651 research outputs found
HST ultraviolet spectral energy distributions for three ultraluminous infrared galaxies
We present HST Faint Object Camera ultraviolet (230 nm and 140 nm) images of
three ultraluminous infrared galaxies (ULIG: L_ir > 10^12 L_sun) selected from
the IRAS Revised Bright Galaxy Sample. The purpose is to estimate spectral
energy distributions (SEDs) to facilitate the identification of similar objects
at high redshift in deep optical, infrared, and submm surveys.
All three galaxies (VII Zw031 = IRAS F12112+0305, and IRAS F22491-1808) were
well detected at 230 nm. Two of the three were marginally detected at 140 nm.
The fluxes, together with ground-based optical and infrared photometry, are
used to compute SEDs over a wide wavelength range. The measured SEDs drop from
the optical to the ultraviolet, but the magnitude of the drop ranges from a
factor of ~3 in IRAS F22491-1808 to a factor of ~100 in VIIZw031. This is most
likely due to different internal extinctions. Such an interpretation is also
suggested by extrapolating to ultraviolet wavelengths the optical internal
extinction measured in VIIZw031. K-corrections are calculated to determine the
colors of the sample galaxies as seen at high redshifts. Galaxies like VIIZw031
have very low observed rest-frame UV fluxes which means that such galaxies at
high redshift will be extremely red or even missing in optical surveys. On the
other hand, galaxies like IRAS F12112+0305 and IRAS F22491-1808, if seen at
high redshift, would be sufficiently blue that they would not easily be
distinguished from normal field galaxies, and therefore, identified as ULIGs.
The implication is then that submillimeter surveys may be the only means of
properly identifying the majority of ULIGs at high redshift.Comment: AJ in press, TeX, 23 pages, 7 tab, 17 figs available also (at higher
resolution) from http://www.ast.cam.ac.uk~trentham/ufigs.htm
Weak lensing observations of the "dark" cluster MG2016+112
We investigate the possible existence of a high-redshift (z=1) cluster of
galaxies associated with the QSO lens system MG2016+112. From an ultra-deep R-
and less deep V- and I-band Keck images and a K-band mosaic from UKIRT, we
detect ten galaxies with colors consistent with the lensing galaxy within
225h^{-1} kpc of the z=1.01 lensing galaxy. This represents an overdensity of
more than ten times the number density of galaxies with similar colors in the
rest of the image. We also find a group of seven much fainter objects closely
packed in a group only 27h^{-1} kpc north-west of the lensing galaxy. We
perform a weak lensing analysis on faint galaxies in the R-band image and
detect a mass peak of a size similar to the mass inferred from X-ray
observations of the field, but located 64" northwest of the lensing galaxy.
From the weak lensing data we rule out a similar sized mass peak centered on
the lensing galaxy at the 2 sigma level.Comment: 9 pages, 10 figures, submitted to A&A version with figure 4 at higher
resolution can be downloaded from
http://www.mpa-garching.mpg.de/~clowe/mg2016aa.ps.g
Starburst-driven Starbursts in the Heart of Ultraluminous Infrared Galaxies
There is increasing evidence for the presence of blue super star clusters in
the central regions of ultraluminous infrared galaxies like Arp 220.
Ultraluminous galaxies are thought to be triggered by galaxy mergers, and it
has often been argued that these super star clusters may form during violent
collisions between gas clouds in the final phase of the mergers. We now
investigate another set of models which differ from previous ones in that the
formation of the super star clusters is linked directly to the very intense
starburst occurring at the very center of the galaxy. Firstly we show that a
scenario in which the super star clusters form in material compressed by shock
waves originating from the central starburst is implausible because the objects
so produced are much smaller than the observed star clusters in Arp 220. We
then investigate a scenario (based on the Shlosman-Noguchi model) in which the
infalling dense gas disk is unstable gravitationally and collapses to form
massive gaseous clumps. Since these clumps are exposed to the external high
pressure driven by the superwind (a blast wave driven by a collective effect of
a large number of supernovae in the very core of the galaxy), they can collapse
and then massive star formation may be induced in them. The objects produced in
this kind of collapse have properties consistent with those of the observed
super star clusters in the center of Arp 220.Comment: 13 pages, 1 figure, ApJ (Letters) in pres
New Probable Dwarf Galaxies in Northern Groups of the Local Supercluster
We have searched for nearby dwarf galaxies in 27 northern groups with
characteristic distances 8-15 Mpc based on the Second Palomar Sky Survey
prints. In a total area of about 2000 square degrees, we have found 90
low-surface-brightness objects, more than 60% of which are absent from known
catalogs and lists. We have classified most of these objects (~80%) as
irregular dwarf systems. The first 21-cm line observations of the new objects
with the 100-m Effelsberg radio telescope showed that the typical linear
diameters (1-2 kpc), internal motions (30 km/s), and hydrogen masses
(~2*10^7M_sun) galaxies correspond to those expected for the dwarf population
of nearby groups.Comment: 8 pages, 1 fugur
The cluster galaxy luminosity function at : a recent origin for the faint-end upturn ?
We derive deep luminosity functions (to ) for galaxies in Abell 1835
() and AC 114 () and compare these with the local
luminosity function for 69 clusters. The data show that the faint-end upturn,
the excess of galaxies above a single Schechter function at , does
not exist in the higher redshift clusters. This suggests that the faint-end
upturn galaxies have been created recently, by infall into clusters of
star-forming field populations or via tidal disruption of brighter objects.^MComment: 6 pages, MNRAS main journal, accepted for publicatio
A SAURON study of dwarf elliptical galaxies in the Virgo Cluster: kinematics and stellar populations
Dwarf elliptical galaxies (dEs) are the most common galaxy type in nearby
galaxy clusters; even so, many of their basic properties have yet to be
quantified. Here we present the results of our study of 4 Virgo dwarf
ellipticals obtained with the SAURON integral field unit on the William
Herschel Telescope (La Palma, Spain). While traditional long-slit observations
are likely to miss more complicated kinematic features, with SAURON we are able
to study both kinematics and stellar populations in two dimensions, obtaining a
much more detailed view of the mass distribution and star formation histories.
What is visible even in such a small sample is that dEs are not a uniform
group, not only morphologically, but also as far as their kinematic and stellar
population properties are concerned. We find the presence of substructures,
varying degrees of flattening and of rotation, as well as differences in age
and metallicity gradients. We confirm that two of our galaxies are
significantly flattened, yet non-rotating objects, which makes them likely
triaxial systems. The comparison between the dwarf and the giant groups shows
that dEs could be a low-mass extension of Es in the sense that they do seem to
follow the same trends with mass. However, dEs as progenitors of Es seem less
likely as we have seen that dEs have much lower abundance ratios.Comment: 8 pages, 6 figures; to appear in the proceedings of the JENAM 2010
Symposium on Dwarf Galaxies (Lisbon, September 9-10, 2010); minor edits and
references adde
Weak Lensing by High-Redshift Clusters of Galaxies II: Mean Redshift of the Faint Background Galaxy Population
We use weak lensing shear measurements of six z>0.5 clusters of galaxies to
derive the mean lensing redshift of the background galaxies used to measure the
shear. Five of these clusters are compared to X-ray mass models and verify a
mean lensing redshift for a 23<R<26.3, R-I<0.9 background galaxy population in
good agreement with photometric redshift surveys of the HDF-S. The lensing
strength of the six clusters is also analyzed as a function of the magnitude of
the background galaxies, and an increase in shear with increasing magnitude is
detected at moderate significance. The change in the strength of the shear is
presumed to be caused by an increase in the mean redshift of the background
galaxies with increasing magnitude, and the degree of change detected is also
in agreement with those in photometric redshift surveys of the HDF-S.Comment: 6 pages, 4 figures, accepted by A&
Photometric Properties of the Arp 220 Super Star Clusters
We investigate the photometric properties of six super stellar clusters
(SSCs) seen in both the optical and near-infrared Hubble Space Telescope images
of the local ultraluminous starburst galaxy Arp 220. Three of the SSCs are
located in the central 0.5 kpc region. The remaining three are in the
circumnuclear region between 0.5 kpc and 2.5 kpc from the centre. Comparing the
observed spectral energy distributions (SEDs) of the SSCs with the Starburst99
models of Leitherer et al., we confirm that all the three nuclear SSCs are
heavily obscured ( mag). Considering the results from this
comparison in conjunction with measurements of the near-infrared CO absorption
index and of millimetre CO line widths and luminosities, we estimate the ages
of the nuclear SSCs to be yrs. The bolometric luminosity of the
three nuclear SSCs is at most one-fifth of the total bolometric luminosity of
Arp 220. On the other hand, the circumnuclear SSCs have little internal
extinction ( 1 mag). These contribute negligibly to the total
bolometric luminosity.Comment: 8 pages, 5 figures. Accepted for publication in MNRA
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