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Optical and IR Imaging of Galaxy Clusters using NOT - NORDFORSK Summer School 2006

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Optical and IR Imaging of Galaxy Clusters using NOT - NORDFORSK Summer School 2006. Elisabet Leitet Laia Mencía Trinchant Tine Bjørn Nielsen Carina Persson Tom Speltincx Supervisor: Tomas Dahlén. Outline. Aim Introduction: The beginning... Stars – galaxies - clusters

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slide1

Optical and IR Imaging of Galaxy Clusters using NOT - NORDFORSK Summer School 2006

Elisabet Leitet

Laia Mencía Trinchant

Tine Bjørn Nielsen

Carina Persson

Tom Speltincx

Supervisor: Tomas Dahlén

outline
Outline
  • Aim
  • Introduction:
      • The beginning... Stars – galaxies - clusters
      • Luminosity function
      • Radial distribution of spectral types
      • Photometric redshift - method
  • Observations
  • Reductions
  • Summary – results
slide3
Aims
  • Plan and perform optical and infrared imaging
  • Reduce the data
  • Science: Clusters of galaxies
why study galaxy clusters
Why study Galaxy clusters?
  • Great cosmological importance:
    • formation and evolution of large scale structures
    • constrain cosmological parameters
    • galaxy interactions
    • evolution of galaxies
slide5
How ?
  • Use photometric redshift method to determine cluster membership of the galaxies and spectral type
  • → radial distribution of different spectral types
  • → luminosity function (LF) of different spectral types and total LF of the cluster
how to determine redshifts
Spectroscopic:

Identify and measure the shift of individual lines

Narrow bands → long exposure time

For galaxy clusters: multi-object spectrograph

Only bright galaxies are reached

Small errors: σz~0.01

Photometric:

Use strong features in spectra (4000 Å break)

Broad band color imaging (UBVRIJHK) → shorter exposure time

Many more objects can be observed and measured simultaneously

Possible to reach much fainter galaxies

Larger errors: σz~0.1

How to determine redshifts?
photometric redshift the method
Photometric redshift: The method
  • We use the Spectral Energy Distribution (SED)-fitting technique to determine the redshifts:
  • A library of template spectra is created.
  • These are redshifted and corrected for extinction
  • Compared with the observed colors to determine the redshift z that best fits the observed colors.
  • Drawbacks using this method:
    • Color/redshift degeneracies and template incompleteness.
    • Solution: Increase the number of filters.
idl code
IDL code
  • Compares observations with templates
  • Gets redshift AND type
  • Selection of objects to include
  • Type and redshift distribution
  • Number of stars in field
observations planning
Observations: Planning
  • Clusters chosen for:
    • high position on the sky
    • low airmass
    • no presence of bright stars
    • intermediate redshift
      • too close does not fit in the field of view
      • too far away is too faint
  • Standards close enough to the cluster to have the same airmass
    • Optical: Landolt et al. 1992
    • IR: Persson et al. 1998
observations planning target zwcl2101 6 1351
Observations planning:Target: ZwCl2101.6+1351
  • Coordinates:

RA: 21 04 53

Dec: +14 01 30

  • Redshift: z = 0.20
  • Cluster diameter: 17 arcmin
observations planning target abell 2100
Observations planning:Target: Abell 2100
  • Coordinates:

RA: 15 36 22

Dec: +37 38 09

  • Redshift: z = 0.15
  • Cluster diameter: 20 arcmin
observations instruments
Observations: Instruments
  • Optical
      • ALFOSC
        • 6.5x6.5 arcmin,
        • 0.19 arcsec/pixel
      • Filters: B V R
  • Infrared
      • NOTCam
        • wide field imaging,
        • 4x4 arcmin,
        • 0.23 arcsec/pixel
      • Filters: J Ks
optical observations
S/N calculator

For an elliptical galaxy we find the ratio

B : V : R = 7.2 : 1.8 : 1

3h in total gives:

6400s in B-band

1440s in V-band

720s in R-band

Outcome

ZwCl (54%)

3300s in B-band

900s in V-band

450s in R-band

Abell2100 (100%)

6400s in B-band

1440s in V-band

720s in R-band

Optical observations
ir observations
We find the ratio

J = 28 % (= 2800s)

Ks = 72 % (= 7200s)

From the frame command

Outcome

ZwCl (114%)

4720s in Ks-band

2208s in J-band

Abell2100 (115%)

2160s in Ks-band

1344s in J-band

IR observations
reductions optical
Reductions: Optical
  • Raw image of ZwCl, taken in the B band

Corrected for:

  • Bias offset
  • Bad pixels (mask)
  • Trimmed

Corrected for:

  • Flat field

Final image:

  • Normalized
  • Rotated
  • Aligned
  • ZP corrected
  • Combined
  • Galactic extinction corrected
reductions near ir
Reductions: Near IR
  • Raw image of Abell 2100 taken in the Ks band

Corrected for:

  • Sky

Corrected for:

  • Flat field

Final image:

  • Normalized
  • Aligned
  • Trimmed
  • ZP corrected
  • Combined
  • Galactic extinction corrected
reductions zero point corrections
Reductions: Zero Point Corrections
  • Corrections for atmospheric extinction, ca
  • ccdproc on standard stars (bias, flat, mask, overscan + trim section)
  • Normalized by exposure time
  • Magnitudes from SExtractor
  • Zpx=magx-magx,measured
  • ca=100.4k(AM-1) ,(k=slope)

re

B

V

R

type distribution
Type distribution
  • Types
    • ellipticals
    • spirals (2 types)
    • SB (3 templates)
  • All galaxies in the field
  • Mostly ellipticals, as expected
redshift distribution
Redshift distribution
  • Peaks around expected z (cluster)
  • Spread distribution  lack of colours
  • fig.1 high peak  R is the last band, results not reliable (z>1)
redshift distribution ellipticals
Redshift distribution, ellipticals
  • Plot per object  probability of type and z based on our data
  • Degeneracy  spirals vs. ellipticals
    • lack of colours
radial distribution
Radial distribution
  • Number of galaxies in the field
  • 1/3 galaxies  cluster
  • Early- & late-types same density distribution, without cluster amount of ellipticals decreases 20%
  • Cluster  early-types more abundant in the inner part
      • late-types rare, increasing towards outskirts
number counts vs magnitude
Number counts vs. Magnitude
  • Limiting magnitude
    • B = 25.8
    • V = 24.5
    • R = 23.6
  • Including all galaxies in the field
  • For cluster galaxies  LF
number counts vs magnitude1
Number counts vs. Magnitude
  • Limiting magnitude
    • B = 25.4
    • V = 24.2
    • R =23.3
future
Future
  • LF
  • Scale NOTCam images to ALFOSC
  • Include IR observations (reduction done)
  • Redo photometric redshifts
  • More observations in optical and IR
  • Publish an article (if we are lucky enough)
thanks nordforsk
Thanks NORDFORSK!!!

After two weeks of standard.sex, group.sex and deep.sex, we’re back to cyber.sex…

Sleep tight! zzzzzzzz...

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