3,384 research outputs found
Effect of bars on the galaxy properties
Aims: With the aim of assessing the effects of bars on disc galaxy
properties, we present an analysis of different characteristics of spiral
galaxies with strong, weak and without bars. Method: We identified barred
galaxies from the Sloan Digital Sky Survey. By visual inspection, we classified
the face-on spiral galaxies brighter than g<16.5 mag into strong-bar, weak-bar
and unbarred. In order to provide an appropiate quantification of the influence
of bars on galaxy properties, we also constructed a suitable control sample of
unbarred galaxies with similar redshift, magnitude, morphology, bulge sizes,
and local density environment distributions to that of barred galaxies.
Results: We found 522 strong-barred and 770 weak-barred galaxies, representing
a 25.82% of the full sample of spiral galaxies, in good agreement with previous
studies. We also found that strong-barred galaxies show less efficient star
formation activity and older stellar populations compared to weak-barred and
unbarred spirals from the control sample. In addition, there is a significant
excess of strong barred galaxies with red colors. The color-color and
color-magnitude diagrams show that unbarred and weak-barred galaxies are more
extended towards the blue zone, while strong-barred objects are mostly grouped
in the red region. Strong-barred galaxies present an important excess of high
metallicity values, compared to the other types, showing similar 12+log(O/H)
distributions. Regarding the mass-metallicity relation, we found that
weak-barred and unbarred galaxies are fitted by similar curves, while
strong-barred ones show a curve which falls abruptly, with more significance in
the range of low stellar masses (log[Mstar/Msun] < 10.0). These results would
indicate that prominent bars produced an accelerating effect on the gas
processing, reflected in the significant changes in the physical properties of
their host
Dynamics of Barred Galaxies
Some 30% of disc galaxies have a pronounced central bar feature in the disc
plane and many more have weaker features of a similar kind. Kinematic data
indicate that the bar constitutes a major non-axisymmetric component of the
mass distribution and that the bar pattern tumbles rapidly about the axis
normal to the disc plane. The observed motions are consistent with material
within the bar streaming along highly elongated orbits aligned with the
rotating major axis. A barred galaxy may also contain a spheroidal bulge at its
centre, spirals in the outer disc and, less commonly, other features such as a
ring or lens. Mild asymmetries in both the light and kinematics are quite
common. We review the main problems presented by these complicated dynamical
systems and summarize the effort so far made towards their solution,
emphasizing results which appear secure. (Truncated)Comment: This old review appeared in 1993. Plain tex with macro file. 82 pages
18 figures. A pdf version with figures at full resolution (3.24MB) is
available at http://www.physics.rutgers.edu/~sellwood/bar_review.pd
Molecular Gas in Candidate Double Barred Galaxies III. A Lack of Molecular Gas?
Most models of double-barred galaxies suggest that a molecular gas component
is crucial for maintaining long-lived nuclear bars. We have undertaken a CO
survey in an attempt to determine the gas content of these systems and to
locate double barred galaxies with strong CO emission that could be candidates
for high resolution mapping. We observed 10 galaxies in CO J=2-1 and J=3-2 and
did not detect any galaxies that had not already been detected in previous CO
surveys. We preferentially detect emission from galaxies containing some form
of nuclear activity. Simulations of these galaxies require that they contain 2%
to 10% gas by mass in order to maintain long-lived nuclear bars. The fluxes for
the galaxies for which we have detections suggest that the gas mass fraction is
in agreement with these models requirements. The lack of emission in the other
galaxies suggests that they contain as little as 7 x 10^6 solar masses of
molecular material which corresponds to < 0.1% gas by mass. This result
combined with the wide variety of CO distributions observed in double barred
galaxies suggests the need for models of double-barred galaxies that do not
require a large, well ordered molecular gas component.Comment: 17 pages (3 figures embedded on pg 17). To appear in the March 10
issue of the Astrophysical Journa
The effect of bars on the M*- e relation: offset, scatter and residuals correlations
We analyse a set of collisionless disc galaxy simulations to study the consequences of bar formation and evolution on the Mâą-Ïe relation of supermassive black holes (SMBHs). The redistribution of angular momentum driven by bars leads to a mass increase within the central region, raising the velocity dispersion of the bulge, Ïe, on average by Ë12 per cent and as much as Ë20 per cent. If a disc galaxy with an SMBH satisfying the Mâą-Ïe relation forms a bar, and the SMBH does not grow in the process, then the increase in Ïe moves the galaxy off the Mâą-Ïe relation. We explore various effects that can affect this result including contamination from the disc and anisotropy. The displacement from the Mâą-Ïe relation for individual model barred galaxies correlates with both the bulge-to-total stellar mass ratio, M(B)/M(B + D), and the 2D anisotropy, ÎČÏ(B + D), both measured within the effective radius of the bulge. Overall, this process leads to an Mâą-Ïe for barred galaxies offset from that of unbarred galaxies, as well as an increase in its scatter. We assemble samples of observed unbarred and barred galaxies with classical bulges and find tentative hints of an offset between the two consistent with the predicted. Including all barred galaxies, rather than just those with a classical bulge, leads to a significantly larger offset, which is mostly driven by the significantly larger offset of pseudo bulge
Gas flow in barred galaxies
I briefly review the properties of the gas flow in and around the region of
the bar in a disc galaxy and discuss the corresponding inflow and the loci of
star formation. I then review the flow of gas in barred galaxies which have an
additional secondary bar. Finally I discuss the signatures of bars in edge-on
galaxies.Comment: 6 pages, 2 figures, style file incl., to appear in the proceedings of
an ESO/CTIO/LCO workshop "Stars, Gas and Dust in Galaxies : Exploring the
Links", eds. Alloin, Olsen & Galaz (ASP Conf. Series
Long-Lived Double-Barred Galaxies From Pseudo-Bulges
A large fraction of barred galaxies host secondary bars that are embedded in
their large-scale primary counterparts. These are common also in gas poor
early-type barred galaxies. The evolution of such double-barred galaxies is
still not well understood, partly because of a lack of realistic -body
models with which to study them. Here we report a new mechanism for generating
such systems, namely the presence of rotating pseudo-bulges. We demonstate with
high mass and force resolution collisionless -body simulations that
long-lived secondary bars can form spontaneously without requiring gas,
contrary to previous claims. We find that secondary bars rotate faster than
primary ones. The rotation is not, however, rigid: the secondary bars pulsate,
with their amplitude and pattern speed oscillating as they rotate through the
primary bars. This self-consistent study supports previous work based on
orbital analysis in the potential of two rigidly rotating bars. The pulsating
nature of secondary bars may have important implications for understanding the
central region of double-barred galaxies.Comment: Paper submitted to ApJ
Photometric Decomposition of Barred Galaxies
We present a non-parametric method for decomposition of the light of disk
galaxies into disk, bulge and bar components. We have developed and tested the
method on a sample of 68 disk galaxies for which we have acquired I-band
photometry. The separation of disk and bar light relies on the single
assumption that the bar is a straight feature with a different ellipticity and
position angle from that of the projected disk. We here present the basic
method, but recognise that it can be significantly refined. We identify bars in
only 47% of the more nearly face-on galaxies in our sample. The fraction of
light in the bar has a broad range from 1.3% to 40% of the total galaxy light.
If low-luminosity galaxies have more dominant halos, and if halos contribute to
bar stability, the luminosity functions of barred and unbarred galaxies should
differ markedly; while our sample is small, we find only a slight difference of
low significance.Comment: Accepted to appear in AJ, 36 pages, 9 figures, full on-line figures
available at http://www.physics.rutgers.edu/~sellwood/Reese.htm
- âŠ