AR-2019-2020

Their total contribution to Ω HI is ∼ 55 − 70%, the variation depending on the definition of popula- tion. The dominant populations at the low mass end, log 10 ( M HI h 2 70 / M ) ≤ 8 . 0 are the faint blue and faint bluer populations, the latter’s dominance being sensitive to its definition. The full blue (blue– bluer luminous and faint) population represents ∼ 80% of Ω HI . A bimodal HIMF suggested by our results is, however, not seen since the amplitude of the HIMF of the luminous red population is small compared to that of the luminous blue population. This work has been done in collaboration with Saili Dutta, and Biprateep Dey. Nagendra Kumar Turbulence effect on the stability of molecular cloud Observations show that molecular clouds are the sites of star formation and have a clumpy struc- ture. Since some properties of massive molecular clouds can not be explained by isothermal equa- tion of state, so an alternative form of equation of state, i.e. logatropic equation of state is consid- ered to study the stability of molecular cloud. So stability of self-gravitating, magnetized and warm molecular cloud is studied taking into account the turbulence effect. We consider molecular cloud as a partially ionized composed of ions and neutrals, self-gravitating, warm and magnetized medium. A logarithmic term is added in the equation of state to include the effect of turbulent motion. A bi- quadratic dispersion relation is obtained, and is dis- cussed in a special case by ignoring friction between ions and neutrals. It is found that waves propagate with faster speed if perturbation wavelength is less than the Jeans length of the ion component and greater than the Jeans length of the neutral com- ponent. This work has been done in collaboration with Meenakshi Yadav. Suresh Kumar Testing the warmness of dark matter Dark matter (DM) as a pressureless perfect fluid provides a good fit of the standard ΛCDM model to the astrophysical and cosmological data. In this work, we investigate two extended properties of DM: a possible time dependence of the equa- tion of state of DM via Chevallier-Polarski-Linder parametrization, w dm = w dm0 + w dm1 (1 − a ), and the constant non-null sound speed ˆ c 2 s , dm . We ana- lyze these DM properties on top of the base ΛCDM model by using the data from Planck cosmic mi- crowave background (CMB) temperature and po- larization anisotropy, baryonic acoustic oscillations (BAO) and the local value of the Hubble constant from the Hubble Space Telescope (HST). We find new and robust constraints on the extended free parameters of DM. The most tight constraints are imposed by CMB + BAO data, where the three parameters w dm0 , w dm1 and ˆ c 2 s , dm are respectively constrained to be less than 1 . 43 × 10 − 3 , 1 . 44 × 10 − 3 and 1 . 79 × 10 − 6 at 95% CL. All the extended parameters of DM show consistency with zero at 95% CL, indicating no evidence beyond the CDM paradigm. We notice that the extended proper- ties of DM significantly affect several parameters of the base ΛCDM model. In particular, in all the analyses performed here, we find significantly larger mean values of H 0 and lower mean values of σ 8 in comparison to the base ΛCDM model. Thus, the well-known H 0 and σ 8 tensions might be recon- ciled in the presence of extended DM parameters within the ΛCDM framework. Also, we estimate the warmness of DM particles as well as its mass scale, and find a lower bound: ∼ 500 eV from our analyses. This work has been done in collaboration with Rafael C. Nunes, and Santosh Kumar Yadav. Constraints on Bianchi type-I spacetime extension of the standard Λ CDM model We consider the simplest anisotropic generaliza- tion, as a correction, to the standard ΛCDM model, by replacing the spatially flat Robertson-Walker metric by the Bianchi type-I metric, which brings in a new term Ω σ 0 a − 6 (mimicking the stiff fluid) in the average expansion rate H ( a ) of the universe. From Hubble and Pantheon data, relevant to the late universe ( z 2 . 4), we obtain the constraint Ω σ 0 10 − 3 , in line with the model independent constraints. When the baryonic acoustic oscilla- tions and cosmic microwave background (CMB) data are included, the constraint improves by 12 orders of magnitude, i.e., Ω σ 0 10 − 15 . We find that this constraint could alter neither the matter- radiation equality redshift nor the peak of the mat- ter perturbations. Demanding that the expansion anisotropy has no significant effect on the stan- dard Big Bang Nucleosynthesis (BBN), we find the constraint Ω σ 0 10 − 23 . We show explicitly that the constraint from BBN renders the expansion