Research Highlights
Absorber-Galaxy Connection at low redshift:
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Absorber-Galaxy Connection at high redshift:
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Dependence of Residual Rotation Measure (RRM) on Intervening MgII Absorbers at Cosmic Distances:
We investigate the dependence of residual rotation measure (RRM) on intervening absorption systems at cosmic distances by using a large sample of 539 SDSS quasars in conjunction with the available rotation measure catalog at around 21cm wavelength. We found an excess extragalactic contribution in standard deviation of observed RRM of about 8.11+/-4.83 Rad/m^2 in our sample with intervening MgII absorber as compare to the sample without MgII absorber. Our results suggest that intervening absorbers could contribute to the enhancement of RRM at around 21cm wavelength, as was found earlier for RM measurements at around 6cm wavelength. |
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Incidence of Strong MgII Absorbers Towards Different Types of Quasars :
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The canonical view of intervening and associated absorber of QSOs got questioned few year back, when factor of about four excess was reported in dN/dz, of Mg ii absorber along GRB sight-line compare to normal QSOs sight line. We investigate this question by searching strong MgII absorbers towards ~9000 radio-loud quasars of core-dominated (CDQs) and lobe-dominated (LDQs) types in SDSS.
We find that dN/dβ distribution (with β=v/c) for CDQs shows a significant excess, at β in the range 0.05-0.1. This leads us to infer that a significant fraction of strong MgII absorption systems seen in this offset velocity range are probably associated with the CDQs and might be accelerated into the line of sight by their powerful jets and/or due to the accretion-disk outflows close to our direction. Thus, it appears that for CDQs the associated strong MgII absorbers can be seen at much larger velocities relative to the nucleus than the commonly adopted upper limit of 5000km/s. |
Origin of continuum variability in quasars: dependence on Black-hole properties
In the context of AGN unification scheme rapid variability properties play an important role in understanding any intrinsic differences between sources in different classes. In this respect any clue based on spectral properties will be very useful toward understanding the mechanisms responsible for the origin of rapid small scale optical variations, or microvariability. We have developed a novel approach for modelling the quasar optical spectra to get the AGN key parameters (e.g., Black-hole mass and Eddington ratio). For this we started a pilot project to get the spectra of quasars searched for optical microvariability using 2m- IGO and HCT telescopes, India. We have ruled out weak jet component model responsible for microvariability nature of radio-quiet quasars. A similar study using simultaneous photometric and spectral variability study will be helpful to constrain the mechanism/factors responsible for the microvariability. |
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Optical microvariability properties of BALQSOs:
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