1. Current Issues in Disk Galaxy Formation van den Bosch, Burkert, Swaters (2001) Abadi et al. (2003) Swaters et al. (2003) van den Bosch, Burkert, Swaters (2001) Abadi et al. (2003) Swaters et al. (2003)

2. MMW Analytic Disk model Given the following parameters: Given the following parameters: V c = Circular velocity at some time, V c = Circular velocity at some time, j d /m d = Specific angular momentum of disk, j d /m d = Specific angular momentum of disk, = Spin parameter (from LSS tidal torques), = Spin parameter (from LSS tidal torques), H(z) = Hubble constant H(z) = Hubble constant … we can determine both the structural properties and evolution of the disk. … we can determine both the structural properties and evolution of the disk.  R d  V c,  j d /m d, ,  1/H(z)  R d  V c,  j d /m d, ,  1/H(z) All cosmology dependence is in H(z)! All cosmology dependence is in H(z)!

3. Specific Angular Momentum Disk properties well reproduced in simple model (e.g. MMW) IF j D /m D ~1. Disk properties well reproduced in simple model (e.g. MMW) IF j D /m D ~1. But… is this assumption justified? But… is this assumption justified? Let’s simulate! Let’s simulate!

4. Abadi et al. (2003) Discussion… Discussion…

5. Hydrodynamic Simulations Initial conditions: A small patch of the Universe, in the linear regime, with dark matter and gas particles. Initial conditions: A small patch of the Universe, in the linear regime, with dark matter and gas particles. Model gravitational force between particles, additional pressure forces, shock heating, and cooling for gas. Model gravitational force between particles, additional pressure forces, shock heating, and cooling for gas. Advance particle positions + velocities, lather, rinse, repeat. Advance particle positions + velocities, lather, rinse, repeat. What happens? What happens?

8. Simulate a Single Disk Galaxy 320 kpc/h 40 kpc/h (last panel only)

9. Successful Photometric Disk Galaxy Thin gaseous disk, bulge, halo. Thin gaseous disk, bulge, halo. SB profile has r 1/4 bulge, exponential disk. SB profile has r 1/4 bulge, exponential disk. Gas is more extended than stars. Gas is more extended than stars. Looks a lot like UGC615, an Sab… even reproduces colors! Looks a lot like UGC615, an Sab… even reproduces colors! SFR ~ 2 M  /yr since last merger at z~1. SFR ~ 2 M  /yr since last merger at z~1.

10. But when AM comes into play, life gets much worse. RC is FAR too centrally concentrated. RC is FAR too centrally concentrated. Owes to large, over- concentrated bulge. Owes to large, over- concentrated bulge. But this is a direct result of early hierarchical growth… and in a relatively quiescent halo! But this is a direct result of early hierarchical growth… and in a relatively quiescent halo!

11. Specific Angular Momentum Specific AM j of stars/baryons << observed late-types. Specific AM j of stars/baryons << observed late-types. Disk-only j agrees well… if it only weren’t for that pesky bulge! Disk-only j agrees well… if it only weren’t for that pesky bulge! DM halo has similar j to observed disks; seems like nature conserves j even though sims don’t. DM halo has similar j to observed disks; seems like nature conserves j even though sims don’t. And this is for favorable quiescent case; typical case produces lower j. And this is for favorable quiescent case; typical case produces lower j.

12. Bottom line… Simulation produces disk with some basic structural and photometric properties as observed. Simulation produces disk with some basic structural and photometric properties as observed. But… best-case scenario only produces an Sab, no later. But… best-case scenario only produces an Sab, no later. Even then, the bulge component is too concentrated and too large. Even then, the bulge component is too concentrated and too large. Specific AM is too low, because bulk of stars form early in a stochastic, non-ordered mode. Specific AM is too low, because bulk of stars form early in a stochastic, non-ordered mode.

13. What Can We Do? Suppress early bulge growth: Suppress early bulge growth: Feedback? Feedback? Preheat gas? Preheat gas? Modify dark matter (e.g. warm)? Modify dark matter (e.g. warm)? Modify cosmological power spectrum? Modify cosmological power spectrum? Ignore it!!! Simulations are wrong, basic model (e.g. MMW) is right. Ignore it!!! Simulations are wrong, basic model (e.g. MMW) is right. Nature somehow conserves specific AM. Nature somehow conserves specific AM. But even that turns out to not work so great… But even that turns out to not work so great…

14. van den Bosch et al. (2001) Discussion… Discussion…

15. LSB Galaxies Low Surface Brightness galaxies: What are they? Low Surface Brightness galaxies: What are they? Late-type Spirals, mostly bulge-less, gas-rich. Why LSBs? Why LSBs? Quiescent history, RC is dark matter dominated: Ideal testbed for simple rotationally-supported collapse. How to measure rotation? How to measure rotation? H  (optical) rotation curves in inner region, HI (21cm) rotation curve in outer region.

16. Angular Momentum Distributions Thick: Data (3 values of M/L) Thin: Halos (3 values of  )

17. Total AM of Disk ( ) For reasonable M/L ratio, of observed disks are similar to that of DM halos. For reasonable M/L ratio, of observed disks are similar to that of DM halos. So total AM is apparently conserved in collapse… as assumed in MMW, but in contrast with simulations that cannot reproduce this. So total AM is apparently conserved in collapse… as assumed in MMW, but in contrast with simulations that cannot reproduce this.

18. Punchline: Halo vs. Disk AM Normalized to total AM: Disk has similar specific AM, but much less total AM because it contains much less than all baryons. Normalized to total AM: Disk has similar specific AM, but much less total AM because it contains much less than all baryons.

19. Key Results Only a rather small fraction of baryons end up in disk. Only a rather small fraction of baryons end up in disk. Challenge to standard cooling model Challenge to standard cooling model Total AM of disk ≈ Total AM of all baryons. Total AM of disk ≈ Total AM of all baryons. Challenge to simulations showing AM loss Challenge to simulations showing AM loss The disk is missing both highest and lowest AM baryons. The disk is missing both highest and lowest AM baryons. Challenge to models that assume simple rotationally-supported collapse Challenge to models that assume simple rotationally-supported collapse

20. So… How do we get rid of all this “unwanted” angular momentum? Need other physical processes! Need other physical processes! Perhaps high-AM material lost in mergers, or tidally stripped, or still left in halo? Perhaps high-AM material lost in mergers, or tidally stripped, or still left in halo? … Yet somehow it’s AM ends up in disk! … Yet somehow it’s AM ends up in disk! Perhaps low-AM material blown out from center of galaxy? Perhaps low-AM material blown out from center of galaxy? … but simple model of feedback where large galaxies retain more baryons is opposite to trend seen in data! … but simple model of feedback where large galaxies retain more baryons is opposite to trend seen in data!

21. Wackier Notions… Perhaps dark matter is not collisionless, and hence halo AM distribution is actually much like that observed. Perhaps dark matter is not collisionless, and hence halo AM distribution is actually much like that observed. … but still have trouble explaining shape of p(s) … but still have trouble explaining shape of p(s) Perhaps baryons decouple from halos early on, acquire different AM. Perhaps baryons decouple from halos early on, acquire different AM. … no evidence for this in more recent work (e.g. Sharma & Steinmetz 2006) … no evidence for this in more recent work (e.g. Sharma & Steinmetz 2006)

22. So the bottom line is… Disk formation is a LOT more complicated than the MMW scenario. Disk formation is a LOT more complicated than the MMW scenario. We still don’t understand it! We still don’t understand it! More recent results (e.g. Governato et al. 2004, Robertson et al. 2005) have used strong feedback to produce later-type spirals. But still not clear that distribution of AM is correct. More recent results (e.g. Governato et al. 2004, Robertson et al. 2005) have used strong feedback to produce later-type spirals. But still not clear that distribution of AM is correct. Maybe there’s a hint from a related but slightly different angle… Maybe there’s a hint from a related but slightly different angle…

23. Swaters et al. (2003) Discussion… Discussion…

24. Universal Halo Profile CDM predicts universal halo profile (NFW). CDM predicts universal halo profile (NFW). All halos well fit by All halos well fit by NFW (1997):  = 1. NFW (1997):  = 1. Moore et al (1998):  ≈ 1.5 Moore et al (1998):  ≈ 1.5 Others: Everything in between Others: Everything in between Observations, at face value:  ≈ 0! Observations, at face value:  ≈ 0! What’s going on? What’s going on?

25. LSBs: Dark Matter Dominated RC’s Slowly rising RC’s, no bulge… can probe inner dark matter profile. Slowly rising RC’s, no bulge… can probe inner dark matter profile.

26. Density Profiles from Inverted RC

27. Stay out of Bars! Bars cause non- circular motions that mimic lower . Bars cause non- circular motions that mimic lower . Non-barred sample fairly consistent with NFW. Non-barred sample fairly consistent with NFW.

28. Fair and Balanced View Observations, at face value, tend to prefer low value of . Observations, at face value, tend to prefer low value of . But there are many systematics… and they almost all tend to lower  ! But there are many systematics… and they almost all tend to lower  ! Misidentifying center of potential Misidentifying center of potential Non-circular motions Non-circular motions Overly edge-on galaxies Overly edge-on galaxies Hence cannot rule out NFW (  =1). Hence cannot rule out NFW (  =1). Can rule out Moore profile (  =1.5). Can rule out Moore profile (  =1.5).

29. If NFW is Right, What About Concentrations? Most agree with simulations, but a few clearly low: Mostly barred galaxies! Most agree with simulations, but a few clearly low: Mostly barred galaxies! Do bars cause lower mass concentration? (Weinberg & Katz 2002) Do bars cause lower mass concentration? (Weinberg & Katz 2002)

30. Bottom Line Overall, no obvious disagreement with NFW, either in inner slope or concentration. Overall, no obvious disagreement with NFW, either in inner slope or concentration. But debate is far from over! 2-D IFU data also shows shallow mass profiles. But debate is far from over! 2-D IFU data also shows shallow mass profiles. Theory debate not over either (paper on astro-ph today claiming a totally new functional form). Theory debate not over either (paper on astro-ph today claiming a totally new functional form). If NFW is right, then can’t solve disk AM problem by changing DM distribution. If NFW is right, then can’t solve disk AM problem by changing DM distribution.

31. That’s It For Today! Some successes, many unresolved issues in theory of disk galaxy formation. Some successes, many unresolved issues in theory of disk galaxy formation. Next time (next Wed): Marcia will tell you all about elliptical galaxies. Next time (next Wed): Marcia will tell you all about elliptical galaxies.