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DESI DR1 Fundamental Plane

Caitlin Ross - University of Queensland

In collaboration with Julian Bautista, Kelly Douglass, Alex Kim, Fei Qin, and many others

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DESC PV Workshop 2025

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Thanks to our sponsors and �72 Participating Institutions!

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Dark Energy Spectroscopic Instrument (DESI)

  • 5000 fiber spectrograph instrument
  • Exposures every ~20min

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Fundamental Plane

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  • Dispersion Supported
  • Non star forming

Early-Type Galaxies!

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Selection Criteria

  • Best measurement of galaxy
  • Quality Control
  • Sigma Clipping (Calibration only)
  • Isolation of Early-Type Galaxies

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Repeat Observations

 

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Indo-U.S. Coudé Feed

Spectral Library

Velocity Dispersions

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Velocity Dispersions

  • Dark time observations have +2.3km/s higher velocity dispersions then their bright time counterparts

Dark time

Bright time

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Velocity Dispersions

  • Increased errors by factor of 1.13 (from pPXF output) to account for scatter in repeat observations

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Secondary

Primary

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Velocity Dispersions

SDSS

DESI

  • In good agreement with SDSS (0.05σ offset)

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FP Fit Systematics

Evolution correction parameter

Corrects for evolution of intrinsic galaxy brightness with redshift

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Galaxy magnitude

Convert to Surface Brightness

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FP Fit Systematics

Aperture correction parameter

 

Corrects for fixed size spectral fiber

Velocity dispersion

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DR1 Fundamental Plane

26% error on distances

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DR1 Fundamental Plane

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Existing Measurements

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DESI FP Sample

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DESI FP Sample

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Summary

DR1 Fundamental Plane sample:

  • PVs for 97 995 Early-type Galaxies
  • ~74 000 of which lie within the BGS footprint and are being used for H0 and fσ8 measurements
  • Part of the DESI DR1 PV paper suite (Hopeful December arXiv release)

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To come in DR2:

  • More in depth velocity dispersion systematics analysis
  • Investigate methods to reduce spiral contamination

Cosmic Flows 2025, C. Ross (UQ)