ASCA Observations of Three Shakhbazyan's Compact Groups of Galaxies

Takahashi, Isao; Fukazawa, Yasushi; Kodaira, Keiichi; Makishima, Kazuo; Nakazawa, K.; Xu, Haiguang

doi:10.1093/pasj/52.5.769

Cited by 4 publications

(9 citation statements)

References 15 publications

(19 reference statements)

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“…The major sources of references include Rizza et al (1998), EF, MME, Arnaud & Evrard (1999), Neumannn & Arnaud (1999), Vikhlinin, Forman, & Jones (1999), and for clusters; and Mulchaey et al (1996), Dahlem & Thiering (2000), Helsdon & Ponman (2000), and Takahashi et al (2000) for groups. In most cases, the fittings were performed by excluding the central cooling components, which is compatible with our model without the inclusion of the radiative cooling.…”

Section: Radial Distribution Of Gas Fractionmentioning

confidence: 99%

Reexamination of the Galaxy Formation–regulated Gas Evolution Model in Groups and Clusters

Xue

2002

ApJ

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As an alternative explanation of the entropy excess and the steepening of the X-ray luminosity-temperature relation in groups and clusters, the galaxy formation-regulated gas evolution (GG) model proposed recently by Bryan makes an attempt to incorporate the formation of galaxies into the evolution of gas without additional heating by nongravitational processes. This seems to provide a unified scheme for our understanding of the structures and evolution of both galaxies and gas in groups and clusters. In this paper, we present an extensive comparison of the X-ray properties of groups and clusters predicted by the GG model and those revealed by current X-ray observations, using various large data sources in the literature and also taking the observational selection effects into account. These include an independent check of the fundamental working hypothesis of the GG model (i.e., galaxy formation was less efficient in rich clusters than in groups), a new test of the radial gas distributions revealed by both the gas mass fraction and the X-ray surface brightness profiles, and a reexamination of the X-ray luminosity-temperature and entropy-temperature relations. In particular, it shows that the overall X-ray surface brightness profiles predicted by the GG model are very similar in shape and insensitive to the X-ray temperature and that the shallower X-ray surface brightness profiles seen at low-temperature systems may arise from the current observational selection effect. This can be used as the simplest approach to distinguishing between the GG model and the preheating scenario. The latter yields an intrinsically shallower gas distribution in groups than in rich clusters.

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Section: Radial Distribution Of Gas Fractionmentioning

confidence: 99%

Reexamination of the Galaxy Formation–regulated Gas Evolution Model in Groups and Clusters

Xue

2002

ApJ

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“…The metal abundance was fixed to 0.3 solar based on results for other groups (Mulchaey et al 1996;Fukazawa et al 1996;Hickson 1997;Mulchaey, Zabludoff 1998). We fixed the plasma temperature in the range of 0.3-1.2 keV, stepping by 0.1 keV, to cover the typical values found in groups of galaxies (Pilidis et al 1995;Fukazawa et al 1996;Mulchaey et al 1996;Mulchaey, Zabludoff 1998;Davis et al 1999;Takahashi et al 2000). Although the small velocity dispersion, about 60 km s −1 , of the Local Group might indicate a considerably lower temperature (e.g., ∼ 0.1 keV) for a hydrostatic hot gas, the GIS does not have sensitivity for such cool emission.…”

Section: Limit To the Physical Parameters Of Hot Gasmentioning

confidence: 99%

“…We assume that the electron density obeys a β model of β = 2/3 based on the results for other groups (Pildis et al 1995;Mulchaey et al 1996;Mulchaey, Zabludoff 1998;Takahashi et al 2000). Then, the observed normalization, F obs ( sr −1 ), for β =2/3, which is the difference of gas emission between the directions of the LGC and LSS, is written as…”

Section: Limit To the Physical Parameters Of Hot Gasmentioning

confidence: 99%

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Search for hot gas in the local group with ASCA

Osone

Makishima

Matsuzaki

et al. 2000

Advances in Space Research

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An X-ray study was made to examine whether some part of the soft X-ray background is coming from hot gas in the Local Group. For this purpose, four consecutive pointings were made with ASCA toward a sky region between M 31 and M 33, which is close to the direction of the center of the Local Group. By comparing the X-ray surface brightness in this sky direction with that in another blank sky region near the north equatorial pole, an upper limit on any soft excess X-ray background was determined to be 2.8×10 −9 erg cm −2 s −1 sr −1 with a 90% confidence level statistical error. Assuming an optically thin thermal bremsstrahlung energy spectrum (Raymond-Smith model) for a temperature of 1 keV and a β-model electron density distribution for a core radius of 100 kpc for the X-ray halo, the upper limit of the central plasma density was obtained to be 1.3×10 −4 cm −3 . The plasma column density is too low to contribute significantly to the observed quadrupole anisotropy in the cosmic microwave background.

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“…SHK 202 . Even though optical and X‐Ray band studies (Kodaira et al 1988, 1990; Takahashi et al 2000, 2001) confirm the physical reality of this group, because of its closeness, resulting in a too low S/N ratio, our diagnostic tools fail to detect it as a statistic excess. Rejected from further analysis.…”

Section: Individual Propertiesmentioning

confidence: 91%

The properties of the heterogeneous Shakhbazyan groups of galaxies in the SDSS

Capozzi

Filippis

Paolillo

et al. 2009

Monthly Notices of the Royal Astronomical Society

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We present a systematic study of the subsample of Shakhbazyan (SHK) groups covered by the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). SHK groups probe an environment with characteristics which are intermediate between those of loose and very compact groups. Surprisingly, we found that several groups identifying algorithms, e. g. Berlind et al. and Tago et al., miss this type of structures. Using the SDSS DR5 spectroscopic data and the photometric redshifts derived in D'Abrusco et al., we identified possible group members in photometric redshift space and derived, for each group, several individual properties (richness, size, mean photometric redshift, fraction of red galaxies, etc.). We also combined pointed and stacked Rosat All Sky Survey (RASS) data to investigate the X-ray luminosities of these systems. Our study confirms that the majority of groups are physical entities with richness in the range 3-13 galaxies, and properties ranging between those of loose and compact groups. We confirm that SHK groups are richer in early-type galaxies than the surrounding environment and the field, as expected from the morphology - density relation and from the selection of groups of red galaxies. Furthermore, our work supports the existence of two subclasses of structures, the first one being formed by compact and isolated groups and the second formed by extended structures. We suggest that while the first class of objects dwells in less dense regions like the outer parts of clusters or the field, possibly sharing the properties of Hickson Compact Groups, the more extended structures represent a mixture of [core + halo] configurations and cores of rich clusters. X-ray luminosities for SHK groups are generally consistent with these results and with the expectations for the L(X)-sigma(v) relation, but also suggest the velocity dispersions reported in literature are underestimated for some of the richest systems

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ASCA Observations of Three Shakhbazyan's Compact Groups of Galaxies

Cited by 4 publications

References 15 publications

Reexamination of the Galaxy Formation–regulated Gas Evolution Model in Groups and Clusters

Reexamination of the Galaxy Formation–regulated Gas Evolution Model in Groups and Clusters

Search for hot gas in the local group with ASCA

The properties of the heterogeneous Shakhbazyan groups of galaxies in the SDSS

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