H$\alpha$ intensity map of the repeating fast radio burst FRB 121102 host galaxy from Subaru/Kyoto 3DII AO-assisted optical integral-field spectroscopy

Understand

We present the H$\alpha$ intensity map of the host galaxy of the repeating fast radio burst FRB 121102 at a redshift of z=0.193 obtained with the AO-assisted Kyoto 3DII optical integral-field unit mounted on the 8.2-m Subaru Telescope.

• We detected a compact H$\alpha$-emitting (i.e., star-forming) region in the galaxy, which has a much smaller angular size [$< 0&#34;.57$ (1.9 kpc) at full width at half maximum (FWHM)] than the extended stellar continuum emission region determined by the Gemini/GMOS z'-band image [$\simeq 1&#34;.4$ (4.6 kpc) at FWHM with ellipticity b/a=0.45].
• The spatial offset between the centroid of the H$\alpha$ emission region and the position of the radio bursts is $0&#34;.08 \pm 0&#34;.02$ ($0.26 \pm 0.07$ kpc), indicating that FRB 121102 is located within the star-forming region.
• This close spatial association of FRB 121102 with the star-forming region is consistent with expectations from young pulsar/magnetar models for FRB 121102, and it also suggests that the observed H$\alpha$ emission region can make a major dispersion measure (DM) contribution to the host galaxy DM component of FRB 121102.