Why are some galaxy clusters underluminous?

Our knowledge of the variety of galaxy clusters has been increasing in the last few years thanks to our progress in understanding the severity of selection effects on samples. To understand the reason for the observed variety, we study CL2015, a cluster (log M500/M⊙ = 14.39) easily missed in X-ray selected observational samples. Its core-excised X-ray luminosity is low for its mass M500, well below the mean relation for an X-ray selected sample, but only ∼1.5σ below that derived for an X-ray unbiased sample. We derived thermodynamic profiles and hydrostatic masses with the acquired deep Swift X-ray data, and we used archival Einstein, Planck, and Sloan Digital Sky Survey data to derive additional measurements, such as integrated Compton parameter, total mass, and stellar mass. The pressure and the electron density profiles of CL2015 are systematically outside the ±2σ range of the universal profiles; in particular the electron density profile is even lower than the one derived from Planck-selected clusters. CL2015 also turns out to be fairly different in the X-ray luminosity vs. integrated pressure scaling compared to an X-ray selected sample, but it is a normal object in terms of stellar mass fraction. CL2015’s hydrostatic mass profile, by itself or when is considered together with dynamical masses, shows that the cluster has an unusual low concentration and an unusual sparsity compared to clusters in X-ray selected samples. The different behavior of CL2015 is caused by its low concentration. When concentration differences are accounted for, the properties of CL2015 become consistent with comparison samples. CL2015 is perhaps the first known cluster with a remarkably low mass concentration for which high quality X-ray data exist. Objects similar to CL2015 fail to enter observational X-ray selected samples because of their low X-ray luminosity relative to their mass. The different radial dependence of various observables is a promising way to collect other examples of low concentration clusters.

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The intracluster magnetic field in the double relic galaxy cluster Abell 2345

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab218 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2518-2535

Author(s):

C Stuardi ◽

A Bonafede ◽

L Lovisari ◽

P Domínguez-Fernández ◽

F Vazza ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Power Spectrum ◽

Electron Density ◽

Galaxy Clusters ◽

Radial Profile ◽

Electron Density Profile ◽

Thermal Electron ◽

X Ray ◽

Radial Profiles

ABSTRACT Magnetic fields are ubiquitous in galaxy clusters, yet their radial profile, power spectrum, and connection to host cluster properties are poorly known. Merging galaxy clusters hosting diffuse polarized emission in the form of radio relics offer a unique possibility to study the magnetic fields in these complex systems. In this paper, we investigate the intracluster magnetic field in Abell 2345. This cluster hosts two radio relics that we detected in polarization with 1–2 GHz Jansky Very Large Array observations. X-ray XMM–Newton images show a very disturbed morphology. We derived the rotation measure (RM) of five polarized sources within ∼1 Mpc from the cluster centre applying the RM synthesis. Both, the average RM and the RM dispersion radial profiles probe the presence of intracluster magnetic fields. Using the thermal electron density profile derived from X-ray analysis and simulating a 3D magnetic field with fluctuations following a power spectrum derived from magneto-hydrodynamical cosmological simulations, we build mock RM images of the cluster. We constrained the magnetic field profile in the eastern radio relic sector by comparing simulated and observed RM images. We find that, within the framework of our model, the data require a magnetic field scaling with thermal electron density as B(r) ∝ ne(r). The best model has a central magnetic field (within a 200 kpc radius) of 2.8$\pm 0.1 \ \mu$G. The average magnetic field at the position of the eastern relic is $\sim 0.3 \ \mu$G, a factor 2.7 lower than the equipartition estimate.

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The determination of the electron density profile of the human erythrocyte ghost membrane by small-angle x-ray diffraction

Biophysical Journal ◽

10.1016/s0006-3495(77)85576-8 ◽

1977 ◽

Vol 19 (2) ◽

pp. 141-161 ◽

Cited By ~ 9

Author(s):

E.H. Pape ◽

K. Klott ◽

W. Kreutz

Keyword(s):

Electron Density ◽

Density Profile ◽

Small Angle ◽

Human Erythrocyte ◽

Electron Density Profile ◽

Erythrocyte Ghost ◽

X Ray Diffraction ◽

X Ray ◽

Human Erythrocyte Ghost

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Determination of D-Region Electron Loss Rates and Electron Density Profiles from VLF Measurements During Solar Flare X-Ray Events

ELF-VLF Radio Wave Propagation ◽

10.1007/978-94-010-2265-1_16 ◽

1974 ◽

pp. 193-197 ◽

Cited By ~ 1

Author(s):

G. Bjøntegaard

Keyword(s):

Solar Flare ◽

Electron Density ◽

Electron Loss ◽

Density Profiles ◽

X Ray ◽

D Region ◽

Electron Density Profiles ◽

Loss Rates

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Redshift measurement through star formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833046 ◽

2019 ◽

Vol 629 ◽

pp. A7

Author(s):

Mikkel O. Lindholmer ◽

Kevin A. Pimbblet

Keyword(s):

Star Formation ◽

Galaxy Clusters ◽

Main Sequence ◽

Formation Rate ◽

Sloan Digital Sky Survey ◽

X Ray ◽

Star Forming ◽

Sky Survey ◽

The Galaxy ◽

Galaxy Population

In this work we use the property that, on average, star formation rate increases with redshift for objects with the same mass – the so called galaxy main sequence – to measure the redshift of galaxy clusters. We use the fact that the general galaxy population forms both a quenched and a star-forming sequence, and we locate these ridges in the SFR–M⋆ plane with galaxies taken from the Sloan Digital Sky Survey in discrete redshift bins. We fitted the evolution of the galaxy main sequence with redshift using a new method and then subsequently apply our method to a suite of X-ray selected galaxy clusters in an attempt to create a new distance measurement to clusters based on their galaxy main sequence. We demonstrate that although it is possible in several galaxy clusters to measure the main sequences, the derived distance and redshift from our galaxy main sequence fitting technique has an accuracy of σz = ±0.017 ⋅ (z + 1) and is only accurate up to z ≈ 0.2.

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Classification of X-ray solar flares regarding their effects on the lower ionosphere electron density profile

Annales Geophysicae ◽

10.5194/angeo-26-1731-2008 ◽

2008 ◽

Vol 26 (7) ◽

pp. 1731-1740 ◽

Cited By ~ 46

Author(s):

D. P. Grubor ◽

D. M. Šulić ◽

V. Žigman

Keyword(s):

Electron Density ◽

Solar Flares ◽

Low Frequency ◽

Lower Ionosphere ◽

Electron Density Profile ◽

Height Range ◽

X Ray ◽

Reflection Height ◽

Single Trace

Abstract. The classification of X-ray solar flares is performed regarding their effects on the Very Low Frequency (VLF) wave propagation along the Earth-ionosphere waveguide. The changes in propagation are detected from an observed VLF signal phase and amplitude perturbations, taking place during X-ray solar flares. All flare effects chosen for the analysis are recorded by the Absolute Phase and Amplitude Logger (AbsPal), during the summer months of 2004–2007, on the single trace, Skelton (54.72 N, 2.88 W) to Belgrade (44.85 N, 20.38 E) with a distance along the Great Circle Path (GCP) D≈2000 km in length. The observed VLF amplitude and phase perturbations are simulated by the computer program Long-Wavelength Propagation Capability (LWPC), using Wait's model of the lower ionosphere, as determined by two parameters: the sharpness (β in 1/km) and reflection height (H' in km). By varying the values of β and H' so as to match the observed amplitude and phase perturbations, the variation of the D-region electron density height profile Ne(z) was reconstructed, throughout flare duration. The procedure is illustrated as applied to a series of flares, from class C to M5 (5×10−5 W/m2 at 0.1–0.8 nm), each giving rise to a different time development of signal perturbation. The corresponding change in electron density from the unperturbed value at the unperturbed reflection height, i.e. Ne(74 km)=2.16×108 m−3 to the value induced by an M5 class flare, up to Ne(74 km)=4×1010 m−3 is obtained. The β parameter is found to range from 0.30–0.49 1/km and the reflection height H' to vary from 74–63 km. The changes in Ne(z) during the flares, within height range z=60 to 90 km are determined, as well.

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LOW X-RAY LUMINOSITY GALAXY CLUSTERS: MAIN GOALS, SAMPLE SELECTION, PHOTOMETRIC AND SPECTROSCOPIC OBSERVATIONS

The Astronomical Journal ◽

10.3847/0004-6256/151/6/151 ◽

2016 ◽

Vol 151 (6) ◽

pp. 151

Author(s):

José Luis Nilo Castellón ◽

M. Victoria Alonso ◽

Diego García Lambas ◽

Carlos Valotto ◽

Ana Laura O’ Mill ◽

...

Keyword(s):

Galaxy Clusters ◽

Sample Selection ◽

X Ray ◽

Spectroscopic Observations ◽

Photometric And Spectroscopic Observations ◽

Low X

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Analysis of space-resolved X-ray spectra from laser plasmas

Laser and Particle Beams ◽

10.1017/s0263034602202104 ◽

2002 ◽

Vol 20 (2) ◽

pp. 223-226 ◽

Cited By ~ 6

Author(s):

L. LABATE ◽

M. GALIMBERTI ◽

A. GIULIETTI ◽

D. GIULIETTI ◽

L.A. GIZZI ◽

...

Keyword(s):

Electron Density ◽

Ad Hoc ◽

Dynamic Range ◽

Spherical Geometry ◽

Ccd Camera ◽

High Dynamic Range ◽

Electron Density Profile ◽

Temperature Profiles ◽

X Ray ◽

Numerical Predictions

High dynamic range, space-resolved X-ray spectra, obtained using a TlAP crystal and a cooled CCD camera as a detector, were used to investigate the electron density and temperature profiles of an aluminum laser plasma with micrometer resolution. The electron density profile retrieved from the measurements is compared with numerical predictions from the two hydrodynamics codes MEDUSA (1D) and POLLUX (2D). It is shown that 2D density profiles can be successfully reproduced by 1D simulations using a spherical geometry with an ad hoc initial radius, leading to similar electron temperature profiles.

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