Renato Falomo

Testing Newtonian gravity with distant globular clusters: NGC 1851 and NGC 1904

Context. Globular clusters are useful for testing the validity of Newtonian dynamics in the low acceleration regime typical of galaxies, without the complications of non-baryonic dark matter. In the absence of disturbing effects, such as tidal heating, the velocity dispersion of globular clusters is expected to vanish at large radii. If this is not observed, and in particular if, as observed in elliptical galaxies, the dispersion is found to be constant at large radii below a certain threshold acceleration, this might indicate a breakdown of Newtonian dynamics. Aims. To minimize the effects of tidal heating that can increase the velocity dispersion at large radii, we study the velocity dispersion profile of two distant globular clusters, NGC 1851 and NGC 1904. Methods. The velocity dispersion profile is derived from accurate radial velocity measurements, obtained at the ESO 8m VLT telescope with the FLAMES multi-object spectrograph. Reliable data for 184 and 146 bona fide cluster star members were obtained for NGC 1851 and NGC 1904, respectively. Results. These data allow us to trace the velocity dispersion profile to ∼2r0 ,w herer0 is the radius at which the cluster internal acceleration of gravity is a0 ∼ 10 −8 cm s −2 . It is found that in both clusters the velocity dispersion is maximal at the center, decreases moving outward, and then becomes constant beyond ∼r0. Since the distance of these clusters from the Milky Way is large, the observed flattening of the velocity dispersion profile cannot be ascribed to tidal heating effects, as proposed in the case of nearer globular clusters. Conclusions. These results are in full agreement with those found for another five globular clusters previously investigated as part of this project. Taken together, our results for these 7 clusters support the claim that the velocity dispersion is constant beyond r0, irrespectively of the specific physical properties of the clusters: mass, size, dynamical history, and distance from the Milky Way. The strong similarity to the constant velocity dispersion observed in elliptical galaxies beyond r0 is indicative of a common origin for this phenomenon in the two class of objects, and possibly a breakdown of Newtonian dynamics below a0.

The Nucleus-Host Galaxy Connection in Radio-Loud AGN

We studied a moderate-redshift (0.15 5 orders of magnitude in nuclear power, and the two sub-samples have indistinguishable luminosity-redshift distributions over the redshift range 0.15 < z < 0.5. No correlation between nuclear brightness (corrected for beaming) and galaxy luminosity is seen. Assuming the host galaxy-black hole mass correlation for local galaxies, the derived Eddington ratios range from 2×10-4 for low-power AGN (BL Lac objects) to 2×10-1 for high power AGN (RL quasars). This implies a considerable difference in rate of fueling. At least for RL AGN, the host galaxy properties appear to have no close connection to the power of the jet.

QSO host galaxies and environments in the ELT era

Quasars represent our main lighthouses to explore the high redshift Universe and to investigate the processes of formation of galaxies and their central supermassive black holes. The characterization of the key parameters of quasar hosts as the galaxy mass, size, morphology and their close environments are hindered by the limited resolution and sensitivity of the present instrumentation. We investigate here the expected capabilities of future observations obtained with near-IR Adaptive Optics imaging cameras foreseen for Extremely Large Telescopes. Detailed simulations are presented to evaluate the accuracy of those observations under different observing conditions.

The Luminosity Function of the Host Galaxies of QSOs and BL Lac Objects

A clear insight of the galaxies hosting active galactic nuclei is of fundamental importance for understanding the processes of galaxies and nuclei formation and their cosmic evolution. A good characterization of the host galaxies properties requires images of excellent quality in order to disentangle the light of the galaxy from that of the bright nucleus. To this aim HST has provided a major improvement of data on QSOs (Disney et al. 1995; Bahcall et al. 1996, 1997; Boyce et al. 1998; McLure et al. 1999; Hamilton et al. 2000; Kukula et al. 2001) and BL Lacs (Scarpa et al. 2000, Urry et al. 2000). We present a comparative study of low redshift QSO and BL Lac host galaxy luminosity function (HGLF). To this aim we have considered samples of BL Lacs (Urry et al. 2000) and QSOs (Bahcall et al. 1997; Boyce et al. 1998; McLure et al. 1999) that have been well resolved by images obtained with WFPC2 on board of HST.A clear insight of the galaxies hosting active galactic nuclei is of fundamental importance for understanding the processes of galaxies and nuclei formation and their cosmic evolution. A good characterization of the host galaxies properties requires images of excellent quality in order to disentangle the light of the galaxy from that of the bright nucleus. To this aim HST has provided a major improvement of data on QSOs (Disney et al. 1995; Bahcall et al. 1996, 1997; Boyce et al. 1998; McLure et al. 1999; Hamilton et al. 2000; Kukula et al. 2001) and BL Lacs (Scarpa et al. 2000, Urry et al. 2000). We present a comparative study of low redshift QSO and BL Lac host galaxy luminosity function (HGLF). To this aim we have considered samples of BL Lacs (Urry et al. 2000) and QSOs (Bahcall et al. 1997; Boyce et al. 1998; McLure et al. 1999) that have been well resolved by images obtained with WFPC2 on board of HST.