2,626 research outputs found
The Oxygen Abundance of Nearby Galaxies from Sloan Digital Sky Survey Spectra
We have derived the oxygen abundance for a sample of nearby galaxies in the
Data Release 5 of the Sloan Digital Sky Survey (SDSS) which possess at least
two independent spectra of one or several HII regions with a detected
[OIII]4363 auroral line. Since, for nearby galaxies, the [OII]3727 nebular line
is out of the observed wavelength range, we propose a method to derive (O/H)_ff
abundances using the classic Te method coupled with the ff relation. (O/H)_7325
abundances have also been determined, based on the [OII]7320,7330 line
intensities, and using a small modification of the standard Te method. The
(O/H)_ff and (O/H)_7325 abundances have been derived with both the one- and
two-dimensional t_2 - t_3 relations. It was found that the (O/H)_ff abundances
derived with the parametric two-dimensional t_2 - t_3 relation are most
reliable. Oxygen abundances have been determined in 29 nearby galaxies, based
on 84 individual abundance determinations in HII regions. Because of our
selection methods, the metallicity of our galaxies lies in the narrow range 8.2
< 12 + log (O/H) < 8.4. The radial distribution of oxygen abundances in the
disk of the spiral galaxy NGC 4490 is determined for the first time.Comment: 39 pages, 10 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Outflows in Infrared-Luminous Starbursts at z < 0.5. I. Sample, NaI D Spectra, and Profile Fitting
We have conducted a spectroscopic survey of 78 starbursting infrared-luminous
galaxies at redshifts up to z = 0.5. We use moderate-resolution spectroscopy of
the NaI D interstellar absorption feature to directly probe the neutral phase
of outflowing gas in these galaxies. Over half of our sample are ultraluminous
infrared galaxies that are classified as starbursts; the rest have infrared
luminosities in the range log(L_IR/L_sun) = 10.2 - 12.0. The sample selection,
observations, and data reduction are described here. The absorption-line
spectra of each galaxy are presented. We also discuss the theory behind
absorption-line fitting in the case of a partially-covered, blended absorption
doublet observed at moderate-to-high resolution, a topic neglected in the
literature. A detailed analysis of these data is presented in a companion
paper.Comment: 59 pages, 18 figures in AASTeX preprint style; to appear in September
issue of ApJ
The IntraCluster Medium: An Invariant Stellar IMF
Evidence supporting the hypothesis of an invariant stellar Initial Mass
Function is strong and varied. The intra-cluster medium in rich clusters of
galaxies is one of the few contrary locations where recent interpretations of
the chemical abundances have favoured an IMF that is biased towards massive
stars, compared to the `normal' IMF. This interpretation hinges upon the
neglect of Type Ia supernovae to the ICM enrichment, and a particular choice of
the nucleosynthesis yields of Type II supernovae. We demonstrate here that when
one adopts yields determined empirically from observations of Galactic stars,
rather than the uncertain model yields, a self-consistent picture may be
obtained with an invariant stellar IMF, and about half of the iron in the ICM
being produced by Type Ia supernovae.Comment: 9 pages, LateX (aaspp4 macro), including one postscript figure.
Accepted, ApJ Letter
Recommended from our members
Patients’ Expectations of the Functional and Psychosocial Outcomes of Orbital Decompression Surgery for Thyroid Eye Disease: A Qualitative Study
Patients with appearance-altering conditions may be dissatisfied with the outcomes of reconstructive surgery due to unmet expectations. This study explored patients’ expectations of orbital decompression surgery for thyroid eye disease (TED) and whether these were met. Semi-structured interviews were conducted at two times: (1) in the weeks after patients were listed for decompression surgery and before surgery; (2) up to 12 months after surgery. Thematic analysis was performed for each time point, to identify themes within the data. Fourteen adults with TED were interviewed prior to surgery and five were followed up after surgery.
Thematic analyses found: (1) Prior to surgery, patients had formed expectations through online information about the procedure, consultations with physicians, the impact TED had on their lives, and speaking to relevant others. Patients had specific expectations about the procedure, the recovery, post-operative appearance and post-operative vision. (2) After surgery, patients generally felt their appearance and well-being had improved. However, dissatisfaction was linked to unanticipated specific aspects of surgical care, recovery, or appearance.
Dissatisfaction can arise from unmet expectations for the outcomes of reconstructive surgery. Physicians should be aware of the processes by which patients form expectations, for example different types and quality of online information. Ensuring that preoperative expectations are realistic could enhance satisfaction after surgery
The oxygen abundance calibrations and N/O abundance ratios of ~40,000 SDSS star-forming galaxies
Using a large sample of 38,478 star-forming galaxies selected from the Second
Data Release of the Sloan Digital Sky Survey database (SDSS-DR2), we derive
analytical calibrations for oxygen abundances from several
metallicity-sensitive emission-line ratios: [N II]/H_alpha, [O III]/[N II], [N
II]/[O II], [N II]/[S II], [S II]/H_alpha, and [O III]/H_beta. This consistent
set of strong-line oxygen abundance calibrations will be useful for future
abundance studies. Among these calibrations, [N II]/[O II] is the best for
metal-rich galaxies due to its independence on ionization parameter and low
scatter. Dust extinction must be considered properly at first. These
calibrations are more suitable for metal-rich galaxies (8.4<12+log(O/H)<9.3),
and for the nuclear regions of galaxies. The observed relations are consistent
with those expected from the photoionization models of Kewley & Dopita (2002).
However, most of the observational data spread in a range of ionization
parameter q from 1*10^7 to 8*10^7 cm s^{-1}, corresponding to logU= -3.5 to
-2.5, narrower than that suggested by the models. We also estimate the (N/O)
abundance ratios of this large sample of galaxies, and these are consistent
with the combination of a "primary" and a dominant "secondary" components of
nitrogen.Comment: 17 pages, 10 figures, 1 table. ApJ in pres
Is There a Fundamental Line for Disk Galaxies?
We show that there are strong local correlations between metallicity, surface
brightness, and dynamical mass-to-light ratio within M33, analogous to the
fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using
near-infrared imaging from 2MASS, the published rotation curve of M33, and
literature measurements of the metallicities of HII regions and supergiant
stars, we demonstrate that these correlations hold for points at radial
distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given
metallicity or surface brightness, M33 has a mass-to-light ratio approximately
four times as large as the Local Group dwarf galaxies; other than this constant
offset, we see broad agreement between the M33 and dwarf galaxy data. We use
analytical arguments to show that at least two of the three fundamental line
correlations are basic properties of disk galaxies that can be derived from
very general assumptions. We investigate the effect of supernova feedback on
the fundamental line with numerical models and conclude that while feedback
clearly controls the scatter in the fundamental line, it is not needed to
create the fundamental line itself, in agreement with our analytical
calculations. We also compare the M33 data with measurements of a simulated
disk galaxy, finding that the simulation reproduces the trends in the data
correctly and matches the fundamental line, although the metallicity of the
simulated galaxy is too high, and the surface brightness is lower than that of
M33.Comment: 14 pages, 14 figures (5 in color). Accepted for publication in Ap
An Old Cluster in NGC 6822
We present spectroscopy of two clusters in the dwarf irregular galaxy NGC
6822. From these we deduce an age for Cluster VII of 11 Gyr and [Fe/H] = -1.95
+/- 0.15 dex. Cluster VII appears to be an analog of the metal-poor galactic
globular clusters. Cluster VI is found to be much younger and more metal rich,
with an age of approximately 2 Gyr. Its derived metallicity, [Fe/H], of
approximately -1.0 dex is comparable to that of the gas seen today in NGC 6822.
The existence of a metal-poor old cluster in NGC 6822 rules out models for the
chemical evolution of this galaxy with significant prompt initial enhancement.
We find that a star formation rate which is constant with time and is within a
factor of two of the present star formation rate can reproduce the two points
on the age-metallicity relationship for NGC 6822 over the past 10 Gyr defined
by these two clusters.Comment: 8 pages; accepted for publication in A
Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift
We investigate the star formation history of the central regions of four
Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact
(MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than
-17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the
most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B
< 19.0 mag arcsec^-2) of this population. The observational data used were
obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the
HST/NICMOS first camera. We find evidence for multiple stellar populations. One
of them is identified as the ionizing population, and the other one corresponds
to the underlying stellar generation.
The estimated masses of the inferred populations are compatible with the
dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also
indicate that the first episodes of star formation the presented LCBGs
underwent happened between 5 and 7 Gyr ago.
We compare the stellar populations found in LCBGs with the stellar
populations present in bright, local HII galaxies, nearby spheroidal systems
and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar
populations of LCBGs are similar yet bluer to those of local HII galaxies. It
is also the case that the passive color evolution of the LCBGs could convert
them into local Spheroidal galaxies if no further episode of star formation
takes place. Our results help to impose constraints on evolutionary scenarios
for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with
pdflatex. Contains png figure
The Relative Orientation of Nuclear Accretion and Galaxy Stellar Disks in Seyfert Galaxies
We use the difference (delta) between the position angles of the nuclear
radio emission and the host galaxy major axis to investigate the distribution
of the angle (beta) between the axes of the nuclear accretion disk and the host
galaxy disk in Seyfert galaxies. We provide a critical appraisal of the quality
of all measurements, and find that the data are limited by observational
uncertainties and biases, such as the well known deficiency of Seyfert galaxies
of high inclination. There is weak evidence that the distribution of delta for
Seyfert 2 galaxies may be different (at the 90% confidence level) from a
uniform distribution, while the Seyfert 1 delta distribution is not
significantly different from a uniform distribution or from the Seyfert 2 delta
distribution. The cause of the possible non-uniformity in the distribution of
delta for Seyfert 2 galaxies is discussed. Seyfert nuclei in late-type spiral
galaxies may favor large values of delta (at the ~96% confidence level), while
those in early-type galaxies show a more or less random distribution of delta.
This may imply that the nuclear accretion disk in non-interacting late-type
spirals tends to align with the stellar disk, while that in early-type galaxies
is more randomly oriented, perhaps as a result of accretion following a galaxy
merger.
We point out that biases in the distribution of inclination translate to
biased estimates of beta in the context of the unified scheme. When this effect
is taken into account, the distributions of beta for all Seyferts together, and
of Seyfert 1's and 2's separately, agree with the hypothesis that the radio
jets are randomly oriented with respect to the galaxy disk. The data are
consistent with the expectations of the unified scheme, but do not demand it.Comment: To appear in the Astrophysical Journal, Vol 516 #1, May 1, 1999.
Corrected figure placement within pape
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