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Physical Sciences and Mathematics Commons™

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

1998

Astrophysics and Astronomy

University of Massachusetts Amherst

Articles 1 - 20 of 20

Full-Text Articles in Physical Sciences and Mathematics

Effect Of The Magellanic Clouds On The Milky Way Disk And Vice Versa, Martin D. Weinberg Nov 1998

Effect Of The Magellanic Clouds On The Milky Way Disk And Vice Versa, Martin D. Weinberg

Astronomy Department Faculty Publication Series

The satellite-disk interaction provides limits on halo properties in two ways: (1) physical arguments motivate the excitation of observable Galactic disk structure in the presence of a massive halo, although precise limits on halo parameters are scenario-dependent; (2) conversely, the Milky Way as a whole has significant dynamical effect on LMC structure and this interaction also leads to halo limits. Together, these scenarios give strong corroboration of our current gravitational mass estimates and suggests a rapidly evolving LMC.

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Co (J = 4 → 3) And 650 Micron Continuum Observations Of The Z = 0.93 Hyperluminous Infrared Galaxy Fsc 15307+3252, Min S. Yun, N Z. Scoville Nov 1998

Co (J = 4 → 3) And 650 Micron Continuum Observations Of The Z = 0.93 Hyperluminous Infrared Galaxy Fsc 15307+3252, Min S. Yun, N Z. Scoville

Min S. Yun

We report the results of our CO J = 4 → 3 line and rest-frame 650 μm continuum observations of the z = 0.93 hyperluminous infrared galaxy FSC 15307+3252 using the Owens Valley Millimeter Array. No line or continuum emission was detected, but the derived limits provide a useful constraint on the temperature, emissivity, and mass of the cold dust associated with FSC 15307+3252 and its molecular gas content. The 3 σ upper limit on the velocity-integrated CO (4-3) line flux is 1.6 Jy km s-1 (for ΔV = 300 km s-1). This corresponds to a surprisingly small total molecular …

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Molecular Gas In The Z = 2.8 Submillimeter Galaxy Smm 02399-0136, D T. Frayer, R J. Ivison, N Z. Scoville, Min S. Yun, A S. Evans, Ian Smail, A W. Blain, J P. Kneib Oct 1998

Molecular Gas In The Z = 2.8 Submillimeter Galaxy Smm 02399-0136, D T. Frayer, R J. Ivison, N Z. Scoville, Min S. Yun, A S. Evans, Ian Smail, A W. Blain, J P. Kneib

Min S. Yun

We report the detection of CO (3→2) emission from the submillimeter-selected hyperluminous galaxy SMM 02399-0136. This galaxy is the brightest source detected in the recent Submillimeter Common-User Bolometer Array surveys of the submillimeter sky. The optical counterpart of the submillimeter source has been identified as a narrow-line active galactic nucleus/starburst galaxy at z=2.8. The CO emission is unresolved, θlesssim5'', and is coincident in redshift and position with the optical counterpart. The molecular gas mass derived from the CO observations is 8×1010 h−275 M_{{\odot}}, after correcting for a lensing amplification factor of 2.5. The large CO luminosity suggests that a significant …

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Redshifted Neutral Hydrogen 21 Centimeter Absorption Toward Red Quasars, C L. Carilli, Karl M. Menten, Mark J. Reid, M P. Rupen, Min S. Yun Feb 1998

Redshifted Neutral Hydrogen 21 Centimeter Absorption Toward Red Quasars, C L. Carilli, Karl M. Menten, Mark J. Reid, M P. Rupen, Min S. Yun

Min S. Yun

We have searched for redshifted neutral hydrogen 21 cm absorption toward sources from the Stickel et al. "red quasar" subsample. The red quasar subsample is taken from the 1 Jy sample of flat-spectrum radio sources and is comprised of the 15 sources that are undetected on the POSS. Five of these red quasars have been searched for redshifted H I 21 cm absorption to optical depth levels of a few percent, and four show strong absorption, with neutral hydrogen column densities between 4 and 80 × 1018 × (Ts/f) cm-2. This 80% success rate for the red quasars compares to …

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Molecular Gas In The Inner 100 Parces Of M51, N Z. Scoville, Min S. Yun, L Armus, H Ford Jan 1998

Molecular Gas In The Inner 100 Parces Of M51, N Z. Scoville, Min S. Yun, L Armus, H Ford

Min S. Yun

We report imaging of CO (2-1) emission in the nucleus of M51 at 1'' (47 pc) resolution. Molecular gas is found closely associated with the nuclear radio jet and the X-shaped dust absorption feature seen in the Hubble Space Telescope images. The CO emission lies along the side of the nuclear radio continuum "jet." The strongest molecular emission is not symmetric in either position or velocity with respect to the nucleus—the dominant feature is at redshifted velocities and peaks 1'' to the west of the radio/optical nucleus. The CO (2-1) emission has an integrated flux implying a molecular gas mass …

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Fluctuations In Finite-N Equilibrium Stellar Systems, Md Weinberg Jan 1998

Fluctuations In Finite-N Equilibrium Stellar Systems, Md Weinberg

Astronomy Department Faculty Publication Series

Gravitational amplification of Poisson noise in stellar systems is important on large scales. For example, it increases the dipole noise power by roughly a factor of 6 and the quadrupole noise by 50 per cent for a King model profile. The dipole noise is amplified by a factor of 15 for the core-free Hernquist model. The predictions are computed by summing over the wakes caused by each star in the system — the dressed-particle formalism of Rostoker & Rosenbluth — and are demonstrated by N-body simulation. This result implies that a collisionless N-body simulation is impossible; the fluctuation noise which …

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Dynamics Of An Interacting Luminous Disc, Dark Halo And Satellite Companion, Md Weinberg Jan 1998

Dynamics Of An Interacting Luminous Disc, Dark Halo And Satellite Companion, Md Weinberg

Astronomy Department Faculty Publication Series

This paper describes a method, based on linear perturbation theory, to determine the dynamical interaction between extended halo and spheroid components and an environmental disturbance. One finds that resonant interaction between a galaxy and passing interlopers or satellite companions can carry the disturbance inward, deep inside the halo, where it can perturb the disc. Applied to the Milky Way for example, the LMC and SMC appear to be sufficient to cause the observed Galactic warp and possibly seed other asymmetries. This is a multi-scale interaction in which the halo wake has a feature at roughly half the satellite orbital radius …

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New Insight On Galaxy Structure From Galphat I. Motivation, Methodology, And Benchmarks For Sersic Models, Ilsang Yoon, Martin D. Weinberg Jan 1998

New Insight On Galaxy Structure From Galphat I. Motivation, Methodology, And Benchmarks For Sersic Models, Ilsang Yoon, Martin D. Weinberg

Astronomy Department Faculty Publication Series

We introduce a new galaxy image decomposition tool, GALPHAT (GALaxy PHotometric ATtributes), to provide full posterior probability distributions and reliable confidence intervals for all model parameters. GALPHAT is designed to yield a high speed and accurate likelihood computation, using grid interpolation and Fourier rotation. We benchmark this approach using an ensemble of simulated Sersic model galaxies over a wide range of observational conditions: the signal-to-noise ratio S/N, the ratio of galaxy size to the PSF and the image size, and errors in the assumed PSF; and a range of structural parameters: the half-light radius $r_e$ and the Sersic index $n$. …

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Morphological Transformation From Galaxy Harassment, B Moore, G Lake, N Katz Jan 1998

Morphological Transformation From Galaxy Harassment, B Moore, G Lake, N Katz

Astronomy Department Faculty Publication Series

Galaxy morphologies in clusters have undergone a remarkable transition over the past several billion yr. Distant clusters at z ~ 0.4 are filled with small spiral galaxies, many of which are disturbed and show evidence of multiple bursts of star formation. This population is absent from nearby clusters, where spheroidals comprise the faint end of the luminosity function. Our numerical simulations follow the evolution of disk galaxies in a rich cluster resulting from encounters with brighter galaxies and the cluster's tidal field, or "galaxy harassment." After a bursting transient phase, they undergo a complete morphological transformation from "disks" to "spheroidals." …

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Recovery Of The Power Spectrum Of Mass Fluctuations From Observations Of The Ly Alpha Forest, Rac Croft, Dh Weinberg, N Katz, L Hernquist Jan 1998

Recovery Of The Power Spectrum Of Mass Fluctuations From Observations Of The Ly Alpha Forest, Rac Croft, Dh Weinberg, N Katz, L Hernquist

Astronomy Department Faculty Publication Series

We present a method to recover the shape and amplitude of the power spectrum of mass fluctuations, P(k), from observations of the high-redshift Lyα forest. The method is motivated by the physical picture that has emerged from hydrodynamic cosmological simulations and related semianalytic models, in which typical Lyα forest lines arise in a diffuse, continuous, fluctuating intergalactic medium. The thermal state of this low-density gas (δρ/ρ 10) is governed by simple physical processes, which lead to a tight correlation between the Lyα optical depth and the underlying matter density. To recover the mass power spectrum, we (1) …

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Nature Of 60Μm Emission In 3c 47, 3c 207 And 3c 334, Ilse M. Van Bemmel, Peter D. Barthel, Min S. Yun Jan 1998

Nature Of 60Μm Emission In 3c 47, 3c 207 And 3c 334, Ilse M. Van Bemmel, Peter D. Barthel, Min S. Yun

Min S. Yun

We try to explain the unusually high far-infrared emission seen by IRAS in the double-lobed radio-loud quasars 3C 47, 3C 207 and 3C 334. High resolution cm–mm observations were carried out to determine their radio core spectra, which are subsequently extrapolated to the far-infrared in order to determine the strength of the synchrotron far-infrared emission. The extrapolated flux densities being considerably lower than the observed values, a significant nonthermal far-infrared component is unlikely in the case of 3C 47 and 3C 334. However, this component could be responsible for the far-infrared brightness of 3C 207. Our analysis demonstrates that nonthermal …

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Effects Of Interaction Induced Activities In Hickson Compact Groups: Co And Fir Study, L Verdes-Montenegro, Min S. Yun, J Perea, A Del Olmo, P T P Ho Jan 1998

Effects Of Interaction Induced Activities In Hickson Compact Groups: Co And Fir Study, L Verdes-Montenegro, Min S. Yun, J Perea, A Del Olmo, P T P Ho

Min S. Yun

A study of 2.6 mm CO J = 1 → 0 and far-infrared (FIR) emission in a distance-limited (z < 0.03) complete sample of Hickson compact group (HCG) galaxies was conducted in order to examine the effects of their unique environment on the interstellar medium of component galaxies and to search for a possible enhancement of star formation and nuclear activity. Ubiquitous tidal interactions in these dense groups would predict enhanced activities among the HCG galaxies compared to isolated galaxies. Instead, their CO and FIR properties (thus, "star formation efficiency") are surprisingly similar to isolated spirals. The CO data for 80 HCG galaxies presented here (including 10 obtained from the literature) indicate that the spirals globally show the same H2 content as the isolated comparison sample, although 20% are deficient in CO emission. Because of their large optical luminosity, low metallicity is not likely the main cause for the low CO luminosity. The CO deficiency appears linked with the group evolution, and gas exhaustion through past star formation and removal of the external gas reserve by tidal stripping of the outer H I disk offer a possible explanation. The IRAS data for the entire redshift-limited complete sample of 161 HCG galaxies were reanalyzed using ADDSCAN/SCANPI, improving the sensitivity by a factor of 3-5 over the existing Point Source Catalog (PSC) and resolving better the contribution from individual galaxies. The new analysis of the IRAS data confirms the previous suggestion that FIR emission in HCG galaxies is similar to isolated, Virgo Cluster, and weakly interacting galaxies. Their H2 and FIR characteristics yield a star formation efficiency that is similar to that of these comparison samples. A factor 2 enhancement in the 25-100 μm flux ratio among the HCG spirals is found, which suggests intense localized nuclear starburst activity similar to that of H II galaxies. A number of early-type galaxies in HCGs are detected in CO and FIR, lending further support to the idea that tidal interactions and tidally induced evolution of the groups and member galaxies are important in our sample.

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Origin And Evolution Of The Cepheus Bubble, Na Patel, Pf Goldsmith, Mh Heyer, Rl Snell, P Pratap Jan 1998

Origin And Evolution Of The Cepheus Bubble, Na Patel, Pf Goldsmith, Mh Heyer, Rl Snell, P Pratap

Astronomy Department Faculty Publication Series

We have imaged a 10° × 10° region of the Cepheus bubble in the J = 1-0 line of CO and the 21 cm line of atomic hydrogen. The CO emission defines a giant expanding shell 120 pc in diameter, which is similar to that seen in the IRAS sky maps. We estimate the total gas mass in the region to be ~4 × 105M☉. The total kinetic energy from the observed spread of velocities of the molecular clouds is ~1051ergs. We suggest that the members of earlier generations of massive stars in NGC 7160 are responsible for …

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Constraining The Metallicity Of The Low-Density Ly Alpha Forest Using O Vi Absorption, R Dave, U Hellsten, L Hernquist, N Katz, Dh Weinberg Jan 1998

Constraining The Metallicity Of The Low-Density Ly Alpha Forest Using O Vi Absorption, R Dave, U Hellsten, L Hernquist, N Katz, Dh Weinberg

Astronomy Department Faculty Publication Series

We present a systematic search for O VI (1032, 1037 Å) absorption in a Keck High-Resolution Echelle Spectrometer spectrum of the z = 3.62 quasar Q1422+231, with the goal of constraining the metallicity and ionization state of the low-density intergalactic medium (IGM). Comparison of C IV absorption measurements to models of the Lyα forest based on cosmological simulations shows that absorbers with NH I 1014.5 cm-2 have a mean carbon abundance [C/H] -2.5, assuming a metagalactic photoionizing background with the spectral shape predicted by Haardt and Madau in 1996. In these models, lower column density absorption arises …

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The Observability Of Metal Lines Associated With The Ly Alpha Forest, U Hellsten, L Hernquist, N Katz, Dh Weinberg Jan 1998

The Observability Of Metal Lines Associated With The Ly Alpha Forest, U Hellsten, L Hernquist, N Katz, Dh Weinberg

Astronomy Department Faculty Publication Series

We develop a prescription for characterizing the strengths of metal lines associated with Lyα forest absorbers (LYFAs) of a given neutral hydrogen column density NH I and metallicity [O/H]. This line observability index (LOX) is line specific and translates, for weak lines, into a measure of the equivalent width. It can be evaluated quickly for thousands of transitions within the framework of a given model of the Lyα forest, providing a ranking of the absorption lines in terms of their strengths and enabling model builders to select the lines that deserve more detailed consideration, i.e., those that should be …

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Cosmological Simulations With Scale-Free Initial Conditions. I. Adiabatic Hydrodynamics, Jm Owen, Dh Weinberg, Ae Evrard, L Hernquist, N Katz Jan 1998

Cosmological Simulations With Scale-Free Initial Conditions. I. Adiabatic Hydrodynamics, Jm Owen, Dh Weinberg, Ae Evrard, L Hernquist, N Katz

Astronomy Department Faculty Publication Series

We analyze hierarchical structure formation based on scale-free initial conditions in an Einstein-de Sitter universe, including a baryonic component with Ωbary = 0.05. We present three independent, smoothed particle hydrodynamics (SPH) simulations, performed at two resolutions (323 and 643 dark matter and baryonic particles) and with two different SPH codes (TreeSPH and P3MSPH). Each simulation is based on identical initial conditions, which consist of Gaussian-distributed initial density fluctuations that have a power spectrum P(k) k-1. The baryonic material is modeled as an ideal gas subject only to shock heating and adiabatic heating …

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The Formation Of Quasars In Low-Luminosity Hosts Via Galaxy Harassment, G Lake, N Katz, B Moore Jan 1998

The Formation Of Quasars In Low-Luminosity Hosts Via Galaxy Harassment, G Lake, N Katz, B Moore

Astronomy Department Faculty Publication Series

We have simulated disk galaxies undergoing continual bombardment by other galaxies in a rich cluster. "Galaxy harassment" leads to dramatic evolution of smaller disk galaxies and provides an extremely effective mechanism for fueling a central quasar. Within a few billion years after a small disk galaxy enters the cluster environment, up to 90% of its gas can be driven into the inner 500 pc. Up to half of the mass can be transferred in a burst lasting just 100-200 Myr. This transport of gas to the center of galaxy is far more efficient than any mechanism proposed before. Galaxy harassment …

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Cosmology With The Lyman-Alpha Forest, Dh Weinberg, S Burles, Rac Croft, R Dave, G Gomez, L Hernquist, N Katz, D Kirkman, S Liu, J Miralda-Escude, M Penttini, J Phillips, D Tytler, J Wright Jan 1998

Cosmology With The Lyman-Alpha Forest, Dh Weinberg, S Burles, Rac Croft, R Dave, G Gomez, L Hernquist, N Katz, D Kirkman, S Liu, J Miralda-Escude, M Penttini, J Phillips, D Tytler, J Wright

Astronomy Department Faculty Publication Series

We outline the physical picture of the high-redshift Ly-alpha forest that has emerged from cosmological simulations, describe statistical characteristics of the forest that can be used to test theories of structure formation, present a preliminary comparison between simulation results and measurements from Keck HIRES spectra, and discuss a recent determination of the slope and amplitude of the linear mass power spectrum P(k) at z=2.5 from moderate resolution spectra. The physical picture is simple if each QSO spectrum is viewed as a continuous non-linear map of the line-of-sight density field rather than a collection of discrete absorption lines. The distribution of …

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Cosmology From The Structure Of The Lyman-Alpha Forest, R Croft, D Weinberg, N Katz, L Hernquist Jan 1998

Cosmology From The Structure Of The Lyman-Alpha Forest, R Croft, D Weinberg, N Katz, L Hernquist

Astronomy Department Faculty Publication Series

A convincing physical picture for the Lyman-alpha forest has emerged from simulations and related semi-analytic studies of structure formation models. Observations can be be used in the context of this picture to study cosmology using the structure of the forest. With the availability of well motivated predictions, not only has it become possible to test models directly, but the physical processes involved appear to be simple enough that we can attempt to reconstruct aspects of the underlying cosmology from observations. We briefly summarise the method of Croft et al (1997) (astro-ph/9708018) for recovering the primordial mass power spectrum …

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Simulating Gas At High Redshift, N Katz, L Hernquist, Dh Weinberg Jan 1998

Simulating Gas At High Redshift, N Katz, L Hernquist, Dh Weinberg

Astronomy Department Faculty Publication Series

We discuss simulations of gas at high redshift. We briefly review the methods used and the results for quasar absorption lines. We present gas mass functions and galaxy correlation functions for 5 different cosmological models. Galaxies should be detectable at redshifts greater than 2 by SKAI, and measurements of the gas maWe discuss simulations of gas at high redshift. We briefly review the methods used and the results for quasar absorption lines. We present gas mass functions and galaxy correlation functions for 5 different cosmological models. Galaxies should be detectable at redshifts greater than 2 by SKAI, and measurements of …

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