265 research outputs found
Anisotropic inverse Compton emission in the radio galaxy 3C 265
We present the results from a Chandra observation of the powerful radio
galaxy 3C 265. We detect X-ray emission from the nucleus, the radio hotspots
and lobes. In particular, the lobe X-ray emission is well explained as
anisotropic inverse Compton scattering of the nuclear photons by the
relativistic electrons in the radio lobes; the comparison between radio
synchrotron and IC emission yields a magnetic field strength a factor about 2
lower than that calculated under minimum energy conditions. The X-ray spectrum
of the nucleus is consistent with that of a powerful, strongly absorbed quasar
and the X-ray emission of the south-eastern hotspot can be successfully
reproduced by a combination of synchro-self Compton and inverse Compton
emission assuming a magnetic field slightly lower than equipartition.Comment: 5 pages, 6 figures, to be published as a Letter on Monthly Notices of
the Royal Astronomical Societ
New Clues on the Nature of Extremely Red Galaxies
We present near-infrared VLT-UT1+ISAAC spectroscopy of a sample of 9
extremely red galaxies (ERGs) with R-K>5 and K<19.0. Neither strong emission
lines (F_lim<1-5 10^{-16} erg s^{-1}cm^{-2}) nor continuum breaks are detected.
From near-infrared spectrophotometry, complemented with broad-band optical
and near-IR photometry, we estimate ``spectro-photometric'' redshifts to be in
the range of 0.8<z_sphot<1.8. We derive upper limits on the star formation
rates in range of SFR<6-30h_50^{-2} M_solar yr^{-1}. Two of the observed ERGs
are dusty starburst candidates because they require strong dust reddening to
reproduce their global spectral energy distributions. The other ERGs are
consistent with being dustless old passively evolved spheroidals at z>0.8. We
discuss the general implications of our findings in relation with the problem
of the formation of early type galaxies.Comment: 6 pages, 2 figures. Astronomy & Astrophysics (Letters), in pres
The MUSE 3D view of feedback in a high-metallicity radio galaxy at z = 2.9
We present a detailed study of the kinematic, chemical and excitation
properties of the giant Ly emitting nebula and the giant \ion{H}{I}
absorber associated with the radio galaxy MRC 0943--242, using
spectroscopic observations from VLT/MUSE, VLT/X-SHOOTER and other instruments.
Together, these data provide a wide range of rest-frame wavelength (765 \AA
-- 6378 \AA at ) and 2D spatial information. We find clear
evidence for jet gas interactions affecting the kinematic properties of the
nebula, with evidence for both outflows and inflows being induced by radio-mode
feedback. We suggest that the regions of relatively lower ionization level,
spatially correlated with the radio hotspots, may be due to localised
compression of photoionized gas by the expanding radio source, thereby lowering
the ionization parameter, or due to a contribution from shock-heating. We find
that photoionization of super-solar metallicity gas ( = 2.1) by an
AGN-like continuum (=--1.0) at a moderate ionization parameter ( =
0.018) gives the best overall fit to the complete X-SHOOTER emission line
spectrum. We identify a strong degeneracy between column density and Doppler
parameter such that it is possible to obtain a reasonable fit to the \ion{H}{I}
absorption feature across the range log N(\ion{H}{I}/cm) = 15.20 and
19.63, with the two best-fitting occurring near the extreme ends of this range.
The extended \ion{H}{I} absorber is blueshifted relative to the emission line
gas, but shows a systematic decrease in blueshift towards larger radii,
consistent with a large scale expanding shell.Comment: 25 pages, 18 figures, 10 tables. Accepted for publication in MNRAS.
Published: 23 November 201
The Mini AGN at the Center of the Elliptical Galaxy NGC 4552 with HST
The complex phenomenology shown by the UV-bright, variable spike first
detected with the Hubble Space Telescope (HST) at the center of the otherwise
normal galaxy NGC 4552 is further investigated with both HST imaging (FOC) and
spectroscopy (FOS). HST/FOC images taken in 1991, 1993, and 1996 in the near UV
have been analyzed in a homogeneous fashion, showing that the central spike has
brightened by a factor ~4.5 between 1991 and 1993, and has decreased its
luminosity by a factor ~2.0 between 1993 and 1996. FOS spectroscopy extending
from the near UV to the red side of the optical spectrum reveals a strong UV
continuum over the spectrum of the underlying galaxy, along with several
emission lines in both the UV and the optical ranges. In spite of the low
luminosity of the UV continuum of the spike (~3*10^5 Lsolar), the spike is
definitely placed among AGNs by current diagnostics based on the emission line
intensity ratios, being just on the borderline between Seyferts and LINERs.
Line profiles are very broad, and both permitted and forbidden lines are best
modelled with a combination of broad and narrow components, with FWHM of ~3000
km s^-1 and ~700 km s^-1, respectively. This evidence argues for the variable
central spike being produced by a modest accretion event onto a central massive
black hole (BH), with the accreted material having possibly being stripped from
a a star in a close fly by with the BH. The 1996 broad Halpha luminosity of
this mini-AGN is ~5.6*10^37 erg s^-1, about a factor of two less than that of
the nucleus of NGC 4395, heretofore considered to be the faintest known AGN.Comment: 40 pages, LaTeX, with 12 PostScript figures. Accepted for publication
in the Astrophysical Journa
GRB 000911: Evidence for an Associated Supernova?
We present photometric and spectroscopic observations of the late afterglow of GRB 000911. We detect a moderately significant re-brightening in the R, I and J lightcurves, associated with a sizable reddening of the spectrum. This can be explained through the presence of an underlying supernova, outshining the afterglow ~ 30 days after the burst event
Comparison between two treatment protocols with recombinant Human Erythropoietin (rHuEpo) in the treatment of late anemia in neonates with Rh-Isoimmunization
Objectve. The Rh-hemolytic disease can lead to a late anemia by hemolytic and hyporigenerative mechanism. We compared the effectiveness of rHuEPO in two care protocols that differ for doses of rHuEPO administrated and for timing of administration. Methods. A cohort of 14 neonates was investigated. The neonates were treated with two different protocols. Protocol A: a dose of 200 U/kg/day of rHuEpo administered subcutaneously starting from the end of the second week of life; Protocol B: a dose of 400 U/kg/day of rHuEpo administered subcutaneously starting from the end of the first week of life. Results. The hematocrit values in the protocol A group decreased during treatment (32,5% vs 25,2%), whereas the hematocrit value in protocol B group remained almost stable (38,7% vs 42,8%). The mean numbers of platelets remained stable in both groups while neutrophils increased in protocol A group and decreased in protocol B (p<0,05). Reticulocyte count increased during treatment in both groups, although only in protocol B group it was statistically significative (p<0,05). Conclusions. Our results suggest a similar efficacy between the two treatment protocols. Increasing doses of rHuEPO do not seem enhancing their effectiveness and the incidence of side effects
The identification of dust heating mechanisms in nearby galaxies using Herschel 160/250 and 250/350 micron surface brightness ratios
We examined variations in the 160/250 and 250/350 micron surface brightness
ratios within 24 nearby (<30 Mpc) face-on spiral galaxies observed with the
Herschel Space Observatory to identify the heating mechanisms for dust emitting
at these wavelengths. The analysis consisted of both qualitative and
quantitative comparisons of the 160/250 and 250/350 micron ratios to H alpha
and 24 micron surface brightnesses, which trace the light from star forming
regions, and 3.6 micron emission, which traces the light from the older stellar
populations of the galaxies. We find broad variations in the heating mechanisms
for the dust. In one subset of galaxies, we found evidence that emission at
<=160 microns (and in rare cases potentially at <=350 microns) originates from
dust heated by star forming regions. In another subset, we found that the
emission at >=250 microns (and sometimes at >=160 microns) originates from dust
heated by the older stellar population. In the rest of the sample, either the
results are indeterminate or both of these stellar populations may contribute
equally to the global dust heating. The observed variations in dust heating
mechanisms does not necessarily match what has been predicted by dust emission
and radiative transfer models, which could lead to overestimated dust
temperatures, underestimated dust masses, false detections of variability in
dust emissivity, and inaccurate star formation rate measurements.Comment: Accepted for publication in MNRA
Blueshifted galaxies in the Virgo Cluster
We examine a sample of 65 galaxies in the Virgo cluster with negative radial
velocities relative to the Local Group. Some features of this sample are
pointed out. All of these objects are positioned compactly within a virial zone
of radius 6{\deg} in the cluster, but their centroid is displaced relative to
the dynamic center of the cluster, M87, by 1.1{\deg} to the northwest. The
dwarf galaxies in this sample are clumped on a scale of ~10' (50 kpc). The
observed asymmetry in the distribution of the blueshifted galaxies may be
caused by infall of a group of galaxies around M86 onto the main body of the
cluster. We offer another attempt to explain this phenomenon, assuming a mutual
tangential velocity of ~300 km/s between the Local Group and the Virgo cluster
owing to their being repelled from the local cosmological void.Comment: 10 pages, 4 figures, 1 table. Published in Astrophysics, Vol. 53, No.
1, pp. 32-41, 201
Near-IR bright galaxies at z~2. Entering the spheroid formation epoch ?
Spectroscopic redshifts have been measured for 9 K-band luminous galaxies at
1.7 < z < 2.3, selected with Ks < 20 in the "K20 survey" region of the Great
Observatories Origins Deep Survey area. Star formation rates (SFRs) of ~100-500
Msun/yr are derived when dust extinction is taken into account. The fitting of
their multi-color spectral energy distributions indicates stellar masses M ~
10^11 Msun for most of the galaxies. Their rest-frame UV morphology is highly
irregular, suggesting that merging-driven starbursts are going on in these
galaxies. Morphologies tend to be more compact in the near-IR, a hint for the
possible presence of older stellar populations. Such galaxies are strongly
clustered, with 7 out of 9 belonging to redshift spikes, which indicates a
correlation length r_0 ~ 9-17 h^-1 Mpc (1 sigma range). Current semianalytical
models of galaxy formation appear to underpredict by a large factor (about 30)
the number density of such a population of massive and powerful starburst
galaxies at z ~ 2. The high masses and SFRs together with the strong clustering
suggest that at z ~ 2 we may have started to explore the major formation epoch
of massive early-type galaxies.Comment: accepted on June 17. To appear on ApJ Letter
The Herschel Virgo Cluster Survey XVI: a cluster inventory
Herschel FIR observations are used to construct Virgo cluster galaxy
luminosity functions and to show that the cluster lacks the very bright and the
numerous faint sources detected in field galaxy surveys. The far-infrared SEDs
are fitted to obtain dust masses and temperatures and the dust mass function.
The cluster is over dense in dust by about a factor of 100 compared to the
field. The same emissivity (beta) temperature relation applies for different
galaxies as that found for different regions of M31. We use optical and HI data
to show that Virgo is over dense in stars and atomic gas by about a factor of
100 and 20 respectively. Metallicity values are used to measure the mass of
metals in the gas phase. The mean metallicity is about 0.7 solar and 50% of the
metals are in the dust. For the cluster as a whole the mass density of stars in
galaxies is 8 times that of the gas and the gas mass density is 130 times that
of the metals. We use our data to consider the chemical evolution of the
individual galaxies, inferring that the measured variations in effective yield
are due to galaxies having different ages, being affected to varying degrees by
gas loss. Four galaxy scaling relations are considered: mass-metallicity,
mass-velocity, mass-star formation rate and mass-radius - we suggest that
initial galaxy mass is the prime driver of a galaxy's ultimate destiny.
Finally, we use X-ray observations and galaxy dynamics to assess the dark and
baryonic matter content compared to the cosmological model
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