414 research outputs found
Far Ultraviolet Emission in the A2597 and A2204 Brightest Cluster Galaxies
We use the Hubble Space Telescope ACS/SBC and Very Large Telescope FORS
cameras to observe the Brightest Cluster Galaxies in Abell 2597 and Abell 2204
in the far-ultraviolet (FUV) F150LP and optical U, B, V, R, I Bessel filters.
The FUV and U band emission is enhanced in bright, filamentary structures
surrounding the BCG nuclei. These filaments can be traced out to 20 kpc from
the nuclei in the FUV. Excess FUV and U band light is determined by removing
emission due to the underlying old stellar population and mapped with 1 arcsec
spatial resolution over the central 20 kpc regions of both galaxies. We find
the FUV and U excess emission to be spatially coincident and a stellar
interpretation requires the existence of a significant amount of 10000-50000 K
stars. Correcting for nebular continuum emission and dust intrinsic to the BCG
further increases the FUV to U band emission ratio and implies that stars alone
may not suffice to explain the observations. However, lack of detailed
information on the gas and dust distribution and extinction law in these
systems prevents us from ruling out a purely stellar origin. Non-stellar
processes, such as the central AGN, Scattering, Synchrotron and Bremsstrahlung
emission are investigated and found to not be able to explain the FUV and U
band measurements in A2597. Contributions from non-thermal processes not
treated here should be investigated. Comparing the FUV emission to the optical
H-alpha line emitting nebula shows good agreement on kpc-scales in both A2597
and A2204. In concordance with an earlier investigation by O'Dea et al. (2004)
we find that O-stars can account for the ionising photons necessary to explain
the observed H-alpha line emission.Comment: accepted by mnra
Legume, cropping intensity, and N-fertilization effects on soil attributes and processes from an eight-year-old semiarid wheat system
Dominant Nuclear Outflow Driving Mechanisms in Powerful Radio Galaxies
In order to identify the dominant nuclear outflow mechanisms in Active
Galactic Nuclei, we have undertaken deep, high resolution observations of two
compact radio sources (PKS 1549-79 and PKS 1345+12) with the Advanced Camera
for Surveys (ACS) aboard the Hubble Space Telescope. Not only are these targets
known to have powerful emission line outflows, but they also contain all the
potential drivers for the outflows: relativistic jets, quasar nuclei and
starbursts. ACS allows the compact nature (<0.15") of these radio sources to be
optically resolved for the first time. Through comparison with existing radio
maps we have seen consistency in the nuclear position angles of both the
optical emission line and radio data. There is no evidence for bi-conical
emission line features on the large-scale and there is a divergance in the
relative position angles of the optical and radio structure. This enables us to
exclude starburst driven outflows. However, we are unable to clearly
distinguish between radiative AGN wind driven outflows and outflows powered by
relativistic radio jets. The small scale bi-conical features, indicative of
such mechanisms could be below the resolution limit of ACS, especially if
aligned close to the line of sight. In addition, there may be offsets between
the radio and optical nuclei induced by heavy dust obscuration, nebular
continuum or scattered light from the AGN.Comment: 9 pages, 8 figures, emulateapj, ApJ Accepte
The Distribution and Condition of the Warm Molecular Gas in Abell 2597 and Sersic 159-03
We have used the SINFONI integral field spectrograph to map the near-infrared
K-band emission lines of molecular and ionised hydrogen in the central regions
of two cool core galaxy clusters, Abell 2597 and Sersic 159-03. Gas is detected
out to 20 kpc from the nuclei of the brightest cluster galaxies and found to be
distributed in clumps and filaments around it. The ionised and molecular gas
phases trace each other closely in extent and dynamical state. Both gas phases
show signs of interaction with the active nucleus. Within the nuclear regions
the kinetic luminosity of this gas is found to be somewhat smaller than the
current radio luminosity. Outside the nuclear region the gas has a low velocity
dispersion and shows smooth velocity gradients. There is no strong correlation
between the intensity of the molecular and ionised gas emission and either the
radio or X-ray emission. The molecular gas in Abell 2597 and Sersic 159-03 is
well described by a gas in local thermal equilibrium (LTE) with a single
excitation temperature T_exc ~ 2300 K. The emission line ratios do not vary
strongly as function of position, with the exception of the nuclear regions
where the ionised to molecular gas ratio is found decrease. These constant line
ratios imply a single source of heating and excitation for both gas phases.Comment: 44 pages, 32 figures, accepted for publication in MNRA
Infrared Emission from the Nearby Cool Core Cluster Abell 2597
We observed the brightest central galaxy (BCG) in the nearby (z=0.0821) cool
core galaxy cluster Abell 2597 with the IRAC and MIPS instruments on board the
Spitzer Space Telescope. The BCG was clearly detected in all Spitzer
bandpasses, including the 70 and 160 micron wavebands. We report aperture
photometry of the BCG. The spectral energy distribution exhibits a clear excess
in the FIR over a Rayleigh-Jeans stellar tail, indicating a star formation rate
of ~4-5 solar masses per year, consistent with the estimates from the UV and
its H-alpha luminosity. This large FIR luminosity is consistent with that of a
starburst or a Luminous Infrared Galaxy (LIRG), but together with a very
massive and old population of stars that dominate the energy output of the
galaxy. If the dust is at one temperature, the ratio of 70 to 160 micron fluxes
indicate that the dust emitting mid-IR in this source is somewhat hotter than
the dust emitting mid-IR in two BCGs at higher-redshift (z~0.2-0.3) and higher
FIR luminosities observed earlier by Spitzer, in clusters Abell 1835 and Zwicky
3146.Comment: Accepted at Ap
RATAN-600 7.6-cm Deep Sky Strip Surveys at the Declination of the SS433 Source During the 1980-1999 Period. Data Reduction and the Catalog of Radio Sources in the Right-Ascension Interval 7h < R.A. < 17h
We use two independent methods to reduce the data of the surveys made with
RATAN-600 radio telescope at 7.6 cm in 1988-1999 at the declination of the
SS433 source. We also reprocess the data of the "Cold" survey (1980-1981). The
resulting RCR (RATAN COLD REFINED) catalog contains the right ascensions and
fluxes of objects identified with those of the NVSS catalog in the
right-ascension interval 7h < R.A. < 17h. We obtain the spectra of the radio
sources and determine their spectral indices at 3.94 and 0.5 GHz. The spectra
are based on the data from all known catalogs available from the CATS, Vizier,
and NED databases, and the flux estimates inferred from the maps of the VLSS
and GB6 surveys. For 245 of the 550 objects of the RCR catalog the fluxes are
known at two frequencies only: 3.94 GHz (RCR) and 1.4 GHz (NVSS). These are
mostly sources with fluxes smaller than 30 mJy. About 65% of these sources have
flat or inverse spectra (alpha > -0.5). We analyze the reliability of the
results obtained for the entire list of objects and construct the histograms of
the spectral indices and fluxes of the sources. Our main conclusion is that all
10-15 mJy objects found in the considered right-ascension interval were already
included in the decimeter-wave catalogs.Comment: 26 pages, 18 figure
An infrared survey of brightest cluster galaxies: Paper I
We report on an imaging survey with the Spitzer Space Telescope of 62
brightest cluster galaxies with optical line emission. These galaxies are
located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky
Survey. We find that about half of these sources have a sign of excess infrared
emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8
micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0.
Altogether 35 of 62 objects in our survey exhibit at least one of these signs
of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron
flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at
8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios
suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and
R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the
four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol
and so can be classified as luminous infrared galaxies (LIRGs). Excluding the
four systems hosting dusty AGNs, the excess mid-infrared emission in the
remaining brightest cluster galaxies is likely related to star formation.Comment: accepted for publication in ApJ
Systematic study of X-ray Cavities in the brightest galaxy of the Draco Constellation NGC 6338
We present results based on the systematic analysis of currently available
Chandra archive data on the brightest galaxy in the Draco constellation NGC
6338, in order to investigate the properties of the X-ray cavities. In the
central ~6 kpc, at least a two and possibly three, X-ray cavities are evident.
All these cavities are roughly of ellipsoidal shapes and show a decrement in
the surface brightness of several tens of percent. In addition to these
cavities, a set of X-ray bright filaments are also noticed which are spatially
coincident with the H{\alpha} filaments over an extent of 15 kpc. The H{\alpha}
emission line filaments are perpendicular to the X- ray cavities. Spectroscopic
analysis of the hot gas in the filaments and cavities reveal that the X-ray
filaments are cooler than the gas contained in the cavities. The emission line
ratios and the extended, asymmetric nature of the H{\alpha} emission line
filaments seen in this system require a harder ionizing source than that
produced by star formation and/or young, massive stars. Radio emission maps
derived from the analysis of 1.4 GHz VLA FIRST survey data failed to show any
association of these X-ray cavities with radio jets, however, the cavities are
filled by radio emission. The total power of the cavities is 17\times 1042 erg
s-1 and the ratio of the radio luminosity to cavity power is ~ 10-4, implying
that most of the jet power is mechanical.Comment: The paper contains 12 figures and 3 tables, Accepted 2011 December 7
for publication in MNRA
HST/STIS Spectroscopy of the Lyman-Alpha Emission Line in the Central Dominant Galaxies in A426, A1795, and A2597: Constraints on Clouds in the Intracluster Medium
We report on HST/STIS spectra of the Lyman-alpha emission in the central
dominant galaxies in three rich clusters of galaxies. We find evidence for a
population of clouds in the intracluster medium.We detect 10 Ly-alpha
absorption systems towards the nucleus of NGC1275 with columns of N(HI)
1E12-1E14 cm-2. The detected absorption features are most consistent with
associated nuclear absorption systems. There is very little nuclear absorption
at the systemic velocity in NGC1275. This implies that the large columns
detected in the 21 cm line towards the parsec scale radio source avoid the line
of sight to the nucleus. This gas may be located in a circumnuclear disk or
torus. We detect at least one and possibly two absorption features towards the
extended Ly-alpha in A426. We do not detect absorption towards the extended
Ly-alpha emission in A1795, and A2597 with upper limits N(HI) 1E13 cm-2 for
optically thin absorbers. Our data constrain the covering factor of any high
column density gas in the ICM to be less than 25%. Our results suggest that the
lack of observed intermediate temperature gas is not explained by obscuration.
In addition, the low columns of gas on the 100 kpc scales in the ICM suggests
that (1) the rate at which cold gas accumulates in the ICM on these scales is
very low, and (2) the dense nebulae in the central 10 kpc must have cooled or
been deposited in situ.Comment: 6 figure
Residual Cooling and Persistent Star Formation amid AGN Feedback in Abell 2597
New Chandra X-ray and Herschel FIR observations enable a multiwavelength
study of active galactic nucleus (AGN) heating and intracluster medium (ICM)
cooling in the brightest cluster galaxy of Abell 2597. The new Chandra
observations reveal the central < 30 kiloparsec X-ray cavity network to be more
extensive than previously thought, and associated with enough enthalpy to
theoretically inhibit the inferred classical cooling flow. Nevertheless, we
present new evidence, consistent with previous results, that a moderately
strong residual cooling flow is persisting at 4%-8% of the classically
predicted rates in a spatially structured manner amid the feedback-driven
excavation of the X-ray cavity network. New Herschel observations are used to
estimate warm and cold dust masses, a lower-limit gas-to-dust ratio, and a star
formation rate consistent with previous measurements. The cooling time profile
of the ambient X-ray atmosphere is used to map the locations of the
observational star formation entropy threshold as well as the theoretical
thermal instability threshold. Both lie just outside the < 30 kpc central
region permeated by X-ray cavities, and star formation as well as ionized and
molecular gas lie interior to both. The young stars are distributed in an
elongated region that is aligned with the radio lobes, and their estimated ages
are both younger and older than the X-ray cavity network, suggesting both
jet-triggered as well as persistent star formation over the current AGN
feedback episode. Bright X-ray knots that are coincident with extended Ly-alpha
and FUV continuum filaments motivate a discussion of structured cooling from
the ambient hot atmosphere along a projected axis that is perpendicular to
X-ray cavity and radio axis. We conclude that the cooling ICM is the dominant
contributor of the cold gas reservoir fueling star formation and AGN activity
in the Abell 2597 BCG.Comment: 20 pages, 7 figures; Accepted for publication in MNRA
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