Amit Pathak
Tezpur University
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Featured researches published by Amit Pathak.
Monthly Notices of the Royal Astronomical Society | 2015
Tanvir Hussain; Sowgat Muzahid; Anand Narayanan; R. Srianand; Bart P. Wakker; Jane C. Charlton; Amit Pathak
We report the detection of Ne VIII in a z_abs = 0.59961 absorber towards the QSO PG 1407+265 (z_em = 0.94). Besides Ne VIII, absorption from HI Lyman series lines (HI 1025 - 915), several other low (C II, N II, O II, and S II), intermediate (C III, N III, N IV, O III, S IV, and S V) and high (S VI, O VI, and Ne VIII) ionization metal lines are detected. Disparity in the absorption line kinematics between different ions implies that the absorbing gas comprises of multiple ionization phases. The low and the intermediate ions (except S V) trace a compact (~ 410 pc), metal-rich (Z ~ Z_sun) and over-dense (log n_H ~ -2.6) photoionized region that sustained star-formation for a prolonged period. The high ions, Ne VIII and O VI, can be explained as arising in a low density (-5.3 Z_sun) and diffuse (~ 180 kpc) photoionized gas. The S V, S VI and C IV (detected in the FOS spectrum) require an intermediate photoionization phase with -4.2 < log n_H < -3.5. Alternatively, a pure collisional ionization model, as used to explain the previous known Ne VIII absorbers, with 5.65 < log T < 5.72, can reproduce the S VI, O VI, and Ne VIII column densities simultaneously in a single phase. However, even such models require an intermediate phase to reproduce any observable S V and/or C IV. Therefore, we conclude that when multiple phases are present, the presence of Ne VIII is not necessarily an unambiguous indication of collisionally ionized hot gas.
Monthly Notices of the Royal Astronomical Society | 2017
Tanvir Hussain; Vikram Khaire; R. Srianand; Sowgat Muzahid; Amit Pathak
Ne VIII absorbers seen in QSO spectra are useful tracers of warm ionized gas, when collisional ionization is the dominant ionization process. While photoionization by the ultraviolet background (UVB) is a viable option, it tends to predict large line-of-sight thickness for the absorbing gas. Here, we study the implications of the recently updated UVB at low-z to understand the ionization mechanisms of intervening Ne VIII absorbers. With the updated UVB, one typically needs higher density and metallicity to reproduce the observed ionic column densities under photoionization. Both reduce the inferred line-of-sight thicknesses of the absorbers. We find a critical density of
Monthly Notices of the Royal Astronomical Society | 2015
Mridusmita Buragohain; Amit Pathak; Peter J. Sarre; Takashi Onaka; Itsuki Sakon
\geq5\times10^{-5}
Planetary and Space Science | 2016
Mridusmita Buragohain; Amit Pathak; Peter J. Sarre; Takashi Onaka; Itsuki Sakon
cm
Monthly Notices of the Royal Astronomical Society | 2015
R. Sarma; S. Tripathi; Ranjeev Misra; Gulab C. Dewangan; Amit Pathak; J. K. Sarma
^{-3}
The Astrophysical Journal | 2017
Aishawnnya Sharma; G. R. Gupta; Durgesh Tripathi; Vinay L. Kashyap; Amit Pathak
above which the observed N(Ne VIII)/N(O VI) can be reproduced by pure collisional processes. If the gas is of near solar metallicity (as measured for the low ions) then the cooling timescales will be small (<
Publications of the Astronomical Society of the Pacific | 2015
P. Shalima; Rupjyoti Gogoi; Amit Pathak; Ranjeev Misra; Ranjan Gupta; D. B. Vaidya
10^{8}
Advances in Space Research | 2014
Rathin Sarma; Amit Pathak; Ananta C. Pradhan; Jayant Murthy; J. K. Sarma
yrs). Therefore, a continuous injection of heat is required in order to enhance the detectability of the collisionally ionized gas. Using photoionization models we find that in almost all Ne VIII systems the inferred low ion metallicity is near solar or supersolar. If we assume the Ne VIII phase to have similar metallicities then photoionization can reproduce the observed N(Ne VIII)/N(O VI) without the line-of-sight thickness being unreasonably large and avoids cooling issues related to the collisional ionization at these metallicities. However the indication of broad Ly
FIRST INTERNATIONAL CONFERENCE ON CHEMICAL EVOLUTION OF STAR FORMING REGION AND ORIGIN OF LIFE: Astrochem2012 | 2013
Mridusmita Buragohain; Amit Pathak; M. Hammonds; Peter J. Sarre
\alpha
The Astrophysical Journal | 2011
Ananta C. Pradhan; Jayant Murthy; Amit Pathak
absorption in a couple of systems, if true, suggests that the Ne VIII phase is distinct from the low ion phase having much lower metallicity.