Day 522

Friday.

1310.0456
Investigating the presence of 500 um submillimeter excess emission in local star forming galaxies
Kirkpatrick et al

Model the FIR peak of the dust emission with a two-temperature modified BB and measure excess of the 500 um photometry relative to that predicted by this model.  Compare excess as well as global galaxy metallicity, and (if available) resolved metallicity measurements.  Do not find any correlation between the 500 um excess and metallicity.  No sources found to have excess larger than the calculated 1 sigma uncertainty, leading to a conclusion that there is no substantial excess at submillimeter wavelengths at or shorter than 500 microns in this sample.  Results differ from previous studies due to new, improved photometry used in this study.

1310.0466
The orbital ellipticity of satellite galaxies and the mass of the Milky Way
Barber, Navarro, et al

Use MW-sized DM Aquarius sims to investigate the orbits of  substructure haloes that are likely to host luminous galaxies: in the most massive subhaloes, and on more radial orbits than the majority of subhaloes found within the halo virial radius.  One reason for this (mild) kinematic bias is that many low-mass subhaloes have apocentres that exceed the virial radius of the main host; they are thus excluded from subhalo samples identified within the virial boundary, reducing the number of subhaloes on radial orbits.  Two other factors contributing to the difference in orbital shape between dark and luminous subhaloes are their dynamical evolution after infall, which affects more markedly low-mass (dark) sub halos, and a weak dependence of ellipticity on the redshift of first infall.  The ellipticity distribution of luminous satellites exhibits little halo-to-halo scatter and it may therefore be compared with that of MW satellites.  Since the latter depends sensitively on the total mass of the MW, use the predicted distribution of satellite ellipticities to place constraints on the MW mass.  Using the latest estimates of position and velocity of dwarfs compiled from the literature, find that the most likely MW mass lies in the range 6e11 Msun < M200 < 3.1e12 Msun, with a best fit values of M200=1.1e12 Msun.  This value is consistent with MW mass estimates based on dynamical tracers or the timing argument.  [how exactly does the ellipticity distribution change as a function of halo mass?]

1310.0500
Objects appear smaller as they recede: how proper motions can directly reveal the cosmic expansion, provide geometric distances, and measure the Hubble constantDarling

Objects and structures [whose (transverse) size are] gravitationally decoupled from the Hubble expansion will appear to shrink in angular size as the universe expands [there is additional shrinkage in angular size as it recedes from us?].  Observations of extragalactic proper motions [between angular separation of gravitationally coupled pair] can thus directly reveal the cosmic expansion [deciphering took a while].  Relatively static structures such as galaxies or galaxy clusters can potentially be used to measure the Hubble constant, and test masses in large scale structures can measure the overdensity.  Since recession velocities and angular separations can be precisely measured, apparent proper motions can also provide geometric distance measurements to static structures.  The apparent fractional angular compression of static objects is 15 microarcseconds per year in the local universe [due to expansion of the universe]; this motion is modulated by the overdenisty in dynamic expansion-decoupled structures.  Use the Titov+2011 quasar proper motion [how much do they move?!  quasars are far away!  I guess this must be radio observation] catalog to examine the pairwise proper motion of a sparse network of test masses.  Small-separation pairs (<200 Mpc comoving) are too few to measure to expected effect, yielding an inconclusive 8.3 pm 14.9 microarcsec/yr.  Large-separation pairs (200-1500 Mpc) show no net convergence or divergence for z<1, -2.7pm3.7 microsrcsec/yr, consistent with pure Hubble expansion and significantly inconsistent with static structures, as expected.  For all pairs a "null test" gives -0.36 pm 0.62 microsrcsec/yr, consistent with Hubble expansion, and excludes a static locus at ~5-10 sigma significance for z~0.5-2.0.  The observed large-separation pairs provide a reference frame for small-separation pairs that will significantly deviate from the Hubble flow.  The current limitation is the number of small-separation objects with precise astrometry, but Gaia will address this and will likely detect the cosmic recession.

1310.0556
Morphology in the era of large surveys
Lintott et al

Role of galaxy morphology as a clue to understanding galaxies has not changed, but obtaining it for large numbers of galaxies is challenging.  A 4 page report on a meeting of this subject.

1310.0577
Time-series photometry of Earth flyby asteroid 2012 DA14
Terai et al

As the title says.  Carried out using the 0.55m telescope at Saitama U., Japan.

1310.0615
Measuring galaxy [OII] emission line doublet with future ground-based wide-field spectroscopic surveys
Comparat, Kneib, Bacon, Mostek, Newman, Schlegel, Yéche

For the next generation of wide-field spectroscopic redshift surveys mapping LS galaxy distribution in 0.7<z<2 to measure BAO.  Simulate observations of the [OII] double for various instrument resolutions, and line velocities.  Foresee two strategies about the choice of the resolution for future spectrographs for BAO surveys: for bright [OII] emitter surveys like eBOSS, a resolution of R~3300 allows separation of 90% of doublets.  Impact of sky lines on the completeness is <6%.  For faint [OII] emitter surveys like DESi, the detection improves continuously with resolution, so recommend the highest possible resolution, the limit being given by the number of pixels on the detector (4k x 4k) and the number of spectroscopic channels (2 or 3).  

1310.0684
Chemical constraints on the contribution of population III stars to cosmic reionization
Kulkarni, Hennawi, Rollinde, Vangioni

Pop III stars produce ~10x more ionizing photons than Pop II stars, but whether the excess ionizing photon can be produced by Pop III stars depends on the duration of the Pop III era, which depends on the rate of galactic enrichment.  Use SAM which tracks galactic chemical evolution to gauge the impact of Pop III stars on reionization.  Pop III SNe produce distinct metal abundances; argue that the duration of the Pop III era can be constrained by precise relative abundance measurements in high-z damped Lya absorbers (DLAs), which provide a chemical record of past SF.  Find that a single generation of Pop III stars can self-enrich galaxies above the critical metallicity Zcrit = 1e-4 Zsun for the Pop III-to-II transition, on a very short timescale of 1e6 yr, owing to the large metal yields and short lifetimes of Pop III stars.  This subsequently terminates the Pop III era, hence they contribute >~50% of the ionizing photons only for z>~30, and at z=10 contribute <1%.  The Pop III contribution can be increased by delaying metal mixing into the ISM.  However, comparing the resulting metal abundance pattern to existing measurements in z<~6 DLAs, show that the fractional contribution of high-mass Pop III stars to the ionization rate must be <~10% at z=10.  Future abundance measurements of z~7-8 QSOs and GRBs should probe the era when the chemical vestiges of Pop III star formation become detectable.  

1310.0814
The universal stellar mass-stellar metallicity relation for dwarf galaxies
Kirby, et al

7 gas-rich dIrrs, and the spectroscopic metallicities of their individual stars: show that the dIrrs obey the same mass-metallicity relation as the dSph satellites of both the MW and M31: Z* ~ M*^0.30pm0.02.  The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry.  This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M*=1e12 Msun.  Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type.  The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions.  The metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of SF due to ram pressure stripping.

1310.0824
The formation history of the ultra-faint dwarf galaxies
Brown, ... Geha, Kirby, ... et al

HST survey of ultra-faint dwarf galaxies.  These appear to be an extension of the classical dwarf spheroidals to low luminosities; a possible clue to understanding the missing satellite problem.  They are the least luminous, more DM dominated, and least chemically evolved galaxies known; they are the best candidate fossils from the early universe.  The primary goal of the survey is to measure the SFH of these galaxies and discern any synchronization due to the reionization of the universe.  Find: 6 galaxies of survey have very similar SFHs, and that each is dominated by stars older than 12 Gyr.

1310.0825
Subhaloes gone Notts: the clustering properties of subhaloes
Pujol, et al

Study substructure finder dependence of subhalo clustering in Aquarius Sim.  Run 11 different subhalo finders; study their differences in the density profile, mass fraction and 2-pt correlation function of subhaloes in haloes.  Also study the mass and vmax dependence of subhalo clustering; study convergence with higher resolutions.  Find: agreement between finders is at around the 10% level inside R200 and at intermediate resolutions when a mass threshold is applied, and better than 5% when vmax is restricted instead of mass.  However, some discrepancies appear in the highest resolution, underlined by an observed resolution dependence of subhalo clustering.  This dependence is stronger for the smallest subhaloes, which are more clustered in the highest resolution, due to the detection of subhaloes within subhaloes (the sub-subhalo term).  This effect modifies the mass dependence of clustering in the highest resolutions.  Discuss implications of results for models of subhalo clustering and their relation with galaxy clustering.

1310.0853
Magnetic field amplification in young galaxies
Schober et al

Universe is magnetized at 1e-5G and coherence lengths larger than 10 kpc in typical galaxies like the MW.  Propose: B-field was amplified to this value during the formation and the early evolution of galaxies.  Turbulence in young galaxies is driven by accretion as well as by SN explosions of the first generation of stars.  The small-scale dynamo can convert the turbulent kinetic energy into magnetic energy and amplify very weak primordial B seed fields on short timescales.  The amplification takes place in 2 phases: in the kinematic phase the B-field grows exponentially, with the largest growth on the smallest non-resistive scale.  In the following NL phase the magnetic energy is shifted towards larger scales until the dynamo saturates on the turbulent forcing scale.  To describe the amplification of the B-field quantitatively, model the microphysics in the ISM of young galaxies and determine the growth rate of the small-scale dynamo.  Estimate the resulting saturation field strengths and dynamo timescales for 2 turbulent forcing mechanisms: accretion-driven turbulence and SN-driven turbulence.  Compare them to the field strength that is reached, when only stellar magnetic fields are distributed by SN explosions.  Compare them to the field strength that is reached, when only stellar B-fields are distributed by SN explosions.  Find that the small-scale dynamo is much more efficient in magnetizing the ISM of young galaxies.  In the case of accretion-driven turbulence a B-field strength of the order of 1e-6G is reached after a time of 24-270 Myr, while in SN-driven turbulence the dynamo saturates at field strengths of typically 1e-5G after only 4-15 Myr.  This is considerably shorter than the Hubble time.  This work can help to understand why present-day galaxies are highly magnetized.  

1310.0859
The formation of massive black holes in z~30 dark matter haloes with large baryonic streaming velocities
Tanaka, Li

Origin of 1e9 Msun quasar SMBHs is a theoretical puzzle.  One possibility: they grew from 1e5 Msun BHs formed in the direct collapse of atomic-cooling >~8000K gas of nearly primordial composition.  For such an event to occur, the H2 fraction must be kept extremely low as gas accumulates inside a DM haloe with virial temperature Tvir > 8000K.  A strong UV BG, such as produced by a nearby SF galaxy or quasar, could photodissociate H2 and lead to direct collapse as early as z=16.  Alternatively, dense, pristine atomic cooling (PAC) gas can suppress the H2 fraction through collisional dissociation, in the absence of a UV BG.  A key obstacle to direct collapse is metal enrichment; a single pair-instability SN may raise the gas metllicity to levels where direct collapse could not occur.  THerefore, the gas must be kept pristine from when Tvir~1000K, when SF typically begins, until Tvir~8000K --- a gap of >20x in halo mass.  Propose that baryonic streaming --- the relic relative motion of gas with respect to DM from cosmological recombination --- provides a natural mechanism for circumventing metal enrichment while the halo bridges this gap.  Baryonic streaming has been shown to delay the formation of the first stars; streaming velocities more than twice the root-mean-square value could forestal SF until Tvir~8000K, and produce rare PAC haloes as early as z~30.  Streaming also enhances supersonic turbulence, which may facilitate direct collapse.  The comoving number density of massive z>6 haloes that contain a direct-collpase BH that formed at z~30 may be as high as 1e-9 to -8 Mpc^-3, even if less than 1% of PAC haloes produce massive BHs.  This mechanism could explain how some quasar BHs became so massive quickly.

1310.1074
Wet disc contraction to galactic blue nuggets and quenching to red nuggets
Dekel, Burkert

Study the origin of high-z, compact, quenched spheroids (red nuggets) through the dissipative shrinkage of gas-rich disc galaxies into compact SF systems (blue nuggets).  The discs, intensely fed by cold streams, undergo violent disc instability (VDI) that drives gas into the center in parallel with mergers.  The inflow is dissipative when the timescale for inflow is shorter than the timescale for SF.  This implies a threshold of ~0.28 in the cold-to-total mass ratio within the disc radius.  For the typical cold-to-baryonic mass ratio ~0.5 at z=2, this threshold can be traced back to a maximum spin parameter of ~0.05.  It implies that about half the SF galaxies contract to blue nuggets, while the rest form extended stellar discs.  Blue nuggets are expected to be much less abundant at low redshifts when the gas fraction is lower.  The SF galaxies at high z are expected to show a corresponding bimodality in stellar surface density about a critical value ~1e9 Msun/kpc^2, slightly increasing with mass.  The blue nuggets quench to red nuggets by complementary mechanisms associated with the bulge and the halo.  Bulge quenching can include starbursts, stellar and AGN feedback, and morphological quenching of instability.  It can be the trigger for fast quenching acting mostly at high z.  Halo quenching is due to the development of a hot medium once the halo grows above a critical mass of 1e12 Msun.  It serves for a slow, maintenance mode of quenching, dominating at low z.  These predictions are confirmed in hydro-cosmo sims and are qualitatively consistent with observations at z=0-3.