We used broad-band imaging data for 10 cool-core brightest cluster galaxies (BCGs) and conducted a Bayesian analysis using stellar population synthesis to determine the likely properties of the constituent stellar populations. Determination of ongoin
g star formation rates (SFRs), in particular, has a direct impact on our understanding of the cooling of the intracluster medium (ICM), star formation and AGN-regulated feedback. Our model consists of an old stellar population and a series of young stellar components. We calculated marginalized posterior probability distributions for various model parameters and obtained 68% plausible intervals from them. The 68% plausible interval on the SFRs is broad, owing to a wide range of models that are capable of fitting the data, which also explains the wide dispersion in the star formation rates available in the literature. The ranges of possible SFRs are robust and highlight the strength in such a Bayesian analysis. The SFRs are correlated with the X-ray mass deposition rates (the former are factors of 4 to 50 lower than the latter), implying a picture where the cooling of the ICM is a contributing factor to star formation in cool-core BCGs. We find that 9 out of 10 BCGs have been experiencing starbursts since 6 Gyr ago. While four out of 9 BCGs seem to require continuous SFRs, 5 out of 9 seem to require periodic star formation on intervals ranging from 20 Myr to 200 Myr. This time scale is similar to the cooling-time of the ICM in the central (< 5 kpc) regions.
SKA is a new technology radio-telescope array, about two orders of magnitude more sensitive and rapid in sky surveys than present instruments. It will probe the dark age of the universe, just afer recombination, and during the epoch of reionisation (
z=6-15); it will be the unique instrument to map the atomic gas in high redshift galaxies, and determine the amount and distribution of dark matter in the early universe. Not only it will detect and measure the redshifts of billions of galaxies up to z=2, but also it will discover and monitor around 20 000 pulsars in our Milky Way. The timing of pulsars will trace the stretching of space, able to detect gravitational waves. Binary pulsars will help to test gravity in strong fields, and probe general relativity. These exciting perspectives will become real beyond 2020.
Evidence of AGN interaction with the IGM is observed in some galaxies and many cool core clusters. Radio jets are suspected to dig large cavities into the surrounding gas. In most cases, very large optical filaments are seen around the central galaxy
. The origin of these filaments is still not understood. Star-forming regions are sometimes observed inside the filaments and are interpreted as evidence of positive feedback. Cen A is a nearby galaxy with huge optical filaments aligned with the AGN radio-jet direction. We searched for line ratio variations along the filaments, kinematic evidence of shock-broadend line widths, and large-scale dynamical structures. We observed a 1x1 region around the inner filament of Cen A with MUSE on the VLT during Science Verification. The brightest lines detected are the Halpha, [NII], [OIII] and [SII]. MUSE shows that the filaments are made of clumpy structures inside a more diffuse medium aligned with the radio-jet axis. We find evidence of shocked shells surrounding the star-forming clumps from the line profiles, suggesting that the star formation is induced by shocks. The clump line ratios are best explained by a composite of shocks and star formation illuminated by a radiation cone from the AGN. We also report a previously undetected large arc-like structure: three streams running perpendicular to the main filament; they are kinematically, morphologically, and excitationally distinct. The clear difference in the excitation of the arcs and clumps suggests that the arcs are very likely located outside of the radiation cone and match the position of the filament only in projection. The three arcs are most consistent with neutral material swept along by a backflow of the jet plasma from the AGN outburst that is ionised through a diffuse radiation field with a low-ionisation parameter that continues to excite gas away from the radiation cone.
We report ALMA and SMA observations of the luminous infrared merger NGC 3256, the most luminous galaxy within z=0.01. Both of the two merger nuclei separated by 5 (0.8 kpc) on the sky have a compact concentration of molecular gas, i.e., nuclear disks
with Sigma_mol > 10^3 Msun pc^-2. The one at the northern nucleus is face-on while the southern nuclear disk is almost edge-on. The northern nucleus is more massive and has molecular arcs and spiral arms around. The high-velocity molecular gas previously found in the system is resolved to two molecular outflows associated with each of the two nuclei. The molecular outflow from the northern nuclear disk is part of a starburst-driven superwind seen nearly pole on. Its maximum velocity is >750 km/s and its mass outflow rate is estimated to be > 60 Msun/yr for a conversion factor N_{H_2}/I_{CO(1-0)}=1x10^20 cm^-2/(K km/s). The outflow from the southern nucleus is a highly collimated bipolar molecular jet seen nearly edge-on. Its line-of-sight velocity increases with distance out to 300 pc from the southern nucleus. Its maximum de-projected velocity is ~2000 km/s for the estimated inclination and should exceed 1000 km/s even allowing for its uncertainty. The mass outflow rate is estimated to be >50 Msun/yr for this outflow. There are possible signs that this southern outflow has been driven by a bipolar radio jet from an AGN that became inactive very recently. The sum of these outflow rates, although subject to the uncertainty in the molecular mass estimate, either exceeds or compares to the total star formation rate in NGC 3256. The feedback from nuclear activities in the form of molecular outflows is therefore significant in the gas consumption budget, and hence evolution, of this luminous infrared galaxy. (abridged)
For the first time, we reveal large amounts of cold molecular gas in a ram pressure stripped tail, out to a large, intracluster distance from the galaxy. With the APEX telescope we have detected 12CO(2-1) emission corresponding to more than 10^9 Msun
of H_2 in three Ha bright regions along the tail of the Norma cluster galaxy ESO 137-001, out to a projected distance of 40 kpc from the disk. ESO 137-001 has an 80 kpc long and bright X-ray tail associated with a shorter (40 kpc) and broader tail of numerous star-forming H II regions. The amount of about 1.5x10^8 Msun of H_2 found in the most distant region is similar to molecular masses of tidal dwarf galaxies, though the standard Galactic CO-to-H_2 factor could overestimate the H_2 content. Along the tail, we find the amount of molecular gas to drop, while masses of the X-ray emitting and diffuse ionized components stay roughly constant. Moreover, the amounts of hot and cold gas are large and similar, and together nearly account for the missing gas from the disk. We find a very low star formation efficiency (tau > 10^10 yr) in the stripped gas in ESO 137-001 and suggest that this is due to a low average gas density in the tail, or turbulent heating of the interstellar medium that is induced by a ram pressure shock. The unprecedented bulk of observed H_2 in the ESO 137-001 tail suggests that some stripped gas may survive ram pressure stripping in the molecular phase.
This talk tries to summarise where we are now, in the nature and nurture questions in galaxy formation and evolution, and briefly describe unsolved problems, and perspectives of progress.
The gas distribution and dynamics in the inner Galaxy present many unknowns as the origin of the asymmetry of the longitude-velocity (lv) diagram of the Central Molecular Zone (CMZ). On the other hand, there are recent evidences in the stellar compon
ent of the presence of a nuclear bar that could be slightly lopsided. Our goal is to characterize the nuclear bar observed in 2MASS maps and to study the gas dynamics in the inner Milky Way taking into account this secondary bar. We have derived a realistic mass distribution by fitting 2MASS star counts maps with three components (disk, bulge and nuclear bar) and we have simulated the gas dynamics, in the deduced gravitational potential, using a sticky-particles code. Our simulations of the gas dynamics reproduce successfully the main characteristics of the Milky Way for a bulge orientation of 20-35 deg with respect to the Sun-Galactic Center (GC) line and a pattern speed of 30-40 km/s/kpc. In our models the Galactic Molecular Ring (GMR) is not an actual ring but the inner parts of the spiral arms, while the 3-kpc arm and its far side counterpart are lateral arms that contour the bar. Our simulations reproduce, for the first time, the parallelogram shape of the lv-diagram of the CMZ as the gas response to the nuclear bar. This bar should be oriented by an angle of ~60-75 deg with respect to the Sun-GC line and its mass amounts to (2-5.5)10e9 Msun. We show that the observed asymmetry of the CMZ cannot be due to lopsidedness of the nuclear bar as suggested by the 2MASS maps. We do not find clear evidences of lopsidedness in the stellar potential. We propose that the observed asymmetry of the central gas layer can be due to the infalling of gas into the CMZ in the l=1.3-complex
Multiple, sequential mergers are unavoidable in the hierarchical build-up picture of galaxies, in particular for the minor mergers that are frequent and highly likely to have occured several times for most present-day galaxies. However, the effect of
repeated minor mergers on galactic structure and evolution has not been studied systematically so far. We present a numerical study of multiple, subsequent, minor galaxy mergers, with various mass ratios ranging from 4:1 to 50:1. The N-body simulations include gas dynamics and star formation. We study the morphological and kinematical properties of the remnants, and show that several so-called minor mergers can lead to the formation of elliptical-like galaxies that have global morphological and kinematical properties similar to that observed in real elliptical galaxies. The properties of these systems are compared with those of elliptical galaxies produced by the standard scenario of one single major merger. We thus show that repeated minor mergers can theoretically form elliptical galaxies without major mergers, and can be more frequent than major mergers, in particular at moderate redshift. This process must then have formed some elliptical galaxies seen today, and could in particular explain the high boxiness of massive ellipticals, and some fundamental relations observed in ellipticals. In addition, because repeated minor mergers, even at high mass ratios, destroy disks into spheroids, these results indicate that spiral galaxies cannot have grown only by a succession of minor mergers.
In an earlier study of the spiral galaxy M33, we photometrically identified arcs or outer spiral arms of intermediate age (0.6 Gyr - 2 Gyr) carbon stars precisely at the commencement of the HI-warp. Stars in the arcs were unresolved, but were likely
thermally-pulsing asymptotic giant branch carbon stars. Here we present Keck I spectroscopy of seven intrinsically bright and red target stars in the outer, northern arc in M33. The target stars have estimated visual magnitudes as faint as V sim 25 mag. Absorption bands of CN are seen in all seven spectra reported here, confirming their carbon star status. In addition, we present Keck II spectra of a small area 0.5 degree away from the centre of M33; the target stars there are also identified as carbon stars. We also study the non-stellar PAH dust morphology of M33 secured using IRAC on board the Spitzer Space Telescope. The Spitzer 8 micron image attests to a change of spiral phase at the start of the HI warp. The Keck spectra confirm that carbon stars may safely be identified on the basis of their red J-K_s colours in the outer, low metallicity disk of M33. We propose that the enhanced number of carbon stars in the outer arms are an indicator of recent star formation, fueled by gas accretion from the HI-warp reservoir.
