A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites

By N. Martin, J. D. de Jong, Hans-Walter Rix. 2008

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We derive the structural parameters of the recently discovered very low luminosity Milky Way satellites through a maximum likelihood algorithm applied to SDSS data. For each satellite, even when only a few tens of stars are available down to the SDSS flux limit, the algorithm yields robust estimates and errors for the centroid, position angle, ellipticity, exponential half-light radius and number of member stars (within the SDSS). This latter parameter is then used in conjunction with stellar population models of the satellites to derive their absolute magnitudes and stellar masses, accounting for color-magnitude diagram shot noise. Most parameters are in good agreement with previous determinations, but we now properly account for parameter covariances. However, we find that faint satellites are somewhat more elliptical than initially thought, and ascribe this effect to the previous use of smoothed maps, which can be dominated by the smoothing (round) kernel. As a result, the faintest half of the Milky Way dwarf galaxies (MV ≳ −7.5) is significantly (4 σ) flatter (⟨ϵ⟩ = 0.47 ± 0.03) than its brightest half (MV≲ − 7.5, ⟨ϵ⟩ = 0.32 ± 0.02). From our best models, we also investigate whether the seemingly distorted shape of the satellites, often taken to be a sign of tidal distortion, can be quantified. We find that, except for tentative evidence of distortion in Canes Venatici I and Ursa Major II, these can be completely accounted for by Poisson scatter in the sparsely sampled systems. We consider three scenarios that could explain the rather elongated shape of faint satellites: rotation supported systems, stars following the shape of more triaxial dark matter subhalos, or elongation due to tidal interaction with the Milky Way. Although none of these is entirely satisfactory, the last one appears the least problematic, but obviously warrants much deeper observations to track evidence of such tidal interaction.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/381f25105b97963d5497831ebe21f6effad96973

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Citations in the corpus

THE BIRTH OF A GALAXY: PRIMORDIAL METAL ENRICHMENT AND STELLAR POPULATIONS (2010, neutral): “(Martin et al. 2008).”
Galactic Searches for Dark Matter (2012, background): “The stellar density in ultra-faint satellites is low enough that it is not possible to obtain photometry from integrated unresolved starlight (Martin et al., 2008; Muñoz et al., 2010).”
THE INVISIBLES: A DETECTION ALGORITHM TO TRACE THE FAINTEST MILKY WAY SATELLITES (2008, methodology): “These figures are identical to those output by the automated algorithm for each detection, aside from the addition of figure titles (MV and distances from Martin et al. 2008 and references therein).”
A BARYONIC SOLUTION TO THE MISSING SATELLITES PROBLEM (2012, background): “…mitigated to a degree by the discovery of a number of additional faint satellite galaxies (Willman et al. 2005; Irwin et al. 2007; Liu et al. 2008; Martin et al. 2008; Simon & Geha 2007; Grebel 2000; van den Bergh 2000; Belokurov et al. 2008; Watkins et al. 2009; Belokurov et al. 2010), there…”
One Law to Rule Them All: The Radial Acceleration Relation of Galaxies (2016, neutral): “They are coded as follows: 1: Pietrzyński et al. (2009), 2: Irwin & Hatzidimitriou (1995), 3: Walker et al. (2009c), 4: Bonanos et al. (2004), 5: Martin et al. (2008), 6: Walker et al. (2007), 7: Bellazzini et al. (2004), 8: Mateo et al. (2008), 9: Bellazzini et al. (2005), 10: Koch et al. (2007),…”
HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES (2009, background): “Our results suggest that for the lowest luminosity galaxies the fraction of EMP stars may be even higher, but for galaxies with stellar masses of ∼ 104 M⊙ (Martin et al. 2008) ∼ 5% should be a representative value.”
DWARF GALAXY ANNIHILATION AND DECAY EMISSION PROFILES FOR DARK MATTER EXPERIMENTS (2014, background): “Original sources are Martin et al. (2008) and/or discovery papers for satellites discovered after that work (Belokurov et al. 2008; Belokurov et al. 2009).”
BEASTS OF THE SOUTHERN WILD: DISCOVERY OF NINE ULTRA FAINT SATELLITES IN THE VICINITY OF THE MAGELLANIC CLOUDS (2015, methodology): “To measure the morphological properties of all the detected objects, we have modelled the on-sky 2D distribution of the likely member stars (see e.g. Martin et al. 2008, for similar approach).”
THE STELLAR INITIAL MASS FUNCTION OF ULTRA-FAINT DWARF GALAXIES: EVIDENCE FOR IMF VARIATIONS WITH GALACTIC ENVIRONMENT (2013, methodology): “Martin et al. (2008) calculated the stellar mass of Hercules and Leo IV assuming both a Kroupa and Salpeter IMF.”
THE OBSERVED PROPERTIES OF DWARF GALAXIES IN AND AROUND THE LOCAL GROUP (2012, background): “Measuring some of these values is challenging: Martin et al. (2008b) and Muñoz et al. (2012) both discuss the problems of determining structural parameters for galaxies in which few bright stars can be identified (generally the case for galaxies much fainter than MV −8).”
THE QUENCHING OF THE ULTRA-FAINT DWARF GALAXIES IN THE REIONIZATION ERA (2014, background): “…dominated by old (>10 Gyr) populations (e.g., Sand et al. 2009, 2010; Okamoto et al. 2008, 2010, 2012; de Jong et al. 2008b; Hughes et al. 2008; Martin et al. 2008a; Greco et al. 2008; Muñoz et al. 2010; Weisz et al. 2014b), while spectroscopy of their giant stars indicates low metallicities,…”
A QUANTITATIVE EXPLANATION OF THE OBSERVED POPULATION OF MILKY WAY SATELLITE GALAXIES (2009, methodology): “The luminosities, distances, and velocity dispersions of the observed Milky Way satellites that we use in all subsequent model - data comparisons were taken from various authors (Mateo 1998; Metz & Kroupa 2007; Martin et al. 2008) and are compiled in Table 2.”