Current Issues Current Issues in Disk Galaxy in Disk Galaxy

FormationFormation

van den Bosch, van den Bosch, BurkertBurkert, , SwatersSwaters (2001) (2001)

AbadiAbadi et al. (2003) et al. (2003)SwatersSwaters et al. (2003) et al. (2003)

MMW Analytic Disk modelMMW Analytic Disk model Given the following parameters:Given the following parameters:

VVcc = Circular velocity at some time, = Circular velocity at some time, jjdd/m/mdd = Specific angular momentum of disk, = Specific angular momentum of disk, = Spin parameter (from LSS tidal torques),= Spin parameter (from LSS tidal torques), H(z) = Hubble constantH(z) = Hubble constant

… … we can determine both the structural we can determine both the structural properties and evolution of the disk.properties and evolution of the disk.

RRddVVcc, , jjdd/m/mdd , , , , 1/H(z)1/H(z) All cosmology dependence is in H(z)!All cosmology dependence is in H(z)!

Specific Angular MomentumSpecific Angular Momentum

Disk properties well reproduced in Disk properties well reproduced in simple model (e.g. MMW) simple model (e.g. MMW) IF jIF jDD/m/mDD~1~1..

But… is this assumption justified?But… is this assumption justified? Let’s simulate!Let’s simulate!

Abadi et al. (2003)Abadi et al. (2003)

Discussion…Discussion…

Hydrodynamic SimulationsHydrodynamic Simulations

Initial conditions: A small patch of the Initial conditions: A small patch of the Universe, in the linear regime, with Universe, in the linear regime, with dark matter and gas particles.dark matter and gas particles.

Model gravitational force between Model gravitational force between particles, additional pressure forces, particles, additional pressure forces, shock heating, and cooling for gas.shock heating, and cooling for gas.

Advance particle positions + Advance particle positions + velocities, lather, rinse, repeat.velocities, lather, rinse, repeat.

What happens?What happens?

Simulate a Single Disk Simulate a Single Disk GalaxyGalaxy

320 kpc/h

40 kpc/h(last panel only)

Successful Photometric Disk Successful Photometric Disk GalaxyGalaxy

Thin gaseous disk, Thin gaseous disk, bulge, halo.bulge, halo.

SB profile has rSB profile has r1/41/4 bulge, exponential bulge, exponential disk.disk.

Gas is more Gas is more extended than extended than stars.stars.

Looks a Looks a lotlot like like UGC615, an Sab… UGC615, an Sab… even reproduces even reproduces colors!colors!

SFR ~ 2 MSFR ~ 2 M/yr since /yr since last merger at z~1.last merger at z~1.

But when AM comes into play, But when AM comes into play, life gets much worse. life gets much worse.

RC is FAR too RC is FAR too centrally centrally concentrated.concentrated.

Owes to large, over-Owes to large, over-concentrated bulge.concentrated bulge.

But this is a direct But this is a direct result of early result of early hierarchical growth… hierarchical growth… and in a relatively and in a relatively quiescentquiescent halo! halo!

Specific Angular MomentumSpecific Angular Momentum Specific AM Specific AM jj of of

stars/baryons << stars/baryons << observed late-types.observed late-types.

Disk-only Disk-only jj agrees agrees well… if it only weren’t well… if it only weren’t for that pesky bulge!for that pesky bulge!

DM halo has similar j to DM halo has similar j to observed disks; seems observed disks; seems like nature conserves like nature conserves jj even though sims don’t.even though sims don’t.

And this is for favorable And this is for favorable quiescent case; typical quiescent case; typical case produces lower case produces lower jj..

Bottom line…Bottom line…

Simulation produces disk with some basic Simulation produces disk with some basic structural and photometric properties as structural and photometric properties as observed.observed.

But… best-case scenario only produces an But… best-case scenario only produces an Sab, no later.Sab, no later.

Even then, the bulge component is too Even then, the bulge component is too concentrated and too large.concentrated and too large.

Specific AM is too low, because bulk of Specific AM is too low, because bulk of stars form early in a stochastic, non-stars form early in a stochastic, non-ordered mode.ordered mode.

What Can We Do?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, Ignore it!!! Simulations are wrong, basic model (e.g. MMW) is right. 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 But even that turns out to not work so great…so great…

van den Bosch et al. (2001)van den Bosch et al. (2001)

Discussion…Discussion…

LSB GalaxiesLSB Galaxies Low Surface Brightness galaxies: What are Low Surface Brightness galaxies: What are

they?they?

Late-type Spirals, mostly bulge-less, gas-rich.Late-type Spirals, mostly bulge-less, gas-rich. Why LSBs?Why LSBs?

Quiescent history, RC is dark matter Quiescent history, RC is dark matter dominated: Ideal testbed for simple dominated: Ideal testbed for simple rotationally-supported collapse.rotationally-supported collapse.

How to measure rotation?How to measure rotation?

HH (optical) rotation curves in inner region, HI (optical) rotation curves in inner region, HI (21cm) rotation curve in outer region.(21cm) rotation curve in outer region.

Angular Momentum Angular Momentum DistributionsDistributions

Thick: Data (3 values of M/L)

Thin: Halos(3 values of )

Total AM of Disk (Total AM of Disk ())

For reasonable M/L ratio, For reasonable M/L ratio, of observed disks of observed disks are similar to that of DM halos.are similar to that of DM halos.

So total AM is apparently conserved in So total AM is apparently conserved in collapse… as assumed in MMW, but in contrast collapse… as assumed in MMW, but in contrast with simulations that cannot reproduce this.with simulations that cannot reproduce this.

Punchline: Halo vs. Disk AMPunchline: Halo vs. Disk AM

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

Key ResultsKey Results

Only a rather small fraction of baryons Only a rather small fraction of baryons end up in disk.end up in disk. Challenge to standard cooling modelChallenge to standard cooling model

Total AM of disk ≈ Total AM of all Total AM of disk ≈ Total AM of all baryons.baryons. Challenge to simulations showing AM lossChallenge to simulations showing AM loss

The disk is missing both highest and The disk is missing both highest and lowest AM baryons.lowest AM baryons. Challenge to models that assume simple Challenge to models that assume simple

rotationally-supported collapserotationally-supported collapse

So… How do we get rid of all So… How do we get rid of all this “unwanted” angular this “unwanted” angular

momentum?momentum? Need other physical processes!Need other physical processes! Perhaps high-AM material lost in Perhaps high-AM material lost in

mergers, or tidally stripped, or still left mergers, or tidally stripped, or still left in halo?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 Perhaps low-AM material blown out from center of galaxy?from center of galaxy? … … but simple model of feedback where but simple model of feedback where

large galaxies retain more baryons is large galaxies retain more baryons is opposite to trend seen in data!opposite to trend seen in data!

Wackier Notions…Wackier Notions…

Perhaps dark matter is not collisionless, Perhaps dark matter is not collisionless, and hence halo AM distribution is actually and hence halo AM distribution is actually much like that observed.much like that observed. … … but still have trouble explaining shape of but still have trouble explaining shape of

p(s)p(s) Perhaps baryons decouple from halos Perhaps baryons decouple from halos

early on, acquire different AM.early on, acquire different AM. … … no evidence for this in more recent work no evidence for this in more recent work

(e.g. Sharma & Steinmetz 2006)(e.g. Sharma & Steinmetz 2006)

So the bottom line is…So the bottom line is… Disk formation is a LOT more Disk formation is a LOT more

complicated than the MMW scenario.complicated than the MMW scenario. We still don’t understand it!We still don’t understand it! More recent results (e.g. Governato et More recent results (e.g. Governato et

al. 2004, Robertson et al. 2005) have al. 2004, Robertson et al. 2005) have used strong feedback to produce used strong feedback to produce later-type spirals. But still not clear later-type spirals. But still not clear that that distributiondistribution of AM is correct. of AM is correct.

Maybe there’s a hint from a related Maybe there’s a hint from a related but slightly different angle…but slightly different angle…

Swaters et al. (2003)Swaters et al. (2003)

Discussion…Discussion…

Universal Halo ProfileUniversal Halo Profile

CDM predicts universal halo profile CDM predicts universal halo profile (NFW).(NFW). All halos well fit by All halos well fit by NFW (1997): NFW (1997): = 1. = 1. Moore et al (1998): Moore et al (1998): ≈ 1.5≈ 1.5 Others: Everything in betweenOthers: Everything in between

Observations, at face value: Observations, at face value: ≈ 0! ≈ 0! What’s going on?What’s going on?

LSBs: Dark Matter Dominated LSBs: Dark Matter Dominated RC’sRC’s

Slowly rising RC’s, no bulge… can Slowly rising RC’s, no bulge… can probe inner dark matter profile.probe inner dark matter profile.

Density Profiles from Inverted Density Profiles from Inverted RCRC

Stay out of Stay out of Bars!Bars!

Bars cause non-Bars cause non-circular motions circular motions that mimic lower that mimic lower ..

Non-barred Non-barred sample fairly sample fairly consistent with consistent with NFW.NFW.

Fair and Balanced ViewFair and Balanced View Observations, at face value, tend to Observations, at face value, tend to

prefer low value of prefer low value of . . But there are many systematics… But there are many systematics…

and they almost all tend to lower and they almost all tend to lower !! Misidentifying center of potentialMisidentifying center of potential Non-circular motionsNon-circular motions Overly edge-on galaxiesOverly edge-on galaxies

Hence cannot rule out NFW (Hence cannot rule out NFW (=1).=1). Can rule out Moore profile (Can rule out Moore profile (=1.5).=1.5).

If NFW is Right, What About If NFW is Right, What About Concentrations?Concentrations?

Most agree with Most agree with simulations, but simulations, but a few clearly a few clearly low: Mostly low: Mostly barred galaxies!barred galaxies!

Do bars cause Do bars cause lower mass lower mass concentration? concentration? (Weinberg & (Weinberg & Katz 2002)Katz 2002)

Bottom LineBottom Line Overall, no obvious disagreement with Overall, no obvious disagreement with

NFW, either in inner slope or NFW, either in inner slope or concentration.concentration.

But debate is far from over! 2-D IFU But debate is far from over! 2-D IFU data also shows shallow mass profiles.data also shows shallow mass profiles.

Theory debate not over either (paper Theory debate not over either (paper on astro-ph today claiming a totally on astro-ph today claiming a totally new functional form).new functional form).

If NFW is right, then can’t solve disk If NFW is right, then can’t solve disk AM problem by changing DM AM problem by changing DM distribution.distribution.

That’s It For Today!That’s It For Today!

Some successes, many unresolved Some successes, many unresolved issues in theory of disk galaxy issues in theory of disk galaxy formation.formation.

Next time (next Wed): Marcia will Next time (next Wed): Marcia will tell you all about elliptical galaxies.tell you all about elliptical galaxies.