34th Annual Report (2021-22)

20 observations of 23 newly discovered radio- loud quasars (RLQs) at 2.7 < z < 3.3 from the SALT survey. Their sample consists of powerful AGN brighter than 200 mJy at 1.4 GHz and is selected on the basis of mid- infrared colours i.e. unbiased to the presence of dust. Based on this survey they reported seven confirmed and five tentative detections of diffuse Ly α emission in the sample. They derived all the properties of diffuse Ly α emission and explored in detail its relationship to different quasar properties. They found strong dependence of Ly α halo detection rate on the extent of radio source, spectral luminosity of RLQ at 420 MHz, presence of associated C IV absorption and nuclear He II emission line equivalent width. As seen in previous surveys, the full width at half-maximum of diffuse Ly α emission in the case of confirmed detections are much higher (i.e. >1000 km/s in all, except one). Using the samples of high-z radio-loud quasars and galaxies from literature, they confirmed the correlation between the Ly α halo luminosity and its size with radio continuum luminosity. The same quantities are found to be correlating weakly with the projected linear size of the radio emission. This sample is the second largest sample of RLQs being studied for the presence of diffuse Ly α emission and fills in a redshift gap between previous such studies. The main results from this survey are presented in a recent paper published in MNRAS. This work also formed the main part of the PhD thesis of Dr. Gitika Shukla. Time variations of Ultra Fast Outflows (UFOs): Broad Absorption Line (BAL) quasars are defined by the presence of absorption lines with large velocity widths ( ~few 1000 km/s ) and ejection velocities (reaching upto few 10000 km/s ). It is believed that these outflows could play an important role in the central black hole growth, the host galaxy evolution and the chemical enrichment of the intergalactic medium (IGM). Detailed investigation of the time variability of BAL profiles is important to obtain tight constraints on the BAL lifetime, location of the outflow etc., and provide significant insights on the origin and physical mechanisms driving the flow. For more than 5 years, IUCAA astronomers (P. Aromal and R. Srianand) have been investigating the time variability of a sample of 62 quasars from SDSS DR15 which show BALs at outflow velocities greater than 15000 km/s in their spectra using SALT. This is by far the largest sample of such objects monitored over a wide range of time scales (i.e from fewmonths to 10 year in the quasar's rest frame). This sample has revealed emergence/disappearance of new outflow components, signatures of acceleration in some absorbing gas, correlated variability between different absorption components spread over large velocity ranges etc. Thanks to the presence of all sky photometric monitoring surveys like Zwicky Transient Factory (ZTF) it is now possible to probe the relationship between the spectral line variability and photometric light curves. Overall it appears that the amplitude of variability seen in absorption lines are much larger than what one will predict based on continuum variability from optical light curves. This either means the absorption line variabilities are either driven by line-of-sight variations in the matter distribution or the UV radiation field in these quasars have a much larger amplitude variability compared to what one sees in the optical light curves. Detailed analysis of couple of very interesting targets were published recently in MNRAS. The main survey results will form the PhD thesis work of P. Aromal. Host galaxies of Ultra Strong Mg II absorbers (USMG II): It is well documented that Mg II absorption lines seen in the spectra of quasar probe the extended gas around normal galaxies. Ultra Strong Mg II absorbers are defined as absorbers (having rest equivalent width in excess of 3 Å, are ideal targets for studying the gas flows at low impact parameters to star-forming galaxies and/or interacting groups of galaxies. Studying such systems can provide important insights into the baryonic cycle that governs the galaxy evolution. Motivated by this, Astronomers from IUCAA (Labanya Guha & Srianand) and their collaborators have embarked on the first systematic survey of of such systems at z~0.5 with the aim to (i) identify their host galaxies and characterise the galaxy environment around these absorbers, (ii) investigate whether we preferentially select a particular galaxy population using the ultra strong absorber selection, (iii) study the connection between the galaxy properties and that of the absorption features, and (iv) identify potential quasar–galaxy pairs where galactic outflow can be studied through down-the-barrel absorption towards the galaxy, and absorption along the quasar line of sight s imu l t aneou s l y . Th i s s u r v e y ha s substantially increased the known host galaxies of such absorbers. The reported that at least ~33 per cent of the USMg II host galaxies (with a limiting magnitude of m < r 23.6) are isolated and the large equivalent widths measured in these cases may originate from gas flows (infall/outflow) in single haloes of massive but not starburst galaxies. They also found galaxy interactions could be responsible for large velocity widths in at least ~17 per cent cases. The catalog of galaxies generated from this survey and main results are published recently in MNRAS. The team has just now completed a complementary survey at z~0.8 using SALT that will enable one to study the evolution of gas flows in galaxies over cosmic time. This survey will form the main body of the PhD work of Labanya Guha.