OA@INAF - Istituto Nazionale di Astrofisica
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The ratio of [Eu/α] differentiates accreted/in situ Milky Way stars across metallicities, as indicated by both field stars and globular clusters
Get PDFWe combine stellar orbits with the abundances of the heavy, -process element europium and the light, -element, silicon to
separate in-situ and accreted populations in the Milky Way across all metallicities. At high orbital energy, the accretion-dominated
halo shows elevated values of [Eu/Si], while at lower energies, where many of the stars were born in-situ, the levels of [Eu/Si]
are lower. These systematically different levels of [Eu/Si] in the MW and the accreted halo imply that the scatter in [Eu/] within
a single galaxy is smaller than previously thought. At the lowest metallicities, we find that both accreted and in-situ populations
trend down in [Eu/Si], consistent with enrichment via neutron star mergers. Through compiling a large dataset of abundances
for 54 globular clusters (GCs), we show that differences in [Eu/Si] extend to populations of in-situ/accreted GCs. We interpret
this consistency as evidence that in -process elements GCs trace the star formation history of their hosts, motivating their use
as sub-Gyr timers of galactic evolution. Furthermore, fitting the trends in [Eu/Si] using a simple galactic chemical evolution
model, we find that differences in [Eu/Si] between accreted and in-situ MW field stars cannot be explained through star formation
efficiency alone. Finally, we show that the use of [Eu/Si] as a chemical tag between GCs and their host galaxies extends beyond
the Local Group, to the halo of M31 - potentially offering the opportunity to do Galactic Archaeology in an external galaxy
Discovery of a Shock-compressed Magnetic Field in the Northwestern Rim of the Young Supernova Remnant RX J1713.7–3946 with X-Ray Polarimetry
Get PDFSupernova remnants (SNRs) provide insights into cosmic-ray acceleration and magnetic field dynamics at shock fronts. Recent X-ray polarimetric measurements by the Imaging X-ray Polarimetry Explorer (IXPE) have revealed radial magnetic fields near particle acceleration sites in young SNRs, including Cassiopeia A, Tycho, and SN 1006. We present here the spatially resolved IXPE X-ray polarimetric observation of the northwestern rim of SNR RX J1713.7–3946. For the first time, our analysis shows that the magnetic field in the particle acceleration sites of this SNR is oriented tangentially with respect to the shock front. Because of the lack of precise Faraday rotation measurements in the radio band, this was not possible before. The average measured polarization degree (PD) of the synchrotron emission is 12.5% ± 3.3%, lower than the one measured by IXPE in SN 1006, comparable to the Tycho one, but notably higher than the one in Cassiopeia A. On subparsec scales, localized patches within RX J1713.7–3946 display a PD of up to 41.5% ± 9.5%. These results are compatible with a shock-compressed magnetic field. However, in order to explain the observed PD, either the presence of a radial net magnetic field upstream of the shock or partial reisotropization of the turbulence downstream by radial magnetohydrodynamical instabilities can be invoked. From comparison of PD and magnetic field distribution with γ-rays and 12CO data, our results provide new inputs in favor of a leptonic origin of the γ-ray emission
Seven-year periodic variations in the methanol maser line displayed by the massive protostar IRAS 20216+4104
Get PDFAims. We report the discovery and analysis of a periodic methanol maser in the massive protostar IRAS 20216+4104. Methods. To obtain the light curve, we used the 6.7 GHz methanol maser spectra collected between 2000–2003 and 2009–2023 with the Hartebeesthoek and Torun radio telescopes, as well as spectra from the literature reported prior to 1992. Results. The velocity-integrated flux density shows sinusoidal-like variations with a period of 6.9±0.03 yr. All but one of the features show periodic changes with a relative amplitude of 2 up to >89. A slightly variable feature displays a moderate anti-correlation between the flux density and the other significantly variable features. The maser emission appears to follow the continuum emission of the red-shifted outflow cavity. A maximum emission of 3.4 and 4.6 µm precedes the maser peak by 15% of the period and the (infrared) IR light centroids show time-dependent displacement. The periodic behaviour of the maser and IR emission is likely due to the eclipsing effect from a wobbling inner disk
Maser polarization through anisotropic pumping
Get PDFContext. Polarized emission from masers is an excellent tool to study magnetic fields in maser sources. The linear polarization of the majority of masers is understood as an interplay of maser saturation and anisotropic pumping. However, for the latter mechanism, no quantitative modeling has been presented yet. Aims. We aim to construct a comprehensive model of maser polarization, including quantitative modeling of both anisotropic pumping and the effects of maser saturation on the polarization of masers. Methods. We extended regular (isotropic) maser excitation modeling with a dimension that describes the molecular population alignments, as well as including the linear polarization dimension to the radiative transfer. The results of the excitation analysis yielded the anisotropic pumping and decay parameters, which were subsequently used in one-dimensional proper maser polarization radiative transfer modeling. Results. We present the anisotropic pumping parameters for a variety of transitions from class I CH3OH masers, H2O masers, and SiO masers. SiO masers are highly anisotropically pumped due to them occurring in the vicinity of a late-type star, which irradiates the maser region with a strong directional radiation field. Class I CH3OH masers and H2O masers occur in association with shocks, and they are modestly anisotropically pumped due to the anisotropy of the excitation region. Conclusions. Our modeling constitutes the first quantitative constraints on the anisotropic pumping of masers. We find that anisotropic pumping can explain the high polarization yields of SiO masers, as well as the modest polarization of unsaturated class I CH3OH masers. The common 22 GHz H2O maser has a relatively weak anisotropic pumping; in contrast, we predict that the 183 GHz H2O maser is strongly anisotropically pumped. Finally, we outline a mechanism through which non-Zeeman circular polarization is produced, when the magnetic field changes direction along the propagation through an anisotropically pumped maser
LeMMINGs. Multiwavelength constraints on the co-existence of nuclear star clusters and AGN in nucleated galaxies
Get PDFThe relation between nuclear star clusters (NSCs) and the growth of the central supermassive black holes (SMBHs), as well as their connection to the properties of the host galaxies, is crucial for understanding the evolution of galaxies. Recent observations have revealed that about 10 per cent of nucleated galaxies host hybrid nuclei, consisting of both NSCs and accreting SMBHs that power active galactic nuclei (AGNs). Motivated by the potential of the recently published multiwavelength data sets from LeMMINGs survey, here we present the most thorough investigation to date of the incidence of hybrid nuclei in a large sample of 100 nearby nucleated galaxies (10 E, 25 S0, 63 S, and 2 Irr), covering a wide range in stellar mass (M∗,gal ∼ 108.7 - 1012 M☉). We identify the nuclei and derive their properties by performing detailed 1D and 2D multicomponent decompositions of the optical and near-infrared HST stellar light distributions of the galaxies using Sérsic and core-Sérsic models. Our AGN diagnostics are based on homogeneously derived nuclear 1.5 GHz e-MERLIN radio, Chandra X-ray (0.3–10 keV), and optical emission-line data. We determine the nucleation fraction (fnuc) as the relative incidence of nuclei across the LeMMINGs HST sample and find fnuc = 100/149 (= 67 ± 7 per cent), confirming previous work, with a peak value of 49/56 (= 88 ± 13 per cent) at bulge masses M∗,bulge ∼ 109.4 - 1010.8 M☉. We identify 30 nucleated LeMMINGs galaxies that are optically active, radio-detected, and X-ray luminous (LX > 1039 erg s-1). This indicates that our nucleated sample has a lower limit ∼ 30 per cent occupancy of hybrid nuclei, which is a function of M∗,bulge and M∗,gal. We find that hybrid nuclei have a number density of (1.5 ± 0.4) × 10-5 Mpc-3, are more common at M∗,gal ∼ 1010.6 - 1011.8 M☉ and occur, at least, three times more frequently than previously reported
Can the splashback radius be an observable boundary of galaxy clusters?
Get PDFThe splashback radius was proposed as a physically motivated boundary of
clusters as it sets the limit between the infalling and the orbitally dominated
regions. However, galaxy clusters are complex objects connected to filaments of
the cosmic web from which they accrete matter that disturbs them and modifies
their morphology. In this context, estimating the splashback radius and the
cluster boundary becomes challenging. In this work, we use a constrained
hydrodynamical simulation of the Virgo cluster's replica embedded in its
large-scale structure to investigate the impact of its local environment on the
splashback radius estimate. We identify the splashback radius from 3D radial
profiles of dark matter density, baryons density, and pressure in three regions
representative of different dynamical states: accretion from spherical
collapse, filaments, and matter outflow. We also identify the splashback radius
from 2D-projected radial profiles of observation-like quantities: mass surface
density, emission measure, and Compton-y. We show that the splashback radius
mainly depends on the dynamics in each region and the physical processes traced
by the different probes. We find multiple values for the splashback radius
ranging from 3.30.2 to 5.50.3 Mpc. Particularly, in the regions of
collapsing and outflowing material, the splashback radii estimated from baryon
density and pressure radial profiles overestimate that of the dark matter
density profiles, which is considered the reference value originally defined
from dark matter simulations. Consequently, caution is required when using the
splashback radius as a boundary of clusters, particularly in the case of highly
disturbed clusters like Virgo. We also discuss the detection of the splashback
radius from pressure radial profiles, which could be more related to an
accretion shock, and its detection from stacked radial profiles
An Eddington-limited Accretion Disk Wind in the Narrow-line Seyfert 1 PG 1448+273
Get PDFPG 1448+273 is a luminous, nearby (z = 0.0645), narrow-line Seyfert 1 galaxy, which likely accretes close to the Eddington limit. Previous X-ray observations of PG 1448+273 with XMM-Newton in 2017 and NuSTAR in 2022 revealed the presence of an ultrafast outflow, as seen through its blueshifted iron (Fe) K absorption profile, where the outflow velocity appeared to vary in the range 0.1‑0.3c. In this work, new X-ray observations of PG 1448+273 are presented, in the form of four simultaneous XMM-Newton and NuSTAR observations performed in 2023 July and August. The X-ray spectra appeared at a similar flux in each observation, making it possible to analyze the mean 2023 X-ray spectrum at high signal-to-noise ratio. A broad (σ = 1 keV) and highly blueshifted (E = 9.8 ± 0.4 keV) Fe K absorption profile is revealed in the mean spectrum. The profile can be modeled by a fast, geometrically thick accretion disk wind, which reveals a maximum terminal velocity of v ∞ = ‑0.43 ± 0.03c, one of the fastest known winds in a nearby active galactic nucleus. As a result, the inferred mass outflow rate of the wind may reach a significant fraction of the Eddington accretion rate
The Gaia-ESO Survey: 3D dynamics of young groups and clusters from GES and Gaia EDR3
Get PDFWe present the first large-scale 3D kinematic study of ∼2700 spectroscopically confirmed young stars (<20 Myr) in 18 star clusters and OB associations (hereafter groups) from the combination of Gaia astrometry and Gaia–ESO Survey spectroscopy. We measure 3D velocity dispersions for all groups, which range from 0.61 to 7.4 km s−1 (1D velocity dispersions of 0.35–4.3 km s−1). We find the majority of groups have anisotropic velocity dispersions, suggesting they are not dynamically relaxed. From the 3D velocity dispersions, measured radii, and estimates of total mass, we estimate the virial state and find that all systems are super-virial when only the stellar mass is considered, but that some systems are sub-virial when the mass of the molecular cloud is taken into account. We observe an approximately linear correlation between the 3D velocity dispersion and the group mass, which would imply that the virial state of groups scales as the square root of the group mass. However, we do not observe a strong correlation between virial state and group mass. In agreement with their virial state, we find that nearly all of the groups studied are in the process of expanding and that the expansion is anisotropic, implying that groups were not spherical prior to expansion. One group, Rho Oph, is found to be contracting and in a sub-virial state (when the mass of the surrounding molecular cloud is considered). This work provides a glimpse of the potential of the combination of Gaia and data from the next generation of spectroscopic surveys
Evidence for transient morning water frost deposits on the Tharsis volcanoes of Mars
Get PDFThe present-day water cycle on Mars has implications for habitability and future human exploration. Water ice clouds and water vapour have been detected above the Tharsis volcanic province, suggesting the active exchange of water between regolith and atmosphere. Here we report observational evidence for extensive transient morning frost deposits on the calderas of the Tharsis volcanoes (Olympus, Arsia and Ascraeus Montes, and Ceraunius Tholus) using high-resolution colour images from the Colour and Stereo Surface Imaging System on board the European Space Agency's Trace Gas Orbiter. The transient bluish deposits appear on the caldera floor and rim in the morning during the colder Martian seasons but are not present by afternoon. The presence of water frost is supported by spectral observations, as well as independent imagery from the European Space Agency's Mars Express orbiter. Climate model simulations further suggest that early-morning surface temperatures at the high altitudes of the volcano calderas are sufficiently low to support the daily condensation of water—but not CO2—frost. Given the unlikely seasonal nature of volcanic outgassing, we suggest the observed frost is atmospheric in origin, implying the role of microclimate in local frost formation and a contribution to the broader Mars water cycle
Massive stars exploding in a He-rich circumstellar medium: X. Flash spectral features in the Type Ibn SN 2019cj and observations of SN 2018jmt
Get PDFWe present optical and near-infrared observations of two Type Ibn supernovae (SNe), SN 2018jmt and SN 2019cj. Their light curves have rise times of about ten days, reaching an absolute peak magnitude of Mg(SN 2018jmt) = - 19.07 ± 0.37 and MV(SN 2019cj) = - 18.94 ± 0.19 mag, respectively. The early-time spectra of SN 2018jmt are dominated by a blue continuum, accompanied by narrow (600- 1000 km s- 1) HeI lines with the P-Cygni profile. At later epochs, the spectra become more similar to those of the prototypical SN Ibn 2006jc. At early phases, the spectra of SN 2019cj show flash ionisation emission lines of CIII, NIII, and HeII superposed on a blue continuum. These features disappear after a few days, and then the spectra of SN 2019cj evolve similarly to those of SN 2018jmt. The spectra indicate that the two SNe exploded within a He-rich circumstellar medium (CSM) lost by the progenitors a short time before the explosion. We modelled the light curves of the two SNe Ibn to constrain the progenitor and the explosion parameters. The ejecta masses are consistent with either what is expected for a canonical SN Ib (~2 M⊙) or for a massive Wolf Rayet star (> ~4 M⊙), with the kinetic energy on the order of 1051 erg. The lower limit on the ejecta mass (> ~2 M⊙) argues against a scenario involving a relatively low-mass progenitor (e.g. MZAMS ~ 10 M⊙). We set a conservative upper limit of ~0.1 M⊙ for the 56Ni masses in both SNe. From the light curve modelling, we determined a two-zone CSM distribution, with an inner, flat CSM component and an outer CSM with a steeper density profile. The physical properties of SN 2018jmt and SN 2019cj are consistent with those expected from the core collapse of relatively massive envelope-stripped stars