Fabio Gastaldello

Artistic image of the XMM satellite

Artistic image of the XMM satellite

My research interests include the physics of clusters and groups of galaxies and their use as tools for cosmology. I'm mainly an X-ray observer using the current generation of X-ray satellites: Chandra, XMM and Suzaku, to gather every piece of information coming from X-ray emission of their hot gas: gravitational mass distribution, mass of the hot gas, entropy and metal abundance distributions.
However clusters of galaxies are among the best examples of the need for multiwavelength astrophysics. I'm therefore interested in the optical (lensing and member galaxies), radio (extended radio sources like radio halos, radio relics and radio mini-halos and member radio galaxies), SZ, infrared (dust in cool cores and their brighest central galaxies) properties of clusters and groups.

Mass profile of the NGC 1550 group

Mass profile of the NGC 1550 group. Black dots represents the total mass, blue line is the dark matter, green is the X-ray emitting gas, red the stars of the central galaxy

Mass profiles of clusters and groups of galaxies

If the mass profiles of clusters of galaxies have been explored in detail, until reccently there was little information about the gravitational mass profiles of groups of galaxies. For this purpose we collected a sample of 16 relaxed groups with the best Chandra and XMM data: the mass profiles are well described by an NFW model for the dark matter, stars from the central galaxy plus the mass of the hot gas. Our results revealed a significant decrease of the nFW concentration with virial mass, similar to that predicted by the standard LambdaCDM cosmology. This provides a further confirmation of our understanding of dark matter collapse, before only tested at the scale of massive clusters, at the mass scale of groups.
In order to improve and refine these results it is crucial to go beyond archive samples and to acquire data for a flux limited, statistically complete X-ray sample of groups. We have been awarded (PI Buote) a large Chandra program to observe 15 groups selected from the NORAS sample. With this sample it will be possible to directly asses the scatter in the distribution of halo concentrations. And for better constraints on the mass profile it is crucial to extend the X-ray measurements at larger radii: we have started a program of offset Suzaku observation of the brightest groups, exploiting the low X-ray background of that satellite.
At the mass scale of clusters we have both analyzing one of the largest sample of clusters (44 object) to investigate the c-M relation and gas fraction and comparing the validity of the hydrostatic equilibrium assumption by comparing X-ray derived results with lensing and member galaxies dynamics, in particular for the spectacular lensing cluster Abell 1703.

X-ray cavities in the NGC 5044 group

X-ray cavities and filaments in the Chandra image of the NGC 5044 group

AGN feedback

Data from Chandra and XMM have revolutionized our models of cooling flows at the center of galaxies and to a larger extent of galaxy formation. The gas in these regions is not cooling as expected and the most promising heating solution is feedback from the central AGN, by means of cavities and shocks by the jets of the supermassive black holes. Again this phenomenon is not explored at the scale of groups as intensively as at the scale of clusters. I have been involved in particular in studying one of the brightes and close groups, the Perseus of groups, NGC 5044 which shows dramatic X-ray cavities and filaments. The Hα emitting gas is a crucial element to reveal the complex dynamics of gas in this region and we have obtained a VIMOS IFU observation to study in detail the emission in NGC 5044.
For galaxy clusters we have selected a sample both X-ray and Hα bright which seems a good criteria to select objects with interesting properties. The first candidate, Zw 1742.1+3306, shows a wealth of interesting features.

Spectral lines of various elements in the spectrum of M87

Spectral lines of metals in the spectrum of M87

Entropy and Metal Abundances

The characterization of the entropy profiles in groups and clusters can precisely reveal the deviations from the prediction of the self-similar model based only on work of gravity and identify the level, epoch and sources (AGNs and supernovae) of the injection of non-gravitational energy in the X-ray emitting gas. Chandra and XMM are extending the minimum luminosity and therefore temperature and mass of clusters which can be studied at intermediate redshift, opening the unexplored territory of the population of objects with temperature less than 4 keV at redshift 0.2-0.6. I'm trying to collect and study objects of this type serendipitously detected in particular by XMM because they are among the best candidates to study the entropy increase.
Tied to the explosions of supernovae and to the history of star formation is the metal enrichment of the intra-cluster and intra-group gas. I have developed the relevant tools in the work on the metal abundances of M87. If we need a model for the formation and evolution of clusters and groups which explains both the cold phase (stars and galaxies) and the hot phase (ICM and IGM) the study of the metal enrichment of the latter is key, being the most direct ling between the two phases. In particular I focused my work on the possible biases in derving elemental abundaces from CCD spectra with moderate spectral resolution.