1,835 research outputs found
Integral Field Spectrographs: a user's view
We easily tend to think of Integral-Field Spectrographs (IFS) along two
opposing trends: as either the beautiful combination between photometry and
spectroscopy, or as our worst nightmare including the dark side of both worlds.
I favour a view where each IFS is considered individually, as one instrument
with specific performances which can be used optimally for a certain range of
scientific programs. It is indeed true that data-wise, IFS do sometime merge
the characteristics of classic (e.g., long-slit) spectrographs with annoying
issues associated with Imagers. This is in fact the price to pay to access a
drastically different perspective of our favourite targets. The challenge is
then to provide the necessary tools to properly handle the corresponding data.
However, this should certainly not be thought as something specific to IFS:
such a challenge should be accepted for any instrument, and most importantly
solved prior to its delivery at the telescope.Comment: 6 pages, 2 figures. Invited talk, to appear in the Proceedings of
"The 2007 ESO Instrument Calibration Workshop", ESO Astrophysics Symposia,
Springe
Systematic trends in total-mass profiles from dynamical models of early-type galaxies
We study trends in the slope of the total mass profiles and dark matter
fractions within the central half-light radius of 258 early-type galaxies,
using data from the volume-limited ATLAS survey. We use three
distinct sets of dynamical models, which vary in their assumptions and also
allow for spatial variations in the stellar mass-to-light ratio, to test the
robustness of our results. We confirm that the slopes of the total mass
profiles are approximately isothermal, and investigate how the total-mass slope
depends on various galactic properties. The most statistically-significant
correlations we find are a function of either surface density, , or
velocity dispersion, . However there is evidence for a break in the
latter relation, with a nearly universal logarithmic slope above
\log_{10}[\sigma_e/(\si{km~s^{-1}})]\sim 2.1 and a steeper trend below this
value. For the 142 galaxies above that critical value, the total
mass-density logarithmic slopes have a mean value
(
error) with an observed rms scatter of only . Considering the observational errors, we estimate an intrinsic scatter
of . These values are
broadly consistent with those found by strong lensing studies at similar radii
and agree, within the tight errors, with values recently found at much larger
radii via stellar dynamics or HI rotation curves (using significantly smaller
samples than this work).Comment: 17 pages, 11 figures, 3 tables. Published in MNRA
Structure and Kinematics of Molecular Disks in Fast-Rotator Early-Type Galaxies
We present interferometric observations resolving the CO emission in the four
gas-rich lenticular galaxies NGC 3032, NGC 4150, NGC 4459, and NGC 4526, and we
compare the CO distribution and kinematics to those of the stars and ionized
gas. Counterrotation documents an external origin for the gas in at least one
case (NGC 3032), and the comparisons to stellar and ionized gas substructures
in all four galaxies offer insights into their formation histories. The
molecular gas is found in kpc-scale disks with mostly regular kinematics and
average surface densities of 100 to 200 \msunsqpc. The disks are well aligned
with the stellar photometric and kinematic axes. In the two more luminous Virgo
Cluster members NGC 4459 and NGC 4526 the molecular gas shows excellent
agreement with circular velocities derived independently from detailed modeling
of stellar kinematic data. There are also two puzzling instances of
disagreements between stellar kinematics and gas kinematics on sub-kpc scales.
In the inner arcseconds of NGC 3032 the CO velocities are significantly lower
than the inferred circular velocities, and the reasons may possibly be related
to the external origin of the gas but are not well understood. In addition, the
very young population of stars in the core of NGC 4150 appears to have the
opposite sense of rotation from the molecular gas.Comment: ApJ, accepte
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 Kinematic Properties of Double-Barred Galaxies: Simulations Vs. Integral-Field Observations
Using high resolution N -body simulations, we recently reported that a dynamically cool inner disk embedded in a hotter outer disk can naturally generate a steady double-barred (S2B) structure. Here we study the kinematics of these S2B simulations, and compare them to integral-field observations from ATLAS3D and SAURON. We show that S2B galaxies exhibit several distinct kinematic features, namely:
(1) significantly distorted isovelocity contours at the transition region between the two bars, (2) peaks in σLOS along the minor axis of inner bars, which we term “σ-humps”, that are often accompanied by
ring/spiral-like features of increased σLOS, (3) h3 − v¯ anti-correlations in the region of the inner bar for
certain orientations, and (4) rings of positive h4 when viewed at low inclinations. The most impressive of these features are the σ-humps; these evolve with the inner bar, oscillating in strength just as the inner bar does as it rotates relative to the outer bar. We show that, in cylindrical coordinates, the inner bar has similar streaming motions and velocity dispersion properties as normal large-scale bars, except for σz , which exhibits peaks on the minor axis, i.e., humps. These σz humps are responsible for producing the σ-humps. For three well-resolved early-type S2Bs (NGC 2859, NGC 2950, and NGC 3941) and a potential S2B candidate (NGC 3384), the S2B model qualitatively matches the integral-field data well, including the “σ-hollows” previously identified. We also discuss the kinematic effect of a nuclear disk in S2Bs
VLT Diffraction Limited Imaging and Spectroscopy in the NIR: Weighing the black hole in Centaurus A with NACO
We present high spatial resolution near-infrared spectra and images of the
nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The
adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K-
and 0.11" in H-band, four times higher than previous studies. The observed gas
motions suggest a kinematically hot disk which is orbiting a central object and
is oriented nearly perpendicular to the nuclear jet. We model the central
rotation and velocity dispersion curves of the [FeII] gas orbiting in the
combined potential of the stellar mass and the (dominant) black hole. Our
physically most plausible model, a dynamically hot and geometrically thin gas
disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the
physical state of the gas is not well understood, we also consider two limiting
cases: first a cold disk model, which completely neglects the velocity
dispersion; it yields an M_bh estimate that is almost two times lower. The
other extreme case is to model a spherical gas distribution in hydrostatic
equilibrium through Jeans equation. Compared to the hot disk model the best-fit
black hole mass increases by a factor of 1.5. This wide mass range spanned by
the limiting cases shows how important the gas physics is even for high
resolution data. Our overall best-fitting black hole mass is a factor of 2-4
lower than previous measurements. With our revised M_bh estimate, Cen A's
offset from the M_bh-sigma relation is significantly reduced; it falls above
this relation by a factor of ~2, which is close to the intrinsic scatter of
this relation. (Abridged)Comment: 12 pages, 14 figures, including minor changes following the referee
report; accepted for publication in The Astrophysical Journa
Systematic Uncertainties in Stellar Mass Estimation for Distinct Galaxy Populations
We show that different stellar-mass estimation methods yield overall mass
scales that disagree by factors up to ~2 for the z=0 galaxy population, and
more importantly, relative mass scales that sometimes disagree by factors >~3
between distinct classes of galaxies (spiral/irregular types, classical E/S0s,
and E/S0s whose colors reflect recent star formation). This comparison
considers stellar mass estimates based on (a) two different calibrations of the
correlation between K-band mass-to-light ratio and B-R color (Bell et al.,
Portinari et al.) and (b) detailed fitting of UBRJHK photometry and optical
spectrophotometry using two different population synthesis models
(Bruzual-Charlot, Maraston), with the same initial mass function in all cases.
We also compare stellar+gas masses with dynamical masses. This analysis offers
only weak arguments for preferring a particular stellar-mass estimation method,
given the plausibility of real variations in dynamical properties and dark
matter content. These results help to calibrate the systematic uncertainties
inherent in mass-based evolutionary studies of galaxies, including comparisons
of low and high redshift galaxies.Comment: 5 pages including 2 enlarged figures, ApJ Letters, accepte
The Quest for the Dominant Stellar Population in the Giant Elliptical NGC 5018
Newly obtained HST/WFPC2 images of the disturbed elliptical galaxy NGC 5018
show that the average amount of internal reddening due to the its complex
``dust web'' is as low as E(B-V)~0.02 within the IUE aperture, thus implying
that its observed and intrinsic energy distributions do not differ
significantly down to UV wavelengths. This, in turn, is quite relevant to the
current debate on the age of its dominant stellar population.Comment: 2 pages, 1 figure. Proceedings of the conference "Galaxy Disks and
Disk Galaxies", ASP Conference Series, eds. J.G. Funes, S.J. and E.M. Corsin
Measuring the low mass end of the Mbh - sigma relation
We show that high quality laser guide star (LGS) adaptive optics (AO)
observations of nearby early-type galaxies are possible when the tip-tilt
correction is done by guiding on nuclei while the focus compensation due to the
changing distance to the sodium layer is made 'open loop'. We achieve
corrections such that 40% of flux comes from R<0.2 arcsec. To measure a black
hole mass (Mbh) one needs integral field observations of both high spatial
resolution and large field of view. With these data it is possible to determine
the lower limit to Mbh even if the spatial resolution of the observations are
up to a few times larger than the sphere of influence of the black hole.Comment: 4 pages, 2 figures, LaTeX. To appear in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista and C.C. Popescu, AIP Conf. Ser., in pres
Monster black holes
A combination of ground-based and spacecraft observations has uncovered two
black holes of 10 billion solar masses in the nearby Universe. The finding
sheds light on how these cosmic monsters co-evolve with galaxies.Comment: 2 pages, 1 figure, LaTeX. Published in Nature "News & Views
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