# Presentation: 349893

## Observational Cosmology at Fermilab: 

**Observational Cosmology at Fermilab: **
**	*****Sloan Digital Sky Survey***
***	******Dark Energy Survey***
***	******SNAP***

*Gajus Miknaitis*
*EAG, Fermilab*

## Sloan Digital Sky Survey (SDSS)

- _Motivation_: study the distribution of matter in the universe by measuring the distribution of galaxies in space (2D + redshift)

- SDSS 2.5 m Telescope
- at Apache Point Observatory

- 125 Mpixel Imaging Cameraa

- Spectrograph fed by
- 640 optical fibers

## Sloan Digital Sky Survey (SDSS)

- _Motivation_: study the distribution of matter in the universe by measuring the distribution of galaxies in space (2D + redshift)

- Imaging camera:
-    find galaxies, measure
-    their angular positions

*CfA Redshift Survey (1986)*

## Sloan Digital Sky Survey (SDSS)

- _Motivation_: study the distribution of matter in the universe by measuring the distribution of galaxies in space (2D + redshift)

- Imaging camera:
-    find galaxies, measure
-    their angular positions

- Multi-object spectrograph:
-  measure galaxy redshifts
-  distance ≈ redshift

*CfA Redshift Survey (1986)*

## SDSS data set

**After ~5 years of operation, SDSS has:**
-  imaged more than 8,000 square degrees of the sky in five bandpasses
-  detected nearly 200 million celestial objects
-  measured spectra of more than 675,000 galaxies, 90,000 quasars, and 185,000 stars

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## visualization: David W. Hogg (NYU)

- visualization: David W. Hogg (NYU)
- with help from Blanton, Finkbeiner,
- Padmanabhan, Schlegel, Wherry

- data: Sloan Digital Sky Survey
- and the Bright Star Catalog

## SDSS & Large Scale Structure

- power spectrum of matter

- 1 megaparsec

## Scientific impact of the SDSS

- As of May 30, 2006, **1080** refereed, published papers use the Sloan Digital Sky Survey data. 1⁄2 of these papers are authored by people *not* in the collaboration, with public SDSS data access from our servers.
- Over 31,000 citations of these papers in the literature.
- 22 SDSS papers with more than 200 citations

**Some science highlights**
-  State-of-the-art Large Scale Structure measurements
- 3D power spectrum; baryonic acoustic oscillations
-  Catalog of 105 quasars out to z≈7
-  Reionization of the universe at z=7 (Gunn-Peterson effect)
-  Catalog of 106 galaxy clusters to z=0.5
-  Tidal tails and stellar streams in our galaxy
-  Discovery of many rare low-mass dwarf stars

## This is the brightest known image of a galaxy from the early Universe.

- Furious star formation makes the galaxy luminous, but the
- image is bright because the gravty of the foreground galaxy (red) acts
- as a natural telescope, focusing its light.
- The newly discovered galaxy, seen as an arc of four elongated images
- that encircle the foreground lens, offers a rare window into the state
- of the Uniferse two billion years after the big bang.

## SDSS II: The Sequel

- SDSS I: april 2000 - june 2005
*completed*
- SDSS II: july 2005 - july 2008

## SDSS II: components

-  **SDSS “legacy”**: complete the original imaging and spectroscopy survey
-  **SEGUE**: study the (dark matter) halo of the Milky Way
-  **Supernovae**: survey to discover ~200 SNe to probe the expansion history of the universe (dark energy)

## 3. Supernovae & Dark Energy

- Type Ia supernovae are standard(izable) candles.
- By measuring their brightness and cosmological redshift, we can trace the expansion rate & thus infer the make-up of the universe as a function of time.
- Initial SN experiments found surprisingly that the universe appears to be **speeding up**, fueled by gravitationally repulsive “**dark energy**”.

## 3. SDSS II Supernovae

*Astier '06*

- SDSS well-suited to finding SNe at *moderate redshifts* that are difficult for other experiments
- Build up **large (~200)** sample of well-observed supernovae to study dark energy and better understand the supernova population
- Study *systematics* which are increasingly important with larger samples

## Finding and measuring supernovae

- supernova

- subtraction artifact

- 1. Take an image
- 2. Take another image later
- 3. Subtract the two

**2.**

**1.**

**3.**

## Finding and measuring supernovae

- supernova

- subtraction artifact

- 1. Take an image
- 2. Take another image later
- 3. Subtract the two
- 4. Continue taking images to measure supernova “light curve”

**2.**

**1.**

**3.**

**4.**

## SDSS II first year

- supernova yield:
- 139
- spectroscopically
- confirmed Type Ia
- Supernovae
- from the
- Fall 2005
- Season
- Analysis is
- underway
- 2 more years to go!

## Summary

- Fermilab is engaged in a variety of exciting observational astrophysics and cosmology projects
- SDSS is the world leader in studies of large scale structure of the universe (and many other fields of astronomy)
- SDSS-II will enhance our understanding of two of the today's greatest mysteries in cosmology:
-  **Dark Matter** and **Dark Energy**
**In the future, Dark Energy Survey and Supernova Accleration Probe will provide precise constraints on the nature of Dark Energy**