Suryadeep Ray

Research Summary:

I have been primarily working on the following projects for the past one year.
1) Performance Characteristics of TreePM codes (with J.S. Bagla) :
The TreePM code is a hybrid technique for carrying out large N-Body simulations to study formation and evolution of the large scale structures in the Universe. It is a combination of the Barnes and Hut (1986) Tree code and a Particle-Mesh code. We have been working on a comprehensive error analysis for the force given by the TreePM code for various possible combinations of the parameters involved in the theory. The error analysis tries to suggest an optimum configuration for the code.
2) A Study of Bias in Scale-Invariant Models (with J.S. Bagla) :
It is a well-established fact that light does not follow mass even on very large scales, i.e., the distribution of galaxies does not necessarily trace the underlying density field. Current observations tell us only about the clustering properties of galaxies. On the other hand, we have analytic and numerical models for clustering properties of dark matter. Thus there is an additional function that we need to define - a function that describes the difference between clustering of dark matter and galaxies. Unless we can model this function there is little hope for a detailed comparison of models with observations. This is particularly true of clustering at small scales. This function is what we call bias in the literature. In this work, we are trying to study the effect of bias on clustering of overdense regions in N-Body simulations. These simulations are being carried out using the TreePM code.
3) Scaling Relations for Gravitational Clustering in Two Dimensions in Scale-Invariant Models (with J.S. Bagla, T. Padmanabhan) :
A number of attempts has been made in recent years to study the evolution of non-linear gravitational clustering using certain non-linear scaling relations between non-linear and linearly extrapolated correlation functions. Attempts have also been made to verify such relations using N-body simulations. However, the limited dynamical range of currently available three-dimensional N-body simulations poses serious difficulties in investigating this problem in greater detail. We can circumvent this problem by simulating a two-dimensional system wherein a much higher dynamic range can be achieved. In this work, we aim to study generic features, like non-linear scaling relations, which are independent of dimension, using a high-resolution two dimensional TreePM code.
4) Testing the Zeldovich Approximation with N-body Simulations (with J.S. Bagla, Jayanti Prasad) :
A long standing puzzle in gravitational collapse in an expanding universe is the favoured geometry of large scale structures. The Zel'dovich approximation predicts that generic local collapse is on to sheet like objects called pancakes. However, N-Body simulations have so far not revealed any tendency of collapse on to sheets even though they compare well with Zel'dovich approximation at large scales. One of the suggestions has been that the sheets fragment into small ellipsoidal objects very rapidly and these objects remain arranged along the original sheet. We are testing this hypothesis with a series of N-Body simulations where we follow the collapse of a single sheet with varying amount of substructure.

Publications:

Performance Characteristics of TreePM codes (J.S. Bagla, Suryadeep Ray) - astro-ph 0212129. Accepted for publication in New Astronomy.

Conference/Workshops Attended:

1) SERC School on Cosmology and Structure Formation, June 2002, I.I.T Kharagpur.
2) Meeting of the Astronomical Society of India, February 2003, Trivandrum.

Visits to other Institutes:

Visited the Department of Physics and Astrophysics, University of Delhi, Delhi, RRI, Bangalore, IIA, Bangalore and TIFR, Mumbai in February 2003 as a TPSC speaker.

Invited Lectures/Seminars:

1) Study of Bias in Power Law Models (TPSC seminar) : delivered at the Department of Physics and Astrophysics, University of Delhi, Delhi, RRI, Bangalore, IIA, Bangalore and TIFR, Mumbai in February 2003.
2) Presented a Poster Paper ``Study of Bias in Power Law Models'' at the A.S.I. meeting, Trivandrum, February 2003.

Other Activities:

Gave a talk titled ``Performance Characteristics of the TreePM code'' in July 2002 at HRI.
Gave an Astrophysics Journal Club talk ``Correlation Function Measurements from the CFRS Survey (Lilly et al, 1996 ApJ, 461, 534)'' in October 2002 at HRI.