TURNING THE TIDES ON THE ULTRA-FAINT DWARF SPHEROIDAL GALAXIES: COMA BERENICES AND URSA MAJOR II

Journal Article · Thu Jul 15 04:00:00 EDT 2010 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/140/1/138· OSTI ID:21443300

Munoz, Ricardo R; Geha, Maria ^[1]; Willman, Beth ^[2]

---

1. Astronomy Department, Yale University, New Haven, CT 06520 (United States)
2. Haverford College, Department of Astronomy, 370 Lancaster Avenue, Haverford, PA 19041 (United States)

We present deep CFHT/MegaCam photometry of the ultra-faint Milky Way satellite galaxies: Coma Berenices (ComBer) and Ursa Major II (UMa II). These data extend to r {approx} 25, corresponding to 3 mag below the main-sequence turn-offs in these galaxies. We robustly calculate a total luminosity of M{sub V} = -3.8 {+-} 0.6 for ComBer and M{sub V} = -3.9 {+-} 0.5 for UMa II, in agreement with previous results and confirming that these galaxies are among the faintest of the known dwarf satellites of the Milky Way. ComBer shows a fairly regular morphology with no signs of active tidal stripping down to a surface brightness limit of 32.4 mag arcsec{sup -2}. Using a maximum likelihood analysis, we calculate the half-light radius of ComBer to be r{sub half} = 74 {+-} 4 pc (5.8 {+-} 0.'3) and its ellipticity {epsilon} = 0.36 {+-} 0.04. In contrast, UMa II shows signs of ongoing disruption. We map its morphology down to {mu}{sub V} = 32.6 mag arcsec{sup -2} and found that UMa II is larger than previously determined, extending at least {approx}600 pc (1.{sup 0}1 on the sky) and it is also quite elongated with an overall ellipticity of {epsilon} = 0.50 {+-} 0.2. However, our estimate for the half-light radius, 123 {+-} 3 pc (14.1 {+-} 0.'3) is similar to previous results. We discuss the implications of these findings in the context of potential indirect dark matter detections and galaxy formation. We conclude that while ComBer appears to be a stable dwarf galaxy, UMa II shows signs of ongoing tidal interaction.

• OSTI ID: 21443300
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 1 Vol. 140; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BRIGHTNESS
GALAXIES
LUMINOSITY
MATHEMATICAL SOLUTIONS
MATTER
MAXIMUM-LIKELIHOOD FIT
MILKY WAY
MORPHOLOGY
NONLUMINOUS MATTER
NUMERICAL SOLUTION
OPTICAL PROPERTIES
PHOTOMETRY
PHYSICAL PROPERTIES
SATELLITES