Christopher S. Kochanek

Black Hole Masses and Eddington Ratios at 0.3 < z < 4

We study the distribution of Eddington luminosity ratios, Lbol/LEdd, of active galactic nuclei (AGNs) discovered in the AGN and Galaxy Evolution Survey (AGES). We combine Hβ, Mg II, and C IV line widths with continuum luminosities to estimate black hole (BH) masses in 407 AGNs, covering the redshift range z ~ 0.3-4 and the bolometric luminosity range Lbol ~ 1045-1047 ergs s-1. The sample consists of X-ray or mid-infrared (24 μm) point sources with optical magnitude R ≤ 21.5 mag and optical emission-line spectra characteristic of AGNs. For the range of luminosity and redshift probed by AGES, the distribution of estimated Eddington ratios is well described as log-normal, with a peak at Lbol/LEdd 1/4 and a dispersion of 0.3 dex. Since additional sources of scatter are minimal, this dispersion must account for contributions from the scatter between estimated and true BH mass and the scatter between estimated and true bolometric luminosity. Therefore, we conclude that (1) neither of these sources of error can contribute more than ~0.3 dex rms, and (2) the true Eddington ratios of optically luminous AGNs are even more sharply peaked. Because the mass estimation errors must be smaller than ~0.3 dex, we can also investigate the distribution of Eddington ratios at fixed BH mass. We show for the first time that the distribution of Eddington ratios at fixed BH mass is peaked, and that the dearth of AGNs at a factor of ~10 below Eddington is real and not an artifact of sample selection. These results provide strong evidence that supermassive BHs gain most of their mass while radiating close to the Eddington limit, and they suggest that the fueling rates in luminous AGNs are ultimately determined by BH self-regulation of the accretion flow rather than galactic-scale dynamical disturbances.

Probing the coevolution of supermassive black holes and galaxies using gravitationally lensed quasar hosts

In the present-day universe, supermassive black hole masses (MBH) appear to be strongly correlated with their galaxy’s bulge luminosity, among other properties. In this study, we explore the analogous relationship between MBH, derived using the virial method, and the stellar R-band bulge luminosity (LR) or stellar bulge mass (M∗) at epochs of 1 . z . 4.5 using a sample of 31 gravitationally lensed AGNs and 20 non-lensed AGNs. At redshifts z > 1.7 (10–12 Gyrs ago), we find that the observed MBH–LR relation is nearly the same (to within ∼ 0.3 mag) as it is today. When the observed LR are corrected for luminosity evolution, this means that the black holes grew in mass faster than their hosts, with the MBH/M∗ mass ratio being a factor of & 4 +21 times larger at z > 1.7 than it is today. By the redshift range 1 . z . 1.7 (8–10 Gyrs ago), the MBH/M∗ ratio is at most two times higher than today, but it may be consistent with no evolution. Combining the results, we conclude that the ratio MBH/M∗ rises with look-back time, although it may saturate at ≈ 6 times the local value. Scenarios in which moderately luminous quasar hosts at z & 1.7 were fully formed bulges that passively faded to the present epoch are ruled out. Subject headings: galaxies: evolution — galaxies: quasars — galaxies: fundamental parameters — galaxies: structure — galaxies: bulges

Is there a cosmological constant

The grant contributed to the publication of 18 refereed papers and 5 conference proceedings. The primary uses of the funding have been for page charges, travel for invited talks related to the grant research, and the support of a graduate student, Charles Keeton. The refereed papers address four of the primary goals of the proposal: (1) the statistics of radio lenses as a probe of the cosmological model (#1), (2) the role of spiral galaxies as lenses (#3), (3) the effects of dust on statistics of lenses (#7, #8), and (4) the role of groups and clusters as lenses (#2, #6, #10, #13, #15, #16). Four papers (#4, #5, #11, #12) address general issues of lens models, calibrations, and the relationship between lens galaxies and nearby galaxies. One considered cosmological effects in lensing X-ray sources (#9), and two addressed issues related to the overall power spectrum and theories of gravity (#17, #18). Our theoretical studies combined with the explosion in the number of lenses and the quality of the data obtained for them is greatly increasing our ability to characterize and understand the lens population. We can now firmly conclude both from our study of the statistics of radio lenses and our survey of extinctions in individual lenses that the statistics of optically selected quasars were significantly affected by extinction. However, the limits on the cosmological constant remain at lambda < 0.65 at a 2-sigma confidence level, which is in mild conflict with the results of the Type la supernova surveys. We continue to find that neither spiral galaxies nor groups and clusters contribute significantly to the production of gravitational lenses. The lack of group and cluster lenses is strong evidence for the role of baryonic cooling in increasing the efficiency of galaxies as lenses compared to groups and clusters of higher mass but lower central density. Unfortunately for the ultimate objective of the proposal, improved constraints on the cosmological constant, the next large survey for gravitational lenses did not release its results during the term of the proposal. The research supported the career development. of six graduate students (polar, Fletcher, Herold, Keeton, Deng and Rusin) and two post-docs (Labor and Munoz).

Ubvri light curves of 44 type ia supernovae

We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SNe Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U - B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional ~40% intrinsic scatter compared to the B band.

QUANTITATIVE INTERPRETATION OF QUASAR MICROLENSING LIGHT CURVES

We develop a general method for analyzing the light curves of microlensed quasars and apply it to the OGLE light curves of the four-image lens Q2237+0305. We simultaneously estimate the effective source velocity, the average stellar mass, the stellar mass function, and the size and structure of the quasar accretion disk. The light curves imply an effective source-plane velocity of 10,200 km s-1 vehM/M?-1/2 39,600 km s-1 (68% confidence). Given an independent estimate for the source velocity, found by combining estimates for the peculiar velocity of the lens galaxy with its measured stellar velocity dispersion, we obtain a mean stellar mass of M 0.037 h2 M? (0.0059 h2 M? M 0.20 h2 M?). We were unable to distinguish a Salpeter mass function from one in which all stars had the same mass, but we do find a strong lower bound of ?*/? 0.5 on the fraction of the surface mass density represented by the microlenses. Our models favor a standard thin accretion disk model as the source structure over a simple Gaussian source. For a face-on, thin disk radiating as a blackbody with temperature profile Ts R-3/4, the radius rs where the temperature matches the filter pass band [2000 ? or Ts(rs) 7 ? 104 K] is 1.4 ? 1015 h-1 cm rs 4.5 ? 1015 h-1 cm. The flux predicted by the disk model agrees with the observed flux of the quasar, so nonthermal or optically thin emission processes are not required. From the disk structure we estimate a black hole mass of MBH 1.1 ? 109 h-3/2?(L/LE)-1/2 M?, consistent with the mass estimated under the assumption that the quasar is radiating at the Eddington luminosity (L/LE = 1).

The Mass of the Milky Way galaxy

We use the Jaffe model as a global mass distribution for the Galaxy and determine the circular velocity

Quantifying Quasar Variability as Part of a General Approach to Classifying Continuously Varying Sources

v_c

The implications of lenses for galaxy structure

and the Jaffe radius

A SURVEY ABOUT NOTHING: MONITORING A MILLION SUPERGIANTS FOR FAILED SUPERNOVAE

r_j

A NEW CLASS OF LUMINOUS TRANSIENTS AND A FIRST CENSUS OF THEIR MASSIVE STELLAR PROGENITORS

using the satellites of the Galaxy, estimates of the local escape velocity of stars, the constraints imposed by the known rotation curve of the disk, and the Local Group timing model. The models include the systematic uncertainties in the isotropy of the satellite orbits, the form of the stellar distribution function near the escape velocity, and the ellipticity of the M31/Galaxy orbit. If we include the Local Group timing constraint, then Leo I is bound,