40 research outputs found
Lensed Quasar Hosts
Gravitational lensing assists in the detection of quasar hosts by amplifying
and distorting the host light away from the unresolved quasar core images. We
present the results of HST observations of 30 quasar hosts at redshifts 1 < z <
4.5. The hosts are small in size (r_e <~ 6 kpc), and span a range of
morphologies consistent with early-types (though smaller in mass) to
disky/late-type. The ratio of the black hole mass (MBH, from the virial
technique) to the bulge mass (M_bulge, from the stellar luminosity) at 1<z<1.7
is broadly consistent with the local value; while MBH/M_bulge at z>1.7 is a
factor of 3--6 higher than the local value. But, depending on the stellar
content the ratio may decline at z>4 (if E/S0-like), flatten off to 6--10 times
the local value (if Sbc-like), or continue to rise (if Im-like). We infer that
galaxy bulge masses must have grown by a factor of 3--6 over the redshift range
3>z>1, and then changed little since z~1. This suggests that the peak epoch of
galaxy formation for massive galaxies is above z~1. We also estimate the duty
cycle of luminous AGNs at z>1 to be ~1%, or 10^7 yrs, with sizable scatter.Comment: 8 pages, 6 figures, review article with C. Impey at the conference on
"QSO Host Galaxies: Evolution and Environment", Aug. 29-Sep. 2, 2005, Lorentz
Center, Leiden, The Netherland
Chandra Observations of the QSO Pair Q2345+007: Binary Quasar or Massive Dark Lens?
The components of the wide (7.3") separation quasar pair Q2345+007A,B
(z=2.15) have the most strikingly similar optical spectra seen to date (Steidel
& Sargent 1991) yet no detected lensing mass, making this system the best
candidate known for a massive (1e14 Msun) dark matter lens system. Here we
present results from a 65ksec Chandra observation designed to investigate
whether it is a binary quasar or a gravitational lens. We find no X-ray
evidence for a lensing cluster to a (0.5-2keV) flux limit of 2e-15 cgs, which
is consistent with lensing only for a reduced baryon fraction. Using the
Chandra X-ray observations of the quasars themselves, together with new and
published optical measurements, we use the observed emission properties of the
quasars for further tests between the lens and binary hypotheses. Assuming
similar line-of-sight absorption to the images, we find that their X-ray
continuum slopes are inconsistent (Gamma_A=2.30 and Gamma_B=0.83) as are their
X-ray to optical flux ratios. The probability that B suffers absorption
sufficient to account for these spectral differences is negligible. We present
new optical evidence that the flux ratio of the pair is variable, so the
time-delay in a lens scenario could cause some of the discrepancies. However,
adequately large variations in overall spectral energy distribution are rare in
individual QSOs. All new evidence here weighs strongly toward the binary
interpretation. Q2345+007 thus may represent the highest redshift example known
of interaction-triggered but as-yet unmerged luminous AGN.Comment: 15 pages, Latex, emulateapj style, including 3 tables and 5 figures.
Accepted Feb 1, 2002 for publication in ApJ Main Journal. See also
http://hea-www.harvard.edu/~pgreen/Papers.htm
Evolution of the Stellar Mass-Metallicity Relation Since z=0.75
We measure the gas-phase oxygen abundances of ~3000 star-forming galaxies at
z=0.05-0.75 using optical spectrophotometry from the AGN and Galaxy Evolution
Survey (AGES), a spectroscopic survey of I_AB<20.45 galaxies over 7.9 deg^2 in
the NOAO Deep Wide Field Survey (NDWFS) Bootes field. We use state-of-the-art
techniques to measure the nebular emission lines and stellar masses, and
explore and quantify several potential sources of systematic error, including
the choice of metallicity diagnostic, aperture bias, and contamination from
unidentified active galactic nuclei (AGN). Combining volume-limited AGES
samples in six independent redshift bins and ~75,000 star-forming galaxies with
r_AB<17.6 at z=0.05-0.2 selected from the Sloan Digital Sky Survey (SDSS) that
we analyze in the identical manner, we measure the evolution of the stellar
mass-metallicity (M-Z) between z=0.05 and z=0.75. We find that at fixed stellar
mass galaxies at z~0.7 have just 30%-60% the metal content of galaxies at the
present epoch, where the uncertainty is dominated by the strong-line method
used to measure the metallicity. Moreover, we find no statistically significant
evidence that the M-Z relation evolves in a mass-dependent way for
M=10^9.8-10^11 Msun star-forming galaxies. Thus, for this range of redshifts
and stellar masses the M-Z relation simply shifts toward lower metallicity with
increasing redshift without changing its shape.Comment: 38 pages, 22 figures, 6 tables, submitted to Ap
An analytical model of surface mass densities of cold dark matter haloes - with an application to MACHO microlensing optical depths
The cold dark matter (CDM) scenario generically predicts the existence of
triaxial dark matter haloes which contain notable amounts of substructure.
However, analytical halo models with smooth, spherically symmetric density
profiles are routinely adopted in the modelling of light propagation effects
through such objects. In this paper, we address the biases introduced by this
procedure by comparing the surface mass densities of actual N-body haloes
against the widely used analytical model suggested by Navarro, Frenk and White
(1996) (NFW).
We conduct our analysis in the redshift range of 0.0 - 1.5. In cluster sized
haloes, we find that triaxiality can cause scatter in the surface mass density
of the haloes up to sigma_+ = +60% and sigma_- = -70%, where the 1-sigma limits
are relative to the analytical NFW model given value. Subhaloes can increase
this scatter to sigma_+ = +70% and sigma_- = -80%. In galaxy sized haloes, the
triaxial scatter can be as high as sigma_+ = +80% and sigma_- = -70%, and with
subhaloes the values can change to sigma_+ = +40% and sigma_- = -80%.
We present an analytical model for the surface mass density scatter as a
function of distance to the halo centre, halo redshift and halo mass. The
analytical description enables one to investigate the reliability of results
obtained with simplified halo models. Additionally, it provides the means to
add simulated surface density scatter to analytical density profiles. As an
example, we discuss the impact of our results on the calculation of
microlensing optical depths for MACHOs in CDM haloes.Comment: 10 pages, 6 figures and 4 tables, accepted to MNRAS October 11th 200
Organic Wastes Amended with Sorbents Reduce N2O Emissions from Sugarcane Cropping
Nutrient-rich organic wastes and soil ameliorants can benefit crop performance and soil health but can also prevent crop nutrient sufficiency or increase greenhouse gas emissions. We hypothesised that nitrogen (N)-rich agricultural waste (poultry litter) amended with sorbents (bentonite clay or biochar) or compost (high C/N ratio) attenuates the concentration of inorganic nitrogen (N) in soil and reduces emissions of nitrous oxide (N2O). We tested this hypothesis with a field experiment conducted on a commercial sugarcane farm, using in vitro incubations. Treatments received 160 kg N haâ1, either from mineral fertiliser or poultry litter, with additional N (2â60 kg N haâ1) supplied by the sorbents and compost. Crop yield was similar in all N treatments, indicating N sufficiency, with the poultry litter + biochar treatment statistically matching the yield of the no-N control. Confirming our hypothesis, mineral N fertiliser resulted in the highest concentrations of soil inorganic N, followed by poultry litter and the amended poultry formulations. Reflecting the soil inorganic N concentrations, the average N2O emission factors ranked as per the following: mineral fertiliser 8.02% > poultry litter 6.77% > poultry litter + compost 6.75% > poultry litter + bentonite 5.5% > poultry litter + biochar 3.4%. All emission factors exceeded the IPCC Tier 1 default for managed soils (1%) and the Australian Government default for sugarcane soil (1.25%). Our findings reinforce concerns that current default emissions factors underestimate N2O emissions. The laboratory incubations broadly matched the field N2O emissions, indicating that in vitro testing is a cost-effective first step to guide the blending of organic wastes in a way that ensures N sufficiency for crops but minimises N losses. We conclude that suitable sorbent-waste formulations that attenuate N release will advance N efficiency and the circular nutrient economy
Organic Wastes Amended with Sorbents Reduce N2O Emissions from Sugarcane Cropping
Nutrient-rich organic wastes and soil ameliorants can benefit crop performance and soil health but can also prevent crop nutrient sufficiency or increase greenhouse gas emissions. We hypothesised that nitrogen (N)-rich agricultural waste (poultry litter) amended with sorbents (bentonite clay or biochar) or compost (high C/N ratio) attenuates the concentration of inorganic nitrogen (N) in soil and reduces emissions of nitrous oxide (N2O). We tested this hypothesis with a field experiment conducted on a commercial sugarcane farm, using in vitro incubations. Treatments received 160 kg N haâ1, either from mineral fertiliser or poultry litter, with additional N (2â60 kg N haâ1) supplied by the sorbents and compost. Crop yield was similar in all N treatments, indicating N sufficiency, with the poultry litter + biochar treatment statistically matching the yield of the no-N control. Confirming our hypothesis, mineral N fertiliser resulted in the highest concentrations of soil inorganic N, followed by poultry litter and the amended poultry formulations. Reflecting the soil inorganic N concentrations, the average N2O emission factors ranked as per the following: mineral fertiliser 8.02% > poultry litter 6.77% > poultry litter + compost 6.75% > poultry litter + bentonite 5.5% > poultry litter + biochar 3.4%. All emission factors exceeded the IPCC Tier 1 default for managed soils (1%) and the Australian Government default for sugarcane soil (1.25%). Our findings reinforce concerns that current default emissions factors underestimate N2O emissions. The laboratory incubations broadly matched the field N2O emissions, indicating that in vitro testing is a cost-effective first step to guide the blending of organic wastes in a way that ensures N sufficiency for crops but minimises N losses. We conclude that suitable sorbent-waste formulations that attenuate N release will advance N efficiency and the circular nutrient economy
Resolved nuclear CO(1-0) emission in APM08279+5255: Gravitational lensing by a naked cusp?
The ultraluminous broad absorption line quasar APM08279+5255 is one of the
most luminous systems known. Here, we present an analysis of its nuclear
CO(1-0) emission. Its extended distribution suggests that the gravitational
lens in this system is highly elliptical, probably a highly inclined disk. The
quasar core, however, lies in the vicinity of naked cusp, indicating that
APM08279+5255 is truly the only odd-image gravitational lens. This source is
the second system for which the gravitational lens can be used to study
structure on sub-kpc scales in the molecular gas associated with the AGN host
galaxy. The observations and lens model require CO distributed on a scale of
pc. Using this scale, we find that the molecular gas mass makes a
significant, and perhaps dominant, contribution to the total mass within a
couple hundred parsecs of the nucleus of APM08279+5255.Comment: 5 Pages, 2 Figures, to appear in MNRAS Letters - Resolution of Figure
2 reduce
Chandra, HST/STIS, NICER, Swift, and TESS Detail the Flare Evolution of the Repeating Nuclear Transient ASASSN-14ko
ASASSN-14ko is a nuclear transient at the center of the AGN ESO 253-G003 that
undergoes periodic flares. Optical flares were first observed in 2014 by the
All-Sky Automated Survey for Supernovae (ASAS-SN) and their peak times are
well-modeled with a period of days and period derivative
of . Here we present ASAS-SN, Chandra, HST/STIS, NICER,
Swift, and TESS data for the flares that occurred in December 2020, April 2021,
July 2021, and November 2021. The HST/STIS UV spectra evolve from blue shifted
broad absorption features to red shifted broad emission features over 10
days. The Swift UV/optical light curves peaked as predicted by the timing
model, but the peak UV luminosities varied between flares and the UV flux in
July 2021 was roughly half the brightness of all other peaks. The X-ray
luminosities consistently decreased and the spectra became harder during the
UV/optical rise but apparently without changes in absorption. Finally, two
high-cadence TESS light curves from December 2020 and November 2018 showed that
the slopes during the rising and declining phases changed over time, which
indicates some stochasticity in the flare's driving mechanism. ASASSN-14ko
remains observationally consistent with a repeating partial tidal disruption
event, but, these rich multi-wavelength data are in need of a detailed
theoretical model.Comment: 25 pages, 14 figures, 4 tables; Submitted to ApJ, comments welcom