Astronomical instrumentation

Abstract:

We investigate the well-known correlations between the dynamical rnass-to-light ratio M/L and other global observables of elliptical (E) arid lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates that dark matter in early-type galaxies contributes ∼30% of the total mass inside one Re, in agreement with previous studies, with significant variations from galaxy to galaxy. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast rotating galaxies have lower dark matter fractions than the slow rotating and generally more massive ones. © EAS, EDP Sciences 2006.

Abstract:

We present ∼0″5 resolution near-infrared integral field spectroscopy of the Hα line emission of 14 z ∼ 2 UV-selected BM/BX galaxies, obtained with SINFONI at the ESO Very Large Telescope. The average Hα half-light radius is r1/2 ≈4 h70^-1 kpc, and line emission is detected over ≳20 h70^-1 kpc in several sources. In nine galaxies, we detect spatially resolved velocity gradients, from 40 to 410 km s^-1 over ∼10 h70 ^-1 kpc. The kinematics of the larger systems are generally consistent with orbital motions. Four galaxies are well described by rotating clumpy disks, and we extracted rotation curves out to radii ≳10 h 70^-1 kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities of vc ∼ 180 ± 90 km s^-1 and dynamical masses from ∼0.5 to 25 × 10¹⁰ h70^-1 M ⊙ within r1/2- The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. Moreover, the specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average vc at 10 h 70^-1 kpc, the virial mass of the typical halo of a galaxy in our sample is 10^11.7±0.5 h70^-1 M ⊙. Kinematic modeling of the three best cases implies a ratio of vc to local velocity dispersion vc/σ ∼ 2-4 and, accordingly, a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ∼500 Myr. We also argue that if our BM/BX galaxies were initially gas-rich, their clumpy disks would subsequently lose their angular momentum and form compact bulges on a timescale of ∼1 Gyr. © 2006. The American Astronomical Socieity. All rights reserved.

Abstract:

To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such a feedback in the optical emission line gas around the z=2.16 powerful radio galaxy MRC1138-262, likely a massive galaxy in formation. The kpc-scale kinematics, with FWHMs and relative velocities <= 2400 km/s and nearly spherical spatial distribution, do not resemble large-scale gravitational motion or starburst-driven winds. Order-of-magnitude timescale and energy arguments favor the AGN as the only plausible candidate to accelerate the gas, with a total energy injection of a few x 10^60 ergs or more, necessary to power the outflow, and relatively efficient coupling between radio jet and ISM. Observed outflow properties are in gross agreement with the models, and suggest that AGN winds might have a similar, or perhaps larger, cosmological significance than starburst-driven winds, if MRC1138-262 is indeed archetypal. Moreover, the outflow has the potential to remove significant gas fractions (<= 50%) from a >L* galaxy within a few 10 to 100 Myrs, fast enough to preserve the observed [alpha/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.