Paper: Andromeda XXXV: The Faintest Dwarf Satellite of the Andromeda Galaxy
Authors: Jose Marco Arias, Eric F. Bell, Katya Gozman, In Sung Jang, Saxon Stockton, Oleg Y. Gnedin, Richard D'Souza, Antonela Monachesi, Jeremy Bailin, David Nidever, Roelof S. de Jong
Figure caption: Left: extinction-corrected CMD of stars within the HST/WFC3 field of view. Old (12.5 Gyr) PARSEC isochrones (A. Bressan et al. 2012) with metallicities of [M/H] = −1.9 and −1.5 dex are overlaid, along with a slightly younger (10 Gyr) isochrone with [M/H] = −1.0 dex. The corresponding horizontal branch tracks, shown as dashed lines in the same colors as their respective isochrones, are also included. All stars meeting our photometric quality metrics are shown as light gray dots, with those within 2 × ah colored by their elliptical radius from And XXXV’s center. Candidate red horizontal branch stars are located around F606W0 − F814W0 ∼ 0.6 mag and F814W0 ∼ 24.6 mag. The elliptical half-light radius ah of the best-fit exponential profile is marked by a red solid line in the color bar. The CMD selection box used to derive the structural parameters of And XXXV is outlined by the light gray region, and the gray dashed lines represent the 80% (50%) completeness limits of the data. Middle: spatial distribution of all point sources within the HST/WFC3 field of view. Sources within 2 × ah are colored based on the normalized stellar surface densities of the best-fit exponential model. The sources outlined in red denote the CMD-selected stars used in our MCMC analysis. The dark blue solid ellipses represent 2 × ah and 3 × ah from the system’s centroid as defined by the exponential profile, and the dashed light blue ellipses indicate 2 × rp and 3 × rp for the Plummer profile. All structural parameters used to plot these ellipses are detailed in Table 1. Top right: I-band luminosity function around the red horizontal branch feature of And XXXV. The observed distribution of stars is shown as a normalized histogram, while the solid red line represents the best-fit model (a Gaussian plus an exponential; see Section 4.2.1). An Epanechnikov kernel density estimate (light pink) is overplotted, highlighting the concentration of stars around the red horizontal brach feature. Bottom right: binned radial density profiles for And XXXV. The curves represent the best-fitting exponential (solid) and Plummer (dashed) density profiles. The light solid lines around the best-fit models represent 100 random draws from the posterior distributions of the free model parameters. The dashed horizontal lines denote the background densities (see Table 1) for each model. The uncertainties are derived assuming Poisson statistics. The machine-readable version of the data behind this figure contains the photometry, the photometry quality output from DOLPHOT, and the spatial positions (R.A. and decl., X and Y pixel positions) of all unmasked stellar sources with a signal-to-noise ratio in both F606W and F814W filters greater than or equal to 2.0. The final photometric catalog that we use to arrive at our results can be constructed by applying the quality metrics described in Section 3. Additionally, we included a flag in the table to identify sources that meet our photometric culls and are located within 2 × ah of And XXXV’s center.(The data used to create this figure are available in the online article.)(The data used to create this figure are available.)