arXiv subjects

Fatemeh S. Tabatabaei

Publications and source records attributed to Fatemeh S. Tabatabaei.

At least 19 recordsLinked to original sources

arXiv2026

Tracing cosmic star formation history through radio continuum spectral energy distribution and non-thermal emission

As a tracer of massive star formation unaffected by dust, the radio continuum emission provides a unique window into the formation of the first stars and galaxies in the Universe. Recent observations show that the integrated rest-frame mid-radio (~1-10 GHz) luminosity of galaxies serves as one of the most robust tracers of the star formation rate (SFR). These studies further demonstrate that the synchrotron spectral index and the shape of the radio spectral energy distribution (SED) evolves with redshift as a consequence of the cosmic evolution of star formation activity. These findings underscore the importance of deep multi-band radio continuum observations in calibrating the SFR of early galaxies and understanding the astrophysical processes governing their assembly and evolution over cosmic time. This chapter presents recent progress in radio SFR calibrations for star-forming galaxies (SFGs) and reviews radio-continuum studies of the cosmic star formation history (SFH). We highlight the transformative potential of SKA AA4, whose broad frequency coverage and high sensitivity will enable well-constrained radio SEDs for SFGs across a wide redshift range.

astro-ph.GA↗

arXiv2026

Advancing Astrophysics with the SKA II

Advancing Astrophysics with the SKA II (AASKAII), written by our science community, outlines the transformative scientific advances that will be enabled by the SKA telescopes. In the decade since the publication of the previous edition, telescope designs have matured, construction has commenced, and the SKA Organisation has evolved into the SKA Observatory (SKAO). At the same time, observations from SKA precursor and pathfinder telescopes have provided new insights into longstanding scientific challenges while revealing entirely new phenomena. Published in advance of the first science verification campaign for the SKA Observatory, this volume looks ahead to the coming decades of discovery and innovation in radio astronomy. AASKAII spans the broad range of scientific research enabled by the SKA telescopes, SKA-Mid and SKA-Low. The contributions are organised into six thematic categories according to their scientific focus. The opening section presents overview chapters from the SKA Science Working Groups, around which our community is organised. Each overview provides the broader context that connects the contributions in this volume to the key scientific questions being pursued by their respective communities.

astro-ph.IM↗

arXiv2026

Unveiling the roles of thermal and nonthermal processes in the ISM & IGM structure formation and evolution of galaxies with SKAO

Investigating the thermal and nonthermal processes in the interstellar medium (ISM) and intergalactic medium (IGM) is vital to understanding the evolution of galaxies over cosmic time. Resolved observations with SKA pathfinders show that the nonthermal processes, in which magnetic fields and cosmic rays are involved, can decelerate the formation of massive stars in strongly magnetized regions in nearby galaxies. They can also contribute to the onset of winds and outflows in galaxies. The effects of these processes are stronger at higher redshifts as a result of star formation activities. The SKA Observatory will allow a major breakthrough by mapping the thermal and nonthermal processes in distant universe galaxies, shedding light on the role of the ISM and IGM in the evolution of galaxies. We demonstrate this by simulating the radio continuum and HI emission from local galaxies back to high redshifts. Our simulations show that the AA4 surveys will make it possible to trace the thermal and nonthermal processes of the ISM in galaxies that are analogs to M51 and NGC6946, traced in continuum beyond cosmic noon (z=2-3) and the gas content traced by HI beyond z=1. Both simulations and precursor observations indicate the importance of nonthermal feedback at cosmic noon.

astro-ph.GA↗

arXiv2026

Opening new parameter space windows on galaxy/AGN co-evolution with SKA radio continuum surveys

In this chapter we provide an overview of the science enabled by the SKAO, focusing on galaxy/AGN co-evolution studies. In particular we discuss a number of radio continuum `reference' surveys with the SKAO, highlighting the role they can play in advancing this research field with respect to the pre-SKAO era. Alongside well-explored scenarios for wedding cake-like, tiered extragalactic surveys at specific frequencies, we also address the scope for complementary efforts to obtain deep multi-frequency imaging over parts of (an) extragalactic field(s). In addition to providing key information on the physical properties of the emitting sources, such multi-frequency imaging will make important contributions to the calibration of observables from surveys with sparser radio spectral coverage. In this context, we explore possible pathways that can fully exploit the SKAO from initial (AA*) to baseline capabilities (AA4). Finally, we highlight observational synergies with other major facilities -- for wide field and targeted follow-up science -- that will be operational in the 2030s, and for which joint coverage of extragalactic fields will generate significant legacy value

astro-ph.GA↗

arXiv2026

Overview: Extragalactic Continuum Science with the SKAO

Radio continuum observations provide a powerful probe of energetic processes that drive galaxy evolution across cosmic time. The combined sensitivity, angular resolution, and survey speed of the SKAO's telescopes will enable transformative advances in extragalactic astronomy by revealing important details into the interplay between star formation, accretion onto supermassive black holes, magnetic fields, and cosmic rays in galaxies and their environments. In this article, we summarize the key science goals of the Extragalactic Continuum Science Working Group and the contributions of related chapters to Advancing Astrophysics with the SKA II (AASKAII). For star forming galaxies, this includes using multi-band SKA continuum observations to provide dust-unbiased measurements of the cosmic star-formation history and enable robust spectral energy distribution analyses of star-forming galaxies (SFGs) across cosmic time. This is alongside studies which will be crucial to uncover the physics and duty cycles of active galactic nuclei (AGN), clarify the origin of radio emission in radio-quiet AGN, and probe the co-evolution of black holes and their host galaxies. Moreover, the SKA's sensitivity will also reveal diffuse synchrotron emission in galaxy clusters and the cosmic web, tracing cosmic-ray acceleration within large-scale magnetic fields. Extragalactic continuum studies with the SKA will combine wide area continuum surveys, multi-band studies and imaging over those fields which have an abundance of data across the electromagnetic spectrum. The capabilities of the SKA telescopes will position it as a cornerstone facility for addressing fundamental questions in galaxy formation and evolution.

astro-ph.GA↗

arXiv2025

Nonthermal Pressures: Key to Energy Balance and Structure Formation Near Sgr A* in the Milky Way

The circumnuclear region of the Galactic Center offers a unique laboratory to study energy balance and structure formation around Sgr A$\star$. This work investigates thermal and nonthermal processes within 7 pc distance from Sgr A$\star$. Using MeerKAT 1.3 GHz radio continuum data and ALMA H40 radio recombination line emission from the ACES survey, we separate free-free and synchrotron components at $\sim$0.2 pc resolution. With a thermal fraction of $\simeq$13%, the 1.3 GHz emission shows tight correlations with the Herschel PACS infrared data. The correlation between the equipartition magnetic field and molecular gas traced by JCMT $^{12}$CO (J=3$\rightarrow$2) observations reveals a balance between the magnetic field, cosmic rays, and molecular gas pressures south of the circumnuclear disk on $\sim$0.7 pc scales. Unlike the magnetic field and ionized gas, the molecular gas density declines in the cavity (R$\leq$2 pc) toward the center, likely due to feedback from Sgr A$\star$. We find that nonthermal pressure from turbulent gas nearly balances magnetic and cosmic ray pressures and exceeds thermal pressure by two orders of magnitude. The medium surrounding Sgr A$\star$ is filled by a low-$β$ (thermal-to-magnetic energy), supersonic plasma, with an Alfvén Mach number $\simeq$ 4 (assuming equipartition). Analysis of the mass-to-magnetic flux ratio suggests that the circumnuclear region is mostly subcritical and, therefore, the magnetic field can help stabilize gas clouds against gravitational collapse.

astro-ph.GA↗

arXiv2025

Exoplanetary radio emission predictions and detectability in the SKA era

Radio observations provide a window into a planet's interior and play a crucial role in studying its atmosphere and surface, key factors to find potential habitability. The discovery of thousands of exoplanets, together with advances in radio astronomy through the Square Kilometre Array (SKA), motivates the search for planetary-scale radio emissions. Here, we employ the radiometric Bode's law (RBL) and machine learning techniques to analyze a dataset of 1330 confirmed exoplanets, aiming to estimate their potential radio emission. Permutation Importance (PI) and SHapley Additive exPlanations (SHAP) analyses indicate that a planet's mass, radius, orbital semi-major axis, and distance from Earth are sufficient to dependably forecast its radio flux and frequency. The random forest model accurately reproduces these radio characteristics, confirming its reliability for exoplanetary radio predictions. Considering observational constraints, we find that 64 exoplanets could generate signals detectable by the SKA, 52 of which remain observable in the intermediate AA* deployment. Among these, MASCARA-1 b stands out with a predicted flux of 7.209 mJy at 135.1 MHz, making it an excellent SKA-Low target. Meanwhile, WASP-18 b, with a flux of 18.638 mJy peaking at 812.9 MHz, is the most promising candidate for SKA-Mid. These results show that the SKA can detect gas giants, such as MASCARA-1 b (SNR>400) and WASP-18 b (SNR>4236), within feasible integration times. Additionally, we identify four candidates (HATS-18 b, WASP-12 b, WASP-103 b, and WASP-121 b) that are likely affected by radio quenching, highlighting the importance of considering this effect in target selection for observation campaigns.

astro-ph.EP↗

arXiv2025

Machine Learning for Exoplanet Detection: A Comparative Analysis Using Kepler Data

The discovery of exoplanets has expanded our understanding of planetary systems and opened new avenues for astronomical research. In this study, we present a machine learning (ML) framework for exoplanet identification using a time-series photometric dataset from the Kepler Space Telescope, comprising 3,198 flux measurements across 5,074 stars. We investigate the performance of four supervised classification algorithms, namely Random Forest, k-Nearest Neighbors (KNN), Decision Tree, and Logistic Regression, using a comprehensive set of evaluation metrics such as accuracy, precision, recall, F1-score, Area Under the Receiver Operating Characteristic Curve (AUC-ROC), confusion matrices, and learning curves. Among the models, Random Forest achieves the highest accuracy (99.8\%) and near-perfect F1-scores, demonstrating superior generalization and robustness. KNN also performs strongly, achieving 99.3\% accuracy, while Decision Tree demonstrates moderate performance with 97.1\% accuracy, and Logistic Regression trails behind with the lowest accuracy and generalization at 95.8\%. Notably, the application of the Synthetic Minority Over-sampling Technique (SMOTE) significantly improves performance across all models by addressing class imbalance. These findings underscore the effectiveness of ensemble-based machine learning techniques, particularly Random Forest, in handling large volumes of photometric data for automated exoplanet detection. This approach holds significant potential for implementation at ground-based facilities, such as the Iranian National Observatory (INO), where such extensive and precise datasets can further advance exoplanet discovery and characterization efforts.

astro-ph.EP↗

arXiv2022

Evolution of thermal and nonthermal radio continuum emission on kpc scales--Predictions for SKA

Resolved maps of the thermal and nonthermal radio continuum (RC) emission of distant galaxies are a powerful tool for understanding the role of the interstellar medium (ISM) in the evolution of galaxies. We simulate the RC surface brightness of present-day star forming galaxies in the past at $0.15<z<3$ considering two cases of radio size evolution: (1)~no evolution, and (2)~same evolution as in the optical. We aim to investigate the a)~structure of the thermal and nonthermal emission on kpc scales, b)~evolution of the thermal fraction and synchrotron spectrum at mid-radio frequencies ($\simeq$1-10\,GHz), and c)~capability of the proposed SKA1-MID reference surveys in detecting the RC emitting structures. The synchrotron spectrum flattens with $z$ causing curvature in the observed mid-radio SEDs of galaxies at higher $z$. The spectral index reported in recent observational studies agrees better with the no size evolution scenario. In this case, the mean thermal fraction observed at 1.4\,GHz increases with redshift by more than 30\% from $z=0.15$ to $z=2$ because of the drop of the synchrotron emission at higher rest-frame~frequencies. More massive galaxies have lower thermal fractions and experience a faster flattening of the nonthermal spectrum. The proposed SKA1-MID band~2 reference survey, unveils the ISM in M51- and NGC6946-like galaxies (with ${\rm M_{\star}}\simeq10^{10}\,{\rm M}_{\odot}$) up to $z=3$. This survey detects lower-mass galaxies like M33 (${\rm M_{\star}}\simeq10^{9}\,{\rm M}_{\odot}$) only at low redshifts $z\lesssim 0.5$. For a proper separation of the RC emitting processes at the peak of star formation, it is vital to include band~1 into the SKA1-MID reference surveys.

astro-ph.GA↗

arXiv2020

Radio emission during the formation of stellar clusters in M33

We investigate thermal and non-thermal radio continuum associated with the early formation and evolution of Young Stellar Clusters (YSCs) selected by their MIR emission in M33. For the first time in an external galaxy it has been possible to identify radio counterparts to more than 300 star forming regions. We proof the nature of candidate YSCs fully embedded in molecular clouds, by recovering their associated faint radio continuum luminosities. Using the Halpha line to identify free-free radio emission at 5 GHz in the more evolved, partially exposed YSCs, we retrieve information on the relevance of magnetic fields and cosmic rays across the M33 disk at 25 pc spatial scales. A cross-correlation of MIR and radio continuum luminosities is established from bright to very faint YSCs, with MIR-to-radio emission ratio showing a gradual decline towards the outer disk, while the magnetic field is pervasive at all radii. We establish and discuss the tight relation between radio continuum and other star formation indicators, such as Halpha. This relation holds for individual YSCs over four orders of magnitude as well as for molecular clouds hosting YSCs. On average about half of radio emission at 5 GHz in YSCs is non-thermal. For exposed but compact YSCs the non-thermal radio fraction increases with source brightness, while for large HII regions the fraction is lower and shows no clear trend. This has been found for YSCs with and without identified SNRs and underlines the possible role of massive stars in triggering particle acceleration through winds and shocks: these particles diffuse throughout the native molecular cloud prior to cloud dispersal.

astro-ph.GA↗

arXiv2018

The Role of Magnetic Fields in The Evolution of Galaxies

Magnetic fields constitute an energetic component of the interstellar medium in galaxies and hence can affect the formation of galactic structures. Sensitive resolved radio continuum observations together with statistical studies in galaxy samples are performed to investigate the origin and the impact of the magnetic fields. The JVLA cloud-scale survey of the local group galaxy, M33, unveils strong tangled magnetic field along the spiral arms and in the galaxy center indicating amplification due to compression and local shear in molecular clouds. Studying a sample of non-cluster, non-interacting galaxies, we find that the large-scale ordered magnetic field scales with the rotation speed of galaxies. The total and disordered magnetic fields scales with the star formation rate in normal star forming galaxies. On the other hand, a strong magnetic field in the center of NGC 1097 -- a massive galaxy undergoing quenching -- is found responsible for decelerating its massive star formation. Putting these results together, it is deduced that 1) the Universe was highly magnetized short after the peak of the massive star birth at about 1 Gyr after the Big Bang and 2) the strong magnetic field has possibly acted as back reaction after this time, quenching the massive star formation and stimulating the creation of low-mass stars in massive galaxies.

astro-ph.GA↗

arXiv2018

Global Correlations Between the Radio Continuum, Infrared and CO Emission in Dwarf Galaxies

Correlations between the radio continuum, infrared and CO emission are known to exist for several types of galaxies and across several orders of magnitude. However, the low-mass, low-luminosity and low-metallicity regime of these correlations is not well known. A sample of metal-rich and metal-poor dwarf galaxies from the literature has been assembled to explore this extreme regime. The results demonstrate that the properties of dwarf galaxies are not simple extensions of those of more massive galaxies; the different correlations reflect different star-forming conditions and different coupling between the star formation and the various quantities. It is found that dwarfs show increasingly weaker CO and infrared emission for their luminosity, as expected for galaxies with a low dust content, slower reaction rates, and a hard ionizing radiation field. In the higher-luminosity dwarf regime (L_1.4GHz > 10^27 W, where L_1.4GHz ~ 10^29 W for a Milky Way star formation rate of ~1 M_sun yr^-1), the total and non-thermal radio continuum emission appear to adequately trace the star formation rate. A breakdown of the dependence of the (Halpha-based) thermal, non-thermal, and, hence, total radio continuum emission on star formation rate occurs below L_1.4GHz ~ 10^27 W, resulting in a steepening or downturn of the relations at extreme low luminosity. Below L_FIR ~ 10^36 W ~ 3 x 10^9 L_sun, the infrared emission ceases to adequately trace the star formation rate. A lack of a correlation between the magnetic field strength and the star formation rate in low star formation rate dwarfs suggests a breakdown of the equipartition assumption. As extremely metal-poor dwarfs mostly populate the low star formation rate and low luminosity regime, they stand out in their infrared, radio continuum and CO properties.

astro-ph.GA↗

arXiv2018

Science with an ngVLA: Radio Continuum Emission from Galaxies: An Accounting of Energetic Processes

Radio continuum observations have proven to be a workhorse in our understanding of the star formation process (i.e., stellar birth and death) from galaxies both in the nearby universe and out to the highest redshifts. In this article we focus on how the ngVLA will transform our understanding of star formation by enabling one to map and decompose the radio continuum emission from large, heterogeneous samples of nearby galaxies on $\gtrsim 10$\,pc scales to conduct a proper accounting of the energetic processes powering it. At the discussed sensitivity and angular resolution, the ngVLA will simultaneously be able to create maps of current star formation activity at $\sim$100\,pc scales, as well as detect and characterize (e.g., size, spectral shape, density, etc.) discrete H{\sc ii} regions and supernova remnants on 10\,pc scales in galaxies out to the distance of the Virgo cluster. Their properties can then be used to see how they relate to the local and global ISM and star formation conditions. Such investigations are essential for understanding the astrophysics of high-$z$ measurements of galaxies, allowing for proper modeling of galaxy formation and evolution.

astro-ph.GA↗

arXiv2016

Uncovering star formation feedback and magnetism in galaxies with radio continuum surveys

Recent studies show the importance of the star formation feedback in changing the energetic and structure of galaxies. Dissecting the physics of the feedback is hence crucial to understand the evolution of galaxies. Full polarization radio continuum surveys can be ideally performed to trace not only star formation but also the energetic components of the interstellar medium (ISM), the magnetic fields and cosmic ray electrons. Using the SKA precursors, we investigate the effect of the massive star formation on the ISM energy balance in nearby galaxies. Our multi-scale and multi-frequency surveys show that cosmic rays are injected in star forming regions and lose energy propagating away from their birth place. Due to the star formation feedback, cosmic ray electron population becomes younger and more energetic. Star formation also amplifies the turbulent magnetic field inserting a high pressure which is important in energy balance in the ISM and structure formation in the host galaxy.

astro-ph.GA↗

arXiv2014

The Astrophysics of Star Formation Across Cosmic Time at $\gtrsim$10 GHz with the Square Kilometre Array

In this chapter, we highlight a number of science investigations that are enabled by the inclusion of Band~5 ($4.6-13.8$ GHz) for SKA1-MID science operations, while focusing on the astrophysics of star formation over cosmic time. For studying the detailed astrophysics of star formation at high-redshift, surveys at frequencies $\gtrsim$10 GHz have the distinct advantage over traditional $\sim$1.4 GHz surveys as they are able to yield higher angular resolution imaging while probing higher rest frame frequencies of galaxies with increasing redshift, where emission of star-forming galaxies becomes dominated by thermal (free-free) radiation. In doing so, surveys carried out at $\gtrsim$10 GHz provide a robust, dust-unbiased measurement of the massive star formation rate by being highly sensitive to the number of ionizing photons that are produced. To access this powerful star formation rate diagnostic requires that Band~5 be available for SKA1-MID. We additionally present a detailed science case for frequency coverage extending up to 30 GHz during full SKA2 operations, as this allows for highly diverse science while additionally providing contiguous frequency coverage between the SKA and ALMA, which will likely be the two most powerful interferometers for the coming decades. To enable this synergy, it is crucial that the dish design of the SKA be flexible enough to include the possibility of being fit with receivers operating up to 30 GHz.

astro-ph.GA↗

arXiv2013

How cosmic-ray electron propagation affects radio-far-infrared correlations in M31 and M33

We investigate the effect of propagation of cosmic-ray electrons (CRE) on the nonthermal (synchrotron) - far-infrared correlations in M31 and M33. The thermal (TH) and nonthermal (NTH) emission components of the radio continuum emission at 1.4 GHz and one higher frequency are compared with dust emission from M31 and M33 using Spitzer data. In both galaxies the TH emission is linearly correlated with the emission from warm dust (24 μm, 70 μm), but the power laws of the NTH-FIR correlations have exponents b < 1 that increase with increasing frequency. Furthermore, the values of b for M33 are significantly smaller (b ~ 0.4) than those for M31 (b ~ 0.6). We interpret the differences in b as differences in the diffusion length of the CRE. We estimate the diffusion length in two ways: (1) by smoothing the NTH emission at the higher frequency until the correlation with NTH emission at 1.4 GHz has b = 1, and (2) by smoothing the TH emission until the correlation with the NTH emission at the same frequency has b = 1, assuming that the TH emission represents the source distribution of the CRE. Our smoothing experiments show that M31 only has a thin NTH disk with a scale height of h = 0.3-0.4 kpc at 1.4 GHz, whereas M33 has a similar thin disk as well as a thick disk with scale height h_thick ~ 2 kpc. In the thin disks, the (deprojected) diffusion length at 1.4 GHz is ~ 1.5 kpc, yielding a diffusion coefficient of ~ 2 10^28 cm^2/s. The structure, strength and regularity of the magnetic field in a galaxy as well as the existence of a thick disk determine the diffusion of the CRE, and hence, the power-law exponent of the NTH-FIR correlations.

astro-ph.GA↗

arXiv2012

The Resolved Radio--FIR Correlation in Nearby Galaxies with Herschel and Spitzer

We investigate the correlation between the far-infrared (FIR) and radio continuum emission from NGC6946 on spatial scales between 0.9 and 17 kpc. We use the Herschel PACS (70, 100, 160$μ$m) and SPIRE (250$μ$m) data from the KINGFISH project. Separating the free-free and synchrotron components of the radio continuum emission, we find that FIR is better correlated with the free-free than the synchrotron emission. Compared to a similar study in M33 and M31, we find that the scale dependence of the synchrotron--FIR correlation in NGC6946 is more similar to M31 than M33. The scale dependence of the synchrotron--FIR correlation can be explained by the turbulent-to-ordered magnetic field ratio or, equivalently, the diffusion length of the cosmic ray electrons in these galaxies.

astro-ph.CO↗

arXiv2010

Lack of Interaction between the Dust Grains and the Anomalous Radio Jet in the Nearby Spiral Galaxy NGC 4258

We obtained Spitzer/IRAC 3.6-8 micron images of the nearby spiral galaxy NGC 4258 to study possible interactions between dust and the radio jet. In our analysis we also included high-resolution radio continuum, H-alpha, CO, and X-ray data. Our data reveal that the 8 micron emission, believed to originate largely from PAH molecules and hot dust, is an excellent tracer of the normal spiral structure in NGC 4258, and hence it originates from the galactic plane. We investigated the possibility of dust destruction by the radio jet by calculating correlation coefficients between the 8 micron and radio continuum emissions along the jet in two independent ways, namely (i) from wavelet-transformed maps of the original images at different spatial scales, and (ii) from one-dimensional intensity cuts perpendicular to the projected path of the radio jet on the sky. No definitive sign of a correlation (or anticorrelation) was detected on relevant spatial scales with either approach, implying that any dust destruction must take place at spatial scales that are not resolved by our observations.

astro-ph.CO↗