Cepheid-based Distances to NGC 4303 and NGC 1068

Abstract

We present Cepheid-based distances to two canonical AGN: NGC 4303 (M 61) and NGC 1068. Data were obtained using the Hubble Space Telescope with nonredundant time spacing over 12 visits for each target, and observations were made with the F555W and F814W filters. We found 32,694 point sources in NGC 4303, and 130 of these were determined to be strong Cepheid candidates with periods ranging ~$13-93$ days. In NGC 1068, we found 20,207 point sources, where 51 of these were strong Cepheid candidates with periods ~$14-92$ days. We fit the period$-$luminosity relationship, calibrated based on a geometric distance to the LMC by Riess et al. (2019), to our Cepheid candidates in each galaxy and correct for potential effects of metallicity. Using a distance constraint for the LMC given by Pietrzyński et al. (2019), this yields a distance modulus of $μ= 31.083 \pm 0.035$ mag for NGC 4303 and $μ= 30.150 \pm 0.106$ mag for NGC 1068. Thus, we measure distances of $D = 16.47 \pm 0.27$ Mpc to NGC 4303 and $D = 10.72 \pm 0.52$ Mpc to NGC 1068.

Figures (10)

• Figure 1: Red (F814W), blue (F555W), and pseudogreen color images of NGC 4303 (left) and NGC 1068 (right) using HST Wide Field Camera 3 data. The field of view of NGC 4303 here is $2.6' \times 2.6'$. This image of NGC 1068 has been cropped to remove a foreground star, and its field of view is $2.1' \times 2.6'$. NGC 4303 is oriented with North approximately up, and NGC 1068 has North oriented $29.22 \degree$ clockwise from up. Credit: Judy Schmidt.
• Figure 2: Variability index $I_V$ for point sources in NGC 4303 (top) and NGC 1068 (bottom), shown against color. The red dashed line represents $I_V = 1.0$, so all sources above these lines were considered to be variable candidates.
• Figure 3: Drizzled "deep frame" F555W-band images of NGC 4303 (left) and NGC 1068 (right) with Cepheid candidate positions marked by cyan boxes. The Cepheid candidates marked here represent our final samples for each galaxy. Compasses are provided in the lower right corners, and $20"$ scale bars are provided in the lower left corners.
• Figure 4: Period$-$luminosity relationships for Cepheid candidates in NGC 4303 (left) and NGC 1068 (right). The three panels display F555W (top), F814W (middle), and Wesenheit magnitudes (bottom). Red x's represent Cepheid candidates that were determined to be blue blends or $>3\sigma$ outliers in the Wesenheit index. The dashed lines in each panel represent the lines of best fit, with fixed slopes based on the findings of riess_large_2019. The dotted vertical lines represent points of completeness in our sample --- NGC 4303 was visually determined at $P=19.5$ days, and NGC 1068 was determined from Figure \ref{['fig:comp']} at $P=25$ days. Corrections for possible metallicity effects and Galactic extinction have not been applied here.
• Figure 5: Color$-$magnitude diagrams of all point sources detected in NGC 4303 (left, shown in black) and NGC 1068 (right, shown in black). The final samples of Cepheid candidates are marked by blue squares, while the blue blends and $>3\sigma$ outliers are marked by red x's. Solid vertical lines delimit our range of acceptable F555W$-$F814W colors.