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Coordinated X-ray and UV absorption within the accretion disk wind of the active galactic nucleus PG 1126-041
Get PDFAccretion disk winds launched close to supermassive black holes (SMBHs) are a
viable mechanism to provide feedback between the SMBH and the host galaxy. We
aim to characterize the X-ray properties of the inner accretion disk wind of
the nearby active galactic nucleus (AGN) PG 1126-041, and to study its
connection with the ultraviolet (UV)-absorbing wind. We perform spectroscopic
analysis of eight XMM-Newton observations of PG 1126-041 taken between 2004 and
2015, using both phenomenological models and the most advanced accretion disk
wind models available. For half of the dataset, we can compare the X-ray
analysis results with the results of quasi-simultaneous, high-resolution
spectroscopic UV observations taken with the Cosmic Origins Spectrograph (COS)
on board the Hubble Space Telescope. The X-ray spectra of PG 1126-041 are
complex and absorbed by ionized material which is highly variable on multiple
time scales, sometimes as short as 11 days. Accretion disk wind models can
account for most of the X-ray spectral complexity of PG 1126-041, with the
addition of massive clumps, represented by a partially covering absorber.
Variations in column density ( cm) of the
partially covering absorber drive the observed X-ray spectral variability of PG
1126-041. The absorption from the X-ray partially covering gas and from the
blueshifted C IV troughs appear to vary in a coordinated way. The line of sight
toward PG 1126-041 offers a privileged view through a highly dynamic nuclear
wind originating on inner accretion disk scales, making the source a very
promising candidate for future detailed studies of the physics of accretion
disk winds around SMBHs
Carbon Dioxide Retrievals From NOMAD-SO on ESA's ExoMars Trace Gas Orbiter and Temperature Profiles Retrievals With the Hydrostatic Equilibrium Equation: 1. Description of the Method
Get PDFThe Solar Occultation (SO) channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument has been scanning the Martian atmosphere for almost 2 Martian years. In this work, we present a subset of the NOMAD SO data measured at the mesosphere at the terminator. From the data set, we investigated 968 vertical profiles of carbon dioxide density and temperature covering the Martian Year (MY) 35 as well as MY 36 up to a solar longitude (Ls) of 135° and altitudes around 60–100 km. While carbon dioxide density profiles are directly retrieved from the spectral signature in the spectra, temperature profiles are more challenging to retrieve as unlike density profiles, temperature profiles can present some spurious features if the regularization is not correctly managed. Comparing seven regularization methods, we found that the expected error estimation method provides the best regularization parameters. The vertical resolution of the profiles is on average 1.6 km. Numerous warm layers and cold pockets appear in this data set. The warm layers are found in the Northern hemisphere at dawn and dusk as well as in the Southern hemisphere at dawn. Strong warm layers are present in more than 13.5% of the profiles. The Southern hemisphere at dusk does not present any warm layer between Ls 50° and 150°. The height and latitudinal distribution of those warm layers were similar in MY 35 and MY 36 during the first half of the year (Ls = 0°–135°)
A sensitive APEX and ALMA CO(1-0), CO(2-1), CO(3-2), and [CI](1-0) spectral survey of 40 local (ultra-)luminous infrared galaxies
Get PDFWe present a high sensitivity, ground-based spectral line survey of low-J carbon monoxide (CO(Jup → Jup − 1) with Jup = 1, 2, 3) and neutral carbon [CI] 3P1−3P0 ([CI](1-0)) in 36 local ultra-luminous infrared galaxies (ULIRGs) and 4 additional LIRGs, all of which have previous Herschel OH 119 μm observations. The study is based on new single-dish observations conducted with the Atacama Pathfinder Experiment (APEX) and complemented with archival APEX and Atacama Large Millimeter Array (ALMA and ACA) data. Our methods are optimized for a multi-tracer study of the total molecular line emission from these ULIRGs, including any extended low-surface-brightness components. We find a tight correlation between the CO and [CI] line luminosities, which suggests that the emission from CO(1-0) (and CO(2-1)) arises from similar regions as the [CI](1-0), at least when averaged over galactic scales. By using [CI] to compute molecular gas masses, we estimate a median CO-to-H2 conversion factor of ⟨αCO⟩ = 1.7 ± 0.5 M⊙ (K km s−1pc2)−1 for ULIRGs. We derive median galaxy-integrated CO line ratios of «r21» = LCO(2-1)'/LCO(1-0)' = 1.09, «r31» = LCO(3-2)'/LCO(1-0)' = 0.76, and «r32» = LCO(3-2)'/LCO(2-1)' = 0.76, significantly higher than normal star-forming galaxies, confirming the exceptional molecular gas properties of ULIRGs. We find that the r21 and r32 ratios are poor tracers of CO excitation in ULIRGs, while r31 shows a positive trend with LIR and star formation rates and a negative trend with the H2 gas depletion timescales (τdep). Our investigation of CO line ratios as a function of gas kinematics shows no clear trends, except for a positive relation between r21 and σv, which can be explained by CO opacity effects. These ULIRGs are also characterized by high L[CI](1-0)'/LCO(1-0)' ratios, with a measured median value of ⟨rCICO⟩ = 0.18, higher than values from previous interferometric studies that were affected by missing [CI] line flux. The rCICO values do not show a significant correlation with any of the galaxy properties investigated, including OH outflow velocities and equivalent widths. We find that the widths of [CI](1-0) lines are ∼10% smaller than those of CO lines, and that this discrepancy becomes more significant in ULIRGs with broad lines (σv > 150 km s−1) and when considering the high-v wings of the lines. This suggests that the low optical depth of [CI] can challenge its detection in diffuse, low-surface-brightness outflows and, therefore, its use as a tracer of CO-dark H2 gas in these components. Finally, we find that higher LAGN are associated with longer τdep, consistent with the hypothesis that active galactic nucleus feedback may reduce the efficiency of star formation. Our study highlights the need for sensitive single-dish multi-tracer H2 surveys of ULIRGs that are able to recover the flux that is missed by interferometers, especially in the high-frequency lines such as [CI]. The Atacama Large Aperture Submillimeter Telescope (AtLAST) will be transformational for this field...
The Gaia-ESO survey: Mapping the shape and evolution of the radial abundance gradients with open clusters
Get PDFContext. The spatial distribution of elemental abundances and their time evolution are among the major constraints to disentangling the scenarios of formation and evolution of the Galaxy. Aims: In this paper we used the sample of open clusters available in the final release of the Gaia-ESO survey to trace the Galactic radial abundance and abundance-to-iron ratio gradients, and their time evolution. Methods: We selected member stars in 62 open clusters, with ages from 0.1 to about 7 Gyr, located in the Galactic thin disc at galactocentric radii (RGC) from about 6 to 21 kpc. We analysed the shape of the resulting [Fe/H] gradient, the average gradients [El/H] and [El/Fe] combining elements belonging to four different nucleosynthesis channels, and their individual abundance and abundance ratio gradients. We also investigated the time evolution of the gradients dividing open clusters in three age bins. Results: The [Fe/H] gradient has a slope of −0.054 dex kpc−1. It can be better approximated with a two-slope shape, steeper for RGC ≤ 11.2 kpc and flatter in the outer regions. We saw different behaviours for elements belonging to different channels. For the time evolution of the gradient, we found that the youngest clusters (age Conclusions: To delineate the shape of the `true' gradient, we should most likely limit our analysis to stars with low surface gravity log g > 2.5 and microturbulent parameter ξ −1. Based on this reduced sample, we can conclude that the gradient has minimally evolved over the time-frame outlined by the open clusters, indicating a slow and stationary formation of the thin disc over the last 3 Gyr. We found a secondary role of cluster migration in shaping the gradient, with a more prominent role of migration for the oldest clusters
First Observations of CH4 and H+3 Spatially Resolved Emission Layers at Jupiter Equator, as Seen by JIRAM/Juno
Get PDFIn this work, we present the detection of CH4 and (Formula presented.) emissions in the equatorial atmosphere of Jupiter as two well-separated layers located, respectively, at tangent altitudes of about 200 and 500–600 km above the 1-bar level using the observations of the Jovian InfraRed Auroral Mapper (JIRAM), on board Juno. This provides details of the vertical distribution of (Formula presented.) retrieving its Volume Mixing Ratio (VMR), concentration, and temperature. The thermal profile obtained from (Formula presented.) shows a peak of 600–800 K at about 550 km, with lower values than the ones reported in Seiff et al. (1998), https://doi.org/10.1029/98JE01766 above 500 km using VMR and temperature as free parameters and above 650 km when VMR is kept fixed with that model in the retrieval procedure. The observed deviations from the Galileo's profile could potentially point to significant variability in the exospheric temperature with time. We suggest that vertically propagating waves are the most likely explanation for the observed VMR and temperature variations in the JIRAM data. Other possible phenomena could explain the observed evidence, for example, dynamic activity driving chemical species from lower layers toward the upper atmosphere, like the advection-diffusion processes, or precipitation by soft electrons, although better modeling is required to test these hypothesis. The characterization of CH4 and (Formula presented.) species, simultaneously observed by JIRAM, offers the opportunity for better constraining atmospheric models of Jupiter at equatorial latitudes
A wide-field view on multiple stellar populations in 28 Milky Way globular clusters
Get PDFThe majority of Galactic globular clusters (GCs) contain multiple stellar populations displaying specific chemical abundance variations. In particular, GCs generally contain a ‘primordial’ population with abundances similar to field stars, along with an ‘enriched’ population exhibiting light element anomalies. In this paper, we present a homogeneous and wide-view analysis of multiple stellar populations in 28 Galactic GCs. By using a combination of HST photometry together with wide-field, ground-based photometry we are able to analyse between 84 per cent and 99 per cent of all stars in each cluster. For each GC, we classify stars into separate sub-populations using the well-established CUBI colour index, and investigate the spatial distributions of these populations. Our results show that dynamically young GCs can contain either centrally concentrated enriched or primordial populations, or no centrally concentrated population. Dynamically old GCs show fully mixed populations as expected. The existence of clusters born with centrally concentrated primordial (and homogeneously mixed) populations exacerbates the mass-budget problem facing many cluster formation scenarios. The diversity in these results also highlights the need for additional theories that can account for the wide variety of initial conditions that we find. We finally investigate the enriched star fraction as a function of different global parameters in our GC sample, using also data for young and low-mass clusters from the Small- and Large Magellanic Clouds and confirm earlier results that the enriched star fraction strongly correlates with the initial mass of a cluster
Gaia Data Release 3. Gaia scan-angle-dependent signals and spurious periods
Get PDFContext. Gaia Data Release 3 (Gaia DR3) time series data may contain spurious signals related to the time-dependent scan angle. Aims: We aim to explain the origin of scan-angle-dependent signals and how they can lead to spurious periods, provide statistics to identify them in the data, and suggest how to deal with them in Gaia DR3 data and in future releases. Methods: Using real Gaia (DR3) data alongside numerical and analytical models, we visualise and explain the features observed in the data. Results: We demonstrated with Gaia (DR3) data that source structure (multiplicity or extendedness) or pollution from close-by bright objects can cause biases in the image parameter determination from which photometric, astrometric, and (indirectly) radial velocity time series are derived. These biases are a function of the time-dependent scan direction of the instrument and thus can introduce scan-angle-dependent signals, which due to the scanning-law-induced sampling of Gaia can result in specific spurious periodic signals. Numerical simulations in which a period search is performed on Gaia time series with a scan-angle-dependent signal qualitatively reproduce the general structure observed in the spurious period distribution of photometry and astrometry, and the associated spatial distributions on the sky. A variety of statistics allows for the deeper understanding and identification of affected sources. Conclusions: The origin of the scan-angle-dependent signals and subsequent spurious periods is well understood and is mostly caused by fixed-orientation optical pairs with a separation Table A.1 is also available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/674/A25 and at the Gaia archive via https://gea.esac.esa.int/archive/..
X-ray polarimetry of the accreting pulsar GX 301−2
Get PDFThe phase- and energy-resolved polarization measurements of accreting X-ray pulsars (XRPs) allow us to test different theoretical models of their emission, and they also provide an avenue to determine the emission region geometry. We present the results of the observations of the XRP GX 301−2 performed with the Imaging X-ray Polarimetry Explorer (IXPE). A persistent XRP, GX 301−2 has one of the longest spin periods known: ∼680 s. A massive hyper-giant companion star Wray 977 supplies mass to the neutron star via powerful stellar winds. We did not detect significant polarization in the phase-averaged data when using spectro-polarimetric analysis, with the upper limit on the polarization degree (PD) of 2.3% (99% confidence level). Using the phase-resolved spectro-polarimetric analysis, we obtained a significant detection of polarization (above 99% confidence level) in two out of nine phase bins and a marginal detection in three bins, with a PD ranging between ∼3% and ∼10% and a polarization angle varying in a very wide range from ∼0° to ∼160°. Using the rotating vector model, we obtained constraints on the pulsar geometry using both phase-binned and unbinned analyses, finding excellent agreement. Finally, we discuss possible reasons for a low observed polarization in GX 301−2
The Sardinia Radio Telescope Metrology System
Get PDFAfter the successful finalisation of the performance upgrade, the Sardinia Radio Telescope will be ready to observe at high frequencies up to 116 GHz. To operate at the highest frequencies, improvement in pointing precision and main reflector surface accuracy (RMS, compared to the ideal profile) are required. In order to achieve these goals, the radio telescope has been equipped with a new sophisticated metrology system. This will make possible to optimise the pointing and antenna gain throughout the elevation range in which SRT scans the sky. The purpose of this paper is to provide an overview of all the components of the new metrology system, describing the main features that will make the Sardinia Radio Telescope a state-of-the-art facility
Gaia Data Release 3. The extragalactic content
Get PDFThe Gaia Galactic survey mission is designed and optimized to obtain astrometry, photometry, and spectroscopy of nearly two billion stars in our Galaxy. Yet as an all-sky multi-epoch survey, Gaia also observes several million extragalactic objects down to a magnitude of G ∼ 21 mag. Due to the nature of the Gaia onboard-selection algorithms, these are mostly point-source-like objects. Using data provided by the satellite, we have identified quasar and galaxy candidates via supervised machine learning methods, and estimate their redshifts using the low resolution BP/RP spectra. We further characterise the surface brightness profiles of host galaxies of quasars and of galaxies from pre-defined input lists. Here we give an overview of the processing of extragalactic objects, describe the data products in Gaia DR3, and analyse their properties. Two integrated tables contain the main results for a high completeness, but low purity (50−70%), set of 6.6 million candidate quasars and 4.8 million candidate galaxies. We provide queries that select purer sub-samples of these containing 1.9 million probable quasars and 2.9 million probable galaxies (both ∼95% purity). We also use high quality BP/RP spectra of 43 thousand high probability quasars over the redshift range 0.05−4.36 to construct a composite quasar spectrum spanning restframe wavelengths from 72−1000 nm. Full Table 8 is only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/674/A41...