Cosmological feedback from a halo assembly perspective

The impact of feedback from galaxy formation on cosmological probes is typically quantified in terms of the suppression of the matter power spectrum in hydrodynamical compared to gravity-only simulations. In this paper, we instead study how baryonic feedback impacts halo assembly histories and thereby imprints on cosmological observables. We investigate the sensitivity of the thermal Sunyaev-Zel’dovich effect (tSZ) power spectrum, X-ray number counts, weak lensing and kinetic Sunyaev-Zel’dovich (kSZ) stacked profiles to halo populations as a function of mass and redshift. We then study the imprint of different feedback implementations in the FLAMINGO suite of cosmological simulations on the assembly histories of these halo populations, as a function of radial scale. We find that kSZ profiles target lower-mass halos (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi>M</a:mi></a:mrow><a:mrow><a:mn>200</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi mathvariant="normal">m</a:mi></a:mrow></a:msub><a:mo>∼</a:mo><a:msup><a:mrow><a:mn>10</a:mn></a:mrow><a:mrow><a:mn>13.1</a:mn></a:mrow></a:msup><a:msub><a:mrow><a:mi>M</a:mi></a:mrow><a:mrow><a:mo stretchy="false">⊙</a:mo></a:mrow></a:msub></a:mrow></a:math>) compared to all other probes considered (<e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msub><e:mrow><e:mi>M</e:mi></e:mrow><e:mrow><e:mn>200</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi mathvariant="normal">m</e:mi></e:mrow></e:msub><e:mo>∼</e:mo><e:msup><e:mrow><e:mn>10</e:mn></e:mrow><e:mrow><e:mn>15</e:mn></e:mrow></e:msup><e:msub><e:mrow><e:mi>M</e:mi></e:mrow><e:mrow><e:mo stretchy="false">⊙</e:mo></e:mrow></e:msub></e:mrow></e:math>). Feedback is inefficient in high-mass clusters with <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mo>∼</i:mo><i:msup><i:mn>10</i:mn><i:mn>15</i:mn></i:msup><i:msub><i:mi>M</i:mi><i:mo stretchy="false">⊙</i:mo></i:msub></i:math> at <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi>z</l:mi><l:mo>=</l:mo><l:mn>0</l:mn></l:math>, but was more efficient at earlier times in the same population, with a <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mrow><n:mo>∼</n:mo><n:mn>5</n:mn><n:mi>–</n:mi><n:mn>10</n:mn><n:mo>%</n:mo></n:mrow></n:math> effect on mass at <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mn>2</p:mn><p:mo><</p:mo><p:mi>z</p:mi><p:mo><</p:mo><p:mn>4</p:mn></p:math> (depending on radial scale). Conversely, for lower-mass halos with <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mo>∼</r:mo><r:msup><r:mn>10</r:mn><r:mn>13</r:mn></r:msup><r:msub><r:mi>M</r:mi><r:mo stretchy="false">⊙</r:mo></r:msub></r:math> at <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mi>z</u:mi><u:mo>=</u:mo><u:mn>0</u:mn></u:math>, feedback exhibits a <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mrow><w:mo>∼</w:mo><w:mn>5</w:mn><w:mi>–</w:mi><w:mn>20</w:mn><w:mo>%</w:mo></w:mrow></w:math> effect on mass at <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:mi>z</y:mi><y:mo>=</y:mo><y:mn>0</y:mn></y:math> but had little impact at earlier times (<ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mi>z</ab:mi><ab:mo>></ab:mo><ab:mn>2</ab:mn></ab:math>). These findings are tied together by noting that, regardless of redshift, feedback most efficiently redistributes baryons when halos reach a mass of <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"><cb:mrow><cb:msub><cb:mrow><cb:mi>M</cb:mi></cb:mrow><cb:mrow><cb:mn>200</cb:mn><cb:mtext> </cb:mtext><cb:mtext> </cb:mtext><cb:mi mathvariant="normal">m</cb:mi></cb:mrow></cb:msub><cb:mo>≃</cb:mo><cb:mrow><cb:msup><cb:mrow><cb:mn>10</cb:mn></cb:mrow><cb:mrow><cb:mn>12.8</cb:mn></cb:mrow></cb:msup></cb:mrow><cb:msub><cb:mrow><cb:mi>M</cb:mi></cb:mrow><cb:mrow><cb:mo stretchy="false">⊙</cb:mo></cb:mrow></cb:msub></cb:mrow></cb:math> and ceases to have any significant effect by the time <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:mrow><gb:msub><gb:mrow><gb:mi>M</gb:mi></gb:mrow><gb:mrow><gb:mn>200</gb:mn><gb:mtext> </gb:mtext><gb:mtext> </gb:mtext><gb:mi mathvariant="normal">m</gb:mi></gb:mrow></gb:msub><gb:mo>≃</gb:mo><gb:mrow><gb:msup><gb:mrow><gb:mn>10</gb:mn></gb:mrow><gb:mrow><gb:mn>15</gb:mn></gb:mrow></gb:msup></gb:mrow><gb:msub><gb:mrow><gb:mi>M</gb:mi></gb:mrow><gb:mrow><gb:mo stretchy="false">⊙</gb:mo></gb:mrow></gb:msub></gb:mrow></gb:math>. We put forward strategies for minimizing sensitivity of lensing analyses to baryonic feedback, and for exploring baryonic resolutions to the unexpectedly low tSZ power in cosmic microwave background observations.