IIA SANTANU MONDALLow-velocity precessing jets can explain observed morphologies in the twin radio galaxy TRGJ104454+354055
Our understanding of large-scale radio jets in merger systems has been drastically improved in the era of the Very Large Array, Very Long Baseline Array/European VLBI Network, upgraded Giant Metrewave Radio Telescope, and MeerKAT. Twin radio galaxies (TRGs) are rare interacting galaxy pairs where both supermassive black holes host kiloparsec-scale bipolar radio jets. Only recently was a third TRG discovered, and it shows significantly different jet morphologies than the previous two. Due to both the extreme paucity and complexity of such systems, the launching of their jets as well as their mutual interaction during the propagation through the ambient medium are not well understood. We have performed three-dimensional hydrodynamic simulations to study the bipolar jets in the third TRG, J104454+354055. Our study indicates that the precession of mutually tilted bipolar jets originating from the two galactic nuclei separated by tens of kiloparsecs and propagating at low velocities can explain the observed morphologies. The simulated jet precession timescales are short compared to the overall dynamical timescale of the jets, and could originate from Lense–Thirring effect in the accretion disks. This approach to understanding TRG jet dynamics could also be applied to other TRG systems with similar helical morphologies that may be discovered in the upcoming era of the Square Kilometre Array and its pathfinder surveys.
IIA HARSH MATHURThe Hα Line as a Probe of Chromospheric Magnetic Fields
We explore the diagnostic potential of the Hα line for probing the chromospheric magnetic field using a realistic 3D radiative magnetohydrodynamic (rMHD) model. The Stokes profiles of the Hα line are synthesized through full 3D radiative transfer under the field-free approximation, alongside the Ca II 8542 Å and Fe I 6173 Å lines for comparison. The line-of-sight (LOS) magnetic fields are inferred using the weak-field approximation for the Hα and Ca II 8542 Å lines, while the Fe I 6173 Å line is analyzed through Milne-Eddington inversion techniques. The comparison between the inferred LOS magnetic field maps and the magnetic fields in the rMHD model revealed that the Hα line core primarily probes the chromospheric magnetic field at log 500 = −5.7, which corresponds to higher layers than the Ca II 8542 Å line core, which is most sensitive to conditions at log 500 = −5.1. On average, the Stokes V profiles of the Hα line core form 500 km higher than those of the Ca II 8542 Å line core. The Hα polarization signals persist after adding noise, and with noise at the level of 10−3 Ic, most simulated magnetic structures remain visible. These findings suggest that spectropolarimetric observations of the Hα line can provide complementary insights into the stratification of the magnetic field at higher altitudes, especially when recorded simultaneously with widely used chromospheric diagnostics such as the Ca II 8542 Å line.
IIA MAHESWAR, GAnalysis of forbidden neon emission lines in HAeBe stars using Spitzer IRS spectra
We analysed high-resolution mid-infrared spectra of 78 well-known Herbig Ae/Be (HAeBe) stars using Spitzer InfraRedSpectrograph data, focusing on the detection of [Ne II] and [Ne III] emission lines as indicators of ionized outflows or disc winds. Emission from [Ne II] at 12.81 μm or [Ne III] at 15.55 μm was identified in 25 sources, constituting the largest sample of HAeBe stars with these detected lines. Our analysis revealed a higher detection frequency of [Ne II] in sources with lower relative accretion luminosity (Lacc/L∗ < 0.1), suggesting a connection to the disc dispersal phase. We examined correlations between neon lines and various spectral features and investigated [Ne III]-to-[Ne II] line flux ratios to explore potential emission mechanisms. Neon emission is predominantly observed in Group I sources (75 per cent), where their flared disc geometry likely contributes to the observed emission, potentially originating from the irradiated disc atmosphere. Interestingly, we also find that Group II sources exhibit a higher median relative [Ne II] line luminosity (L[Ne II]/L∗), suggesting enhanced photoevaporation rates possibly associated with their more settled disc structures. However, larger samples and higher-resolution spectra are required to confirm this trend definitively. The high detection rate of the [Fe II] and [S III] lines, commonly associated with EUV-dominated regions, alongside a [Ne III]-to-[Ne II] emission ratio greater than 0.1 in sources where both lines detected, suggests that EUVradiation is the primary driver of neon emission in our sample.
IIA SAMPOORNA, MFull non-LTE multi-level radiative transfer: I. An atom with three bound infinitely sharp levels
The standard nonlocal thermodynamic equilibrium (non-LTE) multi-level radiative transfer problem only takes into account the deviation of the radiation field and atomic populations from their equilibrium distribution. Aims. We aim to show how to solve for the full non-LTE (FNLTE) multi-level radiative transfer problem, also accounting for deviation of the velocity distribution of the massive particles from Maxwellian. We considered, as a first step, a three-level atom with zero natural broadening. Methods. In this work, we present a new numerical scheme. Its initialisation relies on the classic, multi-level approximate Λ-iteration (MALI) method for the standard non-LTE problem. The radiative transfer equations, the kinetic equilibrium equations for atomic populations, and the Boltzmann equations for the velocity distribution functions were simultaneously iterated in order to obtain self-consistent particle distributions. During the process, the observer’s frame absorption and emission profiles were re-computed at every iterative step by convolving the atomic frame quantities with the relevant velocity distribution function. Results. We validate our numerical strategy by comparing our results with the standard non-LTE solutions in the limit of a two-level atom with Hummer’s partial redistribution in frequency, and with a three-level atom with complete redistribution. In this work, we considered the so-called cross-redistribution problem. We then show new FNLTE results for a simple three-level atom while evaluating the assumptions made for the emission and absorption profiles of the standard non-LTE problem with partial and cross-redistribution.
IIA SANTANU MONDALInterpreting the spectrotemporal properties of the black hole candidate swift J151857.0-572147 during its first outburst in 2024
The transient Galactic black hole candidate Swift J151857.0-572147 went through an outburst in 2024 March for the first time. Using publicly archived Insight-HXMT data, we have analyzed the timing and spectral properties of the source. We have extracted the properties of the quasiperiodic oscillations (QPOs) by fitting the power density spectrum, which inferred that the QPOs are of type C. We have detected QPOs up to ∼48 keV using an energy dependence study of the QPOs. A high-frequency QPO was not observed during this period. We also conclude that the oscillations of the shock in transonic advective accretion flows may be the possible reason for the origin of the QPOs. In the broad energy band of 2–100 keV, simultaneous data from the three onboard instruments of Insight-HXMT were used to perform spectral analysis. Different combinations of models, including a broken power law, a multicolor disk blackbody, interstellar absorption, nonrelativistic reflection in both neutral and ionized medium, and relativistic reflection, were used to understand the spectral properties during the outburst. We discovered that at the beginning of the analysis period, the source was in an intermediate state and later transitioning toward the soft state based on the spectral parameters. It has a high hydrogen column density, which could be due to some local absorption by the source.
IIA AMRUTHA, SA pilot method to determine the high mass end of the stellar initial mass function in galaxies using UVIT, Hα-MUSE observations and applied to NGC 628
We present a pilot method to estimate the high-mass initial mass function (IMF) across the arm, interarm, and spur regions in galaxies and apply it to NGC 628. We extracted star-forming complexes (SFCs) from the Hα Very Large Telescope/Multi Unit Spectroscopic Explorer and Ultraviolet Imaging Telescope (far-ultraviolet (FUV) and near-ultraviolet (NUV)) observations of NGC 628 and used Atacama Large Millimeter/submillimeter Array observations to define the molecular gas distribution. We find that the extinction-corrected Hα and FUV luminosities correlate well. Using the fact that O stars have a shorter lifetime (107 yr) compared to B stars (108 yr), we estimated the approximate number of O stars from Hα emission, and the number of B0 (M* > 10M⊙), and B1 (10M⊙ ≥ M* ≥ 3M⊙) stars using FUV and NUV observations. We derived the IMF index (α) for different regions using O to B0 (α1) and B0 to B1 (α2) stellar ratios. Our findings indicate that if we assume Hα arises only from O8-type stars, the resulting α1 value is consistent with the canonical IMF index. It steepens when we assume O stars with masses up to 100 M⊙ with mean α1 = 3.16 ± 0.62. However, the α2 does not change for large variations in the O-star population, and the mean α = 2.64 ± 0.14. When we include only blue SFCs (FUV − NUV ≤ 0.3), mean α2 is 2.43 ± 0.06. The IMF variation for SFCs in arms and spurs is insignificant. We also find that α2 correlates with different properties of the SFCs, the most prominent being the extinction-corrected UV color (FUV − NUV).
IIA VIVEK, MSpectroscopic quasar anomaly detection (SQuAD): I. Rest-frame UV spectra from SDSS DR16
We present the results of applying anomaly detection algorithms to a quasar spectroscopic subsample from the SDSS DR16 quasar catalog, covering the redshift range of 1.88 ≤ z ≤ 2.47. Methods. A principal component analysis (PCA) was employed for the dimensionality reduction of the quasar spectra, followed by a hierarchical k-means clustering in a 20-dimensional PCA eigenvector hyperspace. To prevent broad absorption line (BAL) quasars from being identified as the primary anomaly group, we conducted separate analyses on BAL and non-BAL quasars (a.k.a. QSOs), comparing both classes for a clearer identification of other anomalous quasar types. Results. We identified 2066 anomalous quasars, categorized into 10 broadly defined groups. The anomalous groups include: C IV peakers: quasars with extremely strong and narrow C IV emission lines; Excess Si IV emitters: quasars where the Si IV line is as strong as the C IV line; and Si IV deficient anomalies: which exhibit significantly weaker Si IV emission compared to typical quasars. The anomalous nature of these quasars is attributed to lower Eddington ratios for C IV peakers, supersolar metallicity for Excess Si IV emitters, and subsolar metallicity for Si IV deficient anomalies. Additionally, we identified four groups of BAL anomalies: blue BALs, flat BALs, reddened BALs, and FeLoBALs, distinguished primarily by the strength of reddening in these sources. Furthermore, among the non-BAL quasars, we identified three types of reddened anomaly groups classified as heavily reddened, moderately reddened, and plateau-shaped spectrum quasars, each exhibiting varying degrees of reddening. We present the detected anomalies as an accompanying value-added catalog.
IIA LABANYA KUMAR GUHACircumgalactic medium of quasar host galaxies at 0.4 ⩽ z ⩽ 0.8 probed by strong Mg II absorption
Using a sample of 166 projected quasar pairs, we investigate the influence of active galactic nuclei on the circumgalactic medium of the quasar host galaxies probed using strong Mg II absorption (i.e. W2796 ≥ 1 Å) at impact parameters (D) <100 kpc. The foreground quasars are restricted to the redshift range 0.4 ≤ z ≤ 0.8 and have median bolometric luminosity and stellar mass of 1045.1 erg s−1 and 1010.89M , respectively. We report detections of Mg II absorption in 29 cases towards the background quasar and in four cases along the line of sight to the foreground quasars. We do not find any difference in the distribution of W2796 and covering fraction (fc) as a function of D between quasar host galaxies and control sample of normal galaxies. These results are different from what has been reported in the literature, possibly because (i) our sample is restricted to a narrow redshift range, (ii) comparative analysis is carried out after matching the galaxy parameters, (iii) we focus mainly on strong Mg II absorption, and (iv) our sample lacks foreground quasars with high bolometric luminosity (i.e. Lbol > 1045.5 erg s−1). Future studies probing luminous foreground quasars, preferably at lower impact parameters and higher equivalent width sensitivity, are needed to consolidate our findings.
IIA ARCHANA SOAMKinematic study of molecular gas in cometary globule – LBN 437
Bright-rimmed, cometary-shaped star-forming globules, associated with H II regions, are remnants of compressed molecular shells exposed to ultraviolet radiation from central OB-type stars. The interplay between dense molecular gas and ionizing radiation, analysed through gas kinematics, provides significant insights into the nature and dynamic evolution of these globules. This study presents the results of a kinematic analysis of the cometary globule, Lynds’ Bright Nebula (LBN) 437, focusing on the first rotational transition of 12CO and C18O molecular lines observed using the Taeduk Radio Astronomy Observatory. The averaged 12CO spectrum shows a slightly skewed profile, suggesting the possibility of a contracting cloud. The molecular gas kinematics reveals signatures of infalling gas in the cometary head of LBN 437, indicating the initial stages of star formation. The mean infall velocity and mass infall rate towards the cometary head of LBN 437 are 0.25 km s−1 and 5.08 × 10−4 M yr−1, respectively, which align well with the previous studies on intermediate or high-mass star formation.