1804.02406
Heating of the intergalactic medium by the cosmic microwave background during cosmic dawn
Venumadhav, Dai, Kaurov, Zaldarriaga
The IGM is expected to be at its coldest point before the formation of the first stars in the universe. Motivated by recent results from the EDGES experiment, revisit the standard calculation of the kinetic temperature of the neutral gas through this period. When the first UV sources turn on, photons redshift into the Lyman lines of neutral H and repeatedly scatter within the Lyman-alpha line. They heat the gas via atomic recoils, and through the Wouthuysen-Field effect, set the spin temperature of the 21-cm hyperfine (spin-flip) line of atomic hydrogen in competition with the resonant CMB photons. Show that the Lya photons also mediate energy transfer between the CMB photons and the thermal motions of the H atoms. In the absence of X-ray heating, this new mechanism is the major correction to the temperature of the adiabatically cooling gas (~10% at z=17) and is several times the size of the heating rate found in previous calculations. Also find that the effect is more dramatic in non-standard scenarios that either enhance the radio background above the CMB or invoke new physics to cool the gas in order to explain the EDGES results. The coupling with the radio background can reduce the depth of the 21-cm absorption feature by almost a factor of 2 relative to the case with no sources of heating, and prevent the feature from developing a flattened bottom. As an inevitable consequence of the UV BG that generates the absorption feature, this heating should be accounted for in any theoretical prediction.
1804.02667
J-PLUS: the Javalambre Photometric Local Universe Survey
Cenarro, et al
J-PLUS is an ongoing 12-band photometric optical survey, observing thousands of square degrees of the Northern Hemisphere from the dedicated JAST/T80 telescope at the Observatory Astrofisico de Javalambre. T80Cam is a 2 sq..deg FoV camera mounted on the 83cm diameter telescope, and is equipped with a unique system of filters spanning the entire optical range. This filter system is a combination of broad, medium and narrow-band filters, optimally designed to extract the rest-frame spectral features (the 3700-4000A Balmer break region, H_delta, Ca H+K, the G-band, the Mgb and Ca triplets) that are key to both characterize stellar types an to deliver a low-resolution photo-spectrum for each pixel of the sky observed. With a typical depth of AB~21.25 mag per band, this filter set thus allows for an indiscriminate and accurate characterization of the stellar population in our Galaxy, it provides an unprecedented 2d photo-spectral information for all resolved galaxies in the local universe, as well las accurate photo-z estimates (Delta z ~ 0.01-0.03) for moderately bright (up to r~20 mag) extragalactic sources. While some narrow band filters are designed for the study of particular emission features ([OII]/lambda3727, H_alpha/lambda6563) up to z<0.015, they also provide ill-defined windows for the analysis of other emission liens at higher redshifts. As a result, J-PLUS has the potential to contribute to a wide range of fields in Astrophysics, both in the nearby universe (MW, 2D IFU-like studies, stellar populations of nearby and moderate redshift galaxies, clusters of galaxies) and at high zs (ELGs at z~0.77, 2.2 and 4.4 QSOs, etc). With this paper, release ~36 sq.deg of J-PLUS data, containing about 1.5e5 stars and 1e5 galaxies at r<21 mag.
1804.02673
J-PLUS: Morphological star/galaxy classification by PDF analysis
López-Sanjuan, et al
The goal is to morphological classify the sources identified in the images of the J-PLUS early data release (EDR) into compact (stars) or extended (galaxies) using a suited Bayesian classifier. J-PLUS sources exhibit two distinct populations in the r-band magnitude vs. concentration plane, corresponding to compact and extended sources. Modeled the 2 population distribution with a skewed Gaussian for compact objects and a log-normal function for the extended ones. The derived model and the number density prior based on J-PLUS EDR data were used to estimate the Bayesian probability of a source to be star or galaxy. This procedure was applied pointing-by-pointing to account for varying observing conditions and sky position. Finally, combine the morphological information from g, r, and i broad bands in order to improve the classification of ow S/N sources. The derived probabilities are used to compute the pointing-by-pointing number counts of stars and galaxies. The former increases as we approach the MW disk, and the latter are similar across the probed area. The comparison with SDSS in the common regions is satisfactory up to r~21, with consistent numbers of stars and galaxies, and consistent distributions in concentration and (g-i) color spaces. Implement a morphological star/galaxy classier based on PDF analysis, providing meaningful probabilities for J-PLUS sources to one magnitude deeper (r~21) than a classical boolean classification. These probabilities are suited for the statistical study of 150k stars and 101k galaxies with 15<r<21 present in the 31.7 deg2 of the J-PUS EDR. In a future version of the classifier, include J-PLUS color information from 12 photometric bands.
1804.02753
Power spectrum in the presence of large-scale overdensity and tidal fields: breaking azimuthal symmetry
Chiang, Slosar
Consider the PS of a biased tracer observed in a finite volume in the presence of a LS overdensity and tidal fields. Expanding both the observed PS and the source fields (linear PS, scalar overdensity and tidal field tensor) in spherical harmonics, explicitly confirm that each (ell, m) source generates just the corresponding (ell, m) modes of PS in real space. In redshift space, each (ell, m) source additionally couples only to (ell+2n,m) modes of tracer power spectra. This generalizes the Kaiser formula for monopole, quadrupole and hexadecapole of the power spectrum to all (ell, m) modes generated to the second order in perturbation thirty. This formalism can find applications in constraining the super-sample covariance and in the local power spectrum based bispectrum estimators. As an example application, forecast the ability to measure these modes a survey with BOSS-like galaxy number densities.
1804.03097
The connection between galaxies and their dark matter haloes
Wechsler, TInker
In the modern understanding of galaxy formation, every galaxy forms within a DM halo. The formation and growth of galaxies over time is connected to the growth of the haloes in which they form. The advent of large galaxy surveys as well as high-resolution cosmological simulations has provided a new window into the statistical relationship between galaxies and halos and its evolution. Here, define this galaxy-halo connection as the multi-variate distribution of galaxy and halo properties that can be derived from observations and simulations. This connection provides a key test of physical galaxy formation models; it also plays an essential role in constraints of cosmological models using galaxy surveys and in elucidating the properties of DM using galaxies. Review techniques for inferring the galaxy-halo connection and the insights that have arisen from these approaches. Some things that were learned are that galaxy formation efficiency is a strong function of halo mass; at its peak in halos around a pivot halo mass of 1e12 Msun, less than 20% of the available baryons have turned into stars by the present day; the intrinsic scatter in galaxy stellar mass is small, less than 0.2 dex at a given halo mass above this pivot mass; below this pivot mass galaxy stellar mass is a strong function of halo mass; the majority of stars over cosmic time were formed in a narrow region around this pivot mass. Also highlight key open questions about how galaxies and halos are connected, including understanding the correlations with secondary properties and the connection of these properties to galaxy clustering.
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