Browsing by Subject "sauron project"

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Angular Momenta, Dynamical Masses, And Mergers Of Brightest Cluster Galaxies
(2013-12) Tran, Kim-Vy; Brough, Sarah; Gebhardt, Karl; von der Linden, Anja; Couch, Warrick J.; Sharp, Rob; Gebhardt, Karl
Using the VIMOS integral field unit (IFU) spectrograph on the Very Large Telescope, we have spatially mapped the kinematic properties of 10 nearby brightest cluster galaxies (BCGs) and 4 BCG companion galaxies located within a redshift of z = 0.1. In the hierarchical formation model, these massive galaxies (10(10.5) M-circle dot < M-dyn < 10(11.9) M-circle dot) are expected to undergo more mergers than lower mass galaxies, and simulations show that dry minor mergers can remove angular momentum. We test whether BCGs have low angular momenta by using the lambda(Re) parameter developed by the SAURON and ATLAS(3D) teams and combine our kinematics with Sloan Digital Sky Survey photometry to analyze the BCGs' merger status. We find that 30% (3/10) of the BCGs and 100% of the companion galaxies (4/4) are fast rotators as defined by the ATLAS(3D) criteria. Our fastest rotating BCG has a lambda(Re) = 0.35 +/- 0.05. We increase the number of BCGs analyzed from 1 in the combined SAURON and ATLAS(3D) surveys to 11 BCGs total and find that above M-dyn similar to 11.5 M-circle dot, virtually all galaxies, regardless of environment, are slow rotators. To search for signs of recent merging, we analyze the photometry of each system and use the G - M-20 selection criteria to identify mergers. We find that 40% +/- 20% of our BCGs are currently undergoing or have recently undergone a merger (within 0.2 Gyr). Surprisingly, we find no correlation between galaxies with high angular momentum and morphological signatures of merging.
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 Black Hole Mass, Stellar Mass-To-Light Ratio, And Dark Halo In M87
(2009-08) Gebhardt, Karl; Thomas, Jens; Gebhardt, Karl
We model the dynamical structure of M87 (NGC4486) using high spatial resolution long-slit observations of stellar light in the central regions, two-dimensional stellar light kinematics out to half of the effective radius, and globular cluster velocities out to eight effective radii. We simultaneously fit for four parameters: black hole mass, dark halo core radius, dark halo circular velocity, and stellar mass-to-light (M/L) ratio. We find a black hole mass of 6.4 (+/- 0.5) x 109 M(circle dot) (the uncertainty is 68% confidence marginalized over the other parameters). The stellar M/L(V) = 6.3 +/- 0.8. The best-fit dark halo core radius is 14 +/- 2 kpc, assuming a cored logarithmic potential. The best-fit dark halo circular velocity is 715 +/- 15 km s(-1). Our black hole mass is over a factor of 2 larger than previous stellar dynamical measures, and our derived stellar M/L ratio is two times lower than previous dynamical measures. When we do not include a dark halo, we measure a black hole mass and stellar M/L ratio that is consistent with previous measures, implying that the major difference is in the model assumptions. The stellar M/L ratio from our models is very similar to that derived from stellar population models of M87. The reason for the difference in the black hole mass is because we allow the M/L ratio to change with radius. The dark halo is degenerate with the stellar M/L ratio, which is subsequently degenerate with the black hole mass. We argue that dynamical models of galaxies that do not include the contribution from a dark halo may produce a biased result for the black hole mass. This bias is especially large for a galaxy with a shallow light profile such as M87, and may not be as severe in galaxies with steeper light profiles unless they have a large stellar population change with radius.
Hobby-Eberly Telescope Observations Of The Dark Halo In NGC 821
(2010-06) Forestell, Amy D.; Gebhardt, Karl; Forestell, Amy D.; Gebhardt, Karl
We present stellar line-of-sight velocity distributions (LOSVDs) of elliptical galaxy NGC 821 obtained to approximately 100 '' (over two effective radii) with long-slit spectroscopy from the Hobby-Eberly Telescope. Our measured stellar LOSVDs are larger than the planetary nebulae measurements at similar radii. We fit axisymmetric orbit-superposition models with a range of dark halo density profiles, including two-dimensional kinematics at smaller radii from SAURON data. Within our assumptions, the best-fitted model gives a total enclosed mass of 2.0 x 10(11) M(circle dot) within 100 '', with an accuracy of 2%; this mass is equally divided between halo and stars. At 1 R(e), the best-fitted dark matter halo accounts for 13% of the total mass in the galaxy. This dark halo is inconsistent with previous claims of little to no dark matter halo in this galaxy from planetary nebula measurements. We find that a power-law dark halo with a slope 0.1 is the best-fitted model; both the no dark halo and Navarro-Frenk-White models are worse fits at a greater than 99% confidence level. NGC 821 does not appear to have the expected dark halo density profile. The internal moments of the stellar velocity distribution show that the model with no dark halo is radially anisotropic at small radii and tangentially isotropic at large radii, while the best-fitted halo models are slightly radially anisotropic at all radii. We test the potential effects of model smoothing and find that there are no effects on our results within the errors. Finally, we run models using the planetary nebula kinematics and assuming our best-fitted halos and find that the planetary nebulae require radial orbits throughout the galaxy.
Hunting for Supermassive Black Holes in Nearby Galaxies With the Hobby-Eberly Telescope
(2015-05) van den Bosch, Remco C. E.; Gebhardt, Karl; Gultekin, Kayhan; Yildirim, Akin; Walsh, Jonelle L.; Gebhardt, Karl; Walsh, Jonelle L.
We have conducted an optical long-slit spectroscopic survey of 1022 galaxies using the 10 m Hobby-Eberly Telescope (HET) at McDonald Observatory. The main goal of the HET Massive Galaxy Survey (HETMGS) is to find nearby galaxies that are suitable for black hole mass measurements. In order to measure accurately the black hole mass, one should kinematically resolve the region where the black hole dominates the gravitational potential. For most galaxies, this region is much less than an arcsecond. Thus, black hole masses are best measured in nearby galaxies with telescopes that obtain high spatial resolution. The HETMGS focuses on those galaxies predicted to have the largest sphere-of-influence, based on published stellar velocity dispersions or the galaxy fundamental plane. To ensure coverage over galaxy types, the survey targets those galaxies across a face-on projection of the fundamental plane. We present the sample selection and resulting data products from the long-slit observations, including central stellar kinematics and emission line ratios. The full data set, including spectra and resolved kinematics, is available online. Additionally, we show that the current crop of black hole masses are highly biased toward dense galaxies and that especially large disks and low dispersion galaxies are under-represented. This survey provides the necessary groundwork for future systematic black hole mass measurement campaigns.
Is There A Black Hole In NGC 4382?
(2011-11) Gultekin, Kayhan; Richstone, Douglas O.; Gebhardt, Karl; Faber, S. M.; Lauer, Tod R.; Bender, Ralf; Kormendy, John; Pinkney, Jason; Gebhardt, Karl
We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph observations of the galaxy NGC 4382 (M85) and axisymmetric models of the galaxy to determine mass-to-light ratio (Gamma(V)) and central black hole mass (M-BH). We find Gamma(V) = 3.74 +/- 0.1 M-circle dot/L-circle dot and M-BH = 1.3(-1.2)(+5.2) x 10(7) M-circle dot at an assumed distance of 17.9 Mpc, consistent with no black hole. The upper limit, M-BH < 9.6 x 10(7) M-circle dot (2 sigma) or M-BH < 1.4 x 10(8)(3 sigma), is consistent with the current M-sigma relation, which predicts M-BH = 8.8 x 10(7) M-circle dot at sigma(e) = 182 km s(-1), but low for the current M-L relation, which predicts M-BH = 7.8 x 10(8) M-circle dot at L-V = 8.9 x 10(10) L-circle dot, (V). HST images show the nucleus to be double, suggesting the presence of a nuclear eccentric stellar disk, analogous to the Tremaine disk in M31. This conclusion is supported by the HST velocity dispersion profile. Despite the presence of this non-axisymmetric feature and evidence of a recent merger, we conclude that the reliability of our black hole mass determination is not hindered. The inferred low black hole mass may explain the lack of nuclear activity.
Overview Of The SDSS-IV Manga Survey: Mapping Nearby Galaxies At Apache Point Observatory
(2015-01) Bundy, Kevin; Bershady, Matthew A.; Law, David R.; Yan, Renbin; Drory, Niv; MacDonald, Nicholas; Wake, David A.; Cherinka, Brian; Sanchez-Gallego, Jose R.; Weijmans, Anne-Marie; Thomas, Daniel; Tremonti, Christy; Masters, Karen; Coccato, Lodovico; Diamond-Stanic, Aleksandar M.; Aragon-Salamanca, Alfonso; Avila-Reese, Vladimir; Badenes, Carles; Falcon-Barroso, Jesus; Belfiore, Francesco; Bizyaev, Dmitry; Blanc, Guillermo A.; Bland-Hawthorn, Joss; Blanton, Michael R.; Brownstein, Joel R.; Byler, Nell; Cappellari, Michele; Conroy, Charlie; Dutton, Aaron A.; Emsellem, Eric; Etherington, James; Frinchaboy, Peter M.; Fu, Hai; Gunn, James E.; Harding, Paul; Johnston, Evelyn J.; Kauffmann, Guinevere; Kinemuchi, Karen; Klaene, Mark A.; Knapen, Johan H.; Leauthaud, Alexie; Li, Cheng; Lin, Lihwai; Maiolino, Roberto; Malanushenko, Viktor; Malanushenko, Elena; Mao, Shude; Maraston, Claudia; McDermid, Richard M.; Merrifield, Michael R.; Nichol, Robert C.; Oravetz, Daniel; Pan, Kaike; Parejko, John K.; Sanchez, Sebastian F.; Schlegel, David; Simmons, Audrey; Steele, Oliver; Steinmetz, Matthias; Thanjavur, Karun; Thompson, Benjamin A.; Tinker, Jeremy L.; van den Bosch, Remco C. E.; Westfall, Kyle B.; Wilkinson, David; Wright, Shelley; Xiao, Ting; Zhang, Kai; Drory, Niv
We present an overview of a new integral field spectroscopic survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) that began on 2014 July 1. MaNGA will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. We summarize essential characteristics of the instrument and survey design in the context of MaNGA's key science goals and present prototype observations to demonstrate MaNGA's scientific potential. MaNGA employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12 '' (19 fibers) to 32 '' (127 fibers). Two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 angstrom at R similar to 2000. With a typical integration time of 3 hr, MaNGA reaches a target r-band signal-to-noise ratio of 4-8 (angstrom(-1) per 2 '' fiber) at 23 AB mag arcsec(-2), which is typical for the outskirts of MaNGA galaxies. Targets are selected with M* greater than or similar to 10(9) M-circle dot using SDSS-I redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. Analysis of our prototype observations demonstrates MaNGA's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. MaNGA's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr.