Nissim Kanekar

My main research interests are in the areas of galaxy formation and evolution, tests of fundamental physics, and the interstellar medium of galaxies. Individual areas are described in more detail below:


Fundamental constant evolution:

Astronomical studies provide the only avenue to test for changes in the fundamental constants of physics, such as the fine structure constant and the proton-electron mass ratio, over cosmological timescales, billions of years. My research in this field involves using radio spectroscopy of high redshift galaxies to accurately measure the redshifts of different types of spectral lines (e.g. the HI 21cm hyperfine line, ammonia inversion lines, hydroxyl Lambda-doubled lines, carbon monoxide rotational lines, etc) to test for changes in the fundamental constants. I also work on devising new techniques for this purpose, based on theoretical studies of new molecules.


Galaxy evolution:

In galaxy evolution, my research has focussed on understanding the nature of and evolution of high redshift gas-rich galaxies that are detected due to their strong absorption of the light of background quasars. I use radio absorption studies of such galaxies to study the evolution of physical conditions in their interstellar media. We have shown that atomic gas in these galaxies is predominantly warm at high redshifts, apparently due to their low metallicity and a paucity of cooling routes. We have also come up with a new method to image such galaxies, based on quasar sightlines with two absorbers, and using the higher-redshift absorber as a ''blocking filter'' to blank out the background quasar at certain wavelengths so that one can then image the lower redshift galaxy. We are currently carrying out imaging and spectroscopic studies of a large sample of such galaxies with the Keck Telescope and the Hubble Space Telescope, as well as radio spectroscopic imaging of low-redshift absorbers, to determine their size, mass, etc.


The Interstellar Medium:

My work on the interstellar medium of the Milky Way has aimed to understand the distribution of gas between different temperature phases, and specifically whether gas exists in the ``unstable'' temperature phase, ~ 1000 K. Our studies have found evidence for significant amounts of gas in this unstable phase, which is not expected in standard three-phase models of the ISM. We are currently attempting to carry out a self-consistent modeling of hydrogen absorption and emission spectra, to obtain a better understanding of physical conditions in the ISM.


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