Browsing by Subject "velocity dispersions"

Now showing 1 - 8 of 8

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.
Circumnuclear Molecular Gas In Megamaser Disk Galaxies NGC 4388 And NGC 1194
(2014-06) Greene, Jenny E.; Seth, Anil; Lyubenova, Mariya; Walsh, Jonelle; van de Ven, Glenn; Lasker, Ronald; Walsh, Jonelle
We explore the warm molecular and ionized gas in the centers of two megamaser disk galaxies using K-band spectroscopy. Our ultimate goal is to determine how gas is funneled onto the accretion disk, here traced by megamaser spots on sub-parsec scales. We present NIR IFU data with a resolution of similar to 50 pc for two galaxies: NGC 4388 with VLT/SINFONI and NGC 1194 with Keck/OSIRIS+AO. The high spatial resolution and rich spectral diagnostics allow us to study both the stellar and gas kinematics as well as gas excitation on scales only an order of magnitude larger than the maser disk. We find a drop in the stellar velocity dispersion in the inner similar to 100 pc of NGC 4388, a common signature of a dynamically cold central component seen in many active nuclei. We also see evidence for noncircular gas motions in the molecular hydrogen on similar scales, with the gas kinematics on 100 parsec scales aligned with the megamaser disk. In contrast, the high ionization lines and Br gamma trace outflow along the 100 parsec-scale jet. In NGC 1194, the continuum from the accreting black hole is very strong, making it difficult to measure robust two-dimensional kinematics, but the spatial distribution and line ratios of the molecular hydrogen and Br gamma have consistent properties between the two galaxies.
Frequency And Properties Of Bars In Cluster And Field Galaxies At Intermediate Redshifts
(2009-04) Barazza, F. D.; Jablonka, P.; Desai, V.; Jogee, S.; Aragon-Salamanca, A.; De Lucia, G.; Saglia, R. P.; Halliday, C.; Poggianti, B. M.; Dalcanton, J. J.; Rudnick, G.; Milvang-Jensen, B.; Noll, S.; Simard, L.; Clowe, D. I.; Pello, R.; White, S. D. M.; Zaritsky, D.; Jogee, S.
We present a study of large-scale bars in field and cluster environments out to redshifts of similar to 0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The properties of bars and disks are determined by ellipse fits to the surface brightness distribution of the galaxies using HST/ACS images in the F814W filter. The bar identification is based on quantitative criteria after highly inclined (> 60 degrees) systems have been excluded. The total optical bar fraction in the redshift range z = 0.4-0.8 (median z = 0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (similar to 31%) than at larger distances (similar to 18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (similar to 45%) than bulge-dominated galaxies (similar to 15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. The question whether internal or external factors are more important for bar formation and evolution cannot be answered definitely. On the one hand, the bar fraction and properties of cluster and field samples of disk galaxies are quite similar, indicating that internal processes are crucial for bar formation. On the other hand, we find evidence that cluster centers are favorable locations for bars, which suggests that the internal processes responsible for bar growth are supported by the typical interactions taking place in such environments.
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.
The L Proportional To Sigma(8) Correlation for Elliptical Galaxies With Cores: Relation With Black Hole Mass
(2013-05) Kormendy, John; Bender, Ralf; Kormendy, John
We construct the Faber-Jackson correlation between velocity dispersion sigma and total galaxy luminosity L-V separately for elliptical galaxies with and without cores. The coreless ellipticals show the well-known, steep relationship d log sigma/d log L-V = 0.268 or L-V proportional to sigma(3.74). This corresponds to d log sigma/d log M = 0.203, where M is the stellar mass and we use M/L proportional to L-0.32. In contrast, the velocity dispersions of core ellipticals increase much more slowly with L-V and M: d log sigma/d log L-V = 0.120, L-V proportional to sigma(8.33), and d log sigma/d log M = 0.091. Dissipationless major galaxy mergers are expected to preserve sigma according to the simplest virial-theorem arguments. However, numerical simulations show that sigma increases slowly in dry major mergers, with d log sigma/d log M similar or equal to +0.15. In contrast, minor mergers cause sigma to decrease, with d log sigma/d log M similar or equal to -0.05. Thus, the observed relation argues for dry major mergers as the dominant growth mode of the most massive ellipticals. This is consistent with what we know about the Formation of cores. We know no viable way to explain galaxy cores except through dissipationless mergers of approximately equal-mass galaxies followed by core scouring by binary supermassive black holes. The observed, shallow sigma proportional to L-V(+ 0.12) relation for core ellipticals provides further evidence that they formed in dissipationless and predominantly major mergers. Also, it explains the observation that the correlation of supermassive black hole mass with velocity dispersion, M-circle proportional to sigma(4), "saturates" at high M-circle such that M-circle becomes almost independent of sigma.
Limits On Intermediate-Mass Black Holes In Six Galactic Globular Clusters With Integral-Field Spectroscopy
(2013-04) Lutzgendorf, N.; Kissler-Patig, M.; Gebhardt, K.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Neumayer, N.; Jalali, B.; Feldmeier, A.; Gebhardt, K.
Context. The formation of supermassive black holes at high redshift still remains a puzzle to astronomers. No accretion mechanism can explain the fast growth from a stellar mass black hole to several billion solar masses in less than one Gyr. The growth of supermassive black holes becomes reasonable only when starting from a massive seed black hole with mass on the order of 10(2)-10(5) M-circle dot. Intermediate-mass black holes are therefore an important field of research. Especially the possibility of finding them in the centers of globular clusters has recently drawn attention. Searching for kinematic signatures of a dark mass in the centers of globular clusters provides a unique test for the existence of intermediate-mass black holes and will shed light on the process of black-hole formation and cluster evolution. Aims. We are investigating six galactic globular clusters for the presence of an intermediate-mass black hole at their centers. Based on their kinematic and photometric properties, we selected the globular clusters NGC 1851, NGC 1904 (M 79), NGC 5694, NGC 5824, NGC 6093 (M 80), and NGC 6266 (M 62). Methods. We used integral field spectroscopy to obtain the central velocity-dispersion profile of each cluster. In addition we completed these profiles with outer kinematic points from previous measurements for the clusters NGC 1851, NGC 1094, NGC 5824, and NGC 6093. We also computed the cluster photometric center and the surface brightness profile using HST data. After combining these datasets we compared them to analytic Jeans models. We used varying M/L-V profiles for clusters with enough data points in order to reproduce their kinematic profiles in an optimal way. Finally, we varried the mass of the central black hole and tested whether the cluster is better fitted with or without an intermediate-mass black hole. Results. We present the statistical significance, including upper limits, of the black-hole mass for each cluster. NGC 1904 and NGC 6266 provide the highest significance for a black hole. Jeans models in combination with a M/L-V profile obtained from N-body simulations (in the case of NGC 6266) predict a central black hole of M-circle = (3 +/- 1) x10(3) M circle dot for NGC 1904 and M-circle = (2 +/- 1) x10(3) M-circle dot for NGC 6266. Furthermore, we discuss the possible influence of dark remnants and mass segregation at the center of the cluster on the detection of an IMBH.
Limits On Intermediate-Mass Black Holes In Six Galactic Globular Clusters With Integral-Field Spectroscopy
(2013-04) Lutzgendorf, N.; Kissler-Patig, M.; Gebhardt, K.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Neumayer, N.; Jalali, B.; Feldmeier, A.; Gebhardt, K.
Context. The formation of supermassive black holes at high redshift still remains a puzzle to astronomers. No accretion mechanism can explain the fast growth from a stellar mass black hole to several billion solar masses in less than one Gyr. The growth of supermassive black holes becomes reasonable only when starting from a massive seed black hole with mass on the order of 10(2)-10(5) M-circle dot. Intermediate-mass black holes are therefore an important field of research. Especially the possibility of finding them in the centers of globular clusters has recently drawn attention. Searching for kinematic signatures of a dark mass in the centers of globular clusters provides a unique test for the existence of intermediate-mass black holes and will shed light on the process of black-hole formation and cluster evolution. Aims. We are investigating six galactic globular clusters for the presence of an intermediate-mass black hole at their centers. Based on their kinematic and photometric properties, we selected the globular clusters NGC 1851, NGC 1904 (M 79), NGC 5694, NGC 5824, NGC 6093 (M 80), and NGC 6266 (M 62). Methods. We used integral field spectroscopy to obtain the central velocity-dispersion profile of each cluster. In addition we completed these profiles with outer kinematic points from previous measurements for the clusters NGC 1851, NGC 1094, NGC 5824, and NGC 6093. We also computed the cluster photometric center and the surface brightness profile using HST data. After combining these datasets we compared them to analytic Jeans models. We used varying M/L-V profiles for clusters with enough data points in order to reproduce their kinematic profiles in an optimal way. Finally, we varried the mass of the central black hole and tested whether the cluster is better fitted with or without an intermediate-mass black hole. Results. We present the statistical significance, including upper limits, of the black-hole mass for each cluster. NGC 1904 and NGC 6266 provide the highest significance for a black hole. Jeans models in combination with a M/L-V profile obtained from N-body simulations (in the case of NGC 6266) predict a central black hole of M-circle = (3 +/- 1) x10(3) M circle dot for NGC 1904 and M-circle = (2 +/- 1) x10(3) M-circle dot for NGC 6266. Furthermore, we discuss the possible influence of dark remnants and mass segregation at the center of the cluster on the detection of an IMBH.
The VIRUS-P Exploration Of Nearby Galaxies (VENGA): Survey Design, Data Processing, And Spectral Analysis Methods
(2013-05) Blanc, Guillermo A.; Weinzirl, Tim; Song, Mimi M.; Heiderman, Amanda; Gebhardt, Karl; Jogee, Shardha; Evans, Neal J.; van den Bosch, Remco C. E.; Luo, Rongxin; Drory, Niv; Fabricius, Maximilian; Fisher, David; Hao, Lei; Kaplan, Kyle; Marinova, Irina; Vutisalchavakul, Nalin; Yoachim, Peter; Weinzirl, Tim; Song, Mimi M.; Heiderman, Amanda; Gebhardt, Karl; Jogee, Shardha; Evans, Neal J.
We present the survey design, data reduction, and spectral fitting pipeline for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies. Targets span a wide range in Hubble type, star formation activity, morphology, and inclination. The VENGA data cubes have 5 ''.6 FWHM spatial resolution, similar to 5 angstrom FWHM spectral resolution, sample the 3600 angstrom-6800 angstrom range, and cover large areas typically sampling galaxies out to similar to 0.7R(25). These data cubes can be used to produce two-dimensional maps of the star formation rate, dust extinction, electron density, stellar population parameters, the kinematics and chemical abundances of both stars and ionized gas, and other physical quantities derived from the fitting of the stellar spectrum and the measurement of nebular emission lines. To exemplify our methods and the quality of the data, we present the VENGA data cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA observations of NGC 628 are described, as well as the construction of the data cube, our spectral fitting method, and the fitting of the stellar and ionized gas velocity fields. We also propose a new method to measure the inclination of nearly face-on systems based on the matching of the stellar and gas rotation curves using asymmetric drift corrections. VENGA will measure relevant physical parameters across different environments within these galaxies, allowing a series of studies on star formation, structure assembly, stellar populations, chemical evolution, galactic feedback, nuclear activity, and the properties of the interstellar medium in massive disk galaxies.