Day 483

Wednesday.

1308.1093
Wide angle effects in galaxy surveys
Yoo, Seljak

Current and future galaxy surveys cover a large fraction of the entire sky with a significant redshift range, and the recent theoretical development shows that general relativistic effects are present in galaxy clustering on very large scales.  This trend has renewed interest in the wide angle effect in galaxy clustering measurements, in which the distant-observer approximation is often adopted.  Using the full wide-angle formula for computing the redshift-space correlation function, show that compared to the sample variance, the deviation in the z-space correlation function from the simple Kaiser formula with the distant-observer approximation is negligible in the SDSS and is completely irrelevant in future galaxy surveys such as Euclid and BigBOSS, if the theoretical prediction from the Kaiser formula is averaged over the survey volume and the non-uniform distribution of cosine angle between the LoS and the pair separation directions is properly considered.  Also find small corrections to the wide-angle formula.  However, in contrast to the z-space correlation function, substantial deviations are present in the z-space PS, because the non-uniform distribution of cosine angle is not considered in the present power spectrum analysis.  In particular, the traditional FKP method cannot be used to estimate the quadrupole and the hexadecapole PS, as it imposes one LoS direction to all galaxy pairs, though this issue can be readily addressed by using pair-dependent LoS directions.  Further refinement of PS estimators will be needed to avoid significant systematic errors in future surveys.

1308.1099
The dust attenuation law in distant galaxies: evidence for variation with spectral type
Kriek, Conroy

Utilize composite SEDs constructed from NEWFIRM Medium-Band survey photometry to constrain the dust attenuation curve in 0.5<z<2.0 galaxies.  Based on similarities between the full SED shapes (0.3-8 um), divide galaxies in 32 different spectral classes and stacked their photometry.  As each class contains galaxies over a range in redshift, the resulting rest-frame SEDs are well-sampled in wavelength and show various spectral features including Ha and the UV dust bump at 2175A.  Fit all composite SEDs with flexible stellar population synthesis models, while exploring attenuation curves with varying slopes and UV bump strengths.  The MW and Calzetti law provide poor fits at UV wavelengths for nearly all SEDs.  Find a strong correlation between the best-fit slope and the bump strength, with steeper laws having stronger UV bumps.  Moreover, the attenuation curve correlates with sSFR, such that galaxies with higher sSFRs have shallower dust curves with weaker UV bumps.  There is also a weak correlation with inclination, which may be suggestive of a two-component dust model. A varying grain size distribution, as a result of differences in UV radiation fields may also contribute to the observed trends.  Results have several implications for galaxy evolution studies.  First, the assumption of a universal dust model will lead to biases in derived galaxy properties.  Second, the presence of a dust bump may result in underestimated values for the UV slope, used to correct SFRs of distant galaxies.

1308.1101
Dissecting the properties of optically-thick hydrogen at the peak of cosmic star formation history
Fumagalli, O'Meara, Prochaska, Worseck

Preset results of a blind survey of Lyman limit systems (LLSs) detected in absorption against 105 quasars at z~3 using the blue sensitive MagE spectrograph at Magellan Clay telescope.  By searching for Lyman limit absorption in the wavelength range ~300-400A, measure the number of LLSs per unit redshift L(z)=1.21pm0.28 at z~2.8.  Using a stacking analysis, further estimate the mean free path of ionizing photons in the z~3 universe lambda^912 = 100pm29 Mpc/h_70.4.  Combined with the LLS survey, conclude that systems with log N_HI > 17.5 cm^-2 contribute only ~40% to the observed mean free path at these redshifts.  Further, with the aid of photo-ionization modeling, infer that a population of ionized and metal poor systems is likely required to reproduce the metal line strengths observed in a composite spectrum of 20 LLSs with N_HI=17.5-19 cm^-2 at z~2.6-3.0.  Finally, with a simple toy model, deduce that gas in the halos of galaxies can alone account for the totality of LLSs at z<~3, but a progressively higher contribution from the IGM is required beyond z~3.5.  Also show how the weakly evolving number of LLSs per unit redshift a z<~3 can be modeled either by requiring that the spatial extent of the circumgalactic medium is redshift invariant in the last ~10 Gyr of cosmic evolution of by postulating that LLSs arise in halos that are rare fluctuations in the density field at each redshift.