We present deep, narrowband imaging of the nearby spiral galaxy M101 and its satellites to analyze the oxygen abundances of their H ii regions. Using Case Western Reserve University’s Burrell Schmidt telescope, we add to the narrowband data set of the M101 Group, consisting of Hα, Hβ, and [O iii] emission lines and the blue [O ii] λ3727 emission line for the first time. This allows for complete spatial coverage of the oxygen abundance of the entire M101 Group. We used the strong-line ratio R 23 to estimate oxygen abundances for the H ii regions in our sample, utilizing three different calibration techniques to provide a baseline estimate of the oxygen abundances. This results in ∼650 H ii regions for M101, 10 H ii regions for NGC 5477, and ∼60 H ii regions for NGC 5474, the largest sample for this Group to date. M101 shows a strong abundance gradient, while the satellite galaxies present little or no gradient. There is some evidence for a flattening of the gradient in M101 beyond R ∼ 14 kpc. Additionally, M101 shows signs of azimuthal abundance variations to the west and southwest. The radial and azimuthal abundance variations in M101 are likely explained by an interaction it had with its most massive satellite, NGC 5474, ∼300 Myr ago combined with internal dynamical effects such as corotation.

We present deep, narrowband imaging of the nearby spiral galaxy M101 and its group environment to search for star-forming dwarf galaxies and outlying H II regions. Using the Burrell Schmidt telescope, we target the brightest emission lines of star-forming regions, Hα, Hβ, and [O III], to detect potential outlying star-forming regions. Our survey covers ∼6 deg 2 around M101, and we detect objects in emission down to an Hα flux level of 5.7 × 10 −17 erg s −1 cm −2 (equivalent to a limiting SFR of 1.7 × 10 −6 M yr −1 at the distance of M101). After careful removal of background contaminants and foreground M stars, we detect 19 objects in emission in all three bands, and 8 objects in emission in Hα and [O III]. We compare the structural and photometric properties of the detected sources to Local Group dwarf galaxies and star-forming galaxies in the 11HUGS and SINGG surveys. We find no large population of outlying H II regions or undiscovered star-forming dwarfs in the M101 Group, as most sources (93 %) are consistent with being M101 outer disk H II regions. Only two sources were associated with other galaxies: a faint star-forming satellite of the background galaxy NGC 5486, and a faint outlying H II region near the M101 companion NGC 5474. We also find no narrowband emission associated with recently discovered ultradiffuse galaxies and starless H I clouds near M101. The lack of any hidden population of low luminosity star-forming dwarfs around M101 suggests a rather shallow faint end slope (as flat as α ∼ −1.0) for the star-forming luminosity function in the M101 Group. We discuss our results in the context of tidally-triggered star formation models and the interaction history of the M101 Group.

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We present deep, narrowband imaging of the nearby spiral galaxy M101 to search for star-forming dwarf galaxies and isolated H ii regions in the group environment. Isolated star-forming regions, unassociated with spiral arms, probe star formation (SF) at the lowest masses and environmental densities. Such objects may be isolated star-forming events or ongoing evidence of tidal interactions. Using the Burrell Schmidt telescope, we target the brightest emission lines of star-forming regions, Hα, Hβ, and [O iii], to detect potential isolated regions. Great care was taken to remove potential source contaminants, such as high-redshift objects and Galactic M stars, from our source list. For each detected source, we compare the emission line fluxes and equivalent widths, along with structural and photometric properties, to samples of Local Group dwarfs and star-forming galaxies in the SINGG/11HUGS samples. We discuss our findings in the context of SF in low-density environments and evolution of the M101 Group.