55 research outputs found
Metals and dust in the neutral ISM: the Galaxy, Magellanic Clouds, and damped Lyman-{\alpha} absorbers
Context. The presence of dust in the neutral interstellar medium (ISM)
dramatically changes the metal abundances that we measure. Understanding the
metal content in the neutral ISM, and a direct comparison between different
environments, has been hampered to date because of the degeneracy to the
observed ISM abundances caused by the effects of metallicity, the presence of
dust, and nucleosynthesis. Aims. We study the metal and dust content in the
neutral ISM consistently in different environments, and assess the universality
of recently discovered sequences of relative abundances. We also intend to
assess the validity of [Zn/Fe] as a tracer of dust in the ISM. This has
recently been cast into doubt based on observations of stellar abundances, and
needs to be addressed before we can safely use it to study the ISM. Methods. In
this letter we present a simple comparison of relative abundances observed in
the neutral ISM in the Galaxy, the Magellanic Clouds, and damped Lyman-{\alpha}
Absorbers (DLAs). The main novelty in this comparison is the inclusion of the
Magellanic Clouds. Results. The same sequences of relative abundances are valid
for the Galaxy, Magellanic Clouds, and DLAs. These sequences are driven by the
presence of dust in the ISM and seem 'universal'. Conclusions. The metal and
dust properties in the neutral ISM appear to follow a similar behaviour in
different environments. This suggests that a dominant fraction of the dust
budget is built up from grain growth in the ISM depending of the physical
conditions and regardless of the star formation history of the system. In
addition, the DLA gas behaves like the neutral ISM, at least from a chemical
point of view. Finally, despite the deviations in [Zn/Fe] observed in stellar
abundances, [Zn/Fe] is a robust dust tracer in the ISM of different
environments, from the Galaxy to DLAs.Comment: A&A Letter in press. 4 pages, 2 figure
The cosmic evolution of dust-corrected metallicity in the neutral gas
Interpreting abundances of Damped Ly- Absorbers (DLAs) from
absorption-line spectroscopy has typically been a challenge because of the
presence of dust. Nevertheless, because DLAs trace distant gas-rich galaxies
regardless of their luminosity, they provide an attractive way of measuring the
evolution of the metallicity of the neutral gas with cosmic time. This has been
done extensively so far, but typically not taking proper dust corrections into
account. The aims of this paper are to: i) provide a simplified way of
calculating dust corrections, based on a single observed [/Fe], ii) assess
the importance of dust corrections for DLA metallicities and their evolution,
and iii) investigate the cosmic evolution of iron for a large DLA sample. We
have derived dust corrections based on the observed [Zn/Fe], [Si/Fe], or
[S/Fe], and confirmed their robustness. We present dust-corrected metallicities
in a scale of [Fe/H] for 236 DLAs over a broad range of , and
assess the extent of dust corrections for different metals at different
metallicities. Dust corrections in DLAs are important even for Zn (typically of
0.1-0.2, and up to ~dex), which is often neglected. Finally, we study the
evolution of the dust-corrected metallicity with . The DLA metallicities
decrease with redshift, by a factor of 50-100 from today to billion
years ago (). When including dust corrections, the average DLA
metallicities are 0.4--0.5~dex higher than without corrections. The upper
envelope of the relation between metallicity and reaches solar metallicity
at , although some systems can have solar metallicity already out
to .Comment: Forthcoming in A&A. 16 pages, 5 figures, 3 table
On the (in)variance of the dust-to-metals ratio in galaxies
Recent works have demonstrated a surprisingly small variation of the
dust-to-metals ratio in different environments and a correlation between dust
extinction and the density of stars. Naively, one would interpret these
findings as strong evidence of cosmic dust being produced mainly by stars. But
other observational evidence suggest there is a significant variation of the
dust-to-metals ratio with metallicity. As we demonstrate in this paper, a
simple star-dust scenario is problematic also in the sense that it requires
that destruction of dust in the interstellar medium (e.g., due to passage of
supernova shocks) must be highly inefficient. We suggest a model where stellar
dust production is indeed efficient, but where interstellar dust growth is
equally important and acts as a replenishment mechanism which can counteract
the effects of dust destruction. This model appears to resolve the seemingly
contradictive observations, given that the ratio of the effective (stellar)
dust and metal yields is not universal and thus may change from one environment
to another, depending on metallicity.Comment: 10 pages, 4 figures. Accepted for publication in MNRA
Light Curves of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average, by about 4 and 2 mag, respectively. The peak absolute magnitudes of SLSNe-I in rest-frame g band span −22 ≾ M g ≾ −20 mag, and these peaks are not powered by radioactive ^(56)Ni, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar decay times. Thus, SLSNe-I can be considered as a separate population based on photometric properties. After peak, SLSNe-I decay with a wide range of slopes, with no obvious gap between rapidly declining and slowly declining events. The latter events show more irregularities (bumps) in the light curves at all times. At late times, the SLSN-I light curves slow down and cluster around the ^(56)Co radioactive decay rate. Powering the late-time light curves with radioactive decay would require between 1 and 10 M⊙ of Ni masses. Alternatively, a simple magnetar model can reasonably fit the majority of SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay of ^(56)Co, up to ~400 days from explosion. The resulting spin values do not correlate with the host-galaxy metallicities. Finally, the analysis of our sample cannot strengthen the case for using SLSNe-I for cosmology
Dust-depletion sequences in damped Lyman-α absorbers II. The composition of cosmic dust, from low-metallicity systems to the Galaxy
Metals in the interstellar medium (ISM) of essentially all types of galaxies are observed to be depleted compared to the expected values. The depletion is most likely due to dust condensation in, for example, cold molecular clouds and various circumstellar and interstellar environments. The relative observed metal abundances should thereby reflect the composition of the ISM dust components. We aim at identifying the most dominant dust species or types, including silicate and iron oxide grains present in the ISM, using recent observations of dust depletion of galaxies at various evolutionary stages. We use the observed elemental abundances in dust of several metals (O, S, Si, Mg, and Fe) in different environments, considering systems with different metallicities and dust content, namely damped Lyman-α absorbers (DLAs) towards quasars and the Galaxy. We derive a possible dust composition by computationally finding the statistically expected elemental abundances in dust assuming a set of key dust species with the iron content as a free parameter. Carbonaceous dust is not considered in the present study. Metallic iron (likely in the form of inclusions in silicate grains) and iron oxides are important components of the mass composition of carbon-free dust. The latter make up a significant mass fraction (~1∕4 in some cases) of the oxygen-bearing dust and there are good reasons to believe that metallic iron constitutes a similar mass fraction of dust. Wüstite (FeO) could be a simple explanation for the depletion of iron and oxygen because it is easily formed. There appears to be no silicate species clearly dominating the silicate mass, but rather a mix of iron-poor as well as iron-rich olivine and pyroxene. To what extent sulphur depletion is due to sulfides remains unclear. In general, there seems to be little evolution of the dust composition (not considering carbonaceous dust) from low-metallicity systems to the Galaxy
Light Curves of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average, by about 4 and 2 mag, respectively. The peak absolute magnitudes of SLSNe-I in rest-frame g band span −22 ≾ M g ≾ −20 mag, and these peaks are not powered by radioactive ^(56)Ni, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar decay times. Thus, SLSNe-I can be considered as a separate population based on photometric properties. After peak, SLSNe-I decay with a wide range of slopes, with no obvious gap between rapidly declining and slowly declining events. The latter events show more irregularities (bumps) in the light curves at all times. At late times, the SLSN-I light curves slow down and cluster around the ^(56)Co radioactive decay rate. Powering the late-time light curves with radioactive decay would require between 1 and 10 M⊙ of Ni masses. Alternatively, a simple magnetar model can reasonably fit the majority of SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay of ^(56)Co, up to ~400 days from explosion. The resulting spin values do not correlate with the host-galaxy metallicities. Finally, the analysis of our sample cannot strengthen the case for using SLSNe-I for cosmology
The {\alpha}-element enrichment of gas in distant galaxies
The chemical evolution of distant galaxies cannot be assessed from
observations of individual stars, in contrast to the case of nearby galaxies.
On the other hand, the study of the interstellar medium (ISM) offers an
alternative way to reveal important properties of the chemical evolution of
distant galaxies. The chemical enrichment of the ISM is produced by all the
previous generations of stars and it is possible to precisely determine the
metal abundances in the neutral ISM in galaxies. The chemical abundance
patterns in the neutral ISM are determined by the gas metallicity, presence of
dust (the depletion of metals into dust grains), and possible deviations due to
specific nucleosynthesis, for example, -element enhancements. We aim to
derive the metallicities, dust depletion, and -element enhancements in
the neutral ISM of gas-rich mostly-metal-poor distant galaxies (Damped
Lyman- absorbers, DLAs). Furthermore, we aim to constrain the
distribution of -element enhancements with metallicity in these
galaxies. We have constrained, for the first time, the distribution of the
-element enhancement with metallicity in the neutral ISM in distant
galaxies. Less massive galaxies show an -element knee at lower
metallicities than more massive galaxies. This can be explained by a lower star
formation rate in less massive galaxies. If this collective behaviour can be
interpreted in the same way as it is for individual systems, this would suggest
that more massive and metal-rich systems evolve to higher metallicities before
the contribution of SN-Ia to [/Fe] levels out that of core-collapse
SNe. This finding may plausibly be supported by different SFRs in galaxies of
different masses. Overall, our results offer important clues to the study of
chemical evolution in distant galaxies.Comment: 22 pages, 20 figures. Submitted to A&
iPTF13beo: The Double-Peaked Light Curve of a Type Ibn Supernova Discovered Shortly after Explosion
We present optical photometric and spectroscopic observations of the Type Ibn
(SN 2006jc-like) supernova iPTF13beo. Detected by the intermediate Palomar
Transient Factory ~3 hours after the estimated first light, iPTF13beo is the
youngest and the most distant (~430 Mpc) Type Ibn event ever observed. The
iPTF13beo light curve is consistent with light curves of other Type Ibn SNe and
with light curves of fast Type Ic events, but with a slightly faster rise-time
of two days. In addition, the iPTF13beo R-band light curve exhibits a
double-peak structure separated by ~9 days, not observed before in any Type Ibn
SN. A low-resolution spectrum taken during the iPTF13beo rising stage is
featureless, while a late-time spectrum obtained during the declining stage
exhibits narrow and intermediate-width He I and Si II features with FWHM ~
2000-5000 km/s and is remarkably similar to the prototypical SN Ibn 2006jc
spectrum. We suggest that our observations support a model of a massive star
exploding in a dense He-rich circumstellar medium (CSM). A shock breakout in a
CSM model requires an eruption releasing a total mass of ~0.1 Msun over a time
scale of couple of weeks prior to the SN explosion.Comment: 8 pages, 5 figures, submitted to MNRA
Dust depletion of of metals from local to distant galaxies II: Cosmic dust-to-metal ratio and dust composition
The evolution of the cosmic dust content and the cycle between metals and
dust in the interstellar medium (ISM) play a fundamental role in galaxy
evolution. The chemical enrichment of the Universe can be traced through the
evolution of the dust-to-metals ratio (DTM) and the dust-to-gas ratio (DTG)
with metallicity. We use a novel method to determine mass estimates of the DTM,
DTG and dust composition based on our previous measurements of the depletion of
metals in different environments (the Milky Way, the Magellanic Clouds, and
damped Lyman- absorbers, DLAs, toward quasars and towards gamma-ray
bursts, GRBs), which were calculated from the relative abundances of metals in
the ISM through absorption-line spectroscopy column densities observed mainly
from VLT/UVES and X-shooter, and HST/STIS. We derive the dust extinction from
the estimated dust depletion () and compare with the
from extinction. We find that the DTM and DTG ratios increase with metallicity
and with the dust tracer [Zn/Fe]. This suggests that grain growth in the ISM is
a dominant process of dust production. The increasing trend of the DTM and DTG
with metallicity is in good agreement with a dust production and evolution
model. Our data suggest that the stellar dust yield is much lower than the
metal yield and thus that the overall amount of dust in the warm neutral medium
that is produced by stars is much lower. We find that is
overall lower than for the Milky Way and a few Magellanic
Clouds lines of sight, a discrepancy that is likely related to the presence of
carbonaceous dust. We show that the main elements that contribute to the dust
composition are, O, Fe, Si, Mg, C, S, Ni and Al for all the environments.
Abundances at low dust regimes suggest the presence of pyroxene and metallic
iron in dust.Comment: Accepted for publication in A&A. Abstract abridge
Light curves of hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
We investigate the light-curve properties of a sample of 26 spectroscopically
confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar
Transient Factory (PTF) survey. These events are brighter than SNe Ib/c and SNe
Ic-BL, on average, by about 4 and 2~mag, respectively. The peak absolute
magnitudes of SLSNe-I in rest-frame band span ~mag, and these peaks are not powered by radioactive Ni,
unless strong asymmetries are at play. The rise timescales are longer for SLSNe
than for normal SNe Ib/c, by roughly 10 days, for events with similar decay
times. Thus, SLSNe-I can be considered as a separate population based on
photometric properties. After peak, SLSNe-I decay with a wide range of slopes,
with no obvious gap between rapidly declining and slowly declining events. The
latter events show more irregularities (bumps) in the light curves at all
times. At late times, the SLSN-I light curves slow down and cluster around the
Co radioactive decay rate. Powering the late-time light curves with
radioactive decay would require between 1 and 10 of Ni masses.
Alternatively, a simple magnetar model can reasonably fit the majority of
SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay
of Co, up to days from explosion. The resulting spin values do
not correlate with the host-galaxy metallicities. Finally, the analysis of our
sample cannot strengthen the case for using SLSNe-I for cosmology.Comment: 120 pages, 48 figures, 78 tables. ApJ in pres
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