6,785 research outputs found
The properties of the extended warm ionised gas around low-redshift QSOs and the lack of extended high-velocity outflows
(Abridged) We present a detailed analysis of a large sample of 31
low-redshift, mostly radio-quiet type 1 QSOs observed with integral field
spectroscopy to study their extended emission-line regions (EELRs). We focus on
the ionisation state of the gas, size and luminosity of extended narrow line
regions (ENLRs), which corresponds to those parts of the EELR dominated by
ionisation from the QSO, as well as the kinematics of the ionised gas. We
detect EELRs around 19 of our 31 QSOs (61%) after deblending the unresolved QSO
emission and the extended host galaxy light in the integral field data. We
identify 13 EELRs to be entirely ionised by the QSO radiation, 3 EELRs are
composed of HII regions and 3 EELRs display signatures of both ionisation
mechanisms at different locations. The typical size of the ENLR is 10kpc at a
median nuclear [OIII] luminosity of log(L([OIII])/[erg/s])=42.7+-0.15. We show
that the ENLR sizes are least a factor of 2 larger than determined with HST,
but are consistent with those of recently reported type 2 QSOs at matching
[OIII] luminosities. The ENLR of type 1 and type 2 QSOs appear to follow the
same size-luminosity relation. Furthermore, we show for the first time that the
ENLR size is much better correlated with the QSO continuum luminosity than with
the total/nuclear [OIII] luminosity. We show that ENLR luminosity and radio
luminosity are correlated, and argue that radio jets even in radio-quiet QSOs
are important for shaping the properties of the ENLR. Strikingly, the
kinematics of the ionised gas is quiescent and likely gravitationally driven in
the majority of cases and we find only 3 objects with radial gas velocities
exceeding 400km/s in specific regions of the EELR that can be associate with
radio jets. In general, these are significantly lower outflow velocities and
detection rates compared to starburst galaxies or radio-loud QSOs.Comment: 34 page, 22 figures (slightly degraded in resolution), 10 tables,
accepted for publication in A&A, minor corrections to match with the
publisher versio
The low-metallicity QSO HE 2158-0107: A massive galaxy growing by the accretion of nearly pristine gas from its environment?
[abridged] The metallicities of AGN are usually well above solar in their
NLR, often reaching up to several times solar in their broad-line regions.
Low-metallicity AGN are rare objects which have so far always been associated
with low-mass galaxies hosting low-mass BHs (M_BH<10^6Msun). In this paper we
present IFS data of the low-redshift QSO HE 2158-0107 for which we find strong
evidence for sub-solar NLR metallicities associated with a massive BH
(M_BH~3x10^8Msun). The QSO is surrounded by a large extended emission-line
region reaching out to 30kpc from the QSO in a tail-like geometry. We present
optical and near-IR images and investigate the properties of the host galaxy.
The SED of the host is rather blue, indicative of a significant young age
stellar population formed within the last 1Gyr. A 3sigma upper limit of
L_bulge<4.5x10^10Lsun for the H band luminosity and a corresponding stellar
mass upper limit of M_bulge<3.4x10^10Msun show that the host is offset from the
local BH-bulge relations. This is independently supported by the kinematics of
the gas. Although the stellar mass of the host galaxy is lower than expected,
it cannot explain the exceptionally low metallicity of the gas. We suggest that
the extended emission-line region and the galaxy growth are caused by the
infall of nearly pristine gas from the environment of the QSO host. Minor
mergers of dwarf galaxies or the theoretically predicted smooth accretion of
cold gas are both potential drivers behind that process. Since the metallicity
of the gas in the NLR is much lower than expected, we suspect that the external
gas has already reached the galaxy centre and may even contribute to the
current feeding of the BH. HE 2158-0107 appears to represent a particular phase
of substantial BH and galaxy growth that can be observationally linked with the
accretion of external material from its environment.Comment: 14 pages, 12 figures, accepted for publication in A&
The globular cluster system of NGC 1316 IV. Nature of the star cluster complex SH2
The light of the merger remnant NGC 1316 is dominated by old and
intermediate-age stars. The only sign of current star formation in this big
galaxy is the HII region SH2, an isolated star cluster complex with a ring-like
morphology and an estimated age of 0.1 Gyr at a galactocentric distance of
about 35 kpc. A nearby intermediate-age globular cluster, surrounded by weak
line emission and a few more young star clusters, is kinematically associated.
The origin of this complex is enigmatic. The nebular emission lines permit a
metallicity determination which can discriminate between a dwarf galaxy or
other possible precursors. We used the Integrated Field Unit of the VIMOS
instrument at the Very Large Telescope of the European Southern Observatory to
study the morphology, kinematics, and metallicity employing line maps, velocity
maps, and line diagnostics of a few characteristic spectra. The line ratios of
different spectra vary, indicating highly structured HII regions, but define a
locus of uniform metallicity. The strong-line diagnostic diagrams and empirical
calibrations point to a nearly solar or even super-solar oxygen abundance. The
velocity dispersion of the gas is highest in the region offset from the bright
clusters. Star formation may be active on a low level. There is evidence for a
large-scale disk-like structure in the region of SH2, which would make the
similar radial velocity of the nearby globular cluster easier to understand.
The high metallicity does not fit to a dwarf galaxy as progenitor. We favour
the scenario of a free-floating gaseous complex having its origin in the merger
2 Gyr ago. Over a long period the densities increased secularly until finally
the threshold for star formation was reached. SH2 illustrates how massive star
clusters can form outside starbursts and without a considerable field
population.Comment: 10 pages, 5 figures, accepted for Astronomy & Astrophysic
Photoionization models of the CALIFA HII regions. I. Hybrid models
Photoionization models of HII regions require as input a description of the
ionizing SED and of the gas distribution, in terms of ionization parameter U
and chemical abundances (e.g. O/H and N/O). A strong degeneracy exists between
the hardness of the SED and U, which in turn leads to high uncertainties in the
determination of the other parameters, including abundances. One way to resolve
the degeneracy is to fix one of the parameters using additional information.
For each of the ~ 20000 sources of the CALIFA HII regions catalog, a grid of
photoionization models is computed assuming the ionizing SED being described by
the underlying stellar population obtained from spectral synthesis modeling.
The ionizing SED is then defined as the sum of various stellar bursts of
different ages and metallicities. This solves the degeneracy between the shape
of the ionizing SED and U. The nebular metallicity (associated to O/H) is
defined using the classical strong line method O3N2 (which gives to our models
the status of "hybrids"). The remaining free parameters are the abundance ratio
N/O and the ionization parameter U, which are determined by looking for the
model fitting [NII]/Ha and [OIII]/Hb. The models are also selected to fit
[OII]/Hb. This process leads to a set of ~ 3200 models that reproduce
simultaneously the three observations.
We find that the regions associated to young stellar bursts suffer leaking of
the ionizing photons, the proportion of escaping photons having a median of
80\%. The set of photoionization models satisfactorily reproduces the electron
temperature derived from the [OIII]4363/5007 line ratio. We determine new
relations between the ionization parameter U and the [OII]/[OIII] or
[SII]/[SIII] line ratios. New relations between N/O and O/H and between U and
O/H are also determined.
All the models are publicly available on the 3MdB database.Comment: Accepted for publication in A&
Integral field spectroscopy of nearby QSOs II. The molecular gas content and condition for star formation
We present single-dish 12CO(1 − 0) and 12CO(2 − 1) observations for 14 low-redshift quasi-stellar objects (QSOs). In combination with optical integral field spectroscopy we study how the cold gas content relates to the star formation rate (SFR) and black hole accretion rate. 12CO(1 − 0) is detected in 8 of 14 targets and 12CO(2 − 1) is detected in 7 out of 11 cases. The majority of disc-dominated QSOs reveal gas fractions and depletion times well matching normal star forming systems. Two gas-rich major mergers show clear starburst signatures with higher than average gas fractions and shorter depletion times. Bulge-dominated QSO hosts are mainly undetected in 12CO(1 − 0) which corresponds, on average, to lower gas fractions than in disc-dominated counterparts. Their SFRs however imply shorter than average depletion times and higher star formation efficiencies. Negative QSO feedback through removal of cold gas seems to play a negligible role in our sample. We find a trend between black hole accretion rate and total molecular gas content for disc-dominated QSOs when combined with literature samples. We interpret this as an upper envelope for the nuclear activity and is well represented by a scaling relation between the total and circum-nuclear gas reservoir accessible for accretion. Bulge-dominated QSOs significantly differ from that scaling relation and appear uncorrelated with the total molecular gas content. This could be explained either by a more compact gas reservoir, blow out of the gas envelope through outflows, or a different ISM phase composition
Resolving galaxies in time and space: II: Uncertainties in the spectral synthesis of datacubes
In a companion paper we have presented many products derived from the
application of the spectral synthesis code STARLIGHT to datacubes from the
CALIFA survey, including 2D maps of stellar population properties and 1D
averages in the temporal and spatial dimensions. Here we evaluate the
uncertainties in these products. Uncertainties due to noise and spectral shape
calibration errors and to the synthesis method are investigated by means of a
suite of simulations based on 1638 CALIFA spectra for NGC 2916, with
perturbations amplitudes gauged in terms of the expected errors. A separate
study was conducted to assess uncertainties related to the choice of
evolutionary synthesis models. We compare results obtained with the Bruzual &
Charlot models, a preliminary update of them, and a combination of spectra
derived from the Granada and MILES models. About 100k CALIFA spectra are used
in this comparison.
Noise and shape-related errors at the level expected for CALIFA propagate to
0.10-0.15 dex uncertainties in stellar masses, mean ages and metallicities.
Uncertainties in A_V increase from 0.06 mag in the case of random noise to 0.16
mag for shape errors. Higher order products such as SFHs are more uncertain,
but still relatively stable. Due to the large number statistics of datacubes,
spatial averaging reduces uncertainties while preserving information on the
history and structure of stellar populations. Radial profiles of global
properties, as well as SFHs averaged over different regions are much more
stable than for individual spaxels. Uncertainties related to the choice of base
models are larger than those associated with data and method. Differences in
mean age, mass and metallicity are ~ 0.15 to 0.25 dex, and 0.1 mag in A_V.
Spectral residuals are ~ 1% on average, but with systematic features of up to
4%. The origin of these features is discussed. (Abridged)Comment: A&A, accepte
The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes
Galaxies, which often contain ionised gas, sometimes also exhibit a so-called
low-ionisation nuclear emission line region (LINER). For 30 years this was
attributed to a central mass-accreting supermassive black hole (AGN) of low
luminosity, making LINER galaxies the largest AGN-sub-population, dominating in
numbers over higher luminosity Seyfert galaxies and quasars. This, however,
poses a serious problem. While the inferred energy balance is plausible, many
LINERs clearly do not contain any other independent signatures of an AGN. Using
integral field spectroscopic data from the CALIFA survey, we aim at comparing
the observed radial surface brightness profiles with what is expected from
illumination by an AGN. Essential for this analysis is a proper extraction of
emission-lines, especially weak lines such as the Balmer Hb line which is
superposed on an absorption trough. To accomplish this, we use the GANDALF code
which simultaneously fits the underlying stellar continuum and emission lines.
We show for 48 galaxies with LINER-like emission, that the radial emission-line
surface brightness profiles are inconsistent with ionisation by a central
point-source and hence cannot be due to an AGN alone. The most probable
explanation for the excess LINER-like emission is ionisation by evolved stars
during the short but very hot and energetic phase known as post-AGB. This leads
us to an entirely new interpretation. Post-AGB stars are ubiquitous and their
ionising effect should be potentially observable in every galaxy with gas
present and stars older than ~1 Gyr, unless a stronger radiation field from
young hot stars or an AGN outshines them. This means that galaxies with
LINER-like emission are in fact not a class defined by a property, but rather
by the absence of a property. It also explains why LINER emission is observed
mostly in massive galaxies with old stars and little star formation.Comment: 8 pages, 7 figure
RBS1423 - a new QSO with relativistic reflection from an ionised disk
We present the analysis and results of a 20 ks XMM-Newton observation of
RBS1423. X-ray spectral analysis is used to establish a significantly broadened
relativistic iron K-alpha line from a highly ionised disk. A QSO at z=2.262 was
considered to be the optical counterpart of this ROSAT Bright Survey X-ray
source. Based on the improved XMM-Newton source position we identified a
z=0.208 QSO as optical counterpart to RBS1423. The 0.2-12 keV X-ray luminosity
of this radio-quiet QSO is 6x10^{44} erg/s. The XMM-EPIC spectra are well
described by a power law with a significantly broadened iron K-alpha line. Disk
line models for both Schwarzschild and Kerr black holes require hydrogen-like
iron ions to fit the measured line profile. Significant ionisation of the
reflection disk is confirmed by model fits with ionised disk models, resulting
in an ionisation parameter xi~2000.Comment: 7 pages, 8 figures, accepted for publication in A&A (2 April 2007
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