1705.08662
Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6
Declare, Walter, et al
The existence of massive (1e11 Msun) elliptical galaxies by z~4 (when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 Msun/year at z>6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their SFRs are more than an order of magnitude lower. The only known galaxies with very high SFRs at z>6 are, with only one exception, the host galaxies of quasars, but these galaxies also host accreting SMBHs (>1e9 Msun), which probably affect the properties of the galaxies. Report here the observations of an emission line of singly ionized carbon ([CII] at a wavelength of 158 um) in 4 galaxies at z>6 that are companions of quasars, with velocity offsets of less than 600 km/s and linear offset of less than 600 kpc. The discovery of these 4 galaxies was serendipitous; they are close to their companion quasars and appear bright in the IR. On the basis of the [CII] measurements, estimate SFRs in the companions of more than 100 Msun per year. These sources are similar to the host galaxies of the quasars in [CII] brightness, line width and implied dynamical masses, but do not show evidence for accreting SMBHs. Similar systems have previously been found at lower z. Find such close companions in 4 out of 25 z>6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [CII] luminosity function, then they can account for the population of massive elliptical galaxies at z~4 in terms of cosmic space density.
1705.05840
Knowledge discovery through text-based similarity searches for astronomy literature
Kerzendorf
The increase in the number of researchers coupled with the ease of publishing and distribution of scientific papers (due to technological advancements) has resulted in a dramatic increase in astronomy literature. This has likely led to the predicament that the body of the literature is too large for traditional human consumption and that related and crucial knowledge is not discovered by researchers. In addition to the increased production of astronomical literature, recent decades have also brought several advancements in computer linguistics. The machine aided processing of literature dissemination might make it possible to convert this stream of papers into a coherent knowledge set. In this paper, present the application of computer linguistics techniques on astronomy literature. In particular, develop a tool that will find similar articles purely based on text content given an input paper. Find that this technique performs robustly in comparison with other tools recommending articles given a reference paper (known as recommender system). The novel tool shows the great power in combining computer linguistics with astronomy literature and suggests that additional research in this endeavor will likely produce even better tools that will help researchers cope with the vast amounts of knowledge being produced.
1706.03173
Modeling CMB lensing cross correlations with CLEFT
Modi, White, Vlah
A new generation of surveys will soon map large fractions of sky to ever greater depths and their science goals can be enhanced by exploiting cross correlations between them. In this paper, study cross correlations between the lensing of the CMB and biased tracers of large-scale structure at high z. Motivate the need for more sophisticated bias models for modeling increasingly biased tracers at these redshifts and propose the use of perturbation theories, specifically Convolution Lagrangian Effective Field Theory (CLEFT). Since such signals reside at large scales and redshifts, they can be well described by perturbative approaches. Compare the model with the current approach of using scale independent bias coupled with fitting functions for non-linear matter power spectra, showing that the latter will not be sufficient for upcoming surveys. Illustrate the ideas by estimating sigma8 from the auto- and cross-spectra of mock surveys, finding that CLEFT returns accurate and unbiased results at high z. Discuss uncertainties due to the redshift distribution of the tracers, and several avenues for future development.
1706.03753
The two-halo term in stacked thermal Sunyaev-Zel'dovich measurements: implications for self-similarity
Hill, Baxter, Lidz, Greco, Jain
Relation between the mass and integrated electron pressure of galaxy group and cluster haloes can be probed by stacking maps of the tSZ effect. Surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as 1e12.5 Msun. Hydrodynamical sims that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, build on the modeling of Vikram, Lidz, & Jain (2017) to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated haloes (the 2-halo term), which has generally been neglected in the literature. Fit theoretical models to a measurement of the tSZ -- galaxy group X-correlation function, accounting explicitly for the 1- and 2-halo contributions. Find moderate evidence of a deviation from self-similarity in the pressure -- mass relation, even after marginalizing over conservative miscentering effects. Explore pressure -- mass models with a break at 1e14 Msun, as well as other variants. Discuss and test for sources of uncertainty in the analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. Compare the findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the 2-halo contribution. Show that ongoing 3rd generation CMB experiments will explicitly resolve the 1-halo term in low-mass groups; the methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot has in low-mass halos.
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