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Full-Text Articles in Physical Sciences and Mathematics
Near-Infrared Emission Line Diagnostics For Agn From The Local Universe To Z ∼ 3*, Mauro Giavalisco, Et. Al.
Near-Infrared Emission Line Diagnostics For Agn From The Local Universe To Z ∼ 3*, Mauro Giavalisco, Et. Al.
Astronomy Department Faculty Publication Series
Optical rest-frame spectroscopic diagnostics are usually employed to distinguish between star formation and active galactic nucleus (AGN) powered emission. However, this method is biased against dusty sources, hampering a complete census of the AGN population across cosmic epochs. To mitigate this effect, it is crucial to observe at longer wavelengths in the rest-frame near-infrared (near-IR), which is less affected by dust attenuation and can thus provide a better description of the intrinsic properties of galaxies. AGN diagnostics in this regime have not been fully exploited so far, due to the scarcity of near-IR observations of both AGN and star-forming galaxies, …
Morphological Transformation From Galaxy Harassment, B Moore, G Lake, N Katz
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." …
Recovery Of The Power Spectrum Of Mass Fluctuations From Observations Of The Ly Alpha Forest, Rac Croft, Dh Weinberg, N Katz, L Hernquist
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) …
The Observability Of Metal Lines Associated With The Ly Alpha Forest, U Hellsten, L Hernquist, N Katz, Dh Weinberg
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 …
The Formation Of Quasars In Low-Luminosity Hosts Via Galaxy Harassment, G Lake, N Katz, B Moore
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 …
The Effect Of The Galactic Spheroid On Globular Cluster Evolution, C Murali, Md Weinberg
The Effect Of The Galactic Spheroid On Globular Cluster Evolution, C Murali, Md Weinberg
Astronomy Department Faculty Publication Series
We study the combined effects of relaxation, tidal heating and binary heating on globular cluster evolution, exploring the physical consequences of external effects and examining evolutionary trends in the MilkyWay population. Our analysis demonstrates that heating on circular and low-eccentricity orbits can dominate cluster evolution. The results also predict rapid evolution on eccentric orbits either due to strong relaxation caused by the high densities needed for tidal limitation or due to efficient bulge shocking of low density clusters. The combination of effects leads to strong evolution of the population as a whole. For example, within the solar circle, tidally-limited 105M⊙ …
Globular Cluster Evolution In M87 And Fundamental Plane Ellipticals, C Murali, Md Weinberg
Globular Cluster Evolution In M87 And Fundamental Plane Ellipticals, C Murali, Md Weinberg
Astronomy Department Faculty Publication Series
The globular cluster population in M87 has decreased measurably through dynamical evolution caused by relaxation, binary heating and time-dependent tidal perturbation. For fundamental plane ellipticals in general, cluster populations evolve more rapidly in smaller galaxies because of the higher mass density. A simple evolutionary model reproduces the observed trend in specific frequency with luminosity for an initially constant relationship. Fits of theoretically evolved populations to M87 cluster data from McLaughlin et al. (1994) show the following: 1) dynamical effects drive evolution in the initial mass and space distributions and can account for the large core in the spatial profile as …
Intergalactic Helium Absorption In Cold Dark Matter Models, Rac Croft, Dh Weinberg, N Katz, L Hernquist
Intergalactic Helium Absorption In Cold Dark Matter Models, Rac Croft, Dh Weinberg, N Katz, L Hernquist
Astronomy Department Faculty Publication Series
Observations from the Hopkins Ultraviolet Telescope and the Hubble Space Telescope have recently detected He II absorption along the lines of sight to two high-redshift quasars. We use cosmological simulations with gas dynamics to investigate He II absorption in the cold dark matter (CDM) theory of structure formation. We consider two Ω = 1 CDM models with different normalizations and one open universe (Ω0 = 0.4) CDM model. The simulations incorporate the photoionizing UV background spectrum computed by Haardt & Madau, which is based on the output of observed quasars and reprocessing by the Lyα forest. The simulated …
Evolution Of The Galactic Globular Cluster System, C Murali, Md Weinberg
Evolution Of The Galactic Globular Cluster System, C Murali, Md Weinberg
Astronomy Department Faculty Publication Series
We study the dynamical evolution of disk and halo globular clusters in the Milky Way using a series of Fokker-Planck calculations combined with parametric statistical models. Our sample of 113 clusters with velocity data is predicted to descend from an initial population of 250 clusters, implying more than a factor of two decrease in population size due to evolution. Approximately 200 of these clusters are in a halo component and 50 in a disk component. The estimated initial halo population follows a coreless R−3.38 density profile in good agreement with current estimates for the distribution of halo field stars. The …
Testing Cosmological Models Against The Abundance Of Damped Lyman-Alpha Absorbers, Jp Gardner, N Katz, Dh Weinberg, L Hernquist
Testing Cosmological Models Against The Abundance Of Damped Lyman-Alpha Absorbers, Jp Gardner, N Katz, Dh Weinberg, L Hernquist
Astronomy Department Faculty Publication Series
We calculate the number of damped Lyα absorbers expected in various popular cosmological models as a function of redshift and compare our predictions with observed abundances. The Press-Schechter formalism is used to obtain the distribution of halos with circular velocity in different cosmologies, and we calibrate the relation between circular velocity and absorption cross section using detailed gasdynamical simulations of a standard cold dark matter (CDM) model. Because of this calibration, our approach makes more realistic assumptions about the absorption properties of collapsed objects than previous, analytic calculations of the damped Lyα abundance. CDM models with Ω0 = 1, …