Con­straints on the spin tem­per­a­ture of inter­galac­tic hydro­gen at a red­shift of z = 8.4, derived from upper lim­its on the 21 cm sig­nal mea­sured by PAPER. Gray regions are excluded at 95% con­fi­dence. At this red­shift, the spin tem­per­a­ture is equiv­a­lent to the phys­i­cal (kinetic) tem­per­a­ture of the gas. These lim­its rule out “cold reion­iza­tion” sce­nar­ios, requir­ing sources of energy to heat the inter­galac­tic medium.

My research is in the field of 21 cm cos­mol­ogy, which uses low fre­quency radio astron­omy to explore the his­tory of the uni­verse.  By observ­ing the highly red­shifted hyper­fine (21 cm) line of neu­tral hydro­gen, one can make a three-dimensional map span­ning cos­mic his­tory, from the dark ages to rel­a­tively recent times.  Depend­ing on the epoch being probed, these obser­va­tions can be used to study dark energy, the physics of early galaxy and star for­ma­tion, and poten­tially even probe the pri­mor­dial con­di­tions of the uni­verse dur­ing the infla­tion­ary epoch.  Because of the chal­lenges to recov­er­ing this infor­ma­tion — such as ter­res­trial radio inter­fer­ence and Galac­tic fore­ground emis­sion — these stud­ies uti­lize spe­cial­ized radio tele­scope exper­i­ments specif­i­cally designed for 21 cm cos­mol­ogy work.

Although I have been involved in nearly all aspects of the 21 cm cos­mol­ogy com­mu­nity, my cur­rent prin­ci­pal con­tri­bu­tions to the field lie at the inter­face between data analy­sis and cos­mol­ogy.  I focus on using the lat­est algo­rithms in fore­ground iso­la­tion and removal to char­ac­ter­ize the chal­lenges fac­ing these exper­i­ments and explore their effects on recov­er­ing the sci­en­tific sig­nal.  Using these lessons, I have also designed a novel 21 cm exper­i­ment tar­get­ing a mea­sure­ment of dark energy: the BAO Broad­band and Broad-beam (BAOBAB) array.  Lately, I have also focused on how to use pre­lim­i­nary upper lim­its from 21 cm exper­i­ments to con­strain the physics of reionization.