LBL INPA
New insights on galaxy evolution since z~1.2 from the CFHT Legacy Survey
Jean Coupon, Tohoku University
Galaxies in low- and high-mass halos experience very distinct fate. Study relationship between stellar mass and halo mass brings valuable clues about physical processes involved in galaxy evolution. Halo model assumes that number of galaxies only depend on halo mass (HOD model), which seems to an accurate analytic prediction of galaxy distribution. Reciprocally, interpreting galaxy clustering using the HOD model allows to make a direct comparison between galaxy properties and halo mass. Use CFHTLS data to see the relationship evolve between the galaxy and DM haloes since z~1.2.
1108.1812
The Bolocam galactic plane survey VII: Characterizing the properties of massive star-forming regions
Dunham, Rosolowsky, Evans, Cyganowski, Urquhart
Toward the high column density regions targeted by BGPS (Bolocam galactic plane survey) with GBT, 72% of the targets (456) were found to have NH3(1,1) lines, demonstrating the high-column density features found there accurately predict the presence of dense gas (what was the original target criteria for BGPS?). Determine kinematic distance and resolved distance ambiguity (what's important about that?) of those with NH3. Locates the Scutum and Sagittarius spiral arms; number of sources detected peak at 4-5 kpc. Depending on the distance, the BGPS objects are mostly clumps, with some cores and clouds. The mean gas kinetic temperature is 15.6K; the NH3 column density and abundance decrease by an order of magnitude between 3 to 11 kpc from the Galaxy center. Similar distance objects have physical properties that are indistinguishable--suggest similarity in clump structure across the Galactic disk. Compared BGPS sources to criteria for efficient star formation. 48% of sample should be forming stars (including massive ones) with high efficiency and 87% contain subregions with should have efficient SF; find 67% of the sample exhibit signs of SF activity based on mid-IR information.
* what is the difference between cores, clumps and clouds?
1108.1796
The effects of a hot gaseous halo on disc thickening in galaxy minor mergers
Moster, Maccio, Somerville, Naab, Cox
Simulate (for the first time) diffuse, rotating, cooling, hot gaseous halo to hydro simulations of minor mergers. Effect of this new gaseous component on MW galaxy to its thickness on 1:10 and 1:5 mergers. For 1:10 mergers the thin disc scale does not show thickening (compared to isolated galaxies)--accretion of new cold gas leads to formation of massive new thin stellar disc that dominates the surface brightness profile. Disc thickening dominated by cold-gas induced SF--the thick disc is the old stellar disc that has been thickened in a minor merger at z>1 ("in this scenario")--the thin disc is the new stellar disc that forms after merger. Evolution of the scale height during a 1:5 merger--a thin disc can be present even after the merger, if enough hot (?) gas is avaliable. ...etc.
1108.2052
No wide spread of stellar ages in the Orion Nebula cluster
Jeffries, Littlefair, Naylor, Mayne
Disc signatures decay monotinically (on average) over timescales of only a few Myr--hence any spread in SF time distribtion should lead to clear differences in the age distribtions of stars with and without discs (if all stars are born with circumstellar discs). Any real age spread must be smaller than the median disc lifetime. For a log-normal age distribution, there is an upper limit of <0.14 dex (>2 sigma) to any real age dispersion, compared to ~0.4 dex implied by the HR diagram. If the mean age for ONC is 2.5 Myr, then 95% the low-mass stellar population should have ages 1.3-4.8 Myr. The obsered luminosity dispersion is caused by a combination of observational uncertainties and physical mechanisms that disorder the conventional relationship between luminosity and age for pre-main-sequence stars.
* ..but is there observational evidence (from stellar discs) that ONC stars all have similar ages? Or is this already true and known--but then the argument all depends on the rate of circumstellar disc dissipation rate? I wish they would explain.
1108.1786
Molecular gas around low-luminosity AGN in late-type spirals
Beoker, Schinnerer, Lisenfeld
Study of molecular gas around low-luminosity AGN in 3 late-type spirals (bulge-less): transitions of gaseous CO clearly detected within the central kpc of all 3 galaxies. The CO emission is faint (expected from low SF activity). Face-on galaxies show elevated intensity ratio of CO(2-1)/CO(1-0) transitions compared to similar galaxies w/o AGN---unlikely due to a very compact CO source; speculate that energetically weak AGN can still impact the physcial state of surrounding gas. No tracers of dense molecular gas (e.g., HCN or HCO+), but can establish upper limits that lie at the low end of the range in more energetic AGN The derived gas density is less than n(H2) ~ 2e3 cm^-3, which is significantly lower than in most other newrby galaxies. Scarsity of dense gas suggests that the conditions for SF are poor in these nuclei. (duh)
* what is the connection between AGN, dense gas and SF? It seems that AGN triggers SF---or is it not a causal effect, but rather the results of a single cause (i.e., mergers)?
UCB Astro Seminar
The Physics of Self-Regulated Star Formation
Andi Burkert
If star formation happened according to the simple cosmological sequence of DM halo collapse, to the gravitational collapse of cold, dense molecular gas that burst into stars, the galaxies should be burned out by now---which is in contrast to observations.
Physics of interstellar medium and star formation is still in its early phase of exploration; high-resolution observations provide insight into the complex structure of the turbulent interstellar medium and its various gas phases. Star formation history of molecular cloud regions like Taurus and Orion have been investigated in great detail; numerical simulations have achieved enough resolution and complexity to study the origin and evolution of turbulent molecular clouds and their fragmentation into stars and stellar clusters within the galactic environment.
First summarize the most puzzling and challenging questions of star formation, then discuss a new approach that links star formation in galaxies to their cosmic baryonic accretion history. Then present new numerical simulations by Dobbs+ (2011a,b) on the evolution of the molecular web in disk galaxies that provide new insight into the self-regulated evolution of the multi-phase interstellar medium and its condensation into stars.
* I should probably read the paper by Dobbs+ (2011a,b). Sounds interesting.
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