optical and ir imaging of galaxy clusters using not - nordforsk summer school 2006

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Carina, Elisabet, Laia, Tine, Tom & Tomas – Cluster Team La Palma, Friday 21 April 2023

Optical and IR Imaging of Galaxy Clusters using NOT -

NORDFORSK Summer School 2006

Elisabet LeitetLaia Mencía TrinchantTine Bjørn NielsenCarina PerssonTom Speltincx

Supervisor: Tomas Dahlén

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Outline

• Aim

• Introduction: The beginning... Stars – galaxies - clusters Luminosity function Radial distribution of spectral types Photometric redshift - method

• Observations

• Reductions

• Summary – results

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Aims

• Plan and perform optical and infrared imaging

• Reduce the data

• Science: Clusters of galaxies

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Why study Galaxy clusters?

• Great cosmological importance: formation and

evolution of large scale structures

constrain cosmological parameters

galaxy interactions evolution of

galaxies

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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

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Luminosity function for clusters

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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

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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.

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IDL code

• Compares observations with templates

• Gets redshift AND type

• Selection of objects to include

• Type and redshift distribution

• Number of stars in field

• …

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Transmission curves

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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

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Observations planning:Target: ZwCl2101.6+1351

• Coordinates: RA: 21 04 53

Dec: +14 01 30

• Redshift: z = 0.20• Cluster diameter:

17 arcmin

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Observations planning:Target: Abell 2100

• Coordinates: RA: 15 36 22

Dec: +37 38 09

• Redshift: z = 0.15

• Cluster diameter: 20 arcmin

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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

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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

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IR observations

• We find the ratioJ = 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

ZwCl Abell2100

J 1728s 864s

Ks 4320s 2160s

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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

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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

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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

VR

Band Zero point Slope

B 25.74 -0.33

V 25.67 -0.20

R 25.57 -0.14

J 22.29

Ks 21.78

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ZwClThree color image (BVR)

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Abell 2100 Three color image (BVR)

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Abell 2100 final in Ks

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Type distribution

• Types– ellipticals– spirals (2 types)– SB (3 templates)

• All galaxies in the field• Mostly ellipticals, as

expected

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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)

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Redshift distribution, ellipticals

• Plot per object probability of type and z based on our data

• Degeneracy spirals vs. ellipticals– lack of colours

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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

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Radial distribution (2)

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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

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Number counts vs. Magnitude

• Limiting magnitude– B = 25.4– V = 24.2 – R =23.3

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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)• …

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Thanks NORDFORSK!!!

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

to cyber.sex…

optical and ir imaging of galaxy clusters using not - nordforsk summer school 2006

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