AR_final file_2018-19

large ensemble of galaxies. With the introduction and tuning of a weighting parameter, noise bias is reduced below one per cent of the shear signal. An iterative method is used to reduce selection bias. The FPFS estimator is developed without any as- sumptions regarding galaxy morphology or any ap- proximations for PSF correction. Moreover, the method does not rely on heavy image manipula- tions or complicated statistical procedures. The FPFS shear estimator was calibrated using sev- eral Subaru HSC-like image simulations and the main results are as follows: (i) For simulations that only contain isolated galaxies, the amplitude of the multiplicative bias is below 1 percent. (ii) For more realistic simulations, which also contain blended galaxies, which are deblended by the first- generation HSC deblender before shear measure- ment a multiplicative bias of ( − 5 . 71 ± 0 . 31) percent is found. The blending bias is calibrated by image simulations. Can primordial black holes constitute dark matter? Primordial black holes (PBHs) have long been sug- gested as a viable candidate for the elusive dark matter (DM). The abundance of such PBHs has been constrained using a number of astrophysical observations, except for a hitherto unexplored mass window of M PBH =[10 − 14 ,10 − 9 ]M ⊙ . Anupreeta More , Surhud More and collaborators have car- ried out a dense-cadence (2 min sampling rate), 7 hour-long observation of the Andromeda galaxy with the Subaru Hyper Suprime-Cam to search for microlensing of stars in Andromeda by PBHs ly- ing in the halo regions of the Milky Way and An- dromeda. Given the simultaneous monitoring of tens of millions of stars in Andromeda, if such light PBHs make up a significant fraction of dark matter, they expected to find many microlensing events for the PBH-dark matter scenario. However, they identified only a single candidate event, which translates into the most stringent upper bounds on the abundance of PBHs in the mass range M PBH =[10 − 11 ,10 − 6 ]M ⊙ . Extragalactic Astronomy Forming lenticular galaxies via violent disk instability The aim of this project has been to understand the formation of lenticular (S0) galaxies which are gen- erally thought to have descended from spirals via morphological transformation, although recent nu- merical simulations have shown that minor or even major mergers can also lead to an S0-like remnant. These mechanisms, however, are active in a dense environment such as a group or a cluster of galaxies making it harder to explain the remarkable fraction of S0s found in the field. Kanak Saha and Arianna Cortesi propose a new mechanism to form S0 galaxies using the clas- sic Toomre instability that leads to disk fragmen- tation. It is shown that an isolated cold ( Q < 1) disk settled into rotational equilibrium becomes vio- lently unstable leading to fragmentation and forma- tion of stellar clumps that, in turn, not only cause the bulge to grow, but also increase the stellar disk velocity dispersion optimally in less than a billion years. Subsequently, the galaxy evolves passively without any conspicuous spiral structure. The fi- nal galaxy models resemble remarkably well the morphology and stellar kinematics of the present day S0s observed by the Planetary Nebulae spec- trograph (See Figure 7). The findings suggest a natural link between the high-redshift clumpy pro- genitors and the present-day S0 galaxies. Evidence for radial variations in the stellar mass-to-light ratio of massive galaxies from weak and strong lensing The initial mass function (IMF) for massive galax- ies expresses the mass distribution of newly formed stars in a galaxy. The IMF can be constrained by combining stellar dynamics with strong grav- itational lensing. However, this method is lim- ited by degeneracies between the density profile of dark matter and the stellar mass-to-light ratio (M/L). Surhud More and his collaborators re- duced this degeneracy by combining weak lensing ( 66 )