319 research outputs found
The clustering of radio galaxies at z~0.55 from the 2SLAQ LRG survey
We examine the clustering properties of low-power radio galaxies at redshift
0.4<z<0.8, using data from the 2SLAQ Luminous Red Galaxy (LRG) survey. We find
that radio-detected LRGs (with optical luminosities of 3-5L* and 1.4GHz radio
powers between 1e24 and 1e26 W/Hz) are significantly more clustered than a
matched sample of radio-quiet LRGs with the same distribution in optical
luminosity and colour. The measured scale length of the 2pt auto-correlation
function, r0, is 12.3+/-1.2 1/h Mpc and 9.02+/-0.52 1/h Mpc for the
radio-detected and radio-quiet samples respectively. Using the halo model
framework we demonstrate that the radio-loud LRGs have typical halo masses of
10.1+/-1.4 x10^13 1/h M_sun compared to 6.44+/-0.32 x10^13 1/h M_sun for the
radio-quiet sample. A model in which the radio-detected LRGs are almost all
central galaxies within haloes provides the best fit, and we estimate that at
least 30% of LRGs with the same clustering amplitude as the radio-detected LRGs
are currently radio-loud. Our results imply that radio-loud LRGs typically
occupy more massive haloes than other LRGs of the same optical luminosity, so
the probability of finding a radio-loud AGN in a massive galaxy at z~0.55 is
influenced by the halo mass in addition to the dependence on optical
luminosity. If we model the radio-loud fraction of LRGs, F_rad, as a function
of halo mass M, then the data are well-fitted by a power law of the form F_rad
\propto M^(0.65+/-0.23). The relationship between radio emission and clustering
strength could arise either through a higher fuelling rate of gas onto the
central black holes of galaxies in the most massive haloes (producing more
powerful radio jets) or through the presence of a denser IGM (providing a more
efficient working surface for the jets, thus boosting their radio luminosity).Comment: Accepted for publication in MNRA
IFU observations of luminous type II AGN - I. Evidence for ubiquitous winds
We present observations of 17 luminous (log(L[O III]/L_Sun) > 8.7) local (z <
0.11) type II AGN. Our aim is to investigate the prevalence and nature of AGN
driven outflows in these galaxies by combining kinematic and ionization
diagnostic information. We use non-parametric methods (e.g. W80, the width
containing 80% of the line flux) to assess the line widths in the central
regions of our targets. The maximum values of W80 in each galaxy are in the
range 400 - 1600 km/s, with a mean of 790 +- 90 km/s. Such high velocities are
strongly suggestive that these AGN are driving ionized outflows. Multi-Gaussian
fitting is used to decompose the velocity structure in our galaxies. 14/17 of
our targets require 3 separate kinematic components in the ionized gas in their
central regions. The broadest components of these fits have FWHM = 530 - 2520
km/s, with a mean value of 920 +- 50 km/s. By simultaneously fitting both the
H{\beta}/[O III] and H{\alpha}/[N II] complexes we construct ionization
diagnostic diagrams for each component. 13/17 of our galaxies show a
significant (> 95 %) correlation between the [N II]/H{\alpha} ratio and the
velocity dispersion of the gas. Such a correlation is the natural consequence
of a contribution to the ionization from shock excitation and we argue that
this demonstrates that the outflows from these AGN are directly impacting the
surrounding ISM within the galaxies.Comment: 37 pages, 30 figures. Accepted for publication in MNRA
The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy
© 2016 The Authors. We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ~ 0.8. The catalogue covers ~800 deg 2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radioloud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc
Optical Properties of High-Frequency Radio Sources from the Australia Telescope 20 GHz (AT20G) Survey
Our current understanding of radio-loud AGN comes predominantly from studies
at frequencies of 5 GHz and below. With the recent completion of the Australia
Telescope 20 GHz (AT20G) survey, we can now gain insight into the
high-frequency radio properties of AGN. This paper presents supplementary
information on the AT20G sources in the form of optical counterparts and
redshifts. Optical counterparts were identified using the SuperCOSMOS database
and redshifts were found from either the 6dF Galaxy survey or the literature.
We also report 144 new redshifts. For AT20G sources outside the Galactic plane,
78.5% have optical identifications and 30.9% have redshift information. The
optical identification rate also increases with increasing flux density.
Targets which had optical spectra available were examined to obtain a spectral
classification.
There appear to be two distinct AT20G populations; the high luminosity
quasars that are generally associated with point-source optical counterparts
and exhibit strong emission lines in the optical spectrum, and the lower
luminosity radio galaxies that are generally associated with passive galaxies
in both the optical images and spectroscopic properties. It is suggested that
these different populations can be associated with different accretion modes
(cold-mode or hot-mode). We find that the cold-mode sources have a steeper
spectral index and produce more luminous radio lobes, but generally reside in
smaller host galaxies than their hot-mode counterparts. This can be attributed
to the fact that they are accreting material more efficiently. Lastly, we
compare the AT20G survey with the S-cubed semi-empirical (S3-SEX) models and
conclude that the S3-SEX models need refining to correctly model the compact
cores of AGN. The AT20G survey provides the ideal sample to do this.Comment: Accepted for publication in MNRA
A small area faint KX redshift survey for QSOs in the ESO Imaging Survey Chandra Deep Field South
In this paper we present preliminary spectroscopic results from a small area
faint K-excess (KX) survey, and compare KX selection against UVX selection. The
aim of the KX method is to produce complete samples of QSOs flux-limited in the
K band, in order to minimize any selection bias in samples of QSOs from the
effects of reddening and extinction. Using the photometric catalogue of the ESO
Imaging Survey Chandra Deep Field South (48 arcmin^2) we have identified
compact objects with J-K colours redder than the stellar sequence, that are
brighter than K=19.5. We have obtained spectra of 33 candidates, using the
LDSS++ spectrograph on the AAT. Amongst the 11 bluer candidates, with V-J<3,
three are confirmed as QSOs. Identification of the 22 redder candidates with
V-J>3 is substantially incomplete, but so far no reddened QSOs have been found.
Near-infrared spectroscopy will be more effective in identifying some of these
targets. Only two UVX (U-B<-0.2) sources brighter than K=19.5 are found which
are not also KX selected. These are both identified as galactic stars. Thus KX
selection appears to select all UVX QSOs. The surface density of QSOs in the
blue subsample (V-J<3) at K<19.5 is 325^+316_-177 deg^-2. Because
identification of the red subsample (V-J>3) is substantially incomplete, the
2sigma upper limit on the density of reddened QSO is large, <1150 deg^-2. As
anticipated, at these faint magnitudes the KX sample includes several compact
galaxies. Of the 14 with measured redshifts, there are roughly equal numbers of
early and late type objects. Nearly all the early type galaxies are found in a
single structure at z=0.66.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
IFU observations of luminous type II AGN - I. Evidence for ubiquitous winds
We present observations of 17 luminous (log(L[O III]/L) > 8.7) local (z < 0.11) type II AGN.
Our aim is to investigate the prevalence and nature of AGN-driven outflows in these galaxies by
combining kinematic and ionization diagnostic information. We use non-parametric methods
(e.g. W80, the width containing 80 per cent of the line flux) to assess the line widths in the central
regions of our targets. The maximum values of W80 in each galaxy are in the range 400–1600 km
s−1, with a mean of 790 ± 90 km s−1. Such high velocities are strongly suggestive that these
AGN are driving ionized outflows. Multi-Gaussian fitting is used to decompose the velocity
structure in our galaxies. 14/17 of our targets require three separate kinematic components in
the ionized gas in their central regions. The broadest components of these fits have FWHM
= 530–2520 km s−1, with a mean value of 920 ± 50 km s−1. By simultaneously fitting
both the Hβ/[O III] and Hα/[N II] complexes, we construct ionization diagnostic diagrams for
each component. 13/17 of our galaxies show a significant (>95 per cent) correlation between
the [N II]/Hα ratio and the velocity dispersion of the gas. Such a correlation is the natural
consequence of a contribution to the ionization from shock excitation and we argue that this
demonstrates that the outflows from these AGN are directly impacting the surrounding ISM
within the galaxies.
Key words: galaxies: active – galaxies: evolution – galaxies: kinematics and dynamic
Do quasar broad-line velocity widths add any information to virial black hole mass estimates?
We examine how much information measured broad-line widths add to virial BH
mass estimates for flux limited samples of quasars. We do this by comparing the
BH mass estimates to those derived by randomly reassigning the quasar
broad-line widths to different objects and re-calculating the BH mass. For 9000
BH masses derived from the H_beta line we find that the distributions of
original and randomized BH masses in the M_BH-redshift plane and the
M_BH-luminosity plane are formally identical. A 2D KS test does not find a
difference at >90% confidence. For the MgII line (32000 quasars) we do find
very significant differences between the randomized and original BH masses, but
the amplitude of the difference is still small. The difference for the CIV line
(14000 quasars) is 2-3sigma and again the amplitude of the difference is small.
Subdividing the data into redshift and luminosity bins we find that the median
absolute difference in BH mass between the original and randomized data is
0.025, 0.01 and 0.04 dex for H_beta, MgII and CIV respectively. The maximum
absolute difference is always <=0.1 dex. We investigate whether our results are
sensitive to corrections to MgII virial masses (e.g. Onken & Kollmeier 2008).
These corrections do not influence our results. Moreover, the mass residual -
Eddington ratio correlation discussed by Onken & Kollmeier is more directly
attributable to the slope of the relation between H_beta and MgII line width.
Our results imply that the measured quasar broad-line velocity widths provide
little extra information, after allowing for the mean velocity width. In this
case virial estimates are equivalent to M_BH L^alpha, with L/L_edd L^(1-alpha)
(with alpha~0.5). This leaves an unanswered question of why the accretion
efficiency changes with luminosity in just the right way to keep the mean
broad-line widths fixed as a function of luminosity. (abridged)Comment: 9 Pages, 9 figures. Accepted by Astrophysical Journa
The SAMI Galaxy Survey: mass-kinematics scaling relations
We use data from the Sydney-AAO Multi-object Integral-field spectroscopy
(SAMI) Galaxy Survey to study the dynamical scaling relation between galaxy
stellar mass and the general kinematic parameter that combines rotation velocity and velocity dispersion
. We show that the relation: (1)~is linear above
limits set by properties of the samples and observations; (2)~has slightly
different slope when derived from stellar or gas kinematic measurements;
(3)~applies to both early-type and late-type galaxies and has smaller scatter
than either the Tully-Fisher relation () for late
types or the Faber-Jackson relation () for early types;
and (4)~has scatter that is only weakly sensitive to the value of , with
minimum scatter for in the range 0.4 and 0.7. We compare to the
aperture second moment (the `aperture velocity dispersion') measured from the
integrated spectrum within a 3-arcsecond radius aperture
(). We find that while and
are in general tightly correlated, the relation has less scatter than the relation.Comment: 14 pages, 8 figures, Accepted 2019 May 22. Received 2019 May 18; in
original form 2019 January
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