OA@INAF - Istituto Nazionale di Astrofisica
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Euclid preparation: LI. Forecasting the recovery of galaxy physical properties and their relations with template-fitting and machine-learning methods
No full textEuclid will collect an enormous amount of data during the mission's lifetime, observing billions of galaxies in the extragalactic sky. Along with traditional template-fitting methods, numerous machine learning (ML) algorithms have been presented for computing their photometric redshifts and physical parameters (PPs), requiring significantly less computing effort while producing equivalent performance measures. However, their performance is limited by the quality and amount of input information entering the model (the features), to a level where the recovery of some well-established physical relationships between parameters might not be guaranteed – for example, the star-forming main sequence (SFMS). To forecast the reliability of Euclid photo-zs and PPs calculations, we produced two mock catalogs simulating the photometry with the UNIONS ugriz and Euclid filters. We simulated the Euclid Wide Survey (EWS) and Euclid Deep Fields (EDF), alongside two auxiliary fields. We tested the performance of a template-fitting algorithm (Phosphoros) and four ML methods in recovering photo-zs, PPs (stellar masses and star formation rates), and the SFMS on the simulated Euclid fields. To mimic the Euclid processing as closely as possible, the models were trained with Phosphoros-recovered labels and tested on the simulated ground truth. For the EWS, we found that the best results are achieved with a mixed labels approach, training the models with wide survey features and labels from the Phosphoros results on deeper photometry, that is, with the best possible set of labels for a given photometry. This imposes a prior to the input features, helping the models to better discern cases in degenerate regions of feature space, that is, when galaxies have similar magnitudes and colors but different redshifts and PPs, with performance metrics even better than those found with Phosphoros. We found no more than 3% performance degradation using a COSMOS-like reference sample or removing u band data, which will not be available until after data release DR1. The best results are obtained for the EDF, with appropriate recovery of photo-z, PPs, and the SFMS
Star formation in G11.497-1.485: Two-epoch VLA study of a 6.7 GHz methanol maser flare
No full textContext. Maser flares are particularly significant in the study of massive star formation as they not only signal but also provide unique insights into transient phenomena such as accretion bursts. Aims: With this project, we aim to investigate the context of the ongoing 6.7 GHz methanol maser flare in the little-known massive star-forming region G11.497-1.485. Methods We carried out two epochs of the Karl G. Jansky Very Large Array (VLA) observation for 6.7 GHz and 12 GHz class II methanol, 22 GHz water masers, and continuum in the C, Ku, and K bands. Results: The VLA overview revealed the presence of five distinct radio-continuum sources (CM1-4 and N) in G11.497-1.485. The central source, CM1, is found to show signs of accretion disc fragmentation, highlighted by the centimetre-continuum-traced fragments, and is found to drive a high-energy jet, the ends of which are marked by non-thermal knots CM2 and CM3. CM1 showed a gradual flaring of methanol masers and a fading of a 22 GHz water maser, which might be signalling an accretion burst. The two remaining sources of the region, CM4 and N, make up one of the most compact jet and disc-jet systems found to date. Conclusions: The obtained data reveal, for the first time, the structure of the G11.497-1.485 region. The change in fluxes of the maser and the continuum emission confirm a transient event and reveal its impact on multiple sources in the region. Full Tables A.1-A.6 are 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/684/A86</A
Detection of X-Ray Polarization from the Blazar 1ES 1959+650 with the Imaging X-Ray Polarimetry Explorer
Get PDFObservations of linear polarization in the 2–8 keV energy range with the Imaging X-ray Polarimetry Explorer (IXPE) explore the magnetic field geometry and dynamics of the regions generating nonthermal radiation in relativistic jets of blazars. These jets, particularly in blazars whose spectral energy distribution peaks at X-ray energies, emit X-rays via synchrotron radiation from high-energy particles within the jet. IXPE observations of the X-ray-selected BL Lac–type blazar 1ES 1959+650 on 2022 May 3–4 showed a significant linear polarization degree of Πx = 8.0% ± 2.3% at an electric-vector position angle ψ x = 123° ± 8°. However, on 2022 June 9–12, only an upper limit of Πx ≤ 5.1% could be derived (at the 99% confidence level). The degree of optical polarization at that time, ΠO ∼ 5%, is comparable to the X-ray measurement. We investigate possible scenarios for these findings, including temporal and geometrical depolarization effects. Unlike some other X-ray-selected BL Lac objects, there is no significant chromatic dependence of the measured polarization in 1ES 1959+650, and its low X-ray polarization may be attributed to turbulence in the jet flow with dynamical timescales shorter than 1 day
Experimental study on the radiation-induced destruction of organic compounds on the surface of the Moon
Get PDFVolatile organic molecules and a complex organic refractory material were detected on the Moon and on lunar samples. The Moon's surface is exposed to a continuous flux of solar UV photons and fast ions, e.g. galactic cosmic rays (GCRs), solar wind (SW), and solar energetic particles (SEPs), that modify the physical and chemical properties of surface materials, thus challenging the survival of organic compounds. With this in mind, the aim of this work is to estimate the lifetime of organic compounds on the Moon's surface under processing by energetic particles. We performed laboratory experiments to measure the destruction cross section of selected organic compounds, namely methane (CH4), formamide (NH2CHO), and an organic refractory residue, under simulated Moon conditions. Volatile species were deposited at low temperature (17 - 18 K) and irradiated with energetic ions (200 keV) in an ultra-high vacuum chamber. The organic refractory residue was produced after warming up of a CO:CH4 ice mixture irradiated with 200 keV H+ at 18 K. All the samples were analyzed in situ by infrared transmission spectroscopy. We found that destruction cross sections are strongly affected (up to one order of magnitude) by the dilution of a given organic in an inert matrix. Among the selected samples, organic refractory residues are the most resistant to radiation. We estimated the lifetime of organic compounds on the surface of the Moon by calculating the dose rate due to GCRs and SEPs at the Moon's orbit and by using the experimental cross section values. Taking into account impact gardening, we also estimated the fraction of surviving organic material as a function of depth. Our results are compatible with the detection of CH4 in the LCROSS eject plume originating from layers deeper than about 0.7 m at the Moon's South Pole and with the identification of complex organic material in lunar samples collected by Apollo 17 mission
RADiff: Controllable Diffusion Models for Radio Astronomical Maps Generation
Get PDFAlong with the nearing completion of the Square Kilometre Array (SKA), comes an increasing demand for accurate and reliable automated solutions to extract valuable information from the vast amount of data it will allow acquiring. Automated source finding is a particularly important task in this context, as it enables the detection and classification of astronomical objects. Deep-learning-based object detection and semantic segmentation models have proven to be suitable for this purpose. However, training such deep networks requires a high volume of labeled data, which is not trivial to obtain in the context of radio astronomy. Since data needs to be manually labeled by experts, this process is not scalable to large dataset sizes, limiting the possibilities of leveraging deep networks to address several tasks. In this work, we propose RADiff, a generative approach based on conditional diffusion models trained over an annotated radio dataset to generate synthetic images, containing radio sources of different morphologies, to augment existing datasets and reduce the problems caused by class imbalances. We also show that it is possible to generate fully synthetic image-annotation pairs to automatically augment any annotated dataset. We evaluate the effectiveness of this approach by training a semantic segmentation model on a real dataset augmented in two ways: 1) using synthetic images obtained from real masks, and 2) generating images from synthetic semantic masks. Finally, we also show how the model can be applied to populate background noise maps for simulating radio maps for Data Challenges. Code is available at: https://github.com/SKA-INAF/radiff</ext-link
A-central model for the geometric calibration of hyper-hemispherical lenses
Get PDFHyper-hemispherical lenses are optical objective lenses with an ultra-wide field of view. Due to their extreme field of view, the geometric calibration introduces several setup difficulties. Various methods have been developed for simplifying the geometric calibration of a camera in the close-range field by defining intrinsic and extrinsic calibration parameters in a limited ambience of a clean room and taking advantage of simple calibration chessboards. A well-known example in this regard is Zhang’s approach for pinhole cameras. A similar approach was pursued by Scaramuzza to model more extensive cameras that include fisheye and panoramic lenses. However, despite this toolbox’s efficiency, it is ineffectual in the case of a hyper-hemispherical lens because of model limitations in the approximation of the corresponding projection system. In this study, we define and validate what we believe to be a novel a-central model extension (AME) for the description of hyper-hemispherical lenses that is able to overcome these limitations and to describe more accurately the physical behavior introduced by the design of these lenses. For this apparently new a-central model, we obtain significantly improved calibration results for one of the cameras designed in our laboratory and planned to become a planetary payload of an ESA mission
Quasars as standard candles. VI. Spectroscopic validation of the cosmological sample
Get PDFA sample of quasars has been recently assembled to investigate the non-linear
relation between their monochromatic luminosities at 2500{\AA}, and 2 keV and
to exploit quasars as a new class of standardized candles. The use of this
technique for cosmological purposes relies on the non-evolution with redshift
of the UV-optical spectral properties of quasars, as well as on the absence of
possible contaminants such as dust extinction and host-galaxy contribution. We
address these possible issues by analysing the spectral properties of our
cosmological quasar sample. We produced composite spectra in different bins of
redshift and accretion parameters (black hole mass, bolometric luminosity), to
investigate any possible evolution of the spectral properties of the continuum
of the composites with these parameters. We found a remarkable similarity
amongst the various stacked spectra. The overall shape of the continuum does
not show any statistically significant trend with the accretion parameters nor
with the redshift. The composite spectrum of our quasar sample is consistent
with negligible levels of both intrinsic reddening (with a colour excess
E(B-V)< 0.01) and host-galaxy emission (less than 10%) in the optical. We
tested whether unaccounted dust extinction could explain the discrepancy
between our cosmographic fit of the Hubble-Lemaitre diagram and the concordance
{\Lambda}CDM model. The average colour excess required to solve the tension
should increase with redshift up to unphysically high values (E(B-V)=0.1 at
z>3) that would imply that the intrinsic emission of quasars is much bluer and
more luminous than ever reported in observed spectra. The similarity of quasar
spectra across the parameter space excludes a significant evolution of the
average continuum properties with any of the explored parameters, confirming
the reliability of our sample for cosmological applications
Exploring the high-density reflection model for the soft excess in RBS 1124
Get PDF'Bare' active galactic nuclei (AGN) are a subclass of Type 1 AGN that show little or no intrinsic absorption. They offer an unobscured view of the central regions of the AGN and therefore serve as ideal targets to study the relativistic reflection features originating from the innermost regions of the accretion disc. We present a detailed broad-band spectral analysis (0.3-70 keV) of one of the most luminous bare AGN in the local Universe, RBS 1124 () using a new, co-ordinated high signal-to-noise observation obtained by XMM-Newton and NuSTAR. The source exhibits a power-law continuum with 1.8 along with a soft excess below 2 keV, a weak neutral iron line and curvature at high energies ( keV). The broad-band spectrum, including the soft excess and the high-energy continuum, is well fit by the relativistic reflection model when the accretion disc is allowed to have densities of log/cm) . Our analysis therefore suggests that when high-density effects are considered, relativistic reflection remains a viable explanation for the soft excess...
Mapping the intracluster medium in the era of high-resolution X-ray spectroscopy
Get PDFHigh-resolution spectroscopy in soft X-rays will open a new window to map multiphase gas in galaxy clusters and probe physics of the intracluster medium (ICM), including chemical enrichment histories, circulation of matter and energy during large-scale structure evolution, stellar and black hole feedback, halo virialization, and gas mixing processes. An eV-level spectral resolution, large field of view, and effective area are essential to separate cluster emissions from the Galactic foreground and efficiently map the cluster outskirts. Several mission concepts that meet these criteria have been proposed recently, e.g. LEM, HUBS, and Super DIOS. This theoretical study explores what information on ICM physics could be recovered with such missions and the associated challenges. We emphasize the need for a comprehensive comparison between simulations and observations to interpret the high-resolution spectroscopic observations correctly. Using Line Emission Mapper (LEM) characteristics as an example, we demonstrate that it enables the use of soft X-ray emission lines (e.g. O VII/VIII and Fe-L complex) from the cluster outskirts to measure the thermodynamic, chemical, and kinematic properties of the gas up to r200 and beyond. By generating mock observations with full backgrounds, analysing their images/spectra with observational approaches, and comparing the recovered characteristics with true ones from simulations, we develop six key science drivers for future missions, including the exploration of multiphase gas in galaxy clusters (e.g. temperature fluctuations, phase-space distributions), metallicity, ICM gas bulk motions and turbulence power spectra, ICM-cosmic filament interactions, and advances for cluster cosmology
CHEX-MATE: the intracluster medium entropy distribution in the gravity-dominated regime
Get PDFWe characterise the entropy profiles of 32 very high mass
() galaxy clusters (HIGHMz), selected from
the CHEX-MATE sample, to study the intracluster medium (ICM) entropy
distribution in a regime where non-gravitational effects are minimised. Using
XMM-Newton measurements, we measure the entropy profiles up to ~ for
all objects. The scaled profiles exhibit large dispersion in the central
regions, but converge rapidly to the expectation from pure gravitational
collapse beyond the core. We quantify the correlation between the ICM
morphological parameters and scaled entropy as a function of radius, showing
that morphologically relaxed (disturbed) objects have low (high) central
entropy. We compare our data to other observational samples, finding
differences in normalisation which are linked to the average mass of the
samples in question. We find that a weaker mass dependence than self-similar in
the scaling (Am ~ -0.25) allows us to minimise the dispersion in the radial
range [0.3-0.8] for clusters spanning over a decade in mass. The
deviation from self-similarity is radially dependent and is more pronounced at
small and intermediate radii than at . We also investigate the
distribution of central entropy , finding no evidence for bimodality, and
outer slopes , which peaks at ~1.1. Using weak lensing masses, we find
indication for a small suppression of the scatter (~30%) beyond the core when
using masses derived from Yx in the rescaling. Finally, we compare to recent
cosmological numerical simulations from THE THREE HUNDRED and MACSIS, finding
good agreement with our observational data. These results provide a robust
observational benchmark in the gravity-dominated regime and will serve as a
future reference for samples at lower mass, higher redshifts, and for ongoing
work using cosmological numerical simulations