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NASA NTRS2006

Precision Astrometry with SIM PlanetQuest: Science and Mission Update

This viewgraph presentation gives a science and mission update of precision Astrometry with the Space Interferometry Mission (SIM) PlanetQuest. The topics include: 1) SIM PlanetQuest - the World s First Long- Baseline Optical Interferometer in Space; 2) National Academy of Sciences / NRC endorses SIM PlanetQuest; 3) Astrometry with an Interferometer; 4) Overall Configuration (deployed); 5) SIM Planet Finding Capabilities; 6) Planet detection with SIM - minimum masses; 7) Searching for Terrestrial Planets with SIM; 8) Planets around Young Stars; 9) SIM PlanetQuest Science Team; 10) SIM Astrophysics; 11) SIM's Reach Extends Across our Entire Galaxy to do Precision Astrophysics; 12) Dynamics of Galaxy Groups within 5 Mpc; 13) Galactic tidal tails; 14) Dark Halo of our Galaxy; 15) Probing Active Galactic Nuclei with Astrometry; 16) Sample tile for relative astrometry; 17) Astrometric signatures of AGN; 18) Snapshot Observing Mode: Astrometry for the masses; and 19) SIM Technology Development is Complete.

space interferometry mission (SIM)↗
NASA NTRS1985

Boxy isophotes, discs and dust lanes in elliptical galaxies

CCD images of 42 elliptical and S0 galaxies are examined for low-contrast structures or subtle distortions of the isophotes from perfect ellipses. 75 percent of the galaxies have isophotes completely describable as concentric ellipses to within the photometry errors. 'Boxy' isophotes, stellar discs, and dust lanes are detected in the remaining 25 percent of the sample. The boxy elliptical galaxies appear dynamically indistinguishable from normal ellipticals and are therefore different from boxy bulges, which rotate rapidly. Most of the galaxies with faint discs, however, appear dynamically similar to S0 galaxies. Nearly edge-on dust lanes are found in four galaxies, which suggests that dust lanes may commonly occur in elliptical galaxies.

Lauer, T. R.↗
NASA NTRS2019

Using Gaia Data 2 to Constrain Local Dark Matter Density and Thin Dark Disk

We use stellar kinematics from the latest Gaia data release (DR2) to measure the local dark matter (DM) density ρDM in a heliocentric cylinder of radius R = 150 pc and half-height z = 200 pc. We also explore the prospect of using our analysis to estimate the DM density in local substructure by setting constraints on the surface density and scale height of a thin dark disk aligned with the baryonic disk and formed due to dissipative dark matter self-interactions. Performing the statistical analysis within a Bayesian framework for three types of tracers, we obtain ρDM = 0.016 ± 0.010 Mꙩ/p c 3 for A stars; early G stars give a similar result, while F stars yield a significantly higher value. For a thin dark disk, A stars set the strongest constraint: excluding surface densities (5–12) Mꙩ/pc 2 for scale heights below 100 pc with 95% confidence. The upper bound of this constraint implies . 1% of the Milky Way DM mass is present in a dissipative dark sector. Comparing our results with those derived using Tycho-Gaia Astrometric Solution (TGAS) data, we find that the uncertainty in our measurements of the local DM content is dominated by systematic errors that arise from assumptions of our dynamical analysis in the low z region. Furthermore, there will only be a marginal reduction in these uncertainties with more data in the Gaia era. We comment on the robustness of our method and discuss potential improvements for future work.

dark matter theory↗
NASA NTRS1994

Dynamics of cD clusters of galaxies. II: Analysis of seven Abell clusters

We have investigated the dynamics of the seven Abell clusters A193, A399, A401, A1795, A1809, A2063, and A2124, based on redshift data reported previously by us (Hill & Oegerle, (1993)). These papers present the initial results of a survey of cD cluster kinematics, with an emphasis on studying the nature of peculiar velocity cD galaxies and their parent clusters. In the current sample, we find no evidence for significant peculiar cD velocities, with respect to the global velocity distribution. However, the cD in A2063 has a significant (3 sigma) peculiar velocity with respect to galaxies in the inner 1.5 Mpc/h, which is likely due to the merger of a subcluster with A2063. We also find significant evidence for subclustering in A1795, and a marginally peculiar cD velocity with respect to galaxies within approximately 200 kpc/h of the cD. The available x-ray, optical, and galaxy redshift data strongly suggest that a subcluster has merged with A1795. We propose that the subclusters which merged with A1795 and A2063 were relatively small, with shallow potential wells, so that the cooling flows in these clusters were not disrupted. Two-body gravitational models of the A399/401 and A2063/MKW3S systems indicate that A399/401 is a bound pair with a total virial mass of approximately 4 x 10(exp 15) solar mass/h, while A2063 and MKW3S are very unlikely to be bound.

Oegerle, William R.↗
NASA NTRS1992

Dynamics of clusters of galaxies with central dominant galaxies. I - Galaxy redshifts

Optical redshifts are presented for a sample of 638 galaxies in the fields of the clusters Abell 85, DC 0107-46, Abell 496, Abell 2052, and DC 1842-63. The velocity histograms and wedge diagrams show evidence for a foreground sheet of galaxies in Abell 85 and background sheets of galaxies in DC 0107-46 and Abell 2052. The foreground group projected against the center of Abell 85 found by Beers et al. (1991) is confirmed. No evidence of substructure was found in Abell 496, Abell 2052, and DC 1842-63. The clusters have global velocity dispersions ranging from 551 km/s for DC 1842-63 to 714 km/s for A496, and flat dispersion profiles. Mass estimates using the virial theorem and the projected mass method range from 2.3 x 10 exp 14 solar masses for DC 0107-46 to 1.1 x 10 exp 15 solar masses for A85.

Malumuth, Eliot M.↗
NASA NTRS2000

Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 From The Nuclear Stellar Dynamics

We analyze the nuclear stellar dynamics of the SBO galaxy NGC 1023, utilizing observational data both from the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and from the ground. The stellar kinematics measured from these long-slit spectra show rapid rotation (V equals approx. 70 km/s at a distance of O.1 deg = 4.9 pc from the nucleus) and increasing velocity dispersion toward the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar kinematics assuming an axisymmetric mass distribution with both two and three integrals of motion. Both modeling techniques point to the presence of a central dark compact mass (which presumably is a supermassive black hole) with confidence > 99%. The isotropic two-integral models yield a best-fitting black hole mass of (6.0 +/- 0.4) x 10(exp 7) solar masses and mass-to-light ratio (M/L(sub v)) of 5.38 +/- 0.08, and the goodness-of-fit (CHI(exp 2)) is insensitive to reasonable values for the galaxy's inclination. The three-integral models, which non-parametrically fit the observed line-of-sight velocity distribution as a function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4) x 10(exp 7) solar masses and M/L(sub v) of 5.56 +/- 0.02 (internal errors), and the edge-on models are vastly superior fits over models at other inclinations. The internal dynamics in NGC 1023 as suggested by our best-fit three-integral model shows that the velocity distribution function at the nucleus is tangentially anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear line of sight velocity distribution has enhanced wings at velocities >= 600 km/s from systemic, suggesting that perhaps we have detected a group of stars very close to the central dark mass.

Bower, G. A.↗
NASA NTRS1994

The dynamical evolution of poor clusters of galaxies: Growth and properties of the first-ranked galaxy

We report N-body simulations of the dynamical evolution of isolated clusters of 50 galaxies containing a dark matter component that comprises 90% of the cluster mass. For our adopted physical scaling, the line-of-sight velocity dispersion of the cluster is 310 km/s and the initial core radius is 250 kpc. Our results are applicable to (1) present-day poor clusters, (2) the small systems that may have merged to produce present-day rich clusters, and (3) virialized subclumps within larger systems, in between major substructure merger events. We have evolved a total of 10 cluster models, using N = 40,000 particles per model. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the gravitational potential arises from the particles alone. Dark matter is apportioned between the galaxy halos and a smoothly distributed common group halo, the intracluster background (ICB). The percentage of cluster mass initially in the ICB, Beta, is chosen to be 50, 75, or 90. Increasing Beta has the effect of removing mass from dark halos around galaxies and distributing it throughout the cluster. The initial conditions were constructed by randomly sampling a King distribution with W(sub 0) = 6. The galaxies are also King models; the masses of the galaxies follow a Schechter distribution function.

Bode, Paul W.↗
NASA NTRS1993

Dynamics of cD clusters of galaxies. I - Redshift data for seven clusters

We present the initial results of a spectroscopic study of a sample of cD galaxy clusters. The goal of this program is to study the dynamics of the clusters, with emphasis on determining the nature and frequency of peculiar velocity cD galaxies. In this paper we present redshifts for 611 galaxies in the fields of the rich Abell clusters A193, A399, A401, A1795, A1809, A2063, and A2124. We discuss our data reduction techniques, and compare our derived velocities with previously published values. We find a frequency of emission line galaxies of about 6 percent in clusters, a factor of 2-3 less than the field.

Hill, John M.↗
NASA NTRS2020

Ultraviolet and X-ray properties of Coma’s ultra-diffuse galaxies

Many ultra-diffuse galaxies (UDGs) have been discovered in the Coma cluster, and there is evidence that some, notably Dragonfly 44, have Milky Way-like dynamical masses despite dwarf-like stellar masses. We used X-ray, ultraviolet (UV), and optical data to investigate the star formation and nuclear activity in the Coma UDGs, and we obtained deep UV and X-ray data (Swift and XMM–Newton) for Dragonfly 44 to search for low-level star formation, hot circumgalactic gas, and the integrated emission from X-ray binaries. Among the Coma UDGs, we find UV luminosities consistent with quiescence but NUV−r colours indicating star formation in the past Gyr. This indicates that the UDGs were recently quenched. The r-band luminosity declines with projected distance from the Coma core. The Dragonfly 44 UV luminosity is also consistent with quiescence, with SFR<6×10^−4M(ʘ)/yr,and no X-rays are detected down to a sensitivity of 10^38erg/s. This rules out a hot corona with a M>10^8M(ʘ) within the virial radius, which would normally be expected for a dynamically massive galaxy. The absence of bright, low-mass X-ray binaries is consistent with the expectation from the Galaxy total stellar mass, but it is unlikely if most low-mass X-ray binaries form in globular clusters, as Dragonfly 44 has a very large population. Based on the UV and X-ray analysis, the Coma UDGs are consistent with quenched dwarf galaxies, although we cannot rule out a dynamically massive population.

Chris H. Lee↗
NASA NTRS2005

Warm Molecular Gas Traced with CO J = 7 --> 6 in the Galaxy's Central 2 Parsecs: Dynamical Heating of the Circumnuclear Disks

We present an 11" resolution map of the central 2 pc of the Galaxy in the CO J = 7 --> 6 rotational transition. The CO emission shows rotation about Sgr A* but also evidence for noncircular turbulent motion and a clumpy morphology. We combine our data set with available CO measurements to model the physical conditions in the disk. We find that the molecular gas in the region is both warm and dense, with T approx. 200-300 K and n(sub H2) approx. (5-7) x 10(exp 4) cm(exp -3). The mass of warm molecular gas we measure in the central 2 pc is at least 2000 M(solar), about 20 times the UV-excited atomic gas mass, ruling out a UV heating scenario for the molecular material. We compare the available spectral tracers with theoretical models and conclude that molecular gas is heated with magnetohydrodynamic shocks with v approx. 10-20 km s(exp -1) and B approx. 0.3- 0.5 mG. Using the conditions derived with the CO analysis, we include the other important coolants, neutral oxygen and molecular hydrogen, to estimate the total cooling budget of the molecular material. We derive a mass-to-luminosity ratio of approx. 2-3 M(solar)(L(solar)exp -1), which is consistent with the total power dissipated via turbulent decay in 0.1 pc cells with v(sub rms) approx. 15 kilometers per second. These size and velocity scales are comparable to the observed clumping scale and the velocity dispersion. At this rate, the material near Sgr A* is dissipating its orbital energy on an orbital timescale and cannot last for more than a few orbits. Our conclusions support a scenario in which the features near Sgr A* such as the circumnuclear disk and northern arm are generated by infalling clouds with low specific angular momentum.

galatic nuclei↗
NASA NTRS1990

The morphology of star clusters in the SMC

The projected ellipticities of 34 populous SMC star clusters have been derived by means of PDS 1010A scans and a computer interactive method of reduction implemented on an Apollo 570 workstation. A pair of J and R plates taken with the 1.2 m UK Schmidt telescope in Australia were used. Radial ellipticity variations within individual globular clusters seem to be a common phenomenon for the SMC clusters, similar to that observed in the LMC clusters where the innerparts are more elliptical than the outer ones in 95 percent of the cases. The derived ellipticities which correspond to the innermost part of the cluster at radial distances near to half-mass radii have been found to be statistically more elliptical than those of the LMC, known to be more elliptical than those of the Galaxy. The dynamical masses of the clusters seem to correlate with ellipticities supporting the hypothesis that, either the gravitational field of the parent galaxy being a dominant factor affect slower the shape of the high mass clusters and/or the most massive clusters, being dynamically younger, retain their original shape.

Kontizas, E.↗
NASA NTRS1982

Environmental effects on galaxies in clusters

Influences from the cluster environment build up steadily over long times so that the internal dynamics of a galaxy in a cluster change appreciably over a cluster crossing time. The galaxy can no longer be considered as an isolated object. Slow rotation of elliptical galaxies and observations on galaxy alignment within clusters of galaxies provide two independent pieces of observational evidence for cluster influence. A first cut at studying cluster influences on the internal dynamics of galaxies is presented by means of numerical experiments started from a rotating barlike galaxy placed in an external force field like that which a galaxy sees in a cluster. Both pattern motion and observable rotation are tidally braked by the cluster force field. The experiments verify that the braking rate scales inversely as the square of the cluster crossing time. Systematic internal motions are reduced so that observational V/sigma is less than 0.2, in agreement with observations on elliptical galaxies but sharply reduced from V/sigma of approximately 1.0 for the original model. The final shapes of tidally braked galaxies need not be spherical.

Miller, R. H.↗
NASA NTRS1988

On the evolution of globular cluster systems. I - Present characteristics and rate of destruction in our Galaxy

The current dynamic state and rate of destruction for the system of globular clusters in the Galaxy are modeled. It is found that gravitational shocks due to the central bulge of the Galaxy are very efficient in destroying clusters on highly radial orbits. This effect, extrapolated at the present unweighted destruction rate over 10 to the 10th yr, can account for the observed difference between the velocity distribution of globular clusters and other tracers of the halo population.

Aguilar, Luis↗
NASA NTRS1993

Quasars in rich galaxy clusters

The evolution of AGN activity in rich clusters of galaxies is found to be approximately 5 times more rapid than that in poor clusters. This rapid evolution may be driven by evolution in the dynamics of galaxy cluster cores. Results from our spectroscopic studies of galaxies associated with quasars are consistent with this scenario, in that bright AGN are preferentially found in regions of lower velocity dispersion. Alternately, the evolution may be driven by formation of a dense intra-cluster medium (ICM). Galaxies close to quasars in rich cluster cores are much bluer (presumably gas rich) than galaxies in the cores of other rich clusters, in support of this model.

Ellingson, Erica↗
NASA NTRS1989

Dynamical models of highly flattened oblate elliptical galaxies with De Vaucouleurs' surface-brightness profiles

Two surveys of dynamical models of E6 elliptical galaxies were constructed with de Vaucouleurs'surface-brightness distributions. One set of models has a constant mass-to-light ratio. The other set consists of models embedded in oblate isothermal gravitational potentials. In both sets, the observed axis ratio of the models is 0.55 when viewed edge-on. When viewed edge-on, it is possible to construct models in either potential that have velocity-dispersion profiles that increase or decrease with radius along either or both principal axes. The observational data seem to indicate that dispersion profiles decrease or remain constant as function of radius. The most surprising result of this work is that in order for a model to have velocity-dispersion profiles that decrease with radius out to 1.5 r(e) along both principal axes, it must be dominated by fairly thin-walled tube orbits at large radii. This is very different from the spherical case, where radial orbits dominate at large radii.

Fillmore, James A.↗
NASA NTRS1988

On infall into the Virgo cluster

The history of the study of the Galaxy's motion with respect to the Local Supercluster is reviewed. Direct measurements of the infall pattern suggest an infall component at the Local Group of about 250 km/s. This value is consistent with that expected if the average mass-to-light ratio of galaxies is similar to that dynamically measured in galaxy clusters, a value that gives an Omega of only about 0.3. The infall pattern is also consistent with galaxy density maps produced by IRAS surveys, although it may be only marginally consistent with the 'Great Attractor'. On smaller scales, there is strong evidence that most of the spiral galaxies near the cluster core are still falling in. Using the best distance estimates to the Virgo cluster, the local value of the Hubble constant is about 85 km/s/Mpc.

Huchra, John P.↗
NASA NTRS1990

Viral coefficient and hidden mass in the galaxy groups

The purpose is the verification of the virial mass estimations for small galaxy groups. The dynamical evolution of triple and quintuple galaxies was studied by the numerical simulations. The dependence of the virial coefficient k(t) versus time was derived. Initial k(O) = O. The function k(t) has some strong oscillations from 0.02 to 0.99. Generally, these oscillations are quasiperiodical ones. Such a behavior of k(t) is caused by formation in a system of close isolated temporary double subsystems. A strong correlation between the virial coefficient and the least mutual distance in the system is observed. Such wide oscillations may add into the estimation of virial mass of the galaxy groups an uncertainty of more than one order. An additional uncertainty is introduced by the projection effect. This uncertainty for the individual estimations of the masses approach three orders. Thus any individual estimation of the virial mass is impossible for small galaxy groups. Some possibility of statistical estimation (median or average) of the total mass, including a hidden mass, is shown for the homogeneous samples. The authors propose a method for these estimations based on a comparison of the medians of dynamical parameters (a mean size in projection and a dispersion of relative radial velocities) for the simulated and observed ensembles of the galaxy groups. This method has been applied to a sample of 46 probably physical triplets of galaxies. The probable median of the hidden mass in a volume of the triplet is about 4 M, where M is the total mass of visible matter.

Anosova, Joanna P.↗