If the form number does not have a hyperlink, the form is not available Blank for Special Measurement/Orthopedic Boots and Shoes, 1/1/, DLA. (FORM DLA, Revised 11/96). Block 1:Send your requests, ALL SIGNED IN Broadway Ave., Suite Denver, CO *If your program monitor. Issue 2, 11 May , Pages –, For the remaining systems (without detections), we devised a new form of spectral . We then compare in Section 4 the DLA Fe-peak element ratios with those.
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Steidel; The explosion energy of early stellar populations: The relative abundances of the Fe-peak elements Ti—Zn at the lowest metallicities are intimately linked to the physics of core-collapse supernova explosions. For the remaining systems without detectionswe devised a new form of spectral stacking to estimate the typical Fe-peak element ratios of the DLA population in this metallicity regime.
We compare these data to analogous measurements in metal-poor stars of the Galactic halo and to detailed calculations of explosive nucleosynthesis in metal-free stars.
Criteria for Higher Rate DLA? – General Discussion – Asperger and ASD UK Online Forum
Only then will we be able to pin down the energy that was released by the supernovae of the first stars. The physical mechanism that drives a core-collapse supernova CCSN explosion is a challenging mystery that remains unsolved. However, it has been widely recognized for dlz time that the vorm abundances fprm the Fe-peak elements Ti—Znwhich predominantly originate from explosive nucleosynthesis see e.
In particular, the ratios of the Fe-peak element yields depend sensitively on the progenitor mass, the explosion energy, and the dlz of material that falls back on to the remnant i. The uncertain physics of the explosion mechanism forces model nucleosynthesis calculations to parametrize the explosion.
There are two favoured prescriptions to define the central engine of the explosion: This is not surprising, given that the Fe-peak elements are intimately linked to the details of the explosion. The observations have uncovered some unexpected trends in the relative abundance of Fe-peak elements with decreasing metallicity, which we now briefly discuss.
Despite these significant advances in the stellar abundance measurements, it would be highly advantageous to have complementary probes to independently confirm the trends uncovered in the most metal-poor stars.
This will ensure that we are not biased by systematics that may affect the modelling of the absorption lines in the stellar atmospheres. At such large column densities the clouds are self-shielded from the metagalactic ionizing background, and most elements are concentrated in a single dominant ionization state, usually the neutrals or the first ions e.
This simple ionization structure makes the measurement of element abundances straightforward. This is perhaps not surprising, since high-redshift very metal poor VMP DLAs likely contain the gas from which the most metal-poor stars may have later condensed. This is a difficult prospect because most Fe-peak elements are less abundant than Fe by one to two orders of magnitude and the absorption lines of their dominant ion stages in VMP DLAs are generally too weak to be detected with current observational facilities.
To circumvent this issue, we introduce a form of spectral stacking that allows us to measure typical Fe-peak element ratios for the whole sample of VMP DLAs.
We excluded three DLAs from that sample. The composition of the DLAs is derived by searching for the absorption lines of elements in their dominant ionization state usually the neutral or singly ionized species for DLAs against the emission spectrum of a more distant, background QSO. The details of this continuum fit i.
The remaining Fe-peak elements are all less abundant than Fe, and their absorption lines are rarely seen in the most metal-poor DLAs; the only reported detections in individual VMP DLAs are foorm discussed here. The reason for such dearth of data can be appreciated by considering the following.
To circumvent this issue, we developed a new type of stacking technique to measure, or place limits on, the ratios of several Fe-peak elements in the DLAs in our sample. The stacking technique that we now describe can be used to combine either: In individual DLAs where we detect at least one absorption line from an Fe-peak element other than Fewe used the former approach and stacked all transitions of that ion covered by our spectrum of the DLA, whether detected or not.
This has the effect of utilizing all of the information available to improve the precision of the ion column density determination over that achievable from the analysis of only the absorption lines that have been detected. To do this, we first convert the spectrum in the vicinity of each transition to a common velocity scale. We then calculate the rest-frame equivalent width for each pixel for all transitions and use equation 2 to convert this to a column density ratio.
Finally, we determine the weighted mean of all transitions for a given species, where the weights correspond to the inverse variance of each ela. We stress that this technique can be implemented for a single DLA without any assumptions. The stacking method just described can only be applied to the few cases where we do detect at least one absorption line vla a given Dlq element.
In these circumstances, however, we can still apply the above method to construct a stacked spectrum of all lines of a given ion for all DLAs with non-detections.
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The first concern is that certain species may be depleted relative to Fe on to dust grains, an effect which is known to depend on metallicity. The most likely source of systematic error is in the choice of the continuum around each absorption line, which is especially important when dealing with weak lines. We used the measured line equivalent widths or upper limits to generate a series of line profiles for each of the transitions used in the stack.
This exercise was repeated times, and the deviations between the equivalent widths derived with and without the continuum adjustments were taken to be a measure of the systematic uncertainty. In general, we found that the systematic errors are of the same order as the random errors. Perhaps more importantly, we also verified that in all of the cases described below 6125 were no significant systematic biases introduced by our estimate of the continuum level. Even in these most favourable cases, however, the only Fe-peak elements detected are Ni and Cr, the two most abundant after Fe.
The stacked profiles for these five DLAs are shown in Figs 1 and 2. All of the right-hand panels in Fig. Stacked spectra black histograms for individual DLAs in which at least one absorption line from an Fe-peak element other than Fe was detected, or a useful upper limit could be determined. We then confirmed that all of the undetected absorption lines used in the stack contained no significant absorption within this velocity interval i.
Furthermore, to be certain that we are not including spurious contributions from coincident, unrelated absorption, we rejected the high and low values for each pixel in the stack. This procedure ensures that we suffer minimal contamination. The results of these stacks are reproduced in Fig. Stacked spectra black histograms for DLAs without individual detections of Fe-peak elements.
To our knowledge, this is the first detailed fotm into the Fe-peak element ratios in very metal-poor DLAs. This is perhaps not surprising, given that there are just a few VMP DLAs that we could find in the literature with column density measurements of Fe-peak elements: All literature values have been adjusted to the solar abundance scale adopted here.
VMP DLAs offer a new probe to verify independently the validity from the stellar trends with metallicity. One advantage 16225 using DLAs to measure relative element abundances is that the derived ratios are model independent; in metal-poor stars, systematic uncertainties in the abundances may arise for some absorption lines that are modelled in one dimension, or if the assumption of local thermodynamic equilibrium LTE is not valid. To obtain independent confirmations of the stellar trends, we compare in Fig.
The red triangles are for individual DLAs where the relevant absorption lines were detected, or where an informative upper limit could be obtained. The single blue triangle in each panel corresponds to the stack of DLAs in which no absorption by the element of interest was detected in individual systems.
Overlaid on the five panels of Fig. The red dlx are for DLAs with detections of Fe-peak element lines, or where a useful upper limit could be derived. We now comment separately on the individual Fe-peak element ratios. As can be seen from Fig. This may explain dls of the mismatch between stars and DLAs. Four bands are considered, colour-coded red, green, blue and black.
Broadly speaking, red corresponds to hypernovae, green is for high-energy Type II supernovae, blue represents a typical Type II supernova and black corresponds to the faint supernovae see text for further details and the specific cuts we have employed. These seven determinations are all in good mutual agreement, and they broadly agree with the stellar data, as can be seen in the second panel from the top in Fig. DLAs can provide new insights cla this problem, and will undoubtedly play an important role in future to help settle the debate.
Ni is the second most abundant Fe-peak element in the Universe. This fact, in addition to the multitude of relatively strong transitions that are easily accessible i. For the sample of metal-poor DLAs considered here, we have seven detections and two upper limits in individual systems, and a total of dls lines contributing to the stack of undetected lines.
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In Galactic stars, the relative abundances of Ni and Fe remain essentially constant over the entire range of metallicity probed. In addition, there are a further two systems in the literature with useful upper limits.
In this section, we will attempt to estimate the typical explosion energy of these supernovae by comparing the abundances of Fe-peak elements deduced above with the relative yields calculated with models of explosive nucleosynthesis in metal-free stars. Progress in this area is highly desirable, fodm we still lack a physical understanding of the mechanism that drives the explosion, despite many fla efforts e.
In fork current generation of massive star nucleosynthesis models this shortcoming is circumvented by parametrizing the physics of the explosion in order to calculate the resulting element yields. The parametrization is typically achieved by employing a simple description of the mixing that occurs between the stellar layers due to either Rayleigh—Taylor or rotationally induced mixingand specifying a mass-coordinate or mass-cut that defines the material that either escapes the binding energy of the exploding star or falls back on to the newly formed compact object.
Each star undergoes a supernova explosion, which is simulated as a moving piston that sla momentum at a specified mass-coordinate. Each exploding star is simulated with 10 different values of the final kinetic energy at infinity, taken to be in the range 0. A simple prescription of the mixing that occurs between the stellar layers during the explosion is also implemented.
For a given final kinetic energy at infinity and amount of mixing, we weight these chemical yields by a power-law stellar initial mass function IMF with fofm exponent that can take values in the range 0. Our conclusions on the explosion energy therefore apply to the mass range of stars with the dominant Fe-peak element yields. We subdivide the weighted yields into four arbitrary groups depending on the final kinetic energy at infinity: Given the large number of models considered, 16625 Fig.
In this way, we can learn how likely a certain explosion energy is, given two measured Fe-peak element ratios. For all panels in the figure, we also show the ranges of Fe-peak element ratios determined from the DLA stacks displayed as shaded boxes.
In all of the panels for Fig. The abundances of Ti, Cr and Co relative to iron, on the other hand, are similar for all four energy groups. As can be seen from the bottom right panel of Fig. As has been shown to be the case for other elements e. This is a very exciting prospect. To illustrate this point better we show in Fig. Thus, the combination of these three elements, Fe, Ni and Zn, offers the prospect of pinning down the explosion energy of the stars that produced most of the Fe-peak elements in the most metal-poor DLAs.
The four sets of models are colour-coded according to the kinetic energy released by the supernovae. The primary motivation of this work was to estimate the energy released by the stars that enriched the most metal-poor DLAs. The results presented here are only a first step in this direction and have mostly highlighted the need for further observations of DLAs at even lower metallicities than the regime probed so far.
It remains to be tested how the relative Ni, Formm and Fe yields depend on the metallicity of the progenitor star, as well as the explosion energy.
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This is a goal for future, high mass-resolution, metallicity-dependent dpa yield calculations. In nine of the 25 DLAs, we could measure element ratios, or useful upper limits, directly from detected absorption lines. In the majority of DLAs, however, the lines are too weak to be detected in available spectra.
The present belief is that the most metal-poor Galactic stars contain the metals synthesized by an earlier generation of massive stars that had ended their lives as hypernovae; however, we have found little evidence so far for this hypothesis in the chemical composition of the most metal-poor DLAs.