544 research outputs found
The Mass-Metallicity and Luminosity-Metallicity Relation from DEEP2 at z ~ 0.8
We present the mass-metallicity (MZ) and luminosity-metallicity (LZ)
relations at z ~ 0.8 from ~1350 galaxies in the Deep Extragalactic Evolutionary
Probe 2 (DEEP2) survey. We determine stellar masses by fitting the spectral
energy distribution inferred from photometry with current stellar population
synthesis models. This work raises the number of galaxies with metallicities at
z ~ 0.8 by more than an order of magnitude. We investigate the evolution in the
MZ and LZ relations in comparison with local MZ and LZ relations determined in
a consistent manner using ~21,000 galaxies in the Sloan Digital Sky Survey. We
show that high stellar mass galaxies (log(M/M_solar)~10.6) at z ~ 0.8 have
attained the chemical enrichment seen in the local universe, while lower
stellar mass galaxies (log(M/M_solar)~9.2) at z ~ 0.8 have lower metallicities
(Delta log(O/H)~0.15 dex) than galaxies at the same stellar mass in the local
universe. We find that the LZ relation evolves in both metallicity and B-band
luminosity between z ~ 0.8 and z~ 0, with the B-band luminosity evolving as a
function of stellar mass. We emphasize that the B-band luminosity should not be
used as a proxy for stellar mass in chemical evolution studies of star-forming
galaxies. Our study shows that both the metallicity evolution and the B-band
luminosity evolution for emission-line galaxies between the epochs are a
function of stellar mass, consistent with the cosmic downsizing scenario of
galaxy evolution.Comment: Accepted Version: 18 pages, 13 figure
Chemical abundances and winds of massive stars in M31: a B-type supergiant and a WC star in OB10
We present high quality spectroscopic data for two massive stars in the OB10
association of M31, OB10-64 (B0Ia) and OB10-WR1 (WC6). Medium resolution
spectra of both stars were obtained using the ISIS spectrograph on the William
Hershel Telescope. This is supplemented with HST-STIS UV spectroscopy and KeckI
HIRES data for OB10-64. A non-LTE model atmosphere and abundance analysis for
OB10-64 is presented indicating that this star has similar photospheric CNO, Mg
and Si abundances as solar neighbourhood massive stars. A wind analysis of this
early B-type supergiant reveals a mass-loss rate of M_dot=1.6x10^-6
M_solar/yr,and v_infty=1650 km/s. The corresponding wind momentum is in good
agreement with the wind momentum -- luminosity relationship found for Galactic
early B supergiants. Observations of OB10W-R1 are analysed using a non-LTE,
line-blanketed code, to reveal approximate stellar parameters of log L/L_solar
\~ 5.7, T~75 kK, v_infty ~ 3000 km/s, M_dot ~ 10^-4.3 M_solar/yr, adopting a
clumped wind with a filling factor of 10%. Quantitative comparisons are made
with the Galactic WC6 star HD92809 (WR23) revealing that OB10-WR1 is 0.4 dex
more luminous, though it has a much lower C/He ratio (~0.1 versus 0.3 for
HD92809). Our study represents the first detailed, chemical model atmosphere
analysis for either a B-type supergiant or a WR star in Andromeda, and shows
the potential of how such studies can provide new information on the chemical
evolution of galaxies and the evolution of massive stars in the local Universe.Comment: 17 pages, 14 figures, MNRAS accepted version, some minor revision
Metal abundances in extremely distant Galactic old open clusters. II. Berkeley 22 and Berkeley 66
We report on high resolution spectroscopy of four giant stars in the Galactic
old open clusters Berkeley~22 and Berkeley~66 obtained with HIRES at the Keck
telescope. We find that and for
Berkeley~22 and Berkeley~66, respectively. Based on these data, we first revise
the fundamental parameters of the clusters, and then discuss them in the
context of the Galactic disk radial abundance gradient. We found that both
clusters nicely obey the most updated estimate of the slope of the gradient
from \citet{fri02} and are genuine Galactic disk objects.Comment: 20 pages, 6 eps figures, accepted for publication in the Astronomical
Journa
The structure and dynamics of the AC114 galaxy cluster revisited
We present a dynamical analysis of the galaxy cluster AC114 based on a
catalogue of 524 velocities. Of these, 169 (32%) are newly obtained at ESO
(Chile) with the VLT and the VIMOS spectrograph. Data on individual galaxies
are presented and the accuracy of the measured velocities is discussed.
Dynamical properties of the cluster are derived. We obtain an improved mean
redshift value z= 0.31665 +/- 0.0008 and velocity dispersion \sigma= 1893+73-82
\kms. A large velocity dispersion within the core radius and the shape of the
infall pattern suggests that this part of the cluster is in a radial phase of
relaxation with a very elongated radial filament spanning 12000 \kms. A radial
foreground structure is detected within the central 0.5/h Mpc radius,
recognizable as a redshift group at the same central redshift value. We analyze
the color distribution for this archetype Butcher-Oemler galaxy cluster and
identify the separate red and blue galaxy sequences. The latter subset contains
44% of confirmed members of the cluster, reaching magnitudes as faint as R_{f}=
21.1 (1.0 magnitude fainter than previous studies). We derive a mass M_{200}=
(4.3 \pm 0.7) x 10^15 Msun/h. In a subsequent paper we will utilize the
spectral data presented here to explore the mass-metallicity relation for this
intermediate redshift cluster.Comment: 17 pages, 11 figures, 4 tables, accepted for publication in MNRA
Maximal decidable fragments of Halpern and Shoham's modal logic of intervals
In this paper, we focus our attention on the fragment of
Halpern and Shoham's modal logic of intervals (HS) that
features four modal operators corresponding to the
relations ``meets'', ``met by'', ``begun by'', and
``begins'' of Allen's interval algebra (AAbarBBbar logic).
AAbarBBbar properly extends interesting interval temporal
logics recently investigated in the literature, such as the
logic BBbar of Allen's ``begun by/begins'' relations and
propositional neighborhood logic AAbar, in its many
variants (including metric ones). We prove that the satisfiability
problem for AAbarBBbar, interpreted over finite linear orders,
is decidable, but not primitive recursive (as a matter of fact,
AAbarBBbar turns out to be maximal with respect to decidability). Then, we show that it becomes undecidable when AAbarBBbar is interpreted over classes of linear orders that contains at least one linear order with an infinitely ascending sequence, thus including the natural time flows N, Z, Q, and R
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