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Register a new userStellar kinematics and metallicities in the Leo I dwarf spheroidal galaxy -- wide field implications for galactic evolution
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We present low-resolution spectroscopy of 120 red giants in the Galactic satellite dwarf spheroidal (dSph) Leo I, obtained with the GeminiN-GMOS and Keck-DEIMOS spectrographs. We find stars with velocities consistent with membership of Leo I out to 1.3 King tidal radii. By measuring accurate radial velocities with a median measurement error of 4.6 km/s we find a mean systemic velocity of 284.2 km/s with a global velocity dispersion of 9.9 km/s. The dispersion profile is consistent with being flat out to the last data point. We show that a marginally-significant rise in the radial dispersion profile at a radius of 3 is not associated with any real localized kinematical substructure. Given its large distance from the Galaxy, tides are not likely to have affected the velocity dispersion, a statement we support from a quantitative kinematical analysis, as we observationally reject the occurrence of a significant apparent rotational signal or an asymmetric velocity distribution. Mass determinations adopting both isotropic stellar velocity dispersions and more general models yield a M/L ratio of 24, which is consistent with the presence of a significant dark halo with a mass of about 3x10^7 M_sun, in which the luminous component is embedded. This suggests that Leo I exhibits dark matter properties similar to those of other dSphs in the Local Group. Our data allowed us also to determine metallicities for 58 of the targets. We find a mildly metal poor mean of -1.31 dex and a full spread covering 1 dex. In contrast to the majority of dSphs, Leo I appears to show no radial gradient in its metallicities, which points to a negligible role of external influences in this galaxys evolution.
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We present the projected velocity dispersion profile for the remote (d=233kpc) Galactic dwarf spheroidal (dSph) galaxy Leo II, based on 171 discrete stellar radial velocities that were obtained from medium-resolution spectroscopy using the FLAMES/GIRAFFE spectrograph at the European Southern Observatory, Chile. The dispersion profile of those stars with good membership probabilities is essentially flat with an amplitude of 6.6+-0.7 km/s over the full radial extent of our data, which probe to the stellar boundary of this galaxy. We find no evidence of any significant apparent rotation or velocity asymmetry which suggests that tidal effects cannot be invoked to explain Leo IIs properties. From basic mass modeling, employing Jeans equation, we derive a mass out to the limiting radius of (2.7+-0.5) 10^7 Msun and a global mass to light ratio of 27-45 in solar units, depending on the adopted total luminosity. A cored halo profile and a mild amount of tangential velocity anisotropy is found to account well for Leo IIs observed kinematics, although we cannot exclude the possibility of a cusped halo with radially varying velocity anisotropy. All in all, this galaxy exhibits dark matter properties which appear to be concordant with the other dSph satellites of the Milky Way, namely a halo mass profile which is consistent with a central core and a total mass which is similar to the common mass scale seen in other dSphs.
We carried out a wide-field V, I imaging survey of the Local Group dwarf spheroidal galaxy Leo II using the Subaru Prime Focus Camera on the 8.2-m Subaru Telescope. The survey covered an area of 26.67 x 26.67 arcmin^2, far beyond the tidal radius of Leo II (8.63 arcmin), down to the limiting magnitude of V ~26, which is roughly 1 mag deeper than the turn-off point of the main sequence stars of Leo II. Radial number density profiles of bright and faint red giant branch (RGB) stars were found to change their slopes at around the tidal radius, and extend beyond the tidal radius with shallower slopes. A smoothed surface brightness map of Leo II suggests the existence of a small substructure of globular cluster luminosity beyond the tidal radius. We investigated the properties of the stellar population by means of the color-magnitude diagram. The horizontal branch (HB) morphology index shows a radial gradient in which red HB stars are more concentrated than blue HB stars, which is common to many Local Group dwarf spheroidal galaxies. The color distribution of RGB stars around the mean RGB sequence shows a larger dispersion at the center than in the outskirts, indicating a mixture of stellar populations at the center and a more homogeneous population in the outskirts. Based on the age estimation using subgiant branch (SGB) stars, we found that although the major star formation took place ~8 Gyr ago, a considerable stellar population younger than 8 Gyr is found at the center; such a younger population is insignificant in the outskirts.
We present metallicities and ages for 52 red giants in the remote Galactic dwarf spheroidal (dSph) galaxy Leo II. These stars cover the entire surface area of Leo II and are radial velocity members. We obtained medium-resolution multi-fiber spectroscopy with ESO/VLTs FLAMES spectrograph. The metallicities were determined based on the near-infrared Ca II triplet. The resulting metallicity distribution (MD) is asymmetric and peaks at [Fe/H]=-1.74 dex on the Carretta & Gratton scale. The full range in metallicities extends from -2.4 to -1.1 dex. As in other dSphs, no extremely metal-poor red giants were found. We compare Leo IIs observed MD with model predictions for several other Galactic dSphs from the literature. Leo II clearly exhibits a lack of more metal poor stars, in analogy to the classical G-dwarf problem, which may indicate a comparable `K-giant problem. Moreover, its evolution appears to have been affected by galactic winds. We use our inferred metallicities as an input parameter for isochrone fits to SDSS photometry and derive approximate ages. The resulting age-metallicity distribution covers the full age range from 2-15 Gyr on our adopted isochrone scale. During the first 7 Gyr relative to the oldest stars [Fe/H] appears to have remained almost constant. The almost constant metallicity at higher ages and a slight drop by about 0.3 dex thereafter may be indicative of rejuvenation by low metallicity gas. Overall, the age-metallicity relation appears to support the formation of Leo II from pre-enriched gas. Evidence for enrichment is seen during the recent 2-4 Gyr. Our findings support earlier photometric findings of Leo II as a galaxy with a prominent old and a dominant intermediate-age population. We do not find a significant radial metallicity gradient nor age gradient in our data.(Abridged)
We have surveyed a complete extent of Leo A - an apparently isolated gas-rich low-mass dwarf irregular galaxy in the Local Group. The $B$, $V$, and $I$ passband CCD images (typical seeing $sim$0.8) were obtained with Subaru Telescope equipped with Suprime-Cam mosaic camera. The wide-field ($20 times 24$) photometry catalog of 38,856 objects ($V sim 16-26$ mag) is presented. This survey is also intended to serve as a finding chart for future imaging and spectroscopic observation programs of Leo A.
We present wide-field spectroscopy of globular clusters around the Leo I group galaxies NGC 3379 and NGC 3384 using the FLAMES multi-fibre instrument at the VLT. We obtain accurate radial velocities for 42 globular clusters (GCs) in total, 30 for GCs around the elliptical NGC 3379, eight around the lenticular NGC 3384, and four which may be associated with either galaxy. These data are notable for their large radial range extending from 07 to 145 (2 to 42 kpc) from the centre of NGC 3379, and small velocity uncertainties of about 10 km/s. We combine our sample of 30 radial velocities for globular clusters around NGC 3379 with 8 additional GC velocities from the literature, and find a projected velocity dispersion of 175(+24/-22) km/s at R < 5 and 147(+44/-39) at R > 5. These velocity dispersions are consistent with a dark matter halo around NGC 3379 with a concentration in the range expected from a LCDM cosmological model and a total mass of ~ 6 x 10^11 Msun. Such a model is also consistent with the stellar velocity dispersion at small radii and the rotation of the HI ring at large radii, and has a M/L_B that increases by a factor of five from several kpc to 100 kpc. Our velocity dispersion for the globular cluster system of NGC 3379 is somewhat higher than that found for the planetary nebulae (PNe) in the inner region covered by the PN data, and we discuss possible reasons for this difference. For NGC 3384, we find the GC system has a rotation signature broadly similar to that seen in other kinematic probes of this SB0 galaxy. This suggests that significant rotation may not be unusual in the GC systems of disc galaxies.
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