observations for an instrument with high spectral resolution, which is a necessary step of selecting sources for the future observations with planned mission such as HUBS. More importantly, we establish connections between the physics of AGN and stellar feedback with the emission spectra from the ISM and CGM to investigate the possibility of using observations to constrain feedback models. We fit the X-ray spectra from these simulations with standard fitting procedures and compare the retrieved physical properties with their counterparts from the simulations to understand whether the future high-resolution observations can reliably reveal the properties of the gas in the galaxies.
Publisher: Oxford University Press (OUP)
Date: 29-01-2022
Abstract: We present low-frequency observations at 315 and 745 MHz of the edge-on, nearby galaxy NGC 4631 with upgraded Giant Metrewave Radio Telescope. We compare the observed surface brightness profiles along the minor axis of the galaxy with those obtained from hydrodynamical simulations of galactic outflows. These are 3D simulations that replicate star formation in a Milky-Way-sized galaxy and follow magnetized outflows emerging from the disc. We detect a plateau-like feature in the observed emission at a height of 2–3 kpc from the mid-plane of the galaxy, in qualitative agreement with that expected from simulations. This feature is believed to be due to the compression of magnetic fields behind the outer shocks of galactic outflows. We model the observed surface brightness profiles by assuming an exponential as well as a Gaussian fitting model. Using χ2 statistics, we find that the exponential model fits the profiles better and we use it to determine the scale heights. We estimate the scale height for the synchrotron radio emission to be ∼1 kpc. The time-scales for advection due to outflows and diffusion of cosmic ray electrons are ≳5 and ∼160 Myr, respectively. Because advection acts on a time-scale much shorter than diffusion, we conclude that in NGC 4631 advection, rather than diffusion, plays the dominant role in the formation of radio halo. The spectral index image with regions of flatter radio spectral index in the halo appears to indicate possible effects of gas outflow from the plane of the galaxy.
Location: India
No related grants have been discovered for Aditi Vijayan.