503 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
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
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
A Photometric and Kinematic Study of AWM 7
We have measured redshifts and Kron-Cousins R-band magnitudes for a sample of
galaxies in the poor cluster AWM 7. We have measured redshifts for 172
galaxies; 106 of these are cluster members.
We determine the luminosity function from a photometric survey of the central
1.2 h^{-1} x 1.2 h^{-1} Mpc. The LF has a bump at the bright end and a
faint-end slope of \alpha = -1.37+-0.16, populated almost exclusively by
absorption-line galaxies.
The cluster velocity dispersion is lower in the core (\sim 530 km/s) than at
the outskirts (\sim 680 km/s), consistent with the cooling flow seen in the
X-ray. The cold core extends \sim 150 h^{-1} kpc from the cluster center. The
Kron-Cousins R-band mass-to-light ratio of the system is 650+-170 h
M_\odot/L_\odot, substantially lower than previous optical determinations, but
consistent with most previous X-ray determinations.
We adopt H_0 = 100 h km/s/Mpc throughout this paper; at the mean cluster
redshift, (5247+-76 km/s), 1 h^{-1} Mpc subtends 65\farcm5.Comment: 37 pages, LaTeX, including 12 Figures and 1 Table. Accepted for
publication in the Astronomical Journa
Barred Galaxies in the Coma Cluster
We use ACS data from the HST Treasury survey of the Coma cluster (z~0.02) to
study the properties of barred galaxies in the Coma core, the densest
environment in the nearby Universe. This study provides a complementary data
point for studies of barred galaxies as a function of redshift and environment.
From ~470 cluster members brighter than M_I = -11 mag, we select a sample of
46 disk galaxies (S0--Im) based on visual classification. The sample is
dominated by S0s for which we find an optical bar fraction of 47+/-11% through
ellipse fitting and visual inspection. Among the bars in the core of the Coma
cluster, we do not find any very large (a_bar > 2 kpc) bars. Comparison to
other studies reveals that while the optical bar fraction for S0s shows only a
modest variation across low-to-intermediate density environments (field to
intermediate-density clusters), it can be higher by up to a factor of ~2 in the
very high-density environment of the rich Coma cluster core.Comment: Proceedings of the Bash symposium, to appear in the Astronomical
Society of the Pacific Conference Series, eds. L. Stanford, L. Hao, Y. Mao,
J. Gree
The Luminosity Distribution in Galaxy Clusters: A Dwarf Population - Density Relation?
Recent work suggests that rich clusters of galaxies commonly have large
populations of dwarf (i.e. low luminosity) members, that is their luminosity
function (LF) turns up to a steep slope at the faint end. This population, or
more particularly the relative numbers of dwarfs to giants, appears to be very
similar for clusters of similar morphology, but may vary between cluster types.
We have previously suggested that dwarfs may be more common in less compact,
spiral rich clusters. Similarly we have found evidence for population gradients
across clusters, in that the dwarf population appears more spatially extended.
In the present paper we summarise the current evidence and propose, in analogy
to the well-known morphology - density relation, that what we are seeing is a
dwarf population - density relation; dwarfs are more common in lower density
environments. Finally we discuss recent semi-analytic models of galaxy
formation in the hierarchical clustering picture, which may give clues as to
the origin of our proposed relation.Comment: 9 pages, LateX (uses AASTeX aas2pp4 style file, included), with two
embedded postscript figures, also available at
http://WWW.star.bris.ac.uk/publs_preprints/preprints.html, accepted for
publication in the Astrophysical Journal Letter
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