73 research outputs found
Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies
The relation between X-ray luminosity and near-infrared luminosity for
early-type galaxies has been examined. Near-infrared (NIR) luminosities should
provide a superior measure of stellar mass compared to optical luminosities
used in previous studies, especially if there is significant star-formation or
dust present in the galaxies. However, we show that the X-ray-NIR relations are
remarkably consistent with the X-ray-optical relations. This indicates that the
large scatter of the relations is dominated by scatter in the X-ray properties
of early-type galaxies, and is consistent with early-types consisting of old,
quiescent stellar populations.
We have investigated scatter in terms of environment, surface brightness
profile, Mg2, H_beta, H_gamma line strength indices, spectroscopic age, and
nuclear H_alpha emission. We found that galaxies with high Mg2 index, low
H_beta and H_gamma indices or a `core' profile have a large scatter in Lx,
whereas galaxies with low Mg2, high H_beta and H_gamma indices or `power-law'
profiles, generally have Lx<10^41 erg/s. There is no clear trend in the scatter
with environment or nuclear H_alpha emission.Comment: Accepted for publication in MNRAS. 22 pages, 15 figure
X-ray properties of early-type galaxies
It has been known for some time that many early–type galaxies possess halos of X–ray emitting gas. However, the properties of these halos and the processes by which they form are as yet not well understood. We have compiled the largest catalogue of X–ray luminosities to date, and use it to examine the relationships between X–ray luminosity and galaxy age, environment and optical luminosity. It is shown that the mass of the X–ray halo increases with galaxy age, and that there is no trend in LX/LBwith environment. Group dominant galaxies are shown to be more X–ray luminous than galaxies in other environments, and the effect of this on the LX:LBrelation is explored. A smaller sample of highly X–ray luminous galaxies is studied in more detail, and their properties compared to those of galaxy groups and clusters. It is shown that while galaxy halos are similar to those of larger structures they differ in that their surface brightness profiles do not vary with system temperature. It is also shown that early–type galaxies have lower gas fractions than groups and clusters, probably owing to gas loss from the system through galaxy winds
The Complete Local Volume Groups Sample - II. A study of the Central Radio Galaxies in the HighRichness Sub-sample
We present a study of the radio properties of the dominant early-type
galaxies in 26 galaxy groups, the high-richness sub-sample of the Complete
Local-volume Groups Sample (CLoGS). Combining new 610 MHz and 235 MHz
observations of 21 groups from the Giant Metrewave Radio Telescope (GMRT) with
archival GMRT and Very Large Array (VLA) survey data, we find a high detection
rate, with 92% of the dominant galaxies hosting radio sources. The sources have
a wide range of luminosities, 10 10 W/Hz in the 235 and 610
MHz bands. The majority (54%) are point-like, but 23% have radio jets, and
another 15% are diffuse radio sources with no clear jet/lobe morphology. The
spectral index of the detected radio sources ranges from very flat values of
~0.2 to typical radio synchrotron spectra of ~0.9 with only two presenting
steep radio spectra with > 1. We find that jet sources are
more common in X-ray bright groups, with radio non-detections found only in
X-ray faint systems. Radio point sources appear in all group environments
irrespective of their X-ray properties or spiral fraction. We estimate the
mechanical power (Pcav) of the jet sources in the X-ray bright groups to be
10 10 erg/s, with the two large-scale jet systems (NGC 193
and NGC 4261) showing jet powers two orders of magnitude greater than the
radiative losses from the cool cores of their groups. This suggests that
central AGN are not always in balance with cooling, but may instead produce
powerful periodical bursts of feedback heating.Comment: Accepted for publication by MNRAS, 19 Manuscript pages with 8 tables
and 8 figures, plus 13 pages of appendice
Interaction between the intergalactic medium and central radio source in the NGC 4261 group of galaxies
Using observations from the Chandra and XMM-Newton X-ray observatories, we
examine the interaction between the intra-group medium and central radio source
in the nearby NGC 4261 galaxy group. We confirm the presence of cavities
associated with the radio lobes and estimate their enthalpy to be ~2.4x10^58
erg. The mechanical power output of the jets is >=10^43 erg/s, at least a
factor of 60 greater than the cooling luminosity in the region the lobes
inhabit. We identify rims of compressed gas enclosing the lobes, but find no
statistically significant temperature difference between them and their
surroundings, suggesting that the lobe expansion velocity is approximately
sonic (Mach<=1.05). The apparent pressure of the radio lobes, based on the
synchrotron minimum energy density argument, is a factor of 5 lower than that
of the intra-group medium. Pressure balance could be achieved if entrainment of
thermal gas provided additional non-radiating particles in the lobe plasma, but
the energy required to heat these particles would be ~20 per cent. of the
mechanical energy output of the radio source. NGC 4261 has a relatively compact
cool core, which should probably be categorised as a galactic corona. The
corona is capable of fuelling the active nucleus for considerably longer than
the inferred source lifetime, but can be only inefficiently heated by the AGN
or conduction. The expansion of the radio lobes has affected the structure of
the gas in the galaxy, compressing and moving the material of the corona
without causing significant shock heating, and expelling gas from the immediate
neighbourhood of the jets. We discuss the possible implications of this
environment for the duration of the AGN outburst, and consider mechanisms which
might lead to the cessation of nuclear activity.Comment: Accepted for publication in MNRAS, 17 pages, 6 figure
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