1. The dust content of galaxy clusters
Carlos M. Gutiérrez
Instituto de Astrofísica de Canarias
Tenerife, Spain
Quy Nhon, August 2013

2. The dust content of galaxy clusters
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

3. The dust content of galaxy clusters
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.

4. The dust content of galaxy clusters
Dust in the Milky Way
External galaxies

5. The dust content of galaxy clusters
Clusters of galaxies: basic facts
Clusters of galaxies are the largest bound systems in the Universe. They contain 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.
Detected in optical surveys
(e. g. DSS, SDSS, etc)
GALAXIES
GAS
Detected in X-rays

6. The dust content of galaxy clusters
But, what about dust in clusters?
Galaxy members can contain significant amount of dust, but
the 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)
So, if dust in the intracluster media exists, it must have been injected at (nearly) present epochs.

7. The dust content of galaxy clusters
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.

8. The dust content of galaxy clusters
Previous searches
Method 1: Indirect detection
-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~ mag
Av<~0.01 mag
-first studies affected by systematics
-NO detection of dust effects, Av~<0.01 mag

9. The dust content of galaxy clusters
Wise et al. (1993): IRAS maps of 56 clusters at 60 and 100 mm. Statistical detection : 138 mJy (60 mm) and 253 mJy (100 mm).
Stickel et al. (2002): ISO/ISOPHOT observations of 6 Abell clusters at 120 and 180 mm. Detection of emission (~2.8 Jy) from COMA.
Montier & Giard (2005); Giard et al. (2008). Statistical detection of the emission in the IR of a large sample of clusters.
Kitayama et al. (2009): SPITZER/MIP observations of COMA no detection (upper limit of 7x10-2 MJy/sr at 160 mm)
Detection of dust in some clusters, but still too much uncertainty to extract firm statistical conclusions.

10. The dust content of galaxy clusters
Our work (Gutiérrez & López-Corredoira in prep.)
Goal: To detect (or constrain) the amount of dust in the intracluster media, and its possible dependence with richness and/or redshift.
Ingredients
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.

11. The dust content of galaxy clusters
Method 1: Reddening of background galaxies
Disadvantages
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
The possible reddening comes from the intracluster media
(i.e. NOT from the cluster galaxies)

12. The dust content of galaxy clusters
Method 1: Comparison of properties of objects behind clusters with those in the field.

13. The dust content of galaxy clusters
Color maps of galaxies in the background of clusters as a function of clustercentric distance
g-r
r-i
g-i
Radius=6 Mpc
No evidence of dependence with clustercentric distance at the level ~0.01 mag

14. The dust content of galaxy clusters
Method 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 disadvantages
Each 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.

15. The dust content of galaxy clusters
Extinction maps (Schlegel et al. 1998) and catalog of galaxy clusters (Wen et al. 2012)
Uncovered by SDSS
North hemisphere
South hemisphere
At |b|>50 degrees, there are 63,598 clusters

16. The dust content of galaxy clusters
Section of extinction maps and clusters

17. The dust content of galaxy clusters
Maps of dust
Mpc Av
FWHM~3.6 Mpc
Extension~18 Mpc
30 Mpc

18. The dust content of galaxy clusters
Maps of dust
From the map of mean cluster extinction and assuming for dust grains similar properties to those of the intergalactic media, we can 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)

19. The dust content of galaxy clusters
Dust surface density
Mean mass of dust
Mdust/Mʘ ~ 5 x 108

20. The dust content of galaxy clusters
Maps of dust for clusters of different redshifts and richness
Dust increases with richness (4s)
Richness
Redshift
Statistical clear detection of extinction in the 3x3 bins

21. The dust content of galaxy clusters
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 detected clearly the presence of dust in clusters, but we do not know yet which part comes from their members and which from the intracluster media.

22. The dust content of galaxy clusters
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.
Analysis combined with X-ray data (gas vs. dust).
Comparison of radial profiles of galaxies and dust.
3. Dependence with redshift and of richness.
Future work
Separation of the contribution from galaxies and from intracluster media.
Use of Planck/Herschel maps for IR emission.