The discovery of a radio galaxy of at least 5 Mpc

We discover what is in projection the largest known structure of galactic origin: a giant radio galaxy with a projected proper length of $4.99 \pm 0.04\ \mathrm{Mpc}$. The source, named Alcyoneus, was first identified in low-resolution LOFAR Two-metre Sky Survey images from which angularly compact sources had been removed. Being an extreme example in its class, Alcyoneus could shed light on the main mechanisms that drive radio galaxy growth. We find that - beyond geometry - Alcyoneus and its host galaxy appear suspiciously ordinary: the total low-frequency luminosity density, stellar mass and supermassive black hole mass are all lower than, though similar to, those of the medial giant radio galaxy (percentiles$45 \pm 3\%$,$25 \pm 9 \%$and$23 \pm 11 \%$, respectively). The source resides in a filament of the Cosmic Web, with which it might have significant thermodynamic interaction. At$5 \cdot 10^{-16}\ \mathrm{Pa}$, the pressures in the lobes are the lowest hitherto found, and Alcyoneus therefore represents one of the most promising radio galaxies yet to probe the warm-hot intergalactic medium.Comment: 18 pages, 14 figures, 3 tables, accepted for publication in Astronomy & Astrophysic

Accretion mode versus radio morphology in the LOFAR Deep Fields

Radio-loud active galaxies have two accretion modes [radiatively inefficient (RI) and radiatively efficient (RE)], with distinct optical and infrared signatures, and two jet dynamical behaviours, which in arcsec- to arcmin-resolution radio surveys manifest primarily as centre- or edge-brightened structures [Fanaroff–Riley (FR) class I and II]. The nature of the relationship between accretion mode and radio morphology (FR class) has been the subject of long debate. We present a comprehensive investigation of this relationship for a sample of 286 well-resolved radio galaxies in the LOFAR Two-metre Sky Survey Deep Fields (LoTSS-Deep) first data release, for which robust morphological and accretion mode classifications have been made. We find that two-thirds of luminous FRII radio galaxies are RI, and identify no significant differences in the visual appearance or source dynamic range (peak/mean surface brightness) of the RI and RE FRIIs, demonstrating that both RI and RE systems can produce FRII structures. We also find a significant population of low-luminosity FRIIs (predominantly RI), supporting our earlier conclusion that FRII radio structures can be produced at all radio luminosities. We demonstrate that in the luminosity range where both morphologies are present, the probability of producing FRI or FRII radio morphology is directly linked to stellar mass, while across all morphologies and luminosities, RE accretion occurs in systems with high specific star formation rate, presumably because this traces fuel availability. In summary, the relationship between accretion mode and radio morphology is very indirect, with host-galaxy environment controlling these two key parameters in different ways

Image Acquisition for Biometric: Face Recognition

Biometrics is mostly used for authentication purposes in security. Due to the covid-19 pandemic situation, nowadays distance-based authentication systems are more focused. Face recognition is one of the best approaches which can use for authentication at distance. Face recognition is a challenging task in various environments. For that taking input from the camera is very important for real-time applications. In this chapter, we are more focusing on how to acquire the face image using MATLAB. The complete chapter is divided into five sections introduction, definition of biometrics, image acquisition devices, image acquisition process in MATLAB

MACS J0553.4−3342: a young merging galaxy cluster caught through the eyes of Chandra and HST

We present a detailed analysis of a young merging galaxy cluster \mac~(z=0.43), from {\it Chandra} X-ray and {\it Hubble Space Telescope} archival data. X-ray observations confirm that the X-ray emitting intra-cluster medium (ICM) in this system is among the hottest (average $T=12.1 \pm 0.6$ keV) and most luminous known. Comparison of X-ray and optical images confirm that this system hosts two merging subclusters SC1 and SC2, separated by a projected distance of about 650\,kpc. The subcluster SC2 is newly identified in this work, while another subcluster (SC0), previously thought to be part of this merging system, is shown to be possibly a foreground object. Apart from two subclusters, we find a tail-like structure in the X-ray image, extending to a projected distance of $\sim$1\,Mpc, along the north-east direction of the eastern subcluster (SC1). From a surface brightness analysis, we detect two sharp surface brightness edges at $\sim$40\arcsec ($\sim$320\,kpc) and $\sim$80\arcsec ($\sim$640\,kpc) to the east of SC1. The inner edge appears to be associated with a merger-driven cold front, while the outer one is likely to be due to a shock front, the presence of which, ahead of the cold front, makes this dynamically disturbed cluster interesting. Nearly all the early-type galaxies belonging to the two subclusters, including their BCGs, are part of a well-defined red sequence.Comment: 13 pages, 12 figures, 6 Tables, Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Search and analysis of giant radio galaxies with associated nuclei (SAGAN). I. New sample and multi-wavelength studies

International audienceWe present the first results of a project called SAGAN, which is dedicated solely to the studies of relatively rare megaparsec-scale radio galaxies in the Universe, called giant radio galaxies (GRGs). We have identified 162 new GRGs primarily from the NRAO VLA Sky Survey with sizes ranging from ∼0.71 Mpc to ∼2.82 Mpc in the redshift range of ∼0.03-0.95, of which 23 are hosted by quasars (giant radio quasars). As part of the project SAGAN, we have created a database of all known GRGs, the GRG catalogue, from the literature (including our new sample); it includes 820 sources. For the first time, we present the multi-wavelength properties of the largest sample of GRGs. This provides new insights into their nature. Our results establish that the distributions of the radio spectral index and the black hole mass of GRGs do not differ from the corresponding distributions of normal-sized radio galaxies (RGs). However, GRGs have a lower Eddington ratio than RGs. Using the mid-infrared data, we classified GRGs in terms of their accretion mode: either a high-power radiatively efficient high-excitation state, or a radiatively inefficient low-excitation state. This enabled us to compare key physical properties of their active galactic nuclei, such as the black hole mass, spin, Eddington ratio, jet kinetic power, total radio power, magnetic field, and size. We find that GRGs in high-excitation state statistically have larger sizes, stronger radio power, jet kinetic power, and higher Eddington ratio than those in low-excitation state. Our analysis reveals a strong correlation between the black hole Eddington ratio and the scaled jet kinetic power, which suggests a disc-jet coupling. Our environmental study reveals that ∼10% of all GRGs may reside at the centres of galaxy clusters, in a denser galactic environment, while the majority appears to reside in a sparse environment. The probability of finding the brightest cluster galaxy as a GRG is quite low and even lower for high-mass clusters. We present new results for GRGs that range from black hole mass to large-scale environment properties. We discuss their formation and growth scenarios, highlighting the key physical factors that cause them to reach their gigantic size. Tables A1-A4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A153</A

Luminous giants populate the dense Cosmic Web

© 2024 The Author(s). Published by EDP Sciences. his is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Context. Giant radio galaxies (GRGs, giant RGs, or giants) are megaparsec-scale, jet-driven outflows from accretion disks of supermassive black holes, and represent the most extreme pathway by which galaxies can impact the Cosmic Web around them. A long-standing but unresolved question is why giants are so much larger than other radio galaxies. Aims. It has been proposed that, in addition to having higher jet powers than most RGs, giants might live in especially low-density Cosmic Web environments. In this work, we aim to test this hypothesis by pinpointing Local Universe giants and other RGs in physically principled, Bayesian large-scale structure reconstructions. Methods. More specifically, we localised a LOFAR Two-metre Sky Survey (LoTSS) DR2–dominated sample of luminous (lν(ν = 150 MHz)≥1024 W Hz−1) giants and a control sample of LoTSS DR1 RGs, both with spectroscopic redshifts up to zmax = 0.16, in the BORG SDSS Cosmic Web reconstructions. We measured the Cosmic Web density on a smoothing scale of ∼2.9 Mpc h−1 for each RG; for the control sample, we then quantified the relation between RG radio luminosity and Cosmic Web density. With the BORG SDSS tidal tensor, we also measured for each RG whether the gravitational dynamics of its Cosmic Web environment resemble those of clusters, filaments, sheets, or voids. Results. For both luminous giants and general RGs, the Cosmic Web density distribution is gamma distribution–like. Luminous giants populate large-scale environments that tend to be denser than those of general RGs. This result is corroborated by gravitational dynamics classification and a cluster catalogue crossmatching analysis. We find that the Cosmic Web density around RGs with 150 MHz radio luminosity lν is distributed as 1 + ΔRG | Lν = lν ∼ Γ(k, θ), where k = 4.8 + 0.2 · √, θ = 1.4 + 0.02 · √, and √:= log10(lν (1023 W Hz−1)−1). Conclusions. This work presents more than a thousand inferred megaparsec-scale densities around radio galaxies, which may be correct up to a factor of order unity – except in clusters of galaxies, where the densities can be more than an order of magnitude too low. We pave the way to a future in which megaparsec-scale densities around RGs are common inferred quantities, which help to better understand their dynamics, morphology, and interaction with the enveloping Cosmic Web. Our data demonstrate that luminous giants inhabit denser environments than general RGs. This shows that – at least at high jet powers – low-density environments are no prerequisite for giant growth. Using general RGs, we quantified the relation between radio luminosity at 150 MHz and Cosmic Web density on a smoothing scale of ∼2.9 Mpc h−1. This positive relation, combined with the discrepancy in radio luminosity between known giants and general RGs, reproduces the discrepancy in Cosmic Web density between known giants and general RGs. Our findings are consistent with the view that giants are regular, rather than mechanistically special, members of the radio galaxy population.Peer reviewe