25 research outputs found
The SCUBA-2 850 follow-up of WISE-selected, luminous dust-obscured quasars
Hot dust-obscured galaxies (Hot DOGs) are a new population recently
discovered in the \wise All-Sky survey. Multiwavelength follow-up observations
suggest that they are luminous, dust-obscured quasars at high redshift. Here we
present the JCMT SCUBA-2 850 follow-up observations of 10 Hot DOGs.
Four out of ten Hot DOGs have been detected at level. Based on the
IR SED decomposition approach, we derive the IR luminosities of AGN torus and
cold dust components. Hot DOGs in our sample are extremely luminous with most
of them having . The torus emissions
dominate the total IR energy output. However, the cold dust contribution is
still non-negligible, with the fraction of the cold dust contribution to the
total IR luminosity being dependent on the choice of torus
model. The derived cold dust temperatures in Hot DOGs are comparable to those
in UV bright quasars with similar IR luminosity, but much higher than those in
SMGs. Higher dust temperatures in Hot DOGs may be due to the more intense
radiation field caused by intense starburst and obscured AGN activities.
Fourteen and five submillimeter serendipitous sources in the 10 SCUBA-2 fields
around Hot DOGs have been detected at and levels,
respectively. By estimating their cumulative number counts, we confirm the
previous argument that Hot DOGs lie in dense environments. Our results support
the scenario in which Hot DOGs are luminous, dust-obscured quasars lying in
dense environments, and being in the transition phase between extreme starburst
and UV-bright quasars.Comment: 26 pages, 7 figures, PASP accepte
BayeSED-GALAXIES I. Performance test for simultaneous photometric redshift and stellar population parameter estimation of galaxies in the CSST wide-field multiband imaging survey
The forthcoming CSST wide-field multiband imaging survey will produce
seven-band photometric spectral energy distributions (SEDs) for billions of
galaxies. The effective extraction of astronomical information from these
massive datasets of SEDs relies on the techniques of both SED synthesis (or
modeling) and analysis (or fitting). We evaluate the performance of the latest
version of BayeSED code combined with SED models with increasing complexity for
simultaneously determining the photometric redshifts and stellar population
parameters of galaxies in this survey. By using an empirical statistics-based
mock galaxy sample without SED modeling errors, we show finding that the random
observational errors in photometries are more important sources of errors than
the parameter degeneracies and Bayesian analysis method and tool. By using a
Horizon-AGN hydrodynamical simulation-based mock galaxy sample with SED
modeling errors about the star formation histories (SFHs) and dust attenuation
laws (DALs), the simple typical assumptions lead to significantly worse
parameter estimation with CSST photometries only. The SED models with more
flexible (or complicated) forms of SFH/DAL do not necessarily lead to better
estimation of redshift and stellar population parameters. We discuss the
selection of the best SED model by means of Bayesian model comparison in
different surveys. Our results reveal that the Bayesian model comparison with
Bayesian evidence may favor SED models with different complexities when using
photometries from different surveys. Meanwhile, the SED model with the largest
Bayesian evidence tends to give the best performance of parameter estimation,
which is more clear for photometries with larger discriminative power.Comment: Accepted for publication in ApJS (49 pages, 23 figures, 5 tables).
Comments are welcome! The new version of BayeSED code, documents, and the
scripts used for the performance tests presented in this work will be
publicly available at https://bitbucket.org/hanyk/bayesed/,
https://bayesed.readthedocs.io/, and
https://github.com/hanyk/BayeSED-performance-test/, respectivel
ALMA Reveals a Gas-rich, Maximum Starburst in the Hyperluminous, Dust-obscured Quasar W0533-3401 at z similar to 2.9
We present ALMA observations and multiwavelength spectral energy distribution analysis in a Wide-field Infrared Survey Explorer-selected, hyperluminous dust-obscured quasar W0533-3401 at z = 2.9. We derive the physical properties of each of its components, such as molecular gas, stars, dust, and the central supermassive black hole (SMBH). Both the dust continuum at 3 mm and the CO (3-2) line are detected. The derived molecular gas mass M-gas = 8.4 x 10(10) M-circle dot and its fraction f(gas) = 0.7 suggest that W0533-3401 is gas-rich. The star formation rate (SFR) has been estimated to be similar to 3000-7000M(circle dot) yr(-1) by using different methods. The high values of SFR and specific SFR suggest that W0533-3401 is a maximum starburst. The corresponding gas depletion timescales are very short (t(depl) similar to 12-28 Myr). The CO (3-2) emission line is marginally resolved and has a velocity gradient, which is possibly due to a rotating gas disk, gas outflow, or merger. Finally, we infer the black hole mass growth rate of W0533-3401 ((M)over dot(BH) = 49 M-circle dot yr(-1)), which suggests a rapid growth of the central SMBH. The observed black hole to stellar mass ratio M-BH/M-* of W0533-3401, which is dependent on the adopted Eddington ratio, is over one order of magnitude higher than the local value, and is evolving toward the evolutionary trend of unobscured quasars. Our results are consistent with the scenario that W0533-3401, with both a gas-rich maximum starburst and a rapid black hole growth, is experiencing a short transition phase toward an unobscured quasar
Decoding spectral energy distributions of dust-obscured starburst-AGN
We present BayeSED, a general purpose tool for doing Bayesian analysis of
SEDs by using whatever pre-existing model SED libraries or their linear
combinations. The artificial neural networks (ANNs), principal component
analysis (PCA) and multimodal nested sampling (MultiNest) techniques are
employed to allow a highly efficient sampling of posterior distribution and the
calculation of Bayesian evidence. As a demonstration, we apply this tool to a
sample of hyperluminous infrared galaxies (HLIRGs). The Bayesian evidences
obtained for a pure Starburst, a pure AGN, and a linear combination of
Starburst+AGN models show that the Starburst+AGN model have the highest
evidence for all galaxies in this sample. The Bayesian evidences for the three
models and the estimated contributions of starburst and AGN to infrared
luminosity show that HLIRGs can be classified into two groups: one dominated by
starburst and the other dominated by AGN. Other parameters and corresponding
uncertainties about starburst and AGN are also estimated by using the model
with the highest Bayesian evidence. We found that the starburst region of the
HLIRGs dominated by starburst tends to be more compact and has a higher
fraction of OB star than that of HLIRGs dominated by AGN. Meanwhile, the AGN
torus of the HLIRGs dominated by AGN tend to be more dusty than that of HLIRGs
dominated by starburst. These results are consistent with previous researches,
but need to be tested further with larger samples. Overall, we believe that
BayeSED could be a reliable and efficient tool for exploring the nature of
complex systems such as dust-obscured starburst-AGN composite systems from
decoding their SEDs.Comment: 12 pages, 9 figure
Birthrates and delay times of Type Ia supernovae
Type Ia supernovae (SNe Ia) play an important role in diverse areas of
astrophysics, from the chemical evolution of galaxies to observational
cosmology. However, the nature of the progenitors of SNe Ia is still unclear.
In this paper, according to a detailed binary population synthesis study, we
obtained SN Ia birthrates and delay times from different progenitor models, and
compared them with observations. We find that the Galactic SN Ia birthrate from
the double-degenerate (DD) model is close to those inferred from observations,
while the birthrate from the single-degenerate (SD) model accounts for only
about 1/2-2/3 of the observations. If a single starburst is assumed, the
distribution of the delay times of SNe Ia from the SD model is a weak
bimodality, where the WD + He channel contributes to the SNe Ia with delay
times shorter than 100Myr, and the WD + MS and WD + RG channels to those with
age longer than 1Gyr.Comment: 11 pages, 2 figures, accepted by Science in China Series G (Dec.30,
2009
CSST Large-scale Structure Analysis Pipeline: II. the CSST Emulator for Slitless Spectroscopy (CESS)
The Chinese Space Station Telescope (CSST) slitless spectroscopic survey will
observe objects to a limiting magnitude of ~ 23 mag (5, point sources)
in U, V, and I over 17500 deg. The spectroscopic observations are expected
to be highly efficient and complete for mapping galaxies over 0 < z < 1 with
secure redshift measurements at spectral resolutions of R ~ 200, providing
unprecedented data sets for cosmological studies. To quantitatively examine the
survey potential, we develop a software tool, namely the CSST Emulator for
Slitless Spectroscopy (CESS), to quickly generate simulated 1D slitless spectra
with limited computing resources. We introduce the architecture of CESS and the
detailed process of creating simulated CSST slitless spectra. The extended
light distribution of a galaxy induces the self-broadening effect on the 1D
slitless spectrum. We quantify the effect using morphological parameters:
S\'ersic index, effective radius, position angle, and axis ratio. Moreover, we
also develop a module for CESS to estimate the overlap contamination rate for
CSST grating observations of galaxies in galaxy clusters. Applying CESS to the
high-resolution model spectra of a sample of ~ 140 million galaxies with m_z <
21 mag selected from the Dark Energy Spectroscopic Instrument LS DR9 catalogue,
we obtain the simulated CSST slitless spectra. We examine the dependence of
measurement errors on different types of galaxies due to instrumental and
observational effects and quantitatively investigate the redshift completeness
for different environments out to z ~ 1. Our results show that the CSST
spectroscopy is able to provide secure redshifts for about one-quarter of the
sample galaxies.Comment: 14 pages, 15 figures, 2 tables, accepted for publication in MNRA