Physical Sciences and Mathematics Commons^™

Bar-Driven Dark Halo Evolution: A Resolution Of The Cusp-Core Controversy, Md Weinberg, N Katz

Astronomy Department Faculty Publication Series

Simulations predict that the dark matter halos of galaxies should have central cusps, while those inferred from observed galaxies do not have cusps. We demonstrate, using both linear perturbation theory and n-body simulations, that a disk bar, which should be ubiquitous in forming galaxies, can produce cores in cuspy cold dark matter profiles within five bar orbital times. Simulations of forming galaxies suggest that one of Milky Way size could have a 10 kpc primordial bar; this bar will remove the cusp out to ~2.5 kpc in ~1.5 Gyr, while the disk would lose only ~8% of its original angular …

Toward A Precise Measurement Of Matter Clustering: Ly Alpha Forest Data At Redshifts 2-4, Rac Croft, Dh Weinberg, M Bolte, S Burles, L Hernquist, N Katz, D Kirkman, D Tytler

Astronomy Department Faculty Publication Series

We measure the filling factor, correlation function, and power spectrum of transmitted flux in a large sample of Lyα forest spectra, comprised of 30 Keck HIRES spectra and 23 Keck LRIS spectra. We infer the linear matter power spectrum P(k) from the flux power spectrum P_F(k), using an improved version of the method of Croft et al. that accounts for the influence of redshift-space distortions, nonlinearity, and thermal broadening on the shape of P_F(k). The evolution of the shape and amplitude of P(k) over the redshift …

Comparing Simulations And Observations Of The Ly Alpha Forest. I. Methodology, Ce Petry, Cd Impey, N Katz, Dh Weinberg, Le Hernquist

Astronomy Department Faculty Publication Series

We describe techniques for comparing spectra extracted from cosmological simulations and observational data, using the same methodology to link Lyα properties derived from the simulations with properties derived from observational data. The eventual goal is to measure the coherence or clustering properties of Lyα absorbers using observations of quasar pairs and groups. We quantify the systematic underestimate in opacity that is inherent in the continuum-fitting process of observed spectra over a range of resolution and signal-to-noise ratio (S/N). We present an automated process for detecting and selecting absorption features over the range of resolution and S/N of typical observational data …

Lyman Alpha Absorber Correlations And The Bias Of The Lyman Alpha Forest, R Dave, N Katz, Dh Weinberg

Astronomy Department Faculty Publication Series

Lyman alpha absorber correlations contain information about the underlying density distribution associated with a particular class of absorbers. As such, they provide an opportunity to independently measure the "bias" of the Lyman alpha forest, i.e. the relationship between HI column density and underlying dark matter density. In these proceedings we use hydrodynamic simulations to investigate whether the evolution of this bias is measurable from observable correlations. Unfortunately, the increasingly complex physics in the IGM at z<1 makes a direct measurement of the bias difficult.>Nevertheless, current simulations do make predictions for HI absorber correlations that are in broad agreement with observations at both high and low redshift, thus …

A Critical Examination Of Hypernova Remnant Candidates In M101. Ii. Ngc 5471b, C-Hr Chen, Y-H Chu, R Gruendl, S-P Lai, Qd Wang

Astronomy Department Faculty Publication Series

NGC 5471B has been suggested to contain a hypernova because of its extraordinarily bright X-ray emission. To assess its true nature, we have obtained high-resolution images in continuum bands and nebular lines with the Hubble Space Telescope, and high-dispersion long-slit spectra with the Kitt Peak National Observatory 4 m echelle spectrograph. The images reveal three supernova remnant (SNR) candidates in the giant H II region NGC 5471, the brightest one being the 77 × 60 pc shell in NGC 5471B. The Hα velocity profile of NGC 5471B can be decomposed into a narrow component (FWHM 41 km s^{-1 …}

A Chandra Observation Of Gro J1744–28: The Bursting Pulsar In Quiescence, R Wijnands, Qd Wang

Astronomy Department Faculty Publication Series

We present a Chandra/Advanced CCD Imaging Spectrometer I-array observation of GRO J1744-28. We detected a source at a position of R.A. = 17^h44^m33.s09, decl. = -28^°44'270 (J2000.0; with a 1 σ error of ~08), consistent with both ROSAT and interplanetary network localizations of GRO J1744-28 when it was in outburst. This makes it likely that we have detected the quiescent X-ray counterpart of GRO J1744-28. Our Chandra position demonstrates that the previously proposed infrared counterpart is not related to GRO J1744-28. The 0.5-10 keV luminosity of the source is (2-4) × 10^{33 …}

Ultraluminous X-Ray Source 1e 0953.8+6918 (M81 X-9): An Intermediate-Mass Black Hole Candidate And Its Environs, Qd Wang

Astronomy Department Faculty Publication Series

We present a ROSAT and ASCA study of the Einstein source X-9 and its relation to a shock-heated shell-like optical nebula in a tidal arm of the M81 group of interacting galaxies. Our ASCA observation of the source shows a flat and featureless X-ray spectrum well described by a multicolour disc blackbody model. The source most likely represents an optically thick accretion disc around an intermediate-mass black hole (M∼10² M_⊙) in its high/soft state, similar to other variable ultraluminous X-ray sources observed in nearby disc galaxies. Using constraints derived from both the innermost stable orbit …

The Apparent Host Galaxy Of Pks 1413+135: Hubble Space Telescope,* Asca, And Very Long Baseline Array ** Observations, Es Perlman, Jt Stocke, Cl Carilli, M Sugiho, M Tashiro, G Madejski, Qd Wang, J Conway

Astronomy Department Faculty Publication Series

PKS 1413+135 (z = 0.24671) is one of very few radio-loud active galactic nuclei (AGNs) with an apparent spiral host galaxy. Previous authors have attributed its nearly exponential infrared cutoff to heavy absorption but have been unable to place tight limits on the absorber or its location in the optical galaxy. In addition, doubts remain about the relationship of the AGN to the optical galaxy given the observed lack of reemitted radiation. We present new Hubble Space Telescope (HST), ASCA, and Very Long Baseline Array observations, which throw significant new light on these issues. The HST …

Studying The Nearby Universe With Chandra, Qd Wang

Astronomy Department Faculty Publication Series

I highlight results from Chandr observations of nearby galaxies, including the Milky Way. These observations have offered insights into old mysteries and indications of new high energy astrophysical phenomena and processes that are yet to be understood.

The Vla H I Observations Of Stephan's Quintet (Hcg 92)*, Ba Williams, Min Yun, L Verdes-Montenegro

Astronomy Department Faculty Publication Series

Using the Very Large Array, we have made spectral-line and continuum observations of the neutral hydrogen in the direction of the compact group of galaxies Stephan's Quintet. The high-velocity clouds between 5600 and 6600 km s^-1, the disk of the foreground galaxy NGC 7320 at 800 km s^-1, the extended continuum ridge near the center of the group, and three faint dwarflike galaxies in the surrounding field were imaged with the C, CS, and D configurations. Four of the H I clouds previously detected are confirmed. The two largest H I features are coincident with and …

Radio-To-Far-Infrared Spectral Energy Distribution And Photometric Redshifts For Dusty Starburst Galaxies, Min Yun, Clc Carilli

Astronomy Department Faculty Publication Series

As a logical next step in improving the radio-to-submillimeter spectral index as a redshift indicator, we have investigated a technique of using the entire radio-to-far-infrared spectral energy distribution (SED) for deriving photometric redshifts for dusty starburst galaxies at high redshift. A dusty starburst SED template is developed from the theoretical understanding of various emission mechanisms related to massive star formation processes, and the template parameters are selected by examining the observed properties of 23 IR-selected starburst galaxies: T_d = 58 K, β = 1.35, and f_nth = 1. The major improvement in using this template SED for deriving …

Star Formation In Bright-Rimmed Clouds. I. Millimeter And Submillimeter Molecular Line Surveys, Ch De Vries, Gopal Narayanan, Ronald L. Snell

Astronomy Department Faculty Publication Series

We present the results of the first detailed millimeter and submillimeter molecular line survey of bright-rimmed clouds, observed at FCRAO in the CO (J = 1 → 0), C¹⁸O (J = 1 → 0), HCO⁺ (J = 1 → 0), H¹³CO⁺ (J = 1 → 0), and N₂H⁺ (J = 1 → 0) transitions, and at the Heinrich Hertz Telescope in the CO (J = 2 → 1), HCO⁺ (J = 3 → 2), HCO⁺ (J = 4 → 3), H …

An Upper Limit To The Age Of The Galactic Bar, Aa Cole, Md Weinberg

Astronomy Department Faculty Publication Series

Using data from the Two Micron All Sky Survey, we identify a population of infrared carbon stars with J-KS ≥ 2 in the Milky Way. These stars are shown to trace the stellar bar previously identified in IR and optical surveys. The properties of C stars strongly suggest that they are of intermediate age. We conclude that the bar is likely to have formed more recently than 3 Gyr ago and must be younger than 6 Gyr. Implications and further tests of this conclusion are briefly discussed.

Sensitive Limits On The Water Abundance In Cold Low-Mass Molecular Cores, Ea Bergin, Ronald L. Snell

Astronomy Department Faculty Publication Series

We present Submillimeter Wave Astronomy Satellite observations of water vapor in two cold starless clouds, B68 and core D in ρ Ophiuchi. Sensitive nondetections of the 1₁₀-1₀₁ transition of o-H₂O are reported for each source. Both molecular cores have been previously examined by detailed observations that have characterized the physical structure. Using these rather well-defined physical properties and a Monte Carlo radiation transfer model, we have removed one of the largest uncertainties from the abundance calculation and set the lowest water abundance limit to date in cold low-mass molecular cores. These limits are x(o-H …

The Growth Of Galaxies In Cosmological Simulations, Jh Choi, N Katz, C Murali, D Weinberg, R Dave, L Hernquist

Astronomy Department Faculty Publication Series

We use hydrodynamic simulations to examine how the baryonic components of galaxies are assembled, focusing on the relative importance of mergers and smooth accretion in the formation of ~L_* systems. In our primary simulation, which models a (50 h^-1 Mpc)³ comoving volume of a Λ-dominated cold dark matter universe, the space density of objects at our (64 particle) baryon mass resolution threshold M_c = 5.4 × 10¹⁰ M corresponds to that of observed galaxies with L ~ L_*/4. Galaxies above this threshold gain most of their mass by accretion rather than by …

High-Redshift Galaxies In Cold Dark Matter Models, Dh Weinberg, L Hernquist, N Katz

Astronomy Department Faculty Publication Series

We use hydrodynamic cosmological simulations to predict the star formation properties of high-redshift galaxies (z = 2-6) in five variants of the inflationary cold dark matter scenario, paying particular attention to z = 3, the redshift of the largest "Lyman break galaxy" (LBG) samples. Because we link the star formation timescale to the local gas density, the rate at which a galaxy forms stars is governed mainly by the rate at which it accretes cooled gas from the surrounding medium. At z = 3, star formation in most of the simulated galaxies is steady on ~200 Myr timescales, and …

X-Ray Scaling Relations Of Galaxy Groups In A Hydrodynamic Cosmological Simulation, R Dave, N Katz, Dh Weinberg

Astronomy Department Faculty Publication Series

We examine the scalings of X-ray luminosity, temperature, and dark matter or galaxy velocity dispersion for galaxy groups in a ΛCDM cosmological simulation, which incorporates gravity, gas dynamics, radiative cooling, and star formation, but no substantial nongravitational heating. In agreement with observations, the simulated L_X-σ and L_X-T_X relations are steeper than those predicted by adiabatic simulations or self-similar models, with L_X σ^4.4 and L_X T for massive groups and significantly steeper relations below a break at σ 180 km s^-1 (T_X 0.7 keV). The T_X-σ relation …

Title: Chandra Observations Of The Galactic Center And Nearby Edge-On Galaxies, Qd Wang

Astronomy Department Faculty Publication Series

I review our recent Chandra surveys of the center region of the Milky Way and other nearby edge-on galaxies. Our Galactic center survey provides an unprecedented high-resolution, broad-band X-ray panorama of a 0.8x2 square degree swath along the Galactic plane. Our preliminary analysis has led a detection of about 1000 discrete sources. We find that the diffuse X-ray emission dominates over the contribution from faint discrete sources and is globally associated with distinct interstellar structures observed at radio and mid-infrared wavelengths. We study how high-energy activities in the center region affect the immediate vicinity and may influence other aspects of …

The Nature Of The Faint Far-Infrared Extragalactic Source Population: Optical/Nir And Radio Follow-Up Observationts Of Isophot Deep-Field Sources Using The Keck, Subaru, And Vla Telescopes., Y Kakazu, Db Sanders, Rd Joseph, Ll Cowie, T Murayama, Y Taniguchi, S Veilleux, Min Yun, K Kawara, Y Sofue, Y Sato, H Okuda, K Wakamatsu, T Matsumoto, H Matsuhara

Astronomy Department Faculty Publication Series

In order to search for obscured objects at high redshifts, we have made deep far-infrared (FIR) deep survey in the Lockman Hole using ISOPHOT onboard ISO (Kawara et al. 1998, A&A, 336, L9). In this survey several tens of FIR sources have been found at 95micron and 175micron. Here we present results of optical and NIR spectroscopic followup observations performed at the W. M.Keck Observatory.

High-Resolution Imaging Of Molecular Line Emission From High-Redshift Qsos, Cl Carilli, K Kohno, R Kawabe, K Ohta, C Henkel, Km Menten, Min Yun, A Petric, Y Tutui

Astronomy Department Faculty Publication Series

We present moderate- (1'') and high-resolution (02) observations of the CO (2–1) emission at 43 GHz and radio continuum emission at 1.47 GHz from the z = 4.7 QSO BRI 1202-0725 and the z = 4.4 QSO BRI 1335-0417 using the Very Large Array. The moderate-resolution observations show that in both cases the CO emission is spatially resolved into two components separated by 1'' for BRI 1335-0417 and 4'' for BRI 1202-0725. The high-resolution observations show that each component has substructure on scales ~02–05, with intrinsic brightness temperatures ≥20 K. The CO ladder from (2–1) up to (7–6) suggests a …

Detection Of Infall Signatures Toward Serpens Smm4, Gopal Narayanan, G Moriarty-Schieven, Ck Walker, Hm Butner

Astronomy Department Faculty Publication Series

We present the detection of kinematic infall signatures toward the Class 0 protostellar system SMM4 in the Serpens cloud core. We have observed the dense molecular gas toward the embedded source using millimeter and submillimeter line transitions of density sensitive molecular tracers. High signal-to-noise ratio maps obtained in HCO⁺ J = 1 → 0, J = 3 → 2, and J = 4 → 3, and CS J = 2 → 1 show the blue-bulge infall signature. The blue-bulge infall signature can be observed in the centroid velocity maps of protostellar objects when infall dominates over rotation. The line …

Physical Parameter Eclipse Mapping Of The Quiescent Disc In V2051 Ophiuchi, S Vrielmann, R Stiening, W Offutt

Astronomy Department Faculty Publication Series

We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping (PPEM) method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions, and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13 500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has …

Discovery Of A 136 Millisecond Radio And X-Ray Pulsar In Supernova Remnant G54.1+0.3, F Camilo, Dr Lorimer, Ndr Bhat, Ev Gotthelf, Jp Halpern, Qd Wang, Fj Lu, N Mirabal

Astronomy Department Faculty Publication Series

We report the discovery of a pulsar with period P = 136 ms and dispersion measure 308 cm^-3 pc in a deep observation of the supernova remnant (SNR) G54.1+0.3 with the Arecibo radio telescope. Timing measurements of the new pulsar, J1930+1852, reveal a characteristic age of P/2 = 2900 yr and a spin-down luminosity of = 1.2 × 10³⁷ ergs s^-1. We have subsequently searched archival ASCA X-ray data of this SNR and detect pulsations with a consistent period. These findings ensure that PSR J1930+1852 is the pulsar that powers the "Crab-like" SNR G54.1+0.3. Together …

Chandra Observations Of The Bursting X-Ray Transient Sax J1747.0–2853 During Low-Level Accretion Activity, R Wijnands, Jm Miller, Qd Wang

Astronomy Department Faculty Publication Series

We present Chandra/ACIS observations of the bursting X-ray transient SAX J1747.0-2853 performed on 2001 July 18. We detected a bright source at the position of R.A. = 17^h47^m02.s60 and decl. = -28°52'589 (J2000.0, with a 1 σ error of ~07), consistent with the BeppoSAX and ASCA positions of SAX J1747.0-2853 and with the Ariel V position of the transient GX +0.2-0.2, which was active during the 1970s. The 0.5-10 keV luminosity of the source during our observations was ~ 3 × 10³⁵ ergs s^-1 (assuming a distance of 9 kpc), demonstrating that the …

X-Ray Thread G0.13–0.11: A Pulsar Wind Nebula?, Qd Wang, F Lu, Cc Lang

Astronomy Department Faculty Publication Series

We have examined Chandra observations of the recently discovered X-ray thread G0.13-0.11 in the Galactic center Radio Arc region. Part of the Chandra data was studied by Yusef-Zadeh, Law, & Wardle, who reported the detection of 6.4 keV line emission in this region. We find, however, that this line emission is not associated with G0.13-0.11. The X-ray spectrum of G0.13-0.11 is well-characterized by a simple power law with an energy slope of 1.8 (90% confidence uncertainties). Similarly, the X-ray spectrum of the pointlike source embedded in G0.13-0.11 has a power-law energy slope of 0.9. The 2-10 keV band luminosities of …

Detection Of X-Ray Emission From The Arches Cluster Near The Galactic Center, F Yusef-Zadeh, C Claw, M Wardle, Qd Wang, A Fruscione, Cc Lang, A Cortera

Astronomy Department Faculty Publication Series

The Arches cluster is an extraordinarily compact massive star cluster with a core radius of about 10'' (~0.4 pc) and consisting of more than 150 O star candidates with initial stellar masses greater than 20 M near G0.12-0.02. X-ray observations of the radio Arc near the Galactic center at l ~ 02, which contains the Arches cluster, have been carried out with the Advanced CCD Imaging Spectrometer (ACIS) on board Chandra X-Ray Observatory. We report the detection of two X-ray sources from the Arches cluster embedded within a bath of diffuse X-ray emission extending beyond the edge of the …

Chandra Observation Of Supernova Remnant G54.1+0.3: A Close Cousin Of The Crab Nebula, Fj Lu, Qd Wang, B Aschenbach, P Durouchoux, Lm Song

Astronomy Department Faculty Publication Series

We present a Chandra Advanced CCD Imaging Spectrometer observation of supernova remnant G54.1+0.3. This supernova remnant is resolved into several distinct X-ray-emitting components: a central bright pointlike source (CXOU J193030.13+185214.1), a surrounding ring, bipolar elongations, plus low surface brightness diffuse emission. The spectra of these components are all well described by power-law models; the spectral index steepens with increasing distance from the pointlike source. We find no evidence for any thermal plasma emission that would correspond to shocked interstellar medium or ejecta. The observed morphological and spectral characteristics suggest that G54.1+0.3 is the closest "cousin" of the Crab Nebula—a pulsar …

Hiccups In The Night: X-Ray Monitoring Of The Two Crab-Like Lmc Pulsars, Ev Gotthelf, W Zhang, Fe Marshall, J Middleditch, Qd Wang

Astronomy Department Faculty Publication Series

We are undertaking an extensive X-ray monitoring campaign of the two Crab-like pulsars in the Large Magellanic Clouds, PSR B0540-69 and PSR J0537-6910. We present our current phase-connected timing analysis derived from a set of 50 pointed X-ray observations spanning several years. From our initial 1.2 yr monitoring program of the young 50 ms pulsar PSR B0540-69, we find the first compelling evidence for a glitch in its rotation. This glitch is characterized by Delta nu / nu = (1.90+-0.05) x 10^-9 and Delta nu_dot / nu_dot = (8.5+-0.5) x 10^-5. Taking into account the …