3,136 research outputs found
Two populations of progenitors for type Ia SNe?
We use recent observations of type Ia Supernova (SN Ia) rates to derive, on
robust empirical grounds, the distribution of the delay time (DTD) between the
formation of the progenitor star and its explosion as a SN. Our analysis finds:
i) delay times as long as 3-4 Gyr, derived from observations of SNe Ia at high
redshift, cannot reproduce the dependence of the SN Ia rate on the colors and
on the radio-luminosity of the parent galaxies, as observed in the local
Universe; ii) the comparison between observed SN rates and a grid of
theoretical "single-population" DTDs shows that only a few of them are possibly
consistent with observations. The most successful models are all predicting a
peak of SN explosions soon after star formation and an extended tail in the
DTD, and can reproduce the data but only at a modest statistical confidence
level; iii) present data are best matched by a bimodal DTD, in which about 50%
of type Ia SNe (dubbed "prompt" SN Ia) explode soon after their stellar birth,
in a time of the order of 10^8 years, while the remaining 50% ("tardy" SN Ia)
have a much wider distribution, well described by an exponential function with
a decay time of about 3 Gyr. This fact, coupled with the well established
bimodal distribution of the decay rate, suggests the existence of two classes
of progenitors. We discuss the cosmological implications of this result and
make simple predictions. [Abridged]Comment: 11 pages, MNRAS, in press, modified after referee's comment
Narrow band imaging and long slit spectroscopy of UGC 5101
UGC 5101 (z = 0.04; D is approximately equal to 240 Mpc) is one of the so called Ultraluminous IRAS sources. Two important properties of the members of this group are their L(sub IR) is greater than or equal to 10(exp 12) solar luminosity, and their space density in the universe up to z is less than 0.1 is equal or even larger than the space density of the quasars. Further noteworthy features of the Ultraluminous IRAS sources are their being morphologically peculiar and the fact that they all seem to host active nuclei in their center. We have observed UGC 5101 in an effort to study the interplay between the gas ionized by the central active nucleus and that gas ionized by other processes which may hold important clues to the understanding of the entire picture of this object. In particular these other ionizing processes could well be massive stars formed recently after the galactic encounter and shocks possibly also related to the galaxy collision. The data that we discuss were obtained between Dec. 1989 and Jan. 1992 with the WHT 4.2 m telescope using the two-arm spectrograph ISIS. Several spectral frames were obtained at three different position angles: PA 84--along the tail of the galaxy; PA 32--along the dust lane; and PA 110. The blue spectra are centered on the H beta line, while the red spectra are centered on the H alpha line. In the configuration we used for the long slit spectra, the spectral scale was 0.74 A per pixel, and the spatial scale was .37 arcsec per pixel; we also observed the H alpha region with a spectral scale of .37 A per pixel, at position angle 84. The narrow band images were obtained at the auxiliary port of ISIS, with a scale of .2 arcsec per pixel, and were centered at the H alpha wavelength, and on the adjacent continuum. The H alpha images and the spectra support the following model. UGC 5101 hosts an active nucleus; the NLR extends up to about 1.5 kpc and shows a complex velocity field, superimposed on the rotation curve of the galaxy. Besides the NLR, in the H alpha image are visible tow bright cones that extend up to 3 kpc along PA 32. The long slit spectra at PA 32 show that the velocity field of the gas in these regions is peculiar, while the ionization structure of the gas is similar to that of the NLR
Age, metallicity and star formation history of spheroidal galaxies in cluster at z~1.2
We present the analysis, based on spectra collected at the Large Binocular
Telescope, of the stellar populations in seven spheroidal galaxies in the
cluster XLSSJ0223 at 1.22. The aim is to constrain the epoch of their
formation and their star formation history. Using absorption line strenghts and
full spectral fitting, we derive for the stellar populations of the seven
spheroids a median age =2.40.6 Gyr, corresponding to a median
formation redshift $\sim2.6_{-0.5}^{+0.7}$ (lookback time =
11$_{-1.0}^{+0.6}$ Gyr). We find a significant scatter in age, showing that
massive spheroids, at least in our targeted cluster, are not coeval. The median
metallicity is [Z/H]=0.09$\pm$0.16, as for early-types in clusters at
0$<z<<\sigma_e_{dyn}\Sigma_e_{dyn}\Sigma_e_{dyn}\Sigma_ez\sim1.3$, i.e.
more massive spheroids are more metal rich, have lower stellar mass density and
tend to be older than lower-mass galaxies.Comment: 16 pages, 6 figures, 6 tables, published on MNRA
The metallicity properties of simulated long-GRB galaxy hosts and the Fundamental Metallicity Relation
We study the implication of the collapsar model for Long Gamma-Ray Bursts
(LGRBs) on the metallicity properties of the host galaxies, by combining
high-resolution N-body simulations with semi-analytic models of galaxy
formation. The cosmological model that we use reproduces the Fundamental
Metallicity Relation recently discovered for the SDSS galaxies, whereby the
metallicity decreases with increasing Star Formation Rate for galaxies of a
given stellar mass. We select host galaxies housing pockets of gas-particles,
young and with different thresholds in metallicities, that can be sites of LRGB
events, according to the collapsar model. The simulated samples are compared
with 18 observed LGRB hosts in the aim at discriminating whether the
metallicity is a primary parameter. We find that a threshold in metallicity for
the LGRB progenitors, within the model galaxies, is not necessary in order to
reproduce the observed distribution of host metallicities. The low
metallicities of observed LGRB hosts is a consequence of the high star
formation environment. The star formation rate appears to be the primary
parameter to generate a burst event. Finally, we show that only a few LGRBs are
observed in massive, highly extincted galaxies, while these galaxies are
expected to produce many such events. We identify these missing events with the
fraction of dark LGRBs.Comment: 9 pages, 5 figures, submitted MNRA
Soft band X/K luminosity ratios in late-type galaxies and constraints on the population of supersoft X-ray sources
We study X-ray to K-band luminosity ratios (L_X/L_K) of late-type galaxies in
the 0.3-0.7 keV energy range. From the Chandra archive, we selected nine spiral
and three irregular galaxies with point source detection sensitivity better
than 5 x 10^36 erg/s in order to minimize the contribution of unresolved X-ray
binaries. In late-type galaxies cold gas and dust may cause significant
interstellar absorption, therefore we also demanded the existence of publicly
available HI maps. The obtained L_X/L_K ratios vary between (5.4-68) x 10^27
erg/s/L_K,sun exceeding by factor of 2-20 the values obtained for gas-poor
early-type galaxies. Based on these results we constrain the role of supersoft
X-ray sources as progenitors of type Ia supernovae (SNe Ia). For majority of
galaxies the upper limits range from ~3% to ~15% of the SN Ia frequency
inferred from K-band luminosity, but for a few of them no meaningful
constraints can be placed. On a more detailed level, we study individual
structural components of spiral galaxies: bulge and disk, and, for grand design
spiral galaxies, arm and interarm regions.Comment: 10 pages, 2 tables, 6 figures, accepted for publication in MNRAS,
minor change
How many supernovae are we missing at high redshift?
Near-infrared and radio searches for core-collapse supernovae (CC SNe) in the
local universe have shown that the vast majority of the events occurring in
massive starburst are missed by the current optical searches as they explode in
very dusty environments. Recent infrared observations have shown that the
fraction of star-formation activity that takes place in very luminous dusty
starbursts sharply increases with redshift and becomes the dominant star
formation component at z>0.5. As a consequence, an increasing fraction of SNe
are expected to be missed by high-redshift optical searches. We estimate that
5-10% of the local CC SNe are out of reach of the optical searches. The
fraction of missing events rises sharply toward z=1, when about 30% of the CC
SNe will be undetected. At z=2 the missing fraction will be about 60%.
Correspondingly, for type Ia SNe, our computations provide missing fractions of
15% at z=1 and 35% at z=2. Such large corrections are crucially important to
compare the observed SN rate with the expectations from the evolution of the
cosmic star formation history, and to design the future SN searches at high
redshifts.Comment: 9 pages, MNRAS, in press, a few typos correcte
Is there any evidence that ionised outflows quench star formation in type 1 quasars at z<1?
The aim of this paper is to test the basic model of negative AGN feedback.
According to this model, once the central black hole accretes at the Eddington
limit and reaches a certain critical mass, AGN driven outflows blow out gas,
suppressing star formation in the host galaxy and self-regulating black hole
growth. We consider a sample of 224 quasars selected from the SDSS at z<1
observed in the infrared band by Herschel. We evaluate the star formation rate
in relation to several outflow signatures traced by the [OIII]4959,5007 and
[OII]3726,3729 emission lines in about half of the sample with high quality
spectra. Most of the quasars show asymmetric and broad wings in [OIII], which
we interpret as outflow signatures. We separate the quasars in two groups,
``weakly'' and ``strongly'' outflowing, using three different criteria. When we
compare the mean star formation rate in five redshift bins in the two groups,
we find that the SFRs are comparable or slightly larger in the strongly
outflowing quasars. We estimate the stellar mass from SED fitting and the
quasars are distributed along the star formation main sequence, although with a
large scatter. The scatter from this relation is uncorrelated with respect to
the kinematic properties of the outflow. Moreover, for quasars dominated in the
infrared by starburst or by AGN emission, we do not find any correlation
between the star formation rate and the velocity of the outflow, a trend
previously reported in the literature for pure starburst galaxies. We conclude
that the basic AGN negative feedback scenario seems not to agree with our
results. Although we use a large sample of quasars, we did not find any
evidence that the star formation rate is suppressed in the presence of AGN
driven outflows on large scale. A possibility is that feedback is effective
over much longer timescales than those of single episodes of quasar activity.Comment: 18 pages, new version that implements the suggestions of the referee
and matches the AA published versio
On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters
The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the
field and in rich galaxy clusters are contrasted by juxtaposing the build-up of
heavy metals in the universe inferred from observed star formation and
supernovae rate histories with data on the evolution of Fe abundances in the
intracluster medium (ICM). Models for the chemical evolution of Fe in these
environments are constructed, subject to observational constraints, for this
purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial
mass function (IMF) are consistent with observations in the field, cluster Fe
enrichment immediately tracks a rapid, top-heavy phase of star formation --
although transport of Fe into the ICM may be more prolonged and star formation
likely continues to redshifts <1. The source of this prompt enrichment is Type
II supernovae (SNII) yielding at least 0.1 solar masses per explosion (if the
SNIa rate normalization is scaled down from its value in the field according to
the relative number of candidate progenitor stars in the 3-8 solar mass range)
and/or SNIa explosions with short delay times associated with the rapid star
formation mode. Star formation is >3 times more efficient in rich clusters than
in the field, mitigating the overcooling problem in numerical cluster
simulations. Both the fraction of baryons cycled through stars, and the
fraction of the total present-day stellar mass in the form of stellar remnants,
are substantially greater in clusters than in the field.Comment: 51 pages including 26 figures and 2 tables, accepted for publication
in ApJ 5/4/0
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