760 research outputs found
XZ: Deriving redshifts from X-ray spectra of obscured AGN
Context: Redshifts are fundamental for our understanding of extragalactic
X-ray sources. Ambiguous counterpart associations, expensive optical
spectroscopy and/or multimission multiwavelength coverage to resolve
degeneracies make estimation often difficult in practice.
Aims: We attempt to constrain redshifts of obscured Active Galactic Nuclei
(AGN) using only low-resolution X-ray spectra.
Methods: Our XZ method fits AGN X-ray spectra with a moderately complex
spectral model incorporating a corona, torus obscurer and warm mirror. Using
the Bayesian X-ray Astronomy (BXA) package, we constrain redshift, column
density, photon index and luminosity simultaneously. The redshift information
primarily comes from absorption edges in Compton-thin AGN, and from the Fe
K fluorescent line in heavily obscured AGN. A new generic background
fitting method allows us to extract more information from limited numbers of
source counts.
Results: We derive redshift constraints for 74/321 hard-band detected sources
in the Chandra deep field South. Comparing with spectroscopic redshifts, we
find an outlier fraction of 8%, indicating that our model assumptions are
valid. For three Chandra deep fields, we release our XZ redshift estimates.
Conclusions: The independent XZ estimate is easy to apply and effective for a
large fraction of obscured AGN in todays deep surveys without the need for any
additional data. Comparing to different redshift estimation methods, XZ can
resolve degeneracies in photometric redshifts, help to detect potential
association problems and confirm uncertain single-line spectroscopic redshifts.
With high spectral resolution and large collecting area, this technique will be
highly effective for Athena/WFI observations.Comment: 20 pages, 16 figures in paper, 14 in appendice
The X-ray properties of quasars: no evident evolution of accretion physics in the first Gyr of the Universe
X-ray emission from QSOs has been used to assess SMBH accretion properties up
to ~6. However, at only ~15 QSOs are covered by sensitive X-ray
observations, preventing a statistically significant investigation of the X-ray
properties of QSOs in the first Gyr of the Universe. We present new Chandra
observations of 10 QSOs, selected to have virial black-hole mass
estimates from Mg II line spectroscopy. Adding archival X-ray data for an
additional 15 QSOs, we investigate the X-ray properties of the QSO
population in the first Gyr of the Universe, focusing in particular on the
relation, which is traced by the parameter, and
the shape of their X-ray spectra. We performed photometric analyses to derive
estimates of the X-ray luminosities, and thus the values and
bolometric corrections (). We compared the resulting
and distributions with the results found for QSO
samples at lower redshift. Finally, we performed a basic X-ray spectral
analysis of the brightest QSOs to derive their individual photon indices,
and joint spectral analysis of the whole sample to estimate the average photon
index. We confirm a lack of significant evolution of with
redshift, extending the results from previous works up to , and the trend
of an increasing bolometric correction with increasing luminosity found for
QSOs at lower redshifts. The average power-law photon index of our sample
( and for sources
with net counts, respectively) is slightly steeper than, but
still consistent with, typical QSOs at . All these results point toward
a lack of substantial evolution of the inner accretion-disk/hot-corona
structure in QSOs from low redshift to . Our data hint at generally high
Eddington ratios at .Comment: 15 pages. 10 figures. 7 tables. Accepted for publication in A&
Discovery of the first heavily obscured QSO candidate at in a close galaxy pair
While theoretical arguments predict that most of the early growth of
supermassive black holes (SMBHs) happened during heavily obscured phases of
accretion, current methods used for selecting quasars (QSOs) are strongly
biased against obscured QSOs, thus considerably limiting our understanding of
accreting SMBHs during the first Gyr of the Universe from an observational
point of view. We report the discovery of the first heavily obscured
QSO candidate in the early universe, hosted by a close ( kpc) galaxy
pair at . One of the members is an optically classified type 1 QSO,
PSO167-13. The companion galaxy was first detected as a [C II] emitter by ALMA.
An X-ray source is significantly () detected by in the 2-5
keV band, with net counts in the 0.5-2 keV band, although the current
positional uncertainty does not allow a conclusive association with either
PSO167-13 or its companion galaxy. From X-ray photometry and hardness-ratio
arguments, we estimated an obscuring column density of
and
at and confidence levels,
respectively. Thus, regardless of which of the two galaxies is associated with
the X-ray emission, this source is the first heavily obscured QSO candidate at
.Comment: A&A Letters, accepte
BASS. XXIV : the BASS DR2 spectroscopic line measurements and AGN demographics
We present the second catalog and data release of optical spectral line measurements and active galactic nucleus (AGN) demographics of the BAT AGN Spectroscopic Survey, which focuses on the Swift-BAT hard X-ray detected AGNs. We use spectra from dedicated campaigns and publicly available archives to investigate spectral properties of most of the AGNs listed in the 70 month Swift-BAT all-sky catalog; specifically, 743 of the 746 unbeamed and unlensed AGNs (99.6%). We find a good correspondence between the optical emission line widths and the hydrogen column density distributions using the X-ray spectra, with a clear dichotomy of AGN types for NH = 1022 cmâ2. Based on optical emission-line diagnostics, we show that 48%â75% of BAT AGNs are classified as Seyfert, depending on the choice of emission lines used in the diagnostics. The fraction of objects with upper limits on line emission varies from 6% to 20%. Roughly 4% of the BAT AGNs have lines too weak to be placed on the most commonly used diagnostic diagram, [O iii]λ5007/HÎČ versus [N ii]λ6584/Hα, despite the high signal-to-noise ratio of their spectra. This value increases to 35% in the [O iii]λ5007/[O ii]λ3727 diagram, owing to difficulties in line detection. Compared to optically selected narrow-line AGNs in the Sloan Digital Sky Survey, the BAT narrow-line AGNs have a higher rate of reddening/extinction, with Hα/HÎČ > 5 (âŒ36%), indicating that hard X-ray selection more effectively detects obscured AGNs from the underlying AGN population. Finally, we present a subpopulation of AGNs that feature complex broad lines (34%, 250/743) or double-peaked narrow emission lines (2%, 17/743)
The evolution of the cosmic molecular gas density
One of the last missing pieces in the puzzle of galaxy formation and
evolution through cosmic history is a detailed picture of the role of the cold
gas supply in the star-formation process. Cold gas is the fuel for star
formation, and thus regulates the buildup of stellar mass, both through the
amount of material present through a galaxy's gas mass fraction, and through
the efficiency at which it is converted to stars. Over the last decade,
important progress has been made in understanding the relative importance of
these two factors along with the role of feedback, and the first measurements
of the volume density of cold gas out to redshift 4, (the "cold gas history of
the Universe") has been obtained. To match the precision of measurements of the
star formation and black-hole accretion histories over the coming decades, a
two orders of magnitude improvement in molecular line survey speeds is required
compared to what is possible with current facilities. Possible pathways towards
such large gains include significant upgrades to current facilities like ALMA
by 2030 (and beyond), and eventually the construction of a new generation of
radio-to-millimeter wavelength facilities, such as the next generation Very
Large Array (ngVLA) concept.Comment: 7 pages, 2 figures, Science White paper submitted to Astro2020
Decadal Surve
ALMA Lensing Cluster Survey: Full Spectral Energy Distribution Analysis of z ⌠0.5â6 Lensed Galaxies Detected with millimeter Observations
Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To search for this population, we have performed an extensive survey with Atacama Large Millimeter/submillimeter Array (ALMA), called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin2 area and securely detects 180 sources at z ⌠0.5â6 with a flux limit of âŒ0.2 mJy at 1.2 mm. Here, we report the results of multiwavelength spectral energy distribution analysis of the whole ALCS sample, utilizing the observed-frame UV to millimeter photometry. We find that the majority of the ALCS sources lie on the star-forming main sequence, with a smaller fraction showing intense starburst activities. The ALCS sample contains high infrared-excess sources ( IRX=log(Ldust/LUV)>1 ), including two extremely dust-obscured galaxies (IRX > 5). We also confirm that the ALCS sample probes a broader range in lower dust mass than conventional submillimeter galaxy samples in the same redshift range. We identify six heavily obscured active galactic nucleus (AGN) candidates that are not detected in the archival Chandra data in addition to the three X-ray AGNs reported by Uematsu et al. (2023). The inferred AGN luminosity density shows a possible excess at z = 2â3 compared with that determined from X-ray surveys below 10 keV
The ALMA Spectroscopic Survey in the HUDF: Nature and Physical Properties of Gas-mass Selected Galaxies Using MUSE Spectroscopy
We discuss the nature and physical properties of gas-mass selected galaxies in the ALMA spectroscopic survey (ASPECS) of the Hubble Ultra Deep Field (HUDF). We capitalize on the deep optical integral-field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) HUDF Survey and multiwavelength data to uniquely associate all 16 line emitters, detected in the ALMA data without preselection, with rotational transitions of carbon monoxide (CO). We identify 10 as CO(2â1) at 1 < z < 2, 5 as CO(3â2) at 2 < z < 3, and 1 as CO(4â3) at z = 3.6. Using the MUSE data as a prior, we identify two additional CO(2â1) emitters, increasing the total sample size to 18. We infer metallicities consistent with (super-)solar for the CO-detected galaxies at z â 1.5, motivating our choice of a Galactic conversion factor between CO luminosity and molecular gas mass for these galaxies. Using deep Chandra imaging of the HUDF, we determine an X-ray AGN fraction of 20% and 60% among the CO emitters at z ⌠1.4 and z ⌠2.6, respectively. Being a CO-flux-limited survey, ASPECS-LP detects molecular gas in galaxies on, above, and below the main sequence (MS) at z ⌠1.4. For stellar masses âŠ1010 (1010.5) M, we detect about 40% (50%) of all galaxies in the HUDF at 1 < z < 2 (2 < z < 3). The combination of ALMA and MUSE integral-field spectroscopy thus enables an unprecedented view of MS galaxies during the peak of galaxy formation
Chandra and Magellan/FIRE follow-up observations of PSO167-13: an X-ray weak QSO at
The discovery of hundreds of QSOs in the first Gyr of the Universe powered by
already grown SMBHs challenges our knowledge of SMBH formation. In particular,
investigations of QSOs presenting notable properties can provide unique
information on the physics of fast SMBH growth in the early universe. We
present the results of follow-up observations of the radio-quiet QSO
PSO167-13, which is interacting with a close companion galaxy. The PSO167-13
system has been recently proposed to host the first heavily obscured X-ray
source at high redshift. We observed PSO167-13 with Chandra/ACIS-S (177 ks),
and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE. No
significant X-ray emission is detected from the PSO167-13 system, suggesting
that the obscured X-ray source previously tentatively detected was either due
to a strong background fluctuation or is highly variable. The upper limit (90%
confidence level) on the X-ray emission of PSO167-13
() is the lowest
available for a QSO. The ratio between the X-ray and UV luminosity of
makes PSO167-13 a strong outlier from the
and relations. In particular, its
X-ray emission is times weaker than the expectation based on its UV
luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by
the unfavorable sky conditions, but the tentatively detected C IV and Mg II
emission lines appear strongly blueshifted. The most plausible explanations for
the X-ray weakness of PSO167-13 are intrinsic weakness or small-scale
absorption by Compton-thick material. The possible strong blueshift of its
emission lines hints at the presence of nuclear winds, which could be related
to its X-ray weakness.Comment: Accepted for publication on A&
The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Nature of the Faintest Dusty Star-forming Galaxies
We present a characterization of the physical properties of a sample of 35 securely detected, dusty galaxies in the deep ALMA 1.2 mm image obtained as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Large Program. This sample is complemented by 26 additional sources identified via an optical/infrared source positional prior. Using their well-characterized spectral energy distributions, we derive median stellar masses and star formation rates (SFR) of and 30 M â yrâ1, respectively, and interquartile ranges of (2.4-11.7) x 1010 M â and 20-50 M â yrâ1. We derive a median spectroscopic redshift of 1.8 with an interquartile range 1.1-2.6, significantly lower than submillimeter galaxies detected in shallower, wide-field surveys. We find that 59% +- 13%, 6% +- 4%, and 34% +- 9% of our sources are within, above, and below+-0.4 dex from the SFR-stellar-mass relation or main sequence (MS), respectively. The ASPECS galaxies closely follow the SFR-molecular gas mass relation and other previously established scaling relations, confirming a factor of five increase of the gas-to-stellar-mass ratio from z = 0.5 to 2.5 and a mild evolution of the gas depletion timescales with a typical value of 0.7 Gyr at z = 1-3. ASPECS galaxies located significantly below the MS, a poorly exploited parameter space, have low gas-to-stellar-mass ratios of ~0.1-0.2 and long depletion timescales >1 Gyr. Galaxies along the MS dominate the cosmic density of molecular gas at all redshifts. Systems above the MS have an increasing contribution to the total gas reservoirs from z < 1 to z = 2.5, while the opposite is found for galaxies below the MS.M.A. has been supported by the grant âCONICYT + PCI +
INSTITUTO MAX PLANCK DE ASTRONOMIA
MPG190030â and âCONICYT+PCI+REDES 190194.â
J.G.-L. acknowledges partial support from ALMA-CONICYT
project 31160033. F.W. and M.N. acknowledge funding from
the ERC Advanced Grant âCosmic Gas.â F.E.B. acknowledges
support from CONICYT grants CATA-Basal AFB-170002
(FEB), FONDECYT Regular 1190818 (FEB), 1200495 (FEB),
and Chileâs Ministry of Economy, Development, and Tourismâs Millennium Science Initiative through grant IC120009,
awarded to The Millennium Institute of Astrophysics, MAS
(FEB). T.D.-S. acknowledges support from ALMA-CONICYT
project 31130005 and FONDECYT project 1151239. D.R.
acknowledges support from the National Science Foundation
under grant Nos. AST-1614213 and AST-1910107 and from
the Alexander von Humboldt Foundation through a Humboldt
Research Fellowship for Experienced Researchers. I.R.S.
acknowledges support from STFC (ST/P000541/1). L.H.I.
acknowledges support from JSPS KAKENHI grant No.
JP19K23462. The National Radio Astronomy Observatory is
a facility of the National Science Foundation operated under
cooperative agreement by Associated Universities, Inc. This
paper makes use of the following ALMA data: 2016.1.00324.
ALMA is a partnership of ESO (representing its member
states), NSF (USA), and NINS (Japan), together with NRC
(Canada), NSC and ASIAA (Taiwan), and KASI (Republic
of Korea), in cooperation with the Republic of Chile. The
Joint ALMA Observatory is operated by ESO, AUI/NRAO,
and NAOJ
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