75 research outputs found
Plan beta: Core or Cusp?
The inner profile of Dark Matter (DM) halos remains one of the central
problems in small-scale cosmology. At present, the problem can not be resolved
in dwarf spheroidal galaxies due to a degeneracy between the DM profile and the
velocity anisotropy beta of the stellar population. We discuss a method which
can break the degeneracy by exploiting 3D positions and 1D line-of-sight (LOS)
velocities. With the full 3D spatial information, we can determine precisely
what fraction of each stars LOS motion is in the radial and tangential
direction. This enables us to infer the anisotropy parameter beta directly from
the data. The method is particularly effective if the galaxy is highly
anisotropic. Finally, we argue that such a test could be applied to Sagittarius
and potentially other dwarfs with RR Lyrae providing the necessary depth
information.Comment: 10 pages, 3 figures Accepted in MNRAS. Extended introduction to match
accepted version. Main conclusions unchange
The black holes of radio galaxies during the "Quasar Era": Masses, accretion rates, and evolutionary stage
We present an analysis of the AGN broad-line regions of 6 powerful radio
galaxies at z>~2 (HzRGs) with rest-frame optical imaging spectroscopy obtained
at the VLT. All galaxies have luminous (L(H-alpha)=few x 10^44 erg s^-1),
spatially unresolved H-alpha line emission with FWHM>= 10,000 km s^-1 at the
position of the nucleus, suggesting their AGN are powered by supermassive black
holes with masses of few x 10^9 M_sun and accretion luminosities of a few
percent of the Eddington luminosity. In two galaxies we also detect the BLRs in
H-beta, suggesting relatively low extinction of A_V~1 mag, which agrees with
constraints from X-ray observations. By relating black hole and bulge mass, we
find a possible offset towards higher black-hole masses of at most ~0.6 dex
relative to nearby galaxies at a given host mass, although each individual
galaxy is within the scatter of the local relationship. If not entirely from
systematic effects, this would then suggest that the masses of the host
galaxies have increased by at most a factor ~4 since z~2 relative to the
black-hole masses, perhaps through accretion of satellite galaxies or because
of a time lag between star formation in the host galaxy and AGN fueling. We
also compare the radiative and mechanical energy output (from jets) of our
targets with predictions of recent models of "synthesis" or "grand unified" AGN
feedback, which postulate that AGN with similar radiative and mechanical energy
output rates to those found in our HzRGs may be nearing the end of their period
of active growth. We discuss evidence that they may reach this stage at the
same time as their host galaxies.Comment: A&A in pres
Dense gas without star formation: The kpc-sized molecular disk in 3C326 N
We report the discovery of a 3 kpc disk of few 10^9 Ms of dense, warm H_2 in
the nearby radio galaxy 3C326 N, which shows no signs of on-going or recent
star formation and falls a factor 60 below the Schmidt-Kennicutt law.
VLT/SINFONI imaging spectroscopy shows broad (FWHM \sim 500 km/s)
ro-vibrational H_2 lines across all of the disk, with irregular profiles and
line ratios consistent with shocks. The ratio of turbulent and gravitational
energy suggests that the gas is highly turbulent and not gravitationally bound.
In absence of the driving by the jet, short turbulent dissipation times suggest
the gas should collapse rapidly and form stars, at odds with the recent
star-formation history. Motivated by hydrodynamic models of rapid H_2 formation
boosted by turbulent compression, we propose that the molecules formed from
diffuse atomic gas in the turbulent jet cocoon. Since the gas is not
self-gravitating, it cannot form molecular clouds or stars while the jet is
active, and is likely to disperse and become atomic again after the nuclear
activity ceases. We speculate that very low star-formation rates are to be
expected under such conditions, provided that the large-scale turbulence sets
the gas dynamics in molecular clouds. Our results illustrate that jets may
create large molecular reservoirs as expected in 'positive feedback' scenarios
of AGN-triggered star formation, but that this alone is not sufficient to
trigger star formation.Comment: A&A accepte
VLT/XSHOOTER and Subaru/MOIRCS spectroscopy of HUDF.YD3: no evidence for Lyman emission at z = 8.55
We present spectroscopic observations with VLT/XSHOOTER and Subaru/MOIRCS of a relatively bright Y-band drop-out galaxy in the Hubble Ultra Deep Field (HUDF), first selected by Bunker et al., McLure et al. and Bouwens et al. to be a likely z â 8â9 galaxy on the basis of its colours in the Hubble Space Telescope (HST) Advanced Camera for Surveys and Wide Field Camera 3 images. This galaxy, HUDF.YD3 (also known as UDFy-38135539), has been targetted for VLT/SINFONI integral field spectroscopy by Lehnert et al., who published a candidate Lyman α emission line at z = 8.55 from this source. In our independent spectroscopy using two different infrared spectrographs (5âh with VLT/XSHOOTER and 11âh with Subaru/MOIRCS), we are unable to reproduce this line. We do not detect any emission line at the spectral and spatial location reported in Lehnert et al., despite the expected signal in our combined MOIRCS and XSHOOTER data being 5Ï. The line emission also seems to be ruled out by the faintness of this object in recently extremely deep F105W (Y band) HST/WFCâ3 imaging from HUDF12; the line would fall within this filter and such a galaxy should have been detected at YAB = 28.6âmag (âŒ20Ï) rather than the marginal YAB â 30âmag observed in the Y-band image, >3 times fainter than would be expected if the emission line was real. Hence, it appears highly unlikely that the reported Lyman α line emission at z > 8 is real, meaning that the highest redshift sources for which Lyman α emission has been seen are at z = 6.9-7.2. It is conceivable that Lyman α does not escape galaxies at higher redshifts, where the GunnâPeterson absorption renders the Universe optically thick to this line. However, deeper spectroscopy on a larger sample of candidate z > 7 galaxies will be needed to test this
An H-alpha survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies II. The H-alpha survey atlas and catalog
In this second paper on the investigation of extraplanar diffuse ionized gas
in nearby edge-on spiral galaxies we present the actual results of the
individual galaxies of our H-alpha imaging survey. A grand total of 74 galaxies
have been studied, including the 9 galaxies of a recently studied sub-sample
(Rossa & Dettmar 2000). 40.5% of all studied galaxies reveal extraplanar
diffuse ionized gas, whereas in 59.5% of the survey galaxies no extraplanar
diffuse ionized gas could be detected. The average distances of this extended
emission above the galactic midplane range from 1-2 kpc, while individual
filaments in a few galaxies reach distances of up to |z| ~ 6 kpc. In several
cases a pervasive layer of ionized gas was detected, similar to the Reynolds
layer in our Milky Way, while other galaxies reveal only extended emission
locally. The morphology of the diffuse ionized gas is discussed for each galaxy
and is compared with observations of other important ISM constituents in the
context of the disk-halo connection, in those cases where published results
were available. Furthermore, we present the distribution of extraplanar dust in
these galaxies, based on an analysis of the unsharp-masked R-band images. The
results are compared with the distribution of the diffuse ionized gas.Comment: LaTeX, 21 pages, 7 figures, accepted for publication in A&A, figs.
22-54 are only available in electronic form and figs. 2-11 + 17-20 are also
available at http://www.astro.rub.de/jrossa/ha-surve
An OSIRIS study of the gas kinematics in a sample of UV-selected galaxies: Evidence of "Hot and Bothered" starbursts in the local Universe
We present data from Integral Field Spectroscopy for 3 supercompact
UV-Luminous Galaxies (ScUVLGs). As nearby (z~0.2), compact (R_50~1-2 kpc),
bright Paschen-alpha sources, with unusually high star formation rates
(SFR=3-100 M_sun/yr), ScUVLGs are an ideal population for studying detailed
kinematics and dynamics in actively star-forming galaxies. In addition, ScUVLGs
appear to be excellent analogs to high redshift Lyman Break Galaxies (LBGs) and
our results may offer additional insight into the dynamics of LBGs. Previous
work by our team has shown that the morphologies of these galaxies exhibit
tidal features and companions, and in this study we find that the dynamics of
ScUVLGs are dominated by disturbed kinematics of the emission line gas--
suggestive that these galaxies have undergone recent feedback, interactions or
mergers. While 2 of the 3 galaxies do display rotation, v/sigma < 1 --
suggesting dispersion dominated kinematics rather than smooth rotation. We also
simulate how these observations would appear at z~2. Lower resolution and loss
of low surface brightness features causes some apparent discrepancies between
the low-z (observed) and high-z (simulated) interpretations and quantitatively
gives different values for v/sigma, yet simulations of these low-z analogs
manage to detect the brightest regions well and resemble actual high-z
observations of LBGs.Comment: 4 pages, 4 figures (bitmapped), accepted for publication in ApJ
Experimental Constraint on Axionlike Particles over Seven Orders of Magnitude in Mass
We use our recent electric dipole moment (EDM) measurement data to constrain the possibility that the HfF+ EDM oscillates in time due to interactions with candidate dark matter axionlike particles (ALPs). We employ a Bayesian analysis method which accounts for both the look-elsewhere effect and the uncertainties associated with stochastic density fluctuations in the ALP field. We find no evidence of an oscillating EDM over a range spanning from 27 nHz to 400 mHz, and we use this result to constrain the ALP-gluon coupling over the mass range 10-22-10-15 eV. This is the first laboratory constraint on the ALP-gluon coupling in the 10-17-10-15 eV range, and the first laboratory constraint to properly account for the stochastic nature of the ALP field
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