1203.1317
A nearby analog of z~2 compact quiescent galaxies with a rotating disk
Jiang, van Dokkum, Bezanson, Franx
Compact galaxies (common at z~2) are very rare today: NGC 5845 is such an example, M_dyn=4.3e10 Msun, r_e=0.45 kpc. HST study of structure and kinematics. Similar to z~2 population in terms of mass vs. size, velocity dispersion versus size, effective velocity dispersion vs dynamical mass. Has a prominent orating disk; contribute to 1/4 of the total light of the galaxy. Fraction of z~2 galaxies have prominent disks and positive M/L gradients (although it is at low z, so it may have different formation history than those at z~2).
1203.1318
How to distinguish starbursts and quiescently SF galaxies: the 'bimodal' submillimeter-seleted galaxy population as a case study
Hayward, Jonsson, Keres, Magnelli, Hernquist, Cox
High-z bright sub-mm-selected galaxy (SMG) population is heterogenous: major mergers contribute both at early (quiescently SF discs blended into one submm source--galaxy pairs) and late (mutual tidal torques drive gas inflows and cause strong starbursts) stages. Combine hydro sim of major mergers with 3d dust radiative transfer to determine observational diagnostics that can distinguish between quiescent SF SMGs and starburst SMGs via integrated data alone: fit the FIR SEDs of simulated galaxies with optically thin single-temperature modified BB, full form of modified BB, and power-law temperature distribution model. Effective dust temperature, Tdust, and power-law index of the dust emissivity in the far IR; power -law index not recovered well, but Tdust is a good indicator of starburst (high Tdust = starburst). 'Hot-dust ULIRGs' are typically starburst galaxies lower in mass than SMGs, but they can also simply be SMGs observed from a different viewing angle.
1203.1319
NGC 4656UV ("hockey stick"): a UV-selected tidal dwarf galaxy candidate
Schechtman-Rook, Hess
Discovery of a UV-bright tidal dwarf galaxy candidate. Use archival data from UV to 1.4 GHz to investigate the gas kinematics and stellar properties of this system. Galaxies in the whole system are disturbed strongly, with counterrotating and extraplanar gas. New method to correct for surface gradients on faint objects. Find: 4656UV has no significant dust opacity, and a blue SED. SFR of 0.027 Msun/yr from FUV flux, total HI mass of 3.8e8 Msun; a low metallicity system; only major burst of SF happened in the last 260~290 Myr. Age of stellar population consistent for a recent tidal interaction between NGC 4656 and 4631, but metallicity is a factor of 10 lower than its parent galaxy. Estimate that 4656UV is marginally bound or unbound. If bound, it contains relatively low amounts of DM. Lots of archival data for this tidal dwarf galaxy.
1203.1323
Cosmological X-ray scattering from intergalactic dust
Corrales, Paerels
Dust grains 0.1-1um in size will scatter X-rays; a diffuse "halo" around a x-ray point source can tell us about IGM dust. Two forms for scattering: (2i) from IGM uniformly enriched with a power-law distribution of grain sizes, and (ii) a DLA-type dust screen at cosmological distances. The surface brightness profile can distinguish between the two scenarios above, place constraints on dusty clumps and constrain the homogeneity of the IGM. Gauge contribution of the first stars, dwarf galaxies, and galactic out flows to cosmic metallicity budget and cosmic history of dust.
1203.1326
Discovery of a protocluster at z~6
Toshikawa, et al
Discovery of a protocluster at z~6 containing at least eight cluster member galaxies with spectro-z confirmations. Overdensity of the protocluster is significant at the 6 sigma level, based on surface number densty of (count=30) i'-dropout galaxies. 15 of the i dropouts are 5.7<z<6.3. 8 of the 15 are clustering in a narrow redshift range centered at z=6.01 (7x increase in number density over the average in z space. Find no significant difference in the observed properties (LyA luminosities and UV continuum magnitudes) between the 8 protocluster members and the 7 non-members. Velocity dispersion of the 8 members is 647 km/s, 3x higher than that predicted by standard CDM model. Discrepancy: possibly due to 3d (positional) distribution; a mature protocluster; an immature cluster composed of 3 subgroups merging.
1203.1327
Two populations of molecular clouds in the antennae galaxies
Wei, Keto, Ho
Super star clusters: extremely massive clusters found predominantly in starburst environments; essential building block in formation of galaxies, dominate SF in the high-z universe. But transformation from molecular gas into ultracompact star clusters is not well understood. Look at Antennae overlap region at high resolution in CO(2-1) to search for molecular progenitors of super star clusters. Resolve many clouds, extend differential cloud mass function down to 3.8e5 Msun (5 sigma). Identify a distinct break in the mass function around M_mo ~ 1e6.5 Msun, which separates the molecular clouds into: (1) smaller, less assive clouds residing in more quiescent areas, and (2) larger, more massive clouds around regions of intense SF. A broken power-law fit to the mass function; well matched to the mass function for super star clusters in the Antennae galaxies [?]. Find large velocity gradients and dispersions at locations of intense SF, suggestive of compressive shocks. Likely that environmental factors contribute to the formation of the observed massive molecular clouds and super star clusters in the Antennae galaxies.
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