On the Evolution of Galactic Morphologies with special emphasis on barred galaxies October 24, 2008 Socorro, New Mexico

1. On the Evolution of Galactic Morphologies with special emphasis on barred galaxies October 24, 2008 Socorro, New Mexico

2. Two Approaches to Science:

3. Two Approaches to Science: • Natural Philosophy (Physics) • argue from first principles

4. Two Approaches to Science: • Natural Philosophy (Physics) • argue from first principles • 2. Natural History • search for repeated patterns

5. Lord Kelvin In 1862, Kelvin calculated the age of the Earth to be between 24 and 400 Myr old In 1892, he recalculated the age of the Earth to be 100 Myr. He later revised this number downwards, to 20 Myr.

6. Alfred Wegener The Origin of Continents and Oceans (1915, 1920, 1922, 1929) "Wegener's hypothesis in general is of the footloose type, in that it takesconsiderable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories.“ "Utter, damned rot!" "If we are to believe [this] hypothesis, we must forget everything we havelearned in the last 70 years and start all over again.“ "[Anyone who] valued his reputation for scientific sanity [would never daresupport such a theory.]”

7. Abraham Ortelius 1570

8. “… the strange similarities between these coastlines are no mere accidental occurrence.” Sir Francis Bacon (1620)

9. "The crust of the Earth must be a shell floating on a fluid interior.... Thus the surface of the globe would be capable of being broken and distorted by the violent movements of the fluids on which it rested". Benjamin Franklin (1782)

10. Alfred Wegener

11. “A barred galaxy looks like a spinning lawn sprinkler, where the water flows through a straight tube, emerges at right angles and then curves around.” Françoise Combes (2005)

12. Although the models vary somewhat in their constructions, the following conclusions are somewhat universal: o Ridge lines build up in the simulated bars. These ridge lines are taken to be analogous to the dust lanes in natural bars. o Of interest, these ridge lines represent the region of highest velocity flow in the computed results, which is always inwards towards the nucleus. o Natural dust lanes, on the other hand, are of such low velocity that their velocities have not yet been unambiguously measured, in either direction. after Athanassoula 2000

13. Although the models vary somewhat in their constructions, the following conclusions are somewhat universal: o Flow circulates as a shearing wind on both edges of the bar. o This seems exceptionally unrealistic. While such a flow may be sufficiently laminar in front of the leading edge of a bar so as to be invisible, that cannot be true for the trailing edges of the bars, which are producing trailing edge streamers orthogonal to the calculated flow. The trailing edge dust streamers appear as if they are being shed from the bar as the consequence of an encountered wind and would be greatly disrupted by any such circulating flow, if it existed. after Athanassoula 2000

14. Although the various models vary somewhat in their constructions, the following conclusions are somewhat universal: o The regions directly behind the calculated ridge lines that form in the simulations are the areas of lowest pressure. As a result, material is calculated to flow in from the shearing flows to equilibrate the deficit pressures. o This conclusion also seems unrealistic given that the calculated flows occur in the reverse direction of the trailing edge streamers commonly observed. after Athanassoula 2000

15. “Details differ, but these conclusions are robust: (1) Everyone [performing simulations] agrees that gas flows towards the center. (2) Star formation is fed by the inflow is often concentrated in a narrow nuclear ring. (3) The inflow is a result of gravitational torques produced by the bar, but its immediate cause is the shocks.In essence, these are produced because gas accelerates as it approaches and decelerates as it leaves the potential minimum of the bar. So it tends to pile up near the ridge line of the bar.” Kormendy & Kennicutt (2004)

16. THE COMMON ATTRIBUTES OF BARS NGC 1300 has often been described as the prototypical barred galaxy. It is a nearby (21 Mpc), single-armed, pole-oriented barred galaxy that has recently been well-resolved by the Hubble Space Telescope. Because of this image, NGC 1300’s structure can be used to illustrate those core features that are presumed to be common to all barred galaxies. 

17. 1. Linear, leading edge dust lanes appear to exist in all barred galaxies. These lanes have been commonly argued to be regions of inflow, feeding an active galactic nucleus, transferring mass from the interstellar medium to the central engine of the galaxy, or creating central bulges that cause late-type spirals to evolve their Hubble type.

18. 2. 90°breakover points exist at the ends of the bar. It would be difficult to hypothesize a physical process that could cause inflowing mass to follow such a trajectory, but the opposite is not true. If the dust lanes were associated with a collimated mass outflow from the galactic nucleus to the outer blades, the point at which the torque of the bar is exceeded would create such highly defined flow deflections.

19. 5. Regions of dust leakage exist on the trailing edges of a strong bar. These trailing streams mirror the perpendicular trajectories at the ends of the bar of the primary dust lanes, similarly reinforcing the idea that the cause of the deflections is due to torque breakover in the face of an encountered wind.

20. 8. The presence of the active mass-transport bar alters the nature and composition of the galaxy, fractionating the star species into distinctly separate geographic realms. province of large-scale Pop I star formation province of intermediate Pop II stars province of large-scale Pop I star formation The halo and nucleus of a spiral galaxy bears a strong resemblance to an elliptical galaxy, suggesting that it is the most ancient component of the galaxy. If the mass flow through the bar were inward, the expectation would be that these two provinces would be reversed.

21. 9. A secondary region of new star formation occurs in advance of the leading edge of the bar. The pressure wave indicated by this star formation is further evidence of the intrinsic strength of the bar.

22. THE EVOLUTION AND DECAY OF A BAR A sufficient number of nearby galaxies have now been imaged so that they may be considered an archipelago of replicates. All nearby galaxies are presumed to be of the same age, ~13 Ga, but are now found in different evolutionary stages, most likely because of their differing initial conditions. The evolution and decay of a bar can be illustrated using three nearby galaxies.

23. NGC 1300 A Bar at Full Strength NGC 1300 is a primary example of a galaxy with a bar at full strength. Mass expulsion is currently underway, and the presumed collimating solenoid is operating at full force.

24. NGC 5236 A Weakening Bar When the collimating solenoid, which is presumably driven by forces from within the nucleus, begins to weaken, the point of torque breakover and the distinct 90° dust lane deflection points at the ends of the bar begin to relax.

25. NGC 2997 A Bar Fully Decayed As the bar arms continue to weaken, their radii contract, ultimately leaving no effective radius subsequent to the collapse of the solenoid. Mass apparently continues to flow, or was already in motion, during the contraction of the bar so that a complete spiral pattern is drawn.

26. MULTIPLANED GALAXIES Multiplaned galaxies are of special interest to the present hypothesis. All of the spiral galaxies in the Local Group are warped to some degree, but these warps have not yet been well explained by theoretical gas kinematics or other considerations. Nonetheless, as Nelson and Tremaine have written, warped galaxies are so common that they must have a commonplace explanation.

27. M31 Plane A M31 exhibits at least two such planes in its visible disk. Plane B

28. To emphasize the flatness expected, Saturn’s disc has a ~170,000:1 width-to-depth ratio. When seen edge-on, the rings are so thin that they virtually disappear.

29. NGC 3190 The present hypothesis offers a simpler, alternate explanation. If the galactic nucleus should precess in its rotation between episodic bar formations, subsequent mass expulsions will occur out-of-plane with respect to the older, outer arms.

30. ESO 510-G13 The right and left edges of ESO 510-G13, as seen in this edge-on image, exhibit the multiple flange pattern evident in M31.

31. M101 Type Sb M101, a similar spiral, is composed of what appears to be a recent well-defined set of arms that has overwritten at least one older set of arms. The presence of these older, less distinct background arms defines the Sb type. 

32. M101 An older, fainter set of arms are traced by the dashed lines. Type Sb

33. Fainter, more ancient arms yet are traced by the dotted lines. M101 Type Sb

35. (i) bars are very linear structures, extending over many kiloparsecs at nearly constant widths • they possess highly defined leading edge dust lanes • dust leakage from the bars’ trailing edges is being shed as if it were encountering a frictional wind • the two arms of the bar are always in nearly perfect symmetry • right-angle breaks in the dust lanes exist at the ends of the bar • contiguous dust lanes exist, running from the nucleus to deep into the blades of the galaxy • regions of massive Pop I star formation exist at the points where the bars terminate and the blades begin. NGC 5383 after Athanassoula 2000 Ultimately, whichever model is deemed correct, that model must adequately explain the commonly observed attributes of barred galaxies. The following properties appear to be ubiquitous in all strong, young bars:

36. Hubble’s Classification of Galaxy Types (1958) In 1923, Edwin Hubble wrote that he was searching for "the thread of physical significance that shall vitalize a system of classification of non-galactic nebulae."

37. Hubble’s Classification of Galaxy Types (1958) “The classifications are based primarily on the structural forms of photographic classification which should be entirely independent of theoretical considerations." (Hubble 1926)

38. Hubble’s Classification of Galaxy Types (1958) Modified evolutionary sequence of galaxies

39. M74 Type Sc In this revised classification, galaxies are typed by the number of nuclear mass expulsion events that they have experienced during the course of their evolutionary histories, and thus by the number of arms they now exhibit.  

40. M101 Type Sb M101, a similar spiral, is composed of what appears to be a recent well-defined set of arms that has overwritten at least one older set of arms. The presence of these older, less distinct background arms defines the Sb type. 

41. NGC 4414 Type Sa “Flocculent” galaxies such as NGC 4414 have experienced a sufficiently large number of independent mass expulsion events, to the point that the individual arms can no longer be readily discerned, and thus become prototypical of the Sa form of galaxy in this classification.

42. Extraordinary Claims of this Thesis The bars are collimated, low-velocity laminar outflows, with a real strength that breaks at a specific radius. Gravity is not the primary determinant of galactic morphologies. The arms of the galaxies appear to persist for hundreds of millions of years. The arms appear to have been written onto a substantive canvas, and once the arms have been written, remain immobile for a very long time. No mechanism is currently proposed for the formation of the bars, but their constructions are clearly promoted somehow by a process internal to the galactic nucleus.

43. “A barred galaxy looks like a spinning lawn sprinkler, where the water flows through a straight tube, emerges at right angles and then curves around.” Françoise Combes (2005)