Browsing by Subject "cluster"
Now showing 1 - 15 of 15
- Results Per Page
- Sort Options
Item A Captured Runaway Black Hole in NGC 1277?(2013-07) Shields, G. A.; Bonning, E. W.; Shields, G. A.Recent results indicate that the compact lenticular galaxy NGC 1277 in the Perseus Cluster contains a black hole of mass similar to 10(10) M-circle dot. This far exceeds the expected mass of the central black hole in a galaxy of the modest dimensions of NGC 1277. We suggest that this giant black hole was ejected from the nearby giant galaxy NGC 1275 and subsequently captured by NGC 1277. The ejection was the result of gravitational radiation recoil when two large black holes merged following the merger of two giant ellipticals that helped to form NGC 1275. The black hole wandered in the cluster core until it was captured in a close encounter with NGC 1277. The migration of black holes in clusters may be a common occurrence.Item Dark Matter Scaling Relations And The Assembly Epoch Of Coma Early-Type Galaxies(2009-01) Thomas, Jens; Saglia, R. P.; Bender, Ralf; Thomas, D.; Gebhardt, Karl; Magorrian, John; Corsini, E. M.; Wegner, G.; Gebhardt, KarlAxisymmetric, orbit-based dynamical models are used to derive dark matter scaling relations for Coma early-type galaxies. From faint to bright galaxies, halo core radii and asymptotic circular velocities increase. Compared to spirals of the same brightness, the majority of Coma early-type galaxies-those with old stellar populations-have similar halo core radii but more than two times larger asymptotic halo velocities. The average dark matter density inside 2r(eff) decreases with increasing luminosity and is 6.8 times larger than in disk galaxies of the same B-band luminosity. Compared at the same stellar mass, dark matter densities in ellipticals are 13.5 times higher than in spirals. Different baryon concentrations in ellipticals and spirals cannot explain the higher dark matter density in ellipticals. Instead, the assembly redshift (1 + z) of Coma early-type halos is likely about two times larger than of comparably bright spirals. Assuming that local spirals typically assemble at a redshift of one, the majority of bright Coma early-type galaxy halos must have formed around z approximate to 2-3. For about half of our Coma galaxies, the assembly redshifts match with constraints derived from stellar populations. We find dark matter densities and estimated assembly redshifts of our observed Coma galaxies in reasonable agreement with recent semi-analytic galaxy formation models.Item A First Look At The Auriga-California Giant Molecular Cloud With Herschel And The CSO: Census Of The Young Stellar Objects And The Dense Gas(2013-02) Harvey, Paul M.; Fallscheer, Cassandra; Ginsburg, Adam; Terebey, Susan; Andre, Phillippe; Bourke, Tyler L.; Di Francesco, James; Konyves, Vera; Matthews, Brenda C.; Peterson, Dawn E.; Harvey, Paul M.We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 mu m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few x 10(22) cm(-2) (N-H2) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to similar to 10 K from values similar to 14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.Item The Herschel Digit Survey Of Weak-Line T Tauri Stars: Implications For Disk Evolution And Dissipation(2013-01) Cieza, Lucas A.; Olofsson, Johan; Harvey, Paul M.; Evans, Neal J.; Najita, Joan; Henning, Thomas; Merin, Bruno; Liebhart, Armin; Gudel, Manuel; Augereau, Jean-Charles; Pinte, Christopher; Harvey, Paul M.; Evans, Neal J.As part of the "Dust, Ice, and Gas In Time (DIGIT)" Herschel Open Time Key Program, we present Herschel photometry (at 70, 160, 250, 350, and 500 mu m) of 31 weak-line T Tauri star (WTTS) candidates in order to investigate the evolutionary status of their circumstellar disks. Of the stars in our sample, 13 had circumstellar disks previously known from infrared observations at shorter wavelengths, while 18 of them had no previous evidence for a disk. We detect a total of 15 disks as all previously known disks are detected at one or more Herschel wavelengths and two additional disks are identified for the first time. The spectral energy distributions (SEDs) of our targets seem to trace the dissipation of the primordial disk and the transition to the debris disk regime. Of the 15 disks, 7 appear to be optically thick primordial disks, including 2 objects with SEDs indistinguishable from those of typical Classical T Tauri stars, 4 objects that have significant deficit of excess emission at all IR wavelengths, and 1 "pre-transitional" object with a known gap in the disk. Despite their previous WTTS classification, we find that the seven targets in our sample with optically thick disks show evidence for accretion. The remaining eight disks have weaker IR excesses similar to those of optically thin debris disks. Six of them are warm and show significant 24 mu m Spitzer excesses, while the last two are newly identified cold debris-like disks with photospheric 24 mu m fluxes, but significant excess emission at longer wavelengths. The Herschel photometry also places strong constraints on the non-detections, where systems with F-70/F-70,(*) greater than or similar to 5-15 and L-disk/L-* greater than or similar to 10(-3) to 10(-4) can be ruled out. We present preliminary models for both the optically thick and optically thin disks and discuss our results in the context of the evolution and dissipation of circumstellar disks.Item The HST/ACS Coma Cluster Survey. VIII. Barred Disk Galaxies In The Core Of The Coma Cluster(2012-02) Marinova, Irina; Jogee, Shardha; Weinzirl, Tim; Erwin, Peter; Trentham, Neil; Ferguson, Henry C.; Hammer, Derek; den Brok, Mark; Graham, Alister W.; Carter, David; Balcells, Marc; Goudfrooij, Paul; Guzman, Rafael; Hoyos, Carlos; Mobasher, Bahram; Mouhcine, Mustapha; Peletier, Reynier F.; Peng, Eric W.; Kleijn, Gus V.; Marinova, Irina; Jogee, Shardha; Weinzirl, TimWe use high-resolution (similar to 0.'' 1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z similar to 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M-V less than or similar to -18, M-* > 10(9.5) M-circle dot) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% +/- 11%, 65% +/- 11%, and 60% +/- 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of +/- 11%) across environments which span two orders of magnitude in galaxy number density (n similar to 300-10,000 galaxies Mpc(-3)) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS (similar to 50 pc) to analyze a sample of 333 faint (MV > -18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.Item McDonald Observatory Archive of Optical Linear Polarization Measurements(2011-06) Wills, Beverley J.; Wills, D.; Breger, Michael; Wills, Beverley J.; Wills, D.; Breger, MichaelWe present 990 previously unpublished optical linear polarization measurements of quasars, active galactic nuclei, and some stars observed for interstellar polarization. The observations, covering the period 1981-2000, were made with McDonald Observatory's 2.1 m Struve reflector and the Breger photopolarimeter.Item Modification Of The MOOG Spectral Synthesis Codes To Account For Zeeman Broadening Of Spectral Lines(2013-09) Deen, Casey P.; Deen, Casey P.In an attempt to widen access to the study of magnetic fields in stellar astronomy, I present MOOGStokes, a version of the MOOG one-dimensional local thermodynamic equilibrium radiative transfer code, overhauled to incorporate a Stokes vector treatment of polarized radiation through a magnetic medium. MOOGStokes is a suite of three complementary programs, which together can synthesize the disk-averaged emergent spectrum of a star with a magnetic field. The first element (a pre-processing script called CounterPoint) calculates for a given magnetic field strength, wavelength shifts, and polarizations for the components of Zeeman-sensitive lines. The second element (a MOOG driver called SynStokes derived from the existing MOOG driver Synth) uses the list of Zeeman-shifted absorption lines together with the existing machinery of MOOG to synthesize the emergent spectrum at numerous locations across the stellar disk, accounting for stellar and magnetic field geometry. The third and final element (a post-processing script called DiskoBall) calculates the disk-averaged spectrum by weighting the individual emergent spectra by limb darkening and projected area, and applying the effects of Doppler broadening. All together, the MOOGStokes package allows users to synthesize emergent spectra of stars with magnetic fields in a familiar computational framework. MOOGStokes produces disk-averaged spectra for all Stokes vectors (I, Q, U, V), normalized by the continuum. MOOGStokes agrees well with the predictions of INVERS10 a polarized radiative transfer code with a long history of use in the study of stellar magnetic fields. In the non-magnetic limit, MOOGStokes also agrees with the predictions of the scalar version of MOOG.Item NGC 4102: High-Resolution Infrared Observations Of A Nuclear Starburst Ring(2010-10) Beck, Sara C.; Lacy, John H.; Turner, Jean L.; Lacy, John H.The composite galaxy NGC 4102 hosts a LINER nucleus and a starburst. We mapped NGC 4102 in the 12.8 mu m line of [Ne II], using the echelon spectrometer TEXES on the NASA IRTF, to obtain a data cube with 1 ''.5 spatial, and 25 km s(-1) spectral, resolution. Combining near-infrared, radio, and the [Ne II] data shows that the extinction to the starburst is substantial, more than 2 mag at the K band, and that the neon abundance is less than half solar. We find that the star formation in the nuclear region is confined to a rotating ring or disk of 4 ''.3 (similar to 300 pc) diameter, inside the inner Lindblad resonance. This region is an intense concentration of mass, with a dynamical mass similar to 3 x 10(9) M(circle dot), and of star formation. The young stars in the ring produce the [Ne II] flux reported by Spitzer for the entire galaxy. The mysterious blue component of line emission detected in the near-infrared is also seen in [Ne II]; it is not a normal active galactic nucleus outflow.Item Nuclear Star-Forming Ring of the Milky Way: Simulations(2011-07) Kim, Sungsoo S.; Saitoh, Takayuki R.; Jeon, Myouungwon; Figer, Donald F.; Merritt, David; Wada, Keiichi; Jeon, MyouungwonWe present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star Formation, and supernova feedback. A ring of dense gas clouds forms as a result of X-1-X-2 orbit transfer, and our potential model results in a ring radius of similar to 200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star Formation rate (SFR) in the CMZ, similar to 2 x 10(7) M-circle dot and similar to 0.1 M-circle dot yr(-1). Star Formation in our simulations takes place mostly in the outermost X-2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star Formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.Item A Parameter Study Of The Dust And Gas Temperature In A Field Of Young Stars(2009-06) Urban, Andrea; Evans, Neal J.; Doty, Steven D.; Urban, Andrea; Evans, Neal J.We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using DUSTY, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with DUSTY, which we can use to calculate the dust temperature in a field of stars with various parameters. We then determine the gas temperature assuming energy balance. Our models can be used to make large-scale simulations of clustered star formation more realistic.Item Regular Frequency Patterns In The Classical Delta Scuti Star HD 144277 Observed By The MOST Satellite(2011-09) Zwintz, K.; Lenz, P.; Breger, M.; Pamyatnykh, A. A.; Zdravkov, T.; Kuschnig, R.; Matthews, J. M.; Guenther, D. B.; Moffat, A. F. J.; Rowe, J. F.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.; Breger, M.Context. We present high-precision time-series photometry of the classical delta Scuti star HD 144277 obtained with the MOST (Microvariability and Oscillations of STars) satellite in two consecutive years. The observed regular frequency patterns are investigated asteroseismologically. Aims. HD 144277 is a hot A-type star that is located on the blue border of the classical instability strip. While we mostly observe low radial order modes in classical delta Scuti stars, HD 144277 presents a different case. Its high observed frequencies, i.e., between 59.9 d(-1) (693.9 mu Hz) and 71.1 d(-1) (822.8 mu Hz), suggest higher radial orders. We examine the progression of the regular frequency spacings from the low radial order to the asymptotic frequency region. Methods. Frequency analysis was performed using Period04 and SigSpec. The results from the MOST observing runs in 2009 and 2010 were compared to each other. The resulting frequencies were submitted to asteroseismic analysis. Results. HD 144277 was discovered to be a delta Scuti star using the time-series photometry observed by the MOST satellite. Twelve independent pulsation frequencies lying in four distinct groups were identified. Two additional frequencies were found to be combination frequencies. The typical spacing of 3.6 d(-1) corresponds to the spacing between subsequent radial and dipole modes, therefore the spacing between radial modes is twice this value, 7.2 d(-1). Based on the assumption of slow rotation, we find evidence that the two radial modes are the sixth and seventh overtones, and the frequency with the highest amplitude can be identified as a dipole mode. Conclusions. The models required to fit the observed instability range need slightly less metallicity and a moderate enhancement of the helium abundance compared to the standard chemical composition. Our asteroseismic models suggest that HD 144277 is a delta Scuti star close to the ZAMS with a mass of 1.66 M(circle dot).Item Spatially Resolved Stellar, Dust, And Gas Properties Of The Post-Interacting Whirlpool Galaxy System(2012-08) Cooper, Erin M.; Wilson, Christine D.; Foyle, Kelly; Bendo, George; Koda, Jin; Baes, Maarten; Boquien, Mederic; Boselli, Alessandro; Ciesla, Laure; Cooray, Asantha; Eales, Steve; Galametz, Maud; Lebouteiller, Vianney; Parkin, Tara; Roussel, Helene; Sauvage, Marc; Spinoglio, Luigi; Smith, Mathew W. L.; Cooper, Erin M.Using infrared imaging from the Herschel Space Observatory, observed as part of the Very Nearby Galaxies Survey, we investigate the spatially resolved dust properties of the interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales of similar to 1 kpc. Spectral energy distribution modeling of the new infrared images in combination with archival optical and near-through mid-infrared images confirms that both galaxies underwent a burst of star formation similar to 370-480 Myr ago and provides spatially resolved maps of the stellar and dust mass surface densities. The resulting average dust-to-stellar mass ratios are comparable to other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at log(M-dust/M-star) = -2.5 +/- 0.2 and NGC 5195 at log(M-dust/M-star) = -3.5 +/- 0.3. The dust-to-stellar mass ratio is constant across NGC 5194 suggesting the stellar and dust components are coupled. In contrast, the mass ratio increases with radius in NGC 5195 with decreasing stellar mass density. Archival mass surface density maps of the neutral and molecular hydrogen gas are also folded into our analysis, revealing a fairly constant gas-to-dust mass ratio, 94 +/- 17 across the system. Somewhat surprisingly, we find the dust in NGC 5195 is heated by a strong interstellar radiation field (ISRF), over 20 times that of the ISRF in the Milky Way, resulting in relatively high characteristic dust temperatures (similar to 30 K). This post-starburst galaxy contains a substantial amount of low-density molecular gas and displays a gas-to-dust ratio (73 +/- 35) similar to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such high temperatures as there is no star formation in the galaxy and its active galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which exhibits only a modest enhancement in the amplitude of its ISRF.Item Suzaku Broad-Band Spectroscopy Of RX J1347.5-1145: Constraints On The Extremely Hot Gas And Non-Thermal Emission(2008-11) Ota, N.; Murase, K.; Kitayama, T.; Komatsu, E.; Hattori, M.; Matsuo, H.; Oshima, T.; Suto, Y.; Yoshikawa, K.; Komatsu, E.Context. We present the results of our analysis of long Suzaku observations (149 ks and 122 ks for XIS and HXD, respectively) of the most X-ray luminous galaxy cluster, RX J1347.5-1145, at z = 0.451. Aims. To understand the gas physics of a violent, cluster merger, we study physical properties of the hot (similar to 20 keV) gas clump in the south-east ( SE) region discovered previously by Sunyaev-Zel'dovich (SZ) effect observations. Using hard X-ray data, a signature of non-thermal emission is also explored. Methods. We perform single as well as multi-temperature fits to the Suzaku XIS spectra. The Suzaku XIS and HXD, and the Chandra ACIS-I data are then combined to examine the properties of the hot gas component in the SE region. We finally look for non-thermal emission in the Suzaku HXD data. Results. The single-temperature model fails to reproduce the 0.5-10 keV continuum emission and Fe-K lines measured by XIS simultaneously. A two-temperature model with a very hot component improves the fit, although the XIS data can only provide a lower limit to the temperature of the hot component. In the Suzaku HXD data, we detect hard X-ray emission above the background in the 12-40 keV band at the 9 sigma level; however, the significance becomes marginal when the systematic error in the background estimation is included. With the joint analysis of the Suzaku and Chandra data, we determine the temperature of the hot gas in the SE region to be 25.3(-4.5)(+6.1) (statistical; 90% confidence level)(-9.5)(+6.9) ( systematic; 90% confidence level) keV, which is in an excellent agreement with the previous joint analysis of the SZ effect in radio and the Chandra X-ray data. This is the first time that the X-ray analysis alone provides a good measurement of the hot component temperature in the SE region, which is possible because of Suzaku's unprecedented sensitivity over the wide X-ray band. These results indicate strongly that RX J1347.5-1145 has undergone a recent, violent merger. The spectral analysis shows that the SE component is consistent with being thermal. We measure the 3 sigma upper limit to the non-thermal flux, F < 8 x 10(-12) erg s(-1) cm(-2) in the 12-60 keV band, which provides a limit on the inverse Compton scattering of relativistic electrons off the CMB photons. Combining this limit with the discovery of a radio mini halo in this cluster at 1.4 GHz, which measures the synchrotron radiation, we find a lower limit to the strength of the intracluster magnetic field, such that B > 0.007 mu G.Item White Dwarf Luminosity And Mass Functions From Sloan Digital Sky Survey Spectra(2008-01) DeGennaro, Steven; von Hippel, Ted; Winget, D. E.; Kepler, S. O.; Nitta, Atsuko; Koester, Detlev; Althaus, Leandro; DeGennaro, Steven; von Hippel, Ted; Winget, D. E.We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g - i) and apparent magnitude (g) that covers the range - 1.0 < g - i < 0.2 and 15 < g < 19.5. We address the observed upturn in log g for WDs with T-eff less than or similar to 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with T-eff < 12,000 K. Finally, we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.Item White Dwarf Luminosity And Mass Functions From Sloan Digital Sky Survey Spectra(2008-01) DeGennaro, Steven; von Hippel, Ted; Winget, D. E.; Kepler, S. O.; Nitta, Atsuko; Koester, Detlev; Althaus, Leandro; DeGennaro, Steven; von Hippel, Ted; Winget, D. E.We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g - i) and apparent magnitude (g) that covers the range - 1.0 < g - i < 0.2 and 15 < g < 19.5. We address the observed upturn in log g for WDs with T-eff less than or similar to 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with T-eff < 12,000 K. Finally, we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.