Thursday. Saw Yoko off, have 1 hr till next train arrives. Have 2 days of astro-ph to read.
1201.4859
The SF history of Leo T from HST imaging
Weisz, ... de Jong, .. Dalcanton, ... Bell, et al
SFH of the faintest SF galaxy Leo T with WFPC2. Color-magnitude diagram of Leo T is 2 mag below the oldest MS turnoff, permit excellent constraints on SF at all ages. Assume 3 different stellar evolution models: (1,2) solar-scaled metallicity (Padova and BaSTI) and (3) alpha-enhanced metallicities. The resulting SFHs are consistent at all ages (SFH robust). 50% of total stellar mass formed z>1 (7.6 Gyr ago). After this, the SFH is roughly constant until 25Myr ago, when it shows an abrupt drop, but could be due to IMF effect (unable to distinguish between the two). HST provides improved age resolution and reduced uncertainties at all epochs. Leo T does not resemble other faint dwarf galaxies from the Local Group, but strongly resembles gas-rich dwarf galaxies (irregular or transition), suggesting that gas-rich dwarf galaxies may share common modes of SF over a large range of stellar mass (1e5-9 Msun).
1201.4863
Optimizing automated classification of periodic variable stars in new synoptic surveys
Long, El Karoui, Rice, Richards, Bloom
Classification of periodic variable stars necessary as survey scales grow. Machine learning, statistics to construct classifiers on multi-epoch sources for automatic classification. But different surveys will yield different features (metrics) from the light curve; survey-dependent mismatch in feature will typically lead to degraded classifier performance. Show how and why feature distributions change, using OGLE and Hipparcos light curves. Apply "noisification" method which attempts to empirically match distributions of features between the labeled sources used to construct the classifier and the unlabeled sources wished to be clarified. Results from simulated and real-world light curves show noisification can significantly improve classifier performance, from 27% to 7%. Recommend use for Gaia and LSST.
1201.4864
Spikes in the SED and ripples in the outskirts of galaxies
Chakrabarti
Describe a new method that quantitatively characterize galactic satellites from analysis of distrubances in outer gas disks, without optical information of the satellite ("Tidal Analysis"). Apply to local spirals with known optical companions (e.g., M51/NGC 1512), which have companions 1/100 to 1/3 mass of the primary galaxy. Present preliminary results on the SEDs and images calculated along the time sequence of dynamical simulations using the 3D self-consistent MC radiative transfer code RADISHE. Explore SF prescriptions and how they affect the emergent SEDs and images. Goal: identify SED colors that are primarily affected by the galaxy's interaction history, and not significantly affected by the choice of SF prescription. If successful, may be able to utilize the emergent UV-IR SED of the primary galaxy to understand its recent interaction history.
1201.4873
Magnetically-levitating disks around SMBH
Gaburov, Johansen, Levin
Report on the formation of magnetically-levitating accretion disks around SMBH. Structure of disks calculated by numerically modelling tidal disruption of magnetized interstellar gas clouds. Find: resulting disks entirely supported by the pressure of the magnetic fields against the component of gravitational force directed perpendicular to the disks. The magnetic field shows ordered LS geometry that remains stable for the duration of numerical experiments extending over 10% of disk lifetime. Strong magnetic pressure allows high accretion and inhibits disk fragmentation: in combination with the repeated feeding of magnetized molecular clouds to a SMBH yields a possible solution to the long-standing puzzle of BH growth in the centers of galaxies.
1201.4878
A consistent comparison of bias models using observational data
Papageorgiou, Plionis, Basilakos, Ragone-Figueroa
Investigate 5 different models for the DM halo bias, by comparing their cosmological evolution using optical QSO and galaxy bias data at different redshifts, consistently scaled to the WMAP7 cosmology. Assuming each halo hosts one extragalactic mass tracer, use a chisq minimization procedure to determine the free parameters of the bias models; statistically quantiyf ability to represent the observational data. Find the best model(s). The average DM halo mass that hosts optical QSOs are M_h=2.7e12 Msun/h, while the corresponding value for optical galaxies is M_h=6.3e11Msun/h.
1201.4889
Standard candles from the Gaia perspective
Eyer et al
ESA Gaia mission will bring a new era to the domain of standard candles. Astrometric precision, whole-sky coverage, and the combination of photometric, spectrophotometric and spectroscopic measurements. Fundamental outcome: DPAC (Gaia Data Analysis and Processing Consortium), which will contain a variable source classification and specific properties for stars of specific variability types. Review what will be produced for Cepheids, RR Lyrae, Long Period Variable stars and eclipsing binaries.
1201.4989
NIR/Optcial selected local mergers: spatial density and sSFR enhancement
Xu
Dependence of local merger rate and the sSFR enhancement on 4 fundamental observables: (1) stellar mass (2) mass ratio (3) separation (4) environment.
1201.4910
The HST/ACS coma cluster survey. VIII. Barred disk galaxies in the core of the Coma cluster
Marinova et al
Use HST images to study bars in massive disk galaxies (S0s) and in dwarf galaxies in the Coma core; to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. (1) Fraction and properties of bars in 32 bright S0 galaxies that dominate the cluster core. About 60%. (2) Compare the S0 bar fraction across different environments (Coma core, A901/902, Virgo). Find bar fraction among bright S0 galaxies does not show a statistically significant variation across environments spanning 2 orders of magnitude in galaxy number density (n~300-10000 gal/Mpc^3). S0 bar fraction not significantly enhanced in rich clusters because S0s in rich clusters are less prone to bar instabilities (they are dynamically hot and gas poor due to ram pressure stripping and accelerated SF). Additionally, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) Analyze a sample of 333 faint dwarf galaxies in Coma core; only 13 with bar and/or spiral structure. Paucity of disk structures in Coma dwarfs suggest that either disks are not common in these galaxies, or that any disks present are too hot to develop instabilities.
1201.4947
Constraints on obscured SF in host galaixes of gamma-ray bursts
Hatsukade, et al
Observe 4 host galaxies of GRBs in 16-cm continuum using Australia Telescope compact array. Radio not detected in any of the host galaxies. Derive upper SF rates, ~30-45 Msun/yr; 10 times less than from UV/optical observations (no significant dust-obscured SF). Results imply that dark GRBs do not always occur in galaxies enshrouded by dust. Suggest cause of dark GRB is the intrinsic faintness of the optical afterglow (dust extinction not observed). High column density observed in afterglow, the likely cause of the dark GRB (extinction in the LoS).
1201.4950
Are nuclear star clusters the precursors of massive black holes?
Neumayer, Walcher
Present upper limits for BH masses in extremely late type spiral galaxies. Confirm: has BH with M<1e6 Msun, if any. Derive new upper limits for nuclear star cluster (NC) masses in massive galaxies with known BH masses. Use new upper limits and literature compilation to study the low mass end of the global-to-nucleus relation. Find: (1) the M_BH-sigma relation cannot flatten at low masses, but may steepen. (2) The M_BH-M_bulge relation may flatten in contrast. (3) The M_BH-Sersic n relation is able to account for the large scatter in BH masses in low-mass disk galaxies; outliers seem to be dwarf ellipticals. When plotting M_BH-M_NC, find 3 different regimes, implying a sequence of NC dominated transitioning into BH dominated, by which the BH grow faster and destroy the NC when M_BH is >100 M_NC. Nuclear star clusters may thus be the precursors of massive BH in galaxy nuclei.
1201.4970
The structure of HI in galactic disks: simulations vs observations
Acreman, et al
Generate synthetic HI galactic plane surveys from spiral galaxy simulations which include stellar feedback processes. Compared to a model without feedback, find a increased scale height of HI emission (in better agreement with observations) and more realistic spatial structure (including SNe blown bubbles). The synthetic data show HI self-absorption with a morphology similar to that seen in observations. The density and temperature of the material responsible for HI self-absorption is consistent with observationally determined values, and is found to be only weakly dependent on absorption strength and SF efficiency.
* what is self-absorption?
1201.4998
Revealing velocity dispersion as the best indicator of a galaxy's color, compared to stellar mass, surface mass density or morphology
Wake, van Dokkum, Franx
Using SDSS nearby galaxies, investigate whether stellar mass, central velocity dispersion, surface mass density, or Sersic n parameter is best correlated with a galaxy's rest-frame color. Specifically, determine how the mean color of galaxies varies with one parameters when another is fixed. When stellar mass is fixed, see that strong trends remain with all other parameters. Residual trends are weaker when surface mass density, n, or velocity dispersion are fixed. Overall, velocity dispersion is the best indicator of a galaxy's typical color, showing the largest residual color dependence when any of the other 3 parameters are fixed, and stellar mass is the poorest. Other studies have indicated that both the halo and BH properties are better correlated with velocity dispersion than with stellar mass, surface mass density or Sersic n. Therefore, results are consistent with a picture where a galaxy's star formation history and present SFR are determined to some significant degree by the current properties and assembly history of its dark matter halo and/or the feedback from its central SMBH.
1201.5018
Looking for the Wind in the Dust
Gallagher, Everett, Keating, Hill, Deo
The blue-shifted broad emission lines and/or broad absorption lines seen in many luminous quasars are evidence for a broad line region in which radiation driving plays an important role. Consider the case for a similar role for radiation driving beyond the dust sublimation radius by focussing on the IR regime where the relationship between luminosity and the prominence of the 3-5 micron bump may be key. [?] Apply 3d hydrodynamic wind model of Everett to predict the IR SED of quasars. The presence of the 3-5 micron bump and strong, broad silicate features can be reproduced with this dynamical wind model when radiation driving on dust is taken into account.
1201.5101
Slicing the Torus: obscuring structures in quasars
Elvis
Quasars and AGNs are often obscured by dust and gas. It is normally assumed that the obscuration occurs in an oblate "obscuring torus", that begins at the radius at which the most refractive dust can remain solid. The most famous form of this torus is a donut-shaped region of molecular gas with a large scale-height. While this model accounts for many phenomena at once, it does not hold up to detailed tests. In stead the obscuration in AGNs must occur on a wide range of scales and be due to a minimum of 3 physically distinct absorbers. Slicing the "torus" into these 3 regions will allow interesting physics of the AGN to be extracted.
1201.5112
Astrophysical models of r-Process nucleosynthesis: An update
Qian
Update on astrophysical models for nucleosynthesis via rapid neutron capture (r process) given. A neutrino-induced r process in SNe He shells may have operated up to metallicities of 1e-3 times the solar value. Another r-process source, possibly neutron star mergers, is required for higher metallicities.
1201.5114
Observations of dark and luminous matter: the radial distribution of satellite galaxies around massive red galaxies
Tal, Wake, van Dokkum
Study the projected radial distribution of satellite galaxies around more than 28k LRGs at z=0.34 and trace the vravitational potential of LRG groups in the range 7<
[...abstract messed up...]
whereas baryons account for more than 50% of the mass at smaller radii. Calculate the total dark-to-baryonic mass ratio and show that it is consistent with measurements from WL for environments dominated by massive early type galaxies. Divide the satellite galaxies into 3 luminosity bins, and show that the satellite light profiles of all brightness levels are consistent with each other outside of roughly 25 kpc. At smaller radii find evidence for a mid mass segregation with an increasing fraction of bright satellites close to the central LRG.
1201.5116
Cooling and heating functions of photoionized gas
Gnedin, Hollon
Cooling functions of cosmic gas are crucial ingredient for any study of gas dynamics and thermodynamics in the interstellar and intergalactic medium. As such, they have been studied extensively in the past under the assumption of collisional ionization equilibrium. However, for a wide range of applications, the local radiation field introduces a non-negligible, often dominant, modification to the cooling and heating functions. In the most general case, these modifications cannot be described in simple terms, and would require a detailed calculation with a large set of chemical species using a radiative transfer code (e.g., "Cloudy"). Show, however, that for a sufficiently general variation in the spectral shape and intensity of the incident radiation field, the cooling and heating functions can be approximated as depending only on (1) the photo-dissociation rate of molecular H, (2) the H photo-ionization rate, and (3) the photo-ionization rate of OVIII; more complex and more accurate approximations also exist. Such dependence is easy to tabulate and implement in cosmological or galactic-scale simulations, thus economically accounting for an important but rarely-included factor in the evolution of cosmic gas. Also show a few examples where the radiation environment has a large effect, the most spectacular of which is a quasar that suppresses gas cooling in its host halo without any mechanical or non-radiative thermal feedback.
Astronomical Colloquium (MPIfR 0.02, Fri. 11am)
The early evolution of protostellar disks: fragmentation, episodic accretion, planet formation and other unexpected effects
Eduard Vorobyov
Review the recent progress in understanding the early stages of protostellar disk evolution when the disk is deeply embedded in the parent core: disks prone to gravitational instability and fragmentation--triggering episodic accretion onto the star; formation of gas giants and brown dwarfs on wide orbits and ejection of brown dwarfs and very-low-mass stars into the intracluster medium; flattening of the mass accretion--stellar mass relation the crystallization of amorphous silicates in the depths of massive fragments. Show how episodic accretion can resolve the long standing luminosity problem, where young stars are systematically underluminous compared to what standard theories of SF predict.
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