Browsing by Subject "galactic"

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The Black Hole Mass In M87 From Gemini/NIFS Adaptive Optics Observations
(2011-03) Gebhardt, Karl; Adams, Joshua; Richstone, Douglas; Lauer, Tod R.; Faber, S. M.; Gultekin, Kayhan; Murphy, Jeremy; Tremaine, Scott; Gebhardt, Karl; Adams, Joshua; Murphy, Jeremy
We present the stellar kinematics in the central 2 '' of the luminous elliptical galaxy M87 (NGC 4486), using laser adaptive optics to feed the Gemini telescope integral-field spectrograph, Near-infrared Integral Field Spectrograph (NIFS). The velocity dispersion rises to 480 km s(-1) at 0 ''.2. We combine these data with extensive stellar kinematics out to large radii to derive a black hole mass equal to (6.6 +/- 0.4) x 10(9) M-circle dot, using orbit-based axisymmetric models and including only the NIFS data in the central region. Including previously reported ground-based data in the central region drops the uncertainty to 0.25 x 10(9) M-circle dot with no change in the best-fit mass; however, we rely on the values derived from the NIFS-only data in the central region in order to limit systematic differences. The best-fit model shows a significant increase in the tangential velocity anisotropy of stars orbiting in the central region with decreasing radius, similar to that seen at the centers of other core galaxies. The black hole mass is insensitive to the inclusion of a dark halo in the models-the high angular resolution provided by the adaptive optics breaks the degeneracy between black hole mass and stellar mass-to-light ratio. The present black hole mass is in excellent agreement with the Gebhardt & Thomas value, implying that the dark halo must be included when the kinematic influence of the black hole is poorly resolved. This degeneracy implies that the black hole masses of luminous core galaxies, where this effect is important, may need to be re-evaluated. The present value exceeds the prediction of the black hole-dispersion and black hole-luminosity relations, both of which predict about 1 x 10(9) M-circle dot for M87, by close to twice the intrinsic scatter in the relations. The high end of the black hole correlations may be poorly determined at present.
The Milky Way Tomography With SDSS. III. Stellar Kinematics
(2010-06) Bond, Nicholas A.; Ivezic, Zeljko; Sesar, Branimir; Juric, Mario; Munn, Jeffrey A.; Kowalski, Adam; Loebman, Sarah; Roskar, Rok; Beers, Timothy C.; Dalcanton, Julianne; Rockosi, Constance M.; Yanny, Brian; Newberg, Heidi J.; Prieto, Carlos Allende; Wilhelm, Ron; Lee, Young Sun; Sivarani, Thirupathi; Majewski, Steven R.; Norris, John E.; Bailer-Jones, Coryn A. L.; Fiorentin, Paola Re; Schlegel, David; Uomoto, Alan; Lupton, Robert H.; Knapp, Gillian R.; Gunn, James E.; Covey, Kevin R.; Smith, J. Allyn; Miknaitis, Gajus; Doi, Mamoru; Tanaka, Masayuki; Fukugita, Masataka; Kent, Steve; Finkbeiner, Douglas; Quinn, Tom R.; Hawley, Suzanne; Anderson, Scott; Kiuchi, Furea; Chen, Alex; Bushong, James; Sohi, Harkirat; Haggard, Daryl; Kimball, Amy; McGurk, Rosalie; Barentine, John; Brewington, Howard; Harvanek, Mike; Kleinman, Scott; Krzesinski, Jurek; Long, Dan; Nitta, Atsuko; Snedden, Stephanie; Lee, Brian; Pier, Jeffrey R.; Harris, Hugh; Brinkmann, Jonathan; Schneider, Donald P.; Prieto, Carlos Allende
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r < 20 and proper-motion measurements derived from Sloan Digital Sky Survey (SDSS) and POSS astrometry, including similar to 170,000 stars with radial-velocity measurements from the SDSS spectroscopic survey. Distances to stars are determined using a photometric-parallax relation, covering a distance range from similar to 100 pc to 10 kpc over a quarter of the sky at high Galactic latitudes (|b| > 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.
Multi-Element Abundance Measurements From Medium-Resolution Spectra. I. The Sculptor Dwarf Spheroidal Galaxy
(2009-11) Kirby, Evan N.; Guhathakurta, Puragra; Bolte, Michael; Sneden, Christopher; Geha, Marla C.; Sneden, Christopher
We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way (MW). This is the largest sample of individual a element (Mg, Si, Ca, and Ti) abundance measurements in any single dSph. The measurements are made from Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectra (6400-9000 angstrom, R similar to 6500). Based on comparisons to published high-resolution (R greater than or similar to 20,000) spectroscopic measurements, our measurements have uncertainties of sigma[Fe/H] = 0.14 and sigma[alpha/Fe] = 0.13. The Sculptor [Fe/H] distribution has a mean <[Fe/H]> = -1.58 and is asymmetric with a long, metal-poor tail, indicative of a history of extended star formation. Sculptor has a larger fraction of stars with [Fe/H] < -2 than the MW halo. We have discovered one star with [Fe/H] = -3.80 +/- 0.28, which is the most metal-poor star known anywhere except the MW halo, but high-resolution spectroscopy is needed to measure this star's detailed abundances. As has been previously reported based on high-resolution spectroscopy, [alpha/Fe] in Sculptor falls as [Fe/H] increases. The metal-rich stars ([Fe/H] similar to -1.5) have lower [alpha/Fe] than Galactic halo field stars of comparable metallicity. This indicates that star formation proceeded more gradually in Sculptor than in the Galactic halo. We also observe radial abundance gradients of -0.030 +/- 0.003 dex arcmin(-1) in [Fe/H] and +0.013 +/- 0.003 dex arcmin(-1) in [alpha/Fe] out to 11 arcmin (275 pc). Together, these measurements cast Sculptor and possibly other surviving dSphs as representative of the dwarf galaxies from which the metal-poor tail of the Galactic halo formed.
Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results
(2013-10) Bennett, C. L.; Larson, D.; Weiland, J. L.; Jarosik, N.; Hinshaw, G.; Odegard, N.; Smith, K. M.; Hill, R. S.; Gold, B.; Halpern, M.; Komatsu, Eiichiro; Nolta, M. R.; Page, L.; Spergel, D. N.; Wollack, E.; Dunkley, J.; Kogut, A.; Limon, M.; Meyer, S. S.; Tucker, G. S.; Wright, E. L.; Komatsu, Eiichiro
We present the final nine-year maps and basic results from the Wilkinson Microwave Anisotropy Probe (WMAP) mission. The full nine-year analysis of the time-ordered data provides updated characterizations and calibrations of the experiment. We also provide new nine-year full sky temperature maps that were processed to reduce the asymmetry of the effective beams. Temperature and polarization sky maps are examined to separate cosmic microwave background (CMB) anisotropy from foreground emission, and both types of signals are analyzed in detail. We provide new point source catalogs as well as new diffuse and point source foreground masks. An updated template-removal process is used for cosmological analysis; new foreground fits are performed, and new foreground reduced CMB maps are presented. We now implement an optimal C-1 weighting to compute the temperature angular power spectrum. The WMAP mission has resulted in a highly constrained Delta CDM cosmological model with precise and accurate parameters in agreement with a host of other cosmological measurements. When WMAP data are combined with finer scale CMB, baryon acoustic oscillation, and Hubble constant measurements, we find that big bang nucleosynthesis is well supported and there is no compelling evidence for a non-standard number of neutrino species (N-eff = 3.84 +/- 0.40). The model fit also implies that the age of the universe is t(0) = 13.772 +/- 0.059 Gyr, and the fit Hubble constant is H-0 = 69.32 +/- 0.80 km s(-1) Mpc(-1). Inflation is also supported: the fluctuations are adiabatic, with Gaussian random phases; the detection of a deviation of the scalar spectral index from unity, reported earlier by the WMAP team, now has high statistical significance (n(s) = 0.9608 +/- 0.0080); and the universe is close to flat/Euclidean (Omega(k) = -0.0027(-0.0038)(+0.0039)). Overall, the WMAP mission has resulted in a reduction of the cosmological parameter volume by a factor of 68,000 for the standard six-parameter Delta CDM model, based on CMB data alone. For a model including tensors, the allowed seven-parameter volume has been reduced by a factor 117,000. Other cosmological observations are in accord with the CMB predictions, and the combined data reduces the cosmological parameter volume even further. With no significant anomalies and an adequate goodness of fit, the inflationary flat Delta CDM model and its precise and accurate parameters rooted in WMAP data stands as the standard model of cosmology.