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Carlos M. Gutiérrez

The dust content of galaxy clusters

Quy Nhon, August 2013

Instituto de Astrofísica de Canarias Tenerife, Spain


Outline

• Dust in astrophysics (galaxies, intergalactic media and clusters)• Galaxy clusters• Previous searches of dust in clusters (direct and indirect searches)• Our work (methods and ingredients)• Results: maps of dust• Conclusions and future work


Dust in astrophysics

• One of the components (the others being gas and stars) of galaxies.

• Clearly detected in the Milky Way and in many other external galaxies (basically of spiral and irregular types).

• Very inhomogeneus spatial distribution.• Relative modest contribution in mass, but dust grains play an

important role in the intergalactic media and in the star formation that occurs within a galaxy.

• Dust grain can absorb and redden background sources, so an accurate knowledge of the amount and distribution of dust is crucial.


Dust in the Milky Way External galaxies


Clusters of galaxies: basic facts• Clusters of galaxies are the largest bound

systems in the Universe. They contain 200-1000 galaxies.

• First clusters formed at z~2 (i. e. age ~10 Gyr)

• Dispersion of velocities between galaxy members indicate (Zwicky 30s’) large amount of dark matter.

• Most of the barionic mass is in very hot gas in the intracluster media.

GALAXIES

GAS

Detected in optical surveys (e. g. DSS, SDSS, etc) Detected in X-rays


Galaxy members can contain significant amount of dust, butthe center of clusters is a hostile environment for intracluster dust grains to survive. In fact, dust grains are easily sputtered and destroyed in t~107-8 years (depending on size of the grains, density and temperature)

But, what about dust in clusters?

So, if dust in the intracluster media exists, it must have been injected at (nearly) present epochs.


Possible mechanisms to inject dust in the intracluster media• Direct accretion from the intercluster media.• Galaxies falling into clusters show gas and dust stripped from them and injected into the intracluster media.• Expelled from the galaxy members: -by processses like SN or AGN jets -during galaxy-galaxy mergers a significant amount of gas (and dust) may be removed by collisional processes.


Previous searches

-Comparison of counts (or reddening) of galaxies, quasars, and/or clusters behind clusters of galaxies with those on the field. -Pioneering works: Zwicky (1962); Karanchetsev & Lipovetskii (1969); Bogart & Wagoner (1973); Boyle et al. (1988); Romani & Maoz (1992)

-Modern works (mostly SDSS based): Nollenberg et al. (2003); Chelouche et al. (2007); Muller et al. (2008); Bovy et al. (2008); McGee & Balogh (2010).

Av~0.2-0.5 mag

Av<~0.01 mag

-first studies affected by systematics-NO detection of dust effects, Av~<0.01 mag

Method 1: Indirect detection


• Wise et al. (1993): IRAS maps of 56 clusters at 60 and 100 Wise et al. (1993): IRAS maps of 56 clusters at 60 and 100 m. Statistical detection : 138 mJy (60 m. Statistical detection : 138 mJy (60 m) and 253 mJy m) and 253 mJy (100 (100 m). m).

• Stickel et al. (2002): ISO/ISOPHOT observations of 6 Abell Stickel et al. (2002): ISO/ISOPHOT observations of 6 Abell clusters at 120 and 180 clusters at 120 and 180 m. Detection of emission (~2.8 Jy) m. Detection of emission (~2.8 Jy) from COMA.from COMA.

• Montier & Giard (2005); Giard et al. (2008). Statistical Montier & Giard (2005); Giard et al. (2008). Statistical detection of the emission in the IR of a large sample of detection of the emission in the IR of a large sample of clusters.clusters.

• Kitayama et al. (2009): SPITZER/MIP observations of Kitayama et al. (2009): SPITZER/MIP observations of COMA no detection (upper limit of 7x10COMA no detection (upper limit of 7x10-2-2 MJy/sr at 160 MJy/sr at 160 m)m)

Detection of dust in some clusters, but still too much uncertainty to extract firm statistical conclusions.


Our work (Gutiérrez & López-Corredoira in prep.)

• Large catalogue of clusters of galaxies: Wen et al. (2012). SDSS based 132,684 clusters in the range 0.05 < z<0.84.• Background galaxies: SDSS/DR9 catalog of galaxies with reliable photometry and redshifts (~3x107 objects)• Extinction maps: Schlegel et al. (1998) based on IRAS and COBE data.

Ingredients

Goal: To detect (or constrain) the amount of dust in the intracluster media, and its possible dependence with richness and/or redshift.


Method 1: Reddening of background galaxies

The possible reddening comes from the intracluster media (i.e. NOT from the cluster galaxies)

Most of the redshifts for galaxies and clusters are photometric, and then have a relatively large uncertainty So, in most of the cases we do not know for sure wether a galaxy projected near a cluster is in the foreground or in the background of such cluster.We do not map the entire cluster, but only the position where each background galaxy is projected.

Advantage

Disadvantages


Method 1: Comparison of properties of objects behind clusters with those in the field.

The dust content of galaxy clustersColor maps of galaxies in the background of clusters as a function of clustercentric distance

No evidence of dependence with clustercentric distance at the level ~0.01 mag

g-r r-i g-i

Radius=6 Mpc


Method 2Method 2

Stacking method (see Montier & Giard 2005).1. Select those clusters above a given galactic latitude (in order to avoid regions with very heavy extinction from our own galaxy). 2. Build an extinction map (size 15 x15 Mpc2) centered on each cluster.3. Average all those maps

Advantages and disadvantagesEach cluster is entirely mapped, but in the case of detection we do not know if that comes from galaxies of the cluster or from the intracluster media.


Extinction maps (Schlegel et al. 1998) and catalog of galaxy clusters (Wen et al. 2012)

North hemisphereSouth hemisphere

At |b|>50 degrees, there are 63,598 clusters

Uncovered by SDSS


Section of extinction maps and clustersSection of extinction maps and clusters


Maps of dust

Mpc

Av

FWHM~3.6 Mpc

Extension~18 Mpc

30 Mpc30 Mpc


Maps of dustFrom the map of mean cluster extinction and assuming for dust From the map of mean cluster extinction and assuming for dust grains similar properties to those of the intergalactic media, we grains similar properties to those of the intergalactic media, we can obtain the mass and the surface distribution of dust in clusterscan obtain the mass and the surface distribution of dust in clusters

External ring (12-15 Mpc)to subtract the mean Galactic extinction

Region (radius~10 Mpc) to estimate the mean cluster extinction

Av~0.001 mag in the central pixel (0.6 Mpc x 0.6 Mpc)


Mean mass of dust

Mdust/Mʘ ~ 5 x 108

Dust surface density


Maps of dust for clusters of different redshifts and richness

Dust increases with richness (4)

Richness

RedshiftRedshiftStatistical clear detection of extinction in the 3x3 bins


The amount of dust correlates with richness of the cluster We have not separated yet

the contribution from member galaxies from those coming from the intracluster media.

Important remark

In other words, we have In other words, we have detected clearly the presence detected clearly the presence of dust in clusters, but we do of dust in clusters, but we do not know yet which part not know yet which part comes from their members comes from their members and which from the and which from the intracluster media. intracluster media.

• Separation of the contribution from galaxies and from intracluster media.

• Use of Planck/Herschel maps for IR emission.

Future work


Conclusions• Analysis of the most complete catalog of clusters of galaxies.• Two methods to estimate the dust in clusters:• -method 1: upper limit at Av~0.01 mags -method 2: clear detection of extinction Av=10-3 mags in the center of the cluster. -both results are compatible.• The extinction detected corresponds to a mean mass per cluster Mdust~5 x 108 Mʘ

• The amount of extinction, and then mass of dust, correlates with richness.• Still unclear which fraction of dust is associated to galaxies and to the intracluster

media respectively.1. Analysis combined with X-ray data (gas vs. dust).2. Comparison of radial profiles of galaxies and dust.3. Dependence with redshift and of richness.

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