17 research outputs found
The life cycle of starbursting circumnuclear gas discs
High-resolution observations from the sub-mm to the optical wavelength regime
resolve the central few 100pc region of nearby galaxies in great detail. They
reveal a large diversity of features: thick gas and stellar discs, nuclear
starbursts, in- and outflows, central activity, jet interaction, etc.
Concentrating on the role circumnuclear discs play in the life cycles of
galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical
simulations with the RAMSES code to self-consistently trace the evolution from
a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the
formation of clumps and stars and the disc's subsequent, partial dispersal via
stellar feedback. Our approach builds upon the observational finding that many
nearby Seyfert galaxies have undergone intense nuclear starbursts in their
recent past and in many nearby sources star formation is concentrated in a
handful of clumps on a few 100pc distant from the galactic centre. We show that
such observations can be understood as the result of gravitational
instabilities in dense circumnuclear discs. By comparing these simulations to
available integral field unit observations of a sample of nearby galactic
nuclei, we find consistent gas and stellar masses, kinematics, star formation
and outflow properties. Important ingredients in the simulations are the
self-consistent treatment of star formation and the dynamical evolution of the
stellar distribution as well as the modelling of a delay time distribution for
the supernova feedback. The knowledge of the resulting simulated density
structure and kinematics on pc scale is vital for understanding inflow and
feedback processes towards galactic scales.Comment: accepted by MNRA
IC 630: Piercing the veil of the nuclear gas
IC 630 is a nearby early-type galaxy with a mass of 6 X 10^10 M⊙with an intense burst of recent (6 Myr) star formation. It shows strong nebular emission lines, with radio and X-ray emission, which classifies it as an AGN. With VLT-SINFONI and Gemini North-NIFS adaptive optics observations (plus supplementary ANU 2.3m WiFeS optical IFU observations), the excitation diagnostics of the nebular emission species show no sign of standard AGN engine excitation; the stellar velocity dispersion also indicate that a super-massive black hole (if one is present) is small (M• = 2:25 X 10^5 M⊙). The luminosity at all wavelengths is consistent with star formation at a rate of about 1-2 M⊙/yr. We measure gas out flows driven by star formation at a rate of 0.18 M⊙/yr in a face-on truncated cone geometry. We also observe a nuclear cluster or disk and other clusters. Photo-ionization from young, hot stars is the main excitation mechanism for [Fe II] and hydrogen, whereas shocks are responsible for the H2 excitation. Our observations are broadly comparable with simulations where a Toomre-unstable, self-gravitating gas disk triggers a burst of star formation, peaking after about 30 Myr and possibly cycling with a period of about 200 Myr
Low-mass compact elliptical galaxies: Spatially resolved stellar populations and kinematics with the Keck Cosmic Web Imager
We present spatially resolved two-dimensional maps and radial trends of the stellar populations and kinematics for a sample of six compact elliptical galaxies (cE) using spectroscopy from the Keck Cosmic Web Imager (KCWI). We recover their star formation histories, finding that all except one of our cEs are old and metal rich, with both age and metallicity decreasing toward their outer radii. We also use the integrated values within one effective radius to study different scaling relations. Comparing our cEs with others from the literature and from simulations we reveal the formation channel that these galaxies might have followed. All our cEs are fast rotators, with relatively high rotation values given their low ellipticites. In general, the properties of our cEs are very similar to those seen in the cores of more massive galaxies, and in particular, to massive compact galaxies. Five out of our six cEs are the result of stripping a more massive (compact or extended) galaxy, and only one cE is compatible with having been formed intrinsically as the low-mass compact object that we see today. These results further confirm that cEs are a mixed-bag of galaxies that can be formed following different formation channels, reporting for the first time an evolutionary link within the realm of compact galaxies (at all stellar masses).AFM has received financial support through the Postdoctoral Junior Leader Fellowship Programme from ‘la Caixa’ Banking Foundation (LCF/BQ/LI18/11630007). AFM, DAF, and RM thank the ARC for financial support via DP160101608. AJR was supported by National Science Foundation grant AST-1616710 and as a Research Corporation for Science Advancement Cottrell Scholar. AA was supported in part by NASA program HST-GO-14747, contract NNG16PJ25C, and grant 80NSSC18K0563, and NSF award 1828315. RMcD is the recipient of an Australian Research Council Future Fellowship (project number FT150100333)