683 research outputs found
Nuclear Cusps and Cores in Early-type Galaxies As Relics of Binary Black Hole Mergers
We present an analysis of the central cusp slopes and core parameters of
early-type galaxies using a large database of surface brightness profiles
obtained from Hubble Space Telescope observations. We examine the relation
between the central cusp slopes, core parameters, and black hole masses in
early-type galaxies, in light of two models that attempt to explain the
formation of cores and density cusps via the dynamical influence of black
holes. Contrary to the expectations from adiabatic-growth models, we find that
the cusp slopes do not steepen with increasing black hole mass fraction.
Moreover, a comparison of kinematic black hole mass measurements with the
masses predicted by the adiabatic models shows that they overpredict the masses
by a factor of approximately 3. Simulations involving binary black hole mergers
predict that both the size of the core and the central mass deficit correlate
with the final black hole mass. These relations are qualitatively supported by
the present data.Comment: To appear in ApJ. 8 page
Magellan Spectroscopy of the Galaxy Cluster RX J1347.5-1145: Redshift Estimates for the Gravitationally Lensed Arcs
We present imaging and spectroscopic observations of the gravitationally
lensed arcs in the field of RX J1347.5-1145, the most X-ray luminous galaxy
cluster known. Based on the detection of the [OII] 3727 emission line, we
confirm that the redshift of one of the arcs is z = 0.806. Its color and [OII]
line strength are consistent with those of distant, actively star forming
galaxies. In a second arc, we tentatively identify a pair of absorption lines
superposed on a red continuum; the lines are consistent with Ca II H & K at z =
0.785. We detected a faint blue continuum in two additional arcs, but no
spectral line features could be measured. We establish lower limits to their
redshifts based on the absence of [OII] emission, which we argue should be
present and detectable in these objects. Redshifts are also given for a number
of galaxies in the field of the cluster.Comment: To appear in The Astrophysical Journal (September 2002). 6 page
Abundances of CNO elements in z ~ 0.3-0.4 LyC leaking galaxies
We present observations with the Space Telescope Imaging Spectrograph (STIS)
onboard the Hubble Space Telescope of eleven Lyman continuum (LyC) leaking
galaxies at redshifts, z, in the range 0.29-0.43, with oxygen abundances
12+log(O/H)=7.64-8.16, stellar masses Mstar~10^7.8-10^9.8 Msun and
O32=[OIII]5007/[OII]3727 of ~5-20, aiming to detect CIII]1908 emission line. We
combine these observations with the optical Sloan Digital Sky Survey (SDSS)
spectra for the determination of carbon, nitrogen and oxygen abundances. Our
sample was supplemented by thirty one galaxies from the literature, for which
carbon, nitrogen and oxygen abundances can be derived from the HST and SDSS
spectra. These additional galaxies, however, do not have LyC observations. We
find that log(C/O) for the entire sample at 12+log(O/H)<8.1 does not depend on
metallicity, with a small dispersion of ~0.13 dex around the average value of ~
-0.75 dex. On the other hand, the log(N/O) in galaxies at z>0.1, including LyC
leakers, is systematically higher compared to the rest of the sample with lower
metallicity. We find that log(C/O) slightly decreases with increasing Mstar
from ~ -0.65 at Mstar=10^6 Msun to ~ -0.80 at Mstar=10^9-10^10 Msun, whereas
log(N/O) is considerably enhanced at Mstar>10^8 Msun. The origin of these
trends remains basically unknown. One of the possible solutions is to assume
that the upper mass limit of the stellar initial mass function (IMF) in more
massive galaxies is higher. This would result in higher production of oxygen
and larger fraction of massive stars with stellar wind polluting interstellar
medium with nitrogen.Comment: 20 pages, 17 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56
Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we
have studied the spatially-resolved dynamics in the z=3.2 strongly lensed
galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high
surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy
(seen at a spatial resolution of about 200 pc in the source plane), whereas the
fainter ``arc'' is a more strongly magnified peripheral region of the same
galaxy at about a half-light radius, which otherwise appears to be a typical
z=3 Lyman break galaxy.
The overall shape of the position-velocity diagram resembles the ``rotation
curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected
velocities rise rapidly to 75 km/s within the core. This implies a dynamical
mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this
system the equivalent of the mass of a present-day L* bulge at the same radius
was already in place by z>=3. Approximating the circular velocity of the halo
by the measured asymptotic velocity of the rotation curve, we estimate a dark
matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with
large-scale clustering studies of Lyman break galaxies. The baryonic collapse
fraction is low compared to actively star-forming ``BX'' and low-redshift
galaxies around z=2, perhaps implying comparatively less gas infall to small
radii or efficient feedback. Even more speculatively, the high central mass
density might indicate highly dissipative gas collapse in very early stages of
galaxy evolution, in approximate agreement with what is expected for
``inside-out'' galaxy formation models.Comment: Accepted for publication in the Astrophysical Journa
Near infrared and optical morphology of the dusty galaxy NGC972
Near infrared (NIR) and optical surface photometric analyses of the dusty
galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can
be fitted with a combination of gaussian and exponential profiles,
corresponding to a starburst nucleus and a stellar disk respectively. The
exponential scale length in the B-band is 2.8 times larger than in the K-band,
which implies a central B-band optical depth as high as 11. A bulge is absent
even in the NIR bands and hence the galaxy must be of a morphological type
later than the usually adopted Sb type. Relatively low rotational velocity and
high gas content also favor a later type, probably Sd, for the galaxy. Only one
arm can be traced in the distribution of old stars; the second arm, however,
can be traced in the distribution of dust and HII regions. Data suggest a short
NIR bar, which ends inside the nuclear ring. The slowly rising nature of the
rotation curve rules out a resonance origin of the the nuclear ring. The ring
is most likely not in the plane of the galaxy, given its circular appearance in
spite of the moderately high inclination of the galaxy. The off-planar nature
of the star forming ring, the unusually high fraction (30%) of the total mass
in molecular form, the presence of a nuclear starburst and the asymmetry of
spiral arms, are probably the result of a merger with a gas-rich companion
galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical
Journal, October 199
Evidences for Tsallis non-extensivity on CMR manganites
We found, from the analysis of vs. curves of some manganese oxides
(manganites), that these systems do not follow the traditional
Maxwell-Boltzmann statistics, but the Tsallis statistics, within the
\QTR{em}{normalized} formalism. Curves were calculated within the mean field
approximation, for various ferromagnetic samples and the results were compared
to measurements of our own and to various other authors published data, chosen
at random from the literature. The agreement between the experimental data and
calculated vs. curve, where is an effective
temperature, is excellent for all the compounds. The entropic parameter, ,
correlates in a simple way with the experimental value of , irrespect
the chemical composition of the compounds, heat treatment or other details on
sample preparation. Examples include (superextensivity),
(extensivity) and (subextensivity) cases.Comment: 12 pages, 3 figure
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