2,876 research outputs found
The Nature of the Peculiar Virgo Cluster Galaxies NGC 4064 and NGC 4424
We present a detailed study of the peculiar HI-deficient Virgo cluster spiral
galaxies NGC 4064 and NGC 4424, using CO 1-0 interferometry, optical
imaging and integral-field spectroscopic observations, in order to learn what
type of environmental interactions have afected these galaxies. Optical imaging
reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped
isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses
a relatively undisturbed outer stellar disk and a central bar. In both galaxies
H-alpha emission is confined to the central kiloparsec. CO observations reveal
bilobal molecular gas morphologies, with H-alpha emission peaking inside the CO
lobes, implying a time sequence in the star formation process.Gas kinematics
reveals strong bar-like non-circular motions in the molecular gas in both
galaxies, suggesting that the material is radially infalling. In NGC 4064 the
stellar kinematics reveal strong bar-like non-circular motions in the central 1
kpc. On the other hand, NGC 4424 has extremely modest stellar rotation
velocities (Vmax ~ 30 km s-1), and stars are supported by random motions as far
out as we can measure it. The observations suggest that the peculiarities of
NGC 4424 are the result of an intermediate-mass merger plus ram pressure
stripping. In the case of NGC 4064, the evidence suggests an already stripped
"truncated/normal" galaxy that recently suffered a minor merger or tidal
interaction with another galaxy. We propose that galaxies with
"truncated/compact" H-alpha morphologies such as these are the result of the
independent effects of ram pressure stripping, which removes gas from the outer
disk, and gravitational interactions such as mergers, which heat stellar disks,
drive gas to the central kpc and increase the central mass concentrations.Comment: 42 pages, 21 figure
The Trouble with Hubble Types in the Virgo Cluster
Quantitative measures of central light concentration and star formation
activity are derived from R and Halpha surface photometry of 84 bright S0-Scd
Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a
good correlation between these two parameters and assigned Hubble types. In the
Virgo Cluster, the correlation between central light concentration and star
formation activity is significantly weaker. Virgo Cluster spirals have
systematically reduced global star formation with respect to isolated spirals,
with severe reduction in the outer disk, but normal or enhanced activity in the
inner disk. Assigned Hubble types are thus inadequate to describe the range in
morphologies of bright Virgo Cluster spirals. In particular, spirals with
reduced global star formation activity are often assigned misleading early-type
classifications, irrespective of their central light concentrations. 45+-25% of
the galaxies classified as Sa in the Virgo Cluster sample have central light
concentrations more characteristic of isolated Sb-Sc galaxies. The misleading
classification of low concentration galaxies with low star formation rates as
early-type spirals may account for part of the excess of `early-type' spiral
galaxies in clusters. Thus the morphology-density relationship is not all due
to a systematic increase in the bulge-to-disk ratio with environmental density.Comment: Accepted for publication in ApJ Letters. Latex aaspp4.sty, 9 pages, 2
Postscript (embedded) figures. Also available at
http://www.astro.yale.edu/koopmann/preprint.htm
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A two-step method for identifying photopigment opsin and rhodopsin gene sequences underlying human color vision phenotypes.
PurposeTo present a detailed, reliable long range-PCR and sequencing (LR-PCR-Seq) procedure to identify human opsin gene sequences for variations in the long wavelength-sensitive (OPN1LW), medium wavelength-sensitive (OPN1MW), short wavelength-sensitive (OPN1SW), and rhodopsin (RHO) genes.MethodsColor vision was assessed for nine subjects using the Farnsworth-Munsell 100 hue test, Ishihara pseudoisochromatic plates, and the Rabin cone-contrast threshold procedure (ColorDX, Konan Medical). The color vision phenotypes were normal trichromacy (n = 3), potential tetrachromacy (n = 3), dichromacy (n = 2), and unexplained low color vision (n = 1). DNA was isolated from blood or saliva and LR-PCR amplified into individual products: OPN1LW (4,045 bp), OPN1MW (4,045 bp), OPN1SW (3,326 bp), and RHO (6,715 bp). Each product was sequenced using specific internal primer sets. Analysis was performed with Mutation Surveyor software.ResultsThe LR-PCR-Seq technique identified known single nucleotide polymorphisms (SNPs) in OPN1LW and OPN1MW gene codons (180, 230, 233, 277, and 285), as well as those for lesser studied codons (174, 178, 236, 274, 279, 298 and 309) in the OPN1LW and OPN1MW genes. Additionally, six SNP variants in the OPN1MW and OPN1LW genes not previously reported in the NCBI dbSNP database were identified. An unreported poly-T region within intron 5(c.36+126) of the rhodopsin gene was also found, and analysis showed it to be highly conserved in mammalian species.ConclusionsThis LR-PCR-Seq procedure (single PCR reaction per gene followed by sequencing) can identify exonic and intronic SNP variants in OPN1LW, OPN1MW, OPN1SW, and rhodopsin genes. There is no need for restriction enzyme digestion or multiple PCR steps that can introduce errors. Future studies will combine the LR-PCR-Seq with perceptual behavior measures, allowing for accurate correlations between opsin genotypes, retinal photopigment phenotypes, and color perception behaviors
A dynamical model for the heavily ram pressure stripped Virgo spiral galaxy NGC 4522
A dynamical model including ram pressure stripping is applied to the strongly
HI deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is
compared with existing VLA HI observations. The model successfully reproduces
the large-scale gas distribution and the velocity field. However it fails to
reproduce the large observed HI linewidths in the extraplanar component, for
which we give possible explanations. In a second step, we solve the induction
equation on the velocity fields of the dynamical model and calculate the large
scale magnetic field. Assuming a Gaussian distribution of relativistic
electrons we obtain the distribution of polarized radio continuum emission
which is also compared with our VLA observations at 6 cm. The observed maximum
of the polarized radio continuum emission is successfully reproduced. Our model
suggests that the ram pressure maximum occurred only ~50 Myr ago. Since NGC
4522 is located far away from the cluster center (~1 Mpc) where the
intracluster medium density is too low to cause the observed stripping if the
intracluster medium is static and smooth, two scenarios are envisaged: (i) the
galaxy moves very rapidly within the intracluster medium and is not even bound
to the cluster; in this case the galaxy has just passed the region of highest
intracluster medium density; (ii) the intracluster medium is not static but
moving due to the infall of the M49 group of galaxies. In this case the galaxy
has just passed the region of highest intracluster medium velocity. This study
shows the strength of combining high resolution HI and polarized radio
continuum emission with detailed numerical modeling of the evolution of the gas
and the large-scale magnetic field.Comment: 15 pages, 11 figures, accepted for publication in A&
Ongoing Gas Stripping in the Virgo Cluster Spiral NGC 4522
The Virgo cluster galaxy NGC 4522 is one of the best spiral candidates for
ICM-ISM stripping in action. Optical broadband and H-alpha images from the WIYN
telescope of the highly inclined galaxy reveal a relatively undisturbed stellar
disk and a peculiar distribution of H-alpha emission. Ten percent of the
H-alpha emission arises from extraplanar HII regions which appear to lie within
filamentary structures >3 kpc long above one side of the disk. The filaments
emerge from the outer edge of a disk of bright H-alpha emission which is
abruptly truncated beyond 0.35R(25). Together the truncated H-alpha disk and
extraplanar H-alpha filaments are reminiscent of a bow shock morphology, which
strongly suggests that the interstellar medium (ISM) of NGC 4522 is being
stripped by the gas pressure of the intracluster medium (ICM). The galaxy has a
line-of-sight velocity of 1300 km/sec with respect to the mean Virgo cluster
velocity, and thus is expected to experience a strong interaction with the
intracluster gas. The existence of HII regions apparently located above the
disk plane suggests that star formation is occuring in the stripped gas, and
that newly formed stars will enter the galaxy halo and/or intracluster space.
The absence of HII regions in the disk beyond 0.35R(25), and the existence of
HII regions in the stripped gas suggest that even molecular gas has been
effectively removed from the disk of the galaxy.Comment: to appear in The Astronomical Journal, 16 pages, 5 figures, 1 tabl
Large-scale radio continuum properties of 19 Virgo cluster galaxies The influence of tidal interactions, ram pressure stripping, and accreting gas envelopes
Deep scaled array VLA 20 and 6cm observations including polarization of 19
Virgo spirals are presented. This sample contains 6 galaxies with a global
minimum of 20cm polarized emission at the receding side of the galactic disk
and quadrupolar type large-scale magnetic fields. In the new sample no
additional case of a ram-pressure stripped spiral galaxy with an asymmetric
ridge of polarized radio continuum emission was found. In the absence of a
close companion, a truncated HI disk, together with a ridge of polarized radio
continuum emission at the outer edge of the HI disk, is a signpost of ram
pressure stripping. 6 out of the 19 observed galaxies display asymmetric 6cm
polarized emission distributions. Three galaxies belong to tidally interacting
pairs, two galaxies host huge accreting HI envelopes, and one galaxy had a
recent minor merger. Tidal interactions and accreting gas envelopes can lead to
compression and shear motions which enhance the polarized radio continuum
emission. In addition, galaxies with low average star formation rate per unit
area have a low average degree of polarization. Shear or compression motions
can enhance the degree of polarization. The average degree of polarization of
tidally interacting galaxies is generally lower than expected for a given
rotation velocity and star formation activity. This low average degree of
polarization is at least partly due to the absence of polarized emission from
the thin disk. Ram pressure stripping can decrease whereas tidal interactions
most frequently decreases the average degree of polarization of Virgo spiral
galaxies. We found that moderate active ram pressure stripping has no influence
on the spectral index, but enhances the global radio continuum emission with
respect to the FIR emission, while an accreting gas envelope can but not
necessarily enhances the radio continuum emission with respect to the FIR
emission.Comment: 37 pages, 26 figures, accepted for publication in A&
Deciphering the radio-star formation correlation on kpc-scales III. Radio-dim and bright regions in spiral galaxies
The relation between the resolved star formation rate per unit area and the
non-thermal radio continuum emission is studied in 21 Virgo cluster galaxies
and the two nearby spiral galaxies, NGC6946 and M51. For the interpretation and
understanding of our results we used a 3D model where star formation, 2D cosmic
ray (CR) propagation, and the physics of synchrotron emission are included.
Based on the linear correlation between the star formation rate per unit area
and the synchrotron emission and its scatter radio-bright and radio-dim regions
can be robustly defined for our sample of spiral galaxies. We identified CR
diffusion or streaming as the physical causes of radio-bright regions of
unperturbed symmetric spiral galaxies as NGC6946. We identified the probable
causes of radio-bright regions in several galaxies as CR transport, via either
gravitational tides (M51) or galactic winds (NGC4532) or ram pressure stripping
(NGC4330 and NGC4522). Three galaxies are overall radio-dim: NGC4298, NGC4535,
and NGC4567. Based on our model of synchrotron-emitting disks we suggest that
the overall radio-dim galaxies have a significantly lower magnetic field than
expected by equipartition between the magnetic and turbulent energy densities.
Radio-bright regions frequently coincide with asymmetric ridges of polarized
radio continuum emission, and we found a clear albeit moderate correlation
between the polarized radio continuum emission and the radio/SFR ratio. When
compression or shear motions of the interstellar medium (ISM) are present in
the galactic disk, the radio-bright regions are linked to the commonly observed
asymmetric ridges of polarized radio continuum emission and represent a useful
tool for the interaction diagnostics. Based on our results, we propose a
scenario for the interplay between star formation, CR electrons, and magnetic
fields in spiral galaxies.Comment: 36 pages, accepted for publication in A&
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