28 research outputs found
Luminosity Dependence in the Fundamental Plane Projections of Elliptical Galaxies
We analyze the fundamental plane projections of elliptical galaxies as a
function of luminosity, using a sample of approximately 80,000 galaxies drawn
from Data Release 4 (DR4) of the Sloan Digital Sky Survey (SDSS). We separate
brightest cluster galaxies (BCGs) from our main sample and reanalyze their
photometry due to a problem with the default pipeline sky subtraction for BCGs.
The observables we consider are effective radius (R_e), velocity dispersion
(sigma), dynamical mass (M_dyn ~ R_e sigma2), effective density (sigma2/R_e2),
and effective surface brightness (mu_e). With the exception of the L-M_dyn
correlation, we find evidence of variations in the slope (i.e. the power-law
index) of the fundamental plane projections with luminosity for our normal
elliptical galaxy population. In particular, the radius-luminosity and
Faber-Jackson relations are steeper at high luminosity relative to low
luminosity, and the more luminous ellipticals become progressively less dense
and have lower surface brightnesses than lower luminosity ellipticals. These
variations can be understood as arising from differing formation histories,
with more luminous galaxies having less dissipation. Data from the literature
and our reanalysis of BCGs show that BCGs have radius-luminosity and
Faber-Jackson relations steeper than the brightest non-BCG ellipticals in our
sample, consistent with significant growth of BCGs via dissipationless mergers.
The variations in slope we find in the Faber-Jackson relation of non-BCGs are
qualitatively similar to that reported in the black hole mass-velocity
dispersion (M_BH-sigma) correlation. This similarity is consistent with a
roughly constant value of M_BH/M_star over a wide range of early type galaxies,
where M_star is the stellar mass.Comment: v2: expanded analysis of BCGs; 17 pages, 9 figures; accepted in MNRA
X-ray Properties of Intermediate-Mass Black Holes in Active Galaxies. II. X-ray-Bright Accretion and Possible Evidence for Slim Disks
We present X-ray properties of optically-selected intermediate-mass
(~10^5--10^6 M_Sun) black holes (BHs) in active galaxies (AGNs), using data
from the Chandra X-Ray Observatory. Our observations are a continuation of a
pilot study by Greene & Ho (2007). Of the 8 objects observed, 5 are detected
with X-ray luminosities in the range L_0.5-2 keV = 10^41--10^43 erg s^-1,
consistent with the previously observed sample. Objects with enough counts to
extract a spectrum are well fit by an absorbed power law. We continue to find a
range of soft photon indices 1 < \Gamma_s < 2.7, where N(E) \propto
E^-\Gamma_s, consistent with previous AGN studies, but generally flatter than
other narrow-line Seyfert 1 active nuclei (NLS1s). The soft photon index
correlates strongly with X-ray luminosity and Eddington ratio, but does not
depend on BH mass. There is no justification for the inclusion of any
additional components, such as a soft excess, although this may be a function
of the relative inefficiency of detecting counts above 2 keV in these
relatively shallow observations. As a whole, the X-ray-to-optical spectral
slope \alpha_ox is flatter than in more massive systems, even other NLS1s. Only
X-ray-selected NLS1s with very high Eddington ratios share a similar \alpha_ox.
This is suggestive of a physical change in the accretion structure at low
masses and at very high accretion rates, possibly due to the onset of slim
disks. Although the detailed physical explanation for the X-ray loudness of
these intermediate-mass BHs is not certain, it is very striking that targets
selected on the basis of optical properties should be so distinctly offset in
their broader spectral energy distributions.Comment: 11 pages, 6 figures, submitted to ApJ, emulateap
Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation-Based Measurement of the Black Hole Mass
A reverberation-mapping program on NGC 4395, the least-luminous known Seyfert
1 galaxy, undertaken with the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope, yields a measurement of the mass of the central black
hole of 360,000 solar masses. The observations consist of two visits of 5
orbits each, in 2004 April and July. During each of these visits, the UV
continuum varied by at least 10% (rms) and only C IV 1549 showed corresponding
variations large enough to reliably determine the emission-line lag, which was
measured to be of order one hour for both visits. The size of the C IV-emitting
region is about a factor of three smaller than expected if the slope of the
broad-line region radius-luminosity relationship is identical to that for the
H-beta emission line. NGC 4395 is underluminous even for its small black hole
mass; the Eddington ratio of 0.0012 is lower than that of any other active
galactic nucleus for which a black hole mass measurement has been made by
emission-line reverberation.Comment: This replacement is an erratum to be published in The Astrophysical
Journal. 3 pages, with one replacement figure and one replacement tabl
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Incorporating Experience Curves in Appliance Standards Analysis
The technical analyses in support of U.S. energy conservation standards for residential appliances and commercial equipment have typically assumed that manufacturing costs and retail prices remain constant during the projected 30-year analysis period. There is, however, considerable evidence that this assumption does not reflect real market prices. Costs and prices generally fall in relation to cumulative production, a phenomenon known as experience and modeled by a fairly robust empirical experience curve. Using price data from the Bureau of Labor Statistics, and shipment data obtained as part of the standards analysis process, we present U.S. experience curves for room air conditioners, clothes dryers, central air conditioners, furnaces, and refrigerators and freezers. These allow us to develop more representative appliance price projections than the assumption-based approach of constant prices. These experience curves were incorporated into recent energy conservation standards for these products. The impact on the national modeling can be significant, often increasing the net present value of potential standard levels in the analysis. In some cases a previously cost-negative potential standard level demonstrates a benefit when incorporating experience. These results imply that past energy conservation standards analyses may have undervalued the economic benefits of potential standard levels
Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. II. X-ray and Ultraviolet Continuum Variability
We report on two Chandra observations, and a simultaneous Hubble Space
Telescope ultraviolet observation, of the dwarf Seyfert 1 galaxy NGC 4395. Each
Chandra observation had a duration of ~30 ks, with a separation of ~50 ks. The
spectrum was observed to harden between these observations via a scaling down
of the soft-band flux. The inter-observation variability is in a different
sense to the observed variability within each observation and is most likely
the result of increased absorption. Spectral variations were seen during the
first observation suggesting that the X-ray emission is produced in more than
one disconnected region. We have also re-analyzed a ~17 ks Chandra observation
conducted in 2000. During the three Chandra observations the 2-10 keV flux is
about a factor of 2 lower than seen during an XMM-Newton observation conducted
in 2003. Moreover, the fractional variability amplitude exhibited during the
XMM-Newton observation is significantly softer than seen during the Chandra
observations. A power-spectral analysis of the first of the two new Chandra
observations revealed a peak at 341s with a formal detection significance of
99%. A similar peak was seen previously in the 2000 Chandra data. However, the
detection of this feature is tentative given that it was found in neither the
second of our two new Chandra observations nor the XMM-Newton data, and it is
much narrower than expected. The Hubble Space Telescope observation was
conducted during part of the second Chandra visit. A zero-lag correlation
between the ultraviolet and X-ray fluxes was detected with a significance of
about 99.5%, consistent with the predictions of the two-phase model for the
X-ray emission from active galactic nuclei.Comment: 31 pages, 10 figures, accepted for publication in Ap
Berkeley Supernova Ia Program I: Observations, Data Reduction, and Spectroscopic Sample of 582 Low-Redshift Type Ia Supernovae
In this first paper in a series we present 1298 low-redshift (z\leq0.2)
optical spectra of 582 Type Ia supernovae (SNe Ia) observed from 1989 through
2008 as part of the Berkeley SN Ia Program (BSNIP). 584 spectra of 199 SNe Ia
have well-calibrated light curves with measured distance moduli, and many of
the spectra have been corrected for host-galaxy contamination. Most of the data
were obtained using the Kast double spectrograph mounted on the Shane 3 m
telescope at Lick Observatory and have a typical wavelength range of
3300-10,400 Ang., roughly twice as wide as spectra from most previously
published datasets. We present our observing and reduction procedures, and we
describe the resulting SN Database (SNDB), which will be an online, public,
searchable database containing all of our fully reduced spectra and companion
photometry. In addition, we discuss our spectral classification scheme (using
the SuperNova IDentification code, SNID; Blondin & Tonry 2007), utilising our
newly constructed set of SNID spectral templates. These templates allow us to
accurately classify our entire dataset, and by doing so we are able to
reclassify a handful of objects as bona fide SNe Ia and a few other objects as
members of some of the peculiar SN Ia subtypes. In fact, our dataset includes
spectra of nearly 90 spectroscopically peculiar SNe Ia. We also present
spectroscopic host-galaxy redshifts of some SNe Ia where these values were
previously unknown. [Abridged]Comment: 34 pages, 11 figures, 11 tables, revised version, re-submitted to
MNRAS. Spectra will be released in January 2013. The SN Database homepage
(http://hercules.berkeley.edu/database/index_public.html) contains the full
tables, plots of all spectra, and our new SNID template
Incorporating Experience Curves in Appliance Standards Analysis
The technical analyses in support of U.S. energy conservation standards for residential appliances and commercial equipment have typically assumed that manufacturing costs and retail prices remain constant during the projected 30-year analysis period. There is, however, considerable evidence that this assumption does not reflect real market prices. Costs and prices generally fall in relation to cumulative production, a phenomenon known as experience and modeled by a fairly robust empirical experience curve. Using price data from the Bureau of Labor Statistics, and shipment data obtained as part of the standards analysis process, we present U.S. experience curves for room air conditioners, clothes dryers, central air conditioners, furnaces, and refrigerators and freezers. These allow us to develop more representative appliance price projections than the assumption-based approach of constant prices. These experience curves were incorporated into recent energy conservation standards for these products. The impact on the national modeling can be significant, often increasing the net present value of potential standard levels in the analysis. In some cases a previously cost-negative potential standard level demonstrates a benefit when incorporating experience. These results imply that past energy conservation standards analyses may have undervalued the economic benefits of potential standard levels