arXiv subjects

Kartheik G. Iyer

Publications and source records attributed to Kartheik G. Iyer.

At least 37 records · Page 2Linked to original sources

arXiv2025

SF-R You Sure? The Conflicting Role of Star Formation Rates in Constraining the Evolution of Milky Way Analogues in Cosmological Simulations

Milky Way analogues (MWAs) have long been studied by astronomers to place our Galaxy within an extragalactic context. With the power of cosmological simulations, we are now able to not only characterize MWAs today, but also watch as they evolve through cosmic time. We use the EAGLE and IllustrisTNG simulations to study a group of MWAs defined by their stellar mass (SM) and star formation rate (SFR). We trace these galaxies back along their evolution to investigate the star forming and mass assembly tracks taken by a galaxy to become a MWA today in light of these chosen parameters. We also take mock-observations of "MWAs" at $z>0$ and trace them forwards in time to determine if galaxies that looked similar to the Milky Way earlier in their evolution still look like the Milky Way today, thus quantifying a selection efficiency which could inform future observational studies of MWAs. We find that most galaxies with Milky Way-SM follow a similar evolution regardless of present-day SFR, although MWAs in IllustrisTNG generally have not quenched, leading to star formation histories that produce "too-blue" galaxies today. Additionally, we find contamination by MWA-"imposters" in our mock-observations, with low selection efficiency at high redshift due to the tight constraint requiring convergence to the Milky Way's present-day SFR. Our work suggests present-day SM may suffice as a stand-alone selection parameter and helps to clarify how MWAs should be selected, and thus will be an important reference for future studies of both simulated and observed MWAs.

astro-ph.GA↗

arXiv2025

From Queries to Criteria: Understanding How Astronomers Evaluate LLMs

There is growing interest in leveraging LLMs to aid in astronomy and other scientific research, but benchmarks for LLM evaluation in general have not kept pace with the increasingly diverse ways that real people evaluate and use these models. In this study, we seek to improve evaluation procedures by building an understanding of how users evaluate LLMs. We focus on a particular use case: an LLM-powered retrieval-augmented generation bot for engaging with astronomical literature, which we deployed via Slack. Our inductive coding of 368 queries to the bot over four weeks and our follow-up interviews with 11 astronomers reveal how humans evaluated this system, including the types of questions asked and the criteria for judging responses. We synthesize our findings into concrete recommendations for building better benchmarks, which we then employ in constructing a sample benchmark for evaluating LLMs for astronomy. Overall, our work offers ways to improve LLM evaluation and ultimately usability, particularly for use in scientific research.

cs.CL↗

arXiv2025

Metal-Poor Star-Forming Clumps in Cosmic Noon Galaxies: Evidence for Gas Inflow and Chemical Dilution Using JWST NIRISS

The formation and evolution of galaxies are intricately linked to the baryon cycle, which fuels star formation while shaping chemical abundances within galaxies. Investigating the relationship between star formation and metallicity for large samples of galaxies requires expensive IFU surveys or sophisticated tools to analyze grism data. Here we analyze JWST NIRISS slitless grism data using Sleuth, a tool that forward models and infers spatially resolved physical properties from grism data, including observations from JWST NIRISS/NIRCam and future grism data like that from the Roman Space Telescope. Sleuth enables extraction of high-quality emission line maps from slitless spectra, overcoming contamination and spatially varying stellar populations, which previously limited such studies. Utilizing Sleuth with data from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), we investigated the relationship between metallicity and star formation in the star-forming clumps of galaxies at 0.6 < z < 1.35. We analyzed a sample of 20 galaxies, extracted high-quality emission line maps with Sleuth, and analyzed, in detail, the spatially resolved properties of star-forming clumps. Using $Hα$, [SII], and [SIII] emission line maps, we examined the spatially resolved metallicities, ionization, and star formation rates of our sample. Our findings reveal that these star-forming clumps show lower metallicities ($\sim$ 0.1 dex) than their surrounding galactic environments, indicating a metallicity dilution of 20 $\%$ within the clumps' gas. Our analysis indicates that these clumps exhibit intensified star formation and reduced metallicity, likely due to the inflow of metal-poor gas. These clumps illustrate the dynamic relationship between star formation and chemical enrichment within galaxies.

astro-ph.GA↗

arXiv2025

MINERVA: A NIRCam Medium Band and MIRI Imaging Survey to Unlock the Hidden Gems of the Distant Universe

We present an overview of the MINERVA survey, a 259.8 hour (prime) and 127 hour (parallel) Cycle 4 treasury program on the James Webb Space Telescope (JWST). MINERVA is obtaining 8 filter NIRCam medium band imaging (F140M, F162M, F182M, F210M, F250M, F300M, F360M, F460M) and 2 filter MIRI imaging (F1280W, F1500W) in four of the five CANDELS Extragalactic fields: UDS, COSMOS, AEGIS and GOODS-N. These fields were previously observed in Cycle 1 with 7 - 9 NIRCam filters by the PRIMER, CEERS and JADES programs. MINERVA reaches a 5$σ$ depth of 28.1 mag in F300M and covers $\sim$ 542 arcmin$^2$, increasing the area of existing JWST medium-band coverage in at least 8 bands by $\sim$ 7$\times$. The MIRI imaging reaches a 5$σ$ depth of 23.9 mag in F1280W and covers $\sim$ 275 arcmin$^2$ in at least 2 MIRI filters. When combined with existing imaging, these data will provide a photometric catalog with 20-26 JWST filters (depending on field) and 26-35 filters total, including HST. This paper presents a detailed breakdown of the filter coverage, exposure times, and field layout relative to previous observations, as well as an overview of the primary science goals of the project. These include uncovering the physics of enigmatic sources hiding in current broadband catalogs, improving systematics on stellar mass functions and number densities by factors of $\gtrsim$ 3, and resolved mapping of stellar mass and star formation at 1 $< z <$ 6. When complete, MINERVA will become an integral part of the treasury deep field imaging datasets, significantly improving population studies with well-understood completeness, robust photometric redshifts, stellar masses, and sizes, and facilitating spectroscopic follow up for decades to come.

astro-ph.GA↗

arXiv2025

Possible environmental quenching in an interacting little red dot pair at $z\sim7$

We report the discovery of a $z\sim7$ group of galaxies that contains two little red dots (LRDs) just 3.3 kpc apart, along with three potential satellite galaxies, as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). The spectral energy distributions (SEDs) of this LRD pair show evidence of a Balmer break, consistent with a recent ($\sim 100$ Myr) quenching of star formation. In contrast, the satellites are compatible with a recent-onset ($\sim 100$ Myr), ongoing burst of star formation. LRD1's SED is consistent with a dust-free active galactic nucleus (AGN) being the source of the UV excess in the galaxy. The optical continuum would be powered by the emission from an obscured post-starburst and the AGN at a subdominant level. LRD2's SED is more ambiguous, but it could also be indicative of a dust-free AGN. In this scenario, these LRDs would be massive ($M_\star\sim10^{10}\,M_\odot$) and dusty (A(V) $>1$ mag) and the three satellites would be lower-mass objects ($M_\star\sim10^{8-9}\,M_\odot$) subject to low dust attenuations. The proximity of the two LRDs suggests that their interaction is responsible for their recent star formation histories, which can be interpreted as environmental bursting and quenching in the epoch of reionization.

astro-ph.GA↗

arXiv2025

In Search of the First Stars: An Ultra-Compact and Very Low Metallicity Lyman-$α$ Emitter Deep Within the Epoch of Reionization

We present {\it JWST} observations of a gravitationally-lensed, extremely metal-poor galaxy at redshift $z=8.203\pm 0.001$ from the CANUCS survey. Based on the low oxygen to Balmer line ratios we infer a gas-phase metallicity of $12+{\rm log(O/H)}=6.85$ (1.4\% solar), making CANUCS-A370-z8-LAE one of the most metal-poor galaxies known at $z>7$. With a high H$β$ equivalent width of $225\pm50$\,Å and a half-light radius of only $r_{\rm hl} = 38 ^{+3}_{-19} $\,pc, the galaxy has a high star-formation-rate density of $50 - 100\,M_{\odot}$\,yr$^{-1}$\,kpc$^{-2}$. The galaxy shows high equivalent width Lyman-$α$ emission with an inferred Lyman-$α$ escape fraction of $0.21 \pm 0.05$. The high escape fraction of Lyman-$α$ is likely due to the compact starbursting nature of the galaxy combined with its location in an overdensity traced by at least two other galaxies spectroscopically confirmed to lie within $δz = 0.01$ that have helped to reionize the environment. The low metallicity of CANUCS-A370-z8-LAE is best explained by a model where infalling metal-poor gas dilutes the interstellar medium, rather than being a young galaxy forming its first stellar populations.

astro-ph.GA↗

arXiv2025

CANUCS/Technicolor Data Release 1: Imaging, Photometry, Slit Spectroscopy, and Stellar Population Parameters

We present the first data release of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), a JWST Cycle 1 GTO program targeting 5 lensing clusters and flanking fields in parallel (Abell 370, MACS0416, MACS0417, MACS1149, MACS1423; survey area \tilda100 arcmin$^{2}$), with NIRCam imaging, NIRISS slitless spectroscopy, and NIRSpec prism multi-object spectroscopy. Fields centered on cluster cores include imaging in 8 bands from 0.9-4.4$μ$m, alongside continuous NIRISS coverage from 1.15-2$μ$m, while the NIRCam flanking fields provide 5 wide and 9 medium band filters for exceptional spectral sampling, all to \tilda29 mag$_{AB}$. We also present JWST in Technicolor, a Cycle 2 follow-up GO program targeting 3 CANUCS clusters (Abell 370, MACS0416, MACS1149). The Technicolor program adds NIRISS slitless spectroscopy in F090W to the cluster fields while adding 8 wide, medium, and narrow band filters to the flanking fields. This provides NIRCam imaging in all wide and medium band filters over \tilda30 arcmin$^{2}$. This paper describes our data reduction and photometry methodology. We release NIRCam, NIRISS, and HST imaging, PSFs, PSF-matched imaging, photometric catalogs, and photometric and spectroscopic redshifts. We provide lens models and stellar population parameters in up to 19 filters for \tilda53,000 galaxies in the cluster fields, and \tilda44,000 galaxies in up to 29 filters in the flanking fields. We further present 733 NIRSpec spectra and redshift measurements up to $z=10.8$. Comparing against our photometric redshifts, we find catastrophic outlier rates of only 4-7\% and scatter of $σ_{\rm NMAD}$ of 0.01-0.03.

astro-ph.GA↗

arXiv2025

ODIN: Star Formation Histories Reveal Formative Starbursts Experienced by Lyman Alpha Emitting Galaxies at Cosmic Noon

In this work, we test the frequent assumption that Lyman Alpha Emitting galaxies (LAEs) are experiencing their first major burst of star formation at the time of observation. To this end, we identify 74 LAEs from the ODIN Survey with rest-UV-through-NIR photometry from UVCANDELS. For each LAE, we perform non-parametric star formation history (SFH) reconstruction using the Dense Basis Gaussian process-based method of spectral energy distribution fitting. We find that a strong majority (67%) of our LAE SFHs align with the frequently assumed archetype of a first major star formation burst, with at most modest star formation rates (SFRs) in the past. However, the rest of our LAE SFHs have significant amounts of star formation in the past, with 28% exhibiting earlier bursts of star formation with the ongoing burst having the highest SFR (dominant bursts), and the final 5% having experienced their highest SFR in the past (non-dominant bursts). Combining the SFHs indicating first and dominant bursts, ~95% of LAEs are experiencing their largest burst yet -- a formative burst. We also find that the fraction of total stellar mass created in the last 200 Myr is ~1.3 times higher in LAEs than in mass-matched Lyman Break Galaxy (LBG) samples, and that a majority of LBGs are experiencing dominant bursts, reaffirming that LAEs differ from other star forming galaxies. Overall, our results suggest that multiple evolutionary paths can produce galaxies with strong observed Ly$α$ emission.

astro-ph.GA↗

arXiv2025

The Abundance and Properties of Barred Galaxies out to $z \sim$ 4 Using $\textit{JWST}$ CEERS Data

We present the first estimate of the observed fraction and properties of bars out to $ z\sim4$ using $\textit{JWST}$ CEERS NIRCam images. We analyze 1770 galaxies with $M_\star > 10^{10} M_\odot$ at $0.5 \leq z \leq 4$ and identify barred galaxies from 839 moderately inclined disk galaxies via ellipse fits and visual classification of both F200W and F444W images. Our results apply mainly to bars with projected semi-major axis $a_{\rm bar}$ $> 1.5 $ kpc ($\sim$ 2 $\times$ PSF in F200W images) that can be robustly traced by ellipse fits. For such bars, the observed bar fraction at $z\sim$ 2-4 is low ($\lesssim 10\%$), and they appear to be emerging at least as early as $z\sim 4$. Our observed bar fraction is consistent with the bar fraction predicted by TNG50 simulations for large bars with $a_{\rm bar}$ $> 1.5$ kpc at $z \sim$ 0.5-4 and with the bar fraction from Auriga simulations out to $z \sim$ 1.5. However, TNG50 simulations predict a large population of smaller bars that our data cannot robustly detect. If such bars exist, the true bar fraction at $z \sim$ 2-4 may be significantly higher than our results. At $z \ge 1.5$, many barred galaxies show nearby neighbors, suggesting bars may be tidally triggered. From $z \sim$ 4-0.5, the observed bar fraction, average projected bar length, and projected bar strength rise. Our results highlight the early emergence and evolution of barred galaxies and the rising importance of bar-driven secular evolution from $z \sim$4 to today.

astro-ph.GA↗

arXiv2025

CANUCS: Constraining the MACS J0416.1-2403 Strong Lensing Model with JWST NIRISS, NIRSpec and NIRCam

(Abridged) The strong lensing models of galaxy clusters rely on the number and quality of multiple images with spectroscopic redshifts. We present an updated strong lensing model of MACS J0416.1-2403 with the largest sample of multiple images with spectroscopic redshifts in a galaxy cluster field to date. Furthermore, we aim to demonstrate the effectiveness of JWST, particularly its NIRISS camera, for strong lensing studies. We used NIRCam imaging and NIRSpec and NIRISS spectroscopy from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The cluster mass model was constrained using Lenstool software. Our new dataset, which we used for constraining the lens model, comprises 303 secure multiple images with spectroscopic redshifts from 111 background sources and includes 95 systems with previously known MUSE redshift and 16 systems (with 46 multiple images) for which we obtained spectroscopic redshift for the first time using NIRISS and NIRSpec spectroscopy. Three of the spectroscopic systems were not identified by previous JWST studies. The total number of secure spectroscopic systems is more than 20% higher than in the previous strong lensing studies of this cluster. The model can reproduce multiple images with the root-mean-square distance of ~ 0.52''. We also provide a full catalogue with 415 multiple images, including less reliable candidates. In total, we provide 15 new multiple-image system candidates (with 38 multiple images) not reported in previous studies. Furthermore, we demonstrate the effectiveness of JWST, particularly NIRISS, for obtaining spectroscopic redshifts of multiple images. As NIRISS F115W, F150W, and F200W grism spectroscopy captures at least two of the [OII], [OIII] and H$α$ lines at 1 < z < 3 (a redshift range particularly relevant for strong lensing studies) without target pre-selection, it complements MUSE and NIRSpec observations extremely well.

astro-ph.CO↗

arXiv2025

A Survey on Hypothesis Generation for Scientific Discovery in the Era of Large Language Models

Hypothesis generation is a fundamental step in scientific discovery, yet it is increasingly challenged by information overload and disciplinary fragmentation. Recent advances in Large Language Models (LLMs) have sparked growing interest in their potential to enhance and automate this process. This paper presents a comprehensive survey of hypothesis generation with LLMs by (i) reviewing existing methods, from simple prompting techniques to more complex frameworks, and proposing a taxonomy that categorizes these approaches; (ii) analyzing techniques for improving hypothesis quality, such as novelty boosting and structured reasoning; (iii) providing an overview of evaluation strategies; and (iv) discussing key challenges and future directions, including multimodal integration and human-AI collaboration. Our survey aims to serve as a reference for researchers exploring LLMs for hypothesis generation.

cs.CL↗

arXiv2025

Improving photometric redshifts of Epoch of Reionization galaxies: a new empirical transmission curve with neutral hydrogen damping wing Ly$α$ absorption

We present a new analytical model for the attenuation to Epoch of Reionization (EoR) galaxies by proximate neutral hydrogen gas. Many galaxy spectra in the EoR taken by JWST have shown a flux deficit at wavelengths just redward of the Lyman break, and this has been regarded as resulting from Ly$α$ damping wing absorption by the increasing amount of neutral hydrogen in the line-of-sight. However, previous attenuation models for the intergalactic medium (IGM) commonly used in photometric redshift template-fitting codes assume that the Lyman break is rather sharp, which leads to systematic overestimation of photometric redshifts at $z>7$. In this letter, we build and empirically calibrate a new attenuation model that takes the increased Ly$α$ damping wing absorption into account. Our model consists of the canonical IGM absorption and an additional absorption component due to dense neutral hydrogen gas clouds proximate to the galaxy, and we derive the redshift evolution of HI column density of the proximate clouds by calibrating the model using CANUCS JWST observations. The resulting total transmission curve resolves the photometric redshift bias at $z>7$, an improvement that is robust to choice of template-fitting code, template set, and photometric catalog used. The new attenuation model can be easily implemented in existing template-fitting codes, and significantly improves the photometric redshift performance in the EoR.

astro-ph.GA↗

arXiv2025

The Spectral Energy Distributions of Galaxies

The spectral energy distribution (SED) of a galaxy represents the distribution of electromagnetic radiation emitted across all wavelengths, from radio waves to gamma rays. The galaxy SED is akin to its fingerprint, and serves as a fundamental tool in modern astrophysics. It enables researchers to determine crucial properties of galaxies, including their star-formation rates, stellar populations, dust content, and evolutionary state. By analyzing galactic SEDs, astronomers can reconstruct the physical processes occurring within galaxies and trace their evolutionary histories. This article explores our current understanding of the components that contribute to galactic SEDs, the observational techniques used to measure them, and their applications in understanding galaxy formation and evolution.

astro-ph.GA↗

arXiv2025

The Cosmic Evolution Early Release Science Survey (CEERS)

We present the Cosmic Evolution Early Release Science (CEERS) Survey, a 77.2 hour Director's Discretionary Early Release Science Program. CEERS demonstrates, tests, and validates efficient extragalactic surveys using coordinated, overlapping parallel observations with the JWST instrument suite, including NIRCam and MIRI imaging, NIRSpec low (R~100) and medium (R~1000) resolution spectroscopy, and NIRCam slitless grism (R~1500) spectroscopy. CEERS targets the Hubble Space Telescope-observed region of the Extended Groth Strip (EGS) field, supported by a rich set of multiwavelength data. CEERS facilitated immediate community science in both of the extragalactic core JWST science drivers ``First Light" and ``Galaxy Assembly," including: 1) The discovery and characterization of large samples of galaxies at z >~ 10 from ~90 arcmin^2 of NIRCam imaging, constraining their abundance and physical nature; 2) Deep spectra of >1000 galaxies, including dozens of galaxies at 6 3; and 4) Characterizing galaxy mid-IR emission with MIRI to study dust-obscured star-formation and supermassive black hole growth at z~1-3. As a legacy product for the community, the CEERS team has provided several data releases, accompanied by detailed notes on the data reduction procedures and notebooks to aid in reproducibility. In addition to an overview of the survey and quality of the data, we provide science highlights from the first two years with CEERS data.

astro-ph.GA↗

arXiv2024

The Multimodal Universe: Enabling Large-Scale Machine Learning with 100TB of Astronomical Scientific Data

We present the MULTIMODAL UNIVERSE, a large-scale multimodal dataset of scientific astronomical data, compiled specifically to facilitate machine learning research. Overall, the MULTIMODAL UNIVERSE contains hundreds of millions of astronomical observations, constituting 100\,TB of multi-channel and hyper-spectral images, spectra, multivariate time series, as well as a wide variety of associated scientific measurements and "metadata". In addition, we include a range of benchmark tasks representative of standard practices for machine learning methods in astrophysics. This massive dataset will enable the development of large multi-modal models specifically targeted towards scientific applications. All codes used to compile the MULTIMODAL UNIVERSE and a description of how to access the data is available at https://github.com/MultimodalUniverse/MultimodalUniverse

astro-ph.IM↗

arXiv2024

UVCANDELS: Catalogs of photometric redshifts and galaxy physical properties

The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) program provides deep HST F275W and F435W imaging over four CANDELS fields (GOODS-N, GOODS-S, COSMOS, and EGS). We combine this newly acquired UV imaging with existing HST imaging from CANDELS as well as existing ancillary data to obtain robust photometric redshifts and reliable estimates for galaxy physical properties for over 150,000 galaxies in the $\sim$430 arcmin$^2$ UVCANDELS area. Here, we leverage the power of the new UV photometry to not only improve the photometric redshift measurements in these fields, but also constrain the full redshift probability distribution combining multiple redshift fitting tools. Furthermore, using the full UV-to-IR photometric dataset, we measure the galaxy physical properties by fitting templates from population synthesis models with two different parameterizations (flexible and fixed-form) of the star-formation histories (SFHs). Compared to the flexible SFH parametrization, we find that the fixed-form SFHs systematically underestimate the galaxy stellar masses, both at the low- ($\lesssim10^9 M_\odot$) and high- ($\gtrsim10^{10} M_\odot$) mass end, by as much as $\sim0.5$ dex. This underestimation is primarily due the limited ability of fixed-form SFH parameterization to simultaneously capture the chaotic nature of star-formation in these galaxies.

astro-ph.GA↗

arXiv2024

pathfinder: A Semantic Framework for Literature Review and Knowledge Discovery in Astronomy

The exponential growth of astronomical literature poses significant challenges for researchers navigating and synthesizing general insights or even domain-specific knowledge. We present Pathfinder, a machine learning framework designed to enable literature review and knowledge discovery in astronomy, focusing on semantic searching with natural language instead of syntactic searches with keywords. Utilizing state-of-the-art large language models (LLMs) and a corpus of 350,000 peer-reviewed papers from the Astrophysics Data System (ADS), Pathfinder offers an innovative approach to scientific inquiry and literature exploration. Our framework couples advanced retrieval techniques with LLM-based synthesis to search astronomical literature by semantic context as a complement to currently existing methods that use keywords or citation graphs. It addresses complexities of jargon, named entities, and temporal aspects through time-based and citation-based weighting schemes. We demonstrate the tool's versatility through case studies, showcasing its application in various research scenarios. The system's performance is evaluated using custom benchmarks, including single-paper and multi-paper tasks. Beyond literature review, Pathfinder offers unique capabilities for reformatting answers in ways that are accessible to various audiences (e.g. in a different language or as simplified text), visualizing research landscapes, and tracking the impact of observatories and methodologies. This tool represents a significant advancement in applying AI to astronomical research, aiding researchers at all career stages in navigating modern astronomy literature.

astro-ph.IM↗

arXiv2024

CEERS Key Paper. IX. Identifying Galaxy Mergers in CEERS NIRCam Images Using Random Forests and Convolutional Neural Networks

A crucial yet challenging task in galaxy evolution studies is the identification of distant merging galaxies, a task which suffers from a variety of issues ranging from telescope sensitivities and limitations to the inherently chaotic morphologies of young galaxies. In this paper, we use random forests and convolutional neural networks to identify high-redshift JWST CEERS galaxy mergers. We train these algorithms on simulated $3<z<5$ CEERS galaxies created from the IllustrisTNG subhalo morphologies and the Santa Cruz SAM lightcone. We apply our models to observed CEERS galaxies at $3<z<5$. We find that our models correctly classify $\sim60-70\%$ of simulated merging and non-merging galaxies; better performance on the merger class comes at the expense of misclassifying more non-mergers. We could achieve more accurate classifications, as well as test for the dependency on physical parameters such as gas fraction, mass ratio, and relative orbits, by curating larger training sets. When applied to real CEERS galaxies using visual classifications as ground truth, the random forests correctly classified $40-60\%$ of mergers and non-mergers at $3<z<4$, but tended to classify most objects as non-mergers at $4<z<5$ (misclassifying $\sim70\%$ of visually-classified mergers). On the other hand, the CNNs tended to classify most objects as mergers across all redshifts (misclassifying $80-90\%$ of visually-classified non-mergers). We investigate what features the models find most useful, as well as characteristics of false positives and false negatives, and also calculate merger rates derived from the identifications made by the models.

astro-ph.GA↗