216 research outputs found
UGC 7388: a galaxy with two tidal loops
We present the results of spectroscopic and morphological studies of the
galaxy UGC7388 with the 8.1-m Gemini North telescope. Judging by its observed
characteristics, UGC7388 is a giant late-type spiral galaxy seen almost
edge-on. The main body of the galaxy is surrounded by two faint (\mu(B) ~ 24
and \mu(B) ~ 25.5) extended (~20-30 kpc) loop-like structures. A large-scale
rotation of the brighter loop about the main galaxy has been detected. We
discuss the assumption that the tidal disruption of a relatively massive
companion is observed in the case of UGC7388. A detailed study and modeling of
the observed structure of this unique galaxy can give important information
about the influence of the absorption of massive companions on the galactic
disks and about the structure of the dark halo around UGC7388.Comment: 8 pages, 5 figure
Pair Analysis of Field Galaxies from the Red-Sequence Cluster Survey
We study the evolution of the number of close companions of similar
luminosities per galaxy (Nc) by choosing a volume-limited subset of the
photometric redshift catalog from the Red-Sequence Cluster Survey (RCS-1). The
sample contains over 157,000 objects with a moderate redshift range of 0.25 < z
< 0.8 and absolute magnitude in Rc (M_Rc) < -20. This is the largest sample
used for pair evolution analysis, providing data over 9 redshift bins with
about 17,500 galaxies in each. After applying incompleteness and projection
corrections, Nc shows a clear evolution with redshift. The Nc value for the
whole sample grows with redshift as (1+z)^m, where m = 2.83 +/- 0.33 in good
agreement with N-body simulations in a LCDM cosmology. We also separate the
sample into two different absolute magnitude bins: -25 < M_Rc < -21 and -21 <
M_Rc < -20, and find that the brighter the absolute magnitude, the smaller the
m value. Furthermore, we study the evolution of the pair fraction for different
projected separation bins and different luminosities. We find that the m value
becomes smaller for larger separation, and the pair fraction for the fainter
luminosity bin has stronger evolution. We derive the major merger remnant
fraction f_rem = 0.06, which implies that about 6% of galaxies with -25 < M_Rc
< -20 have undergone major mergers since z = 0.8.Comment: ApJ, in pres
Formation of a polar-ring galaxy in a galaxy merger
We numerically investigate stellar and gas dynamics in star-forming and
dissipative galaxy mergers between two disk galaxies with specific orbital
configurations. We find that violent relaxation combined with gaseous
dissipation in galaxy merging transforms two disk galaxies into one S0 galaxy
with polar-rings: Both the central S0-like host and the polar-ring component in
a polar-ring galaxy are originally disk galaxies. We also find that morphology
of the developed polar-rings reflects both the initial orbit configuration of
galaxy merging and the initial mass ratio of the two merger progenitor disk
galaxies. Based upon these results, we discuss the origin of the fundamental
observational properties of polar-ring galaxies, such as the prevalence of S0
galaxies among polar-ring galaxies, the rarity of polar-ring galaxies among S0
galaxies, the dichotomy between narrow polar-rings and annular ones, shapes of
polar-ring warps, and an appreciably larger amount of interstellar gas in the
polar-ring component.Comment: 42 pages, 19 figures, ApJ in pres
Polar Ring Galaxies and the Tully Fisher relation: implications for the dark halo shape
We have investigated the Tully-Fisher relation for Polar Ring Galaxies
(PRGs), based on near infrared, optical and HI data available for a sample of
these peculiar objects. The total K-band luminosity, which mainly comes from
the central host galaxy, and the measured HI linewidth at 20% of the peak line
flux density, which traces the potential in the polar plane, place most polar
rings of the sample far from the Tully-Fisher relation defined for spiral
galaxies, with many PRGs showing larger HI linewidths than expected for the
observed K band luminosity. This result is confirmed by a larger sample of
objects, based on B-band data. This observational evidence may be related to
the dark halo shape and orientation in these systems, which we study by
numerical modeling of PRG formation and dynamics: the larger rotation
velocities observed in PRGs can be explained by a flattened polar halo, aligned
with the polar ring.Comment: 22 pages, 8 postscript figures, accepted for publication in
Astrophysical Journa
New photometric investigation of the double ringed galaxy ESO474-G26. Unveiling the formation scenario
We present a detailed photometric study of the peculiar double ringed galaxy
ESO474-G26. Near-Infrared (NIR) and optical data have been used, with the main
goal to constrain the formation history of ESO474-G26. NIR photometry is
fundamental in this kind of study, because gives better constraints on the
Spectral Energy Distribution (SED) and well traces the older stellar population
of the galaxy. This galaxy presents a very complex structure, with two almost
orthogonal rings, one in the equatorial and another in the polar plane, around
an elliptical-like object. Due to the peculiar morphology of ESO474-G26, we
used both NIR images (J and K bands) to derive accurate analysis of the stellar
light distribution, and optical images (in the B, V and R bands) to derive
color profiles and color maps to study the structure of the rings. The
observational characteristic of ESO474-G26 are typical of galaxies which have
experienced some kind of interactions during their evolution. We investigated
two alternatives: a merging process and an accretion event.Comment: 19 pages, 20 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
The line-of-sight warp of the spiral galaxy ESO 123-G23
We present 3-D modelling of the distribution and kinematics of the neutral
hydrogen in the spiral galaxy ESO 123-G23. The optical appearance of this
galaxy is an almost perfectly edge-on disk, while the neutral hydrogen is found
to extend vertically out to about 15 kpc on either side of the galactic plane.
The HI layer and the major features of the HI data cube can be successfully
explained by a model dominated by a strong (about 30 degrees) line-of-sight
warp. Other models were tried, including a flare model and a two-component
model, but they clearly do not reproduce the data. This is the first
unambiguous detection of a galactic warp that has the maximum deviation from
the central plane almost along the line-of-sight. No evidence for the presence
of any companion galaxy is found in the HI data cube. Line-of-sight warps in
edge-on galaxies are probably frequent, but escape detection as they are too
weak. Moreover they may easily be mistaken as flares or 'thick disks'. A 3-D
modelling of the HI layer as the one presented here is needed in order to
distinguish between these possibilities.Comment: 5 pages, 5 figures, accepted by A&
Optical Imaging and Spectroscopy of the Edge-On Sbc Galaxy UGC10043: Evidence for a Galactic Wind and a Peculiar Triaxial Bulge
We present new optical imaging and spectroscopy of the peculiar, edge-on Sbc
galaxy UGC10043. B & R imaging reveals that the inner bulge of UGC10043 is
elongated perpendicular to the major axis. At larger r, the bulge isophotes
twist to become oblate and nearly circular, suggesting the bulge is triaxial.
Based on stellar and ionized gas kinematics, the bulge shows no clear evidence
for rotation about either its major or minor axis. The southwestern quadrant of
the bulge is girdled by a narrow dust lane parallel to the minor axis that may
be part of an inner polar ring. The stellar disk of UGC10043 has a low optical
surface brightness, a small scale height, a mild integral sign warp, and a
dusty, inner region that appears tilted relative to the outlying disk. The HA
and [NII] emission lines in UGC10043 resolve into multiple velocity components,
indicating the presence of a large-scale galactic wind with an outflow velocity
of ~104 km/s. HA+[NII] imaging reaffirms this picture by revealing ionized gas
extended to |z|~3.5kpc in a biconical structure. The [NII]/HA line intensity
ratio increases with increasing distance from the plane, reaching values as
high as 1.7. Unlike most galaxies with large-scale winds, UGC10043 has only a
modest global star formation rate (~1M_sun/yr), implying the wind is powered by
a rather feeble central starburst. We discuss evolutionary scenarios that could
account for both the structural complexities of UGC10043 and its large-scale
wind. [Abridged]Comment: accepted to the Astronomical Journal (July 2004); version with
full-resolution and color figures available at
http://cfa-www.harvard.edu/~lmatthe
Gemini Deep Deep Survey VI: Massive Hdelta-strong galaxies at z=1
We show that there has been a dramatic decline in the abundance of massive
galaxies with strong Hdelta stellar absorption lines from z=1.2 to the present.
These ``Hdelta-strong'', or HDS, galaxies have undergone a recent and rapid
break in their star-formation activity. Combining data from the Gemini Deep
Deep and the Sloan Digital Sky Surveys to make mass-matched samples
(M*>=10^10.2 Msun), with 25 and 50,255 galaxies, respectively), we find that
the fraction of galaxies in an HDS phase has decreased from about 50% at z=1.2
to a few percent today. This decrease in fraction is due to an actual decrease
in the number density of massive HDS systems by a factor of 2-4, coupled with
an increase in the number density of massive galaxies by about 30 percent. We
show that this result depends only weakly on the threshold chosen for the
Hdelta equivalent width to define HDS systems (if greater than 4 A) and
corresponds to a (1+z)^{2.5\pm 0.7} evolution. Spectral synthesis studies of
the high-redshift population using the PEGASE code, treating Hdelta_A, EW[OII],
Dn4000, and rest-frame colors, favor models in which the Balmer absorption
features in massive Hdelta-strong systems are the echoes of intense episodes of
star-formation that faded about 1 Gyr prior to the epoch of observation. The
z=1.4-2 epoch appears to correspond to a time at which massive galaxies are in
transition from a mode of sustained star formation to a relatively quiescent
mode with weak and rare star-formation episodes. We argue that the most likely
local descendants of the distant massive HDS galaxies are passively evolving
massive galaxies in the field and small groups.Comment: 16 pages, 12 figures, 3 tables, uses emulateapj.sty; updated to match
the version accepted by ApJ. One figure added, conclusions unchange
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