Browsing by Autor "S. P. Ahlen"

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Atacama Cosmology Telescope DR6 and DESI: Structure growth measurements from the cross-correlation of DESI legacy imaging galaxies and CMB lensing from ACT DR6 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>P</mml:mi><mml:mi>l</mml:mi><mml:mi>a</mml:mi><mml:mi>n</mml:mi><mml:mi>c</mml:mi><mml:mi>k</mml:mi></mml:math> PR4
(American Physical Society, 2025) Frank J. Qu; Qianjun Hang; Gerrit S. Farren; Boris Bolliet; J. Aguilar; S. P. Ahlen; Shadab Alam; D. Brooks; Yan-Chuan Cai; E. Calabrese
We measure the growth of cosmic density fluctuations on large scales and across the redshift range <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>0.3</a:mn><a:mo><</a:mo><a:mi>z</a:mi><a:mo><</a:mo><a:mn>0.8</a:mn></a:math> through galaxy clustering and the cross-correlation of the ACT data release 6 cosmic microwave background (CMB) lensing map and galaxies from the Dark Energy Spectroscopic Instrument Legacy Survey, using three galaxy samples spanning the redshifts of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>0.3</c:mn><c:mo>≲</c:mo><c:mi>z</c:mi><c:mo>≲</c:mo><c:mn>0.45</c:mn></c:math>, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>0.45</e:mn><e:mo>≲</e:mo><e:mi>z</e:mi><e:mo>≲</e:mo><e:mn>0.6</e:mn></e:math>, <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mn>0.6</g:mn><g:mo>≲</g:mo><g:mi>z</g:mi><g:mo>≲</g:mo><g:mn>0.8</g:mn></g:math>. We adopt a scale cut where nonlinear effects are negligible, so that the cosmological constraints are derived from the linear regime. We determine the amplitude of matter fluctuations over all three redshift bins using Atacama Cosmology Telescope (ACT) data alone to be <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>S</i:mi><i:mn>8</i:mn></i:msub><i:mo>≡</i:mo><i:msub><i:mi>σ</i:mi><i:mn>8</i:mn></i:msub><i:mo stretchy="false">(</i:mo><i:msub><i:mi mathvariant="normal">Ω</i:mi><i:mi>m</i:mi></i:msub><i:mo>/</i:mo><i:mn>0.3</i:mn><i:msup><i:mo stretchy="false">)</i:mo><i:mn>0.5</i:mn></i:msup><i:mo>=</i:mo><i:mn>0.772</i:mn><i:mo>±</i:mo><i:mn>0.040</i:mn></i:math> in a joint analysis combining the three redshift bins and ACT lensing alone. Using a combination of ACT and data we obtain <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:msub><n:mi>S</n:mi><n:mn>8</n:mn></n:msub><n:mo>=</n:mo><n:mn>0.765</n:mn><n:mo>±</n:mo><n:mn>0.032</n:mn></n:math>. The lowest redshift bin used is the least constraining and exhibits a <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mo>∼</p:mo><p:mn>2</p:mn><p:mi>σ</p:mi></p:math> tension with the other redshift bins; thus we also report constraints excluding the first redshift bin, giving <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:msub><r:mi>S</r:mi><r:mn>8</r:mn></r:msub><r:mo>=</r:mo><r:mn>0.785</r:mn><r:mo>±</r:mo><r:mn>0.033</r:mn></r:math> for the combination of ACT and . This result is in excellent agreement at the <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mn>0.3</t:mn><t:mi>σ</t:mi></t:math> level with measurements from galaxy lensing, but is <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:mn>1.8</v:mn><v:mi>σ</v:mi></v:math> lower than predictions based on primary CMB data. Understanding whether this hint of discrepancy in the growth of structure at low redshifts arises from a fluctuation, from systematics in data, or from new physics is a high priority for forthcoming CMB lensing and galaxy cross-correlation analyses.
Backlighting extended gas halos around luminous red galaxies: Kinematic Sunyaev-Zel’dovich effect from DESI Y1 and ACT data
(American Physical Society, 2025) Bernardita Ried Guachalla; Emmanuel Schaan; Boryana Hadzhiyska; Simone Ferraro; J. Aguilar; S. P. Ahlen; Nicholas Battaglia; D. Bianchi; Richard Bond; David J. Brooks
The gas density profile around galaxies, shaped by feedback and affecting the galaxy lensing signal, is imprinted on the cosmic microwave background (CMB) by the kinematic Sunyaev-Zel'dovich effect (kSZ). We precisely measure this effect ($S/N\ensuremath{\approx}10$) via velocity stacking with 825,283 spectroscopically confirmed luminous red galaxies (LRG) from the Dark Energy Spectroscopic Instrument Year 1 (DESI Y1) survey, which overlap with the Atacama Cosmology Telescope (ACT) Data Release 6 temperature maps over $\ensuremath{\ge}4,000\text{ }\text{ }{\mathrm{deg}}^{2}$. We explore the kSZ dependence with various galaxy parameters and find no significant trend with redshift but clear trends with stellar mass and absolute magnitude in $g$, $r$, and $z$ bands. Our analysis suggests that the gas extends beyond the dark matter halo (99.5% confidence level, i.e., probability to exceed $(\mathrm{PTE})=0.005$). We find a tentative preference for hydrodynamical simulation models with stronger feedback that drives gas further out (Illustris $z=0.5$, $\mathrm{PTE}=0.37$) over weaker-feedback cases (IllustrisTNG $z=0.8$, $\mathrm{PTE}=0.045$), though with limited statistical significance. In all cases, a free multiplicative amplitude was fit to the simulated profiles, and further modeling work is required to firm up these conclusions. We find consistency between kSZ profiles around spectroscopic and photometric LRG, with comparable statistical power, thus increasing our confidence in the photometric analysis. Additionally, we present the first kSZ measurement around the DESI Y1 bright galaxy sample (BGS) and the emission-line galaxies (ELG) whose features match qualitative expectations. Finally, we forecast $S/N\ensuremath{\sim}50$ for future stacked kSZ measurements using data from the ACT, the DESI Y3, and the Rubin Observatory. These measurements will serve as an input for galaxy formation models and baryonic uncertainties in galaxy lensing.
Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect
(2025) M. Rashkovetskyi; Daniel J. Eisenstein; J. Aguilar; S. P. Ahlen; Abhijeet Anand; D. Bianchi; David Brooks; F. J. Castander; T. Claybaugh; Andrei Cuceu
The thermal Sunyaev-Zeldovich (tSZ) effect is associated with galaxy clusters - extremely large and dense structures tracing the dark matter with a higher bias than isolated galaxies. We propose to use the tSZ data to separate galaxies from redshift surveys into distinct subpopulations corresponding to different densities and biases independently of the redshift survey systematics. Leveraging the information from different environments, as in density-split and density-marked clustering, is known to tighten the constraints on cosmological parameters, like <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>Ω</mml:mi> <mml:mi>m</mml:mi> </mml:msub> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mn>8</mml:mn> </mml:msub> </mml:math> and neutrino mass. We use data from the Dark Energy Spectroscopic Instrument (DESI) and the Atacama Cosmology Telescope (ACT) in their region of overlap to demonstrate informative tSZ splitting of Luminous Red Galaxies (LRGs). We discover a significant increase in the large-scale clustering of DESI LRGs corresponding to detections starting from 1-2 sigma in the ACT DR6 + Planck tSZ Compton- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>y</mml:mi> </mml:math> map, below the cluster candidate threshold (4 sigma). We also find that such galaxies have higher line-of-sight coordinate (and velocity) dispersions and a higher number of close neighbors than both the full sample and near-zero tSZ regions. We produce simple simulations of tSZ maps that are intrinsically consistent with galaxy catalogs and do not include systematic effects, and find a similar pattern of large-scale clustering enhancement with tSZ effect significance. Moreover, we observe that this relative bias pattern remains largely unchanged with variations in the galaxy-halo connection model in our simulations. This is promising for future cosmological inference from tSZ-split clustering with semi-analytical models. Thus, we demonstrate that valuable cosmological information is present in the lower signal-to-noise regions of the thermal Sunyaev-Zeldovich map, extending far beyond the individual cluster candidates.
CMB lensing and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Ly</mml:mi><mml:mi>α</mml:mi></mml:math> forest cross bispectrum from DESI’s first-year quasar sample
(American Physical Society, 2024) Naim Göksel Karaçaylı; Paul Martini; David H. Weinberg; Simone Ferraro; Roger de Belsunce; J. Aguilar; S. P. Ahlen; E. Armengaud; D. Brooks; T. Claybaugh
The squeezed cross-bispectrum ${B}_{\ensuremath{\kappa},\mathrm{Ly}\ensuremath{\alpha}}$ between the gravitational lensing in the cosmic microwave background and the 1D $\mathrm{Ly}\ensuremath{\alpha}$ forest power spectrum can constrain bias parameters and break degeneracies between ${\ensuremath{\sigma}}_{8}$ and other cosmological parameters. We detect ${B}_{\ensuremath{\kappa},\mathrm{Ly}\ensuremath{\alpha}}$ with $4.8\ensuremath{\sigma}$ significance at an effective redshift ${z}_{\mathrm{eff}}=2.4$ using Planck PR3 lensing map and over 280,000 quasar spectra from the Dark Energy Spectroscopic Instrument's first-year data. We test our measurement against metal contamination and foregrounds such as Galactic extinction and clusters of galaxies by deprojecting the thermal Sunyaev-Zeldovich effect. We compare our results to a tree-level perturbation theory calculation and find reasonable agreement between the model and measurement.
Constraining the phase shift of relativistic species in DESI BAOs
(Oxford University Press, 2025) Abbé M Whitford; Cullan Howlett; M. Vargas-Magaña; S. Fromenteau; T. M. Davis; Ignasi Pérez-Ràfols; Arnaud de Mattia; S. P. Ahlen; D. Bianchi; David Brooks
ABSTRACT In the early Universe, neutrinos decouple quickly from the primordial plasma and propagate without further interactions. The impact of free-streaming neutrinos is to create a temporal shift in the gravitational potential that impacts the acoustic waves known as baryon acoustic oscillations (BAOs), resulting in a non-linear spatial shift in the Fourier-space BAO signal. In this work, we make use of and extend upon an existing methodology to measure the phase shift amplitude $\beta _{\phi }$ and apply it to the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) BAOs with an anisotropic BAO fitting pipeline. We validate the fitting methodology by testing the pipeline with two publicly available fitting codes applied to highly precise cubic box simulations and realistic simulations representative of the DESI DR1 data. We find further study towards the methods used in fitting the BAO signal will be necessary to ensure accurate constraints on $\beta _{\phi }$ in future DESI data releases. Using DESI DR1, we present individual measurements of the anisotropic BAO distortion parameters and the $\beta _{\phi }$ for the different tracers, and additionally a combined fit to $\beta _{\phi }$ resulting in $\beta _{\phi } = 2.7 \pm 1.7$. After including a prior on the distortion parameters from constraints using Planck we find $\beta _{\phi } = 2.7^{+0.60}_{-0.67}$ suggesting $\beta _{\phi } &gt; 0$ at 4.3$\sigma$ significance. This result may hint at a phase shift that is not purely sourced from the standard model expectation for $N_{\rm {eff}}$ or could be a upwards statistical fluctuation in the measured $\beta _{\phi }$; this result relaxes in models with additional freedom beyond Lambda-cold dark matter.
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
(American Physical Society, 2025) A. Brodzeller; Molly Wolfson; D. Martínez Santos; Ming-Feng Ho; T. Tan; Matthew M. Pieri; Andrei Cuceu; M. Karim; J. Aguilar; S. P. Ahlen
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>></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">></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">></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>></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>></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>></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">></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.
DESI DR2 results. II. Measurements of baryon acoustic oscillations and cosmological constraints
(American Physical Society, 2025) M. Abdul Karim; J. Aguilar; S. P. Ahlen; Shadab Alam; L. Allen; Carlos Allende Prieto; O. Alves; Abhijeet Anand; U. Andrade; E. Armengaud
We present baryon acoustic oscillation (BAO) measurements from more than 14 million galaxies and quasars drawn from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2), based on three years of operation. For cosmology inference, these galaxy measurements are combined with DESI Lyman- <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>α</a:mi> </a:math> forest BAO results presented in a companion paper (M. Abdul-Karim , companion paper, .). The DR2 BAO results are consistent with DESI DR1 and the Sloan Digital Sky Survey, and their distance-redshift relationship matches those from recent compilations of supernovae (SNe) over the same redshift range. The results are well described by a flat <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi mathvariant="normal">Λ</c:mi> </c:math> cold dark matter ( <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mi mathvariant="normal">Λ</f:mi> <f:mi>CDM</f:mi> </f:math> ) model, but the parameters preferred by BAO are in mild, <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mn>2.3</i:mn> <i:mi>σ</i:mi> </i:math> tension with those determined from the cosmic microwave background (CMB), although the DESI results are consistent with the acoustic angular scale <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msub> <k:mi>θ</k:mi> <k:mo>*</k:mo> </k:msub> </k:math> that is well measured by Planck. This tension is alleviated by dark energy with a time-evolving equation of state parametrized by <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msub> <m:mi>w</m:mi> <m:mn>0</m:mn> </m:msub> </m:math> and <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mi>w</o:mi> <o:mi>a</o:mi> </o:msub> </o:math> , which provides a better fit to the data, with a favored solution in the quadrant with <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:msub> <q:mi>w</q:mi> <q:mn>0</q:mn> </q:msub> <q:mo>></q:mo> <q:mo>−</q:mo> <q:mn>1</q:mn> </q:math> and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:msub> <s:mi>w</s:mi> <s:mi>a</s:mi> </s:msub> <s:mo><</s:mo> <s:mn>0</s:mn> </s:math> . This solution is preferred over <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"> <u:mi mathvariant="normal">Λ</u:mi> <u:mi>CDM</u:mi> </u:math> at <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"> <x:mn>3.1</x:mn> <x:mi>σ</x:mi> </x:math> for the combination of DESI BAO and CMB data. When also including SNe, the preference for a dynamical dark energy model over <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"> <z:mi mathvariant="normal">Λ</z:mi> <z:mi>CDM</z:mi> </z:math> ranges from <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"> <cb:mn>2.8</cb:mn> <cb:mo>−</cb:mo> <cb:mn>4.2</cb:mn> <cb:mi>σ</cb:mi> </cb:math> depending on which SNe sample is used. We present evidence from other data combinations which also favor the same behavior at high significance. From the combination of DESI and CMB we derive 95% upper limits on the sum of neutrino masses, finding <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"> <eb:mo>∑</eb:mo> <eb:msub> <eb:mi>m</eb:mi> <eb:mi>ν</eb:mi> </eb:msub> <eb:mo><</eb:mo> <eb:mn>0.064</eb:mn> <eb:mtext> </eb:mtext> <eb:mtext> </eb:mtext> <eb:mi>eV</eb:mi> </eb:math> assuming <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"> <gb:mi mathvariant="normal">Λ</gb:mi> <gb:mi>CDM</gb:mi> </gb:math> and <jb:math xmlns:jb="http://www.w3.org/1998/Math/MathML" display="inline"> <jb:mo>∑</jb:mo> <jb:msub> <jb:mi>m</jb:mi> <jb:mi>ν</jb:mi> </jb:msub> <jb:mo><</jb:mo> <jb:mn>0.16</jb:mn> <jb:mtext> </jb:mtext> <jb:mtext> </jb:mtext> <jb:mi>eV</jb:mi> </jb:math> in the <lb:math xmlns:lb="http://www.w3.org/1998/Math/MathML" display="inline"> <lb:msub> <lb:mi>w</lb:mi> <lb:mn>0</lb:mn> </lb:msub> <lb:msub> <lb:mi>w</lb:mi> <lb:mi>a</lb:mi> </lb:msub> </lb:math> model. Unless there is an unknown systematic error associated with one or more datasets, it is clear that <nb:math xmlns:nb="http://www.w3.org/1998/Math/MathML" display="inline"> <nb:mi mathvariant="normal">Λ</nb:mi> <nb:mi>CDM</nb:mi> </nb:math> is being challenged by the combination of DESI BAO with other measurements and that dynamical dark energy offers a possible solution.
Detection of the large-scale tidal field with galaxy multiplet alignment in the DESI Y1 spectroscopic survey
(Oxford University Press, 2024) C Lamman; Daniel J. Eisenstein; J. E. Forero-Romero; J. Aguilar; S. P. Ahlen; S. Bailey; D. Bianchi; David J. Brooks; T. Claybaugh; Axel de la Macorra
ABSTRACT We explore correlations between the orientations of small galaxy groups, or ‘multiplets’, and the large-scale gravitational tidal field. Using data from the Dark Energy Spectroscopic Instrument (DESI) Y1 survey, we detect the intrinsic alignment (IA) of multiplets to the galaxy-traced matter field out to separations of $100\,h^{-1}$ Mpc. Unlike traditional IA measurements of individual galaxies, this estimator is not limited by imaging of galaxy shapes and allows for direct IA detection beyond redshift $z=1$. Multiplet alignment is a form of higher order clustering, for which the scale-dependence traces the underlying tidal field and amplitude is a result of small-scale ($\lt 1h^{-1}$ Mpc) dynamics. Within samples of bright galaxies, luminous red galaxies (LRG) and emission-line galaxies, we find similar scale-dependence regardless of intrinsic luminosity or colour. This is promising for measuring tidal alignment in galaxy samples that typically display no IA. DESI’s LRG mock galaxy catalogues created from the A bacusS ummitN-body simulations produce a similar alignment signal, though with a 33 per cent lower amplitude at all scales. An analytic model using a non-linear power spectrum (NLA) only matches the signal down to 20 $h^{-1}$ Mpc. Our detection demonstrates that galaxy clustering in the non-linear regime of structure formation preserves an interpretable memory of the large-scale tidal field. Multiplet alignment complements traditional two-point measurements by retaining directional information imprinted by tidal forces, and contains additional line-of-sight information compared to weak lensing. This is a more effective estimator than the alignment of individual galaxies in dense, blue, or faint galaxy samples.
Early time solution as an alternative to the late time evolving dark energy with DESI DR2 BAO
(American Physical Society, 2025) E. Chaussidon; Martin White; Arnaud de Mattia; Rafaela Gsponer; S. P. Ahlen; Davide Bianchi; D. Brooks; T. Claybaugh; S. Cole; A. Cuceu
Supplementary material to DESI's publication 'Early time solution as an alternative to the late time evolving dark energy with DESI DR2 BAO' to comply with the data management plan.
Evidence for large baryonic feedback at low and intermediate redshifts from kinematic Sunyaev-Zel’dovich observations with ACT and DESI photometric galaxies
(American Physical Society, 2025) Boryana Hadzhiyska; Simone Ferraro; Bernardita Ried Guachalla; Emmanuel Schaan; José Aguilar; S. P. Ahlen; Nicholas Battaglia; J. Richard Bond; D. Brooks; E. Calabrese
Recent advances in cosmological observations have provided an unprecedented opportunity to investigate the distribution of baryons relative to the underlying matter. In this work, we show that the gas is more extended than the dark matter, and the amount of baryonic feedback at $z\ensuremath{\lesssim}1$ disfavors low-feedback models such as that of state-of-the-art hydrodynamical simulation IllustrisTNG compared with high-feedback models such as that of the original Illustris simulation. This has important implications for bridging the gap between theory and observations and understanding galaxy formation and evolution. Furthermore, a better grasp of the baryon-dark matter link is critical to future cosmological analyses, which are currently impeded by our limited knowledge of baryonic feedback. Here, we measure the kinematic Sunyaev-Zel'dovich (kSZ) effect from the Atacama Cosmology Telescope, stacked on the luminous red galaxy sample of the Dark Energy Spectroscopic Instrument (DESI) imaging survey. This is the first analysis to use photometric redshifts for reconstructing galaxy velocities. Due to the large number of galaxies comprising the DESI imaging survey, this is the highest signal-to-noise stacked kSZ measurement to date; we detect the signal at $13\ensuremath{\sigma}$, finding strong evidence that the gas is more spread out than the dark matter, as well as a preference for larger feedback compared to some commonly used state-of-the-art hydrodynamical simulations. Our work opens up the possibility of recalibrating large hydrodynamical simulations using the kSZ effect. In addition, our findings highlight the importance of properly accounting for baryonic feedback with future surveys such as LSST through direct probes such as the kSZ, and shed light on long-standing enigmas in astrophysics, such as the ``missing baryon'' problem.
Galaxy-multiplet clustering from DESI DR2
(Oxford University Press, 2025) Hanyue Wang; Daniel J. Eisenstein; J. Aguilar; S. P. Ahlen; D. Bianchi; David H. Brooks; T. Claybaugh; Axel de la Macorra; Arjun Dey; Biprateep Dey
ABSTRACT We present an efficient estimator for higher order galaxy clustering using small groups of nearby galaxies, or multiplets. Using the Luminous Red Galaxy sample from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2, we identify galaxy multiplets as discrete objects and measure their cross-correlations with the general galaxy field. Our results show that the multiplets exhibit stronger clustering bias as they trace more massive dark matter haloes than individual galaxies. When comparing the observed clustering statistics with the mock catalogues generated from the N-body simulation AbacusSummit, we find that the mocks underpredict multiplet clustering despite reproducing the galaxy two-point autocorrelation reasonably well. This discrepancy indicates that the standard Halo Occupation Distribution (HOD) model is insufficient to describe the properties of galaxy multiplets, revealing the greater constraining power of this higher order statistic on galaxy–halo connection and the possibility that multiplets are specific to additional assembly bias. We demonstrate that incorporating secondary biases into the HOD model improves agreement with the observed multiplet statistics, specifically by allowing galaxies to preferentially occupy haloes in denser environments. Our results highlight the potential of utilizing multiplet clustering, beyond traditional two-point correlation measurements, to break degeneracies in models describing the galaxy–dark matter connection.
Identifying Anomalous DESI Galaxy Spectra with a Variational Autoencoder
(Oxford University Press, 2026) C. Nicolaou; Rowina S Nathan; O Lahav; A. Palmese; A. Saintonge; J. Aguilar; S. P. Ahlen; C. Allende Prieto; S. Bailey; S. BenZvi
ABSTRACT The tens of millions of spectra being captured by the Dark Energy Spectroscopic Instrument (DESI) provide tremendous discovery potential. In this work we show how Machine Learning, in particular Variational Autoencoders (VAE), can detect anomalies in a sample of approximately 200 000 DESI spectra comprising galaxies, quasars and stars. We demonstrate that the VAE can compress the dimensionality of a spectrum by a factor of 100, while still retaining enough information to accurately reconstruct spectral features. We detect anomalous spectra as those with high reconstruction error and those which are isolated in the VAE latent representation. The anomalies identified fall into two categories: spectra with artefacts and spectra with unique physical features. Awareness of the former could improve the DESI spectroscopic pipeline; whilst the latter could help us discover new and unusual objects. To further curate the list of outliers identified, we use the Astronomaly package which employs Active Learning to provide personalized outlier recommendations for visual inspection. In this work we also explore the VAE latent space, finding that different object classes and subclasses are separated despite being unlabelled. We inject controlled synthetic anomalies and analyse their locations in the latent space to illustrate how the VAE responds to atypical spectral features; and we demonstrate the interpretability of this latent space by identifying tracks within it that correspond to various spectral characteristics. In upcoming work we hope to apply the methods presented here to search for both systematics and astrophysically interesting objects in much larger datasets of DESI spectra.
Measurements of the thermal Sunyaev-Zel’dovich effect with ACT and DESI luminous red galaxies
(American Physical Society, 2025) R. Henry Liu; Simone Ferraro; Emmanuel Schaan; Rongpu Zhou; J. Aguilar; S. P. Ahlen; Nicholas Battaglia; Davide Bianchi; David Brooks; T. Claybaugh
Cosmic Microwave Background (CMB) photons scatter off the free-electron gas in galaxies and clusters, allowing us to use the CMB as a backlight to probe the gas in and around low-redshift galaxies. The thermal Sunyaev-Zel'dovich effect, sourced by hot electrons in high-density environments, measures the thermal pressure of the target objects, shedding light on halo thermodynamics and galaxy formation, and providing a path toward understanding the baryon distribution around cosmic structures. We use a combination of high-resolution CMB maps from the Atacama Cosmology Telescope and photometric luminous red galaxy catalogs from the Dark Energy Spectroscopic Instrument to measure the thermal Sunyaev-Zel'dovich signal in four redshift bins from $z=0.4$ to $z=1.2$, with a combined detection significance of $19\ensuremath{\sigma}$ when stacking on the fiducial CMB Compton-$y$ map. We discuss possible sources of contamination, finding that residual dust emission associated with the target galaxies is important and limits current analyses. We discuss several mitigation strategies and quantify the residual modeling uncertainty. This work complements closely related measurements of the kinematic Sunyaev-Zel'dovich and weak lensing of the same galaxies.
Spectroscopic Characterization of redMaPPer Galaxy Clusters with DESI
(Oxford University Press, 2025) J. Myles; D. Gruen; T Jeltema; Shaojun Fu; S. W. Allen; Shenming Fu; S. P. Ahlen; José Aguilar; David H. Brooks; D. Bianchi
ABSTRACT Optical galaxy cluster identification algorithms such as redMaPPer promise to enable an array of astrophysical and cosmological studies, but suffer from biases whereby galaxies in front of and behind a galaxy cluster are mistakenly associated with the primary cluster halo. These projection effects caused by irreducible photometric redshift uncertainty must be quantified to facilitate the use of optical cluster catalogues. We present measurements of galaxy cluster projection effects and velocity dispersion using spectroscopy from the Dark Energy Spectroscopic Instrument. Our findings are as follows: we confirm that the fraction of redMaPPer putative member galaxies mistakenly associated with cluster haloes is richness dependent, being more than twice as large at low richness than high richness; we present the first spectroscopic evidence of an increase in projection effects with increasing redshift, by as much as 25 per cent from $z\sim 0.1$ to $z\sim 0.2$; moreover, we find qualitative evidence for luminosity dependence in projection effects, with fainter galaxies being more commonly far behind clusters than their bright counterparts; finally, we fit the scaling relation between measured mean spectroscopic richness and velocity dispersion, finding an implied linear scaling between spectroscopic richness and halo mass. We discuss further directions for the application of spectroscopic data sets to improve use of optically selected clusters to test cosmological models.
Spectroscopic search for optical emission lines from dark matter decay
(American Physical Society, 2024) Hanyue Wang; Daniel J. Eisenstein; J. Aguilar; S. P. Ahlen; S. Bailey; David J. Brooks; T. Claybaugh; Axel de la Macorra; Peter Doel; J. E. Forero-Romero
We search for narrow-line optical emission from dark matter decay by stacking dark-sky spectra from the Dark Energy Spectroscopic Instrument (DESI) at the redshift of nearby galaxies from DESI's Bright Galaxy and Luminous Red Galaxy samples. Our search uses regions separated by 5 to 20 arcsec from the centers of the galaxies, corresponding to an impact parameter of approximately 50 kpc. No unidentified spectral line shows up in the search, and we place a line flux limit of ${10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{ergs}/\mathrm{s}/{\mathrm{cm}}^{2}/{\mathrm{arcsec}}^{2}$ on emissions in the wavelength range of $2000--9000\stackrel{\ensuremath{\circ}}{\mathrm{A}}$. This places the tightest constraints yet on the two-photon decay of dark matter in the mass range of 5 to 12 eV, with a particle lifetime exceeding $3\ifmmode\times\else\texttimes\fi{}{10}^{25}\text{ }\text{ }\mathrm{s}$. This detection limit also implies that the line surface brightness contributed from all dark matter along the line of sight is at least 2 orders of magnitude lower than the measured extragalactic background light (EBL), ruling out the possibility that narrow optical-line emission from dark matter decay is a major source of the EBL.
The atomic gas sequence and mass–metallicity relation from dwarfs to massive galaxies
(Oxford University Press, 2024) D. Scholte; A. Saintonge; John Moustakas; Barbara Catinella; Hu Zou; Biprateep Dey; J. Aguilar; S. P. Ahlen; Abhijeet Anand; Robert Blum
ABSTRACT Galaxy scaling relations provide insights into the processes that drive galaxy evolution. The extension of these scaling relations into the dwarf galaxy regime is of particular interest. This is because dwarf galaxies represent a crucial stage in galaxy evolution, and understanding them could also shed light on their role in reionizing the early Universe. There is currently no consensus on the processes that dominate the evolution of dwarfs. In this work, we constrain the atomic gas sequence (stellar mass versus atomic gas fraction) and mass–metallicity relation (stellar mass versus gas-phase metallicity) from dwarf ($10^{6.5} \, {\rm M}_{\odot }$) to massive ($10^{11.5} \, {\rm M}_{\odot }$) galaxies in the local Universe. The combined optical and 21-cm spectroscopic observations of the Dark Energy Spectroscopic Instrument and Arecibo Legacy Fast ALFA surveys allow us to constrain both scaling relations simultaneously. We find a slope change of the atomic gas sequence at a stellar mass of ${\sim} 10^{9} \, \textrm{M}_{\odot }$. We also find that the shape and scatter of the atomic gas sequence and mass–metallicity relation are strongly linked for both dwarfs and more massive galaxies. Consequently, the low-mass slope change of the atomic gas sequence is imprinted onto the mass–metallicity relation of dwarf galaxies. The mass scale of the measured slope change is consistent with a predicted escape velocity threshold below which low-mass galaxies experience significant supernova-driven gas loss, as well as with a reduction in cold gas accretion onto more massive galaxies.
The rate of extreme coronal line emitters in the Baryon Oscillation Spectroscopic Survey LOWZ sample
(Oxford University Press, 2025) J. A. Callow; Or Graur; P. Clark; Alex Kim; Brendan O’Connor; José Aguilar; S. P. Ahlen; D. Bianchi; D Brooks; Axel de la Macorra
ABSTRACT Extreme coronal line emitters (ECLEs) are a rare class of galaxy that exhibit strong, high-ionization iron coronal emission lines in their spectra. In some cases, these lines are transient and may be the result of tidal disruption event (TDEs). To test this connection, we calculate the rate of variable ECLEs (vECLEs) at redshift $\sim 0.3$. We search for ECLEs in the Baryon Oscillation Spectroscopic Survey (BOSS) LOWZ sample and discover two candidate ECLEs. Using follow-up spectra from the Dark Energy Spectroscopic Instrument and Gemini Multi-Object Spectrograph, and mid-infrared observations from the Wide-field Infrared Survey Explorer, we determine that one of these galaxies is a vECLE. Using this galaxy, we calculate the galaxy-normalized vECLE rate at redshift $\sim 0.3$ to be $R_\mathrm{G}=1.6~^{+3.8}_{-1.4}\times 10^{-6}~\mathrm{galaxy}^{-1}~\mathrm{yr}^{-1}$and the mass-normalized rate to be $R_\mathrm{M}=7~^{+16}_{-6}\times 10^{-18}~\mathrm{M_\odot ^{-1}}~\mathrm{yr}^{-1}$. This is then converted to a volumetric rate of $R_\mathrm{V}=1.8~^{+4.5}_{-1.5}\times 10^{-9}~\mathrm{Mpc}^{-3}~\mathrm{yr}^{-1}$. Formally, the LOWZ vECLE rates are $2 \!-\! 4$ times lower than the rates calculated from the Sloan Digital Sky Survey Legacy sample at redshift $\sim 0.1$. However, given the large uncertainties on both measurements, they are consistent with each other at $1\sigma$. Both the galaxy-normalized and volumetric rates are one to two orders of magnitude lower than TDE rates from the literature, consistent with vECLEs being caused by $5 \!-\! 20$ per cent of all TDEs.
The rate of extreme coronal line emitting galaxies in the Sloan Digital Sky Survey and their relation to tidal disruption events
(Oxford University Press, 2024) J. A. Callow; Or Graur; P. Clark; A. Palmese; J. Aguilar; S. P. Ahlen; S. BenZvi; David H. Brooks; T. Claybaugh; Axel de la Macorra
ABSTRACT High-ionization iron coronal lines (CLs) are a rare phenomenon observed in galaxy and quasi-stellar object spectra that are thought to be created by high-energy emission from active galactic nuclei and certain types of transients. In cases known as extreme coronal line emitting galaxies (ECLEs), these CLs are strong and fade away on a time-scale of years. The most likely progenitors of these variable CLs are tidal disruption events (TDEs), which produce sufficient high-energy emission to create and sustain the CLs over these time-scales. To test the possible connection between ECLEs and TDEs, we present the most complete variable ECLE rate calculation to date and compare the results to TDE rates from the literature. To achieve this, we search for ECLEs in the Sloan Digital Sky Survey (SDSS). We detect sufficiently strong CLs in 16 galaxies, more than doubling the number previously found in SDSS. Using follow-up spectra from the Dark Energy Spectroscopic Instrument and Gemini Multi-Object Spectrograph, Wide-field Infrared Survey Explorer mid-infrared observations, and Liverpool Telescope optical photometry, we find that none of the nine new ECLEs evolve in a manner consistent with that of the five previously discovered variable ECLEs. Using this sample of five variable ECLEs, we calculate the galaxy-normalized rate of variable ECLEs in SDSS to be $R_\mathrm{G}=3.6~^{+2.6}_{-1.8}~(\mathrm{statistical})~^{+5.1}_{-0.0}~(\mathrm{systematic})\times 10^{-6}~\mathrm{galaxy}^{-1}~\mathrm{yr}^{-1}$. The mass-normalized rate is $R_\mathrm{M}=3.1~^{+2.3}_{-1.5}~(\mathrm{statistical})~^{+4.4}_{-0.0}~(\mathrm{systematic})\times 10^{-17}~\mathrm{M_\odot ^{-1}}~\mathrm{yr}^{-1}$ and the volumetric rate is $R_\mathrm{V}=7~^{+20}_{-5}~(\mathrm{statistical})~^{+10}_{-0.0}~(\mathrm{systematic})\times 10^{-9}~\mathrm{Mpc}^{-3}~\mathrm{yr}^{-1}$. Our rates are one to two orders of magnitude lower than TDE rates from the literature, which suggests that only 10–40 per cent of all TDEs produce variable ECLEs. Additional uncertainties in the rates arising from the structure of the interstellar medium have yet to be included.
Updated cosmological constraints on axion dark energy with DESI
(American Physical Society, 2025) L. Arturo Ureña–López; F. Lozano-Rodríguez; J. O. Román-Herrera; José Edgar Madriz Aguilar; S. P. Ahlen; D. Bianchi; David J. Brooks; T. Claybaugh; Axel de la Macorra; Arjun Dey
We present updated constraints on the parameters of an axion dark energy model, for which we took into account the properties of its characteristic potential and its full cosmological evolution. We show that the values of the axion parameters appear sufficiently constrained by the data, including the latest DESI DR1, and are consistent with the theoretical expectations of a field mass ${m}_{a}$ in the ultralight regime $\mathrm{log}({m}_{a}{c}^{2}/\mathrm{eV})\ensuremath{\simeq}\ensuremath{-}32.60\ifmmode\pm\else\textpm\fi{}0.12$, and an effective energy scale ${f}_{a}$ close to the reduced Planck energy $\mathrm{log}({f}_{a}/{M}_{\mathrm{Pl}})\ensuremath{\simeq}\ensuremath{-}0.28\ifmmode\pm\else\textpm\fi{}0.19$. Our results also support the idea of dynamical dark energy, although Bayesian evidence still favors the phenomenological dark energy model ${w}_{0}{w}_{a}$ over the axion dark energy, with the Bayes factor indicating moderate and weak strength of the evidence, respectively, when the models are compared to the cosmological constant $\mathrm{\ensuremath{\Lambda}}$. However, the results suggest that axion dark energy remains a well-motivated model and its parameters may be better constrained if the upcoming DESI data show further evidence for dynamical dark energy.