Search for: All records

Abstract We used the Condor Array Telescope to obtain deep imaging observations through luminance broadband and Heii, [Oiii], Hei, Hα, [Nii], and [Sii] narrowband filters of an extended region of the M81 Group spanning ≈8 × 8 deg²on the sky centered near M81 and M82. Here, we report aspects of these observations that are specifically related to (1) a remarkable filament known as the “Ursa Major Arc” that stretches ≈30° across the sky roughly in the direction of Ursa Major, (2) a “giant shell of ionized gas” that stretches ≈0.8 deg across the sky located ≈0.6 deg northwest of M82, and (3) a remarkable network of ionized gaseous filaments revealed by the new Condor observations that appear to connect the arc, the shell, and various galaxies of the M81 Group and, by extension, the group itself. We measure flux ratios between the various ions to help to distinguish photoionized from shock-ionized gas, and we find that the flux ratios of the arc and shell are not indicative of shock ionization. This provides strong evidence against a previous interpretation of the arc as an interstellar shock produced by an unrecognized supernova. We suggest that all of these objects, including the arc, are associated with the M81 Group and are located at roughly the distance (≈3.6 Mpc) of M81, that the arc is an intergalactic filament, and that the objects are associated with the low-redshift cosmic web. 

Abstract We used the Condor Array Telescope to obtain deep imaging observations through the luminance broadband and Heii468.6 nm, [Oiii] 500.7 nm, Hei587.5 nm, Hα, [Nii] 658.4 nm, and [Sii] 671.6 nm narrowband filters of an extended region comprising 13 “Condor fields” spanning ≈ 8 × 8 deg²on the sky centered near M81 and M82. Here we describe the acquisition and processing of these observations, which together constitute unique very deep imaging observations of a large portion of the M81 Group through a complement of broad- and narrowband filters. The images are characterized by an intricate web of faint, diffuse, continuum produced by starlight scattered from Galactic cirrus, and all prominent cirrus features identified in the broadband image can also be identified in the narrowband images. We subtracted the luminance image from the narrowband images to leave, more or less, only line emission in the difference images, and we masked regions of the resulting images around stars at an isophotal limit. The difference images exhibit extensive extended structures of ionized gas in the direction of the M81 Group, from known galaxies of the M81 Group, clouds of gas, filamentary structures, and apparent or possible bubbles or shells. Specifically, the difference images show a remarkable filament known as the “Ursa Major Arc;” a remarkable network of criss-crossed filaments between M81 and NGC 2976, some of which intersect and overlap the Ursa Major Arc; and details of a “giant shell of ionized gas.”