The curious case of offset bars : markers for a baby galaxy disk or signposts of an interaction with dark matter sub halos?

>Magister Scientiae - MScWe have used the Spitzer Survey of Stellar Structure in Galaxies (S⁴G) as a representative sample of the local universe (total of 2352 galaxies in S⁴G) to make a catalog of offset disk barred galaxies. Using the combined variation of the position angle and the ellipticity (provided by ellipse fit) and also through visual inspection, we have been able to identify all offset structures in S⁴G. While primary bars are present in 2=3 of the disk galaxies in the visible universe, offset bars have a much lower fraction. Of the ̴ 1500 (3.6µm images) disk galaxies available in S⁴G, we classified only 49 as offset barred disk galaxies. We have determined basic properties (bar to total luminosity ratio, bar length, disk scale-length and bars of offset bars shape) using GALFIT, a widely used galaxy decomposition software package. Our main conclusion is that all the offset bars are boxy, independent of their offset from the galaxy center, or the mass of the host galaxy. Additionally we find that, the early type offset bars seem to be more boxy than the late types. The comparison of our offset sample with two other samples, respectively, low mass and high mass normal barred galaxies ("normal" for bars located at the photometric center of the host galaxy), reveals them to be at an intermediate position between the two normal samples. The bar length, disk scale-length and bar to total luminosity ratio are on average larger than the low mass normal and smaller than high mass normal barred galaxies. We have found, overall, a tighter correlation between the disk and bar properties for offset bars in comparison to the two normal samples. Our explanation is that, although the offset has no visible impact on the global shape of the bars, the process responsible for these disturbances seems to affect the star formation rate such that their disk and bars are on average more active than the normal barred galaxies in the same mass range, but not enough to surpass normal barred galaxies with much higher mass

Diagram of spherical cavity expansion theory.

Diagram of spherical cavity expansion theory.</p

Probe penetration resistance diagram.

Probe penetration resistance diagram.</p

Indoor test of probe penetration into soil.

Indoor test of probe penetration into soil.</p

Effect of diet modification on lipid accumulation in the liver.

<p>Liver tissue slides were stained with oil red O and photographed under a microscope. Compared with control mice (A), lipid droplets could be detected obviously in the HFR mice (B), HFA mice (C) and HFF mice (D). The length of the scale is 20 μm.</p

Effect of diet modification on the basal metabolic rate.

<p>The levels of the consumed O₂ (VO₂, A), the produced CO₂ (VCO₂, B), energy expenditure (EE, C), and respiratory quotient (RQ, D) were examined in the control, HFR, HFA and HFF mice. Data are presented as means ± SD (n = 5 in each group). A significant difference was determined by one-way analysis of variance. *P<0.05 versus control in the same phase, **P<0.01 versus control in the same phase.</p

Effect of diet modification on lipid metabolism.

<p>The levels of total cholesterol (TC, A), low-density lipoprotein cholesterol (LDL, B), high-density lipoprotein cholesterol (HDL, C) and triglyceride (TG, D) were detected in the control, HFR, HFA and HFF groups. Data are presented as means ± SD (n ≥ 6 in each group). A significant difference was determined by one-way analysis of variance. *P < 0.05 versus control, **P < 0.01 versus control.</p

Effect of diet modification on insulin sensitivity.

<p>Mice fed with fructose water or high fat diet were subjected to intraperitoneal glucose tolerance tests (A) and intraperitoneal insulin tolerance tests (B). The areas under the curve (AUC, C and D) and the glucose disappearance rate (E and F) were calculated to detect differences among the groups. Data are presented as means ± SD (n ≥ 6 in each group). A significant difference was determined by one-way analysis of variance. *P < 0.05 versus control at the same time point, **P < 0.01 versus control at the same time point.</p