1808.02525
Angular momentum and galaxy formation revisited: scaling relations for disks and bulges
Fall, Romanowsky
Show that the stellar specific angular momentum j*, mass M* and bulge fraction beta* of normal galaxies of all morphological types are consistent with a simple model based on a linear superposition of independent disks and bulges. In this model, disks and bulges follow scaling relations of the form j*, d~M*, d^alpha and j*, b~M*, b^alpha with alpha=0.67±0.07 but offset from each other by a factor 8±3, over the mass range 8.9 <= log(M*/M_sun)<=11.8. Separate fits for disks and bulges alone give apha=0.58±0.10 and alpha=0.83±0.16, respectively. This model correctly predicts that galaxies follow a curved 2d surface in the 3d space of j*, M*, and beta*. Find no statistical significant indication that galaxies with classical and pseudo bulges follow different relations in this space, although some differences are permitted within the observed scatter and the inherent uncertainties in decomposing galaxies into disks and bulges. As a byproduct of this analysis, show that the j*-M* scaling relations for disk-dominated galaxies from several previous studies are in excellent agreement with each other. In addition, resolve some conflicting claims about the beta*-dependence of the j*-M* scaling relations. The results presented here reinforce and extend the earlier suggestion path the distribution of galaxies with different beta* in the j*-M* diagram constitutes an objective, physically-motivated alternative to subjective classification schemes such as the Hubble sequence.
1808.02532
Predictions for the sky-averaged depth of the 21cm absorption signal at high redshift in cosmologies with and without non-baryonic cold dark matter
McGaugh
Consider the 21cm absorption signal expected at high z in cosmologies with and without non-baryonic cold dark matter. The expansion of the early universe decelerates strongly with dark matter, but approximately coasts without it. This results in a different path length across the epochs when absorption is expected, with the consequence that the absorption is predicted to be a factor of ~2 greater without dark matter than with it. Observation of such a signal would motivate consideration of extended theories of gravity in lieu of dark matter.
1808.02593
Testing shear recovery with field distortion
Zhang, et al
The tilt, rotation, or offset of each CCD with respect to the focal plane, as well as the distortion of the focal plane itself, cause shape distortions to the observed objects, an effect typically known as field distortion (FD). Point out that FD provides a unique way of quantifying the accuracy of cosmic shear measurement. The idea is to stack the shear estimators from galaxies that share similar FD-induced shape distortions. Given that the latter can be calculated with parameters from astrometric calibrations, the accuracy of the shear estimator can be directly tested on real images. It provides a way to calibrate the multiplicative and additive shear recovery biases within the scientific data itself, without incurring simulations or any external data sets. Use the CFHTLenS images to demonstrate the accuracy of the Fourier+Quad shear recovery method. Highlight some details in the image processing pipeline, including background removal, source identification and deblending, astrometric calibration, star selection for PSF reconstruction, noise reduction, etc. Show that in the shear ranges of -0.005 < g1 < 0.005 and -0.008 < g2 < 0.008, there are no visible multiplicative biases on the order of 0.04. Slight additive biases on the order of 5e-4 (6 sigma) are identified for sources provided by the official CFHTLenS catalog (not using its shear catalog), but are minor (4 sigma) for source catalog generated by the Fourier_Quad pipeline.
1808.02828
The 'Cosmic Seagull': a highly magnified disk-like galaxy at z~2.8 behind the Bullet Cluster
Motta, et al
Present Atacama Large Millimeter/submillimeter Array measurements of the 'Cosmic Seagull', a strongly magnified galaxy at z=2.7779 behind the Bullet Cluster. Report CO(3-2) and continuum 344 um (rest-frame) data at one of the highest differential magnifications ever recorded at sub millimeter wavelengths (mu up to ~50), facilitating a characterization of the kinematics of a rotational curve in great detail (at ~620 pc resolution in the source plane). Find no evidence for a decreasing rotation curve, from which a dynamical mass of (6.3±0.7)e10 Msun within r=2.6±0.1 kpc is derived. The discovery of a third, unpredicted, image provides key information for a future improvement of the lensing modeling of the Bullet Cluster and allows a measure of the stellar mass, 1.6+1.9-0.86e10 Msun, unaffected by strong differential magnification. The baryonic mass is expected to be dominated by the molecular gas content (f_gas=80±20%) based on an M_H2 mass estimated from the difference between dynamical and stellar masses. The star formation rate is estimated via the spectral energy distribution (SFR=190±10 Msun/yr), implying a molecular gas depletion time of 0.25±0.08 Gyr.
1808.02573
Investigation of the orientation of galaxies in clusters: the importance, methods and results of research
Pajowska, et al
Various models of structure formation can account for various aspects of the galaxy formation process on different scales, as well as for various observational features of structures. Thus, the investigation of galaxies orientation constitute a standard test of galaxies formation scenarios since observed variations in angular momentum represent fundamental constraints for any model of galaxy formation. Improve upon the method of analysis of the alignment of galaxies in clusters. The method allows analysis of both position angles of galaxy major axes and two angles describing the spatial orientation of galaxies. The distributions of analyzed angles were tested for isotropy by applying different statistical tests. For the sample of analyzed clusters, compute the mean values of analyzed statistics, checking whether they are the same as the expected ones in the case of random distribution of analyzed angles. The detailed discussion of this method has been performed. Show how to proceed in many particular cases in order to improve the statistical reasoning when analyzing the distribution of the angles in the observational data. Separately, compare these new results with those obtained from numerical simulations. Show the power of the method on the example of galaxy orientation analysis in 247 Abell rich galaxy clusters. Find that the orientations of galaxies in analyzed clusters are not random. This confirms an existence of the alignment of galaxies in rich Abells' galaxy clusters. This result is independent for the clusters of Bautz-Morgan types.
1808.02896
The evolution of assembly bias
Contreras, Zehavi, et al
Examine the evolution of assembly bias using a semi-analytical model of galaxy formation implemented in the Millennium-WMAP7 N-body sim. Consider fixed number density galaxy samples ranked by stellar mass or SFR. Investigate how the clustering of haloes and their galaxy content depend on halo formation time and concentration, and how these relationships evolve with redshift. At z=0 the dependencies of halo clustering on halo concentration and formation time are similar. However, at higher redshift, halo assembly bias weakens for haloes selected by age, and reverses and increases for haloes selected by concentration. The variation of the halo occupation with concentration and formation time is also similar at z=0 and changes at higher redshifts. In this case, the occupancy variation with halo age stays mostly constant with redshift but decreases for concentration. Finally, look at the evolution of assembly bias reflected in the galaxy distribution by examining the galaxy correlation functions relative to those of shuffled galaxy samples which remove the occupancy variation. This correlation functions ratio monotonically decreases with larger redshift and for lower number density samples, going below unity in some cases, leading to reduced galaxy clustering. While the halo occupation functions themselves vary, the assembly bias trends are similar whether selecting galaxies by stellar mass or SFR. The results provide further insight into the origin and evolution of assembly bias. The extensive occupation function measurements and fits are publicly available and can be used to create realistic mock catalogues.
1808.03088
The central cusps in dark matter haloes: fact or fiction?
Bauschev, Pilipenko
Investigate the reliability of standard N-body simulations by modeling of the well-known Hernquist halo with the help of GADGET-2 code (which uses the tree algorithm to calculate the gravitational force) and ph4 code (which uses the direct summation). Comparing the results, find that the core formation in the halo center (which is conventionally considered as the first sign of numerical effects, to be specific, of the collisional relaxation) has nothing to do with the collisional relaxation, being defined by the properties of the tree algorithm. This result cases doubts on the universally adopted criteria of the simulation reliability in the halo center. Though a halo model is used, which is theoretically proved to be stationary and stable, a sort of numerical 'violent relaxation' occurs. Its properties suggest that this effect is highly likely responsible for the central cusp formation in cosmological modeling of the large-scale structure, and then the 'core-cusp problem' is no more than a technical problem of N-body simulations.
1808.03294
Extragalactic imprinted in galactic dust maps
Chiang, Ménard
Extragalactic astronomy relies on the accurate estimation of source photometry corrected for Milky Way dust extinction. This has motivated the creation of a number of "Galactic" dust maps. Investigate whether these maps are contaminated by extragalactic signals using the so-called clustering redshift technique, i.e., by measuring a set of angular cross-correlations with spectroscopic galaxies and quasars as a function of redshift. The tomographic analysis reveals imprints of extragalactic large-scale structure patterns in 9 (out of 10) Galactic dust maps, including all infrared-based maps as well as "stellar" reddening maps. When such maps are used for extinction corrections, this extragalactic contamination introduces redshift- and scale-dependent biases in photometric estimates at the milli-magnitude level. It can affect both object-based analyses such as the estimation of the Hubble diagram with SNe as well as spatial statistics. The bias can be appreciable when measuring angular correlation functions with low amplitudes such as lensing-induced correlations or angular correlations for sources distributed over a broad redshift range. As expected, do not detect any extragalactic contamination for the dust map inferred from the distribution of HI from 21 cm observations. Such a map provides an alternative to widely used IR-based maps but relies on the assumption of a constant dust-to-gas ratio. Note that using the WISE 12 um map sensitive to Polycyclic Aromatic Hydrocarbons (PAH), an indirect dust tracer, detect the diffuse extragalactic PAH background up to z~2. For precision cosmology experiments using optical photometry, recommend to test the robustness of the final results against different dust maps used. Finally, provide a procedure to correct for or decrease the level of biased magnitude corrections in maps with extragalactic imprints.
1808.03410
The missing satellite problem outside of the Local Group: I -- Pilot observation
Tanaka, et al
Present results from a pilot observation of nearby (~20 Mpc) galaxies with mass similar to that of the MW to address the missing satellite problem. This is the first paper from an on-gong project to address the problem with a statistical sample of galaxies outside of the LG without employing an assumption that the LG is a typical halo in the Universe. Thanks to the close distances of the targets, dwarf galaxies around them can be identified as extended, diffuse galaxies. By applying a surface brightness cut tighter with a careful visual screening to remove artifacts and background contamination, construct a sample of dwarf galaxies. The luminosity function (LF) of one of the targets is broadly consistent with that of the MW, but the other has a more abundant dwarf population. Numerical simulations by Okamoto (2013) seem to over predict the number of dwarfs on average, while more recent predictions from Copernius Complexio are in a better agreement. In both observations and simulations there is a large diversity in the LFs, demonstrating the importance of addressing the missing satellite problem with a statistically representative sample. Also characterize the projected spatial distributions of the satellites and do not observe strong evidence for alignments around the central galaxies. Based on this successful pilot observation, carry out further observations to increase the sample of nearby galaxies, which is planned to be reported in future paper(s).
1808.03501
Quantifying the power spectrum of small-scale structure in semi-analytic galaxies
Brennan, et al
In the CDM picture of structure formation, galaxy mass distributions are predicted to have a considerable amount of structure on small scales. Strong gravitational lensing has proven to be a useful tool for studying this small-scale structure. Much of the attention has been given to detecting individual DM sub haloes through lens modeling, but recent work has suggested that the full population of sub haloes could be probed using a power spectrum analysis. In this paper, quantify the PS of small-scale structure in simulated galaxies, with the goal of understanding theoretical predictions and setting the stage for using measurements of the PS to test DM models. Use a sample of simulated galaxies generated from the Galactic semi-analytic model to determine the PS distribution first in the CDM paradigm and then in a warm dark matter scenario. Find that a measurement of the slope and amplitude of the power spectrum on galaxy strong lensing scales (k~1kpc^{-1}) could be used to distinguish between CDM and alternate DM models, especially if the most massive sub haloes can be directly detected via gravitational imaging.
1808.03940
Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies
Deligny
Important observational results have been recently reported on the angular distributions of cosmic rays at all energies, calling into question the perception of CRs a decade ago. These results together with their in-progress interpretations are summarized in this review paper, covering both large-scale and small-scale anisotropies from TeV energies to the highest ones. While the magnetic field in the Galaxy has long been considered as an external data imprinting a quasi-random walk to particles and thus shaping the angular distributions of Galactic cosmic rays through the induced average density gradient, the information encompassed in the angular distributions in the TeV-PeV energy range appear today as a promising tool to infer some properties of the local magnetic field environments. At the highest energies, the extragalactic origin of the particles has been recently determined observationally. While no discrete source of ultrahigh-energy cosmic rays has been identified so far, the noose is tightening around nearby extragalactic objets, and some prospects are discussed.
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