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Astrophysics and Astronomy

2004

University of Massachusetts Amherst

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Articles 1 - 21 of 21

Full-Text Articles in Physical Sciences and Mathematics

Evidence For Correlated Titanium And Deuterium Depletion In The Galactic Ism, Jason X. Prochaska, Todd M. Tripp, Christopher Howk Dec 2004

Evidence For Correlated Titanium And Deuterium Depletion In The Galactic Ism, Jason X. Prochaska, Todd M. Tripp, Christopher Howk

Todd M. Tripp

Current measurements indicate that the deuterium abundance in diffuse interstellar gas varies spatially by a factor of ~4 among sightlines extending beyond the Local Bubble. One plausible explanation for the scatter is the variable depletion of D onto dust grains. To test this scenario, we have obtained high signal-to-noise, high resolution profiles of the refractory ion Ti II along seven Galactic sightlines with D/H ranging from 0.65 to 2.1 × 10−5. These measurements, acquired with the recently upgraded Keck/HIRES spectrometer, indicate a correlation between Ti/H and D/H at the > 95% c.l. Therefore, our observations support the interpretation that D/H scatter …

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Evidence For Correlated Titanium And Deuterium Depletion In The Galactic Ism, Jason X. Prochaska, Todd M. Tripp, Christopher Howk Dec 2004

Evidence For Correlated Titanium And Deuterium Depletion In The Galactic Ism, Jason X. Prochaska, Todd M. Tripp, Christopher Howk

Astronomy Department Faculty Publication Series

Current measurements indicate that the deuterium abundance in diffuse interstellar gas varies spatially by a factor of ~4 among sightlines extending beyond the Local Bubble. One plausible explanation for the scatter is the variable depletion of D onto dust grains. To test this scenario, we have obtained high signal-to-noise, high resolution profiles of the refractory ion Ti II along seven Galactic sightlines with D/H ranging from 0.65 to 2.1 × 10−5. These measurements, acquired with the recently upgraded Keck/HIRES spectrometer, indicate a correlation between Ti/H and D/H at the > 95% c.l. Therefore, our observations support the interpretation that D/H scatter …

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The O Vi Absorbers Toward Pg 0953+415: High-Metallicity, Cosmic-Web Gas Far From Luminous Galaxies, Todd M. Tripp, Bastien Aracil, David V. Bowen, Edward B. Jenkins Nov 2004

The O Vi Absorbers Toward Pg 0953+415: High-Metallicity, Cosmic-Web Gas Far From Luminous Galaxies, Todd M. Tripp, Bastien Aracil, David V. Bowen, Edward B. Jenkins

Todd M. Tripp

The spectrum of the low-redshift QSO PG0953+415 shows two strong, intervening O VI absorption systems. To study the nature of these absorbers, we have used the Gemini Multiobject Spectrograph to conduct a deep spectroscopic galaxy redshift survey in the 5' x 5' field centered on the QSO. This survey is fully complete for r' < 19.7 and is 73% complete for r' < 21.0. We find three galaxies at the redshift of the higher-z O VI system (z = 0.14232) including a galaxy at projected distance rho = 155 kpc. We find no galaxies in the Gemini field at the redshift of the lower-z O VI absorber (z = 0.06807), which indicates that the nearest galaxy is more than 195 kpc away or has L < 0.04 L*. Previous shallower surveys covering a larger field have shown that the z = 0.06807 O VI absorber is affiliated with a group/filament of galaxies, but the nearest known galaxy has rho = 736 kpc. The z = 0.06807 absorber is notable for several reasons. The absorption profiles reveal simple kinematics indicative of quiescent material. The H I line widths and good alignment of the H I and metal lines favor photoionization and, moreover, the column density ratios imply a high metallicity: [M/H] = -0.3 +/- 0.12. The z = 0.14232 O VI system is more complex and less constrained but also indicates a relatively high metallicity. Using galaxy redshifts from SDSS, we show that both of the PG0953+415 O VI absorbers are located in large-scale filaments of the cosmic web. Evidently, some regions of the web filaments are highly metal enriched. We discuss the origin of the high-metallicity gas and suggest that the enrichment might have occurred long ago (at high z).

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Dark Matter Constraints From The Sagittarius Dwarf And Tail System, Steven R. Majewski, David R. Law, Kathryn V. Johnston, Michael F. Skrutskie, Martin D. Weinberg Jan 2004

Dark Matter Constraints From The Sagittarius Dwarf And Tail System, Steven R. Majewski, David R. Law, Kathryn V. Johnston, Michael F. Skrutskie, Martin D. Weinberg

Astronomy Department Faculty Publication Series

2MASS has provided a three-dimensional map of the >360 degree, wrapped tidal tails of the Sagittarius (Sgr) dwarf spheroidal galaxy, as traced by M giant stars. With the inclusion of radial velocity data for stars along these tails, strong constraints exist for dynamical models of the Milky Way-Sgr interaction. N-body simulations of Sgr disruption with model parameters spanning a range of initial conditions (e.g., Sgr mass and orbit, Galactic rotation curve, halo flattening) are used to find parameterizations that match almost every extant observational constraint of the Sgr system. We discuss the implications of the Sgr data and models for …

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Galaxy Clustering And Galaxy Bias In A Lambda Cdm Universe, Dh Weinberg, R Dave, N Katz, L Hernquist Jan 2004

Galaxy Clustering And Galaxy Bias In A Lambda Cdm Universe, Dh Weinberg, R Dave, N Katz, L Hernquist

Astronomy Department Faculty Publication Series

We investigate galaxy clustering and the correlations between galaxies and mass in the ΛCDM cosmological model (inflationary cold dark matter with Ωm = 0.4, ΩΛ = 0.6, h = 0.65, n = 0.95, and σ8 = 0.8), using a large, smoothed particle hydrodynamics simulation (SPH; with 2 × 1443 particles in a 50 h-1 Mpc cube). Simulated galaxies can be unambiguously identified as clumps of stars and cold gas a few kpc to a few tens of kpc across, residing in extended halos of hot gas and dark matter; the space density of the resolved …

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The Canada-Uk Deep Submillimetre Survey - Viii. Source Identifications In The 3-Hour Field, D Clements, S Eales, K Wojciechowski, T Webb, S Lilly, L Dunne, R Ivison, H Mccracken, Min Yun, A James, M Brodwin, O Le Fevre, W Gear Jan 2004

The Canada-Uk Deep Submillimetre Survey - Viii. Source Identifications In The 3-Hour Field, D Clements, S Eales, K Wojciechowski, T Webb, S Lilly, L Dunne, R Ivison, H Mccracken, Min Yun, A James, M Brodwin, O Le Fevre, W Gear

Astronomy Department Faculty Publication Series

We present optical, near-infrared (IR) and radio observations of the 3-hour field of the Canada–UK Deep Submillimetre Survey (CUDSS). Of the 27 submillimetre sources in the field, nine have secure identifications with either a radio source or a near-IR source. We show that the percentage of sources with secure identifications in the CUDSS is consistent with that found for the bright ‘8-mJy’ submillimetre survey, once allowance is made for the different submillimetre and radio flux limits. Of the 14 secure identifications in the two CUDSS fields, eight are very red objects (VROs) or extremely red objects (EROs), five have colours …

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Galaxy Cluster Formation From The Large-Scale Structure: A Case Study Of The Abell 2125 Complex At Z=0.247, Qd Wang, F Owen, M Ledlow, W Keel Jan 2004

Galaxy Cluster Formation From The Large-Scale Structure: A Case Study Of The Abell 2125 Complex At Z=0.247, Qd Wang, F Owen, M Ledlow, W Keel

Astronomy Department Faculty Publication Series

The structure of the universe is believed to have formed by clustering hierarchically from small to large scales. Much of this evolution occurs very slowly but at a few special times more rapid, violent activity may occur as major subunits collide at high velocities. The Abell 2125 complex ($z=0.247$) appears to be undergoing such an event as shown by modeling of the optical velocity field and by the detection with the VLA of an unusually large number of associated radio active galaxies. We present an 80 ksec Chandra imaging of Abell 2125, together with extensive complementary multi-wavelength data. We show …

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Confronting The Superbubble Model With X-Ray Observations Of 30 Doradus C, Da Smith, Qd Wang Jan 2004

Confronting The Superbubble Model With X-Ray Observations Of 30 Doradus C, Da Smith, Qd Wang

Astronomy Department Faculty Publication Series

We present an analysis of XMM-Newton observations of the superbubble 30 Dor C and compare the results with the predictions from the standard wind-blown bubble model. We find that the observed X-ray spectra cannot be fitted satisfactorily with the model alone and that there is evidence for nonthermal X-ray emission, which is particularly important at 4 keV. The combination of the bubble model and a power law gives a reasonable fit to the observed spectra. The thermal pressure and central temperature of the bubble are 3.3 × 10-11 dynes cm-2 and 7.4 × 106 K, respectively, and …

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A Chandra Acis View Of The Thermal Composite Supernova Remnant 3c 391, Y Chen, Y Su, Po Slane, Qd Wang Jan 2004

A Chandra Acis View Of The Thermal Composite Supernova Remnant 3c 391, Y Chen, Y Su, Po Slane, Qd Wang

Astronomy Department Faculty Publication Series

We present a 60 ks Chandra ACIS-S observation of the thermal composite supernova remnant 3C 391. The southeast-northwest elongated morphology is similar to that previously found in radio and X-ray studies. This observation unveils a highly clumpy structure of the remnant. Detailed spatially resolved spectral analysis of the small-scale features reveals that the interior gas is generally of normal metal abundance and has approached or basically reached ionization equilibrium. The hydrogen column density increases from southeast to northwest. Three mechanisms, radiative rim, thermal conduction, and cloudlet evaporation, may all play roles in the X-ray appearance of 3C 391 as a …

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Xmm-Newton Spectra Of Intermediate-Mass Black Hole Candidates: Application Of A Monte Carlo Simulated Model, Qd Wang, Y Yao, W Fukui, Sn Zhang, R Williams Jan 2004

Xmm-Newton Spectra Of Intermediate-Mass Black Hole Candidates: Application Of A Monte Carlo Simulated Model, Qd Wang, Y Yao, W Fukui, Sn Zhang, R Williams

Astronomy Department Faculty Publication Series

We present a systematic spectral analysis of six ultraluminous X-ray sources (NGC 1313 X-1 and X-2, IC 342 X-1, Ho IX X-1, NGC 5408 X-1, and NGC 3628 X-1) observed with the XMM-Newton observatory. These extranuclear X-ray sources in nearby late-type galaxies have been considered as intermediate-mass black hole candidates. We have performed Monte Carlo simulations of Comptonized multicolor blackbody accretion disks. This unified and self-consistent spectral model assumes a spherically symmetric, thermal corona around each disk and accounts for the radiation transfer in the Comptonization. We find that the model provides satisfactory fits to the XMM-Newton spectra of the …

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A New Population Of X-Ray Transients In The Galactic Centre, M Sakano, Rs Warwick, A Decourchelle, Qd Wang Jan 2004

A New Population Of X-Ray Transients In The Galactic Centre, M Sakano, Rs Warwick, A Decourchelle, Qd Wang

Astronomy Department Faculty Publication Series

A comparison of the XMM-Newton and Chandra Galactic Centre (GC) Surveys has revealed two faint X-ray transients with contrasting properties. The X-ray spectrum of XMM J174544-2913.0 shows a strong iron line with an equivalent width of ~2 keV, whereas that of XMM J174457-2850.3 is characterised by a very hard continuum with photon index ~1.0. The X-ray flux of both sources varied by more than 2 orders of magnitude over a period of months with a peak X-ray luminosity of 5 x 10^34 erg/s. We discuss the nature of these peculiar sources.

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Radial Gas Flows In Colliding Galaxies: Connecting Simulations And Observations, D Iono, Min Yun, Jc Mihos Jan 2004

Radial Gas Flows In Colliding Galaxies: Connecting Simulations And Observations, D Iono, Min Yun, Jc Mihos

Astronomy Department Faculty Publication Series

We investigate the detailed response of gas to the formation of transient and long-lived dynamical structures induced in the early stages of a disk-disk collision and identify observational signatures of radial gas inflow through a detailed examination of the collision simulation of an equal-mass bulge-dominated galaxy. Our analysis and discussion mainly focuses on the evolution of the diffuse and dense gas in the early stages of the collision, when the two disks are interacting but have not yet merged. Stars respond to the tidal interaction by forming both transient arms and long-lived m = 2 bars, but the gas response …

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High-Density Molecular Gas In The Infrared-Bright Galaxy System Vv 114, D Iono, Ptp Ho, Min Yun, S Matsushita, Ab Peck, K Sakamoto Jan 2004

High-Density Molecular Gas In The Infrared-Bright Galaxy System Vv 114, D Iono, Ptp Ho, Min Yun, S Matsushita, Ab Peck, K Sakamoto

Astronomy Department Faculty Publication Series

The new high-resolution CO (3-2) interferometric map of the IR-bright interacting galaxy system VV 114 observed with the Submillimeter Array reveals a substantial amount of warm and dense gas in the IR-bright but optically obscured galaxy, VV 114E, and the overlap region connecting the two nuclei. A 1.8 × 1.4 kpc concentration of CO (3-2) emitting gas with a total mass of 4 × 109 M coincides with the peaks of near-IR, mid-IR, and radio continuum emission found previously by others, identifying the dense fuel for the active galactic nucleus and/or the starburst activity there. Extensive CO (2-1) emission …

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Water Absorption From Line-Of-Sight Clouds Toward W49a, R Plume, Mj Kaufman, Da Neufeld, Ronald L. Snell, Dj Hollenbach, Pf Goldsmith, J Howe, Ea Bergin, Gj Melnick, F Bensch Jan 2004

Water Absorption From Line-Of-Sight Clouds Toward W49a, R Plume, Mj Kaufman, Da Neufeld, Ronald L. Snell, Dj Hollenbach, Pf Goldsmith, J Howe, Ea Bergin, Gj Melnick, F Bensch

Astronomy Department Faculty Publication Series

We have observed six clouds along the line of sight toward W49A using the Submillimeter Wave Astronomy Satellite and several ground-based observatories. The ortho-H2O 110 → 101 and OH (1665 and 1667 MHz) transitions are observed in absorption, whereas the low-J CO, 13CO, and C18O lines, as well as the [C I] 3P1-3P0 transition, are seen in emission. The emission lines allow us to determine the gas density (n ~ 1500-3000 cm-3) and CO column densities [N(CO) ~ 7.9 …

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A Two Micron All Sky Survey View Of The Sagittarius Dwarf Galaxy. Ii. Swope Telescope Spectroscopy Of M Giant Stars In The Dynamically Cold Sagittarius Tidal Stream, Sr Majewski, We Kunkel, Dr Law, Rj Patterson, Aa Polak, Hj Rocha-Pinto, Jd Crane, Pm Frinchaboy, Cb Hummels, Kv Johnston, J Rhee, Mf Skrutskie, M Weinberg Jan 2004

A Two Micron All Sky Survey View Of The Sagittarius Dwarf Galaxy. Ii. Swope Telescope Spectroscopy Of M Giant Stars In The Dynamically Cold Sagittarius Tidal Stream, Sr Majewski, We Kunkel, Dr Law, Rj Patterson, Aa Polak, Hj Rocha-Pinto, Jd Crane, Pm Frinchaboy, Cb Hummels, Kv Johnston, J Rhee, Mf Skrutskie, M Weinberg

Astronomy Department Faculty Publication Series

We have obtained moderate resolution (~6 km s-1) spectroscopy of several hundred M giant candidates selected from Two Micron All Sky Survey photometry. Radial velocities are presented for stars mainly in the southern Galactic hemisphere, and the primary targets have Galactic positions consistent with association to the tidal tail system of the Sagittarius (Sgr) dwarf galaxy. M giant stars selected from the apparent trailing debris arm of Sgr have velocities showing a clear trend with orbital longitude, as expected from models of the orbit and destruction of Sgr. A minimum 8 kpc width of the trailing stream about the Sgr …

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A Study Of Co Emission In High-Redshift Qsos Using The Owens Valley Millimeter Array, Lj Hainline, Nz Scoville, Min Yun, Dw Hawkins, Dt Frayer, Kg Isaak Jan 2004

A Study Of Co Emission In High-Redshift Qsos Using The Owens Valley Millimeter Array, Lj Hainline, Nz Scoville, Min Yun, Dw Hawkins, Dt Frayer, Kg Isaak

Astronomy Department Faculty Publication Series

Searches for CO emission in high-redshift objects have traditionally suffered from the accuracy of optically derived redshifts for lack of bandwidth in correlators at radio observatories. This problem has motivated the creation of the new COBRA continuum correlator with 4 GHz available bandwidth at the Owens Valley Radio Observatory Millimeter Array. Presented here are the first scientific results from COBRA. We report detections of redshifted CO (J = 3 → 2) emission in the QSOs SMM J04135+10277 and VCV J140955.5+562827, as well as a probable detection in RX J0911.4+0551. At redshifts of z = 2.846, 2.585, and 2.796, we …

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Multiwavelength Observations Of The Gas-Rich Host Galaxy Of Pds 456: A New Challenge For The Ulirg-To-Qso Transition Scenario, Min Yun, Na Reddy, Nz Scoville, Dt Frayer, Ei Robson, Rpj Tilanus Jan 2004

Multiwavelength Observations Of The Gas-Rich Host Galaxy Of Pds 456: A New Challenge For The Ulirg-To-Qso Transition Scenario, Min Yun, Na Reddy, Nz Scoville, Dt Frayer, Ei Robson, Rpj Tilanus

Astronomy Department Faculty Publication Series

We report new K-band, radio continuum, and CO (1-0) imaging observations and 850 μm photometric observations of PDS 456, the most luminous QSO in the local universe (z < 0.3). The 06 resolution K-band image obtained using the Keck Telescope shows three compact mK ~ 16.5 (MK ~ -21) sources at a projected distance of ~10 kpc to the southwest, and the host galaxy of PDS 456 may be interacting or merging with one or more companions. Observations using the Owens Valley Radio Observatory millimeter array have revealed a narrow CO (1-0) line (FWHM = 181 km s-1 …

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Radio And Far-Infrared Emission As Tracers Of Star Formation And Active Galactic Nuclei In Nearby Cluster Galaxies, Na Reddy, Min Yun Jan 2004

Radio And Far-Infrared Emission As Tracers Of Star Formation And Active Galactic Nuclei In Nearby Cluster Galaxies, Na Reddy, Min Yun

Astronomy Department Faculty Publication Series

We have studied the radio and far-infrared (FIR) emission from 114 galaxies in the seven nearest clusters (<100 Mpc) with prominent X-ray emission to investigate the impact of the cluster environment on the star formation and active galactic nucleus (AGN) activity in the member galaxies. The X-ray selection criterion is adopted to focus on the most massive and dynamically relaxed clusters. A large majority of cluster galaxies show an excess in radio emission over that predicted from the radio-FIR correlation, the fraction of sources with radio excess increases toward cluster cores, and the radial gradient in the FIR/radio flux ratio is a result of radio enhancement. Of the radio-excess sources, 70% are early-type galaxies, and the same fraction host an AGN. The galaxy density drops by a factor of 10 from the composite cluster center out to 1.5 Mpc, yet galaxies show no change in FIR properties over this region and show no indication of mass segregation. We have examined in detail the physical mechanisms that might impact the FIR and radio emission of cluster galaxies. While collisional heating of dust may be important for galaxies in cluster centers, it appears to have a negligible effect on the observed FIR emission for our sample galaxies. The correlations between radio and FIR luminosity and radius could be explained by magnetic compression from thermal intracluster medium pressure. We also find that simple delayed harassment cannot fully account for the observed radio, FIR, and mid-IR properties of cluster galaxies.

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Dense, Ionized, And Neutral Gas Surrounding Sagittarius A*, H Shukla, Min Yun, Nz Scoville Jan 2004

Dense, Ionized, And Neutral Gas Surrounding Sagittarius A*, H Shukla, Min Yun, Nz Scoville

Astronomy Department Faculty Publication Series

We present high-resolution H41α hydrogen recombination line observations of the 12 (3 pc) region surrounding Sagittarius A* (Sgr A*) at 92 GHz using the Millimeter Array at the Owens Valley Radio Observatory (OVRO) with an angular resolution of 7'' × 3'' and velocity resolution of 13 km s-1. New observations of H31α, H35α, H41α, and H44α lines were obtained using the NRAO 12 m telescope, and their relative line strengths are interpreted in terms of various possible emission mechanisms. These NRAO 12 m measurements are the most extensive recombination line survey of this region to date. These OVRO …

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Correction For The Flux Measurement Bias In X-Ray Source Detection, Qd Wang Jan 2004

Correction For The Flux Measurement Bias In X-Ray Source Detection, Qd Wang

Astronomy Department Faculty Publication Series

With a high spatial resolution imaging instrument such as the Chandra ACIS, one can confidently identify an X-ray source with only a few detected counts. The detection threshold of such sources, however, varies strongly across the field of view of the instrument. Furthermore, the low-detection counting statistics, together with a typical steep source number-flux relation, causes more intrinsically faint sources to be detected at apparently higher fluxes than the other way around. We quantify this "X-ray Eddington bias" as well as the detection threshold variation and devise simple procedures for their corrections. To illustrate our technique, we present results from …

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X-Raying A2125: A Large-Scale Hierarchical Complex Of Galaxies And Hot Gas, Qd Wang, F Owen, M Ledlow Jan 2004

X-Raying A2125: A Large-Scale Hierarchical Complex Of Galaxies And Hot Gas, Qd Wang, F Owen, M Ledlow

Astronomy Department Faculty Publication Series

We present an 82 ks Chandra ACIS-I observation of a large-scale hierarchical complex, which consists of various clusters/groups of galaxies and low surface brightness X-ray emission at z = 0.247. This high-resolution Chandra observation allows us for the first time to separate unambiguously the X-ray contributions from discrete sources and large-scale diffuse hot gas. We detect 99 X-ray sources in a 17' × 17' field. Ten of these sources are identified as members of the complex and are mostly radio-bright. Whereas unresolved X-ray sources tend to be associated with galaxies in intermediate density environments, extended X-ray emission peak at bright …

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