OVI Absorbers in SDSS Spectra
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The Ohio State University / OhioLINK
2008
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu12221163792021-08-03T05:54:35Z OVI Absorbers in SDSS Spectra Frank, Stephan Astronomy Astrophysics IGM QSO Absorption lines <p>We conducted a systematic search for signatures of the Intergalactic Medium in Quasar spectra of the Sloan Digital Sky Survey, focusing on intervening absorbers via detection of their OVI doublet. We present a search algorithm, and criteria for distinguishing candidates from spurious Lyman lines. In addition, we compare our findings with simulations of the Lyα forest to estimate the detectability of OVI over various redshift intervals. We obtain a sample of 1866 candidates with equivalent widths > 0.05 A in 855 AGN spectra (out of 3702 objects with redshifts in the range for OVI detection). We divide the sample into 3 groups according to the likelihood of being real and potential for follow-up observations. The best group is comprised of 145 candidates, 69 of these reside at a velocity separation > 5000 km/s from the QSO, and can be classified tentatively as intervening absorbers. Most of these have not been picked up by earlier absorption line detection algorithms. This sample increases the number of OVI absorbers at redshifts beyond 2.7 substantially. We propose to obtain observations of some candidates with high signal-to-noise and resolution to better constrain the physical state of the absorbers.</p><p>We then focus on 387 sightlines with a S/N > 5.0, allowing for the detections above a rest-frame EW > 0.19 A for the 1032 A component. Accounting for random interlopers, we derive for the first time a lower limit for the redshift number density for z > 2.8. With extensive Monte Carlo simulations we quantify losses of absorbers due to blending with Lyα forest lines, and estimate the success rate of retrieving individual candidates. This allows us to derive the ‘incompleteness corrected’ redshift number density.</p><p>We place a secure lower limit for the contribution of OVI to the mass density at the redshifts probed here. We show that the strong lines account for 65% of the mass in the OVI absorbers; weak absorbers, dominant in line number density, do not contribute significantly.</p><p>Making conservative assumptions about the ionisation fraction, we derive the mean metallicity of the gas, which is in good agreement with other studies. These results demonstrate that large spectroscopic datasets as SDSS play an important role in QSO absorption line studies, despite their relatively low resolution.</p><p>Lastly, we performed a stacking analysis whereby we shift individual spectra to the rest-frame of the absorber, and derive a mean spectrum. Besides further validating the reality of candidates, we use stacked spectra for a variety of purposes. First, we judge effects of additional cuts like a minimal strength for CIV absorption, and produce cleaner subsamples, increasing the strength of proposals for high-resolution studies. Secondly, the stack itself contains information about the gas probed in our search. We have begun to measure absorption features for an OVI+CIV selected subsample, and compared them with multiple transitions found in a CIV-only selected sample. One of the first results is that we probe gas with large OVI column densities lacking many of the lower ionisation lines frequently seen in CIV-selected systems.</p> 2008-10-01 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1222116379 http://rave.ohiolink.edu/etdc/view?acc_num=osu1222116379 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Astronomy Astrophysics IGM QSO Absorption lines |
| spellingShingle |
Astronomy Astrophysics IGM QSO Absorption lines Frank, Stephan OVI Absorbers in SDSS Spectra |
| author |
Frank, Stephan |
| author_facet |
Frank, Stephan |
| author_sort |
Frank, Stephan |
| title |
OVI Absorbers in SDSS Spectra |
| title_short |
OVI Absorbers in SDSS Spectra |
| title_full |
OVI Absorbers in SDSS Spectra |
| title_fullStr |
OVI Absorbers in SDSS Spectra |
| title_full_unstemmed |
OVI Absorbers in SDSS Spectra |
| title_sort |
ovi absorbers in sdss spectra |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2008 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1222116379 |
| work_keys_str_mv |
AT frankstephan oviabsorbersinsdssspectra |
| _version_ |
1719427584027000832 |