The Quasar Mass-Luminosity Plane I: A Sub-Eddington Limit for Quasars

We use 62185 quasars from the Sloan Digital Sky Survey Data Release 5 sample to explore the relationship between black hole mass and luminosity. Black hole masses were estimated based on the widths of their H{\beta}, MgII and CIV lines and adjacent continuum luminosities using standard virial mass estimate scaling laws. We find that, over the range 0.2 < z < 4.0, the most luminous low-mass quasars are at their Eddington luminosity, but the most luminous high-mass quasars in each redshift bin fall short of their Eddington luminosities, with the shortfall of the order of 10 or more at 0.2 < z < 0.6. We examine several potential sources of measurement uncertainty or bias and show that none of them can account for this effect. We also show the statistical uncertainty in virial mass estimation to have an upper bound of ~0.15 dex, smaller than the 0.4 dex previously reported. We also examine the highest mass quasars in every redshift bin in an effort to learn more about quasars that are about to cease their luminous accretion. We conclude that the quasar mass-luminosity locus contains a number of new puzzles that must be explained theoretically.Comment: 14 pages, MNRA

Nonparametric Methods in Astronomy: Think, Regress, Observe -- Pick Any Three

Telescopes are much more expensive than astronomers, so it is essential to minimize required sample sizes by using the most data-efficient statistical methods possible. However, the most commonly used model-independent techniques for finding the relationship between two variables in astronomy are flawed. In the worst case they can lead without warning to subtly yet catastrophically wrong results, and even in the best case they require more data than necessary. Unfortunately, there is no single best technique for nonparametric regression. Instead, we provide a guide for how astronomers can choose the best method for their specific problem and provide a python library with both wrappers for the most useful existing algorithms and implementations of two new algorithms developed here.Comment: 19 pages, PAS

Do Anomalous Narrow Line Quasars Cast Doubt on Virial Mass Estimation?

Anomalous Narrow-Line Quasars (ANLs) are a population of quasars with narrow H\beta, and sometimes [O III] broader than ~1000 km/s, in total comprising \sim 10-30% (most likely ~25%) of Type I quasars at 0.2 < z < 0.8. We find that virial masses using the H\beta and Mg II lines systematically differ for ANLs by an average of as much as 0.5 dex. Because the broad H\beta component width increases in ANLs but Mg II does not, we might suspect H\beta-based virial masses for ANLs are wrong but Mg II masses are correct. If this is due to an outflow reaching the lower-ionization potential H\beta line, C IV masses will be similarly flawed. However, we cannot be certain of this explanation without followup work, and may be unable to identify which quasars are ANLs at z > 0.8. Therefore, it is essential that ANLs be well-understood and well-modeled in order to allow the use of virial mass estimators on large optical spectroscopic catalogs, particularly at z 2.0 where only one broad line is available for use in mass estimation.Comment: 5 pages, submitte

Reconciling Mass Functions with the Star-Forming Main Sequence Via Mergers

We combine star formation along the `main sequence', quiescence, and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally-independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging.Comment: MNRAS, in pres

The Cosmic Microwave Background and the Stellar Initial Mass Function

We argue that an increased temperature in star-forming clouds alters the stellar initial mass function to be more bottom-light than in the Milky Way. At redshifts $z \gtrsim 6$, heating from the cosmic microwave background radiation produces this effect in all galaxies, and it is also present at lower redshifts in galaxies with very high star formation rates (SFRs). A failure to account for it means that at present, photometric template fitting likely overestimates stellar masses and star formation rates for the highest-redshift and highest-SFR galaxies. In addition this may resolve several outstanding problems in the chemical evolution of galactic halos.Comment: 9 pages, 5 figures. Published in MNRAS. Added further reference

Evolutionary Tracks of Individual Quasars in the Mass-Luminosity Plane

Previous work on the quasar mass-luminosity plane indicates the possibility that quasars of the same central black hole mass might follow a common evolutionary track, independent of the properties of the host galaxy. We consider two simple models for the evolution of individual quasars. Requiring these tracks to lie within the observed quasar locus at all redshifts strongly constrains the model parameters, but does allow some solutions. These solutions include a family of tracks with similar shape but different initial masses that might match the observed quasar distributions at all redshifts z < 2.0. This family of solutions is characterized by short (1-2 Gyr) lifetimes, a duty cycle in which the quasar is on at least 25% of the time, and a rapid decline in Eddington ratio, perhaps with L/L_Edd ~ t^-6 or steeper.Comment: Accepted by MNRA

A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6

Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) Main Sequence (MS) in stellar mass and star formation rate (SFR) out to $z \sim 6$. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations ($\sim 0.1$ dex 1$\sigma$ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bins. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is $\sim 0.2$ dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best fit $\log\textrm{SFR}(M_*,t) = \left(0.84 \pm 0.02 - 0.026 \pm 0.003 \times t\right) \log M_* - \left(6.51 \pm 0.24 - 0.11 \pm 0.03 \times t\right)$, with $t$ the age of the Universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-$\tau$ models, (2) the decline in fractional stellar mass growth for a "typical" MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial $1\sigma$ spread in formation times of $\sim 1.4$ Gyr.Comment: 59 pages, 10 tables, 12 figures, accepted to ApJS; v2, slight changes to text, added new figure and fit