Friday, at Kitt Peak. Lots happened: Took a long flight from Frankfurt to SFO to Tucson. Picked up my new MacBook Air (it's awesome). Set it up as fast as I could, so that I can schedule the observation. But now I'm 3 days behind in astro-ph. Try to get at least one day's worth read today. Last night: snowstorm, no observation.
1202.2850
Collisional excitation of FIR line emissions from warm interstellar CO
Neufeld
* "rotation diagram" technique: population per sub level is plotted against the (log) energy of the upper level involved in the transition. The slope on a semi-log plot gives (rotation) temperature, and the y-intercept the column density.
New rate coefficients for collisional excitation of CO + Herschel/PACS observation: revisit warm astrophysical CO with numerical and analytic methods. ... observation of a positively-curved CO rotational diagram does not necessarily require the presence of multiple temperature components. The diagram (column density vs magnetic substrate) is linear for PACS range; curvature can be positive or negative depending on n[H2]. ...
1202.2851
Quantifying the universality of the stellar IMF in old star clusters
Leigh, Unbreit, Sills, Knigge, de Marchi, Glebbeek, Sarajedini
New technique to quantify cluster-tocluster variations in the observed present-day stellar mass functions of a large sample of star clusters. ... Show that the present-day mass functions of the clusters in the sample can be reproduced by assuming an universal initial mass function for all clusters, and that the cluster-to-cluster differences are consistent with what is expected from 2-body relaxation. More complete exploration of the initial cluster conditions will be needed in future studies to better constrain the precise functional form of the IMF. A first step toward using this technique to constrain the dynamical histories of large sample of old Galactic star clusters and (hence) SF in the early Universe.
1202.2852
Constraints on scalar and tensor perturbations in phenomenological and two-field inflation models: Bayesian evidences for primordial isocurvature and tensor modes
Valiviita, Savelainen, Talvitie, Kurki-Suonio, Rusak
Constrain cosmological models where the primordial perturbations have both an adiabatic and a (possibly correlated CDM or baryon isocurvature component. Use both phenomenological (primordial power spectra parameterized with amplitudes and spectral indices) and a slow-roll two-field inflation approach where slow-rol parameters are used as primary parameters. In phenomenological approach, CDM isocurvature fraction is alpha < 7%. The CMB constraint on the tensor-to-scalar ratio is r<0.26 at k=0.01 Mpc^-1; not affected by the non adiabatic modes. In slow-roll two-field inflation approach, spectral indices constrained close to 1; so this leads to tighter limits on the isocurvature fraction (<3%). [what is alpha_T?]. When all spectral indices are close to each other, the isocurvature fraction is somewhat degenerate with the tensor-to-scalar ratio. Special cases where the perturbation modes are uncorrelated or fully (anti)correlated. Calculate Bayesian evidences (model probabilities) in 21 different cases for the non adiabatic models and for the corresponding adiabatic models, and find that in all cases the data support the pure adiabatic model.
1202.2853
Special and general relativistic effects in galactic rotation curves
Cooney, Psaltis, Zaritzky
Observed flat rotation curves of galaxies require either the presence of DM in Newtonian gravitational potentials, or a modification to GR at galactic scales. Detecting Doppler shifts and gravitational effects in the rotation curves offers a tool for distinguishing between predictions of gravity theories that modify the inertia of particles [but that's not exactly describing DM] and those that modify the field equations. These higher-order effete also allow us in principle, to test whether DM particles obey the equivalence principle. Calculate the magnitude of relativistic Doppler and gravitational shifts expected in realistic models of galaxies in a general metric theory of gravity. Identify a number of observable quantities that measure independently the SR and GR effects in each galaxy and suggest that both effects might be detected in a statistical sense by combining appropriately the rotation curves of a large number of galaxies.
(Calculate the 2nd order SR and GR effects on rotationally broadened lines; compare with observed line widths to test the validity of the equivalence principle at galactic scales.)
1202.2856
Anisotropes in the diffuse gamma-ray BG measured by the Fermi LAT
Ackermann, et al
Contribution of unresolved sources to the diffuse gamma-ray BG could induce anisotropies in this emission on small angular scales. Analyze power spectra of diffuse emission measured by Fermi LAT at galactic latitudes |b| > 30 deg in 4 energy bins spanning 1 to 50 GeV. >99.99% CL detection at l~155 detected (2 deg scale) above photon noise, at 1-2 GeV, 2-5 GeV, and 5-10 GeV energy bins, and at >99% CL at 10-50 GeV. Measured angular power takes approximately the same value at all multipoles l >= 155, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, while the energy dependence of C_P is consistent with the anisotropy arising from one ore more source populations with power-law photon spectra with spectral index Gamma_x=2.4. Discuss the impactions of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray BG. Blazars / SF galaxies (most likely) / Extragalactic DM annihilation (likely) / Galactic DM annihilation / Millisecond pulsars (not likely).
1202.2857
The clustering of galaxies as a function of their photometrically-estimated atomic gas content
Li, Kaufmann, Fu, Wang, Catinella, Fabello, Schiminovich, Zhang
New photometric estimator for the HI mass fraction (M_HI/M*) in local galaxies. A linear combination of 4 parameters: stellar mass, stellar surface mass density, NUV-r color and g-i color gradient. Calibrate using samples of nearby galaxies (0.025<z<0.05) with HI line detections from GASS and ALFALFA surveys; demonstrated to provide unbiased M_HI/N* estimates even for HI-rich galaxies. Apply estimator to 24k galaxies in SDSS DR7, bin by stellar mass and HI mass fraction, and compute projected 2pt cross-correlation functions with respect to a reference galaxy sample. Results compared with predictions from current SAM of galaxy formation. The agreement is good for galaxies with stellar masses > 1e10 Msun, but not for lower mass systems. Extend the analysis by studying the bias of HI-poor or HI-rich galaxies with respect to galaxies with normal HI content on scales between 100 kpc and 5 Mpc. For the HI-poor population, the strongest bias effects arise when the HI-deficiency is defined in comparison to galaxies of the same stellar mass and size. [I don't understand what the bias is. Is it for the mass ratio? ... oh, it seems to be the correlation function bias.] This is not reproduced by the SAM, where the quenching of SF in satellites occurs by "starvation" and does not depend on their internal structure. HI-rich galaxies with masses greater than 1e10 Msun are found to be anti-biased compared to galaxies with "normal" HI content. No such effect is found for lower mass galaxies.
(*) 1202.2858
The inner structure of haloes in cold+warm DM models
Maccio, Ruchayskiy, Boyarsky, Munoz-Cuartas
Analyze the properties of DM haloes in the cold-plus-warm dark matter cosmologies (CWDM). Study dependence on the fraction and velocity dispersion on the warm particle, keeping the free-streaming scale fixed. Consider 3 models with the same free-streaming: (1) a mixture of 90% CDM and 10% WDM with the mass 1 keV; (2) a mixture of 50%/50% with WDM mass 5 keV; and (3) pure WDM with mass 10 keV. Warm particles have rescaled Fermi-Direc spectrum of primordial velocities (as non-resonantly produced sterile neutrinos would have) [?]. Compare the properties of haloes among these models and with LCDM with the same cosmological parameters. Demonstrate that although these models have the same free-streaming length and the suppression of matter spectra are similar at scales probed by the Lyman-alpha forest (comoving wave-numbers k<3-5 h/Mpc), the resulting properties of haloes with masses below ~1e11 Msun are different due to the different behavior of matter power spectra at smaller scales. In particular, find that while the number of galaxies remain the same as in LCDM case, their density profiles become much less concentrated. Results imply that a single parameter (e.g. free streaming length) description of these models is not enough to fully capture their effects on the structure formation process.
1202.2859
The role of thermohaline mixing in intermediate- and low-metallicity globular clusters
Angelou, Stancliffe, Church, Lattanzio, Smith
Globular cluster red giant branch stars owe their strange [elemental?] abundance patterns to a combination of pollution from progenitor stars and in situ extra mixing. In this hybrid theory, a first generation of stars imprint abundance patterns into the gas from which a second generation forms. The hybrid theory suggest that extra mixing is operating in tooth populations; use variation of [C/Fe] with luminosity to examine how efficient this mixing is. Investigate M3, M13, M92, M15 and NGC 5466 to test a theory of thermohaline mixing. M3/M13: able to account for the volition of carbon along the RGB in both (intermediate metallicity). Carbon-depleted MS require a model whose initial [C/Fe] abundance leads to carbon abundance lower than observed, in M13. Suggests that M13 formed with some primary nitrogen (higher C+N+O than M3). In the metal-poor regime, only NGC 5466 can be explained by thermohaline mixing operating in multiple populations. Find thermohaline mixing unable to model the depletion of [C/Fe] with magnitude in M92 and M15. Appears as if extra mixing is occurring before the luminosity function bump in these clusters. To reconcile the data with the models would require first dredge-up to be deeper than found in extant models.
1202.2860
Typical density profile for WDM haloes
Vinas, Salvador-Sole, Manrique
Derive the typical spherically averaged halo density profile from power-spectrum of density perturbations in the concordant LWDM cosmology with 2 keV non-thermal sterile neutrinos. Allows separate analysis of effects on (1) the density profile at small radii of the spectrum cutoff caused by free-steraming and (2) the bound in the fine-grained phase-space density, both due to the non-negligible particle velocities at decoupling.
1202.2861
Optimal filters for detecting cosmic bubble collisions
McEwen, Feeney, Johnson, Peiris
Testing for signature of cosmic bubble collisions (which arise in models of eternal inflation) is computationally impractical on WMAP or Planck. A method to approximate the full posterior has been developed recently, which requires as an input at set of candidate sources which are most likely to give the largest contribution to the likelihood. Present improved algorithm for detecting candidates sources using optimal filters, and apply it to detect candidate bubble collision signatures in WMAP7. Show that this algorithm provides an enhancement in sensitivity over previous methods by a factor of 2. No other filter-based approach can provide a superior enhancement of these signatures. Detect 8 new candidate bubble collision signatures for follow-up analysis.
1202.2862
Turbulent molecular gas and star formation in the shocked intergalactic medium of Stephan's Quintet
Guillard, Boulanger, des Forets, Falgarone, Gusdorf, Cluver, Appleton, Lisenfeld, Duc, Ogle, Xu
Report on radio CO observation towards IGM of SQ group of galaxies. In the kpc-scale shock region, extremely bright midIR H2 rotational line emission from warm molecular gas detected by Spitzer. IGM CO emission show velocity range of 1000 km/s. Total H2 mass of 5e9 Msun detected in the shock (lower, depending on CO to H2 conversion factor). Molecular gas carries a large fraction of the gas kinetic energy (not thermalized). Kinetic energy of H2 gas from CO observations comparable to Spitzer IRS observations. The turbulent kinetic energy of the H2 gas is at least a factor of 5 greater than the thermal energy of the hot plasma heated by the collision. Spectra exhibit the pre-shock recession velocities of the two colliding gas systems, but also intermediate velocities: some of the molecular gas originates from the cooling of the post-shock gas, which had time to cool and be accelerated by the shock. The ratio between the warm H2 mass derived from Spitzer IRS spectroscopy and the H2 mass derived from CO fluxes is ~0.3 in the IGM of SQ, which is 10-100 times higher than in SF galaxies. The dissipation of turbulent kinetic energy maintains a high heating ratio within the H2 gas. This interpretation implies that the velocity dispersion on the scale of giant molecular clouds in SQ is an order of magnitude larger than the galactic value. This may explain why this molecular gas is not forming stars efficiently.
1202.2864
General relativistic modeling of magnetized jets from accreting black holes
Tchekhovskoy McKinney, Narayan
Accreting BHs that power the jets in AGN and other systems: GR MHD modeling of jets offer insights. Recent studies that determine spin-dependence of jet power and discuss the implications for the AGN radio loud/quiet dichotomy and recent observations of high jet power in a number of AGN.
1202.2865
A flux-limited sample of z~1 Ly-a emitting galaxies in the CDFS
Barger, Cowie, Wold
Describe a method for obtaining a flux-lmited sample of Ly-a emitters from GALEX grism data; by converting into a 3d data cube. Treat wavelength slices as narrowband images and search for emission-line galaxies. For the GALEX NUV grism data, the method provides a Ly-alpha flux-limited sample over the redshift range z=0.67-1.16. Test the method on CDFS, where 28 Ly-a emitters with faint continuum magnitudes (NUV > 22) that are not present in the GALEX pipeline sample. Measure completeness by adding artificial emitters and measuring the fraction recovered: 80% completeness above 1e-15 erg/cm2/s Ly-a flux. Estimate fraction of AGN in the selection from UV spectra and x-ray data. Report Ly-a blob at z<1 (much less common than at z=3). Compute limits on the z~1 Lya luminosity function and confirm that there is a dramatic evolution in the luminosity function of the redshift range z=0-1.
1202.2867
Limits on the extragalactic background light in the Fermi era
Meyer, Raue, Mazin, Horns
Very high energy (VHE, E>100 GeV) gamma rays from cosmological sources are attenuated due to the interaction with photons of extragalactic background light (EBL) in the UV to IR. The EBL leaves an imprint on the observed energy spectra of the gamma-ray sources. Upper limits on the EBL intensity are derived by considering the most extensive VHE source sample used in this context. Construct a large number of generic EBL shapes and combine spectral info from Fermi, etc., together with minimum assumptions about the source physics at high and very high gamma-ray energies. The evolution of the EBL with redshift is accounted for the possibility of the formation of an electromagnetic cascade and the implications of the upper limits are explored. The EBL density at z=0 is constrained over a broad wavelength range between 0.4 and 100 um. At optical wavelengths, the EBL density is constrained below 24/5 nW/m2/sr between 8/31 um.
1202.2872
Gas-grain models for interstellar anion chemistry
Cordiner, Charnley
Long-chain hydrocarbon anions CnH- (N=4,6,8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n_H2 > 1e5/cm3). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars can thus be explained without the need for warm carbon-chain chemistry. The C6H- anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. As a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally-stable anion-to-neutral ratio, in better agreement with observations. Modles include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment.
1202.2873
Estimating the star formation rate at 1 kpc Scales in Nearby Galaxies
Leroy, et al
Combining Halpha, UV and IR emission, estimate the SFR surface density at 1pc resolution for 30 disk galaxies that are targets of the IRSM HERACLES CO survey. Present a new physically-motivated IR SED-based approach to account for possible contributions to 24 um emission not associated with recent SF. Considering a variety of "reference" SFRs from literature, revisit the calibration of the 24 um term in hybrid (UV+IR or Halpha+IR) tracers. Show that the overall calibration of this term remains uncertain at the factor of two level because of the lack of wide-field, robust reference SFR estimates. Within this uncertainty, published calibrations represent a reasonable starting point for 1kpc-wide areas of SF disk galaxies but re-derive and refine the calibration of the IR term in these tracers ...
1202.2874
Propagation of UHE CR nuclei in cosmic B-fields and implications for anisotropy measurements
Takami, Inoue, Yamamoto
Distribution of arrival direction UHECR sources: consistent with no auto-correlation at 95%, taking into account extragalactic B-field and galactic B field, assuming only Fe nuclei injection. [how did they do that?] Also find : contribution of Centaurus A is required to reproduce the currently observed UHECR excess in the Centaurus region. Secondary protons generated by photo disintegration of primary heavy nuclei during propagation play a crucial role in all cases, and the resulting anisotropy at small angular scales should provide a strong hint of the source location if the maximum energies of the heavy nuclei are sufficiently high.
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