Extrasolar satellites are generally too small to be detected by nominal searches. By analogy to the most active body in the solar system, Io, we describe how sodium (Na i) and potassium (K i) gas ...could be a signature of the geological activity venting from an otherwise hidden exo-Io. Analyzing ∼a dozen close-in gas giants hosting robust alkaline detections, we show that an Io-sized satellite can be stable against orbital decay below a planetary tidal . This tidal energy is also focused into the satellite driving an ∼105 2 higher mass-loss rate than Io's supply to Jupiter's Na exosphere based on simple atmospheric loss estimates. The remarkable consequence is that several exo-Io column densities are, on average, more than sufficient to provide the ∼1010 1 Na cm−2 required by the equivalent width of exoplanet transmission spectra. Furthermore, the benchmark observations of both Jupiter's extended (∼1000 RJ) Na exosphere and Jupiter's atmosphere in transmission spectroscopy yield similar Na column densities that are purely exogenic in nature. As a proof of concept, we fit the "high-altitude" Na at WASP-49b with an ionization-limited cloud similar to the observed Na profile about Io. Moving forward, we strongly encourage time-dependent ingress and egress monitoring along with spectroscopic searches for other volcanic volatiles.
Abstract
The ratio of
α
-elements to iron in galaxies holds valuable information about the star formation history (SFH) since their enrichment occurs on different timescales. The fossil record of ...stars in galaxies has mostly been excavated for passive galaxies, since the light of star-forming galaxies is dominated by young stars, which have much weaker atmospheric absorption features. Here we use the largest reference cosmological simulation of the EAGLE project to investigate the origin of variations in stellar
α
-enhancement among star-forming galaxies at
z
= 0, and their impact on integrated spectra. The definition of
α
-enhancement in a composite stellar population is ambiguous. We elucidate two definitions—termed “mean” and “galactic”
α
-enhancement—in more detail. While a star-forming galaxy has a high “mean”
α
-enhancement when its stars formed rapidly, a galaxy with a large “galactic”
α
-enhancement generally had a delayed SFH. We find that absorption-line strengths of Mg and Fe correlate with variations in
α
-enhancement. These correlations are strongest for the “galactic”
α
-enhancement. However, we show that these are mostly caused by other effects that are cross-correlated with
α
-enhancement, such as variations in the light-weighted age. This severely complicates the retrieval of
α
-enhancements in star-forming galaxies. The ambiguity is not severe for passive galaxies, and we confirm that spectral variations in these galaxies are caused by measurable variations in
α
-enhancements. We suggest that this more complex coupling between
α
-enhancement and SFHs can guide the interpretation of new observations of star-forming galaxies.
ABSTRACT
Hydrostatic equilibrium is an excellent approximation for the dense layers of planetary atmospheres, where it has been canonically used to interpret transmission spectra of exoplanets. Here, ...we exploit the ability of high-resolution spectrographs to probe tenuous layers of sodium and potassium gas due to their formidable absorption cross-sections. We present an atmosphere–exosphere degeneracy between optically thick and optically thin mediums, raising the question of whether hydrostatic equilibrium is appropriate for Na i lines observed at exoplanets. To this end we simulate three non-hydrostatic, evaporative, density profiles: (i) escaping, (ii) exomoon, and (iii) torus to examine their imprint on an alkaline exosphere in transmission. By analysing an evaporative curve of growth, we find that equivalent widths of $W_{\mathrm{Na D2}} \sim 1{\!-\!} 10\, \mathrm{m\mathring{\rm A}}$ are naturally driven by evaporation rates ∼103−105 kg s−1 of pure atomic Na. To break the degeneracy between atmospheric and exospheric absorption, we find that if the line ratio is D2/D1 ≳ 1.2 the gas is optically thin on average roughly indicating a non-hydrostatic structure of the atmosphere/exosphere. We show this is the case for Na i observations at hot Jupiters WASP-49b and HD189733b and also simulate their K i spectra. Lastly, motivated by the slew of metal detections at ultra-hot Jupiters, we suggest a toroidal atmosphere at WASP-76b and WASP-121b is consistent with the Na i data at present.
The many colours of the TNG100 simulation Gebek, Andrea; Trčka, Ana; Baes, Maarten ...
Monthly Notices of the Royal Astronomical Society,
06/2024, Letnik:
531, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We apply the 3D dust radiative transfer code skirt to the low-redshift (z ≤ 0.1) galaxy population in the TNG100 cosmological simulation, the fiducial run of the IllustrisTNG project. We ...compute global fluxes and spectral energy distributions (SEDs) from the far-ultraviolet to the submillimetre for $\approx 60\, 000$ galaxies, with the same post-processing methodology that was previously applied to the TNG50 simulation. We verify that TNG100 reproduces observational luminosity functions at low redshifts to excellent precision, unlike TNG50. Additionally, we test the realism of our TNG100 plus skirt fluxes by comparing various flux and colour relations to data from the GAMA survey. TNG100 broadly reproduces the observed distributions, but we predict ultraviolet colours that are too blue by $\approx 0.4\, \mathrm{mag}$, possibly related to the extinction in the star-forming regions subgrid model not being selective enough. Furthermore, we find that the simulated galaxies exhibit mid-infrared fluxes elevated by up to $\approx 0.5\, \mathrm{mag}$ that we attribute to overly effective stochastic heating of the diffuse dust. All synthetic broad-band fluxes and SEDs are made publicly available in three orientations and four apertures, and can readily be used to study TNG100 galaxies in a mock observational fashion.
ABSTRACT
Cold gas in galaxies provides a crucial test to evaluate the realism of cosmological hydrodynamical simulations. To extract the atomic and molecular hydrogen properties of the simulated ...galaxy population, post-processing methods taking the local UV field into account are required. We improve upon previous studies by calculating realistic UV fields with the dust radiative transfer code SKIRT to model the atomic-to-molecular transition in TNG50, the highest-resolution run of the IllustrisTNG suite. Comparing integrated quantities such as the H i mass function, we study to what detail the UV field needs to be modelled in order to calculate realistic cold gas properties. We then evaluate new, spatially resolved comparisons for cold gas in galaxies by exploring synthetic maps of atomic hydrogen at redshift zero and compare them to 21-cm observations of local galaxies from the WHISP survey. In terms of non-parametric morphologies, we find that TNG50 H i maps are less concentrated than their WHISP counterparts (median ΔC ≈ 0.3), due in part to central H i deficits related to the ejective character of supermassive black hole feedback in TNG. In terms of the H i column density distribution function, we find discrepancies between WHISP and IllustrisTNG that depend on the total H i abundance in these data sets as well as the post-processing method. To fully exploit the synergy between cosmological simulations and upcoming deep H i/H2 data, we advocate the use of accurate methods to estimate the UV radiation field and to generate mock maps.
ABSTRACT
We present and publicly release a new star-forming regions emission library TODDLERS (Time evolution of Observables including Dust Diagnostics and Line Emission from Regions containing young ...Stars) for the publicly available radiative transfer code SKIRT. The library generation involves the spherical evolution of a homogeneous gas cloud around a young stellar cluster that accounts for stellar feedback processes including stellar winds, supernovae, and radiation pressure, as well as the gravitational forces on the gas. The semi-analytical evolution model is coupled with the photoionization code Cloudy to calculate time-dependent UV–mm spectral energy distributions (SEDs) from star-forming regions of varying metallicity, star-formation efficiency, birth-cloud density, and mass. The calculated SEDs include the stellar, nebular, and dust continuum emission along with a wide range of emission lines originating from H ii, photodissociation, and molecular gas regimes tabulated at high resolution. The SEDs incorporated in SKIRT are generated by calculating a stellar-mass normalized luminosity, which assumes that each emission source is composed of a power-law population of star-forming clouds. When compared to the previous treatment of star-forming regions in SKIRT, TODDLERS shows a better agreement with low-redshift observational data in the IR wavelength range while offering a more comprehensive line-emission support. This paves the way for a variety of applications using simulated galaxies at low and high redshift.
Galaxy sizes correlate with many other important properties of galaxies, and the cosmic evolution of galaxy sizes is an important observational diagnostic for constraining galaxy evolution models. ...The effective radius is probably the most widely used indicator of galaxy size. We used the TNG50-SKIRT Atlas to investigate the wavelength dependence of the effective radius of galaxies at optical and near-infrared (NIR) wavelengths. We find that, on average, the effective radius in every band exceeds the stellar mass effective radius, and that this excess systematically decreases with increasing wavelength. The optical g -band (NIR K s -band) effective radius is on average 58% (13%) larger than the stellar mass effective radius. Effective radii measured from dust-obscured images are systematically larger than those measured from dust-free images, although the effect is limited (8.7% in the g -band, 2.1% in the K s -band). We find that stellar population gradients are the dominant factor (about 80%) in driving the wavelength dependence of the effective radius, and that differential dust attenuation is a secondary factor (20%). Comparing our results to recent observational data, we find offsets in the absolute values of the median effective radii, up to 50% for the population of blue galaxies. We find better agreement in the slope of the wavelength dependence of the effective radius, with red galaxies having a slightly steeper slope than green–blue galaxies. Comparing our effective radii with those of galaxies from the Siena Galaxy Atlas in separate bins in z -band absolute magnitude and g − z colour, we find excellent agreement for the reddest galaxies, but again significant offsets for the blue populations: up to 70% for galaxies around M z = −21.5. This difference in median effective radius for the bluer galaxies is most probably due to intrinsic differences in the morphological structure of observed and TNG50 simulated galaxies. Finally, we find that the median effective radius in any broadband filter increases systematically with decreasing u − r colour and with increasing galaxy stellar mass, total SFR, sSFR, and dust-to-stellar-mass ratio. For the slope of the wavelength dependence of R e , however, there does not seem to be a systematic, monotonic correlation with any of these global properties.
Galaxy morphology is a powerful diagnostic to assess the realism of cosmological hydrodynamical simulations. Determining the morphology of simulated galaxies requires the generation of synthetic ...images through 3D radiative transfer post-processing that properly accounts for different stellar populations and interstellar dust attenuation. We use the SKIRT code to generate the TNG50-SKIRT Atlas, a synthetic UV to near-infrared broadband image atlas for a complete stellar-mass selected sample of 1154 galaxies extracted from the TNG50 cosmological simulation at z = 0. The images have a high spatial resolution (100 pc) and a wide field of view (160 kpc). In addition to the dust-obscured images, we also release dust-free images and physical parameter property maps with matching characteristics. As a sanity check and preview application we discuss the UVJ diagram of the galaxy sample. We investigate the effect of dust attenuation on the UVJ diagram and find that it affects both the star-forming and the quiescent galaxy populations. The quiescent galaxy region is polluted by younger and star-forming highly inclined galaxies, while dust attenuation induces a separation in inclination of the star-forming galaxy population, with low-inclination galaxies remaining at the blue side of the diagram and high-inclination galaxies systematically moving towards the red side. This image atlas can be used for a variety of other applications, including galaxy morphology studies and the investigation of local scaling relations. We publicly release the images and parameter maps, and we invite the community to use them.
The ratio of $\alpha$-elements to iron in galaxies holds valuable information
about the star formation history since their enrichment occurs on different
timescales. The fossil record of stars in ...galaxies has mostly been excavated
for passive galaxies, since the light of star-forming galaxies is dominated by
young stars which have much weaker atmospheric absorption features. Here we use
the largest reference cosmological simulation of the EAGLE project to
investigate the origin of variations in stellar $\alpha$-enhancement among
star-forming galaxies at $z=0$, and their impact on integrated spectra. The
definition of $\alpha$-enhancement in a composite stellar population is
ambiguous. We elucidate two definitions - termed `mean' and `galactic'
$\alpha$-enhancement - in more detail. While a star-forming galaxy has a high
`mean' $\alpha$-enhancement when its stars formed rapidly, a galaxy with a
large `galactic' $\alpha$-enhancement generally had a delayed star formation
history. We find that absorption-line strengths of Mg and Fe correlate with
variations in $\alpha$-enhancement. These correlations are strongest for the
`galactic' $\alpha$-enhancement. However, we show that these are mostly caused
by other effects which are cross-correlated with $\alpha$-enhancement, such as
variations in the light-weighted age. This severely complicates the retrieval
of $\alpha$-enhancements in star-forming galaxies. The ambiguity is not severe
for passive galaxies and we confirm that spectral variations in these galaxies
are caused by measurable variations in $\alpha$-enhancements. We suggest that
this more complex coupling between $\alpha$-enhancement and star formation
histories can guide the interpretation of new observations of star-forming
galaxies.
Hydrostatic equilibrium is an excellent approximation for the dense layers of planetary atmospheres where it has been canonically used to interpret transmission spectra of exoplanets. Here we exploit ...the ability of high-resolution spectrographs to probe tenuous layers of sodium and potassium gas due to their formidable absorption cross-sections. We present an atmosphere-exosphere degeneracy between optically thick and optically thin mediums, raising the question of whether hydrostatic equilibrium is appropriate for Na I lines observed at exoplanets. To this end we simulate three non-hydrostatic, evaporative, density profiles: (i) escaping, (ii) exomoon, and (iii) torus to examine their imprint on an alkaline exosphere in transmission. By analyzing an evaporative curve of growth we find that equivalent widths of \(W_{\mathrm{Na D2}} \sim 1- 10\) mA are naturally driven by evaporation rates \(\sim 10^3 - 10^5\) kg/s of pure atomic Na. To break the degeneracy between atmospheric and exospheric absorption, we suggest that if the line ratio is \(\mathrm{D2/D1} \gtrsim 1.2\) the gas is optically thin on average and roughly indicating a non-hydrostatic structure of the atmosphere/exosphere. We show this is the case for Na I observations at hot Jupiters WASP-49b and HD189733b and also simulate their K I spectra. Lastly, motivated by the slew of metal detections at ultra-hot Jupiters, we suggest a toroidal atmosphere at WASP-76b and WASP-121b is consistent with the Na I data at present.
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