121 research outputs found
Optical/near-infrared selection of red QSOs: Evidence for steep extinction curves towards galactic centers?
We present the results of a search for red QSOs using a selection based on
optical imaging from SDSS and near-infrared imaging from UKIDSS. For a sample
of 58 candidates 46 (79%) are confirmed to be QSOs. The QSOs are predominantly
dust-reddened except a handul at redshifts z>3.5. The dust is most likely
located in the QSO host galaxies. 4 (7%) of the candidates turned out to be
late-type stars, and another 4 (7%) are compact galaxies. The remaining 4
objects we could not identify. In terms of their optical spectra the QSOs are
similar to the QSOs selected in the FIRST-2MASS red Quasar survey except they
are on average fainter, more distant and only two are detected in the FIRST
survey. We estimate the amount of extinction using the SDSS QSO template
reddened by SMC-like dust. It is possible to get a good match to the observed
(restframe ultraviolet) spectra, but for nearly all the reddened QSOs it is not
possible to match the near-IR photometry from UKIDSS. The likely reasons are
that the SDSS QSO template is too red at optical wavelengths due to
contaminating host galaxy light and that the assumed SMC extinction curve is
too shallow. Our survey has demonstrated that selection of QSOs based on
near-IR photometry is an efficent way to select QSOs, including reddened QSOs,
with only small contamination from late-type stars and compact galaxies. This
will be useful with ongoing and future wide-field near-IR surveys such as the
VISTA and EUCLID surveys. [Abridged]Comment: 74 pages, 6 figures. Accepted for for publication in ApJ
Serendipitous discovery of a projected pair of QSOs separated by 4.5 arcsec on the sky
We present the serendipitous discovery of a projected pair of quasi-stellar
objects (QSOs) with an angular separation of arcsec. The
redshifts of the two QSOs are widely different: one, our programme target, is a
QSO with a spectrum consistent with being a narrow line Seyfert 1 AGN at
. For this target we detect Lyman-, \ion{C}{4}, and
\ion{C}{3]}. The other QSO, which by chance was included on the spectroscopic
slit, is a Type 1 QSO at a redshift of , for which we detect
\ion{C}{4}, \ion{C}{3]} and \ion{Mg}{2}. We compare this system to previously
detected projected QSO pairs and find that only about a dozen previously known
pairs have smaller angular separation.Comment: 4 pages, 3 figures. Accepted for publication in A
Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths
The sub-population of quasars reddened by intrinsic or intervening clouds of
dust are known to be underrepresented in optical quasar surveys. By defining a
complete parent sample of the brightest and spatially unresolved quasars in the
COSMOS field, we quantify to which extent this sub-population is fundamental to
our understanding of the true population of quasars. By using the available
multiwavelength data of various surveys in the COSMOS field, we built a parent
sample of 33 quasars brighter than mag, identified by reliable X-ray to
radio wavelength selection techniques. Spectroscopic follow-up with the
NOT/ALFOSC was carried out for four candidate quasars that had not been
targeted previously to obtain a 100\% redshift completeness of the sample. The
population of high quasars (HAQs), a specific sub-population of quasars
selected from optical/near-infrared photometry, is found to contribute
of the parent sample. The full population of bright spatially
unresolved quasars represented by our parent sample consists of
reddened quasars defined by having , and
of the sample having assuming the extinction
curve of the Small Magellanic Cloud. We show that the HAQ selection works well
for selecting reddened quasars, but some are missed because their optical
spectra are too blue to pass the color cut in the HAQ selection. This is
either due to a low degree of dust reddening or anomalous spectra. We find that
the fraction of quasars with contributing light from the host galaxy is most
dominant at . At higher redshifts the population of spatially
unresolved quasars selected by our parent sample is found to be representative
of the full population at mag. This work quantifies the bias against
reddened quasars in studies that are based solely on optical surveys.Comment: 22 pages, 10 figures, accepted for publication in A&A. The ArXiv
abstract has been shortened for it to be printabl
Discovery of a Perseus-like cloud in the early Universe: HI-to-H2 transition, carbon monoxide and small dust grains at zabs=2.53 towards the quasar J0000+0048
We present the discovery of a molecular cloud at zabs=2.5255 along the line
of sight to the quasar J0000+0048. We perform a detailed analysis of the
absorption lines from ionic, neutral atomic and molecular species in different
excitation levels, as well as the broad-band dust extinction. We find that the
absorber classifies as a Damped Lyman-alpha system (DLA) with
logN(HI)(cm^-2)=20.8+/-0.1. The DLA has super-Solar metallicity with a
depletion pattern typical of cold gas and an overall molecular fraction ~50%.
This is the highest f-value observed to date in a high-z intervening system.
Most of the molecular hydrogen arises from a clearly identified narrow (b~0.7
km/s), cold component in which CO molecules are also found, with logN(CO)~15.
We study the chemical and physical conditions in the cold gas. We find that the
line of sight probes the gas deep after the HI-to-H2 transition in a ~4-5
pc-size cloud with volumic density nH~80 cm^-3 and temperature of only 50 K.
Our model suggests that the presence of small dust grains (down to about 0.001
{\mu}m) and high cosmic ray ionisation rate (zeta_H a few times 10^-15 s^-1)
are needed to explain the observed atomic and molecular abundances. The
presence of small grains is also in agreement with the observed steep
extinction curve that also features a 2175 A bump. The properties of this cloud
are very similar to what is seen in diffuse molecular regions of the nearby
Perseus complex. The high excitation temperature of CO rotational levels
towards J0000+0048 betrays however the higher temperature of the cosmic
microwave background. Using the derived physical conditions, we correct for a
small contribution (0.3 K) of collisional excitation and obtain TCMB(z =
2.53)~9.6 K, in perfect agreement with the predicted adiabatic cooling of the
Universe. [abridged]Comment: 24 pages, 24 figures, accepted for publication in A&
The High A(V) Quasar Survey: Reddened quasi-stellar objects selected from optical/near-infrared photometry - II
Quasi-stellar objects (QSOs) whose spectral energy distributions (SEDs) are
reddened by dust either in their host galaxies or in intervening absorber
galaxies are to a large degree missed by optical color selection criteria like
the one used by the Sloan Digital Sky Survey (SDSS). To overcome this bias
against red QSOs, we employ a combined optical and near-infrared color
selection. In this paper, we present a spectroscopic follow-up campaign of a
sample of red candidate QSOs which were selected from the SDSS and the UKIRT
Infrared Deep Sky Survey (UKIDSS). The spectroscopic data and SDSS/UKIDSS
photometry are supplemented by mid-infrared photometry from the Wide-field
Infrared Survey Explorer. In our sample of 159 candidates, 154 (97%) are
confirmed to be QSOs. We use a statistical algorithm to identify sightlines
with plausible intervening absorption systems and identify nine such cases
assuming dust in the absorber similar to Large Magellanic Cloud sightlines. We
find absorption systems toward 30 QSOs, 2 of which are consistent with the
best-fit absorber redshift from the statistical modeling. Furthermore, we
observe a broad range in SED properties of the QSOs as probed by the rest-frame
2 {\mu}m flux. We find QSOs with a strong excess as well as QSOs with a large
deficit at rest-frame 2 {\mu}m relative to a QSO template. Potential solutions
to these discrepancies are discussed. Overall, our study demonstrates the high
efficiency of the optical/near-infrared selection of red QSOs.Comment: 64 pages, 18 figures, 16 pages of tables. Accepted to ApJ
Low-ionization iron-rich Broad Absorption-Line Quasar SDSS J1652+2650: Physical conditions in the ejected gas from excited FeII and metastable HeI
We present high-resolution VLT/UVES spectroscopy and a detailed analysis of
the unique Broad Absorption-Line system towards the quasar SDSS
J165252.67+265001.96. This system exhibits low-ionization metal absorption
lines from the ground states and excited energy levels of Fe II and Mn II, and
the meta-stable 2^3S excited state of He I. The extended kinematics of the
absorber encompasses three main clumps with velocity offsets of -5680, -4550,
and -1770 km s from the quasar emission redshift, ,
derived from [O II] emission. Each clump shows moderate partial covering of the
background continuum source, . We discuss the
excitation mechanisms at play in the gas, which we use to constrain the
distance of the clouds from the Active Galactic Nucleus (AGN) as well as the
density, temperature, and typical sizes of the clouds. The number density is
found to be and the temperature , with longitudinal cloudlet sizes of pc. Cloudy
photo-ionization modelling of He I, which is also produced at the
interface between the neutral and ionized phases, assuming the number densities
derived from Fe II, constrains the ionization parameter to be .
This corresponds to distances of a few 100 pc from the AGN. We discuss these
results in the more general context of associated absorption-line systems and
propose a connection between FeLoBALs and the recently-identified
molecular-rich intrinsic absorbers. Studies of significant samples of FeLoBALs,
even though rare per se, will soon be possible thanks to large dedicated
surveys paired with high-resolution spectroscopic follow-ups.Comment: Accepted for publication in MNRAS, 27 pages, 21 Figure
Near- infrared spectroscopic observations of high redshift C-I absorbers
We study a sample of 17 z>1.5 absorbers selected based on the presence of
strong CI absorption lines in SDSS spectra and observed with the ESO-VLT
spectrograph X-shooter. We derive metallicities, depletion onto dust, and
extinction by dust, and analyse the absorption from MgII, MgI, CaII and NaI
that are redshifted into the near infrared wavelength range. We show that most
of these CI absorbers have high metallicity and dust content. We detect nine
CaII absorptions with (CaII3934) >0.23 \AA out of 14 systems where
we have appropriate wavelength coverage. The observed equivalent widths are
similar to what has been measured in other lower redshift surveys of CaII
systems. We detect ten NaI absorptions in the 11 systems where we could observe
this absorption. The median equivalent width ((NaI5891) = 0.68 \AA)
is larger than what is observed in local clouds with similar HI column
densities but also in z<0.7 CaII systems detected in the SDSS. The systematic
presence of NaI absorption in these CI systems strongly suggests that the gas
is neutral and cold, maybe part of the diffuse molecular gas in the ISM of
high-redshift galaxies. Most of the systems (12 out of 17) have
(MgII2796) > 2.5 \AA and six of them have log N(HI) < 20.3, with
the extreme case of J1341+1852 that has log N(HI) = 18.18. The MgII absorptions
are spread over more than 400 km s for half of the
systems; three absorbers have > 500 km s. The kinematics are
strongly perturbed for most of these systems, which probably do not arise in
quiet disks and must be close to regions with intense star-formation activity
and/or are part of interacting objects. All this suggests that a large fraction
of the cold gas at high redshift arises in disturbed environments.Comment: 26 pages, 49 figures, 3 tables, accepted by Astronomy & Astrophysics
(A&A
Safety Evaluation of α-Lipoic Acid Supplementation: A Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical Studies.
Alpha-lipoic acid (ALA) is a natural short-chain fatty acid that has attracted great attention in recent years as an antioxidant molecule. However, some concerns have been recently raised regarding its safety profile. To address the issue, we aimed to assess ALA safety profile through a systematic review of the literature and a meta-analysis of the available randomized placebo-controlled clinical studies. The literature search included EMBASE, PubMed Medline, SCOPUS, Google Scholar, and ISI Web of Science by Clarivate databases up to 15th August 2020. Data were pooled from 71 clinical studies, comprising 155 treatment arms, which included 4749 subjects with 2558 subjects treated with ALA and 2294 assigned to placebo. A meta-analysis of extracted data suggested that supplementation with ALA was not associated with an increased risk of any treatment-emergent adverse event (all p > 0.05). ALA supplementation was safe, even in subsets of studies categorized according to smoking habit, cardiovascular disease, presence of diabetes, pregnancy status, neurological disorders, rheumatic affections, severe renal impairment, and status of children/adolescents at baseline
Chemical diversity of gas in distant galaxies: The metal and dust enrichment and variations within absorbing galaxies
The chemical composition of gas in galaxies can be measured in detail from
absorption spectroscopy. By studying gas in galaxies in this way, it is
possible to investigate the small and faint galaxies, which are the most
numerous in the universe. In particular, the chemical distribution of gas in
absorbing systems gives us insight into cycles of gas in and around galaxies.
Here we study chemical enrichment within 64 Damped Lyman-alpha Absorption (DLA)
systems between . We use high-resolution spectra from VLT/UVES
to infer dust depletion from relative abundances of several metals. We perform
a component-by-component analysis within DLAs, and characterise variations in
their chemical enrichment. Unlike hydrogen, the metal columns can be
characterised for individual components. We use them to derive the dust
depletion ([Zn/Fe]fit), as an indicator for chemical enrichment. We find that
some DLAs are chemically diverse within themselves, with [Zn/Fe]fit ranging up
to 0.62 dex within a single system. This suggests that absorbing gas within
these galaxies is chemically diverse. Although we do not find a clear trend of
decreasing dust depletion with redshift, we do see that the most chemically
enriched systems are at lower redshifts. We also observe evidence for dust-poor
components at all redshifts, which may be due to the accretion of pristine gas
onto galaxies. We combine the chemical and kinematic properties of the
individual gas components and observe potential signatures of infalling gas,
with low depletion at velocities below 100km/s, and outflows, with high
depletion and velocities of 600km/s. We find over-abundances of
alpha-elements (an enhancement of 0.3dex) and under-abundances of Mn in
several components, which is likely a signature of core-collapse SNe
nucleosythesis in the ISM. We observe these effects mostly at lower levels of
chemical enrichment.Comment: 56 pages, 99 figures, Accepted for publication in A&A, Abstract
abridged for arXi
On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
Recently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.Comment: Accepted for publishing in MNRAS lette
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