lit: evolution of dwarf galaxies: a dynamical perspective

I was tasked with presenting Lelli et al. 2013 in our group meeting. Here are the slides [pdf].

Daily paper: The Tully-Fisher relations of early-type spiral and S0 galaxies

I gave a talk at our group meeting yesterday, this was one of several useful suggestions and references I got. bWilliams et al. 2010, The Tully-Fisher relations of early-type spiral and S0 galaxies
Offsets which are ascribed to fading or brightening could in fact be due to systematic biases that differ between the measures of rotation used. For typical slopes of the TFR, a relatively small systematic difference in velocity of ∼0.1 dex introduces an offset in the TFR that is indistinguishable from a ∼ 1mag difference in luminosity.
Our conclusions in this section have three consequences for previous works that measure the TFR of S0 galaxies using stellar kinematics corrected for asymmetric drift (e.g. Neistein et al. 1999; Hinz et al. 2001, 2003, BAM06): (i) the asymmetric drift correction they use yields similar results to detailed Jeans modelling; (ii) the drift correction does not seem to introduce a systematic bias between spirals and S0s and, if applied to samples of both spirals and S0s, can indeed be used to compare the TFRs of the two classes; (iii) however, a TFR derived from asymmetric drift-corrected stellar kinematics cannot be directly compared to TFRs derived from global HI line widths or resolved emission line PVDs. ==== There's a really interesting section on the ADC, and a nice comparison of gas/HI/AD corrected stellar kinematics. Also I should check their section on TFR fitting, intrinsic scatter in it, etc.In addition, I ought to take a look at the references therein, esp. the introduction.

Daily Paper #7: Galaxy groups in the 2dFGRS: the number density of groups

Title: Galaxy groups in the 2dFGRS: the number density of groups
Authors: Eke, Baugh, Cole et al.
Year: 2006, http://adsabs.harvard.edu/abs/2006MNRAS.370.1147E
The authors determine the galaxy groups mass and luminosity functions from 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue (getting about 29 000 groups). The catalogue and the mock catalogues used to determine and correct for bias are described in Eke 2004 paper.
They obtain dynamical masses of the clusters (I think they use the words 'cluster' and 'group' interchangeably here) from their velocity dispersions, and obtain their luminosities by simply adding up the members' luminosities with weighting to account for spectroscopic incompleteness and galaxies below the flux limit. Then they correct the mass and luminosity functions using the Vmax method. However, they claim that a more robust way to determine the group mass function is deriving it from the luminosity function by multiplying it by a mass-to-light ratio. They also show that the total group luminosity function depends on the group finding algorithm used.
The main goal of the article is to determine the \sigma_8 parameter, but they make a comparison between halo velocities and circular velocities, claiming that the two are similar. The authors claim it is possible to convert a halo luminosity to its circular rotation velocity directly, then convert group luminosities (which are very similar to those of the brightest galaxy of the group) to circular velocities using Bell & de Jong B-band TF relation, and compare the two (see the attached figure).


I think it is an important article, because it is observational, and worth citing while discussing the halo/galaxy velocities issue (the ratio of v_c/v_200 is around 1.2, at least from the simulations, not close to 1 as they find here). Anyway, I'll remember this article in case I have enough time to work on the velocity function.

lit: Baryonic T-F relation

S. McGaugh et al, somehow the baryons know how many stars to form'.
There is also a reference to Mo 1998, which may provide insights into the origin of the T-F relation.

lit: Rotational support in galaxies

I was wondering how to derive v_rot/sigma ratio for my sample, here is a review: Rotation and anisotropy of galaxies revisited, by J. Binney.

lit review: The shape of the dark matter halo in the early-type galaxy NGC 2974

The shape of the dark matter halo in the early-type galaxy NGC 2974, by Weijmans, Krajnovic et al. They use kinemetry to analyse gas and stellar kinematics, with clear description of the AD correction. (Thanks, Mariya!)

lit review: a generalization of photometry to the higher moments of the line-of-sight velocity distribution

by Krajnovic et al.. This will probably be one of the important papers when writing: an interesting breakdown and discussion of velocity map moments, also many useful references (esp. Schoenmakers et al. (1997), the degeneracy of q, center and systemic velocity v0.
We have presented a generalization of surface photometry to the higher-order moments of the LOSVD, observed with integral-field spectrograph. We call our method kinemetry. For even moments of the LOSVD, kinemetry reduces to photometry. For odd moments, kinemetry is based on the assumption that it is possible to define an ellipse such that the kinematic profile extracted along the ellipse can be well described by a simple cosine law. This assumption is satisfied in the case of simple axisymmetric rotators.

lit: Galactic Dynamics

I'm reading Binney & Tremaine's section on LSR, asymmetric drift and its correction, as I plan to do the corrections for my stellar velocity fields. Some definitions:
LSR is the hypotetical local standard of rest: velocity of some imaginary stars in precisely circular orbits at the Solar radius.
Characteristic thickness is the ratio of surface density to its volume density at the galactic plane: it's different for different stellar populations (like their vertical scale lengths), arising due to interactions w/ molecular clouds and/or spiral arms.
The collisionless Boltzmann equation states that the flow of stellar phase points through phase space is incompressible: phase space density around a phase point of a given star remains constant. A nice example of such incompressible flow is a marathon race where all participants run at constant speeds: at the begining the density of runners is large, but their speed distribution is wide. At the end of the race the density is low, but the speeds of all runners passing a point are very similar. The coordinates of stars in phase space are (x, v).
Asymmetric drift is the difference between the LSR (local circular speed) and the mean rotation velocity of a population. Velocity dispersion and asymmetric drift: see eq. 4.32-4.34 for the correction formulae; also Neistein, Maoz, Rix et al. for their application.

lit: Asymmetric Drift and the Stellar Velocity ellipsoid

Asymmetric Drift and the Stellar Veloocity ellipsoid by Westfall, Bershady et al.:
The shape of the stellar velocity ellipsoid, defined by \sigma_R, \sigma_{phi}, and \sigma_z, provides key insights into the dynamical state of a galactic disk: \sigm_z:\sigma_R provides a measure of disk heating and  \sigma_{phi}:\sigma_R yields a check on the validity of the epicycle approximation (EA). Additionally, \sigma_R is a key component in measuring the stability criterion and in correcting rotation curves for asymmetric drift (AD), while \sigma_z is required for measuring the disk mass-to-light ratio.
See also p.2 on asymmetric drift corrections for stellar velocities.

Jerusalem WS lecture notes: 12. Galactic dynamics II

By R. Sari, slides of both talks here.

• stability: dispersion relation
• spiral density waves: leading and trailing, pattern speed
• resonances: co-rotation, Lindblad resonances: drift through arms: epicyclic motion of particles in the disk. Pressure: away from CR, gravity: towards the center. Each epicyclic period a particle drifts one potential peak
• migration: dynamical friction, one-sided torques from the outer disk and the inner disks: push from inner side stronger than pull from the outer (? shouldn't it be the inverse?)
• marginally stable galaxies
• centrifugal barrier: disk stability
• 18 \pi^2: overdensity
  • final semi-major axis of the overdense region:
  • Keplerian elliptical orbit: t_{vir} = 2\pi/(sqrt(GM/a^3))
  • density ratio: \rho_0(r_0/a)^3/\rho_0*(t_{vir}/t0) = r_0^3/a^3 \cdot 4\pi^2/GMt^2_0 = 9/4 \cdot v_0^2 \cdot 4 \pi^2/1/2 v_0^2 = 18 \pi^2
• virial theorem:
  • relaxation: two-body, resonant (in almost Keplerian systems), violent. two-body relaxation time t_{rd} = R/V\cdot N/lnN
  • tidal breakup: binaries (interaction with BH), stars, extended objects: 'black hole worshipping' - BH destroys objects, relaxation brings them back
  • binaries destruction: r_{tidal}: when the rotation period of the binary is equal to rotation around the BH (forces are equal)
  • differential force for the binary system: r_{tidal} = a(M_{BH}/m)^{1/3}
  • density: spread out the masses
  • largest orbital velocity for a binary member: v_{esc}, few hundred km/s for MS stars. BHs enhance the velocity by orders of magnitude -> hypervelocity stars
• loss cone
• filling rates