Space Telescope Research Articles

Constraining z lesssim 2 ultraviolet emission with the upcoming ULTRASAT satellite

The extragalactic background light (EBL) carries a huge astrophysical and cosmological content. Its frequency spectrum and redshift evolution are determined by the integrated emission of unresolved sources, with these being galaxies, active galactic nuclei, or more exotic components. The near-UV region of the EBL spectrum is currently not well constrained, yet a significant improvement can be expected thanks to the soon-to-be launched Ultraviolet Transient Astronomy Satellite (ULTRASAT). Intended to study transient events in the 2300-2900\ band, this detector will provide wide field maps tracing the UV intensity fluctuations at the largest scales. In this paper, we suggest how to exploit the ULTRASAT full-sky map as well as its low-cadence survey in order to reconstruct the redshift evolution of the UV-EBL volume emissivity. We build upon the work of Chiang et al.\ (2019), who used the clustering-based redshift (CBR) technique to study diffuse light maps from GALEX. Their results showed the capability of the cross correlation between GALEX and SDSS spectroscopic catalogs in constraining UV emissivity, highlighting how CBR is sensitive only to extragalactic emissions, avoiding foregrounds and Galactic contributions. In our analysis, we introduce a framework to forecast the CBR constraining power when applied to ULTRASAT and GALEX in cross correlation with the five-year DESI spectroscopic survey. We show that these will yield a strong improvement in the measurement of the UV-EBL volume emissivity. For $ continuum below $z 2$, we forecast a $1 uncertainty $ 26<!PCT!>\,(9<!PCT!>)$ with conservative (optimistic) bias priors using the ULTRASAT full-sky map. Similar constraints can be obtained from its low-cadence survey, which will provide a smaller but deeper map. Finally, we discuss how these results will foster our understanding of UV-EBL models.

Toward an Auditory Virtual Observatory

The large ecosystem of observations generated by major space telescope missions can be remotely analyzed using interoperable virtual observatory technologies. In this context of astronomical big data analysis, sonification has the potential of adding a complementary dimension to visualization, enhancing the accessibility of the archives, and offering an alternative strategy to be used when overlapping issues are found in purely graphical representations. This article presents a collection of sonification and musification prototypes that explore the case studies of the MILES and STELIB stellar libraries from the Spanish Virtual Observatory and the Kepler and TESS light curve databases from the Space Telescope Science Institute archive. Using automation and deep learning algorithms, it offers a “palette” of resources that could be used in future developments oriented toward an auditory virtual observatory proposal. The work includes a user study with quantitative and qualitative feedback from specialized and nonspecialized users analyzing the use of sine waves and musical instrument mappings for revealing overlapped lines in galaxy transmission spectra, confirming the need for training and prior knowledge for the correct interpretation of accurate sonifications, and providing potential guidelines to inspire future designs of widely accepted auditory representations for outreach purposes.

Radio Emission from High-redshift Active Galactic Nuclei in the JADES and CEERS Surveys

Recent calculations indicate that radio emission from quasars at z ∼ 6–7 could be detected at much earlier stages of evolution, at z ∼ 14–15, by the Next-Generation Very Large Array (ngVLA) and the Square Kilometer Array (SKA). However, the James Webb Space Telescope has now discovered less luminous active galactic nuclei (AGNs) at z > 4 and a few massive black holes (BHs) at z > 10, which may be the progenitors of supermassive black holes (SMBHs) but at different stages of growth. Radio detections of these new AGNs would provide complementary measures of their properties and those of their host galaxies. Here we estimate radio flux densities for 19 new AGNs found by the JADES, CEERS, and UNCOVER surveys. We find that ngVLA should be able to detect most of these sources in targeted surveys with integration times of 10–100 hr (and in just 1 hr for a few of them) but most would require at least 100 hr of SKA time in spite of its greater sensitivities at low frequencies. In some cases, radio emission from the BH can be distinguished from that of H ii regions and supernovae in their host galaxies, which could be used to estimate their star formation rates. Such detections would be yet another example of the useful synergies between near-infrared and radio telescopes in SMBH science in the coming decade.

Growing a nuclear star cluster from star formation and cluster mergers: The JWST NIRSpec view of NGC 4654

We present a detailed study of the centre of NGC\,4654, a Milky Way-like spiral galaxy in the Virgo cluster that has been reported to host a double stellar nucleus, thus promising a rare view of ongoing star cluster infall into a galaxy nucleus. Analysing JWST NIRSpec integral-field spectroscopic data in combination with Hubble Space Telescope Wide Field Camera 3 imaging of the inner 330 times 330 pc, we find that the NGC\,4645 nucleus is in fact more complex than previously thought, harbouring three massive star clusters within 32 pc of the centre. Maps of infrared emission lines in the NIRSpec spectra show different morphologies for the ionised and molecular gas components. The emission from molecular hydrogen gas is concentrated at the nuclear star cluster (NSC) location, while emission from hydrogen recombination lines is more extended beyond the central cluster. The velocity fields of both gas and stars indicate that the three clusters are part of a complicated dynamical system, with the NSC having an elevated velocity dispersion in line with its high stellar mass. To investigate the stellar populations of the three clusters in more detail, we used surface brightness modelling to measure their fluxes from UV to mid-infrared wavelengths. This information, together with spectroscopically derived extinction values, are then used to fit the spectral energy distributions (SEDs) of the clusters. Two of the clusters are UV-bright and well described by single stellar populations with young ages (sim 3 and 5 Myr) and relatively low masses ($M_ M_ and $M_ M_ respectively), whereas the central cluster is much more massive ($M_ 10^7 M_ and cannot be fitted by a single stellar population. Instead, we find that the presence of a minor young population (sim 1\,Myr, $M_ M_ embedded in a dominant old population (sim 8\,Gyr) is required to explain its SED. Given its complex composition and the close proximity of two young star clusters that are likely to merge with it within a few hundred million years, we consider the nucleus of NGC\,4654 a unique laboratory to study NSC growth from both in situ star formation and the infall of star clusters.

Dark matter search in the Perseus cluster with simultaneous analysis of Hitomi and Suzaku data

Abstract The reported detection of a 3.5 keV emission line in the Perseus cluster, possibly originating from dark matter decay, is still under scrutiny. Despite extensive observations, the detection has not yet been confirmed, and its origin remains a topic of active debate. Most of the previous searches relied on spectroscopy with X-ray charge-coupled devices, such as the X-ray Imaging Spectrometer on Suzaku. Although this provided a large amount of observational data, it only offered moderate spectral resolution. The X-ray astronomy satellite Hitomi offers new results using its high-resolution X-ray spectrometer (Soft X-ray Spectrometer). However, the data gathered were somewhat limited in terms of statistics. In this work, we present the results of a new spectral analysis of the Perseus cluster that combines the spectra from the XIS and SXS, along with the Soft X-ray Imager on Hitomi, thereby complementing each other’s capability. Our search was conducted for a line emission or absorption in the energy range of 2.6–5.9 keV assuming the Navarro–Frenk–White mass distribution with a concentration parameter of 5.0 and virial radius, r200, of 1.79 Mpc. We also considered the instrumental systematic uncertainty caused by the effective area calibration, which we empirically evaluated using the Crab Nebula spectra. On combining these results, we found no significant line features above the baryonic thermal emission from the intra-cluster medium. The upper limit at 3.5 keV, at a 3σ confidence level, is tightly constrained to 4.2 × 10−5 photons cm−2 s−1 for the $15^{\prime }$ circular sky region, which encloses a dark matter mass of $1.67\times 10^{14}\, M_{\odot }$, assuming a line velocity dispersion of 180 km s−1. This constraint is three times tighter than the previous one, which only used the SXS. On the basis of these findings, we provide the upper limit of the dark matter decay rate and the mixing angle for the sterile neutrino origin.

Exploring Low-mass Black Holes through Tidal Disruption Events in the Early Universe: Perspectives in the Era of the JWST, Roman Space Telescope, and LSST Surveys

The James Webb Space Telescope (JWST) has recently uncovered the presence of low-luminosity active galactic nuclei (AGNs) at z = 4–11. Spectroscopic observations have provided estimates of the nuclear black hole (BH) masses for these sources, extending the low-mass boundary down to M • ∼ 106–7 M ⊙. Despite this breakthrough, the observed lowest mass of BHs is still ≳1–2 orders of magnitude heavier than the predicted mass range of their seed population, thereby leaving the initial mass distribution of massive BHs poorly constrained. In this paper, we focus on UV-to-optical (in the rest frame) flares of stellar tidal disruption events (TDEs) embedded in low-luminosity AGNs as a tool for exploring low-mass BH populations with ≲104–6 M ⊙. We provide an estimate of the TDE rate over z = 4–11, associated with the properties of JWST-detected AGN host galaxies, and we find that deep and wide survey programs with JWST and the Roman Space Telescope (RST) can detect and identify TDEs up to z ≃ 4–7. The predicted detection numbers of TDEs at z > 4 in 1 yr are NTDE∼2–10(0.2–2) for the JADES-Medium (and COSMOS-Web) survey with JWST and NTDE∼2–10(8–50) for the deep (and wide) tiers of the High Latitude Time Domain Survey with RST. We further discuss survey strategies for hunting for transient high-redshift TDEs in wide-field surveys with RST, as well as a joint observation campaign with the Vera C. Rubin Observatory for enhancing the detection number. The high-redshift TDE search will give us a unique opportunity to probe the mass distribution of early BH populations.

Methods for Incorporating Model Uncertainty into Exoplanet Atmospheric Analysis

A key goal of exoplanet spectroscopy is to measure atmospheric properties, such as abundances of chemical species, in order to connect them to our understanding of atmospheric physics and planet formation. In this new era of high-quality JWST data, it is paramount that these measurement methods are robust. When comparing atmospheric models to observations, multiple candidate models may produce reasonable fits to the data. Typically, conclusions are reached by selecting the best-performing model according to some metric. This ignores model uncertainty in favor of specific model assumptions, potentially leading to measured atmospheric properties that are overconfident and/or incorrect. In this paper, we compare three ensemble methods for addressing model uncertainty by combining posterior distributions from multiple analyses: Bayesian model averaging, a variant of Bayesian model averaging using leave-one-out predictive densities, and stacking of predictive distributions. We demonstrate these methods by fitting the Hubble Space Telescope (HST) + Spitzer transmission spectrum of the hot Jupiter HD 209458b using models with different cloud and haze prescriptions. All of our ensemble methods lead to uncertainties on retrieved parameters that are larger but more realistic and consistent with physical and chemical expectations. Since they have not typically accounted for model uncertainty, uncertainties of retrieved parameters from HST spectra have likely been underreported. We recommend stacking as the most robust model combination method. Our methods can be used to combine results from independent retrieval codes and from different models within one code. They are also widely applicable to other exoplanet analysis processes, such as combining results from different data reductions.

An Empirical Calibration of the Tip of the Red Giant Branch Distance Method in the Near Infrared. I. Hubble Space Telescope WFC3/IR F110W and F160W Filters

The tip of the red giant branch (TRGB) based distance method in the I band is one of the most efficient and precise techniques for measuring distances to nearby galaxies (D ≲ 15 Mpc). The TRGB in the near-infrared (NIR) is 1–2 mag brighter relative to the I band, and has the potential to expand the range over which distance measurements to nearby galaxies are feasible. Using Hubble Space Telescope (HST) imaging of 12 fields in eight nearby galaxies, we determine color-based corrections and zero-points of the TRGB in the Wide Field Camera 3 IR (WFC3/IR) F110W and F160W filters. First, we measure TRGB distances in the I band equivalent Advanced Camera System (ACS) F814W filter from resolved stellar populations with the HST. The TRGB in the ACS F814W filter is used for our distance anchor and to place the WFC3/IR magnitudes on an absolute scale. We then determine the color dependence (a proxy for metallicity/age) and zero-point of the NIR TRGB from photometry of WFC3/IR fields that overlap with the ACS fields. The new calibration is accurate to ∼1% in distance relative to the F814W TRGB. Validating the accuracy of the calibrations, we find that the distance modulus for each field using the NIR TRGB calibration agrees with the distance modulus of the same field as determined from the F814W TRGB. This is a JWST preparatory program, and the work done here will directly inform our approach to calibrating the TRGB in JWST NIRCam and NIRISS photometric filters.

Young Metal-Rich Stars in the Halo of M82: a tidal dwarf galaxy?

Abstract We present Hubble Space Telescope Advanced Camera for Surveys photometry of an arc structure of stars in the southern halo of M82. The structure is located at a projected height of ≈5 kpc from the disk of M82 but its stellar content exhibits a younger mean age than that of typical halo stars. We measured the distance, mean age, and peak metallicity of the stars in the arc and used them to determine the structure’s origin. The arc color-magnitude diagram yields a tip of red giant branch (RGB) distance of 3.63 ± 0.08 Mpc, similar to that of M82, confirming its association with the galaxy. The color-magnitude diagram also reveals a population of predominantly young stars with a mean age of ≈100 - 160 Myr, which is similar to that of the young stars formed in the tidal debris between M81, M82, and NGC 3077. We derived the mean metallicity of the halo stars surrounding the arc to be [Fe/H] ≈ -1.0, similar to that of the RGB population of the halo of M81. The RGB stars in the arc, while they are slightly more metal-rich than the halo RGB, show no spatial correlation with the young stars, suggesting that the arc is consist of mainly young stellar population. Furthermore, the observed age gradient along the structure of the arc indicates that the arc began forming from the closer side to M82, then moving outward. Taken together, the results suggest that the formation of the young stars which gives rise to the arc structure could have been triggered by the interactions between M82’s southern outflow and the HI gas clouds surrounding it, representing a snapshot of a tidal dwarf galaxy in the process of forming.

Galaxy morphology from z ∼ 6 through the lens of JWST

Context. The James Webb Space Telescope’s (JWST’s) unprecedented combination of sensitivity, spatial resolution, and infrared coverage has enabled a new era of galaxy morphology exploration across most of cosmic history. Aims. We analyze the near-infrared (NIR ∼ 0.8 − 1 μm) rest-frame morphologies of galaxies with log M*/M⊙ > 9 in the redshift range of 0 < z < 6, compare with previous HST-based results and release the first JWST-based morphological catalog of ∼20 000 galaxies in the CEERS survey. Methods. We classified the galaxies in our sample into four main broad classes: spheroid, disk+spheroid, disk, and disturbed, based on imaging with four filters: F150W, F200W, F356W, and F444W. We used convolutional neural networks (CNNs) trained on HST/WFC3 labeled images and domain-adapted to JWST/NIRCam. Results. We find that ∼90% and ∼75% of galaxies at z < 3 have the same early and late and regular and irregular classification, respectively, in JWST and HST imaging when considering similar wavelengths. For small (large) and faint objects, JWST-based classifications tend to systematically present less bulge-dominated systems (peculiar galaxies) than HST-based ones, but the impact on the reported evolution of morphological fractions is less than ∼10%. Using JWST-based morphologies at the same rest-frame wavelength (∼0.8 − 1 μm), we confirm an increase in peculiar galaxies and a decrease in bulge-dominated galaxies with redshift, as reported in previous HST-based works, suggesting that the stellar mass distribution, in addition to light distribution, is more disturbed in the early Universe. However, we find that undisturbed disk-like systems already dominate the high-mass end of the late-type galaxy population (log M*/M⊙ > 10.5) at z ∼ 5, and bulge-dominated galaxies also exist at these early epochs, confirming a rich and evolved morphological diversity of galaxies ∼1 Gyr after the Big Bang. Finally, we find that the morphology-quenching relation is already in place for massive galaxies at z > 3, with massive quiescent galaxies (log M*/M⊙ > 10.5) being predominantly bulge-dominated.

Impact of Planetary Parameters on Water Clouds Microphysics

Potentially habitable exoplanets are targets of great interest for the James Webb Space Telescope and upcoming mission concepts such as the Habitable Worlds Observatory. Clouds strongly affect climate and habitability, but predicting their properties is difficult. In Global Climate Models (GCMs), especially those aiming at simulating Earth, cloud microphysics is often crudely approximated by assuming that all cloud particles have a single, constant size or a prescribed size distribution and that all clouds in a grid cell are identical. For exoplanets that range over a large phase space of planetary properties, this method could result in large errors. In this work, our goal is to determine how cloud microphysics on terrestrial exoplanets, whose condensable is mainly water vapor, depend on aerosol properties and planetary parameters such as surface pressure, surface gravity, and incident stellar radiation. We use the Community Aerosol and Radiation Model for Atmospheres as a 1D microphysical model to simulate the formation and evolution of clouds including the processes of nucleation, condensation, evaporation, coagulation, and vertical transfer. In these 1D idealized experiments, we find that the parameters that determine the macrophysical thermal structure of the atmospheres, including surface pressure and stellar flux, impact cloud radiative effect (CRE) most significantly. Parameters such as gravity and number density of aerosols working as cloud condensation nuclei affect the microphysical processes of cloud formation, including activation and vertical transfer. They also have a significant, though weaker effect on CRE. This work motivates the development of more accurate GCM cloud schemes and should aid in the interpretation of future observations.

Constraints on the narrow-line region of the X-ray quasi-periodic eruption source GSN 069

Abstract The origins of quasi-periodic eruptions (QPEs) are poorly understood, although most theoretical explanations invoke an accretion disk around a supermassive black hole. The gas and stellar environments in the galactic nuclei of these sources are also poorly constrained. In this paper, we present an analysis of archival Hubble Space Telescope (HST) images to study the narrow-line [O III] emission in the QPE source GSN 069. We find strong evidence for a compact nuclear [O III] emission region of size ≲ 35 pc, overlaid on top of extended [O III] emission up to 2 kpc away from the nucleus. The age of the accretion system is estimated to be between 10 and 100 yr. The [O III] luminosity of the compact region was measured to be $(2.1 \pm 0.3) \times 10^{40}\, \rm erg\, s^{-1}$. Based on Cloudy simulations, we constrain that the [O III] emitting gas has a hydrogen number density in the range $2 \times 10^{3} < n_{\rm H} \lesssim 10^{8}\, \rm cm^{-3}$ and volume filling factor fV < 4 × 10−3. We suggest that the dense gas in the nuclear region of GSN 069 originates from molecular clouds (with total mass ≳ 3 × 103 M⊙), which are freshly ionised by the soft X-ray photons from the accretion disk. We predict possible evolution of the compact narrow-line region on emission-line diagnostic diagrams, and hence future HST or integral-field unit observations can be used to further pin down the age of this puzzling system.

Efficient ultra-broadband low-resolution astrophotonic spectrographs

Broadband low-resolution near-infrared spectrographs in a compact form are crucial for ground- and space-based astronomy and other fields of sensing. Astronomical spectroscopy poses stringent requirements including high efficiency, broad band operation (> 300 nm), and in some cases, polarization insensitivity. We present and compare experimental results from the design, fabrication, and characterization of broadband (1200 - 1650 nm) arrayed waveguide grating (AWG) spectrographs built using the two most promising low-loss platforms - Si3N4 (rectangular waveguides) and doped-SiO2 (square waveguides). These AWGs have a resolving power (λ/Δλ) of ∼200, free spectral range of ∼ 200-350 nm, and a small footprint of ∼ 50-100 mm2. The peak overall (fiber-chip-fiber) efficiency of the doped-SiO2 AWG was ∼ 79% (1 dB), and it exhibited a negligible polarization-dependent shift compared to the channel spacing. For Si3N4 AWGs, the peak overall efficiency in TE mode was ∼ 50% (3 dB), and the main loss component was found to be fiber-to-chip coupling losses. These broadband AWGs are key to enabling compact integrations such as multi-object spectrographs or dispersion back-ends for other astrophotonic devices such as photonic lanterns or nulling interferometers.

Gas-dynamical Mass Measurements of the Supermassive Black Holes in the Early-type Galaxies NGC 4786 and NGC 5193 from ALMA and HST Observations* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs 15226 and 15909.

We present molecular gas-dynamical mass measurements of the central black holes in the giant elliptical galaxies NGC 4786 and NGC 5193, based on CO (2−1) observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope near-infrared imaging. The central region in each galaxy contains a circumnuclear disk that exhibits orderly rotation with projected line-of-sight velocities of ∼270 km s−1. We build gas-dynamical models for the rotating disk in each galaxy and fit them directly to the ALMA data cubes. At 0.″31 resolution, the ALMA observations do not fully resolve the black hole sphere of influence (SOI), and neither galaxy exhibits a central rise in rotation speed, indicating that emission from deep within the SOI is not detected. As a result, our models do not tightly constrain the central black hole mass in either galaxy, but they prefer the presence of a central massive object in both galaxies. We measure the black hole mass to be (MBH/108M⊙)=5.0±0.2[1σstatistical]−1.3+1.4[systematic] in NGC 4786 and (MBH/108M⊙)=1.4±0.03[1σstatistical]−0.1+1.5[systematic] in NGC 5193. The largest component of each measurement’s error budget is from the systematic uncertainty associated with the extinction correction in the host galaxy models. This underscores the importance of assessing the impact of dust attenuation on the inferred M BH.

Search for Chirality in Hydrogenated Magnesium Nanosilicates: A DFT and TD-DFT Investigation.

The formation of silicate grains in the interstellar medium (ISM), especially those containing chiral surfaces such as clinopyroxenes, is poorly understood. Moreover, silicate interactions with various forms of hydrogen-proton (H+), neutral H (HI), and molecular hydrogen (H2) are of high importance as hydrogen comprises >90% of the ISM gas budget, and these species play important roles in the formation of new molecules in space. Furthermore, silicate surfaces catalyze the formation of H2 in the interstellar medium formed on dust grain surfaces by H-H association. The technical difficulty of in situ laboratory investigations of nanosilicate nucleation using astrophysically relevant environmental conditions makes computational chemistry a useful tool for studying potential nanosilicate structures. Furthermore, chiral surfaces interacting with chiral organic molecules could serve as templates that lead to the enantiomeric excess of l-amino acids and d-polyols detected in carbonaceous meteorites. However, in order for this effect to take place, an excess of one chiral form of a mineral is required to break the symmetry. This symmetry-breaking event could have been due to the asymmetric absorption of circularly polarized light by the nanosilicate as it traverses star-forming regions. We investigate this possibility using a metastable chiral form of an enstatite dimer as an input for density functional theory (DFT) and time-dependent (TD)-DFT calculations to obtain various properties and circular dichroism spectra. All in all, twenty-six magnesium nanosilicate structures were studied using varying degrees of hydrogenation: none, with HI, with H+, and with H2. The HSE06/aug-cc-pVQZ level of theory was used for the DFT calculations. TD-DFT calculations utilized the CAM-B3LYP/cc-pVQZ and ωB97X-D3/cc-pVQZ functional and basic set pairings. Results show that (1) all twenty-six structures have absorption bands that fall within the 0.6-28.3 μm range available with the newly launched James Webb Space Telescope and (2) there is a small enantioselective effect by UV-CPL on the eight chiral enstatite dimers (predicted g-values of up to 0.007). While the observed effect is small, it opens up the possibility that it is the inorganic material that becomes enantiomerically biased by UV-CPL, driving chiral enhancements in meteoric organic molecules.

Constraints on the z ∼ 5 Star-forming Galaxy Luminosity Function From Hubble Space Telescope Imaging of an Unbiased and Complete Sample of Long Gamma-Ray Burst Host Galaxies

We present rest-frame UV Hubble Space Telescope imaging of the largest and most complete sample of 23 long-duration gamma-ray burst (GRB) host galaxies between redshifts 4 and 6. Of these 23, we present new WFC3/F110W imaging for 19 of the hosts, which we combine with archival WFC3/F110W and WFC3/F140W imaging for the remaining four. We use the photometry of the host galaxies from this sample to characterize both the rest-frame UV luminosity function (LF) and the size–luminosity relation of the sample. We find that when assuming the standard Schechter-function parameterization for the UV LF, the GRB host sample is best fit with α=−1.30−0.25+0.30 and M*=−20.33−0.54+0.44 mag, which are consistent with results based on z ∼ 5 Lyman-break galaxies. We find that ∼68% of our size–luminosity measurements fall within or below the same relation for Lyman-break galaxies at z ∼ 4. This study observationally confirms expectations that at z ∼ 5 Lyman-break and GRB host galaxies should trace the same population and demonstrates the utility of GRBs as probes of hidden star formation in the high-redshift Universe. Under the assumption that GRBs unbiasedly trace star formation at this redshift, our nondetection fraction of 7/23 is consistent at the 95% confidence level with 13%–53% of star formation at redshift z ∼ 5 occurring in galaxies fainter than our detection limit of M 1600Å ≈ −18.3 mag.

SMART: Spectral energy distributions Markov chain Analysis with Radiative Transfer models

Abstract In this paper we present the publicly available open-source spectral energy distribution (SED) fitting code SMART (Spectral energy distributions Markov chain Analysis with Radiative Transfer models). Implementing a Bayesian Markov chain Monte Carlo (MCMC) method, SMART fits the ultraviolet to millimetre SEDs of galaxies exclusively with radiative transfer models that currently constitute four types of pre-computed libraries, which describe the starburst, active galactic nucleus (AGN) torus, host galaxy and polar dust components. An important novelty of SMART is that, although it fits SEDs exclusively with radiative transfer models, it takes comparable time to popular energy balance methods to run. Here we describe the key features of SMART and test it by fitting the multi-wavelength SEDs of the 42 local ultraluminous infrared galaxies (ULIRGs) that constitute the HERschel Ultraluminous Infrared Galaxy Survey (HERUS) sample. The Spitzer spectroscopy data of the HERUS ULIRGs are included in the fitting at a spectral resolution, which is matched to that of the radiative transfer models. We also present other results that highlight the performance and versatility of SMART. SMART promises to be a useful tool for studying galaxy evolution in the James Webb Space Telescope (JWST) era. SMART is developed in Python and is available at https://github.com/ch-var/SMART.git.

Stellar Mapping Using Quadratic Limb-Darkening

Abstract In this thesis, I create useful visualizations of stars empirically from transit observations and theoretically from stellar parameters. Transit photometry has been a popular method to find exoplanets and information about star and planet systems many light-years away. Since most stars are too far away to be seen directly, creating stellar visualizations is an important tool for modeling stars. When creating visualizations, limb-darkening must be considered. Limb-darkening is the visual darkening along the outside, or limbs, of a star. This effect is more dramatic at shorter wavelengths, such as visible light, making it easier to see the darkening of limbs. A recent transit of WASP-39 captured from the James Webb Space Telescope is used to create stellar models for this star, using fitted empirical limb-darkening coefficients. Theoretical models for WASP-39 will also be created using theoretically determined coefficients. While complicated, generating empirical and theoretical limb-darkening profiles is a useful way of modeling stars too far away to observe. Lay summary  We can locate brand new exoplanets, many light years away, without ever actually seeing them. Better yet, we can classify and learn vital information about the star and planet system from the exoplanet detection methods. One commonly used detection method is the transit method. The transit method captures the slight dimming of a star’s light as a planet crosses in front of it. This decrease in brightness is temporary and regular. Transits provide information about the composition and properties of stars. One such phenomenon is limb-darkening where the brightness of the star appears darker around its edges. Limb-darkening coefficients are calculated using a quadratic relationship between the intensity at a certain point of the star to the intensity at the center of the star. As the coefficients increase, the “limbs” or edges of the star appear darker. The wavelength in which we are measuring the transit also impacts the limb-darkening. At lower wavelengths, the darkening effect is more dramatic. Using these coefficients at different wavelengths we can create theoretical models to show what stars should look like without being able to see them.  The James Webb Telescope (JWST) is capturing numerous exoplanets through the transit method. Launched in December 2021, the JWST contains instruments capable of measuring the slightest changes in the brightness of distant stars. The transit data, collected from the JWST, are fit to infer the best limb-darkening coefficients. We also calculate theoretical coefficients using known physical properties of the star. One particular star captured by the JWST is WASP-39, located 700 light years away. WASP-39 is a dwarf star slightly smaller than our Sun. Models of WASP-39 are created using the empirical and theoretical coefficients. These stellar movies show the appearance of the star at various wavelengths and their corresponding limb-darkening coefficients. The appearances are compared to show how different actual data presents from theoretical models. Providing visual models for stars is an easy way to quantify differences, rather than numerical data. To see the complete thesis, please visit https://scholar.colorado.edu/concern/undergraduate_honors_theses/5m60qt492

GausSN: Bayesian time-delay estimation for strongly lensed supernovae

Abstract We present GausSN, a Bayesian semi-parametric Gaussian Process (GP) model for time-delay estimation with resolved systems of gravitationally lensed supernovae (glSNe). GausSN models the underlying light curve non-parametrically using a GP. Without assuming a template light curve for each SN type, GausSN fits for the time delays of all images using data in any number of wavelength filters simultaneously. We also introduce a novel time-varying magnification model to capture the effects of microlensing alongside time-delay estimation. In this analysis, we model the time-varying relative magnification as a sigmoid function, as well as a constant for comparison to existing time-delay estimation approaches. We demonstrate that GausSN provides robust time-delay estimates for simulations of glSNe from the Nancy Grace Roman Space Telescope and the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (Rubin-LSST). We find that up to 43.6 % of time-delay estimates from Roman and 52.9 % from Rubin-LSST have fractional errors of less than 5 %. We then apply GausSN to SN Refsdal and find the time delay for the fifth image is consistent with the original analysis, regardless of microlensing treatment. Therefore, GausSN maintains the level of precision and accuracy achieved by existing time-delay extraction methods with fewer assumptions about the underlying shape of the light curve than template-based approaches, while incorporating microlensing into the statistical error budget. GausSN is scalable for time-delay cosmography analyses given current projections of glSNe discovery rates from Rubin-LSST and Roman.

The Disappearance of the Blue and Luminous Progenitor of the Type IIn SN 2010jl

Type IIn supernovae (SNe) exhibit narrow hydrogen lines that arise from the strong interaction between ejecta and circumstellar material. It remains poorly understood, however, what progenitor stars give rise to these explosions. In this work, we perform a detailed analysis of the progenitor and environment of the nearby Type IIn SN 2010jl. With newer images taken by the Hubble Space Telescope, we confirm that the previously reported progenitor candidate is a blend of the progenitor itself and a field star cluster in its close vicinity. SN 2010jl has now become much fainter than the progenitor. The progenitor is very blue and luminous with an effective temperature of log T eff/K = 4.26 −0.09+0.11 and a luminosity of log L/L ⊙ = 6.52 −0.16+0.20 . It is located in a very young star-forming region, but its luminosity is much higher than that expected from the environmental stellar populations. We suggest that the progenitor was in outburst when observed. Its nature and evolutionary history remain to be investigated.