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A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XX. Star formation in the tidal tail of NGC 4254
Authors:
A. Boselli,
A. Lupi,
P. Serra,
P. Andreani,
F. Calura,
M-A. Miville-Deschenes,
G. Hensler,
M. Boquien,
M. Fossati,
S. Boissier,
J. Braine,
P. Cote,
J. C. Cuillandre,
F. de Gasperin,
H. Edler,
L. Ferrarese,
G. Gavazzi,
S. Gwyn,
J. Hutchings,
K. Kianfar,
A. Longobardi,
E. S. Mangola,
S. Martocchia,
E. Peng,
H. Plana
, et al. (4 additional authors not shown)
Abstract:
ALMA 12CO(1-0) observations of 42 star-forming regions located outside the disc of the Virgo Cluster galaxy NGC4254 within an HI gas tail produced during the galaxy's interaction with another cluster member have revealed the presence of ten giant molecular clouds (GMCs) in four of these regions. All of the GMCs were resolved at the angular resolution of the observations (~160 pc) and have molecula…
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ALMA 12CO(1-0) observations of 42 star-forming regions located outside the disc of the Virgo Cluster galaxy NGC4254 within an HI gas tail produced during the galaxy's interaction with another cluster member have revealed the presence of ten giant molecular clouds (GMCs) in four of these regions. All of the GMCs were resolved at the angular resolution of the observations (~160 pc) and have molecular gas masses of M(H2)~(0.8-2.0)x10^6} Mo. These ten clouds are characterised by gas column densities [S(H2)~10 Mo pc^-2] and velocity dispersions [sigma_v(CO)~3-12 km s^-1] respectively lower and comparable to those encountered in similar GMCs in the Milky Way. They follow the relation between the gas column density and the star formation activity (Schmidt law) derived using similar data over the stellar disc of NGC4254 and other local and Virgo cluster galaxies. With analytic calculations and tuned simulations, we show that these clouds are unstable and thus expected to dissolve on relatively short timescales (~10-30 Myr). We show that they probably formed after the collapse of dense gas clouds in the HI gas tail stripped during the gravitational interaction that the galaxy suffered several hundreds millions of years ago. The clouds are short-lived and isolated given the low density of the surrounding intracluster medium, which cannot confine the gas expelled by stellar feedback. We discuss the implications of these results in the general context of the fate of stripped gas in hostile cluster environments.
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Submitted 18 June, 2026;
originally announced June 2026.
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A Causal Probabilistic Framework for Perception-Informed Closed-Loop Simulation of Autonomous Driving
Authors:
Zhennan Fei,
Rickard Johansson,
Mikael Andersson,
Matthias Eng,
Mattias Eriksson,
Kaveh Kianfar,
Sadegh Rahrovani,
Chris van der Ploeg,
Michael Borth,
Maren Buermann,
Michiel Braat,
Henk Goossens,
Zijian Han,
Majid Khorsand Vakilzadeh,
Gabriel Rodrigues de Campos
Abstract:
Software-in-the-loop (SIL) simulation is a cornerstone for the validation of modern automotive safety functions. However, many current frameworks utilize ideal sensing, which bypasses the functional insufficiencies of perception algorithms, leading to over-optimistic safety assessments. This paper proposes a perception-informed SIL testing methodology that bridges the gap between ground-truth simu…
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Software-in-the-loop (SIL) simulation is a cornerstone for the validation of modern automotive safety functions. However, many current frameworks utilize ideal sensing, which bypasses the functional insufficiencies of perception algorithms, leading to over-optimistic safety assessments. This paper proposes a perception-informed SIL testing methodology that bridges the gap between ground-truth simulation and real-world perception behavior. We present a framework for incorporating causal probabilistic models into standardized, scenario-based simulation toolchains, applicable to both Advanced Driver Assistance Systems (ADAS) and Autonomous Driving Systems (ADS). Our approach enables the systematic injection of realistic perception errors, such as loss of detection, sizing inaccuracies, and positioning offsets, derived from physical triggering conditions like fog, rain, and object-merging scenarios. By evaluating these ``faults'' within a standardized simulation environment, we demonstrate that perception-informed testing reveals latent operational risks that ideal SIL environments fail to capture, providing a scalable pathway for SOTIF (ISO 21448) validation.
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Submitted 5 June, 2026;
originally announced June 2026.
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Double White Dwarf Mergers as Progenitors of Long-Period Transients
Authors:
Manuel Malheiro,
Sarah V. Borges,
Jaziel G. Coelho,
Khashayar Kianfar,
Ronaldo V. Lobato,
Edson Otoniel,
Jorge A. Rueda,
Manoel F. Sousa,
Fridolin Weber
Abstract:
There is an ongoing discussion in the literature on the nature of long-period transients (LPTs), radio-emitting sources with periods ranging from hundreds to tens of thousands of seconds. Although some of these objects have been identified as white dwarf (WD) + M-dwarf binaries, this description currently does not fit the entire class. An example is GLEAM-X J162759.5-523504.3 (hereafter GLEAM-X J1…
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There is an ongoing discussion in the literature on the nature of long-period transients (LPTs), radio-emitting sources with periods ranging from hundreds to tens of thousands of seconds. Although some of these objects have been identified as white dwarf (WD) + M-dwarf binaries, this description currently does not fit the entire class. An example is GLEAM-X J162759.5-523504.3 (hereafter GLEAM-X J1627-5235), with a period of 1091 s, for which the lack of an optical counterpart disfavors the presence of such a binary system. In this case, GLEAM-X J1627-5235 could be interpreted as an isolated, massive, fast-rotating, and highly magnetized (~ 1e+9 G) WD pulsar. Its properties are consistent with a carbon-oxygen WD of mass ~1.3 Msun and radius ~2500 km, possibly supported by small-scale multipolar magnetosphere structures that keep it above the death line for WD-pulsars. We assess a double WD merger origin, modeling the post-merger rotational evolution under accretion, propeller, and magnetic braking torques. We find rotational age of ~572 Myr for GLEAM-X J1627-5235, i.e., the post-merger time required to reach its observed period. This result is consistent with current optical upper limits for GLEAM-X J1627-5235 and support the WD pulsar interpretation for this source. We also discuss how the same model can apply to other LPTs.
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Submitted 9 March, 2026;
originally announced March 2026.
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FLAME: A Federated Learning Approach for Multi-Modal RF Fingerprinting
Authors:
Kasra Borazjani,
Kiarash Kianfar,
Seyyedali Hosseinalipour,
Rajeev Sahay
Abstract:
Authorization systems are increasingly relying on processing radio frequency (RF) waveforms at receivers to fingerprint (i.e., determine the identity of) the corresponding transmitter. Federated learning (FL) has emerged as a popular paradigm to perform RF fingerprinting in networks with multiple access points (APs), as they allow effective deep learning-based device identification without requiri…
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Authorization systems are increasingly relying on processing radio frequency (RF) waveforms at receivers to fingerprint (i.e., determine the identity of) the corresponding transmitter. Federated learning (FL) has emerged as a popular paradigm to perform RF fingerprinting in networks with multiple access points (APs), as they allow effective deep learning-based device identification without requiring the centralization of locally collected RF signals stored at multiple APs. Yet, FL algorithms that operate merely on in-phase and quadrature (I/Q) time samples incur high convergence rates, resulting in excessive training rounds and inefficient training times. In this work, we propose FLAME: an FL approach for multi-modal RF fingerprinting. Our framework consists of simultaneously representing received RF waveforms in multiple complementary modalities beyond I/Q samples in an effort to reduce training times. We theoretically demonstrate the feasibility and efficiency of our methodology and derive a convergence bound that incurs lower loss and thus higher accuracies in the same training round in comparison to single-modal FL-based RF fingerprinting. Extensive empirical evaluations validate our theoretical results and demonstrate the superiority of FLAME in comparison to multiple considered baselines.
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Submitted 1 July, 2026; v1 submitted 6 March, 2025;
originally announced March 2025.
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AGN feeding along a one-armed spiral in NGC 4593: A study using ALMA CO(2-1) observations
Authors:
K. Kianfar,
P. Andreani,
J. A. Fernández-Ontiveros,
F. Combes,
L. Spinoglio,
E. Hatziminaoglou,
C. Ricci,
A. Bewketu-Belete,
M. Imanishi,
M. Pereira-Santaella,
R. Slater,
M. Malheiro
Abstract:
We investigate active galactic nuclei (AGN) feeding through the molecular gas (CO(2-1) emission) properties of the local Seyfert 1 galaxy NGC 4593, using Atacama Large Millimeter Array (ALMA) observations and other multi-wavelength data. Our study aims to understand the interplay between the AGN and the interstellar medium (ISM) in this galaxy, examining the role of the AGN in steering gas dynamic…
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We investigate active galactic nuclei (AGN) feeding through the molecular gas (CO(2-1) emission) properties of the local Seyfert 1 galaxy NGC 4593, using Atacama Large Millimeter Array (ALMA) observations and other multi-wavelength data. Our study aims to understand the interplay between the AGN and the interstellar medium (ISM) in this galaxy, examining the role of the AGN in steering gas dynamics within its host galaxy, evaluating the energy injected into the ISM, and determining whether gas is inflowing or outflowing from the galaxy. After reducing the ALMA CO(2-1) images, we employed two models, 3D-Barolo and DISCFIT, to construct a disc model and fit its emission to the ALMA data. Additionally, we used photometric data to build a spectral energy distribution (SED) and applied the CIGALE code to derive key physical properties of the AGN and its host. Our analysis reveals a complex interplay within NGC 4593, including a clear rotational pattern, the influence of a non-axisymmetric bar potential, and a central molecular zone (CMZ)-like ring. We observe an outflow of CO(2-1) gas along the minor axis, at a distance of approximately 220 pc from the nucleus. The total molecular gas mass is estimated to be between $1 - 5 \times 10^8 \, M_{\odot}$, with non-circular motions contributing about 10\%. Our SED analysis indicates an AGN fraction of 0.88 and a star formation rate (SFR) of 0.42 $M_{\odot} \, \text{yr}^{-1}$. These findings highlight the complex dynamics in the centre of NGC 4593, which are significantly influenced by the presence of the AGN. The overall physical properties of this system suggest that the AGN has a substantial impact on the evolution of NGC 4593.
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Submitted 13 October, 2024;
originally announced October 2024.
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A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).XII. Ionised gas emission in the inner regions of lenticular galaxies
Authors:
A. Boselli,
M. Fossati,
A. Longobardi,
K. Kianfar,
N. Z. Dametto,
P. Amram,
J. P. Anderson,
P. Andreani,
S. Boissier,
M. Boquien,
V. Buat,
G. Consolandi,
L. Cortese,
P. Côté,
J. C. Cuillandre,
L. Ferrarese,
L. Galbany,
G. Gavazzi,
S. Gwyn,
G. Hensler,
J. Hutchings,
E. W. Peng,
J. Postma,
J. Roediger,
Y. Roehlly
, et al. (2 additional authors not shown)
Abstract:
As part of the VESTIGE survey, a blind narrow-band Ha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered 8 massive lenticular galaxies with prominent ionised gas emission features in their inner (few kpc) regions. These features are either ionised gas filaments similar to those observed in cooling flows (2 gal), or thin discs with sizes 0.7<R(Ha)<2.0 kpc…
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As part of the VESTIGE survey, a blind narrow-band Ha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered 8 massive lenticular galaxies with prominent ionised gas emission features in their inner (few kpc) regions. These features are either ionised gas filaments similar to those observed in cooling flows (2 gal), or thin discs with sizes 0.7<R(Ha)<2.0 kpc (6 gal), thus significantly smaller than those of the stellar disc. These discs have morphological properties similar to those of the dust seen in absorption in high-resolution HST images. Using a unique set of multifrequency data we show that while the gas located within these inner discs is photoionised by young stars, signaling ongoing star formation, the gas in the filamentary structures is shock-ionised. These discs have a star formation surface brightness similar to those observed in late-type galaxies. Because of their reduced size, however, these lenticular galaxies are located below the main sequence of unperturbed or cluster star-forming systems. By comparing the dust masses measured from absorption maps in optical images, from the Balmer decrement, or estimated by fitting the UV-to-far-IR spectral energy distribution of the target galaxies, we confirm that those derived from optical attenuation maps are heavily underestimated because of geometrical effects due to the relative distribution of the absorbing dust and the emitting stars. We have also shown that these galaxies have gas-to-dust ratios of G/D~80, and that the star formation within these discs follows the Schmidt relation, albeit with an efficiency reduced by a factor of ~ 2.5. Using our unique set of multifrequency data, we discuss the possible origin of the ionised gas in these objects, which suggests multiple and complex formation scenarios for massive lenticular galaxies in clusters.
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Submitted 12 November, 2021;
originally announced November 2021.
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Magnetically charged stars with nonlinear electrodynamics
Authors:
Khashayar Kianfar
Abstract:
In this research, we introduce magnetically charged stars in the framework of non-singular metric which is explained with nonlinear electrodynamics(NED). This model allows us to have an upper limit for the maximum limit for the mass of stars in the presence of NED. We explain our model for magnetized compact object by considering the polytropic equation of states(EoS)
In this research, we introduce magnetically charged stars in the framework of non-singular metric which is explained with nonlinear electrodynamics(NED). This model allows us to have an upper limit for the maximum limit for the mass of stars in the presence of NED. We explain our model for magnetized compact object by considering the polytropic equation of states(EoS)
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Submitted 6 June, 2024; v1 submitted 19 March, 2021;
originally announced March 2021.
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Optimum Search Schemes for Approximate String Matching Using Bidirectional FM-Index
Authors:
Kiavash Kianfar,
Christopher Pockrandt,
Bahman Torkamandi,
Haochen Luo,
Knut Reinert
Abstract:
Finding approximate occurrences of a pattern in a text using a full-text index is a central problem in bioinformatics and has been extensively researched. Bidirectional indices have opened new possibilities in this regard allowing the search to start from anywhere within the pattern and extend in both directions. In particular, use of search schemes (partitioning the pattern and searching the piec…
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Finding approximate occurrences of a pattern in a text using a full-text index is a central problem in bioinformatics and has been extensively researched. Bidirectional indices have opened new possibilities in this regard allowing the search to start from anywhere within the pattern and extend in both directions. In particular, use of search schemes (partitioning the pattern and searching the pieces in certain orders with given bounds on errors) can yield significant speed-ups. However, finding optimal search schemes is a difficult combinatorial optimization problem.
Here for the first time, we propose a mixed integer program (MIP) capable to solve this optimization problem for Hamming distance with given number of pieces. Our experiments show that the optimal search schemes found by our MIP significantly improve the performance of search in bidirectional FM-index upon previous ad-hoc solutions. For example, approximate matching of 101-bp Illumina reads (with two errors) becomes 35 times faster than standard backtracking. Moreover, despite being performed purely in the index, the running time of search using our optimal schemes (for up to two errors) is comparable to the best state-of-the-art aligners, which benefit from combining search in index with in-text verification using dynamic programming. As a result, we anticipate a full-fledged aligner that employs an intelligent combination of search in the bidirectional FM-index using our optimal search schemes and in-text verification using dynamic programming outperforms today's best aligners. The development of such an aligner, called FAMOUS (Fast Approximate string Matching using OptimUm search Schemes), is ongoing as our future work.
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Submitted 5 March, 2018; v1 submitted 6 November, 2017;
originally announced November 2017.