The dust content of galaxy clusters. Carlos M. Gutiérrez. Instituto de Astrofísica de Canarias Tenerife, Spain. Quy Nhon, August 2013. The dust content of galaxy clusters. Outline. Dust in astrophysics ( galaxies , intergalactic media and clusters )
Carlos M. Gutiérrez
Instituto de Astrofísica de Canarias
Quy Nhon, August 2013
Dust in astrophysics
Dust in theMilkyWay
Clusters of galaxies: basic facts
Detected in optical surveys
(e. g. DSS, SDSS, etc)
Detected in X-rays
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.
Possiblemechanismstoinjectdust in theintracluster media
Method 1: Indirect detection
-Comparison of counts (or reddening) of galaxies, quasars, and/or clusters behind clusters of galaxies with those on the field.
-Pioneeringworks: 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).
-first studies affected by systematics
-NO detection of dust effects, Av~<0.01 mag
Detection of dust in some clusters, but still too much uncertainty to extract firm statistical conclusions.
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.
Method 1: Reddening of background 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.
The possible reddening comes from the intracluster media
(i.e. NOT from the cluster galaxies)
Method 1: Comparison of properties of objects behind clusters with those in the field.
Color 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
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.
Extinction maps (Schlegel et al. 1998) and catalog of galaxy clusters (Wen et al. 2012)
Uncovered by SDSS
At |b|>50 degrees, there are 63,598 clusters
Section of extinctionmaps and clusters
Maps of dust
Maps of dust
Av~0.001 mag in the central pixel (0.6 Mpc x 0.6 Mpc)
Fromthemap of mean clusterextinction and assumingfordustgrains similar propertiestothose of theintergalactic media, we can obtainthemass and thesurfacedistribution 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
Dust surface density
Mean mass of dust
Mdust/Mʘ ~ 5 x 108
Maps of dust for clusters of different redshifts and richness
Statistical clear detection of extinction in the 3x3 bins
Dust increases with richness (4s)
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.
In otherwords, wehavedetectedclearlythepresence of dust in clusters, butwe do notknowyetwhichpart comes fromtheirmembers and whichfromtheintracluster media.