1,219 research outputs found
The Tully-Fisher relation of distant field galaxies
We examine the evolution of the Tully-Fisher relation (TFR) using a sample of
89 field spirals, with 0.1 < z < 1, for which we have measured confident
rotation velocities (Vrot). By plotting the residuals from the local TFR versus
redshift, or alternatively fitting the TFR to our data in several redshift
bins, we find evidence that luminous spiral galaxies are increasingly offset
from the local TFR with redshift, reaching a brightening of -1.0+-0.5 mag, for
a given Vrot, by approximately z = 1. Since selection effects would generally
increase the fraction of intrinsically-bright galaxies at higher redshifts, we
argue that the observed evolution is probably an upper limit.
Previous studies have used an observed correlation between the TFR residuals
and Vrot to argue that low mass galaxies have evolved significantly more than
those with higher mass. However, we demonstrate that such a correlation may
exist purely due to an intrinsic coupling between the Vrot scatter and TFR
residuals, acting in combination with the TFR scatter and restrictions on the
magnitude range of the data, and therefore it does not necessarily indicate a
physical difference in the evolution of galaxies with different Vrot.
Finally, if we interpret the luminosity evolution derived from the TFR as due
to the evolution of the star formation rate (SFR) in these luminous spiral
galaxies, we find that SFR(z) is proportional to (1+z)^(1.7+-1.1), slower than
commonly derived for the overall field galaxy population. This suggests that
the rapid evolution in the SFR density of the universe observed since
approximately z = 1 is not driven by the evolution of the SFR in individual
bright spiral galaxies. (Abridged.)Comment: 14 pages, 10 figures, accepted by MNRA
Star formation rates and chemical abundances of emission line galaxies in intermediate-redshift clusters
We examine the evolutionary status of luminous, star-forming galaxies in
intermediate-redshift clusters by considering their star formation rates and
the chemical and ionsiation properties of their interstellar emitting gas. Our
sample consists of 17 massive, star-forming, mostly disk galaxies with
M_{B}<-20, in clusters with redshifts in the range 0.31< z <0.59, with a median
of =0.42. We compare these galaxies with the identically selected and
analysed intermediate-redshift field sample of Mouhcine et al. (2006), and with
local galaxies from the Nearby Field Galaxy Survey of Jansen et al. (2000).
From our optical spectra we measure the equivalent widths of OII, Hbeta and
OIII emission lines to determine diagnostic line ratios, oxygen abundances, and
extinction-corrected star formation rates. The star-forming galaxies in
intermediate-redshift clusters display emission line equivalent widths which
are, on average, significantly smaller than measured for field galaxies at
comparable redshifts. However, a contrasting fraction of our cluster galaxies
have equivalent widths similar to the highest observed in the field. This
tentatively suggests a bimodality in the star-formation rates per unit
luminosity for galaxies in distant clusters. We find no evidence for further
bimodalities, or differences between our cluster and field samples, when
examining additional diagnostics and the oxygen abundances of our galaxies.
This maybe because no such differences exist, perhaps because the cluster
galaxies which still display signs of star-formation have recently arrived from
the field. In order to examine this topic with more certainty, and to further
investigate the way in which any disparity varies as a function of cluster
properties, larger spectroscopic samples are needed.Comment: 10 pages, 6 figures, MNRAS in pres
Evolution of Cluster Ellipticals at 0.2 < z < 1.2 from Hubble Space Telescope Imaging
Two-dimensional surface photometry derived from Hubble Space Telescope
imaging is presented for a sample of 225 early-type galaxies (assumed to be
cluster members) in the fields of 9 clusters at redshifts .
The 94 luminous ellipticals (; selected by morphology alone with
no reference to color) form tight sequences in the size-luminosity plane. The
position of these sequences shifts, on average, with redshift so that an object
of a given size at z=0.55 is brighter by mag than
its counterpart (measured with the same techniques) in nearby clusters. At
z=0.9 the shift is mag. If the relation between
size and luminosity is universal so that the local cluster galaxies represent
the evolutionary endpoints of those at high redshift, and if the
size-luminosity relation is not modified by dynamical processes then this
population of galaxies has undergone significant luminosity evolution since z=1
consistent with expectations based on models of passively evolving, old stellar
populations.Comment: 7 pages, 3 figures, and 1 Tabl
The Tully-Fisher relation of intermediate redshift field and cluster galaxies from Subaru spectroscopy
We have carried out spectroscopic observations in 4 cluster fields using
Subaru's FOCAS multi-slit spectrograph and obtained spectra for 103 bright disk
field and cluster galaxies at . Seventy-seven of these
show emission lines, and 33 provide reasonably-secure determinations of the
galaxies' rotation velocity. The rotation velocities, luminosities, colours and
emission-line properties of these galaxies are used to study the possible
effects of the cluster environment on the star-formation history of the
galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at
similar reshifts we find no measurable difference in rest-frame -band
luminosity at a given rotation velocity (the formal difference is mag). The colours of the cluster emission line galaxies are only marginally
redder in rest-frame (by mag) than the field galaxies in
our sample. Taken at face value, these results seem to indicate that bright
star-forming cluster spirals are similar to their field counterparts in their
star-formation properties. However, we find that the fraction of disk galaxies
with absorption-line spectra (i.e., with no current star formation) is larger
in clusters than in the field by a factor of --5. This suggests that the
cluster environment has the overall effect of switching off star formation in
(at least) some spiral galaxies. To interpret these observational results, we
carry out simulations of the possible effects of the cluster environment on the
star-formation history of disk galaxies and thus their photometric and
spectroscopic properties. Finally, we evaluate the evolution of the rest-frame
absolute -band magnitude per unit redshift at fixed rotation velocity.Comment: 21 pages, 13 figures, accepted for publication in MNRA
The Molecular Gas in the Circumnuclear Region of Seyfert Galaxies
Sub-arcsecond IRAM Plateau de Bure mm-interferometric observations of the
12CO (2-1) line emission in the Seyfert~1 NGC 3227 and the Seyfert~2 NGC 1068
have revealed complex kinematic systems in the inner 100 pc to 300 pc that are
not consistent with pure circular motion in the host galaxies. Modeling of
these kinematic systems with elliptical orbits in the plane of the host galaxy
(representing gas motion in a bar potential) is a possible solution but does
not reproduce all features observed. A better description of the complex
kinematics is achieved by circular orbits which are tilted out of the plane of
the host galaxy. This could indicate that the thin circumnuclear gas disk is
warped. In the case of NGC 1068 the warp model suggests that at a radius of
about 70 pc, the gas disk is oriented edge-on providing material for the
obscuration of the AGN nucleus. The position-velocity diagrams show rising
rotation curves at r 2
x 10^7 M_solar for NGC 3227 and > 10^8 M_solar for NGC 1068 within the central
25 pc.Comment: 14 pages, Ap.J. letter, accepte
The First VLT FORS1 spectra of Lyman-break candidates in the HDF-S and AXAF Deep Field
We report on low-resolution multi-object spectroscopy of 30 faint targets (R
\~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal
Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with
2.75< z < 4 have been identified. The spectroscopic redshifts are in good
agreement with the photometric ones with a dispersion at z<2
and at z>2. The inferred star formation rates of the
individual objects are moderate, ranging from a few to a few tens solar masses
per year. Five out of the eight high-z objects do not show prominent emission
lines. One object has a spectrum typical of an AGN. In the AXAF field two
relatively close pairs of galaxies have been identified, with separations of
8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.Comment: 5 pages Latex, with 2 PostScript figures. Astronomy and Astrophysics,
in pres
Variability of Fe II Emission Features in the Seyfert 1 Galaxy NGC 5548
We study the low-contrast Fe II emission blends in the ultraviolet
(1250--2200A) and optical (4000--6000A) spectra of the Seyfert 1 galaxy NGC
5548 and show that these features vary in flux and that these variations are
correlated with those of the optical continuum. The amplitude of variability of
the optical Fe II emission is 50% - 75% that of Hbeta and the ultraviolet Fe II
emission varies with an even larger amplitude than Hbeta. However, accurate
measurement of the flux in these blends proves to be very difficult even using
excellent Fe II templates to fit the spectra. We are able to constrain only
weakly the optical Fe II emission-line response timescale to a value less than
several weeks; this upper limit exceeds all the reliably measured emission-line
lags in this source so it is not particularly meaningful. Nevertheless, the
fact that the optical Fe II and continuum flux variations are correlated
indicates that line fluorescence in a photoionized plasma, rather than
collisional excitation, is responsible for the Fe II emission. The iron
emission templates are available upon request.Comment: 34 pages including 12 figures and 2 tables. Accepted for publication
by ApJ (tentatively in vol. 626 June 10, 2005
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