Gas s In Inflo flow and nd Sec ecula ular r Evoluti lution n in in Disk isk Gala laxie xies s Michael Regan
Mergers of disks galaxies can form ellipticals Dubinski 2005
The time of mergers is past.
Current and future galaxy evolution will be dominated by internal processes. Gas loses angular momentum to the stars and flows inward Leads to gas in the center and the formation of a “pseudo - bulge” (Kormendy & Kennicutt 2004) Bars driven inflow is the fastest
Bar driven mass inflow affects galaxy evolution several different ways. Providing fuel for nuclear starbursts and AGN(?) (Shlosman, Frank, & Begelman 1989; Heller & Shlosman 1994) Altering radial chemical gradients (Roy & Belley 1993; Friedli, Benz, & Kennicutt 1994; Martin & Roy 1994) Increasing the central mass concentration Bar destruction (Friedli & Benz 1993; Norman, Sellwood, & Hasan 1996, Shein & Sellwood 2004) Bulge formation (Norman et al 1996)
A Pseudo-bulge is not a mini-elliptical but is really more like a disk. A high rotational velocity A light profile that is less steep than a r ¼ law compared to an elliptical
How bar characteristics affect mass inflow (Regan & Teuben 2004) How and why nuclear rings form (Regan &Teuben 2003) Kinematic observations of gas flow in barred galaxies Central gas concentrations and pseudo-bulges
How bar characteristics affect mass inflow (Regan & Teuben 2004) How and why nuclear rings form (Regan &Teuben 2003) Kinematic observations of gas flow in barred galaxies Central gas concentrations and pseudo-bulges
We performed hydrodynamic modeling of gas flow in a barred potential. (Regan & Teuben 2003, 2004) Cylindrical coordinate system Cells range from 2x2pc at 100 pc radius to 100x100pc at 5 kpc. Three free parameters were varied: Central Mass Concentration [Bulge to Disk ratio](6 values) Bar Quadrupole Moment [Mass in the bar](5 values) Bar Axis Ratio (5 values)
Hydrodynamic simulation shows gas flow in a barred potential
Bar Axis Ratio = 1.5 Bar Strength Central Mass Concentration
Bar Axis Ratio = 2.5 Bar Axis Ratio = 2.5 Bar Strength Central Mass Concentration
Bar Axis Ratio = 3.5 Bar Axis Ratio = 3.5 Bar Strength Central Mass Concentration
Only when nuclear rings form is there significant inflow. Bar Axis Ratio = 1.5 Inflo Inflow rate rate to to 100pc 100pc radius radius Strength ar Strengt Bar Inflow rate Inflo rate to to inner inne r Kpc pc Regan & Teuben 2004 Centra entral Mass Mass Conce oncentra ratio ion
Only when nuclear rings form is there significant inflow. Bar Axis Ratio = 2.5 Inflo Inflow rate rate to to 100pc 100pc radius radius Strength ar Strengt Bar Inflow rate Inflo rate to to inner inne r Kpc pc Regan & Teuben 2004 Centra entral Mass Mass Conce oncentra ratio ion
Only when nuclear rings form is there significant inflow. Bar Axis Ratio = 3.5 Inflo Inflow rate rate to to 100pc 100pc radius radius Strength ar Strengt Bar Inflow rate Inflo rate to to inner inne r Kpc pc Regan & Teuben 2004 Centra entral Mass Mass Conce oncentra ratio ion
How bar characteristics affect mass inflow (Regan & Teuben 2004) How and why nuclear rings form (Regan & Teuben 2003) Kinematic observations of gas flow in barred galaxies Central gas concentrations and pseudo-bulges
There are many ideas that try to explain nuclear ring formation. Why do they form? Trapped between the Inner Lindblad Resonances (ILRs) (Combes 1996; Buta & Combes 1996) Circular orbits are stable (Shlosman, Begleman, & Frank 1990) Remnant of nuclear starburst (Kenney, Carlstrom, & Young 1993) Where do they form? Peak of rotation curve Peak of W-k /2 curve (Piner, Stone, & Teuben 1995) At the Inner Inner Lindblad Resonance (IILR) when there are two or at the ILR if only one ( Buta & Combes 1996)
The epicyclic orbits are nearly circular orbits.
When the radial and angular frequencies are multiples you get a resonance.
ILRs are only weakly correlated with nuclear rings. Bar Axis Ratio = 1.5 Bar Strength Regan & Teuben 2003 Central Mass Concentration
ILRs are only weakly correlated with nuclear rings. Bar Axis Ratio = 2.5 Bar Strength Regan & Teuben 2003 Central Mass Concentration
ILRs are only weakly correlated with nuclear rings. Bar Axis Ratio = 3.5 Bar Strength Regan & Teuben 2003 Central Mass Concentration
Bar Orbit Theory
X 1 orbits form the backbone of the bar.
There are also perpendicular orbits(x 2 ) that may be stable.
The perpendicular orbits (x 2 Orbits) are related to nuclear rings. Bar dust lanes and x 2 orbit are strongly correlated (Athanassoula 1992) Because nuclear rings and bar dust lanes are also strongly correlated expect to see x 2 and nuclear ring correlation. Each potential we found the existence and extent of x 2 orbits.
The nuclear ring forms at the largest x 2 orbit. Bar Axis Ratio = 1.5 Bar Strength X 2 orbits Regan & Teuben 2003 Central Mass Concentration
The nuclear ring forms at the largest x 2 orbit. Bar Axis Ratio = 2.5 Bar Strength X 2 orbits Regan & Teuben 2003 Central Mass Concentration
The nuclear ring forms at the largest x 2 orbit. Bar Axis Ratio = 3.5 Bar Strength X 2 orbits Regan & Teuben 2003 Central Mass Concentration
Nuclear rings form due to the intersection of gas on x 1 -like and x 2 -like streamlines. Gas cannot exist on both x 1 -like and x 2 -like streamlines in the same region Gas appears to favor the x 2 -like streamlines Consistent with van Albada & Sanders (1982) Gas prefers more circular orbit X 2 orbits have lower energy Nuclear ring is not in equilibrium. It’s the orbits, stupid.
How bar characteristics affect mass inflow (Regan & Teuben 2004) How and why nuclear rings form (Regan & Teuben 2003) Kinematic observations of gas flow in barred galaxies Central gas concentrations and pseudo-bulges
When the gas is in circular orbits the “Spider” diagram is symmetrical. Minor Axis Major Axis
The H a gas in NGC 1530 is clearly not rotating in circular orbits. NGC 1530 I-band Fabry-Perot observations of NGC 1530 Strong shock along dust lanes Isovelocity parallel in nuclear region Kink along spiral arms Kinematic major axis shifted Regan, Vogel & Teuben 1997
The hydrodynamic models are a good match to the observations. Hydro model Only Circular Motion velocity field Observed Velocities
The molecular gas (CO) in NGC 1530 shows the fast jumps on the bar dust lanes. Reynaud & Downs 1998
The CO in NGC 2903 shows strong velocity gradients. Regan, Sheth & Vogel 1999 Regan, Sheth & Vogel 1999
The CO emission in NGC 3627 also shows this with gas at systemic on the major axis. Regan, Sheth & Vogel 1999
How bar characteristics affect mass inflow (Regan & Teuben 2004) How and why nuclear rings form (Regan & Teuben 2003) Kinematic observations of gas flow in barred galaxies Central gas concentrations and pseudo-bulges
OVRO and BIMA SONG results showed evidence for a central excess of molecular gas. (Sakamoto et al 1999, Regan et al 2001, Sheth et al 2005) Regan et al 2001
CO maps suffer from many limitations that limit their usefulness in studying ISM radial profiles. CO Interferometric maps have problems: limited FOV missing atomic gas surface brightness cutoff CO/H 2
Spitzer Space Telescope Spitzer Infrared Nearby Galaxies Survey (SINGS) Science Core Characterize star formation in 75 nearby galaxies
IRAC on the Spitzer Space Telescope observes emission from both stars and dust. Stellar photospheres
In M51 the Channel 1 (3.6 m m) emission looks like dust free stellar emission. I-band
In M51 the Channel 1 (3.6 m m) emission looks like dust free stellar emission. 3.6 m m
In M51 the dust extinction shows a similar morphology to the 8 m m emission. I-3.6 m m color map
In M51 the dust extinction shows a similar morphology to the 8 m m emission. 8 m m
Spitzer IRAC 8 m m emission provides a new probe of the ISM. CO flux 8 m m flux Regan et al. 2006
Both NGC 3351 and NGC 3627 show central excesses in CO and 8 m m . Barred 8 m m Surface Brightness CO Surface Brightness Barred CO – 8 m m Surface Brightness Regan et al. 2006
Only NGC 5055 does not show an excess in the 8 m m emission. Barred 8 m m Surface Brightness CO Surface Brightness CO - 8 m m CO relatively Surface brighter in the Brightness nucleus Regan et al. 2006
Only NGC 6946 shows an excess in the central 8 m m emission. 8 m m Surface Barred Brightness CO Surface Brightness CO – 8 m m Surface Brightness Regan et al. 2006
For each galaxy we measure two quantities. How bulge-like is the central light, The central gas concentration Sersic index from 3.6 m m SINGS from 8 m m SINGS images
High central concentrations of 8 micron PAH emission is strongly correlated with pseudobulges Pseudobulges Classical bulges Central gas concentration Fornax A NGC 1316
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