88 research outputs found
Retention capacity of random surfaces
We introduce a "water retention" model for liquids captured on a random
surface with open boundaries, and investigate it for both continuous and
discrete surface heights 0, 1, ... n-1, on a square lattice with a square
boundary. The model is found to have several intriguing features, including a
non-monotonic dependence of the retention on the number of levels in the
discrete case: for many n, the retention is counterintuitively greater than
that of an n+1-level system. The behavior is explained using percolation
theory, by mapping it to a 2-level system with variable probability. Results in
1-dimension are also found.Comment: 5 page
Secular evolution and a non-evolving black hole to galaxy mass ratio in the last 7 Gyr
We present new constraints on the ratio of black hole (BH) mass to total
galaxy stellar mass at 0.3<z<0.9 for a sample of 32 type-1 active galactic
nuclei (AGNs) from the XMM-COSMOS survey covering the range
M_BH/M_sun~10^(7.2--8.7). Virial M_BH estimates based on H_beta are available
from the COSMOS Magellan/IMACS survey. We use high-resolution Hubble Space
Telescope (HST) imaging to decompose the light of each type-1 AGN and host
galaxy, and employ a specially-built mass-to-light ratio to estimate the
stellar masses (M_*). The M_BH-M_* ratio shows a zero offset with respect to
the local relation for galactic bulge masses, and we also find no evolution in
the mass ratio M_BH/M_*=(1+z)^{0.02+-0.34} up to z~0.9. Interestingly, at the
high-M_BH end there is a positive offset from the z=0 relation, which can be
fully explained by a mass function bias with a cosmic scatter of 0.3,
reaffirming that the intrinsic distribution is consistent with zero evolution.
From our results we conclude that since z~0.9 no substantial addition of
stellar mass is required: the decline in star formation rates and merger
activity at z<1 support this scenario. Nevertheless, given that a significant
fraction of these galaxies show a disk component, their bulges are indeed
undermassive. This is a direct indication that for the last 7 Gyr the only
essential mechanism required in order that these galaxies obey the z=0 relation
is a redistribution of stellar mass to the bulge, likely driven by secular
processes, i.e., internal instabilities and minor merging.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letter
An Extension of a Volumetric Method for Aluminum to the Determination of Milligram Quantities
Snyder (3) has given a rapid and precise titrimetric procedure for the determination of aluminum in the presence of moderate amounts of other substances. The original method was applied to samples containing from 0.025 to 0.13 gram of aluminum. In the present work it was found that, with certain modifications, the same procedure could also be used for the determination of alumim1m in the range of 5 to 25 milligrams. The precision of the modified method was found to correspond to a standard deviation of about 0.1 milligram throughout this range
An archaeoacoustic study of the Ħal Saflieni Hypogeum on Malta
The remarkable subterranean architecture of the Ħal Saflieni Hypogeum on Malta has generated many claims about its dramatic acoustic effects, but previous studies have lacked rigour. A systematic, methodical approach has now been applied to measure the acoustic properties of the site, and to test earlier assertions. The results confirm some, but not all, prior observations, and demonstrate how a sound-based approach can contribute to an understanding of the archaeological context. It is argued that for the people who created the Hypogeum, the acoustics must have had particular significance and ritual
power
Massive Galaxies in COSMOS: Evolution of Black hole versus bulge mass but not versus total stellar mass over the last 9 Gyrs?
We constrain the ratio of black hole (BH) mass to total stellar mass of
type-1 AGN in the COSMOS survey at 1<z<2. For 10 AGN at mean redshift z~1.4
with both HST/ACS and HST/NICMOS imaging data we are able to compute total
stellar mass M_(*,total), based on restframe UV-to-optical host galaxy colors
which constrain mass-to-light ratios. All objects have virial BH mass-estimates
available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find zero
difference between the M_BH--M_(*,total)-relation at z~1.4 and the
M_BH--M_(*,bulge)-relation in the local Universe.
Our interpretation is: (a) If our objects were purely bulge-dominated, the
M_BH--M_(*,bulge)-relation has not evolved since z~1.4. However, (b) since we
have evidence for substantial disk components, the bulges of massive galaxies
(logM_(*,total)=11.1+-0.25 or logM_BH~8.3+-0.2) must have grown over the last 9
Gyrs predominantly by redistribution of disk- into bulge-mass. Since all
necessary stellar mass exists in the galaxy at z=1.4, no star-formation or
addition of external stellar material is required, only a redistribution e.g.
induced by minor and major merging or through disk instabilities. Merging, in
addition to redistributing mass in the galaxy, will add both BH and
stellar/bulge mass, but does not change the overall final M_BH/M_(*,bulge)
ratio.
Since the overall cosmic stellar and BH mass buildup trace each other tightly
over time, our scenario of bulge-formation in massive galaxies is independent
of any strong BH-feedback and means that the mechanism coupling BH and bulge
mass until the present is very indirect.Comment: Published in ApJL; 7 pages, 2 figures; updated to accepted version
(methods changed, results unchanged
The First High Redshift Quasar from Pan-STARRS
We present the discovery of the first high redshift (z > 5.7) quasar from the
Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1 or PS1).
This quasar was initially detected as an i dropoutout in PS1, confirmed
photometrically with the SAO Widefield InfraRed Camera (SWIRC) at Arizona's
Multiple Mirror Telescope (MMT) and the Gamma-Ray Burst Optical/Near-Infrared
Detector (GROND) at the MPG 2.2 m telescope in La Silla. The quasar was
verified spectroscopically with the the MMT Spectrograph, Red Channel and the
Cassegrain Twin Spectrograph (TWIN) at the Calar Alto 3.5 m telescope. It has a
redshift of 5.73, an AB z magnitude of 19.4, a luminosity of 3.8 x 10^47 erg/s
and a black hole mass of 6.9 x 10^9 solar masses. It is a Broad Absorption Line
quasar with a prominent Ly-beta peak and a very blue continuum spectrum. This
quasar is the first result from the PS1 high redshift quasar search that is
projected to discover more than a hundred i dropout quasars, and could
potentially find more than 10 z dropout (z > 6.8) quasars.Comment: 8 pages, 7 figure
The environment of weak emission-line quasars
The nature of weak emission-line quasars (WLQs) is probed by comparing the
Baldwin effect (BEff) in WLQs and normal quasars (QSOs). We selected 81
high-redshift (z>2.2) and 2 intermediate-redshift (z=1.66 and 1.89) WLQs. Their
rest-frame equivalent widths (EWs) of the C IV emission-line and their
Eddington ratio were obtained from the Sloan Digital Sky Survey Data Release 7
(SDSS DR7) Quasar Catalogue or from Diamond-Stanic et al. We compare the
parameters of WLQs with these of 81 normal quasars from Bright Quasar Survey
(BQS) and 155 radio-quiet and radio-intermediate quasars detected by SDSS and
Chandra. The influence of the Eddington ratio, Lbol/Ledd, and the X-ray to
optical luminosity ratio,alpha_ox, on the BEff is analysed. We find that WLQs
follow a different relationship on the EW(CIV)-Lbol/Ledd plane than normal
quasars. This relationship disagrees with the super-Eddington hypothesis. The
weakness/absence of emission-lines in WLQs does not seem to be caused by their
extremely soft ionizing continuum but by low covering factor (Omega) of their
broad line region (BLR). Comparing emission-line intensities indicates that the
ratios of high-ionization line and low-ionization line regions (i.e.
Omega_(HIL)/Omega_(LIL)) are lower in WLQs than in normal QSOs. The covering
factor of the regions producing C IV and Lyalpha emission-lines are similar in
both WLQs and QSOs.Comment: 9 pages, 3 figures, 2 tables. Accepted for publication in MNRAS.
Minor changes (corrected typos) to match published versio
Properties of the molecular gas in a starbursting QSO at z=1.83 in the COSMOS field
Using the IRAM 30m telescope, we have detected the CO J=2-1, 4-3, 5-4, and
6-5 emission lines in the millimeter-bright, blank-field selected AGN COSMOS
J100038+020822 at redshift z=1.8275. The sub-local thermodynamic equilibrium
(LTE) excitation of the J=4 level implies that the gas is less excited than
that in typical nearby starburst galaxies such as NGC253, and in the
high-redshift quasars studied to date, such as J1148+5251 or BR1202-0725. Large
velocity gradient (LVG) modeling of the CO line spectral energy distribution
(CO SED; flux density vs. rotational quantum number) yields H2 densities in the
range 10^{3.5}--10^{4.0} cm-3, and kinetic temperatures between 50 K and 200 K.
The H2 mass of (3.6 - 5.4) x 10^{10} M_sun implied by the line intensities
compares well with our estimate of the dynamical mass within the inner 1.5 kpc
of the object. Fitting a two-component gray body spectrum, we find a dust mass
of 1.2 x 10^{9} M_sun, and cold and hot dust temperatures of 42+/-5 K and
160+/-25 K, respectively. The broad MgII line allows us to estimate the mass of
the central black hole as 1.7 x 10^{9} M_sun. Although the optical spectrum and
multi-wavelength SED matches those of an average QSO, the molecular gas content
and dust properties resemble those of known submillimeter galaxies (SMGs). The
optical morphology of this source shows tidal tails that suggest a recent
interaction or merger. Since it shares properties of both starburst and AGN,
this object appears to be in a transition from a strongly starforming
submillimeter galaxy to a QSO.Comment: Accepted for publication in Astronomy & Astrophysics (A&A
A Quasar Catalog with Simultaneous UV, Optical and X-ray Observations by Swift
We have compiled a catalog of optically-selected quasars with simultaneous
observations in UV/optical and X-ray bands by the Swift Gamma Ray Burst
Explorer. Objects in this catalog are identified by matching the Swift
pointings with the Sloan Digital Sky Survey Data Release 5 quasar catalog. The
final catalog contains 843 objects, among which 637 have both UVOT and XRT
observations and 354 of which are detected by both instruments. The overall
X-ray detection rate is ~60% which rises to ~85% among sources with at least 10
ks of XRT exposure time. We construct the time-averaged spectral energy
distribution for each of the 354 quasars using UVOT photometric measurements
and XRT spectra. From model fits to these SEDs, we find that the big blue bump
contributes about 0.3 dex to the quasar luminosity. We re-visit the
alpha_ox-L_uv relation by selecting a clean sample with only type 1 radio-quiet
quasars; the dispersion of this relation is reduced by at least 15% compared to
studies that use non-simultaneous UV/optical and X-ray data. We only found a
weak correlation between L/L_Edd and alpha_uv. We do not find significant
correlations between alpha_x and alpha_ox, alpha_ox and alpha_uv, and alpha_x
and Log L(0.3-10 keV). The correlations between alpha_uv and alpha_x, alpha_ox
and alpha_x, alpha_ox and alpha_uv, L/L_Edd and alpha_x, and L/L_Edd and
alpha_ox are stronger amongst low-redshift quasars, indicating that these
correlations are likely driven by the changes of SED shape with accretion
state.Comment: 63 pages, 22 figures, accepted by ApJ
Selection effects in the black hole-bulge relation and its evolution
We present an investigation of sample selection effects that influence the
observed black hole - bulge relations and its evolution with redshift. We
provide a common framework in which all kinds of selection effects on the
BH-bulge relations can be investigated, but our main emphasis is on the
consequences of using broad-line AGN and their host galaxies to search for
evolution in the BH-bulge relation. We identified relevant sources of bias that
were not discussed in the literature so far. A particularly important effect is
caused by the fact that the active fraction among SMBHs varies considerably
with BH mass, in the sense that high-mass BHs are less likely to be active than
lower mass ones. In the connection with intrinsic scatter of the BH-bulge
relation this effect implies a bias towards a low BH mass at given bulge
property. This effect adds to the bias caused by working with luminosity or
flux limited samples that were already discussed by others. A quantitative
prediction of these biases requires (i) a realistic model of the sample
selection function, and (ii) knowledge of relevant underlying distribution
functions. For low-redshift AGN samples we can naturally reproduce the
flattening of the relation observed in some studies. When extending our
analysis to higher redshift samples we are clearly hampered by limited
empirical constraints on the various relevant distribution functions. Using a
best-guess approach for these distributions we estimate the expected magnitude
of sample selection biases for a number of recent observational attempts to
study the BH-bulge evolution. In no case do we find statistically significant
evidence for an evolving BH-bulge relation. We suggest a possible practical
approach to circumvent several of the most problematic issues connected with
AGN selection; this could become a powerful diagnostic in future investigations
(abridged).Comment: 20 pages, 20 figures, accepted for publication in A&
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