Dark Matter on Small Scales: Merging and Cosmogony David W. Hogg New York University CCPP
summary galaxy merger rates suggest growth of ~1 percent per Gyr galaxy evolution is over can we rule out CDM now or soon?
information and physics look at quantities that can be predicted, or will be in the near future, and do the experiments that are most informative (ie, that produce the largest amount of Fisher information)
data: Sloan Digital Sky Survey and the Bright Star Catalog visualization: David W. Hogg (NYU) with help from Blanton, Finkbeiner, Padmanabhan, Schlegel, Wherry
redshift one tenth: cons don t span huge time intervals only see evolution within the sample at low significance
redshift one tenth: pros huge, complete, uniform survey volumes, especially the SDSS high spatial resolution on tens of thousands and adequate resolution on millions of sources high signal-to-noise ratio measurements (spectral and imaging)
properties star-formation histories current and past activity, including luminosities kinematically hot and cold structures bulges and disks tidal features central black holes detailed chemical abundances gravitationally bound structures
CDM CDM is incredibly successful on large scales (>10 Mpc) it s not unlike QED in terms of experimental verification there are infinitely many possible behaviors on small scales (<1 Mpc) attractions, repulsions, bound states crystals, collective behavior winds, shocks only the stupidest possibilities have been ruled out
galaxy merger rate CDM is incredibly successful on large scales if it is also correct on Mpc scales, then virialized halos are merging prodigiously at the present day (even in accelerating models) when halos merge, at least some galaxies must merge galaxy mergers are observationally tractable
the point If you want to investigate dark matter on small scales (<1 Mpc), you must study galaxies and their interactions (or do particle theory, or build huge accelerators)
Masjedi, Hogg, et al 2006
merger rate of LRGs LRGs (red, brighter than L-star) reside in (are at the centers of?) very massive halos Eisenstein et al 2003; Zehavi et al 2004, 2005 stellar populations and morphologies are relatively simple NB: need to use cross-correlation techniques to escape spectrograph constraints 55-arcsec constraint in SDSS SDSS algorithm is extremely simple (Blanton et al)
Masjedi, Hogg, et al 2006, ApJ in press
merger rate of LRGs at very small scales (<100 kpc), dynamical friction must become important merger rate is (at most) the mean number of close pairs divided by the dynamical time each LRG has <1 percent probability of an LRG merger every Gyr at redshift 0.3 Masjedi, Hogg, et al 2006 ApJ in press see also papers by Carlberg and collaborators this maximal rate is low?
evidence of late merging close pairs tidal features and morphological mergers post-starburst galaxies
data: SDSS / image: Hogg
stars OBAFGKMLT OB lifetimes ~107 yr 105 K; fully ionize their environments A lifetimes ~109 yr 104 K; strong Balmer absorption G 103.7 K; lifetimes ~10 10 yr
time scales OB stars ~107 yr dynamical times ~107.5 yr A stars ~109 yr Hubble time ~1010 yr
Quintero, Hogg, et al 2004 (models from Fioc)
Quintero, Hogg, et al 2004
Quintero, Hogg, et al 2004
post-starburst galaxies galaxies that are not forming stars (no Hα) but formed many recently (lots of A stars) Quintero et al, see also Goto et al, Blake et al primordial papers by Dressler and Gunn, and Zabludoff these are the progenitors of early-type galaxies, theoretically and observationally alpha-enhancement colors, radial profiles, and surface brightnesses because A stars are clocks, we can infer formation rates
post-starburst galaxies event rate: ~10-4 h 3 Mpc -3 Gyr -1 Quintero, Hogg, et al 2004 ApJ 602 190 the bulge-dominated ( early type ) galaxy population is growing by one percent per Gyr if this is a merger rate, this rate is low but this might be a limit not a measurement
Quintero, Hogg, et al 2004
evidence of late merging close pairs tidal features and morphological mergers post-starburst galaxies
morphological merger rate clearly merging galaxies are rare to get a rate, you need a time scale some features can last for many dynamical times even individual systems might have things to say about dark matter dynamics a great goal that has been abandoned by the youth
summary galaxy merger rates can be constrained observationally observations suggest growth of ~1 percent per Gyr galaxy evolution is over can we rule out CDM now or soon?
the end