Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1807.05441

Towards building a first northern-sky sample of 'Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS)'

Mukul Mhaskey·Gopal-Krishna·Surajit Paul
View original source ↗Read source document ↗Export metadata ↓

Abstract

We present here an extension of our search for EISERS (Extremely Inverted Spectrum Extragalactic Radio Sources) to the northern hemisphere. With an inverted radio spectrum of slope $α$ $>$ + 2.5, these rare sources would either require a non-standard particle acceleration mechanism (in the framework of synchrotron self-absorption hypothesis), or a severe free-free absorption which attenuates practically all of their synchrotron radiation at metre wavelengths. A list of 15 EISERS candidates is presented here. It was assembled by applying a sequence of selection filters, starting with the two available large-sky radio surveys, namely the WENSS (325 MHz) and the ADR-TGSS (150 MHz). These surveys offer the twin advantages of being fairly deep (typical rms $<$ 10 mJy/beam) and having a sub-arcminute resolution. Their zone of overlap spreads over 1.3$π$ steradian in the northern hemisphere. Radio spectra are presented for the entire sample of 15 EISERS candidates, of which 8 spectra are of GPS type. Eleven members of the sample are associated with previously known quasars. Information on the parsec-scale radio structure, available for several of these sources, is also summarized.

Explore related subjects

astro-ph.GA

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Mukul Mhaskey, Gopal-Krishna, Surajit Paul. 2018-07-14. Towards building a first northern-sky sample of 'Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS)'. https://arxiv.org/abs/1807.05441

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Computational advances and challenges in simulations of turbulence and star formation

We review recent advances in the numerical modeling of turbulent flows and star formation. An overview of the most widely used simulation codes and their core capabilities is provided. We then examine methods for achieving the highest-resolution magnetohydrodynamical turbulence simulations to date, highlighting challenges related to numerical viscosity and resistivity. State-of-the-art approaches to modeling gravity and star formation are discussed in detail, including implementations of star particles and feedback from jets, winds, heating, ionization, and supernovae. We review the latest techniques for radiation hydrodynamics, including ray tracing, Monte Carlo, and moment methods, with comparisons between the flux-limited diffusion, moment-1, and variable Eddington tensor methods. The final chapter summarizes advances in cosmic-ray transport schemes, emphasizing their growing importance for connecting small-scale star formation physics with galaxy-scale evolution.

astro-ph.GA↗
arXiv2026

How significant is the lensing interpretation of GW231123?

GW231123 is one of the most unusual gravitational-wave (GW) events, with exceptionally large inferred masses and near-extremal spins, offering an opportunity to test whether propagation effects contribute to these properties. We therefore examine whether the data support wave-optics microlensing embedded in a strong-lensing galaxy, whose detection becomes increasingly likely as observations accumulate, whether this interpretation can explain these properties, and how significant the preference remains under detector noise and waveform systematics. We compare six hypotheses: unlensed, isolated point mass, and embedded point-mass (EPM) and binary-lens (EB) effective models in Type-I (minimum) and Type-II (saddle) macro images. The EB Type-I model is most favored. For the most accurate waveform model NRSur7dq4, it gives $\log_{10}B^{\rm EB-I}_{\rm U}=2.60$, versus $0.89$ for Type II, indicating sensitivity to macro-image geometry. Within Type I, however, the binary improves over the point mass by only $\log_{10}B^{\rm EB-I}_{\rm EPM-I}=0.16$ and $Δ\ln\mathcal{L}_{\max}=0.56$, providing no clear evidence for structure beyond a single effective perturber. Moreover, under embedded lensing, waveform-template discrepancies and inferred masses and spins are reduced. However, real O4a backgrounds from numerical-relativity injections show that the apparent lensing evidence is sensitive to waveform systematics and realistic detector noise: although the commonly used waveform IMRPhenomXPHM gives the largest Bayes factor, $\log_{10}B^{\rm EB-I}_{\rm U}=4.52$, it is less exceptional relative to its own background, with a false-alarm probability of $6.5$--$8\%$, whereas NRSur7dq4 gives only $2$--$3\%$. Thus, waveform systematics can amplify apparent lensing evidence, but GW231123 remains an intriguing lensing candidate.

astro-ph.GA↗
arXiv2026

MusE GAs FLOw and Wind (MEGAFLOW) XIV: Background-Galaxy Absorption Reveals Kiloparsec-Scale Structure in the Cool Circumgalactic Medium

The properties of the cool ($T\sim10^4$~K) gas in the circumgalactic medium (CGM) are closely linked to the physical mechanisms that create and maintain this multiphase medium. The cool CGM is thought to consist of discrete clouds, whose characteristic size is unknown. Here we present a geometric and direct approach to constrain the coherence scale of these cool structures using stacked MgII absorption lines measured against extended background galaxies and effectively point-like background quasars, whose sizes are a few kpc and $\lesssim 0.01$pc, respectively. When the background-source size is smaller than the coherence scale of the foreground clouds, incomplete covering lowers the detection fraction and causes the median stacked absorption to differ from the mean. For stacked MgII absorption against background galaxies, the mean and median equivalent width (EW) profiles are broadly consistent. For stacked MgII absorption against background quasars, by contrast, the median and mean EW profiles differ significantly, reaching a $\approx10σ$ difference beyond 100 kpc. Furthermore, we find that the median and mean EW profiles are broadly consistent for large background galaxies (median half-light radius $\approx 6.6$ kpc), but differ at the $\approx3σ$ level for small background galaxies ($\approx 1.5$ kpc). This suggests that the MgII-bearing gas has an effective transverse coherence scale of order a few kiloparsecs, broadly consistent with the $\sim$2--7 kpc range probed by the background galaxies. Using a toy model in which the CGM is populated with discrete cool clouds, we show that the observed differences arise naturally from the combination of partial covering and beam averaging. Our results provide a new geometry-based measure of the small-scale structure of cool CGM gas.

astro-ph.GA↗