128 research outputs found
Two channels of supermassive black hole growth as seen on the galaxies mass-size plane
We investigate the variation of black hole masses (Mbh) as a function of
their host galaxy stellar mass (Mstar) and half-light radius (Re). We confirm
that the scatter in Mbh within this plane is essentially the same as that in
the Mbh - sigma relation, as expected from the negligible scatter reported in
the virial mass estimator sigma_v^2=GxMstar/(5xRe). All variation in Mbh
happens along lines of constant sigma_v on the (Mstar, Re) plane, or Mstar
Re for Mstar <2x10^11 Msun. This trend is qualitatively the same as
those previously reported for galaxy properties related to stellar populations,
like age, metallicity, alpha enhancement, mass-to-light ratio and gas content.
We find evidence for a change in the Mbh variation above the critical mass of
Mcrit ~ 2x10^11 Msun. This behaviour can be explained assuming that Mbh in
galaxies less massive than Mcrit can be predicted by the Mbh - sigma relation,
while Mbh in more massive galaxies follow a modified relation which is also
dependent on Mstar once Mstar >Mcrit. This is consistent with the scenario
where the majority of galaxies grow through star formation, while the most
massive galaxies undergo a sequence of dissipation-less mergers. In both
channels black holes and galaxies grow synchronously, giving rise to the black
hole - host galaxy scaling relations, but there is no underlying single
relation that is universal across the full range of galaxy masses.Comment: 11 pages, 5 figures; MNRAS accepted (minor text changes
The origin and properties of massive prolate galaxies in the Illustris simulation
We study galaxy shapes in the Illustris cosmological hydrodynamic simulation.
We find that massive galaxies have a higher probability of being prolate. For
galaxies with stellar mass larger than , 35 out of total
839 galaxies are prolate. For 21 galaxies with stellar mass larger than
, 9 are prolate, 4 are triaxial while the others are
close to being oblate. There are almost no prolate galaxies with stellar mass
smaller than . We check the merger history of the
prolate galaxies, and find that they are formed by major dry mergers. All the
prolate galaxies have at least one such merger, with most having mass ratios
between and . The gas fraction (gas mass to total baryon mass) of
the progenitors is 0-3 percent for nearly all these mergers, except for one
whose second progenitor contains gas mass, while its main
progenitor still contains less than . For the 35 massive prolate galaxies
that we find, 18 of them have minor axis rotation, and their angular momenta
mostly come from the spin angular momenta of the progenitors (usually that of
the main progenitor). We analyse the merger orbits of these prolate galaxies
and find that most of them experienced a nearly radial merger orbit. Oblate
galaxies with major dry mergers can have either radial or circular merger
orbits. We further discuss various properties of these prolate galaxies, such
as spin parameter , spherical anisotropy parameter ,
dark matter fraction, as well as inner density slopes for the stellar, dark
matter and total mass distributions.Comment: Accepted for publication in MNRAS. 24 pages, 14 figure
MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of Sodium
Based on MUSE integral-field data we present evidence for a radial variation
at the low-mass end of the stellar initial-mass function (IMF) in the central
regions of the giant early-type galaxy NGC4486 (M87). We used state-of-the-art
stellar population models and the observed strength of various IMF-sensitive
absorption-line features to solve for the best low-mass tapered "bimodal" form
of the IMF, while accounting also for radial variations in stellar metallicity,
the overall -elements abundance, and the abundance of individual
elements such as Ti, O, Na and Ca. Our analysis reveals a strong IMF gradient
in M87, corresponding to an exceeding fraction of low-mass stars compared to
the case of the Milky Way toward the center of M87 that drops to nearly
Milky-way levels by 0.4 . This IMF gradient is found to correlate well
with both the radial profile for stellar metallicity and for -elements
abundance but not with stellar velocity dispersion. Such IMF variations
correspond to over a factor two increase in stellar mass-to-light M/L ratio
compared to the case of a Milky-way like IMF, consistent with other
investigations into IMF gradients in early-type galaxies, including recent
dynamical constraints on M/L radial variations in M87 by Oldham & Auger. In
addition to constraining the IMF in M87 we also looked into the abundance of
Sodium, which turned up to be super-Solar over the entire radial range of our
MUSE observations and to exhibit a considerable negative gradient. These
findings suggest an additional role of metallicity in boosting the Na-yields in
the central, metal-rich regions of M87 during its early and brief
star-formation history. Our work adds the case of M87 to the few objects that
as of today have radial constraints on their IMF or [Na/Fe] abundance, while
also illustrating the accuracy that MUSE could bring to this kind of
investigations.Comment: 17 pages, 13 figures, re-submitted for publication on MNRAS following
the referee's comment
The ATLAS^(3D) Project – XXIII. Angular momentum and nuclear surface brightness profiles
We investigate nuclear light profiles in 135 ATLAS^(3D) galaxies for which the Hubble Space Telescope (HST) imaging is available and compare them to the large-scale kinematics obtained with the SAURON integral-field spectrograph. Specific angular momentum, λ_R, correlates with the shape of nuclear light profiles, where, as suggested by previous studies, cores are typically found in slow rotators and core-less galaxies are fast rotators. As also shown before, cores are found only in massive galaxies and only in systems with the stellar mass (measured via dynamical models) M ≳ 8 × 10^(10) M⊙. Based on our sample, we, however, see no evidence for a bimodal distribution of nuclear slopes. The best predictor for finding a core is based on the stellar velocity dispersion within an effective radius, σ_e, and specific angular momentum, where cores are found for λ_R ≲ 0.25 and σ_e ≳ 160 km s^(−1). We estimate that only about 10 per cent of nearby early-type galaxies contain cores. Furthermore, we show that there is a genuine population of fast rotators with cores. We also show that core fast rotators are morphologically, kinematically and dynamically different from core slow rotators. The cores of fast rotators, however, could harbour black holes of similar masses to those in core slow rotators, but typically more massive than those found in core-less fast rotators. Cores of both fast and slow rotators are made of old stars and found in galaxies typically lacking molecular or atomic gas (with a few exceptions). Core-less galaxies, and especially core-less fast rotators, are underluminous in the diffuse X-ray emission, but the presence of a core does not imply high X-ray luminosities. Additionally, we postulate (as many of these galaxies lack HST imaging) a possible population of core-less galaxies among slow rotators, which cannot be explained as face-on discs, but comprise a genuine sub-population of slow rotators. These galaxies are typically less massive and flatter than core slow rotators, and show evidence for dynamical cold structures and exponential photometric components. Based on our findings, major non-dissipative (gas-poor) mergers together with black hole binary evolution may not be the only path for formation of cores in early-type galaxies. We discuss possible processes for formation of cores and their subsequent preservation
Morphology and kinematics of the ionised gas in early-type galaxies
We present results of our ongoing study of the morphology and kinematics of
the ionised gas in 48 representative nearby elliptical and lenticular galaxies
using the SAURON integral-field spectrograph on the 4.2m William Herschel
Telescope. Making use of a recently developed technique, emission is detected
in 75% of the galaxies. The ionised-gas distributions display varied
morphologies, ranging from regular gas disks to filamentary structures.
Additionally, the emission-line kinematic maps show, in general, regular
motions with smooth variations in kinematic position angle. In most of the
galaxies, the ionised-gas kinematics is decoupled from the stellar counterpart,
but only some of them present signatures of recent accretion of gaseous
material. The presence of dust is very common in our sample and is usually
accompanied by gas emission. Our analysis of the [OIII]/Hbeta emission-line
ratios, both across the whole sample as well as within the individual galaxies,
suggests that there is no unique mechanism triggering the ionisation of the
gas.Comment: 8 pages, 2 figures, submitted to "Adaptive Optics-Assisted
Integral-Field Spectroscopy", Rutten R.G.M., Benn C.R., Mendez J., eds., May
2005, La Palma (Spain), New Astr. Rev. For full resolution PS, see
http://www.strw.leidenuniv.nl/~jfalcon/JFB_AOmeeting_color_hires.ps.g
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