320 research outputs found
Deep spectroscopy of the FUV-optical emission lines from a sample of radio galaxies at z~2.5: metallicity and ionization
We present long-slit NIR spectra, obtained using the ISAAC instrument at the
Very Large Telescope, for nine radio galaxies at z~2.5. One-dimensional spectra
have been extracted and cross calibrated with optical spectra from the
literature to produce line spectra spanning a rest wavelength of ~1200-7000 A.
We have also produced a composite of the rest-frame UV-optical line fluxes of
powerful, z~2.5 radio galaxies. We have investigated the relative strengths of
Ly-alpha, H-beta, H-alpha, HeII 1640 and HeII 4687, and we find that Av can
vary significantly from object to object. In addition, we identify new line
ratios to calculate electron temperature: [NeV] 1575/[NeV] 3426, [NeIV]
1602/[NeIV] 2423, OIII] 1663/[OIII] 5008 and [OII] 2471/[OII]3728. We model the
emission line spectra and conclude they are best explained by
AGN-photoionization with the ionization parameter U varying between objects.
Single slab photoionization models are unable to reproduce the high- and the
low-ionization lines simultaneously: this may be alleviated either by combining
two or more single slab photoionization models with different U, or by using
mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann (1996).
On the basis of NV/NIV] and NIV]/CIV we argue that shocks make a fractional
contribution to the ionization of the EELR. We find that in the EELR of z~2
radio galaxies the N/H abundance ratio is close to its solar value. We conclude
that N/H and metallicity do not vary by more than a factor of two in our
sample. This is consistent with the idea that massive ellipticals are assembled
very early in the history of the universe, and then evolve relatively passively
up to the present day.Comment: Accepted for publication by MNRA
VIMOS-VLT spectroscopy of the giant Ly-alpha nebulae associated with three z~2.5 radio galaxies
The morphological and spectroscopic properties of the giant (>60 kpc)
Ly-alpha nebulae associated with three radio galaxies at z~2.5 (MRC 1558-003,
MRC 2025-218 and MRC 0140-257) have been investigated using integral field
spectroscopic data obtained with VIMOS on VLT.
The morphologies are varied. The nebula of one source has a centrally peaked,
rounded appearance. In the other two objects, it consists of two spatial
components. The three nebulae are aligned with the radio axis within <30 deg.
The total Ly-alpha luminosities are in the range (0.3-3.4) x 1e44 erg s-1. The
Ly-alpha spectral profile shows strong variation through the nebulae, with FWHM
values in the range ~400-1500 km s-1 and velocity shifts V~120-600 km s-1.
We present an infall model which can explain successfully most Ly-alpha
morphological and spectroscopic properties of the nebula associated with MRC
1558-003. This adds further support to our previous conclusion that the
_quiescent_ giant nebulae associated with this and other high redshift powerful
radio galaxies are in infall. A problem for this model is the difficulty to
reproduce the large Ly-alpha FWHM values.
We have discovered a giant (~85 kpc) Ly-alpha nebula associated with the
radio galaxy MRC 0140-257 at z=2.64. It shows strikingly relaxed kinematics
(FWHM2) radio galaxies.Comment: 14 pages, 13 figures. Accepted for publication in MNRA
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
Cosmological Birefringence: an Astrophysical test of Fundamental Physics
We review the methods used to test for the existence of cosmological
birefringence, i.e. a rotation of the plane of linear polarization for
electromagnetic radiation traveling over cosmological distances, which might
arise in a number of important contexts involving the violation of fundamental
physical principles. The main methods use: (1) the radio polarization of radio
galaxies and quasars, (2) the ultraviolet polarization of radio galaxies, and
(3) the cosmic microwave background polarization. We discuss the main results
obtained so far, the advantages and disadvantages of each method, and future
prospects.Comment: To appear in the Proceedings of the JENAM 2010 Symposium "From
Varying Couplings to Fundamental Physics", held in Lisbon, 6-10 Sept. 201
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
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