OA@INAF - Istituto Nazionale di Astrofisica
Not a member yet
15494 research outputs found
Sort by
Portraying the missing baryonic mass at the cosmic noon: the contribution of CUBES
Get PDFThe cosmological and galactic missing baryon problems are briefly reviewed with a particular focus on the contributions to the baryonic census derived from the analysis of quasar absorption spectra. The CUBES spectrograph foreseen for the ESO VLT, with its exceptional efficiency (> 40 %), blue wavelength coverage (λ≃ 300 - 405 nm) and intermediate resolution (R≃ 24 , 000) will allow us to tackle this issue with two approaches: using H i Lyman-α lines at z≃ 1.5 - 2.3 , just after the peak of star formation, and using O vi absorbers at z≃ 1.9 - 2.9 , at the cosmic noon. In both cases, in order to derive the baryonic masses it will be necessary to acquire also higher-resolution spectra of the same target quasars to cover the region at longer wavelengths. We simulate the observations with the CUBES E2E simulator considering a sample of 40 bright quasars at redshifts zem∼ 2 - 3 observed for a total time of ∼ 13 h to reach a signal-to-noise ratio of ∼ 15 in the H i Lyman-α, O vi forests
Outflows in the gaseous disks of active galaxies and their impact on black hole scaling relations
Get PDFTo tackle the still unsolved and fundamental problem of the role of Active
Galactic Nuclei (AGN) feedback in shaping galaxies, in this work we implement a
new physical treatment of AGN-driven winds into our semi-analytic model of
galaxy formation. To each galaxy in our model, we associate solutions for the
outflow expansion and the mass outflow rates in different directions, depending
on the AGN luminosity, on the circular velocity of the host halo, and on gas
content of the considered galaxy. To each galaxy we also assign an effective
radius derived from energy conservation during merger events, and a stellar
velocity dispersion self-consistently computed via Jeans modelling. We derive
all the main scaling relations between Black hole (BH) mass and total/bulge
stellar mass, velocity dispersion, host halo dark matter mass, and star
formation efficiency. We find that our improved AGN feedback mostly controls
the dispersion around the relations but plays a subdominant role in shaping
slopes and/or normalizations of the scaling relations. Including possible
limited-resolution selection biases in the model provides better agreement with
the available data. The model does not point to any more fundamental galactic
property linked to BH mass, with velocity dispersion playing a similar role
with respect to stellar mass, in tension with present data. In line with other
independent studies carried out on comprehensive semi-analytic and hydrodynamic
galaxy-BH evolution models, our current results signal either an inadequacy of
present cosmological models of galaxy formation in fully reproducing the local
scaling relations, in terms of both shape and residuals, and/or point to an
incompleteness issue affecting the local sample of dynamically-measured BHs
Radio astronomical images object detection and segmentation: a benchmark on deep learning methods
Get PDFIn recent years, deep learning has been successfully applied in various scientific domains. Following these promising results and performances, it has recently also started being evaluated in the domain of radio astronomy. In particular, since radio astronomy is entering the Big Data era, with the advent of the largest telescope in the world - the Square Kilometre Array (SKA), the task of automatic object detection and instance segmentation is crucial for source finding and analysis. In this work, we explore the performance of the most affirmed deep learning approaches, applied to astronomical images obtained by radio interferometric instrumentation, to solve the task of automatic source detection. This is carried out by applying models designed to accomplish two different kinds of tasks: object detection and semantic segmentation. The goal is to provide an overview of existing techniques, in terms of prediction performance and computational efficiency, to scientists in the astrophysics community who would like to employ machine learning in their research
Jets in FR0 radio galaxies
Get PDFThe local radio-loud AGN population is dominated by compact sources named
FR0s. These sources show features, for example the host type, the mass of the
supermassive black hole (SMBH), and the multi-band nuclear characteristics,
that are similar to those of FRI radio galaxies. However, in the radio band,
while FR0 and FRI share the same nuclear properties, the kiloparsec-scale
diffuse component dominant in FRI is missing in FR0s. With this project we
would like to study the parsec-scale structure in FR0s in comparison with that
of FRI sources. To this end we observed 18 FR0 galaxies with the VLBA at 1.5
and 5 GHz and/or with the EVN at 1.7 GHz and produced detailed images at
milliarcsec resolution of their nuclear emission to study the jet and core
structure. All sources have been detected but one. Four sources are unresolved,
even in these high-resolution images; jets have been detected in all other
sources. We derived the distribution of the jet-to-counter-jet ratio of FR0s
and found that it is significantly different from that of FRIs, suggesting
different jet bulk speed velocities. Combining the present data with published
data of FR0 with VLBI observations, we derive that the radio structure of FR0
galaxies shows strong evidence that parsec-scale jets in FR0 sources are mildly
relativistic with a bulk velocity on the order of 0.5c or less. A jet structure
with a thin inner relativistic spine surrounded by a low-velocity sheath could
be in agreement with the SMBH and jet launch region properties
Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
Get PDFWe present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (∼150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude (Mi ∼ −16.7 mag), and the r-band decline rate of ∼1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only ∼0.1 M⊙, with 56Ni comprising ∼20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns
Magnetic Structures and Turbulence in SN 1006 Revealed with Imaging X-Ray Polarimetry
Get PDFYoung supernova remnants strongly modify the surrounding magnetic fields, which in turn play an essential role in accelerating cosmic rays (CRs). The X-ray polarization measurements probe magnetic field morphology and turbulence at the immediate acceleration site. We report the X-ray polarization distribution in the northeastern shell of SN 1006 from a 1 Ms observation with the Imaging X-ray Polarimetry Explorer. We found an average polarization degree of 22.4% ± 3.5% and an average polarization angle of -45.°4 ± 4.°5 (measured on the plane of the sky from north to east). The X-ray polarization angle distribution reveals that the magnetic fields immediately behind the shock in the northeastern shell of SN 1006 are nearly parallel to the shock normal or radially distributed, similar to that in the radio observations, and consistent with the quasi-parallel CR acceleration scenario. The X-ray emission is marginally more polarized than that in the radio band. The X-ray polarization degree of SN 1006 is much larger than that in Cas A and Tycho, together with the relatively tenuous and smooth ambient medium of the remnant, favoring that CR-induced instabilities set the magnetic turbulence in SN 1006, and CR acceleration is environment-dependent
Discovery of X-ray polarization angle rotation in the jet from blazar Mrk 421
Get PDFThe magnetic-field conditions in astrophysical relativistic jets can be probed by multiwavelength polarimetry, which has been recently extended to X-rays. For example, one can track how the magnetic field changes in the flow of the radiating particles by observing rotations of the electric vector position angle Ψ. Here we report the discovery of a ΨX rotation in the X-ray band in the blazar Markarian 421 at an average flux state. Across the 5 days of Imaging X-ray Polarimetry Explorer observations on 4-6 and 7-9 June 2022, ΨX rotated in total by ≥360°. Over the two respective date ranges, we find constant, within uncertainties, rotation rates (80 ± 9° per day and 91 ± 8° per day) and polarization degrees (ΠX = 10% ± 1%). Simulations of a random walk of the polarization vector indicate that it is unlikely that such rotation(s) are produced by a stochastic process. The X-ray-emitting site does not completely overlap the radio, infrared and optical emission sites, as no similar rotation of Ψ was observed in quasi-simultaneous data at longer wavelengths. We propose that the observed rotation was caused by a helical magnetic structure in the jet, illuminated in the X-rays by a localized shock propagating along this helix. The optically emitting region probably lies in a sheath surrounding an inner spine where the X-ray radiation is released
The Global Mapping of Mercury’s Surface From SIMBIO-SYS Onboard BepiColombo: VIS-NIR Hyperspectral Coverage by the VIHI Channel
Get PDFOne of the main goals of SIMBIO-SYS, the Spectrometer and Imagers for Mercury Planet Orbiter (MPO) BepiColombo (BC)-Integrated Observatory SYStem, on board ESA's BC mission is to image the entire surface of Mercury. During the first year of operations, the visible and infrared hyperspectral imager (VIHI), one of the three optical channels of SIMBIO-SYS, will be used in accordance with the scientific requirements of the mission, to build a global map of the planet in the spectral range 0.4- with a spectral sampling of 12.5 nm/band and a spatial resolution of 400 m/px. This map will be employed to derive mineralogy and surface regolith physical properties by means of spectrophotometric analyses. For the purpose of reaching this goal, a deterministic method able to predict the best GM strategy for VIHI in terms of time sequences, coverage, spatial sampling, integration/repetition times, signal-to-noise ratio (SNR) optimization, and data redundancy is discussed. Starting from these criteria, the determination of the timeline containing the sequence of the instrumental telecommands is derived from the orbital kernels of the spacecraft and within the limitation of the allocated data volume which poses strict operational constraints on the data generation and redundancy
A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star
Get PDFCarbon is an essential element for life but how much can be delivered to young planets is still an open question. The chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. Very low-mass stars (less than 0.2 M⊙) are interesting targets because they host a rich population of terrestrial planets. Here we present the James Webb Space Telescope detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the Mid-InfraRed Instrument mid-INfrared Disk Survey (MINDS). In addition to very strong and broad emission from C2H2 and its 13C12CH2 isotopologue, C4H2, benzene and possibly CH4 are identified, but water, polycyclic aromatic hydrocarbons and silicate features are weak or absent. The lack of small silicate grains indicates that we can look deep down into this disk. These detections testify to an active warm hydrocarbon chemistry with a high C/O ratio larger than unity in the inner 0.1 astronomical units (AU) of this disk, perhaps due to destruction of carbonaceous grains. The exceptionally high C2H2/CO2 and C2H2/H2O column density ratios indicate that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. This, in turn, will have important consequences for the composition of forming exoplanets
Diffusive shock acceleration at EeV and associated multimessenger flux from ultra-fast outflows driven by active galactic nuclei
Get PDFActive galactic nuclei (AGN) can launch and sustain powerful winds featuring mildly relativistic velocity and wide opening angle. Such winds, known as ultra-fast outflows (UFOs), can develop a bubble structure characterized by a forward shock expanding in the host galaxy and a wind termination shock separating the fast, cool wind from the hot shocked wind. In this work, we explore whether diffusive shock acceleration can take place efficiently at the wind termination shock of UFOs. We calculate the spectrum of accelerated particles and find that protons can be energized up to the EeV range promoting UFOs to promising candidates for accelerating ultra-high energy cosmic rays (UHECRs). We also compute the associated gamma-ray and neutrino fluxes and compare them with available data in the literature. We observe that high-energy (HE) neutrinos are efficiently produced up to hundreds of PeV while the associated gamma rays could be efficiently absorbed beyond a few tens of GeV by the optical-ultraviolet AGN photon field. By assuming a typical source density of non-jetted AGN, we expect that UFOs could play a dominant role as diffuse sources of UHECRs and HE neutrinos. We finally apply our model to the recently observed NGC1068 and we find out that under specific parametric conditions an obscured UFO could provide a sizeable contribution to the observed gamma-ray flux while only contributing up to ∼10 per cent to the associated neutrino flux