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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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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


  • 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


    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


    Zwcl three color image bvr
    ZwClThree color image (BVR)


    Abell 2100 three color image bvr
    Abell 2100Three color image (BVR)



    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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