Properties of barred spiral galaxies ELMEGREEN, B. G; ELMEGREEN, D. M
The Astrophysical journal,
01/1985, Letnik:
288, Številka:
2
Journal Article
Recenzirano
Blue and near-infrared surface photometry of 15 barred spiral galaxies, combined with results from photometric and kinematic studies of barred galaxies, reveals that: (1) early Hubble types have flat ...bars with uniform intensities along their lengths and stellar spiral arms with amplitudes that decrease with radius, and (2) late Hubble types have bars with exponential-like intensity profiles and spiral arm amplitudes that increase or remain constant with radius. Relative bar luminosities are derived using Fourier decompositions of the bar azimuthal profiles. It is concluded that bars in early-type galaxies probably contain highly elongated stellar orbits out to the corotation vicinity and also stimulate stellar spiral structure either by continuously growing, in the case of a non-self-gravitating stellar disk, or by exciting a wave mode at a resonance, in the case of a strongly self-gravitating stellar disk. It is shown that bars in some late-type galaxies may extend out only to the inner Lindbald resonances and that they appear to be too short or too weak to drive prominent stellar spirals because the spirals in these galaxies are often irregular.
GEMS and GOODS fields were examined to z similar to 1.4 for galaxy interactions and mergers. The basic morphologies are familiar: antennae with long tidal tails, tidal dwarfs, and merged cores; ...M51-type galaxies with disk spirals and tidal arm companions; early-type galaxies with diffuse plumes; equal-mass grazing collisions; and thick J -shaped tails beaded with star formation and double cores. One type is not common locally and is apparently a loose assemblage of smaller galaxies. Photometric measurements were made of the tails and clumps, and physical sizes were determined assuming photometric redshifts. Antennae tails are a factor of similar to 3 smaller in GEMS and GOODS systems compared to local antennae; their disks are a factor of similar to 2 smaller than locally. Collisions among early type galaxies generally show no fine structure in their tails, indicating that stellar debris is usually not unstable. One exception has a 5 x 10 M smooth red clump that could be a pure stellar condensation. Most tidal dwarfs are blue and probably form by gravitational instabilities in the gas. One tidal dwarf looks like it existed previously and was incorporated into the arm tip by tidal forces. The star-forming regions in tidal arms are 10-1000 times more massive than star complexes in local galaxies, although their separations are about the same. If they all form by gravitational instabilities, then the gaseous velocity dispersions in interacting galaxies have to be larger than in local galaxies by a factor of similar to 5 or more; the gas column densities have to be larger by the square of this factor.
We present a detailed study of the flocculent spiral galaxy NGC 7793, part of the Sculptor group. By analyzing the resolved stellar populations of the galaxy, located at a distance of ∼3.7 Mpc, we ...infer for the first time its radial star formation history (SFH) from Hubble Space Telescope photometry, thanks to both archival and new data from the Legacy ExtraGalactic UV Survey. We determine an average star formation rate (SFR) for the galaxy portion covered by our F555W and F814W data of 0.23 0.02 M yr−1 over the whole Hubble time, corresponding to a total stellar mass of (3.09 0.33) × 109 M , in agreement with previous determinations. Thanks to the new data extending to the F336W band, we are able to analyze the youngest stellar populations with a higher time resolution. Most importantly, we recover the resolved SFH in different radial regions of the galaxy; this shows an indication of a growing trend of the present-to-past SFR ratio, increasing from internal to more external regions, supporting previous findings of the inside-out growth of the galaxy.
unk -band images of 20 barred galaxies show an increase in the peak amplitude of the normalized m = 2 Fourier component with the R sub(25) -normalized radius at this peak. This implies that longer ...bars have higher m = 2 amplitudes. The long bars also correlate with an increased density in the central parts of the disks, as measured by the luminosity inside 0.25R sub(25) divided by the cube of this radius in kpc. Because denser galaxies evolve faster, these correlations suggest that bars grow in length and amplitude over a Hubble time, with the fastest evolution occurring in the densest galaxies. All but three of the sample have early-type flat bars; there is no clear correlation between the correlated quantities and the Hubble type.
The ultra-luminous infrared galaxy Arp2 20 is a late-stage merger with several tidal structures in the outskirts and two very compact, dusty nuclei that show evidence for extreme star formation and ...host at least one AGN. New and archival high-resolution images taken by the Hubble Space Telescope provide a state-of-the-art view of the structures, dust, and stellar clusters in Arp 220. We find that ~90% of the Halpha emission arises from a shock-ionized bubble emanating from the AGN in the western nucleus, while the nuclear disks dominate the Pbeta emission. Four very young (~3-6 Myr) but lower mass (< 10^4 Msun) clusters are detected in Halpha within a few arcsec of the nuclei, but produce less than 1% of the line emission. We see little evidence for a population of massive clusters younger than 100Myr anywhere in Arp 220. From the masses and ages of the detected clusters, we find that star formation took place more-or-less continuously starting ~few Gyr ago with a rate between ~3-12 Msun/yr. Approximately 100Myr ago, star formation shut off suddenly everywhere, except in the nuclear disks. A very recent flicker of weak star formation produced the four young, low-mass clusters, while the rest of the galaxy appears to have remained in a post-starburst state. Cluster ages indicate that the tidal structures on the west side of the galaxy are older than those on the east side, but all appear to pre-date the shutoff of star formation. Arp 220 has many of the characteristics expected of a 'Shocked Post-Starburst Galaxy' or SPOG, since most of the system has been in a post-starburst state for the past ~100Myr and the detected Halpha emission arises from shocked rather than photo-ionized gas.
We investigate how the properties of spiral arms relate to other fundamental galaxy properties. To this end, we use previously published measurements of those properties, and our own measurements of ...arm-interarm luminosity contrasts for a large sample of galaxies, using 3.6\(\mu\)m images from the Spitzer Survey of Stellar Structure in Galaxies. Flocculent galaxies are clearly distinguished from other spiral arm classes, especially by their lower stellar mass and surface density. Multi-armed and grand-design galaxies are similar in most of their fundamental parameters, excluding some bar properties and the bulge-to-total luminosity ratio. Based on these results, we discuss dense, classical bulges as a necessary condition for standing spiral wave modes in grand-design galaxies. We further find a strong correlation between bulge-to-total ratio and bar contrast, and a weaker correlation between arm and bar contrasts.
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