127 research outputs found
Comment on "Biases in the Quasar Mass-Luminosity Plane"
Comment on "Biases in the Quasar Mass-Luminosity Plane"Comment: Comment on Biases in the Quasar Mass-Luminosity Plane; 3 page
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
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
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 , 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
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