Herzberg Institute for Astrophysics
Wesson P.S.,University of Waterloo |
Wesson P.S.,Herzberg Institute for Astrophysics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011
In 5D, I take the metric in canonical form and define causality by null-paths. Then spacetime is modulated by a factor equivalent to the wave function, and the 5D geodesic equation gives the 4D Klein-Gordon equation. These results effectively show how general relativity and quantum mechanics may be unified in 5D. © 2011 Elsevier B.V.
Tapping K.F.,Herzberg Institute for Astrophysics |
Valdes J.J.,National Research Council Canada
Solar Physics | Year: 2011
The activity minimum between the end of cycle 23 and the beginning of cycle 24 was the longest and deepest since at least the beginning of the 20th century. This has led to speculation that the Sun is changing its behaviour. The sunspot number and 10.7-cm solar radio flux indices have traditionally been highly correlated, so a change in the relationship between them might flag at such a change. An examination of this relationship suggests a significant change in the relationship between activity in the photosphere and in the chromosphere/corona happened soon after the maximum of cycle 23 and has continued into cycle 24. However, there are indications of change as early as 1980. © 2011 Springer Science+Business Media B.V.
Hutchings J.B.,Herzberg Institute for Astrophysics |
Bianchi L.,Johns Hopkins University
Astronomical Journal | Year: 2010
We discuss a sample of ∼60,000 objects from the combined Sloan Digital Sky Survey-Galaxy Evolution Explorer (SDSS-GALEX) database with UV-optical colors that should isolate QSOs in the redshift range 0.5-1.5. We use SDSS spectra of a subsample of ∼4500 to remove stellar and galaxy contaminants in the sample to a very high level, based on the 7-band photometry. We discuss the distributions of redshift, luminosity, and reddening of the 19,100 QSOs (∼96%) that we estimate to be present in the final sample of 19,812 point sources. The catalog is available as an online table. 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Willott C.J.,Herzberg Institute for Astrophysics |
Omont A.,CNRS Paris Institute of Astrophysics |
Bergeron J.,CNRS Paris Institute of Astrophysics
Astrophysical Journal | Year: 2013
We present Atacama Large Millimeter Array observations of rest-frame far-infrared continuum and [C II] line emission in two z = 6.4 quasars with black hole masses of 108 M ⊙. CFHQS J0210-0456 is detected in the continuum with a 1.2 mm flux of 120 ± 35 μJy, whereas CFHQS J2329-0301 is undetected at a similar noise level. J2329-0301 has a star formation rate limit of <40 M ⊙ yr-1, considerably below the typical value at all redshifts for this bolometric luminosity. Through comparison with hydro simulations, we speculate that this quasar is observed at a relatively rare phase where quasar feedback has effectively shut down star formation in the host galaxy. [C II] emission is also detected only in J0210-0456. The ratio of [C II] to far-infrared luminosity is similar to that of low-redshift galaxies of comparable luminosity, suggesting that the previous finding of an offset in the relationships between this ratio and far-infrared luminosity at low and high redshifts may be partially due to a selection effect due to the limited sensitivity of previous continuum data. The [C II] line of J0210-0456 is relatively narrow (FWHM = 189 ± 18 km s-1), indicating a dynamical mass substantially lower than expected from the local black hole-velocity dispersion correlation. The [C II] line is marginally resolved at 0.″7 resolution with the blue and red wings spatially offset by 0.″5 (3 kpc) and a smooth velocity gradient of 100 km s-1 across a scale of 6 kpc, possibly due to the rotation of a galaxy-wide disk. These observations are consistent with the idea that stellar mass growth lags black hole accretion for quasars at this epoch with respect to more recent times. © 2013. The American Astronomical Society. All rights reserved.
McConnachie A.W.,Herzberg Institute for Astrophysics
Astronomical Journal | Year: 2012
Positional, structural, and dynamical parameters for all dwarf galaxies in and around the Local Group are presented, and various aspects of our observational understanding of this volume-limited sample are discussed. Over 100 nearby galaxies that have distance estimates reliably placing them within 3Mpc of the Sun are identified. This distance threshold samples dwarfs in a large range of environments, from the satellite systems of the MW and M31, to the quasi-isolated dwarfs in the outer regions of the Local Group, to the numerous isolated galaxies that are found in its surroundings. It extends to, but does not include, the galaxies associated with the next nearest groups, such as Maffei, Sculptor, and IC 342. Our basic knowledge of this important galactic subset and their resolved stellar populations will continue to improve dramatically over the coming years with existing and future observational capabilities, and they will continue to provide the most detailed information available on numerous aspects of dwarf galaxy formation and evolution. Basic observational parameters, such as distances, velocities, magnitudes, mean metallicities, as well as structural and dynamical characteristics, are collated, homogenized (as far as possible), and presented in tables that will be continually updated to provide a convenient and current online resource. As well as discussing the provenance of the tabulated values and possible uncertainties affecting their usage, the membership and spatial extent of the MW sub-group, M31 sub-group, and the Local Group are explored. The morphological diversity of the entire sample and notable sub-groups is discussed, and timescales are derived for the Local Group members in the context of their orbital/interaction histories. The scaling relations and mean stellar metallicity trends defined by the dwarfs are presented, and the origin of a possible "floor" in central surface brightness (and, more speculatively, stellar mean metallicity) at faint magnitudes is considered. © 2012. National Research Council Canada. All rights reserved.
McConnachie A.W.,Herzberg Institute for Astrophysics |
Cote P.,Herzberg Institute for Astrophysics
Astrophysical Journal Letters | Year: 2010
Velocity dispersion measurements of recently discoveredMilkyWay satelliteswithMV ≳ -7 imply that they posses high mass-to-light ratios. The expected velocity dispersions due to their baryonic mass are ∼0.2 km s -1, but values ≳3 km s-1 are measured. We perform Monte Carlo simulations of mock radial velocity measurements of these systems assuming that they have mass-to-light ratios similar to globular clusters and posses an unidentified binary star population, to determine if these stars could boost the velocity dispersion to the observed values. We find that this hypothesis is unlikely to produce dispersions much in excess of ∼4.5 km s-1, in agreement with previous work. However, for the systems with the potentially smallest velocity dispersions, values consistent with observations are produced in5%-40%of our simulations for binary fractions in excess of fbin(P ≲ 10 yr) ∼5%.This sample includes the dwarf galaxy candidates that lie closest to classical globular clusters inM V -rh space. Considered as a population, it is unlikely that all of these dwarf galaxy candidates have mass-to-light ratios typical of globular clusters, but boosting of the observed dispersion by binaries from near-zero values cannot be ruled out at high confidence for several individual dwarf galaxy candidates. Given the importance of obtaining accurate velocity dispersions and dynamical masses for the faintest satellites, it is clearly desirable to directly exclude the possible effect of binaries on these systems. This requires multi-epoch radial velocity measurements with individual uncertainties of ≲1 km s-1 to identify spectroscopic binaries with orbital velocities of the order of the observed velocity dispersion. © 2010. The American Astronomical Society. All rights reserved.
Andersen D.R.,Herzberg Institute for Astrophysics |
Bershady M.A.,University of Wisconsin - Madison
Astrophysical Journal | Year: 2013
Using the integral field unit DensePak on the WIYN 3.5 m telescope we have obtained Hα velocity fields of 39 nearly face-on disks at echelle resolutions. High-quality, uniform kinematic data and a new modeling technique enabled us to derive accurate and precise kinematic inclinations with mean i kin = 23° for 90% of these galaxies. Modeling the kinematic data as single, inclined disks in circular rotation improves upon the traditional tilted-ring method. We measure kinematic inclinations with a precision in sin i of 25% at 20° and 6% at 30°. Kinematic inclinations are consistent with photometric and inverse Tully-Fisher inclinations when the sample is culled of galaxies with kinematic asymmetries, for which we give two specific prescriptions. Kinematic inclinations can therefore be used in statistical "face-on" Tully-Fisher studies. A weighted combination of multiple, independent inclination measurements yield the most precise and accurate inclination. Combining inverse Tully-Fisher inclinations with kinematic inclinations yields joint probability inclinations with a precision in sin i of 10% at 15° and 5% at 30°. This level of precision makes accurate mass decompositions of galaxies possible even at low inclination. We find scaling relations between rotation speed and disk-scale length identical to results from more inclined samples. We also observe the trend of more steeply rising rotation curves with increased rotation speed and light concentration. This trend appears to be uncorrelated with disk surface brightness. © 2013. The American Astronomical Society. All rights reserved..
Gwyn S.D.J.,Herzberg Institute for Astrophysics
Astronomical Journal | Year: 2012
This paper describes the image stacks and catalogs of the Canada-France-Hawaii Telescope Legacy Survey produced using the MegaPipe data pipeline at the Canadian Astronomy Data Centre. The Legacy Survey is divided into two parts. The Deep Survey consists of four fields each of 1deg 2, with magnitude limits (50% completeness for point sources) of u = 27.5, g = 27.9, r = 27.7, i = 27.4, and z = 26.2. It contains 1.6 × 10 6 sources. The Wide Survey consists of 150deg 2 split over four fields, with magnitude limits of u = 26.0, g = 26.5, r = 25.9, i = 25.7, and z = 24.6. It contains 3 × 10 7 sources. This paper describes the calibration, image stacking, and catalog generation process. The images and catalogs are available on the web through several interfaces: normal image and text file catalog downloads, a "Google Sky" interface, an image cutout service, and a catalog database query service. © 2012. National Research Council Canada. All rights reserved.
Correia C.,Herzberg Institute for Astrophysics |
Veran J.-P.,Herzberg Institute for Astrophysics
Optics Letters | Year: 2012
Many adaptive optics applications require wavefront correctors with a high stroke, and at a high bandwidth. Often, these two requirements cannot be met by a single wavefront corrector, and, instead, the combination of a lowbandwidth, high-stroke woofer and a high-bandwidth low-stroke tweeter is used in a so-called woofer-tweeter architecture. The optimal (minimum residual phase variance) way to split the correction between the woofer and the tweeter in the context of a linear-quadratic-Gaussian (LQG) controller has been addressed previously. However, the necessity to fold the temporal characteristics of the woofer and tweeter into the LQG controller significantly increases its complexity. In this Letter, this optimal strategy is compared to a simpler, ad hoc approach, which consists in optimizing the LQG controller as if it were controlling a high-bandwidth, high-stroke corrector and splitting the correction using first-order high- and low-pass temporal filters. In the case of tilt correction for NFIRAOS on the Thirty Meter Telescope, it is found that the ad hoc approach, which is already used or planned for several systems, holds the same overall correction performance compared to the optimal strategy. © 2012 Optical Society of America.
Willott C.J.,Herzberg Institute for Astrophysics
Astrophysical Journal Letters | Year: 2011
It has been claimed that there is a large population of obscured, accreting black holes at high redshift and that the integrated black hole density at z = 6 as inferred from X-ray observations is ∼ 100 times greater than that inferred from optical quasars. I have performed a stacking analysis of very deep Chandra X-ray data at the positions of photometrically selected z = 6 galaxy candidates. It is found that there is no evidence for a stacked X-ray signal in either the soft (0.5-2 keV) or hard (2-8 keV) X-ray bands. Previous work which reported a significant signal is affected by an incorrect method of background subtraction which underestimates the true background within the target aperture. The puzzle remains as to why the z = 6 black hole mass function has such a flat slope and a low normalization compared to the stellar mass function. © 2011. The American Astronomical Society. All rights reserved.