arXiv subjects

John L. Tonry

Publications and source records attributed to John L. Tonry.

120 records · Page 7Linked to original sources

arXiv1999

A Tully Fisher Relation for S0 Galaxies

We present an I-band Tully-Fisher relation (TFR) for 18 nearby S0 galaxies using kinematics derived from long slit spectroscopy of stellar absorption lines. Our estimates of the circular velocity, V_c, at 2-3 exponential disk scale lengths account for line-of-sight projection and for the stellar random motions through an asymmetric drift correction. Uniform and accurate distance calibration for all objects is available from surface brightness fluctuation measurements of Tonry et al. (1998). Despite the care taken in estimating both V_c and M_I, the TFR shows an intrinsic scatter, $\sim 0.7$ mag in M_I, or 0.15 in log_10(V_c). This result is surprising, as S0 galaxies appear to have both the simple kinematics of disk galaxies, and the simple stellar populations of early-type galaxies. Remarkably, in this sample of overall rotation-dominated galaxies, the central stellar velocity dispersion is a better predictor of the total I-band luminosity (through the Fundamental Plane relations) than the circular speed at several exponential scale lengths. Furthermore, the TFR zeropoint, or the mean stellar I-band luminosity at a given V_c, differs by only $\sim 0.5$ mag between our sample of S0s and Mathewson et al.'s (1992) sample of late-type spirals, once both data sets are brought onto a consistent distance scale. This offset is less than expected if S0s are former spiral galaxies with prematurely truncated star-formation ($\gtorder 4$ Gyrs ago).

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arXiv1998

Redshifts of the Gravitational Lenses MG0414+0534 and MG0751+2716

We report redshifts in two gravitational lens systems, MG0414+0534 and MG0751+2716. The lens galaxy in MG0414+0534 lies at z_l=0.9584+/-0.0002. The luminosity and extreme red color of the lens are then typical of a passively evolving, early-type, ~2L* galaxy. The galaxy cannot have a significant global mean extinction without being anomalously luminous. The lens galaxy in MG0751+2716 has a redshift of z_l=0.3502+/-0.0003 and it is a member of a small group. The group includes the nearby, bright companion galaxy whose redshift we confirmed to be z=0.3501+/-0.0001 and a nearby emission line galaxy with z=0.3505+/-0.0003. A second emission line galaxy with z=0.5216+/-0.0001 was found nearly superposed on the first emission line galaxy. The source in MG0751+2716 is a z_s=3.200+/-0.001 radio quasar. For flat universes with Omega_0=1.0 (0.3), 96% (87%) of lenses like MG0414+0534 and 7% (3%) of lenses like MG0751+2716 are expected to have lower lens redshifts than observed.

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arXiv1998

Velocity Dispersion of the Gravitational Lens 0957+561

0957+561 is the first gravitational lens system to be discovered and first for which a time delay was measured. Because the system is unusually rich in observables such as image positions, fluxes, VLBI structure, and polarization it has been modelled quite extensively. However, since it resides in a cluster providing substantial convergence, the velocity dispersion of the lensing galaxy is an important component to models. We have measured this dispersion to be 288+/-9 kms (1-sigma), which implies a Hubble constant of 72+/-7 kms/Mpc (1-sigma) according to the preferred FGS model of Grogin and Narayan, and 70+/-7 kms/Mpc (1-sigma) using the SPLS model. The unknown velocity dispersion anisotropy of the central galaxy produces an additional uncertainty of perhaps 15% or more. We see no variation in dispersion with position to a radius of +/-3". In addition to a galaxy from the background cluster at z=0.5, our slit serendiptously picked up a galaxy at z = 0.448, and two galaxies which may be part of a background cluster at a redshift of z=0.91.

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arXiv1998

The Infrared Surface Brightness Fluctuation Distances to the Hydra and Coma Clusters

We present IR surface brightness fluctuation (SBF) distance measurements to NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster. We explicitly corrected for the contributions to the fluctuations from globular clusters, background galaxies, and residual background variance. We measured a distance of 85 +/- 10 Mpc to NGC 4889 and a distance of 46 +/- 5 Mpc to the Hydra cluster. Adopting recession velocities of 7186 +/- 428 km/s for Coma and 4054 +/- 296 km/s for Hydra gives a mean Hubble constant of H_0 = 87 +/- 11 km/s/Mpc. Corrections for residual variances were a significant fraction of the SBF signal measured, and, if underestimated, would bias our measurement towards smaller distances and larger values of H_0. Both NICMOS on the Hubble Space Telescope and large-aperture ground-based telescopes with new IR detectors will make accurate SBF distance measurements possible to 100 Mpc and beyond.

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arXiv1998

Distances from Surface Brightness Fluctuations

The practice of measuring galaxy distances from their spatial fluctuations in surface brightness is now a decade old. While several past articles have included some review material, this is the first intended as a comprehensive review of the surface brightness fluctuation (SBF) method. The method is conceptually quite simple, the basic idea being that nearby (but unresolved) star clusters and galaxies appear "bumpy", while more distant ones appear smooth. This is quantified via a measurement of the amplitude of the Poisson fluctuations in the number of unresolved stars encompassed by a CCD pixel (usually in an image of an elliptical galaxy). Here, we describe the technical details and difficulties involved in making SBF measurements, discuss theoretical and empirical calibrations of the method, and review the numerous applications of the method from the ground and space, in the optical and near-infrared. We include discussions of stellar population effects and the "universality" of the SBF standard candle. A final section considers the future of the method.

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arXiv1998

Measuring Distances Using Infrared Surface Brightness Fluctuations

Surface brightness fluctuations (SBFs) are much brighter in the IR than they are at optical wavelengths, making it possible to measure greater distances using IR SBFs. We report new K' (2.1 micron) SBF measurements of 9 galaxies in the Fornax and Eridanus clusters using a 1024^2-pixel HgCdTe array. We used improved analysis techniques to remove contributions from globular clusters and background galaxies, and we assess the relative importance of other sources of residual variance. We applied the improved methodology to Fornax and Eridanus images and to previously published Virgo cluster data. Apparent fluctuation magnitudes were used in conjunction with Cepheid distances to M31 and the Virgo cluster to calibrate the K' SBF distance scale. We find the absolute fluctuation magnitude MK'= -5.61+/-0.12, with an intrinsic scatter to the calibration of 0.06 mag. No statistically significant change in MK' is detected as a function of (V-I). Our calibration is consistent with constant age and metallicity stellar population models. The lack of a correlation with (V-I) in the context of the stellar population models implies that elliptical galaxies bluer than (V-I)=1.2 have SBFs dominated by younger (5-8 Gyr) populations. K' SBFs prove to be a reliable distance indicator as long as the residual variance from globular clusters and background galaxies is properly removed. Also, it is important that a sufficiently high S/N ratio be achieved to allow reliable sky subtraction because residual spatial variance can bias the measurement of the SBF power spectrum. (abridged)

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arXiv1997

The Far Field Hubble Constant

We used HST to obtain surface brightness fluctuation (SBF) observations of four nearby brightest cluster galaxies (BCG) to calibrate the BCG Hubble diagram of Lauer & Postman (1992). This BCG Hubble diagram contains 114 galaxies covering the full celestial sphere and is volume limited to 15,000 km/s, providing excellent sampling of the far field Hubble flow. The SBF zero point is based on the Cepheid calibration of the ground I_KC method (Tonry et al. 1997) as extended to the WFPC2 F814W filter by Ajhar et al. (1997). The BCG globular cluster luminosity functions give distances essentially identical to the SBF results. Using the velocities and SBF distances of the four BCG alone gives H_0 = 82 +/- 8 km/s/Mpc in the CMB frame, valid on ~4,500 km/s scales. Use of BCG as photometric redshift estimators allows the BCG Hubble diagram to be calibrated independently of recession velocities, yielding a far field H_0 = 89 +/- 10 km/s/Mpc with an effective depth of ~11,000 km/s. The error in this case is dominated by the photometric cosmic scatter in using BCG as distance estimators. The concordance of the present results with other recent H_0 determinations, and a review of theoretical treatments on perturbations in the near field Hubble flow, argue that going to the far field removes an important source of uncertainty, but that there is not a large systematic error to be corrected for to begin with. Further improvements in H_0 depend more on understanding nearby calibrators than on improved sampling of the distant flow.

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arXiv1997

Redshifts of the Gravitational Lenses B1422+231 and PG1115+080

B1422+231 and PG1115+080 are gravitational lens systems producing quadruple QSO images where there is real promise that time delays can constrain the Hubble constant. In addition, the lensing galaxies are both part of groups which can play an important role in modelling the lens potential. This article reports redshifts for the lensing galaxies and three neighboring galaxies in each of the two systems. B1422+231 consists of a group at z=0.339 with a dispersion of 733 km/s, and PG1115+080 is a group at z=0.311 with a dispersion of 326 km/s. One of the neighboring galaxies in the B1422+231 system turned out to be an emission line galaxy at z=0.536, suggesting that QSO light passing through B1422+231 may have been subjected to lensing by a cluster at this more distant redshift. The velocity dispersion of the lensing galaxy in PG1115+080 is determined to be 281+/-25 km/s (1" square aperture), which is surprisingly large given the image splittings of 1.2" in that system.

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arXiv1997

The Orthogonal Transfer CCD

We have designed and built a new type of CCD that we call an orthogonal transfer CCD (OTCCD), which permits parallel clocking horizontally as well as vertically. The device has been used successfully to remove image motion caused by atmospheric turbulence at rates up to 100 Hz, and promises to be a better, cheaper way to carry out image motion correction for imaging than by using fast tip/tilt mirrors. We report on the device characteristics, and find that the large number of transfers needed to track image motion does not significantly degrade the image either because of charge transfer inefficiency or because of charge traps. For example, after 100 sec of tracking at 100 Hz approximately 3% of the charge would diffuse into a skirt around the point spread function. Four nights of data at the Michigan-Dartmouth-MIT (MDM) 2.4-m telescope also indicate that the atmosphere is surprisingly benign, in terms of both the speed and coherence angle of image motion. Image motion compensation improved image sharpness by about 0.5 arcsec in quadrature with no degradation over a field of at least 3 arcminutes.

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arXiv1997

Globular Clusters in 19 Northern Abell Clusters

We study the globular cluster (GC) populations of 21 giant elliptical galaxies in 19 Abell clusters. This method, applied here primarily in the R band, is based on the surface brightness fluctuations technique of extragalactic distance measurement. The sample galaxies range in redshift from 5000 to 10,000 \kms, and were selected primarily from the Lauer & Postman (1994) survey of brightest cluster galaxies (BCGs). We find a tight correlation between the GC specific frequency S_N of the central bright galaxy in the cluster and the cluster velocity dispersion. S_N also correlates well with the cluster X-ray temperature and with the number of bright neighboring galaxies, less well with the galaxy profile, and only marginally with galaxy luminosity and overall cluster richness. It does not correlate with cluster morphology class. Thus, unlike galaxy luminosity, S_N is determined by the cluster mass, or density. To account for this situation, we propose that the GCs formed early and in proportion to the available mass, while the luminosity growth of the galaxy was later halted, yielding the observed correlations of S_N with density. We introduce a quantity called $η_{GC}$, the number of GCs per unit local cluster mass. For a simple cluster mass model, $η_{GC}$ is found to be constant, indicating a uniform GC production rate per unit available mass. A measurement of the Gaussian width $σ$ of the GC luminosity function (GCLF) is one of the byproducts of our analysis. In the cosmic microwave background frame, the mean width for this sample is $< σ> = 1.43$ mag, virtually identical to the HST value for M87, the galaxy used to calibrate the mean of the GCLF in this analysis.

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arXiv1996

The SBF Survey of Galaxy Distances. I. Sample Selection, Photometric Calibration, and the Hubble Constant

We describe a program of surface brightness fluctuation (SBF) measurements for determining galaxy distances. This paper presents the photometric calibration of our sample and of SBF in general. Basing our zero point on observations of Cepheid variable stars, we find that the absolute SBF magnitude in the Kron-Cousins I band correlates well with the mean (V-I)o color of a galaxy according to M_Ibar = (-1.74 +/- 0.07) + (4.5 +/- 0.25) [ (V-I)o - 1.15 ] for 1.0 < (V-I) < 1.3. This agrees well with theoretical estimates from stellar population models. Comparisons between SBF distances and a variety of other estimators, including Cepheid variable stars, the Planetary Nebula Luminosity Function (PNLF), Tully-Fisher (TF), Dn-sigma, SNII, and SNIa, demonstrate that the calibration of SBF is universally valid and that SBF error estimates are accurate. The zero point given by Cepheids, PNLF, TF (both calibrated using Cepheids), and SNII is in units of Mpc; the zero point given by TF (referenced to a distant frame), Dn-sigma and SNIa is in terms of a Hubble expansion velocity expressed in km/s. Tying together these two zero points yields a Hubble constant of H_0 = 81 +/- 6 km/s/Mpc. As part of this analysis, we present SBF distances to 12 nearby groups of galaxies where Cepheids, SNII, and SNIa have been observed.

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arXiv1996

Globular Clusters in Fornax: Does $M^0$ Depend on Environment?

We present the $V$-band globular cluster luminosity functions (GCLFs) of the Fornax Cluster galaxies NGC 1344, NGC 1380, NGC 1399, and NGC 1404. Our observations reach to $V = 24.8$, roughly one magnitude beyond the GCLF turnover $m^0_V$, with $\sim90\%$ completeness. From the amplitude of the galaxy surface brightness fluctuations, we also estimate the number of globular clusters fainter than this cutoff magnitude. The GCLFs of these galaxies are well fitted by Gaussians; the weighted means of their turnover magnitudes and dispersions are $\langle m^0_V\rangle = 23.88 \pm 0.10$ mag and $\langleσ\rangle = 1.35\pm 0.07$ mag. The assumption of a universal value for the absolute magnitude of the turnover $M^0_V$ places the Fornax cluster $0.13 \pm 0.11$ mag more distant than Virgo. However, in light of recent Cepheid and other high-precision distance measurements, as well as ongoing HST observations of GCLFs for the purpose of determining the extra-galactic distance scale, we choose to re-examine the universal GCLF hypothesis. Based on data from groups and clusters of galaxies, we find evidence that $M^0_V$ becomes fainter as the local density of galaxies increases. We speculate on the possible cause of this trend; if it is confirmed, GCLF observations will be less useful for determining distances, but may provide important information for constraining theories of star formation in primordial galaxy halos.

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