19 research outputs found
VLT spectropolarimetry of two powerful radio galaxies at z~1.4: UV continuum, emission-line properties and the nature of high-redshift dust
(Abridged) Deep VLT spectropolarimetric observations are presented for two
powerful radio galaxies, 0850-206 and 1303+091. These observations cover the
rest-frame wavelength range ~ 1450 - 3750 A. New radio observations and
continuum images of the same sources are also presented. These galaxies are the
first two observed from a complete sample of nine radio sources with redshifts
in the range 1.3 < z < 1.5 (selected from the equatorial sample of powerful
radio sources of Best, Rottgering & Lehnert), as part of a project aimed to
investigate the multi-component nature of the UV continuum in radio galaxies
and any variations of the continuum properties with the radio source age.
The larger radio source of the two, 0850-206, presents a high continuum
fractional polarization, averaging 17% across the observed wavelength range and
reaching 24% at rest-frame wavelengths of <2000 A. The smaller radio source,
1303+091, shows a lower continuum polarization, averaging 8% and rising to 11%
for rest-frame wavelengths >3000 A. For both galaxies, the position angle of
the electric vector is generally constant with wavelength and within ~15
degrees of perpendicular to the radio axis. Both their total flux spectra and
polarized flux spectra reveal the 2200 A dust feature, and comparison with dust
scattering models suggests that the composition of the dust in these galaxies
is similar to that of Galactic dust. In 0850-206, scattered quasar radiation
dominates the UV continuum emission, with the nebular continuum accounting for
no more than ~22% and no requirement for any additional emission component such
as emission from young stars. By contrast, in 1303+091, unpolarized radiation
could be a major constituent of the UV continuum emission, with starlight
accounting for up to ~50% and the nebular continuum accounting for ~11%.Comment: 20 pages, including 14 figures. MNRAS accepte
Outflows and shocks in compact radio sources
We report some key results from the optical emission line study of a complete
sample of compact radio sources. We find strong evidence for jet-driven
outflows in the circum-nuclear emission line gas namely: 1) highly broadened
and blueshifted emission line components (up to 2000 km/s), 2) shock ionised
gas (broader, shifted components), 3) consistency in the scales of the emission
line gas and the radio source and 4) trends between the maximum outflow
velocity and radio source size (and orientation). Full details can be found in
Holt (2005).Comment: 4 pages, 4 figures, to be published in Astronomische Nachrichten
(proceedings of the Granada workshop on High Redshift Radio Galaxies
Shocks, illumination cones and intrinsic gas structures in the extreme radio galaxy 3C265
We present deep, narrow-band and continuum images of the powerful z=0.811
radio galaxy 3C265, taken with the TTF on the WHT, together with detailed
long-slit spectroscopic observations along the axis defined by the UV/optical
emission elongation. The deep images reveal the existence of cones in the
ionization structure within ~7 arcsec (58 kpc) of the nucleus, where the
emission-line structure is not closely aligned with the radio axis. This
indicates that anisotropic illumination from the central AGN dominates on a
small scale. At larger distances (>10 arcsec) from the nucleus, low-ionization
emission gas is closely aligned with the radio axis, suggesting that jet-cloud
interactions may be the dominant mechanism in the line-emitting gas on a larger
scale. Moreover, the presence of a high-velocity cloud at 2.5 arcsec from the
nucleus, close to the radio axis, indicates that even close to the nucleus
jet-induced shocks have an important kinematic effect. While on a large scale
the low-ionization emission-line structures are aligned with the radio axis, on
a smaller scale, where AGN-photoionization dominates, the highest surface
brightness structure is aligned with the closest companion galaxy. This suggest
that much of the emission-line structure reflects the intrinsic gas
distribution, rather than the ionization pattern imprinted by the radio jets or
by AGN illumination. Overall, our results underline the need for a variety of
mechanisms to explain the properties of the extended emission-line gas of radio
galaxies (abridged).Comment: 12 pages, including 6 figures, MNRAS in pres
Ionized outflows in luminous type 2 AGNs at z < 0.6: no evidence for significant impact on the host galaxies
We investigate the presence of extended ionized outflows in 18 luminous type 2 AGNs (11
quasars and 7 high-luminosity Seyfert 2s) at 0.3 <z< 0.6 based on VLT-FORS2 spectroscopy.
We infer typical lower limits on the radial sizes of the outflows Ro several × 100 pc and
upper limits Ro 1–2 kpc. Our results are inconsistent with related studies which suggest that
large scale (Ro ∼ several-15 kpc) are ubiquitous in QSO2. We study the possible causes of
discrepancy and propose that seeing smearing is the cause of the large inferred sizes. The
implications in our understanding of the feedback phenomenon are important since the mass
Mo (through the density), mass injection M˙ o and energy injection E˙ o rates of the outflows
become highly uncertain. One conclusion seems unavoidable: Mo, M˙ o and E˙ o are modest
or low compared with previous estimations. We obtain typically Mo (0.4–22) × 106 M
(median 1.1 × 106 M) assuming n = 1000 cm−3. These are ∼102–104 times lower than
values reported in the literature. Even under the most favourable assumptions, we obtain M˙ o
10 M yr−1 in general, 100–1000 times lower than claimed in related studies. Although the
uncertainties are large, it is probable that these are lower than typical star-forming rates. In
conclusion, no evidence is found supporting that typical outflows can affect the interstellar
medium of the host galaxies across spatial scales 1–2 kpc
A jet-cloud interaction in the 3C 196 environment
Powerful radio galaxies and radio-loud quasars at high redshifts are
frequently associated with extended emission-line regions (EELRs). Here we
investigate the [O II] EELR around the quasar 3C 196 at z=0.871 using integral
field spectroscopy. We also detect extended [Ne II] emission at a distance of
about 30 kpc from the core. The emission is aligned with the radio hot spots
and shows a redshifted and a blueshifted component with a velocity difference
of ~800 km s^-1. The alignment effect and large velocities support the
hypothesis that the EELR is caused by a jet-cloud interaction, which is
furthermore indicated by the presence of a pronounced bend in the radio
emission at the location of the radio hot spots. We also report observations of
two other systems which do not show as clear indications of interactions. We
find a weaker alignment of an [O II] EELR from the z=0.927 quasar 3C 336, while
no EELR is found around the core-dominated quasar OI 363 at z=0.63.Comment: 7 pages, accepted for publication in A&
PKS 0537-441: extended [O II] emission and a binary QSO?
We present high-resolution imaging and low-resolution spectroscopy of the BL
Lac object PKS 0537-441 (z = 0.893) and its environment. The observations were
designed to clarify, whether the properties of PKS 0537-441 are affected by
gravitational microlensing, or whether PKS 0537-441 and its environment act as
a lensing system itself. Our observations show that neither case seems to be
likely. We did not find a galaxy along the line-of-sight to the BL Lac as
claimed previously, our spectroscopy shows that none of the four closest
companion galaxies is at high redshift. Two of the four nearby companion
galaxies to PKS 0537-441 are within 200 km/s of the systemic velocity of the BL
Lac (z = 0.892 and 0.895, respectively). The third companion galaxy is at
higher redshift (z = 0.947). The fourth companion galaxy shows evidence of Mg
II absorption redwards of its systemic velocity and is perhaps a mini low
ionization BAL QSO at z = 0.885. If the latter can be confirmed, PKS 0537-441
is the first BL Lacertae object being a member of a binary Quasar. We also
detected extended [O II] emission in the off-nuclear spectrum of PKS 05371-441,
which is most likely due to photoionization from the active nucleus.
Alternatively, the extended [O II] emission is due to jet-cloud interaction
with the counterjet of PKS 0537-441. Our clustering analysis indicates that PKS
0537-441 is located in a cluster environment as rich as Abell type 0-1. This is
supported by the detection of four galaxies in the field with similar redshifts
as the BL Lac (Delta z < 0.002). We found serendipitously even more galaxies at
somewhat higher redshifts (z = 0.9-1). Thus, PKS0537-441 might be located in
front of a galaxy cluster at somewhat higher redshift or even be part of a
large-scale structure with an extension towards the BL Lac.Comment: 13 pages, 9 figures, accepted for publication in A&
Simulations of multiphase turbulence in jet cocoons
M. Krause and P. Alexander, 'Simulations of multiphase turbulence in jet cocoons', Monthly Notices of the Royal Astronomical Society, Vol. 376, pp. 465-478, April 2007, the version of record is available online at doi: 10.1111/j.1365-2966.2007.11480.x. Published by Oxford University Press on behalf of the Royal Astronomical Society. © 2007 The Authors. Journal compilation © 2007 RASThe interaction of optically emitting clouds with warm X-ray gas and hot, tenuous radio plasma in radio jet cocoons is modelled by 2D compressible hydrodynamic simulations. The initial setup is the Kelvin–Helmholtz instability at a contact surface of density contrast 104. The denser medium contains clouds of higher density. Optically thin radiation is realized via a cooling source term. The cool phase effectively extracts energy from the other gas which is both, radiated away and used for acceleration of the cold phase. This increases the system’s cooling rate substantially and leads to a massively amplified cold mass dropout. We show that it is feasible, given small seed clouds of the order of 100 M, that all of the optically emitting gas in a radio jet cocoon may be produced by this mechanism on the propagation time-scale of the jet. The mass is generally distributed as T−1/2 with temperature, with a prominent peak at 14 000 K. This peak is likely to be related to the counteracting effects of shock heating and a strong rise in the cooling function. The volume filling factor of cold gas in this peak is of the order of 10−5–10−3 and generally increases during the simulation time. The simulations tend towards an isotropic scale-free Kolmogorov-type energy spectrum over the simulation time-scale. We find the same Mach-number density relation as Kritsuk & Norman and show that this relation may explain the velocity widths of emission lines associated with high-redshift radio galaxies, if the environmental temperature is lower, or the jet-ambient density ratio is less extreme than in their low-redshift counterparts.Peer reviewe
Star formation in high-redshift quasars: excess [O II] emission in the radio-loud population
We investigate the [O II] emission line properties of 18,508 quasars at z<1.6
drawn from the Sloan Digital Sky Survey (SDSS) quasar sample. The quasar sample
has been separated into 1,692 radio-loud and 16,816 radio-quiet quasars (RLQs
and RQQs hereafter) matched in both redshift and i'-band absolute magnitude.
We use the [O II]\lambda3726+3729 line as an indicator of star formation.
Based on these measurements we find evidence that star-formation activity is
higher in the RLQ population. The mean equivalent widths (EW) for [O II] are
EW([O II])_RL=7.80\pm0.30 \AA, and EW([O II])_RQ=4.77\pm0.06 \AA, for the RLQ
and RQQ samples respectively. The mean [O II] luminosities are \log[L([O
II])_RL/W]=34.31\pm0.01 and \log[L([O II])_RQ/W]=34.192\pm0.004 for the samples
of RLQs and RQQs respectively. Finally, to overcome possible biases in the EW
measurements due to the continuum emission below the [O II] line being
contaminated by young stars in the host galaxy, we use the ratio of the [O II]
luminosity to rest-frame i'-band luminosity, in this case, we find for the RLQs
\log[L([O II])_RL/L_opt]=-3.89\pm0.01 and \log[L([O
II])_RQ/L_opt]=-4.011\pm0.004 for RQQs. However the results depend upon the
optical luminosity of the quasar. RLQs and RQQs with the same high optical
luminosity \log(L_opt/W)>38.6, tend to have the same level of [O II] emission.
On the other hand, at lower optical luminosities \log(L_opt/W)<38.6, there is a
clear [O II] emission excess for the RLQs. As an additional check of our
results we use the [O III] emission line as a tracer of the bolometric
accretion luminosity, instead of the i'-band absolute magnitude, and we obtain
similar results.
Radio jets appear to be the main reason for the [O II] emission excess in the
case of RLQs. In contrast, we suggest AGN feedback ensures that the two
populations acquire the same [O II] emission at higher optical luminosities.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Extinction curves expected in young galaxies
We investigate the extinction curves of young galaxies in which dust is
supplied from Type II supernovae (SNe II) and/or pair instability supernovae
(PISNe). We adopt Nozawa et al. (2003) for compositions and size distribution
of grains formed in SNe II and PISNe. We find that the extinction curve is
quite sensitive to internal metal mixing in supernovae (SNe). The extinction
curves predicted from the mixed SNe are dominated by SiO2 and is characterised
by steep rise from infrared to ultraviolet (UV). The dust from unmixed SNe
shows shallower extinction curve, because of the contribution from large-sized
(~ 0.1 um) Si grains. However, the progenitor mass is important in unmixed SNe
II: If the progenitor mass is smaller than ~ 20 Msun, the extinction curve is
flat in UV; otherwise, the extinction curve rises toward the short wavelength.
The extinction curve observed in a high-redshift quasar (z=6.2) favours the
dust production by unmixed SNe II. We also provide some useful observational
quantities, so that our model might be compared with future high-z extinction
curves.Comment: 11 pages, 6 figures, Accepted for publication in MNRA