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Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

2007

University of Massachusetts Amherst

Astronomy Department Faculty Publication Series

Articles 1 - 27 of 27

Full-Text Articles in Physical Sciences and Mathematics

The Bar-Halo Interaction - I. From Fundamental Dynamics To Revised N-Body Requirements, Md Weinberg, N Katz Jan 2007

The Bar-Halo Interaction - I. From Fundamental Dynamics To Revised N-Body Requirements, Md Weinberg, N Katz

Astronomy Department Faculty Publication Series

A galaxy remains near equilibrium for most of its history. Only through resonances can non-axisymmetric features, such as spiral arms and bars, exert torques over large scales and change the overall structure of the galaxy. In this paper, we describe the resonant interaction mechanism in detail, derive explicit criteria for the particle number required to simulate these dynamical processes accurately using N-body simulations, and illustrate them with numerical experiments. To do this, we perform a direct numerical solution of perturbation theory, in short, by solving for each orbit in an ensemble and make detailed comparisons with N-body simulations. The criteria …

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The Opacity Of Spiral Galaxy Disks. Viii. Structure Of The Cold Ism, Bw Holwerda, B Draine, Kd Gordon, Ra Gonzalez, D Calzetti, M Thornley, B Buckalew, Rj Allen, Pc Van Der Kruit Jan 2007

The Opacity Of Spiral Galaxy Disks. Viii. Structure Of The Cold Ism, Bw Holwerda, B Draine, Kd Gordon, Ra Gonzalez, D Calzetti, M Thornley, B Buckalew, Rj Allen, Pc Van Der Kruit

Astronomy Department Faculty Publication Series

The quantity of dust in a spiral disk can be estimated using the dust's typical emission or the extinction of a known source. In this paper we compare two techniques, one based on emission and one on absorption, applied to sections of 14 disk galaxies. The two measurements reflect, respectively, the average and apparent optical depth of a disk section. Hence, they depend differently on the average number and optical depth of ISM structures in the disk. The small-scale geometry of the cold ISM is critical for accurate models of the overall energy budget of spiral disks. ISM geometry, relative …

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Warm Molecular Hydrogen In The Spitzer Sings Galaxy Sample, H Roussel, G Helou, Dj Hollenbach, Bt Draine, Jd Smith, L Armus, E Schinnerer, F Walter, Cw Engelbracht, Md Thornley, Rc Kennicutt, D Calzetti, Da Dale, Ej Murphy, C Bot Jan 2007

Warm Molecular Hydrogen In The Spitzer Sings Galaxy Sample, H Roussel, G Helou, Dj Hollenbach, Bt Draine, Jd Smith, L Armus, E Schinnerer, F Walter, Cw Engelbracht, Md Thornley, Rc Kennicutt, D Calzetti, Da Dale, Ej Murphy, C Bot

Astronomy Department Faculty Publication Series

Results on the properties of warm molecular hydrogen in 57 normal galaxies are derived from measurements of H2 rotational transitions, obtained as part of SINGS. This study extends previous extragalactic surveys of emission lines of H2 to fainter and more common systems (LFIR = 107-6 × 1010 L). The 17 μm S(1) transition is securely detected in the nuclear regions of 86% of galaxies with stellar masses above 109.5 M. The derived column densities of warm H2 (T ≥ 100 K), although averaged over kiloparsec-scale areas, are commensurate with values observed in resolved photodissociation regions. They amount to between 1% …

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The Incidence Of Highly Obscured Star-Forming Regions In Sings Galaxies, Mkm Prescott, Rc Kennicutt, Gj Bendo, Ba Buckalew, D Calzetti, Cw Engelbracht, Kd Gordon, Dj Hollenbach, Jc Lee, J Moustakas, Da Dale, G Helou, Th Jarrett, Ej Murphy, Jdt Smith, S Akiyama, Ml Sosey Jan 2007

The Incidence Of Highly Obscured Star-Forming Regions In Sings Galaxies, Mkm Prescott, Rc Kennicutt, Gj Bendo, Ba Buckalew, D Calzetti, Cw Engelbracht, Kd Gordon, Dj Hollenbach, Jc Lee, J Moustakas, Da Dale, G Helou, Th Jarrett, Ej Murphy, Jdt Smith, S Akiyama, Ml Sosey

Astronomy Department Faculty Publication Series

Using the new capabilities of Spitzer and extensive multiwavelength data from SINGS, it is now possible to study the infrared properties of star formation in nearby galaxies down to scales equivalent to large H II regions. We are therefore able to determine what fraction of large, infrared-selected star-forming regions in normal galaxies are highly obscured and address how much of the star formation we miss by relying solely on the optical portion of the spectrum. Employing a new empirical method for deriving attenuations of infrared-selected star-forming regions, we investigate the statistics of obscured star formation on 500 pc scales in …

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Gaps In The Cloud Cover? Comparing Extinction Measures In Spiral Disks, Bw Holwerda, M Meyer, M Regan, D Calzetti, Kd Gordon, Jd Smith, D Dale, Cw Engelbracht, T Jarrett, M Thornley, C Bot, B Buckalew, Rc Kennicutt, Ra Gonzalez Jan 2007

Gaps In The Cloud Cover? Comparing Extinction Measures In Spiral Disks, Bw Holwerda, M Meyer, M Regan, D Calzetti, Kd Gordon, Jd Smith, D Dale, Cw Engelbracht, T Jarrett, M Thornley, C Bot, B Buckalew, Rc Kennicutt, Ra Gonzalez

Astronomy Department Faculty Publication Series

Dust in galaxies can be mapped either by the FIR/submillimeter emission, the optical or infrared reddening of starlight, or the extinction of a known background source. We compare two dust extinction measurements for a set of 15 sections in 13 nearby galaxies to determine the scale of the dusty interstellar medium (ISM) responsible for disk opacity: one using stellar reddening and the other a known background source. In our earlier papers, we presented extinction measurements of 29 galaxies, based on calibrated counts of distant background objects identified though foreground disks in Hubble Space Telescope WFPC2 images. For the 13 galaxies …

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Stellar Clusters In Ngc 1313: Evidence Of Infant Mortality, Anne Pellerin, Martin Meyer, Jason Harris, Daniela Calzetti Jan 2007

Stellar Clusters In Ngc 1313: Evidence Of Infant Mortality, Anne Pellerin, Martin Meyer, Jason Harris, Daniela Calzetti

Astronomy Department Faculty Publication Series

We present evidence that infant mortality of stellar clusters is likely to be a major and very efficient process for the dissolution of young clusters in the spiral galaxy NGC 1313. Performing stellar PSF photometry on archival HST/ACS images of the galaxy, we find that a large fraction of early B-type stars are seen outside of star clusters and well spread within the galactic disk, consistent with the scenario of infant mortality. We also calculate the UV flux produced by the stars in and out the clusters and find that 75 to 90% of the UV flux in NGC 1313 …

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Multiwavelength Study Of Massive Galaxies At Z Similar To 2. I. Star Formation And Galaxy Growth, E Daddi, M Dickinson, G Morrison, R Chary, A Cimatti, D Elbaz, D Frayer, A Renzini, A Pope, Dm Alexander, Fe Bauer, M Giavalisco, M Huynh, J Kurk, M Mignoli Jan 2007

Multiwavelength Study Of Massive Galaxies At Z Similar To 2. I. Star Formation And Galaxy Growth, E Daddi, M Dickinson, G Morrison, R Chary, A Cimatti, D Elbaz, D Frayer, A Renzini, A Pope, Dm Alexander, Fe Bauer, M Giavalisco, M Huynh, J Kurk, M Mignoli

Astronomy Department Faculty Publication Series

No abstract provided.

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The Spatial Clustering Of Mid-Ir Selected Star Forming Galaxies At Z Similar To 1 In The Goods Fields, R Gilli, E Daddi, R Chary, M Dickinson, D Elbaz, M Giavalisco, M Kitzbichler, D Stern, E Vanzella Jan 2007

The Spatial Clustering Of Mid-Ir Selected Star Forming Galaxies At Z Similar To 1 In The Goods Fields, R Gilli, E Daddi, R Chary, M Dickinson, D Elbaz, M Giavalisco, M Kitzbichler, D Stern, E Vanzella

Astronomy Department Faculty Publication Series

We present the first spatial clustering measurements of z~1, 24um-selected, star forming galaxies in the Great Observatories Origins Deep Survey (GOODS). The sample under investigation includes 495 objects in GOODS-South and 811 objects in GOODS-North selected down to flux densities of f_24>20 uJy and z_AB<23.5 mag, for which spectroscopic redshifts are available. The median redshift, IR luminosity and star formation rate (SFR) of the samples are z~0.8, L_IR~4.4 x 10^10 L_sun, and SFR~7.6 M_sun/yr, respectively. We measure the projected correlation function w(r_p) on scales of r_p=0.06-10 h^-1 Mpc, from which we derive a best fit comoving correlation length of r_0 = 4.0 +- 0.4 h^-1 Mpc and slope of gamma=1.5 +- 0.1 for the whole f_24>20uJy sample after combining the two fields. We find indications of a larger correlation length for objects of higher luminosity, with Luminous Infrared Galaxies (LIRGs, L_IR>10^11 L_sun) reaching r_0~5.1 h^-1 Mpc. This would imply that galaxies with larger SFRs are hosted in progressively more massive halos, reaching minimum halo masses of ~3 x …

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On The Evolutionary History Of Stars And Their Fossil Mass And Light, Ma Fardal, N Katz, Dh Weinberg, R Dave Jan 2007

On The Evolutionary History Of Stars And Their Fossil Mass And Light, Ma Fardal, N Katz, Dh Weinberg, R Dave

Astronomy Department Faculty Publication Series

The total extragalactic background radiation can be an important test of the global star formation history (SFH). Using direct observational estimates of the SFH, along with standard assumptions about the initial mass function (IMF), we calculate the total extragalactic background radiation and the observed stellar density today. We show that plausible SFHs allow a significant range in each quantity, but that their ratio is very tightly constrained. Current estimates of the stellar mass and extragalactic background are difficult to reconcile, as long as the IMF is fixed to the Salpeter slope above 1 M⊙. The joint confidence interval …

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Accretion, Feedback And Galaxy Bimodality: A Comparison Of The Galics Semi-Analytic Model And Cosmological Sph Simulations, A Cattaneo, J Blaizot, Dh Weinberg, D Keres, S Colombi, R Dave, J Devriendt, B Guiderdoni, N Katz Jan 2007

Accretion, Feedback And Galaxy Bimodality: A Comparison Of The Galics Semi-Analytic Model And Cosmological Sph Simulations, A Cattaneo, J Blaizot, Dh Weinberg, D Keres, S Colombi, R Dave, J Devriendt, B Guiderdoni, N Katz

Astronomy Department Faculty Publication Series

We compare the galaxy population of a smoothed particle hydrodynamics (SPH) simulation to those predicted by the GalICS (Galaxies In Cosmological Simulations) N-body + semi-analytic model and a stripped down version of GalICS that omits the effects of supernova and active galactic nucleus (AGN) feedback. The SPH simulation and the no-feedback GalICS model make similar predictions for the baryonic mass functions of galaxies and for the dependence of these mass functions on environment and redshift. The two methods also make similar predictions for the galaxy content of dark matter haloes as a function of halo mass and for the …

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Evidence For A Population Of High-Redshift Submillimeter Galaxies From Interferometric Imaging, Jd Younger, Gg Fazio, Js Huang, Min Yun, Gw Wilson, Mln Ashby, Ma Gurwell, K Lai, Ab Peck, Gr Petitpas, Dj Wilner, D Iono, K Kohno, R Kawabe, Dh Hughes, I Aretxaga, T Webb, A Martinez-Sansigre, S Kim, Ks Scott, J Austermann, T Perera, Jd Lowenthal, E Schinnerer, V Smolcic Jan 2007

Evidence For A Population Of High-Redshift Submillimeter Galaxies From Interferometric Imaging, Jd Younger, Gg Fazio, Js Huang, Min Yun, Gw Wilson, Mln Ashby, Ma Gurwell, K Lai, Ab Peck, Gr Petitpas, Dj Wilner, D Iono, K Kohno, R Kawabe, Dh Hughes, I Aretxaga, T Webb, A Martinez-Sansigre, S Kim, Ks Scott, J Austermann, T Perera, Jd Lowenthal, E Schinnerer, V Smolcic

Astronomy Department Faculty Publication Series

We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 μ m with ~2'' resolution. All of the sources—two radio-bright and five radio-dim—are detected as single point sources at high significance (>6 σ), with positions accurate to ~0.2'' that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST ACS imaging. As compared to the two radio-bright sources in the sample, …

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The Chandra View Of Da 530: A Subenergetic Supernova Remnant With A Pulsar Wind Nebula?, B Jiang, Y Chen, Qd Wang Jan 2007

The Chandra View Of Da 530: A Subenergetic Supernova Remnant With A Pulsar Wind Nebula?, B Jiang, Y Chen, Qd Wang

Astronomy Department Faculty Publication Series

DA 530 (G93.3+6.9) is a high Galactic latitude supernova (SN) remnant with a well-defined shell-like radio morphology and an exceptionally low X-ray-to-radio luminosity ratio. Based on a Chandra ACIS observation, we report the detection of an extended X-ray feature close to the center of the remnant at 5.3 σ above the background within a circle of 20'' radius. The spectrum of this feature can be characterized by a power law with photon index Γ = 1.6 ± 0.8. This feature, which is spatially coincident with a nonthermal radio source, most likely represents a pulsar wind nebula. We have further examined …

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Vla And Xmm-Newton Observations Of The Snr W41/Tev Gamma-Ray Source Hess J1834–087, Ww Tian, Z Li, Da Leahy, Qd Wang Jan 2007

Vla And Xmm-Newton Observations Of The Snr W41/Tev Gamma-Ray Source Hess J1834–087, Ww Tian, Z Li, Da Leahy, Qd Wang

Astronomy Department Faculty Publication Series

The recently discovered extended TeV source HESS J1834-087 is associated with both a diffuse X-ray enhancement and a molecular cloud, projected at the center of an old radio supernova remnant, G23.3-0.3 (SNR W41). New H I observations from the VLA Galactic Plane Survey (VGPS) show unambiguous structures associated with W41 in the radial velocity range of 53-63 km s-1, so we obtain for W41 a distance of 4 ± 0.2 kpc. A new higher sensitivity VGPS continuum image of W41 at 1420 MHz shows faint emission in its eastern part not detected by previous observations, so we provide …

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The Nonisothermality And Extent Of Galactic Diffuse Hot Gas Toward Markarian 421, Y Yao, Qd Wang Jan 2007

The Nonisothermality And Extent Of Galactic Diffuse Hot Gas Toward Markarian 421, Y Yao, Qd Wang

Astronomy Department Faculty Publication Series

Diffuse hot gas can be traced effectively by its X-ray absorption and emission. We present a joint analysis of these tracers to characterize the spatial and temperature distributions of the Galactic hot gas along the sight line toward the nearby bright active galactic nucleus Mrk 421. We also complement this analysis with far-UV O VI absorption observations. We find that the observed absorption line strengths of O VII and O VIII are inconsistent with the diffuse background emission-line ratio of the same ions, if the gas is assumed to be isothermal in a collisional ionization equilibrium state. But all these …

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The Galactic Central Diffuse X-Ray Enhancement: A Differential Absorption/Emission Analysis, Y Yao, Qd Wang Jan 2007

The Galactic Central Diffuse X-Ray Enhancement: A Differential Absorption/Emission Analysis, Y Yao, Qd Wang

Astronomy Department Faculty Publication Series

The soft X-ray background shows a general enhancement toward the inner region of the Galaxy. But whether this enhancement is a local feature (e.g., a superbubble within a distance of 200 pc) and/or a phenomenon related to energetic outflows from the Galactic center/bulge remains unclear. Here we report a comparative X-ray emission and absorption study of diffuse hot gas along the sight lines toward 3C 273 and Mrk 421, on and off the enhancement, but at similar Galactic latitudes. The diffuse 3/4 keV emission intensity, as estimated from the ROSAT All Sky Survey, is about 3 times higher toward 3C …

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High-Resolution Imaging Of Warm And Dense Molecular Gas In The Nuclear Region Of The Luminous Infrared Galaxy Ngc 6240, D Iono, Cd Wilson, S Takakuwa, Min Yun, Gr Petitpas, Ab Peck, Ptp Ho, S Matsushita, Ym Pihlstrom, Z Wang Jan 2007

High-Resolution Imaging Of Warm And Dense Molecular Gas In The Nuclear Region Of The Luminous Infrared Galaxy Ngc 6240, D Iono, Cd Wilson, S Takakuwa, Min Yun, Gr Petitpas, Ab Peck, Ptp Ho, S Matsushita, Ym Pihlstrom, Z Wang

Astronomy Department Faculty Publication Series

We present ~2'' resolution CO (3-2), HCO+(4-3), and 880 μm continuum images of the luminous infrared galaxy NGC 6240 obtained at the Submillimeter Array. We find that the spatially resolved CO (3-2), HCO + (4-3), and the 880 μm emission peaks between the two nuclear components that are both known to harbor AGNs. Our large velocity gradient (LVG) analysis performed on each velocity channel suggests that the peak of the molecular gas emission traced in our observations is warm (T = 20-100 K), dense (nH2 = 105.0-105.4 cm-3), and …

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Spitzer Spectral Line Mapping Of Supernova Remnants. I. Basic Data And Principal Component Analysis, Da Neufeld, Dj Hollenbach, Mj Kaufman, Ronald L. Snell, Gj Melnick, Ea Bergin, P Sonnentrucker Jan 2007

Spitzer Spectral Line Mapping Of Supernova Remnants. I. Basic Data And Principal Component Analysis, Da Neufeld, Dj Hollenbach, Mj Kaufman, Ronald L. Snell, Gj Melnick, Ea Bergin, P Sonnentrucker

Astronomy Department Faculty Publication Series

We report the results of spectroscopic mapping observations carried out toward small (1' × 1') regions within the supernova remnants W44, W28, IC 443, and 3C 391 using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. These observations, covering the 5.2-37 μm spectral region, have led to the detection of a total of 15 fine-structure transitions of Ne+, Ne++, Si+, P+, S, S++, Cl+, Fe+, and Fe++; the S(0)-S(7) pure rotational lines of molecular hydrogen; and the R(3) …

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The Dynamics Of Tidal Tails From Massive Satellites, Jh Choi, Md Weinberg, N Katz Jan 2007

The Dynamics Of Tidal Tails From Massive Satellites, Jh Choi, Md Weinberg, N Katz

Astronomy Department Faculty Publication Series

We investigate the dynamical mechanisms responsible for producing tidal tails from dwarf satellites using N-body simulations. We describe the essential dynamical mechanisms and morphological consequences of tail production in satellites with masses greater than 0.0001 of the host halo virial mass. We identify two important dynamical coconspirators: (1) the points where the attractive force of the host halo and satellite are balanced (X-points) do not occur at equal distances from the satellite centre or at the same equipotential value for massive satellites, breaking the morphological symmetry of the leading and trailing tails and (2) the escaped ejecta in the leading …

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Variations In 24-Mu M Morphologies Among Galaxies In The Spitzer Infrared Nearby Galaxies Survey: New Insights Into The Hubble Sequence, Gj Bendo, D Calzetti, Cw Engelbracht, Rc Kennicutt, Mj Meyer, Md Thornley, F Walter, Da Dale, A Li, Ej Murphy Jan 2007

Variations In 24-Mu M Morphologies Among Galaxies In The Spitzer Infrared Nearby Galaxies Survey: New Insights Into The Hubble Sequence, Gj Bendo, D Calzetti, Cw Engelbracht, Rc Kennicutt, Mj Meyer, Md Thornley, F Walter, Da Dale, A Li, Ej Murphy

Astronomy Department Faculty Publication Series

To study the distribution of star formation and dust emission within nearby galaxies, we measured five morphological parameters in the 3.6- and 24-μm wavebands for 65 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS) and eight galaxies that were serendipitously observed by SINGS. The morphological parameters demonstrate strong variations along the Hubble sequence, including statistically significant differences between S0/a-Sab and Sc-Sd galaxies. Early-type galaxies are generally found to be compact, centralized, symmetric sources in the 24-μm band, while late-type galaxies are generally found to be extended, asymmetric sources. These results suggest that the processes that increase the real or …

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The Calibration Of Mid-Infrared Star Formation Rate Indicators, D Calzetti, Rc Kennicutt, Cw Engelbracht, C Leitherer, Bt Draine, L Kewley, J Moustakas, M Sosey, Da Dale, Kd Gordon, Gx Helou, Dj Hollenbach, L Armus, G Bendo, C Bot, B Buckalew, T Jarrett, A Li, M Meyer, Ej Murphy, M Prescott, Mw Regan, Gh Rieke, H Roussel, K Sheth, Jdt Smith, Md Thornley, F Walter Jan 2007

The Calibration Of Mid-Infrared Star Formation Rate Indicators, D Calzetti, Rc Kennicutt, Cw Engelbracht, C Leitherer, Bt Draine, L Kewley, J Moustakas, M Sosey, Da Dale, Kd Gordon, Gx Helou, Dj Hollenbach, L Armus, G Bendo, C Bot, B Buckalew, T Jarrett, A Li, M Meyer, Ej Murphy, M Prescott, Mw Regan, Gh Rieke, H Roussel, K Sheth, Jdt Smith, Md Thornley, F Walter

Astronomy Department Faculty Publication Series

With the goal of investigating the degree to which the MIR emission traces the SFR, we analyze Spitzer 8 and 24 μm data of star-forming regions in a sample of 33 nearby galaxies with available HST NICMOS images in the Paα (1.8756 μm) emission line. The galaxies are drawn from the SINGS sample and cover a range of morphologies and a factor ~10 in oxygen abundance. Published data on local low-metallicity starburst galaxies and LIRGs are also included in the analysis. Both the stellar continuum-subtracted 8 μm emission and the 24 μm emission correlate with the extinction-corrected Paα line emission, …

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Star Formation In Ngc 5194 (M51a). Ii. The Spatially Resolved Star Formation Law, Rc Kennicutt, D Calzetti, F Walter, G Helou, Dj Hollenbach, L Armus, G Bendo, Da Dale, Bt Draine, Cw Engelbracht, Kd Gordon, Mkm Prescott, Mw Regan, Md Thornley, C Bot, E Brinks, E De Blok, D De Mello, M Meyer, J Moustakas, Ej Murphy, K Sheth, Jdt Smith Jan 2007

Star Formation In Ngc 5194 (M51a). Ii. The Spatially Resolved Star Formation Law, Rc Kennicutt, D Calzetti, F Walter, G Helou, Dj Hollenbach, L Armus, G Bendo, Da Dale, Bt Draine, Cw Engelbracht, Kd Gordon, Mkm Prescott, Mw Regan, Md Thornley, C Bot, E Brinks, E De Blok, D De Mello, M Meyer, J Moustakas, Ej Murphy, K Sheth, Jdt Smith

Astronomy Department Faculty Publication Series

We have studied the relationship between the star formation rate (SFR), surface density, and gas surface density in the spiral galaxy M51a (NGC 5194), using multiwavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of Hα emission-line and 24 μm continuum luminosities, which provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis H I and CO maps has allowed us to probe the form of the spatially resolved star …

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Radio And X-Ray Images Of The Snr G18.8+0.3 Interacting With Molecular Clouds, Ww Tian, Da Leahy, Qd Wang Jan 2007

Radio And X-Ray Images Of The Snr G18.8+0.3 Interacting With Molecular Clouds, Ww Tian, Da Leahy, Qd Wang

Astronomy Department Faculty Publication Series

New HI images from the VLA Galactic Plane Survey (VGPS) show clear absorption features associated with the supernova remnant (SNR) G18.8+0.3. High-resolution 13CO images reveal that molecular clouds overlap the radio filaments of G18.8+0.3. The 13CO emission spectrum over the full velocity range in the direction of G18.8+0.3 shows two molecular components with high brightness-temperature and three molecular components with low brightness-temperature, all with respective HI absorption. This implies that these clouds are in front of G18.8+0.3. In the HI images, the highest velocity absorption feature seen against the continuum image of G18.8+0.3 is at 129 km s …

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Hot Gaseous Halos Of Nearby Disk Galaxies, Qd Wang Jan 2007

Hot Gaseous Halos Of Nearby Disk Galaxies, Qd Wang

Astronomy Department Faculty Publication Series

I review studies of the hot gaseous medium in and around nearby normal disk galaxies, including the Milky Way. This medium represents a reservoir of materials required for lasting star formation, a depository of galactic feedback (e.g., stellar mass loss and supernovae), and an interface between the interstellar and intergalactic media. Important progress has been made recently with the detection of X-ray absorption lines in the spectra of X-ray binaries and AGNs. The X-ray absorption line spectroscopy, together with existing X-ray emission and far-UV O IV absorption measurements now allows for the first time to characterize the global …

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Chandra Detection Of Diffuse Hot Gas In And Around The M31 Bulge, Z Li, Qd Wang Jan 2007

Chandra Detection Of Diffuse Hot Gas In And Around The M31 Bulge, Z Li, Qd Wang

Astronomy Department Faculty Publication Series

We report the detection of diffuse hot gas in M31, using archival Chandra observations that allow us to map out a 30' × 30' field (covering a galactocentric radius up to 4.5 kpc) and to detect sources in the galaxy down to a 0.5-8 keV luminosity limit of ~1035 ergs s-1. We estimate the remaining stellar contribution from fainter X-ray sources (primarily cataclysmic variables and coronally active binaries), assuming that they spatially follow the stellar distribution. Indeed, the near-IR K-band light of the galaxy closely traces the 2-8 keV unresolved X-rays, indicating a collective stellar X-ray …

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Chandra And Xmm–Newton Detection Of Large-Scale Diffuse X-Ray Emission From The Sombrero Galaxy, Z Li, Qd Wang, S Hameed Jan 2007

Chandra And Xmm–Newton Detection Of Large-Scale Diffuse X-Ray Emission From The Sombrero Galaxy, Z Li, Qd Wang, S Hameed

Astronomy Department Faculty Publication Series

We present an X-ray study of the massive edge-on Sa galaxy, Sombrero (M 104; NGC 4594), based on XMM–Newton and Chandra observations. A list of 62 XMM–Newton and 175 Chandra discrete X-ray sources is provided, the majority of which are associated with the galaxy. Spectral analysis is carried out for relatively bright individual sources and for an accumulated source spectrum. At energies ≳2 keV, the source-subtracted X-ray emission is distributed similarly as the stellar K-band light and is primarily due to the residual emission from discrete sources. At lower energies, however, a substantial fraction of the source-subtracted emission arises …

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X-Ray Timing Observations Of Psr J1930+1852 In The Crab-Like Snr G54.1+0.3, F Lu, Qd Wang, Ev Gotthelf, J Qu Jan 2007

X-Ray Timing Observations Of Psr J1930+1852 In The Crab-Like Snr G54.1+0.3, F Lu, Qd Wang, Ev Gotthelf, J Qu

Astronomy Department Faculty Publication Series

We present new X-ray timing and spectral observations of PSR J1930+1852, the young energetic pulsar at the center of the nonthermal supernova remnant G54.1+0.3. Using data obtained with the Rossi X-Ray Timing Explorer (RXTE) and Chandra X-ray observatories we have derived an updated timing ephemeris of the 136 ms pulsar spanning 6 years. During this interval, however, the period evolution shows significant variability from the best-fit constant spin-down rate of = 7.5112(6) × 10-13 s s-1, suggesting strong timing noise and/or glitch activity. The X-ray emission is highly pulsed (71% ± 5% modulation) and is …

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Measuring Star Formation In Local And Distant Galaxies, D Calzetti Jan 2007

Measuring Star Formation In Local And Distant Galaxies, D Calzetti

Astronomy Department Faculty Publication Series

I review measurements of star formation in nearby galaxies in the UV-to-FIR wavelength range, and discuss their impact on SFR determinations in intermediate and high redshift galaxy populations. Existing and upcoming facilities will enable precise cross-calibrations among the various indicators, thus bringing them onto a common scale.

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