3,126 research outputs found
Early star formation traced by the highest redshift quasars
The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page
The Nuclear Stellar Cluster in the Seyfert~1 Galaxy NGC 3227: High Angular Resolution NIR Imaging and Spectroscopy
NIR high angular resolution speckle imaging and imaging spectroscopy of the
nuclear region (10'' ~ 840pc) of the Seyfert1 galaxy NGC3227 are presented. A
nuclear stellar cluster is slightly resolved in the J and H band with
increasing contribution to the NIR continuum from the K to the J band. The
stellar absorption lines are extended compared to the neighboring continuum
suggesting a cluster size of ~ 70pc FWHM. Analysis of those lines suggests that
the stars are contributing about 65% (40%) of the total continuum emission in
the H (K) band in a 3.6'' aperture. Population synthesis in conjunction with
NIR spectral synthesis indicates an age of 25 to 50 Myr when red supergiants
contribute most to the NIR light. This is supported by published optical data
on the MgIb line and the CaII triplet. Although a higher age of ~ 0.5 Gyr where
AGB stars dominate the NIR light can not be excluded, the observed parameters
are at the limit of those expected for a cluster dominated by AGB stars.
However, in either case the resolved stellar cluster contributes only about ~
15 % of the total dynamical mass in the inner 300pc implying another much older
stellar population. Pure constant star formation over the last 10 Gyr can be
excluded. Therefore, at least two star formation/starburst events took place in
the nucleus of NGC3227. Since such sequences in the nuclear star formation
history are also observed in the nuclei of other galaxies a link between the
activity of the star formation and the AGN itself seems likely.Comment: accepted for publication in the Astrophysical Journal, 46 pages, 15
figure
Stellar and gaseous abundances in M82
The near infrared (IR) absorption spectra of starburst galaxies show several
atomic and molecular lines from red supergiants which can be used to infer
reliable stellar abundances. The metals locked in stars give a picture of the
galaxy metallicity prior to the last burst of star formation. The enrichment of
the new generation of stars born in the last burst can be traced by measuring
the hot gas in the X-rays. For the first time detailed stellar abundances in
the nuclear region of the starburst galaxy M82 have been obtained. They are
compared with those of the hot gas as derived from an accurate re-analysis of
the XMM and Chandra nuclear X-ray spectra. The cool stars and the hot gas
suggest [Fe/H]=-0.35+/-0.2 dex, and an overall [Si,Mg/Fe] enhancement by 0.4
and 0.5 dex, respectively. This is consistent with a major chemical enrichment
by SNe II explosions in recursive bursts on short timescales. Oxygen is more
puzzling to interpret since it is enhanced by 0.3 dex in stars and depleted by
0.2 dex in the hot gas. None of the standard enrichment scenarios can fully
explain such a behavior when compared with the other alpha-elements.Comment: APJ, in pres
High precision radial velocities with GIANO spectra
Radial velocities (RV) measured from near-infrared (NIR) spectra are a
potentially excellent tool to search for extrasolar planets around cool or
active stars. High resolution infrared (IR) spectrographs now available are
reaching the high precision of visible instruments, with a constant improvement
over time. GIANO is an infrared echelle spectrograph at the Telescopio
Nazionale Galileo (TNG) and it is a powerful tool to provide high resolution
spectra for accurate RV measurements of exoplanets and for chemical and
dynamical studies of stellar or extragalactic objects. No other high spectral
resolution IR instrument has GIANO's capability to cover the entire NIR
wavelength range (0.95-2.45 micron) in a single exposure. In this paper we
describe the ensemble of procedures that we have developed to measure high
precision RVs on GIANO spectra acquired during the Science Verification (SV)
run, using the telluric lines as wavelength reference. We used the Cross
Correlation Function (CCF) method to determine the velocity for both the star
and the telluric lines. For this purpose, we constructed two suitable digital
masks that include about 2000 stellar lines, and a similar number of telluric
lines. The method is applied to various targets with different spectral type,
from K2V to M8 stars. We reached different precisions mainly depending on the H
-magnitudes: for H ~ 5 we obtain an rms scatter of ~ 10 m s-1, while for H ~ 9
the standard deviation increases to ~ 50 - 80 m s-1. The corresponding
theoretical error expectations are ~4 m s-1 and 30 m s-1, respectively. Finally
we provide the RVs measured with our procedure for the targets observed during
GIANO Science Verification.Comment: 26 pages, 15 figures, 6 table
NGC 5506 Unmasked as a Narrow Line Seyfert 1: A Direct View of the Broad Line Region using Near-IR Spectroscopy
This letter presents incontrovertible evidence that NGC5506 is a Narrow Line
Seyfert 1 (NLSy1). Our new 0.9-1.4 micron spectrum of its nucleus clearly shows
the permitted OI 1.1287 micron line (with full width at half maximum <2000
km/s) and the `1 micron FeII lines'. These lines can only originate in the
optically-thick broad line region (BLR) and, among Seyfert nuclei the latter
series of lines are seen only in NLSy1s. The obscuration to the BLR, derived
from a rough estimate of the OI 1.1287 micron / OI 8446 Angstrom ratio and from
the reddening of the near-IR Paschen lines, is A_v > 5. Together, these results
make NGC5506 the first identified case of an optically-obscured NLSy1. This new
classification helps explain its radio to X-ray properties, which until now
were considered highly anomalous. However, interesting new concerns are raised:
e.g., NGC5506 is unusual in hosting both a `type 1' AGN and a nuclear water
vapor megamaser. As the brightest known NLSy1, NGC5506 is highly suitable for
study at wavebands less affected by obscuration.Comment: 4 pages, to appear in A&A Letter
Detecting Primordial Stars
We discuss the expected properties of the first stellar generations in the
Universe. We find that it is possible to discern truly primordial populations
from the next generation of stars by measuring the metallicity of high-z star
forming objects. The very low background of the future James Webb Space
Telescope (JWST) will enable it to image and study first-light sources at very
high redshifts, whereas its relatively small collecting area limits its
capability in obtaining spectra of z~10-15 first-light sources to either the
bright end of their luminosity function or to strongly lensed sources. With a
suitable investment of observing time JWST will be able to detect individual
Population III supernovae, thus identifying the very first stars that formed in
the Universe.Comment: [8 pages, 5 figures] Invited Talk, to appear in IMF@50: The Stellar
Initial Mass Function Fifty Years Later, eds E. Corbelli, F. Palla, and H.
Zinnecker (Dordrecht: Kluwer
A Second Luminous Blue Variable in the Quintuplet Cluster
H and K band moderate resolution and 4 m high resolution spectra have
been obtained for FMM#362, a bright star in the Quintuplet Cluster near the
Galactic Center. The spectral features in these bands closely match those of
the Pistol Star, a luminous blue variable and one of the most luminous stars
known. The new spectra and previously-obtained photometry imply a very high
luminosity for FMM#362, L \Lsun, and a temperature of 10,000 -
13,000 K. Based on its luminosity, temperature, photometric variability, and
similarities to the Pistol Star, we conclude that FMM#362 is a luminous blue
variable.Comment: Accepted for publication in The Astrophysical Journal Letters, 4
PostScript figures, 2 table
Sequential drain amylase to guide drain removal following pancreatectomy
BACKGROUND:
Although used as criterion for early drain removal, postoperative day (POD) 1 drain fluid amylase (DFA) ≤ 5000 U/L has low negative predictive value for clinically relevant postoperative pancreatic fistula (CR-POPF). It was hypothesized that POD3 DFA ≤ 350 could provide further information to guide early drain removal.
METHODS:
Data from a pancreas surgery consortium database for pancreatoduodenectomy and distal pancreatectomy patients were analyzed retrospectively. Those patients without drains or POD 1 and 3 DFA data were excluded. Patients with POD1 DFA ≤ 5000 were divided into groups based on POD3 DFA: Group A (≤350) and Group B (>350). Operative characteristics and 60-day outcomes were compared using chi-square test.
RESULTS:
Among 687 patients in the database, all data were available for 380. Fifty-five (14.5%) had a POD1 DFA > 5000. Among 325 with POD1 DFA ≤ 5000, 254 (78.2%) were in Group A and 71 (21.8%) in Group B. Complications (35 (49.3%) vs 87 (34.4%); p = 0.021) and CR-POPF (13 (18.3%) vs 10 (3.9%); p < 0.001) were more frequent in Group B.
CONCLUSIONS:
In patients with POD1 DFA ≤ 5000, POD3 DFA ≤ 350 may be a practical test to guide safe early drain removal. Further prospective testing may be useful
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