F. D. A. Hartwick

University of Victoria, Victoria, British Columbia, Canada

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Publications (133)565.15 Total impact

  • R. G. Carlberg, F. D. A. Hartwick
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    ABSTRACT: Early-type galaxies have projected central density brightness profile logarithmic slopes, γ', ranging from about 0 to 1. We show that γ' is strongly correlated, r = 0.83, with the coarse grain phase density of the galaxy core, Q 0 ≡ ρ/σ3. The luminosity-γ' correlation is much weaker, r = –0.51. Q 0 also serves to separate the distribution of steep core profiles, γ' > 0.5, from shallow profiles, γ' < 0.3, although there are many galaxies of intermediate slope, at intermediate Q 0, in a volume-limited sample. The transition phase density separating the two profile types is approximately 0.003 M ☉ pc–3 km–3 s3, which is also where the relation between Q 0 and core mass shows a change in slope, the rotation rate of the central part of the galaxy increases, and the ratio of the black hole to core mass increases. These relations are considered relative to the globular cluster inspiral core buildup and binary black hole core scouring mechanisms for core creation and evolution. Mass-enhanced globular cluster inspiral models have quantitative predictions that are supported by data, but no single model yet completely explains the correlations.
    The Astrophysical Journal 06/2014; 789(1):11. · 6.73 Impact Factor
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    Pavel A. Denissenkov, F. D. A. Hartwick
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    ABSTRACT: We propose that the abundance anomalies of proton-capture elements in globular clusters, such as the C-N, Na-O, Mg-Al and Na-F anti-correlations, were produced by super-massive stars with M ~ 10,000 Msun. Such stars could form in the runaway collisions of massive stars that sank to the cluster center as a result of dynamical friction, or via the direct monolithic collapse of the low-metallicity gas cloud from which the cluster formed. To explain the observed abundance anomalies, we assume that the super-massive stars had lost significant parts of their initial masses when only a small mass fraction of hydrogen, Delta X ~ 0.15, was transformed into helium. We speculate that the required mass loss might be caused by the super-Eddington radiation continuum-driven stellar wind or by the diffusive mode of the Jeans instability.
    Monthly Notices of the Royal Astronomical Society 05/2013; · 5.52 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: Observations show that the underlying rotation curves at intermediate radii in spiral and low-surface brightness galaxies are nearly universal. Further, in these same galaxies, the product of the central density and the core radius ($\rho_{0}r_{0}$) is constant. An empirically motivated model for dark matter halos which incorporates these observational constraints is presented and shown to be in accord with the observations. A model fit to the observations of the galaxy cluster Abell 611 shows that $\rho_{0}r_{0}$ for the dark matter halo in this more massive structure is larger by a factor of $\sim 20$ over that assumed for the galaxies. The model maintains the successful NFW form in the outer regions although the well defined differences in the inner regions suggest that modifications to the standard CDM picture are required.
    The Astronomical Journal 10/2012; 144(6). · 4.97 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: A statistical method is presented for determining the velocity field in the immediate vicinity of groups of galaxies using only positional and redshift information with the goal of studying the perturbation of the Hubble flow around groups more distant than the Local Group. The velocities are assumed to obey a Hubble-like expansion law, i.e. $V=H_{exp}R$ where the expansion rate $H_{exp}$ is to be determined. The method is applied to a large, representative group catalog and evidence is found for a sub-Hubble expansion rate within two well defined radii beyond the virial radii of the groups. This result is consistent with that of Teerikorpi et al. (2008) who found a similar expansion law around 3 nearby groups and extends it to a more representative volume of space.
    The Astronomical Journal 04/2011; 141(6). · 4.97 Impact Factor
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    ABSTRACT: While the spectral features and their phase evolution of the majority of Type Ia supernovae (SNe Ia) are remarkably uniform, the advent of large spectroscopic data sets reveal subtle, but real, diversity among SNe Ia. To understand the origin of the observed variations, we conduct a systematic study of the feature shapes using the technique of principal component analysis (PCA). With the aid of PCA, the multidimensional spectral information is reduced to a few components, quantifying the subtle variations in the feature shape. Using the projections of the data on these principal components, it is shown here that light-curve shape is the main driver of the spectroscopic diversity at maximum light for every spectral feature in the rest-frame optical. The correlation points to composition of the ejecta and temperature which governs the speed of the ionization evolution as the main driver of the variation, while the effects of asymmetry appear to be sub-dominant at this phase. We also employ the same technique to study any differences in the spectroscopic properties between high-redshift and nearby SNe Ia, and also between SNe Ia of a range of host mass.
    01/2011;
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    ABSTRACT: If a galaxy cluster is effectively in dynamical equilibrium, then all galaxy populations within the cluster must have distributions in velocity and position that individually reflect the same underlying mass distribution, although the derived virial masses can be quite different. Specifically, within the Canadian Network for Observational Cosmology cluster sample, the virial radius of the red galaxy population is, on the average, a factor of 2.05 ± 0.34 smaller than that of the blue population. The red galaxies also have a smaller rms velocity dispersion, a factor of 1.31 ± 0.13 within our sample. Consequently, the virial mass calculated from the blue galaxies is 3.5 ± 1.3 times larger than from the red galaxies. However, applying the Jeans equation of stellar hydrodynamic equilibrium to the red and blue subsamples separately gives statistically identical cluster mass profiles. This is strong evidence that these clusters are effectively equilibrium systems and therefore demonstrates empirically that the masses in the virialized region are reliably estimated using dynamical techniques.
    The Astrophysical Journal 01/2009; 476(1):L7. · 6.73 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: Based on the earlier work of Gunn and McCrea we model the formation of globular clusters in merging galaxies. Neutral hydrogen observations of dwarf irregular galaxies as well as more luminous systems are used to provide the key parameters of the model. The observations indicate that clusters with the mass of globular clusters should still be forming today. The model is incorporated into a phenomenological picture of galaxy evolution making use of a simple chemical evolution model. These results are compared to recent observations of the metallicity distributions of F and G stars from a recent large SDSS survey. The comparisons are consistent with an anisotropic collapse and merging of a large number of dwarf irregular galaxies for the formation of the Galaxy.
    The Astrophysical Journal 10/2008; 691. · 6.73 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: A halo model is presented which possesses a constant phase space density (Q) core followed by a radial CDM-like power law decrease in Q. The motivation for the core is the allowance for a possible primordial phase space density limit such as the Tremaine-Gunn upper bound. The space density profile derived from this model has a constant density core and falls off rapidly beyond. The new model is shown to improve the fits to the observations of LSB galaxy rotation curves, naturally provides a model which has been shown to result in a lengthened dynamical friction time scale for the Fornax dwarf spheroidal galaxy and predicts a flattening of the density profile within the Einstein radius of galaxy clusters. A constant gas entropy floor is predicted whose adiabatic constant provides a lower limit in accord with observed galaxy cluster values. While `observable-sized' cores are not seen in standard cold dark matter (CDM) simulations, phase space considerations suggest that they could appear in warm dark matter (WDM) cosmological simulations and in certain hierarchically consistent SuperWIMP scenarios. Comment: 14 pages, 3 figures, accepted for publication in ApJ
    The Astrophysical Journal 11/2007; · 6.73 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: Nucleosynthetic signatures in common between the gas responsible for the high redshift Lyman alpha forest and a subsample of extremely metal poor stars are found. A simple mass loss model of chemical evolution with physically motivated parameters provides a consistent picture in which the gas is identified with that lost by supernova-driven winds during the first generation of star formation. Substantial mass loss occurs which can account for a diffuse IGM with up to 80% of the total baryon content and a peak [C-O/H] abundance of \~-2.9. This mass loss component differs from one produced later during galaxy formation and evolution that contributes to a circum-galactic medium (CGM). The CGM was shown earlier to have a mass of ~10% of all baryons and peak [Fe/H]~-1. Comment: 15 pages including 4 figures, accepted for publication in ApJ
    The Astrophysical Journal 11/2005; · 6.73 Impact Factor
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    ABSTRACT: We measure the build-up of the stellar mass of galaxies from z=6 to z=1. Using 15 band multicolour imaging data in the NICMOS Ultra Deep Field we derive photometric redshifts and masses for 796 galaxies down to H_AB=26.5. The derived evolution of the global stellar mass density of galaxies is consistent with previous star formation rate density measurements over the observed range of redshifts. Ongoing research in the CFHTLS Deep Fields confirms this result at lower redshifts. Further, if the sample is split by morphological type, a substantial increase is seen in the number of bulge dominated galaxies relative to disk-dominated galaxies since z=1.
    11/2005;
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    S. D. J. Gwyn, F. D. A. Hartwick
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    ABSTRACT: We measure the build-up of the stellar mass of galaxies from z=6 to z=1. Using 15 band multicolor imaging data in the NICMOS Ultra Deep Field we derive photometric redshifts and masses for 796 galaxies down to H(AB)=26.5. The derived evolution of the global stellar mass density of galaxies is consistent with previous star formation rate density measurements over the observed range of redshifts. Beyond the observed range, maintaining consistency between the global stellar mass and the observed star formation rate suggests the epoch of galaxy formation was z=16.
    The Astronomical Journal 04/2005; · 4.97 Impact Factor
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    F D A Hartwick, D Schade
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    ABSTRACT: A review of the current understanding of the space density (expressed in the form of luminsoity functions) and clustering properties of quasars is presented. It is pointed out that the present knowledge of the quasar luminosity function for z less than 2.2 would appear to be quite secure. In addition, the statistics of the luminosity function for z greater than 3 are improving rapidly owing to several large surveys currently underway. Deep surveys are required to determine whether the decline in space density at z greater than 3 observed for the most luminous quasars also applies to the intrinsically faintest objects. It is expected that the focus of future work will be on determining the relationship between classical quasars and their less luminous and/or obscured relatives.
    Annual Review of Astronomy and Astrophysics 11/2003; 28:437-489. · 23.33 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: The goal of this investigation is to reconstruct the cosmic star formation rate density history from local observations and in doing so to gain insight into how galaxies might have formed and evolved. A new chemical evolution model is described which accounts for the formation of globular clusters as well as the accompanying field stars. When this model is used in conjunction with the observed age metallicity relations for the clusters and with input which allows for the formation of the nearly universally observed bimodal distribution of globular clusters, star formation rates are obtained. By confining attention to a representative volume of the local universe, these rates allow a successful reconstruction of the Madau plot while complementary results similtaneously satisfy many local cosmological constraints. A physical framework for galaxy formation is presented which incorporates the results from this chemical evolution model and assumes an anisotropic collapse. In addition to providing the `classical' halo, bulge and disk components, the model also predicts a new stellar halo component with peak [Fe/H] ~ -0.8 and disk-like angular momentum and allows for the formation of a thick disk as outlined by the group of metal rich globular clusters. Milky Way counterparts of the latter two components are identified. Comment: 32 pages, 6 figs accepted by ApJ
    The Astrophysical Journal 11/2003; · 6.73 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: The velocity ellipsoid for 38 globular clusters with [Fe/H] <= -1.0 is derived and shown to be significantly anisotropic with major axis directed towards low Galactic latitude. Principal axes of the spatial distribution of different groups of clusters are derived and compared with the velocity ellipsoid. The metal poor cluster spatial distribution is significantly flattened along an axis which coincides within the uncertainties with the major axis of the velocity ellipsoid. Given the observed steep age-metallicity relation for metal poor clusters, one speculative interpretation of the data is that an initially flattened filament underwent a relatively rapid initial transverse collapse forming satellite galaxies and metal poor globular clusters while the protogalaxy collapsed and assembled more slowly along the filament acquiring and/or redistributing angular momentum in the process. Comment: 10 pages, 1 figure, accepted for publication in ApJ Letters
    The Astrophysical Journal 07/2002; · 6.73 Impact Factor
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    F. D. A. Hartwick
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    ABSTRACT: We present evidence to support an earlier indication that the Galaxy is embedded in an extended, highly inclined, triaxial halo outlined by the spatial distribution of companion galaxies to the Milky Way. Signatures of this spatial distribution are seen in 1) the angular variation of the radial-velocity dispersion of the companion galaxies, 2) the spatial distribution of the M 31 sub-group of galaxies, 3) the spatial distribution of the isolated, mainly dwarf irregular, galaxies of the Local Group, 4) the velocity anisotropy quadrupole of a sub-group of high-velocity clouds, and 5) the spatial distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M 31 and surrounding galaxies on the Galaxy are not strong enough to have affected the observed structure. We conclude that this distribution is a reflection of initial conditions. A simple galaxy formation scenario is proposed which ties together the results found here with those of Holmberg (1969) and Zaritsky et al. (1997) o...
    The Astronomical Journal 01/2000; · 4.97 Impact Factor
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    ABSTRACT: We present new data on several z=1.54 radio-loud quasar fields from a sample of 31 at z=1-2 in which we have previously identified an excess population of predominantly red galaxies. Narrow-band H-alpha observations detect five candidate galaxies at the quasar redshifts in three fields totaling 10.156 arcmin^2, a surface density 30 times higher than in previous surveys, even targeted ones. SCUBA observations of three fields detect at least one candidate quasar-associated galaxy. Many galaxies with SEDs indicating considerable dust are not detected, but the limits are only sufficient to rule out hyperluminous infrared galaxies. Finally, quantitative photometric redshifts and SED fits are presented for one "J-band dropout" galaxy with J-K>2.5 which is confirmed to be very dusty (E(B-V)~=0.5) and background to the quasar at >99.9% confidence.
    09/1999;
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    ABSTRACT: this paper). The two resulting subsamples have approximately the same number of members and
    03/1999;
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    F. D. A. Hartwick
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    ABSTRACT: . We use observations and evolutionary models of local objects to interpret a recent determination of the star-formation history of the universe. By fitting the global star-formation rate, the model predicts the ratio of spheroid to disk mass of ¸1, an intergalactic medium (IGM) whose mass is ¸2.3 times the mass in stars, and whose metallicity is ¸0.1 Z fi . 1. Introduction It is conventional to interpret observations of high-redshift galaxies using sophisticated galaxy evolution models. However, unless the observed spectra are of sufficiently high S/N, the resulting interpretations may not be unique (c.f. O'Connell 1996). On the other hand, deep color-magnitude diagrams of objects like globular clusters, dwarf spheroidals, and gas-rich systems such as the Galactic disk and the Magellanic Clouds in principle show us their complete star formation history (c.f. contributions in Leitherer et al. 1996 and this volume). To the extent that these systems can be considered representative of ...
    Proceedings of the International Astronomical Union 11/1998;
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    ABSTRACT: The CNOC redshift survey of galaxy clusters measures Omega_M from Omega_e(z)= M/L x j/\rho_c which can be applied on a cluster-by-cluster basis. The mass-to-light ratios, M/L, are estimated from rich galaxy clusters, corrected to the field population over the 0.18 to 0.55 redshift range. Since the luminosity density depends on cosmological volumes, the resulting Omega_e(z) has a strong dependence on cosmology which allows us to place the results in the Omega_M-Omega_Lambda plane. The resulting Omega_M declines if Omega_Lambda>0 and we find that Omega_Lambda<1.5.
    05/1998;
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    ABSTRACT: The CNOC2 field galaxy redshift survey is designed to provide measurements of the evolution of galaxies and their clustering over the redshift range 0 to 0.7. The sample is spread over four sky patches with a total area of about 1.5 square degrees. Here we report preliminary results based on two of the sky patches, and the redshift range of 0.15 to 0.55. We find that galaxy evolution can be statistically described as nearly pure luminosity evolution of early and intermediate SED types, and nearly pure density evolution of the late SED types. The correlation of blue galaxies relative to red galaxies is similar on large scales but drops by a factor of three on scales less than about 0.3/h mpc, approximately the mean scale of virialization. There is a clear, but small, 60%, change in clustering with 1.4 mag of luminosity. To minimize these population effects in our measurement of clustering evolution, we choose galaxies with M_r^{k,e}<= -20 mag as a population whose members are most likely to be conserved with redshift. Remarkably, the evolution of the clustered density in proper co-ordinates at r < 10/h Mpc, proportional to r_0^gamma (1+z)^3, is best described as a ``de-clustering'', (1+z)^{0.6+/-0.4}. Or equivalently, there is a weak growth of clustering in co-moving co-ordinates, x_0~ (1+z)^{-0.3 +/- 0.2}. This conclusion is supported by the pairwise peculiar velocities which rise slightly, but not significantly, into the past. The Cosmic Virial Theorem applied to the CNOC2 data gives Q Omega_M/b=0.11 +/- 0.04$, where Q is the three point correlation parameter and b the bias. Similarly, galaxy groups have a virial mass-to-light ratio (evolution corrected) of M_{virial}/L_R^{k,e} = 215h Lsun/Msun, or Omega_M=0.15 +/- 0.05. Comment: Presented at Royal Society Discussion Meeting, March 1998, "Large Scale Structure in the Universe" 20 pages, uses rspublic_mod style file included
    Philosophical Transactions of The Royal Society B Biological Sciences 05/1998; · 6.23 Impact Factor

Publication Stats

2k Citations
565.15 Total Impact Points

Institutions

  • 1978–2014
    • University of Victoria
      • Department of Physics and Astronomy
      Victoria, British Columbia, Canada
  • 1997
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1984–1991
    • Arizona State University
      • School of Earth and Space Exploration
      Phoenix, Arizona, United States
  • 1983
    • University of Canberra
      Canberra, Australian Capital Territory, Australia
  • 1979
    • University of Michigan
      Ann Arbor, Michigan, United States