Construction of the damped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>Ly</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> absorber catalog for DESI DR2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi>Ly</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> BAO

Abstract

We present the Damped <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>Ly</a:mi> <a:mi>α</a:mi> </a:mrow> </a:math> Toolkit for automated detection and characterization of damped <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mi>Ly</c:mi> <c:mi>α</c:mi> </c:mrow> </c:math> absorbers (DLAs) in quasar spectra. Our method uses quasar spectral templates with and without absorption from intervening DLAs to reconstruct observed quasar forest regions. The best-fitting model determines whether a DLA is present while estimating the redshift and column density. With an optimized quality cut on detection significance ( <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi mathvariant="normal">Δ</e:mi> <e:msubsup> <e:mi>χ</e:mi> <e:mi>r</e:mi> <e:mn>2</e:mn> </e:msubsup> <e:mo>&gt;</e:mo> <e:mn>0.03</e:mn> </e:math> ), the technique achieves an estimated 80% purity and 79% completeness when evaluated on simulated spectra with <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mi mathvariant="normal">S</h:mi> <h:mo>/</h:mo> <h:mrow> <h:mi mathvariant="normal">N</h:mi> <h:mo stretchy="false">&gt;</h:mo> <h:mn>2</h:mn> </h:mrow> </h:math> that are free of broad absorption lines (BALs). We provide a catalog containing candidate DLAs from the DLA Toolkit detected in DESI DR1 quasar spectra, of which 21 719 were found in <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mi mathvariant="normal">S</m:mi> <m:mo>/</m:mo> <m:mrow> <m:mi mathvariant="normal">N</m:mi> <m:mo stretchy="false">&gt;</m:mo> <m:mn>2</m:mn> </m:mrow> </m:math> spectra with predicted <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"> <r:mrow> <r:msub> <r:mrow> <r:mi>log</r:mi> </r:mrow> <r:mn>10</r:mn> </r:msub> <r:mo stretchy="false">(</r:mo> <r:msub> <r:mrow> <r:mi>N</r:mi> </r:mrow> <r:mrow> <r:mi mathvariant="monospace">HI</r:mi> </r:mrow> </r:msub> <r:mo stretchy="false">)</r:mo> <r:mo>&gt;</r:mo> <r:mn>20.3</r:mn> </r:mrow> </r:math> and detection significance <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"> <w:mi mathvariant="normal">Δ</w:mi> <w:msubsup> <w:mi>χ</w:mi> <w:mi>r</w:mi> <w:mn>2</w:mn> </w:msubsup> <w:mo>&gt;</w:mo> <w:mn>0.03</w:mn> </w:math> . We compare the Damped <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"> <z:mrow> <z:mi>Ly</z:mi> <z:mi>α</z:mi> </z:mrow> </z:math> Toolkit to two alternative DLA finders based on a convolutional neural network and Gaussian process models. We present a strategy for combining these three techniques to produce a high-fidelity DLA catalog from DESI DR2 for the <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"> <bb:mrow> <bb:mi>Ly</bb:mi> <bb:mi>α</bb:mi> </bb:mrow> </bb:math> forest baryon acoustic oscillation measurement. The combined catalog contains 41 152 candidate DLAs with <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"> <db:mrow> <db:msub> <db:mrow> <db:mi>log</db:mi> </db:mrow> <db:mn>10</db:mn> </db:msub> <db:mo stretchy="false">(</db:mo> <db:msub> <db:mrow> <db:mi>N</db:mi> </db:mrow> <db:mrow> <db:mi mathvariant="monospace">HI</db:mi> </db:mrow> </db:msub> <db:mo stretchy="false">)</db:mo> <db:mo>&gt;</db:mo> <db:mn>20.3</db:mn> </db:mrow> </db:math> from quasar spectra with <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"> <ib:mi mathvariant="normal">S</ib:mi> <ib:mo>/</ib:mo> <ib:mrow> <ib:mi mathvariant="normal">N</ib:mi> <ib:mo stretchy="false">&gt;</ib:mo> <ib:mn>2</ib:mn> </ib:mrow> </ib:math> . We estimate this sample to be approximately 85% pure and 79% complete when BAL quasars are excluded.