OA@INAF - Istituto Nazionale di Astrofisica
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The Advanced Virgo+ status
Get PDFThe gravitational wave detector Advanced Virgo+ is currently in the commissioning phase in view of the fourth Observing Run (O4)
Measuring the photoionization rate, neutral fraction, and mean free path of H I ionizing photons at 4.9 ≤ z ≤ 6.0 from a large sample of XShooter and ESI spectra
Get PDFWe measure the mean free path (), photoionization rate (), and neutral fraction () of hydrogen in 12 redshift bins at 4.85 4, respectively from z ~ 5 to z ~ 6. By comparing our , and evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ~ 5.2. Our best-fitting model that matches the distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters
Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6
Get PDFThe mean free path of ionizing photons, λ mfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of λ mfp from QSO spectra over the redshift range 5 mfp increases steadily and rapidly with time over 5 mfp deviates significantly from predictions based on a fully ionized and relaxed IGM as late as z = 5.3. By comparing our results to model predictions and indirect λ mfp constraints based on IGM Lyα opacity, we find that the evolution of λ mfp is consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6
The Radial Distribution and Excitation of H<SUB>2</SUB> around Young Stars in the HST-ULLYSES Survey
Get PDFThe spatial distribution and evolution of gas in the inner 10 au of protoplanetary disks form the basis for estimating the initial conditions of planet formation. Among the most important constraints derived from spectroscopic observations of the inner disk are the radial distributions of the major gas phase constituents, how the properties of the gas change with inner disk dust evolution, and how the chemical abundances and excitation conditions are influenced by the high-energy radiation from the central star. We present a survey of the radial distribution, excitation, and evolution of inner disk molecular hydrogen (H2) obtained as part of the Hubble Space Telescope-ULLYSES program. We analyze far-UV spectroscopy of 71 (63 accreting) pre-main-sequence systems in ULLYSES DR5 to characterize the H2 emission lines, H2 dissociation continuum emission, and major photochemical/disk evolution driving the UV emissions (Lyα, UV continuum, and C IV). We use the widths of the H2 emission lines to show that most fluorescent H2 arises between 0.1 and 1.4 au from the parent star, and show positive correlations of the average emitting radius with the accretion luminosity and with the dust disk mass. We find a strong correlation between H2 dissociation emission and both the accretion-dominated Lyα luminosity and the inner disk dust clearing, painting a picture where water molecules in the inner 3 au are exposed to and dissociated by strong Lyα emission as the opacity of the inner disk declines with time
First Constraints on Dense Molecular Gas at z = 7.5149 from the Quasar Pōniuā‘ena
Get PDFWe report the detection of CO(6-5) and CO(7-6) and their underlying continua from the host galaxy of quasar J100758.264+211529.207 (Pōniuā‘ena) at z = 7.5149, obtained with the NOrthern Extended Millimeter Array. Pōniuā‘ena belongs to the HYPerluminous quasars at the Epoch of ReionizatION sample of 18 z > 6 quasars selected to be powered by supermassive black holes, which experienced the fastest mass growth in the first cosmic gigayear. The one reported here is the highest-redshift measurement of the cold and dense molecular gas to date. The host galaxy is unresolved, and the line luminosity implies a molecular reservoir of M(H2) = (2.2 ± 0.2) × 1010 M ⊙, assuming a CO spectral line energy distribution typical of high-redshift quasars and a conversion factor α = 0.8 M ⊙ ( K km s − 1 pc 2 ) − 1 . We model the cold dust spectral energy distribution to derive a dust mass of M dust = (1.7 ± 0.6) × 108 M ⊙ and thus, a gas-to-dust ratio ∼130. Both the gas and dust mass are remarkably similar to the reservoirs found for luminous quasars at z ∼ 6-7. We use the CO detection to derive an estimate of the cosmic mass density of H2, Ω H 2 ≃ 1.31 × 10 − 5 . This value is in line with the general trend suggested by literature estimates at z < 7 and agrees fairly well with the latest theoretical expectations of nonequilibrium molecular-chemistry cosmological simulations of cold gas at early times
Evidence of First Stars-enriched Gas in High-redshift Absorbers*
Get PDFThe first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H] +0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z ∼ 3-4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars
Do the early galaxies observed by JWST disagree with Planck's CMB polarization measurements?
Get PDFThe recent observations from the James Webb Space Telescope have led to a surprising discovery of a significant density of massive galaxies with masses of M ≥ 1010.5 M ⊙ at redshifts of approximately z ∼ 10. This corresponds to a stellar mass density of roughly ρ * ∼ 106 M ⊙ Mpc-3. Despite making conservative assumptions regarding galaxy formation, this finding may not be compatible with the standard ΛCDM cosmology that is favored by observations of CMB Anisotropies from the Planck satellite. In this paper, we confirm the substantial discrepancy with Planck's results within the ΛCDM framework. Assuming a value of ϵ = 0.2 for the efficiency of converting baryons into stars, we indeed find that the ΛCDM model is excluded at more than 99.7 % confidence level (C.L.). An even more significant exclusion is found for ϵ ∼ 0.1, while a better agreement, but still in tension at more than 95 %, is obtained for ϵ = 0.32. This tension, as already discussed in the literature, could arise either from systematics in the JWST measurements or from new physics. Here, as a last-ditch effort, we point out that disregarding the large angular scale polarization obtained by Planck, which allows for significantly larger values of the matter clustering parameter σ 8, could lead to better agreement between Planck and JWST within the ΛCDM framework. Assuming ΛCDM and no systematics in the current JWST results, this implies either an unknown systematic error in current large angular scale CMB polarization measurements or an unidentified physical mechanism that could lower the expected amount of CMB polarization produced during the epoch of reionization. Interestingly, the model compatible with Planck temperature-only data and JWST observation also favors a higher Hubble constant H 0 = 69.0±1.1 km/s/Mpc at 68% C.L., in better agreement with observations based on SN-Ia luminosity distances
A New Sample of Transient Ultraluminous X-Ray Sources Serendipitously Discovered by Swift/XRT
Get PDFUltraluminous X-ray sources (ULXs) are our best laboratories for studying extreme super-Eddington accretion. Most studies of these objects are of relatively persistent sources; however, there is growing evidence to suggest a large fraction of these sources are transient. Here we present a sample of five newly reported transient ULXs in the galaxies NGC 4945, NGC 7793, and M81 serendipitously discovered in Swift/XRT observations. Swift monitoring of these sources have provided well-sampled lightcurves, allowing for us to model the lightcurves with the disk-instability model of Hameury & Lasota, which implies durations of 60-400 days and that the mass-accretion rate through the disk is close to or greater than the Eddington rate. Of the three source regions with prior Hubble Space Telescope imaging, color-magnitude diagrams of the potential stellar counterparts show varying ages of the possible stellar counterparts. Our estimation of the rates of these sources in these three galaxies is 0.4-1.3 yr−1. We find that, while persistent ULXs dominate the high end of galaxy luminosity functions, the number of systems that produce ULX luminosities are likely dominated by transient sources
Infall and outflow towards high-mass starless clump candidates
Get PDFThe evolutionary sequence for high-mass star formation starts with massive starless clumps that go on to form protostellar, young stellar objects and then compact H II regions. While there are many examples of the three later stages, the very early stages have proved to be elusive. We follow-up a sample of 110 mid-infrared dark clumps selected from the ATLASGAL catalogue with the IRAM telescope in an effort to identify a robust sample of massive starless clumps. We have used the HCO+ and HNC (1-0) transitions to identify clumps associated with infall motion and the SiO (2-1) transition to identity outflow candidates. We have found blue asymmetric line profile in 65 per cent of the sample, and have measured the infall velocities and mass infall rates (0.6-36 × 10-3 M⊙ yr-1) for 33 of these clumps. We find a trend for the mass infall rate decreasing with an increase of bolometric luminosity to clump mass, i.e. star formation within the clumps evolves. Using the SiO 2-1 line, we have identified good outflow candidates. Combining the infall and outflow tracers reveals that 67 per cent of quiescent clumps are already undergoing gravitational collapse or are associated with star formation; these clumps provide us with our best opportunity to determine the initial conditions and study the earliest stages of massive star formation. Finally, we provide an overview of a systematic high-resolution ALMA study of quiescent clumps selected that allows us to develop a detailed understanding of earliest stages and their subsequent evolution
The NuSTAR view of the changing look AGN ESO 323-G77
Get PDFThe presence of an obscuring torus at pc-scale distances from the central
black hole is the main ingredient for the Unified Model of Active Galactic
Nuclei (AGN), as obscured sources are thought to be seen through this
structure. However, the Unified Model fails to describe a class of sources that
undergo dramatic spectral changes, transitioning from obscured to unobscured
and vice-versa through time. The variability in such sources, so-called
Changing Look AGN (CLAGN), is thought to be produced by a clumpy medium at much
smaller distances than the conventional obscuring torus. ESO 323-G77 is a CLAGN
that was observed in various states through the years with Chandra, Suzaku,
Swift-XRT and XMM-Newton, from unobscured (
cm) to Compton-thin ( cm) and even
Compton-thick ( cm), with timescales as short
as one month. We present the analysis of the first NuSTAR monitoring of ESO
323-G77, consisting of 5 observations taken at different timescales (1, 2, 4
and 8 weeks from the first one) in 2016-2017, in which the AGN was caught in a
persistent Compton-thin obscured state (
cm). We find that a Compton-thick reflector is present ( cm), most likely associated with the presence of
the putative torus. Two ionized absorbers are unequivocally present, located
within maximum radii of pc and pc. In
one of the observations, the inner ionized absorber is blueshifted, indicating
the presence of a possible faster () ionized absorber,
marginally detected at . Finally, we are able to constrain the coronal
temperature and the optical depth of ESO 323-G77, obtaining keV or
keV, and or , depending on the coronal geometry
assumed