On the X-Ray Emission of the Low-Mass Galaxy Groups

Tovmassian, H. M.; Yam, O.; Tiersch, H.

doi:10.1086/339769

Cited by 12 publications

(18 citation statements)

References 25 publications

(31 reference statements)

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“…Moreover, there is an increasing scatter to smaller systems, since there are only a few galaxy tracers with which to estimate the dispersion. This scatter could be larger still in observational studies because of projection effects (Tovmassian, Yam, & Tiersch 2002).…”

Section: Velocity-dispersion Biasmentioning

confidence: 97%

X‐Ray Scaling Relations of Galaxy Groups in a Hydrodynamic Cosmological Simulation

Davé

Katz

Weinberg

2002

ApJ

107

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We examine the scalings of X-ray luminosity, temperature, and dark matter or galaxy velocity dispersion for galaxy groups in a ÃCDM cosmological simulation, which incorporates gravity, gas dynamics, radiative cooling, and star formation, but no substantial nongravitational heating. In agreement with observations, the simulated L X -and L X -T X relations are steeper than those predicted by adiabatic simulations or self-similar models, with L X / 4:4 and L X / T 2:6 X for massive groups and significantly steeper relations below a break at % 180 km s À1 (T X % 0:7 keV). The T X -relation is fairly close to the self-similar scaling relation, with T X / 1:75 , provided that the velocity dispersion is estimated from the dark matter or from e10 galaxies. The entropy of hot gas in low-mass groups is higher than predicted by self-similar scaling or adiabatic simulations, and it agrees with observational data that suggest an '' entropy floor.'' The steeper scalings of the luminosity relations are driven by radiative cooling, which reduces the hot (X-ray-emitting) gas fraction from 50% of the total baryons at % 500 km s À1 to 20% at % 100 km s À1 . A secondary effect is that hot gas in smaller systems is less clumpy, further driving down L X . A smaller volume simulation with 8 times higher mass resolution predicts nearly identical X-ray luminosities at a given group mass, demonstrating the insensitivity of the predicted scaling relations to numerical resolution. The higher resolution simulation predicts higher hot gas fractions at a given group mass, and these predicted fractions are in excellent agreement with available observations. There remain some quantitative discrepancies: the predicted mass scale of the L X -T X and L X -breaks is somewhat too low, and the luminosity-weighted temperatures are too high at a given , probably because our simulated temperature profiles are flat or rising toward small radii, while observed profiles decline at rd0:2R vir . We conclude that radiative cooling has an important quantitative impact on group X-ray properties and can account for many of the observed trends that have been interpreted as evidence for nongravitational heating. Improved simulations and observations are needed to understand the remaining discrepancies and to decide the relative importance of cooling and nongravitational heating in determining X-ray scalings.

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Section: Velocity-dispersion Biasmentioning

confidence: 97%

X‐Ray Scaling Relations of Galaxy Groups in a Hydrodynamic Cosmological Simulation

Davé

Katz

Weinberg

2002

ApJ

107

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“…The third possibility is that much of the orbital motion of the galaxy groups takes place in the plane of the sky and does not contribute to the line of sight velocity dispersion. Tovmassian et al (2002) showed that it is expected to find elongation and an anisotropic velocity dispersion tensor in many systems, since groups generally form within cosmic filaments.…”

Section: X-bootesmentioning

confidence: 99%

X-Ray-Selected Galaxy Groups in Boötes

Vajgel

Jones

Lopes

et al. 2014

ApJ

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We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. We used follow-up Chandra observations to better define the group sample and their X-ray properties. Group redshifts were measured from the AGES spectroscopic data. We used photometric data from the NOAO Deep Wide Field Survey (NDWFS) to estimate the group richness (N gals ) and the optical luminosity (L opt ). Our final sample comprises 32 systems at z < 1.75, with 14 below z = 0.35. For these 14 systems we estimate velocity dispersions (σ gr ) and perform a virial analysis to obtain the radii (R 200 and R 500 ) and total masses (M 200 and M 500 ) for groups with at least five galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (L X ). We examine the performance of the group properties σ gr , L opt and L X , as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the L X -M 500 relation at approximately. Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions and projection effects which reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group luminosity function estimates, eROSITA will identify ∼1800 groups (L X = 10 41 − 10 43 ergs s −1 ) within a distance of 200 Mpc. Since groups lie in large scale filaments, this group sample will map the large scale structure of the local universe.

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“…For galaxies, such an assumption is very unlikely to be accurate, even taking into account the fact that early-type galaxies will have potentials determined by the density of the Universe at the redshift of last major merger rather than that at which the majority of their stellar population formed. In order to calculate R 200 , we assume a mean redshift of formation for ellipticals of z form = 2 (Kauffmann, Charlot & White 1996;van Dokkum & Franx 2001). Using this value, we can calculate R 200 as described in Balogh, Babul & Patton (1999) and Babul et al (2002), taking variation of overdensity with redshift from Eke, Cole & Frenk (1996).…”

Section: β Fit and Entropymentioning

confidence: 99%

X-ray scaling properties of early-type galaxies

O’Sullivan

Ponman

Collins

2003

Monthly Notices of the Royal Astronomical Society

127

139

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We present an analysis of 39 X‐ray luminous early‐type galaxies observed with the ROSAT PSPC. Using multicomponent spectral and spatial fits to these data, we have measured halo abundance, temperature, luminosity and surface brightness profile. We compare these measurements to similar results from galaxy groups and clusters, fitting a number of relations commonly used in the study of these larger objects. In particular, we find that the σ–TX relation for our sample is similar to that reported for clusters, consistent with βspec= 1, and that the LX–TX relation has a steep slope (gradient 4.8 ± 0.7) comparable with that found for galaxy groups. Assuming isothermality, we construct three‐dimensional models of our galaxies, allowing us to measure gas entropy. We find no correlation between gas entropy and system mass, but do find a trend for low‐temperature systems to have reduced gas fractions. We conclude that the galaxies in our sample are likely to have developed their haloes through galaxy winds, influenced by their surrounding environment.

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On the X-Ray Emission of the Low-Mass Galaxy Groups

Cited by 12 publications

References 25 publications

X‐Ray Scaling Relations of Galaxy Groups in a Hydrodynamic Cosmological Simulation

X‐Ray Scaling Relations of Galaxy Groups in a Hydrodynamic Cosmological Simulation

X-Ray-Selected Galaxy Groups in Boötes

X-ray scaling properties of early-type galaxies

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