Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 25 of 25
Full-Text Articles in Physical Sciences and Mathematics
The Great Observatories Origins Deep Survey - Vlt/Fors2 Spectroscopy In The Goods-South Field: Part Iii, E Vanzella, S Cristiani, M Dickinson, M Giavalisco, H Kuntschner, J Haase, M Nonino, P Rosati, C Cesarsky, Hc Ferguson, Rae Fosbury, A Grazian, La Moustakas, A Rettura, P Popesso, A Renzini, D Stern
The Great Observatories Origins Deep Survey - Vlt/Fors2 Spectroscopy In The Goods-South Field: Part Iii, E Vanzella, S Cristiani, M Dickinson, M Giavalisco, H Kuntschner, J Haase, M Nonino, P Rosati, C Cesarsky, Hc Ferguson, Rae Fosbury, A Grazian, La Moustakas, A Rettura, P Popesso, A Renzini, D Stern
Astronomy Department Faculty Publication Series
No abstract provided.
Spitzer Observations Of Star Formation In The Extreme Outer Disk Of M83 (Ngc5236), H Dong, D Calzetti, M Regan, D Thilker, L Bianchi, Gr Meurer, F Walter
Spitzer Observations Of Star Formation In The Extreme Outer Disk Of M83 (Ngc5236), H Dong, D Calzetti, M Regan, D Thilker, L Bianchi, Gr Meurer, F Walter
Astronomy Department Faculty Publication Series
Spitzer Infrared Array Camera (IRAC) observations of two fields in the extended UV disk (XUV-disk) of M83 have been recently obtained, ~3 R HII away from the center of the galaxy (R HII = 6.6 kpc). Galaxy Evolution Explorer (GALEX) UV images have shown the two fields to host in situ recent star formation. The IRAC images are used in conjunction with GALEX data and new H I imaging from The H I Nearby Galaxy Survey (THINGS) to constrain stellar masses and ages of the UV clumps in the fields, and to relate the local recent star formation to the …
Spectroscopic Confirmation Of An Extreme Starburst At Redshift 4.547, P Capak, Cl Carilli, N Lee, T Aldcroft, H Aussel, E Schinnerer, Gw Wilson, Min Yun, A Blain, M Giavalisco, O Ilbert, J Kartaltepe, Ks Lee, H Mccracken, B Mobasher, M Salvato, S Sasaki, Ks Scott, K Sheth, Y Shioya, D Thompson, M Elvis, Db Sanders, Nz Scoville, Y Tanaguchi
Spectroscopic Confirmation Of An Extreme Starburst At Redshift 4.547, P Capak, Cl Carilli, N Lee, T Aldcroft, H Aussel, E Schinnerer, Gw Wilson, Min Yun, A Blain, M Giavalisco, O Ilbert, J Kartaltepe, Ks Lee, H Mccracken, B Mobasher, M Salvato, S Sasaki, Ks Scott, K Sheth, Y Shioya, D Thompson, M Elvis, Db Sanders, Nz Scoville, Y Tanaguchi
Astronomy Department Faculty Publication Series
We report the spectroscopic confirmation of a submillimeter galaxy (SMG) at z = 4.547 with an estimated LIR = (0.5-2.0) × 1013 L. The spectra, mid-IR, and X-ray properties indicate the bolometric luminosity is dominated by star formation at a rate of >1000 M yr−1. Multiple, spatially separated components are visible in the Lyα line with an observed velocity difference of up to 380 km s−1 and the object morphology indicates a merger. The best-fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >1010 M …
Ongoing Assembly Of Massive Galaxies By Major Merging In Large Groups And Clusters From The Sdss, Dh Mcintosh, Yc Guo, J Hertzberg, N Katz, Hj Mo, Fc Van Den Bosch, Xh Yang
Ongoing Assembly Of Massive Galaxies By Major Merging In Large Groups And Clusters From The Sdss, Dh Mcintosh, Yc Guo, J Hertzberg, N Katz, Hj Mo, Fc Van Den Bosch, Xh Yang
Astronomy Department Faculty Publication Series
We investigate the incidence of major mergers creating massive (Mstar > 1011 M⊙) galaxies in present-day (z≤ 0.12) groups and clusters. Using a volume-limited sample of 845 groups with dark matter halo masses above 2.5 × 1013 M⊙, we isolate 221 galaxy pairs with ≤1.5 r-band magnitude differences, ≤30 kpc projected separations and combined masses above 1011 M⊙. We fit the r-band images of each pair as the line-of-sight projection of symmetric models and identify 38 mergers by the presence of residual asymmetric structure associated with …
The Bar-Halo Interaction - I. From Fundamental Dynamics To Revised N-Body Requirements, Md Weinberg, N Katz
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 …
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
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.
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
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 …
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
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 …
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
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, …
The Dynamics Of Tidal Tails From Massive Satellites, Jh Choi, Md Weinberg, N Katz
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 …
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
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 …
The Morphological Diversities Among Star-Forming Galaxies At High Redshifts In The Great Observatories Origins Deep Survey, S Ravindranath, M Giavalisco, Hc Ferguson, C Conselice, N Katz, M Weinberg, J Lotz, M Dickinson, Sm Fall, B Mobasher, C Papovich
The Morphological Diversities Among Star-Forming Galaxies At High Redshifts In The Great Observatories Origins Deep Survey, S Ravindranath, M Giavalisco, Hc Ferguson, C Conselice, N Katz, M Weinberg, J Lotz, M Dickinson, Sm Fall, B Mobasher, C Papovich
Astronomy Department Faculty Publication Series
We used the deep, multiwavelength images obtained by the Great Observatories Origins Deep Survey (GOODS) to identify ~4700 Lyman break galaxies (LBGs) at z > 2.5, and 292 starburst galaxies at z ~ 1.2. We present the results from morphological analysis based on light profile shape and ellipticity for ~1333 of the most luminous LBGs. About 40% of LBGs at z ~ 3 have exponential profiles, ~30% of the galaxies have steep (r1/4-like) profiles, and ~30% of LBGs have multiple cores of disturbed morphologies suggestive of close pairs or mergers. The fraction of spheriod-like LBGs decrease by about 15% from z …
Dark Matter Halo Response To The Disc Growth, Jh Choi, Y Lu, Hj Mo, Md Weinberg
Dark Matter Halo Response To The Disc Growth, Jh Choi, Y Lu, Hj Mo, Md Weinberg
Astronomy Department Faculty Publication Series
We consider the sensitivity of the circular-orbit adiabatic contraction approximation to the baryon condensation rate and the orbital structure of dark matter haloes in the Λ cold dark matter (ΛCDM) paradigm. Using one-dimensional hydrodynamic simulations including the dark matter halo mass accretion history and gas cooling, we demonstrate that the adiabatic approximation is approximately valid even though haloes and discs may assemble simultaneously. We further demonstrate the validity of the simple approximation for ΛCDM haloes with isotropic velocity distributions using three-dimensional N-body simulations. This result is easily understood: an isotropic velocity distribution in a cuspy halo requires more circular orbits …
On The Origin Of Cold Dark Matter Halo Density Profiles, Y Lu, Hj Mo, N Katz, Md Weinberg
On The Origin Of Cold Dark Matter Halo Density Profiles, Y Lu, Hj Mo, N Katz, Md Weinberg
Astronomy Department Faculty Publication Series
N-body simulations predict that cold dark matter (CDM) halo-assembly occurs in two phases: (i) a fast-accretion phase with a rapidly deepening potential well; and (ii) a slow-accretion phase characterized by a gentle addition of mass to the outer halo with little change in the inner potential well. We demonstrate, using one-dimensional simulations, that this two-phase accretion leads to CDM haloes of the Navarro, Frenk & White (NFW) form and provides physical insight into the properties of the mass-accretion history that influence the final profile. Assuming that the velocities of CDM particles are effectively isotropized by fluctuations in the gravitational potential …
How Do Galaxies Get Their Gas?, D Keres, N Katz, Dh Weinberg, R Dave
How Do Galaxies Get Their Gas?, D Keres, N Katz, Dh Weinberg, R Dave
Astronomy Department Faculty Publication Series
We examine the temperature history of gas accreted by forming galaxies in smoothed particle hydrodynamics simulations. About half of the gas follows the track expected in the conventional picture of galaxy formation, shock heating to roughly the virial temperature of the galaxy potential well (T∼ 106 K for a Milky Way type galaxy) before cooling, condensing and forming stars. However, the other half radiates its acquired gravitational energy at much lower temperatures, typically T < 105 K, and the histogram of maximum gas temperatures is clearly bimodal. The ‘cold mode’ of gas accretion dominates for low-mass galaxies (baryonic …
Measuring The Halo Mass Of Z Similar To 3 Damped Ly Alpha Absorbers From The Absorber-Galaxy Cross-Correlation, N Bouche, Jp Gardner, N Katz, Dh Weinberg, R Dave, Jd Lowenthal
Measuring The Halo Mass Of Z Similar To 3 Damped Ly Alpha Absorbers From The Absorber-Galaxy Cross-Correlation, N Bouche, Jp Gardner, N Katz, Dh Weinberg, R Dave, Jd Lowenthal
Astronomy Department Faculty Publication Series
We test the reliability of a method to measure the mean halo mass of absorption-line systems such as damped Lyα absorbers (DLAs). The method is based on measuring the ratio of the cross-correlation between DLAs and galaxies to the autocorrelation of the galaxies themselves, which is (in linear theory) the ratio of their bias factor . We show that the ratio of the projected cross- and autocorrelation functions [wdg(rθ)/wgg(rθ)] is also the ratio of their bias factor, irrespective of the galaxy distribution, provided that one uses the same …
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
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 …
The Optical And Near-Infrared Properties Of Galaxies. I. Luminosity And Stellar Mass Functions, Ef Bell, Dh Mcintosh, N Katz, Md Weinberg
The Optical And Near-Infrared Properties Of Galaxies. I. Luminosity And Stellar Mass Functions, Ef Bell, Dh Mcintosh, N Katz, Md Weinberg
Astronomy Department Faculty Publication Series
We use a large sample of galaxies from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to calculate galaxy luminosity and stellar mass functions in the local universe. We estimate corrections for passband shifting and galaxy evolution, as well as present-day stellar mass-to-light (M/L) ratios, by fitting the optical-near-infrared galaxy data with simple models. Accounting for the 8% galaxy overdensity in the SDSS early data release region, the optical and near-infrared luminosity functions we construct for this sample agree with most recent literature optical and near-infrared determinations within the uncertainties. We argue that 2MASS …
The Canada-Uk Deep Submillimeter Survey. Vii. Optical And Near-Infrared Identifications For The 14 Hour Field, Tma Webb, Sj Lilly, Dl Clements, S Eales, Min Yun, M Brodwin, L Dunne, Wk Gear
The Canada-Uk Deep Submillimeter Survey. Vii. Optical And Near-Infrared Identifications For The 14 Hour Field, Tma Webb, Sj Lilly, Dl Clements, S Eales, Min Yun, M Brodwin, L Dunne, Wk Gear
Astronomy Department Faculty Publication Series
We present the multiwavelength identifications for 23 sources in the Canada-UK Deep Submillimeter Survey (CUDSS) 14h field. The identifications have been selected on the basis of radio and near-infrared data, and we argue that, to our observational limits, both are effective at selecting the correct counterparts of the SCUBA sources. We discuss the properties of these identifications and find that they are very red in near-infrared color, with many classified as extremely red objects, and show disturbed morphologies. Using the entire CUDSS catalog of 50 sources, we use a combination of spectroscopic redshifts (four objects), 1.4 GHz : 850 …
Bar-Driven Dark Halo Evolution: A Resolution Of The Cusp-Core Controversy, Md Weinberg, N Katz
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 …
High-Redshift Galaxies In Cold Dark Matter Models, Dh Weinberg, L Hernquist, N Katz
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 …
Noise-Driven Evolution In Stellar Systems - Ii. A Universal Halo Profile, Md Weinberg
Noise-Driven Evolution In Stellar Systems - Ii. A Universal Halo Profile, Md Weinberg
Astronomy Department Faculty Publication Series
Disc instabilities such as arm and bar formation, minor mergers and tidal encounters drive a galaxy from equilibrium. Using the theory that describes the evolution of a galaxy halo as a result of stochastic fluctuations developed in the companion paper to this one, we show that this sort of noise evolves a halo toward a standard profile, independent of its initial profile and concentration. This process can substantially redistribute the mass in dark-matter haloes in the 10 Gyr since formation. Three different noise processes are studied: (i) a bombardment by blobs of mass that are small compared to the halo …
Noise-Driven Evolution In Stellar Systems - I. Theory, Md Weinberg
Noise-Driven Evolution In Stellar Systems - I. Theory, Md Weinberg
Astronomy Department Faculty Publication Series
We present a theory for describing the evolution of a galaxy caused by stochastic events such as weak mergers, transient spiral structure, orbiting blobs, etc. This noise excites large-scale patterns that drive the evolution of the galactic density profile. In a dark matter halo, the repeated stochastic perturbations preferentially ring the lowest-order modes with only a very weak dependence on the details of their source. The subsequent redistribution of halo mass is determined only by the mechanics of these modes. The halo profile then evolves toward a universal asymptotic form for a wide variety of noise sources. Such a convergence …
Effect Of The Milky Way On Magellanic Cloud Structure, Md Weinberg
Effect Of The Milky Way On Magellanic Cloud Structure, Md Weinberg
Astronomy Department Faculty Publication Series
A combination of analytic models and n-body simulations implies that the structural evolution of the Large Magellanic Cloud (LMC) is dominated by its dynamical interaction with the Milky Way. Although expected at some level, the scope of the involvement has significant observational consequences. First, LMC disk orbits are torqued out of the disk plane, thickening the disk and populating a spheroid. The torque results from direct forcing by the Milky Way tide and, indirectly, from the drag between the LMC disk and its halo resulting from the induced precession of the LMC disk. The latter is a newly reported mechanism …
Fluctuations In Finite-N Equilibrium Stellar Systems, Md Weinberg
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 …