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Thursday.
1504.07629
Gravitational lens modeling with basis sets
Birrer, Amara, Refregier
Present a lensing modeling technique based on versatile basis sets for the lens and source planes. The method uses high performance MC algorithms, allows for an adaptive build up of complexity and bridges the gap between parametric and pixel based reconstruction methods. Apply the method to a HST image of the strong lens system RXJ1131-1231 and show that the method finds a reliable solution and is able to detect substructure in the lens and source planes simultaneously. Using mock data, show that the method is sensitive to sub-clumps with masses four orders of magnitude smaller than the main lens, which corresponds to about 1e8 Msun, without prior knowledge on the position and mass of the sub-clump. The modeling approach is flexible and maximises automation to facilitate the analysis of the large number of strong lensing systems expected in upcoming wide field surveys. The resulting search for dark sub-clumps in these systems, without M/L priors, offers promise for probing physics beyond the standard model in the DM sector.
1504.07632
On detecting halo assembly bias with galaxy populations
Lin, Mandelbaum, Huang, Huang, Dalal, Diemer, Jian, Kravtsov
The fact that the clustering and concentration of DM haloes depend not only on their mass, but also the formation epoch, is a prominent, albeit subtle, feature of the CDM structure formation theory, and is known as assembly bias. At low mass scales (~1e12 Msun/h), early-forming haloes are predicted to be more strongly clustered than the late-forming ones. In this study, aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low mass haloes as a proxy for the halo formation history. WL is employed to ensure the early- and late- forming halo samples have similar masses, and are free of contamination of satellites from more massive haloes. For the two formation time indicators used (resolved SFH and current sSFR), do not find convincing evidence of assembly bias. For a pair of early- and late-forming galaxy samples with mean mass M_200c~9e11 Msun/h, the relative bias is 1.00±0.12. Attribute the lack of detection to the possibilities that either the current measurements of these indicators are too noisy, or they do not correlate well with the halo formation history. Alternative proxies for the halo formation history that should perform better are suggested for future studies.
1504.07686
A pilot survey for CIII] Emission in the reionization era: gravitationally-lensed z$\sim7-8$ galaxies in the Frontier Fields Cluster Abell 2744
Zitrin, Ellis, Belli, Stark
Report results of a search for CIII] ll1907,1909 A emission using Keck's MOSFIRE spectrograph in a sample of 7 z_phot~7-8 candidates (H~27) lensed by the HFF cluster A2744. Earlier work has suggested the promise of using the CIII] doublet for z confirmation of galaxies in the reionization era given Lya (l1216A) is likely attenuated by the neutral IGM. The primary challenge of the approach is the feasibility of locating CIII] emission without advanced knowledge of the spectroscopic z. With an integration time of 5 hrs in the H-band, reach a 5 sigma median flux limit (in between the sky lines) of 1.5e-18 ergs/cm2/sec, but no convincing CIII] emission found. Also incorporate preliminary measurements from to two other CLASH/HFF clusters in which, similarly, no line was detected, but these were observed to lesser depth. Using the known distribution of OH emission and the photometric z likelihood distribution of each lensed candidate, present statistical upper limits on the mean total CIII] rest-frame equivalent width for the z~7-8 sample. For a signal/noise ratio of 5, estimate the typical CIII] doublet rest-frame equivalent width is, with 95% confidence, <26±5A. Although consistent with the strength of earlier detection in brighter objects at z~6-7, the study illustrates the necessity of studying more luminous or strongly-lensed examples prior to the launch of JWST.
Wednesday.
1504.07246
Microlensing events from the 11-year observations of the Wendelstein Calar Alto Pixellensing Project
Lee, Riffeser, Seitz, Bender, Koppenhoefer
Present the results of the decade-long M31 observation from the Wendelstein Calar Alto Pixellensing Project (WeCAPP). WeCAPP has monitored M31 from 1997 till 2008 in both R- and I-filters, thus provides the longest baseline of all M31 microlensing surveys. The dat are analyzed with the difference imaging analysis, which is most suitable to study variability in crowded stellar fields. Extracted light curves based on each pixel, and devised selection criteria that are optimized to identify microlensing events. This leads to 10 new events, and sums up to a total of 12 microlensing events from WeCAPP, for which their timescales, flux excesses, and colors from their light curves are derived. The color of the lensed stars fall between (R-I)=0.56 to1.36, with a median of 1.0 mag, in agreement with the expectation that the sources are mostly likely bright, red stars at post main-sequence stage. The event FWHM timescales range from 0.5 to 15 days, with a median of 3 days, in good agreement with predictions based on the model of Riffeser+2006.
1504.07248
Coevolution between supermassive black holes and bulges is not via internal feedback regulation but by rationed gas supply due to angular momentum distribution
Cen
As the title says. Without physical fine-tuning, neither the SMBHs nor the stellar bulges can self-regulate or inter-regulate by driving away already fallen cold gas to produce theo served correlation between them. Suggest an alternative scenario where the observed mass ratios of the SMBHs to bulges reflect the angular momentum distribution of in fallen gas such that the mass reaching the stable accretion disc is a small fraction of that reaching the bulge region, averaged over the cosmological time scales. Test this scenario using high-res, large-scale cosmo hydro sims without AGN feedback, assuming the angular momentum distribution of gas landing in the bulge region to yield a Mestel disc that is supported by independent simulation resolving the Bondi radii of SMBHs. A mass ratio of 0.1-0.3% between the very low angular momentum gas that free-falls to the sub-parsec region to accrete to the SMBH and the overall SFR is found. This ratio is found to increase with increasing redshift to within a factor of ~2, suggesting that the SMBH to bulge ratio is nearly redshift independent, with a modest increase with z, a testable prediction. Furthermore, the duty cycle of AGN with high Eddington ratios is expected to increase significantly with z. Finally, while SMBHs and bulges are found to coevolve on ~30-150 Myr time scales or longer, there is indication that, on shorter time scales, the SMBH accretion rate and SF may be less correlated.
1504.07250
Genetically modified haloes: towards controlled experiments in $\Lambda$ CDM galaxy formation
Roth, Pontzen, Peiris
Proposed a method to generate 'genetically-modified' (GM) initial conditions for high-res sims of galaxy formation in a cosmo context. Building on Hoffman-Ribas algorithm, start from a reference sim with fully random ICs, then make controlled changes to specific properties of a single halo (such as its mass and merger history). The algorithm demonstrably makes minimal changes to other properties of the halo and its environment, allowing isolation of the impact of a given modification. As a significant improvement over previous work, able to calculate the abundance of the resulting objects relative to the LCDM reference cosmology. The approach can be applied to a wide range of cosmic structures and epochs; here, study two problems as a proof-of-concept. First, investigate the change in density profile and concentration as the collapse time of three individual halos are varied at fixed final mass, showing good agreement with previous statistical studies using large simulation suites. Second, modify the z=0 mass of haloes to show that the theoretical abundance calculations correctly recover the halo mass function. The results demonstrate that the technique is robust, opening the way to controlled experiments in galaxy formation using hydro zoom sims.
1504.07255
Measuring photometric redshifts using galaxy images and deep neural networks
Hoyle
Propose a new method to estimate the photo-z of galaxies by using the full galaxy image in each measured band. This method draws from the latest techniques and advances in machine learning, in particular Deep Neural Networks. Pass the entire multi-band galaxy image into the machine learning architecture to obtain a z estimate that is competitive with the best existing standard machine learning techniques. The standard techniques estimate z using post-processed features, such as magnitudes and colors, which are extracted from the galaxy images and are deemed to be salient by the user. This new method removes the user from the photo-z estimation pipeline. However, note that Deep Neural Networks require many orders of magnitude more computing resources than standard machine learning architectures.
Tuesday.
icarus 2014.01.030
Glory on Vemus cloud tops ad the unknown UV absorber
Report on the implications of the observations of the glory phenomenon by Venus Express orbiter. Obtain a very accurate estimate of the cloud particle size at 70 km altitude of 1.2 um with a very narrow size distribution. Also find that the two observations presented the clouds are homogeneous in cloud particle sizes, on scale of at least 1200km. This is in contrast to previous estimates that were either local, from entry probes data, or averaged over space and time from polarization data. Secondly, find that the refractive index for the data discussed here is higher than that of sulfuric acid previously proposed for the clouds composition. Assuming that the species contributing to the increase of the refractive index is the same as the unknown UV absorber, able to constrain the list of candidates. Investigated several possibilities and argue that either small ferric chloride (FeCL3) cores inside sulfuric acid particles or elemental sulfur coating their surface are good explanations of the observation.
1504.06621
The local group as time machine: studying the high-redshift universe with nearby galaxies
Boylan-Kolchin, et al
Infer the UV luminosities of LG galaxies at early cosmic times (z~2 and ~7) by combining stellar population synthesis modeling with SFHs derived from deep color-magnitude diagrams constructed from HST observations. Analysis provides a basis for understanding high-z galaxies - including those that may be unobservable even with the JWST - in context of familiar, well-studied objects in the very low-z Universe. Find that, at the epoch of reionization, all LG dwarfs were less luminous than the faintest galaxies detectable in deep HST observations of blank fields. Predict that JWST will observe z~7 progenitors of galaxies similar to the LMC today; however, the HST Frontier Fields initiative may already be observing such galaxies, highlighting the power of gravitational lensing. Consensus reionization models require an extrapolation of the observed blank-field luminosity function at z~7 by at least two orders of magnitude in order to maintain reionization. This scenario requires the progenitors of the Fornax and Sagittarius dwarf spheroidal galaxies to be contributors to the ionizing background at z~7. Combined with numerical simulations, the results argue for a break in the UV luminosity function from a faint-end slope of alpha~-2 at M_UV<-13 to alpha~1.2 at lower luminosities. Applied to photometric samples at lower redshifts, the analysis suggests that HST observations in lensing fields at z~2 are capable of probing galaxies with luminosities comparable to the expected progenitor of Fornax.
1504.06821
From outside-in to inside-out: galaxy assembly mode depends on stellar mass
Pan, et al
Investigate how galaxy mass assembly mode depends on stellar mass M*, using a large sample of ~10k low z galaxies. The sample is selected to have SDSS R_90>5.0", which allows the measures of both the integrated and the central NUV-r color indices. Find that: in the M*-(NUV-r) green valley, the M*<1e10 Msun galaxies mostly have positive or flat color gradients, while most f the M*>1e10.5 Msun galaxies have negative color gradients. When their central Dn4000 index values exceed 1.6, the M*<1e10.0 Msun galaxies have moved to the UV red sequence, whereas a large fraction of the M*>1e10.5 Msun galaxies still lie on the UV blue cloud or the green valley region. Conclude that the main galaxy assembly mode is transiting from the "outside-in" mode to the "inside-out" mode at M*<1e10 Msun and at M*>1e10.5 Msun. Argue tat the physical origin of this is the compromise between the internal and the external process that driving the SF quenching in galaxies. These results can be checked with the upcoming large data produced by the on-going IFS survey projects, such as CALIFA, MaNGA and SAMI in the near future.
1504. 06974
Properties of weak lensing clusters detected on Hyper Suprime-Cam 2.3 square degree field
Miyazaki, et al
Present properties of moderately massive clusters of galaxies detected by the newly developed HSC on Subaru using WL. 8 peaks exceeding a S/N ratio of 4.5 are identified on the convergence SN map of a 2.3 sq deg field observed during the early commissioning phase of the camera. Multi-color photometric data is used to generate optically selected clusters using the CAMIRA algorithm. The optical cluster positions were correlated with the peak positions from the convergence map. All 8 significant peaks have optical counterparts. The velocity dispersion of clusters are evaluated by adopting the SIS fit to the tangential shear profiles, yielding viral mass estimates, M500c, of the clusters which range from 2.7e13 to 4.4e14 Msun . The number of peaks is considerably larger than the average number expected from LCDM cosmology but this is not extremely unlikely if one takes the large sample variance in the small field into account. However, could safely argue that the peak count strongly favors the recent Planck result suggesting high sigma8 value of 0.83. The ratio of stellar mass to the DM halo mass shows a clear decline as the halo mass increases. If the gas mass fraction, fg, in haloes is universal, as has been suggested in the literature, the observed baron mass in stars and gas shows a possible deficit compared with the total baryon density estimated from the baryon oscillation peaks in anisotropy of the cosmic microwave background.
Monday.
1504.06328
Luminous red galaxies: selection and classification by combining optical and infrared photometry
Prakash, Licquia, Newman, Rao
A new method of combining optical and IR photometry to select LRGs at z>0.6. Combine optical photometry from CFHTLS and HST, IR photometry from WISE, and spectroscopic or photometry z from the DEEP2 Galaxy redshift survey or COSMOS. Present a variety of methods for testing the success of the selection, and present methods for optimization given a set of rest-frame color and z requirements. Tested this selection in two different regions of the sky, the COSMOS and EGS fields, to reduce the effect of cosmic/sample variance. Used these methods to assemble large samples of LRGs for 2 different ancillary programs as a part of the SDSS-III/BOSS spectroscopic survey. This technique is now being used to select ~600k LRG targets for eBOSS, which began observations in fall 2014, and will be adapted for the proposed DESI survey. Found these methods can select high-z LRGs efficiently with minimal stellar contamination; this is extremely difficult to achieve with selection that rely on optical photometry alone.
Friday.
1504.06148
Space Warps: I. Crowd-sourcing the discovery of gravitational lenses
Marshall, et al
Space Warps is a novel GL discovery service that yields samples of high purity and completeness through crowd-sourced visual inspection. Carefully produced color composite images are displayed to volunteers via a classification interface which records their estimates of the positions of candidate lensed features. Simulated lenses, and expert-classified images which lack lenses, are inserted into the image stream at random intervals; this training set is used to give the volunteers feedback on their performance, as well as to calibrate it in order to allow dynamical updates to the probability of any image they classify to contain a lens Low probability systems are retired from the site periodically, concentrating the sample towards a set of candidates. Having divided 160 sq deg of CFHTLS imaging into some 430k overlapping 84x84" tiles and displaying them on the site, 37k volunteers joined who contributed 11e6 image classifications over the course of 8 months. The sample was reduced to 3368 Stage I candidates; these were then refined to yield a sample that are expected to be over 90% complete and 30% pure. Comment on the scalability of the Space Warps system to the wide field survey era, based on the finding that searches of 1e5 images can be performed by a crowd of 1e5 volunteers in 6 days.
Thursday.
1504.05578
On the physical origin of galactic conformity
Hearin, Behroozi, van den Bosch
Correlation between the SFRs of nearby galaxies (so-called galactic conformity) have been observed for projected separaitons up to 4 Mpc, an effect not predicted by current SAM. Investigate correlations between the mass accretion rates (dMvir/dt) of nearby haloes as a potential physical origin for this effect. Find that pairs of host haloes "know about" each others' assembly histories even when their present-day separation is greater than thirty times the viral radius of either halo. These distances are far too large for direct interaction between the halos to explain the correlation in their dMvir/dt. Instead, halo pairs at these distances reside in the same large-scale tidal environment, which regulates dMvir/dt for both haloes. Larger haloes are less affected by external forces, which naturally gives rise to a mass dependence of the halo conformity signal. SDSS measurements of galactic conformity exhibit a qualitatively similar dependence on stellar mass, including how the signal varies with distance. Based on the expectation that halo accretion and galaxy SFR are correlated, predict the scale-, mass- and z-dependence of large-scale galactic conformity, finding that the signal should drop to undetectable levels by z>1. These predictions are testable with current surveys to z~1; confirmation would establish a strong correlation between DM halo accretion rate and central galaxy SFR.
1504.05591
The splash back radius as a physical halo boundary and the growth of halo mass
More, Diemer, Kravtsov
The boundaries of CDM haloes are commonly defined to enclose a density contrast Delta relative to a reference (mean or critical) density. Argue that a more physical boundary of haloes is the radius at which accreted matter reaches its first orbital epicenter after turnaround. This splash back radius, Rsp, manifests itself as a sharp density drop in the halo outskirts, at a location that depends upon the mass accretion rate. Present calibrations of Rsp and the enclosed mass, Msp, as a function of the accretion rate and alternatively peak height. Find that Rsp varies between ~0.8-1 R200m for rapidly accreting haloes and ~1.5 R200m for slowly accreting haloes. The extent of a halo and its associated environmental effects can thus extend well beyond the conventionally defined "viral" radius. Show that Msp and Rsp evolve relatively strongly compared to other commonly used definitions. In particular, Msp evolves significantly even for the smallest dwarf-sized haloes at z=0. Also contrast Msp with the mass enclosed within 4 scale radii of the halo density profile, M<4rs, which characterizes the inner halo. During the early stages of halo assembly, Msp and M<4rs evolve similarly, but in the late stages M<4rs stops increasing while Msp continues to grow significantly. This illustrates that haloes at low z can have "quiet" interiors while continuing to accrete mass in their outskirts. Discuss potential observational estimates of the splash back radius and show that it may already have been detected in galaxy clusters.
1504.05598
Cross-correlation of Planck CMB Lensing and CFHTLenS galaxy weak lensing maps
Liu, Hill
CFHT: probes LSS at z~0.9, cross correlate with WL maps using Planck 2013 and 2015 data. Forecast a S/N of ~4.6. Noise as expected, but signal low, with A=0.48 or 0.44 for 2013 and 2015, respectively (A=1 corresponds to fiducial Planck 2015 LCDM prediction); detection significance is moderate (~2 sigma). WMAP9 parameter does slightly better, A-0.56/0.52. Systematic effects: photo-z uncertainty, contamination by IA, masking of galaxy clusters have ~10% each effect to resolve the tension. An overall multiplicative bias in CFHTLenS can also play a role. Close with forecasts for measurement of this cross-correlation using ongoing and future WL surveys, which will definitively test the significance of the tension in the results with respect to LCDM.
1504.05672
Probing cosmology with weak lensing selected clusters I: halo approach and all-sky simulations
Shirasaki, Hamana, Yoshida
Explore a variety of statistics of clusters selected with cosmic shear measurement by utilizing both analytic models and large numerical sims. First develop a halo model to predict the abundance and the clustering of WL selected clusters. Observational effects such as galaxy shape noise are included in the model. Then generate realistic mock WL catalogs to test the accuracy of the analytic model. To this end, perform full-sky ray-tracing simulations that allow multiple realizations of a large continuous area. Model the masked regions on the sky using the actual positions of bright stars, and generate 200 mock WL catalogs with sky coverage of ~1000 sq deg. Utilize the large set of mock catalogs to evaluate the covariance matrices between the local and non-local statistics. Show that the theoretical model agrees well with the ensemble average of statistics and their covariances calculated directly from the mock catalogues. With a typical selection threshold, ignoring shape noise correction causes overestimation of the clustering of WL selected clusters with a level of about 10%, and shape noise correction boosts the cluster abundance by a factor of a few. Calculate the cross-covariances using the halo model with accounting for the effective reduction of the survey area due to masks. The covariance of the cosmic shear auto power spectrum is affected by the mode-coupling effect that originates from sky masking. Model and the results can be readily used for a cosmo analysis with ongoing and future WL surveys.
Wednesday.
1504.05183
Comparison of weak lensing by NFW and Einasto halos and systematic errors
Sereno, Fedeli, Moscardini
Recent N-body sims have shown that Einasto radial profiles provide the most accurate description of DM haloes. Predictions based on the traditional NFW functional form may fail to describe the structural properties of cosmic objects at the % level required by precision cosmology. Compute the systematic errors expected for WL analyses of clusters of galaxies if one wrongly models the lens properties. Even though the NFW fits of observed tangential shear profiles can be excellent, virial masses and concentrations of very massive halos (>~1e15 Msun/h) can be over- and underestimated by ~10%, respectively. Misfitting effects also steepen the observed mass-concentration relation, in a way similar to that seen in multi wavelength observations of galaxy groups and clusters. Einasto lenses can be distinguished from NFW haloes either with deep observations of very massive structures (>~1e15 Msun/h) or by stacking the shear profiles of thousands of group-sized lenses (~1e14 Msun/h).
1504.05186
Early structure formation from primordial density fluctuations with a blue-tilted power spectrum
Hirano, Zhu, Yoshida, Spergel, Yorke
CMB provides strong constraints on the amplitude of primordial PS (PPS) on scales larger than 10Mc, the amplitude of the PS on sub-galactic length scales is much more poorly constrained. Study early structure formation in a cosmo model with a blue-tilted PPS. Assume that the standard scale-invariant PPS is modified at small length scales as P(k)~k^m_s with m_s>1. Run a series of cosmo hydro is to examine the dependence of the formation epoch and the characteristic mass of primordial stars on the tilt of the PPS. In models with m_s>1, SF gas clouds are formed at z>100, when formation of H2 molecules is inefficient because the intense CMB radiation destroys chemical intermediates. Without efficient coolant, the gas clouds gravitationally contract while keeping a high temperature. The protostars formed in such "hot" clouds grow very rapidly by accretion to become extremely massive stars that may leave massive BHs with a few hundred Msun at z>100. The shape of the PPS critically affects the properties and the formation epoch of the fist generation of stars. Future experiments of the CMB polarization and the spectrum distortion may provide important information on the nature of the first stars and their formation epoch, and hence on the shape of the small-scale PS.
1504.05209
Stellar and quasar feedback in concert: effects on AGN accretion, obscuration, and outflows
Hopkins, Torrey, Faucher-Giguere, Quataert, Murray
Use hydro sims to study the interaction of AGN feedback mechanisms (accretion-disk winds & Compton heating) with a multi-phase ISM. The ISM model includes radiative cooling and explicit stellar feedback from multiple processes. Simulate radii ~0.1-100 pc around around an isolated (non-merging) BH. These are the scales where the accretion rate onto the BH is determined and where AGN-powered winds and radiation couple to the ISM. The primary results include: (1) The BH accretion rate on these scales is determined by exchange of angular momentum between gas and stars in gravitational instabilities. This produces accretion rates of ~0.03-1 Msunyr, sufficient to power a luminous AGN. (2) the gas disk in the galactic nucleus undergoes an initial burst of SF followed by several Myrs where stellar feedback suppresses the SFR per dynamical time. (3) AGN winds injected at small radii with momentum fluxes ~L/c couple efficiently to the ISM and have a dramatic effect on the ISM properties in the central ~100 pc. AGN winds suppress the nuclear SFR by a factor of ~10-30 and the BH accretion rate by a factor of ~3-30. They increase the total outflow rate from the galactic nucleus by a factor of ~10. The latter is broadly consistent with observational evidence for galaxy-scale atomic and molecular outflows driven by AGN rather than SF. (4) In simulations that include AGN feedback, the predicted column density distribution towards the BH is reasonably consistent with observations, whereas absent AGN feedback, the BH is isotropically obscured and there are not enough optically-thin sight lines to explain observed Type I AGN. A 'torus-like' geometry arises self-consistently because AGN feedback evacuates the gas in the polar regions.
1504.05249
SLoWPoKES-II: 100,000 wide binaries identified in SDSS without proper motions
Dhital, West, ... et al
Present catalog of low-mass visual binaries identified from SDSS by matching photometric distances. The candidate pairs are vetted by comparing the stellar information. The candidate pairs are vetted by comparing the stellar density at their respective Galactic positions to MC realizations of a simulated MW. In this way, able to identify large numbers of bona fide wide binaries without need of proper motions. 105k visual binaries with angular separations of ~1-20" were identified, each with a probability of chance alignment of <5%. This is the largest catalog of bona fide wide binaries to date, and it contains a diversity of systems --- in mass, mass ratios, binary separations, metallicity, and evolutionary states---that should facilitate follow-up studies to characterize the properties of M dwarfs and white dwarfs. There is a subtle but definitive suggesting of multiple populations in the physical separation distribution, supporting earlier findings. Suggest that wide binaries are comprised of multiple populations, most likely representing different formation modes. There are 141 M7 or later wide binary candidates, representing a 7-fold increase in the number currently known. These binaries are too wide to have been formed via the ejection mechanism. Finally, found a 6% of spectroscopically confirmed M dwarfs are not included in the SDSS STAR catalog; they are misclassified as extended sources due to the presence of nearby or partially resolved companion. The SLoWPoKES-II catalog is publicly available to the entire community on the WWW via the Filtergraph data visualization portal.
1504.05456
Galaxy alignments: an overview
Joachimi, Cacciato, Kitching, ... et al
The alignment between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe. Provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience. The development of the field over the past one hundred years is briefly reviewed. Also discuss the impact of galaxy alignments on measurements of WL, and discuss avenues for making theoretical and observational progress over the coming decade.
1504.05465
Galaxy alignments: observations and impact on cosmology
Kirk, Brown, Hoekstra, Joachimi, et al
Galaxy shapes are not randomly oriented, rather they are statistically aligned in a way that can depend on formation environment, history and galaxy type. Studying the alignment of galaxies can therefore deliver important information about the astrophysics of galaxy formation and evolution as well as the growth of structure in the Universe. In this review paper, summarize key measurements of IA, divided by galaxy type, scale and environment. Also cover the statistic and formalism necessary to understand the observations in the literature. With the emergence of WL as a precision probe of cosmo, galaxy alignments took on an added importance because they can mimic cosmic shear, the effect of gravitational lensing by LSS on observed galaxy shapes. This makes IA an important systematic effect in WL studies. Quantify the impact of IA on cosmic shear surveys and finish by reviewing practical mitigation techniques which attempt to remove contamination by IA.
1504.05546
Galaxy alignments: theory, modeling and simulations
Kiessling, Cacciato, Joachimi, et al
The shapes of galaxies are not randomly oriented on the sky. During the galaxy formation and evolution process, environment has a strong influence, as tidal gravitational fields in LSS tend to align the shapes and angular momenta of nearby galaxies. Additionally, events such as galaxy mergers affect the relative alignments of galaxies throughout their history. These "intrinsic galaxy alignments" are known to exist, but are still poorly understood. This review will offer a pedagogical introduction to the current theories that describe IA, including the apparent difference in IA between early- and late-type galaxies and the latest efforts to model them analytically. It will then describe the ongoing efforts to simulate IA using both N-body and hydrodynamic sims. Due to the relative youth of this field, there is still much to be done to understand intrinsic galaxy alignments and this review summaries the current state of the field, providing a solid bases for future work.
Tuesday.
1504.04623
Cosmological tests of gravity
Koyama
Einstein's GR is tested accurately within the local universe (SS), but this leaves open the possibility that it is not a good description at the largest scales in the Universe. The standard model of cosmology assumes GR as the theory to describe gravity on all scales. In 1998, astronomers made the discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown DE. Alternatively, it could be that there is no DE and GR itself is in error on cosmological scales. The standard model of cosmology is based on a huge extrapolation of the limited knowledge of gravity. This discovery of the late time acceleration of the Universe may require a revision of the theory of gravity and the standard model of cosmology based on GR. Review recent progress in constructing modified gravity model as an alternative to DE and developing cosmological tests of gravity.
1504.04988
Formation of elongated galaxies with low masses at high redshift
Ceverino, Primack, Dekel
Report the identification of elongated (triaxial or prolate) galaxies in cosmological sims at z~2. These are preferentially low-mass galaxies (M_s<1e9.5 Msun), residing in DM haloes with strongly elongated inner parts, a common feature of high-z DM haloes in the LCDM cosmology. Feedback slows formation of stars at the centers of these haloes, so that a dominant and prolate DM distribution gives rise to galaxies elongated along the DM major axis. As galaxies grow in stellar mass, stars dominate the total mass within the galaxy half-mass radius, making stars and DM rounder and more oblate. A large population of elongated galaxies produces a very asymmetric distribution of projected axis ratios, as observed in high-z galaxy surveys. This indicates that the majority of the galaxies at high z are not discs or spheroids but rather galaxies with elongated morphologies.
Monday.
1504.04372
Satellites of LMCs: close friendships ruined by Milky Way Mass Halos
Deason, Wentzel, Garrison-Kimmel, Belokurov
Motivated by the recent discovery of several dwarf galaxies near the LMC, study the accretion of massive satellites onto MW/M31-like halos using the ELVIS suite of N-body simulations. Identify 25 surviving subhalos near the expected mass of the LMC, and investigate the lower-mass satellite that were associated with these subclass before they fell into the MW/M31 halos. Typically, 7% of the overall z=0 satellite population of MW/M31 halos were in a surviving LMC-group poor to falling into the MW/M31 halo. This fraction, however, can vary between 1% and 25% being higher for groups with higher-mass and/or more recent infall times. Groups of satellite disperse rapidly in phase space after infall, and their distances and velocities relative to the group center become statistically similar to the overall satellite population after 4-8 Gyr. Quantify the likelihood that satellites were associated with an LMC-mass group as a function of both distance and velocity relative to the LMC at z=0. The close proximity in distance of the nine DES candidate dwarf galaxies to the LMC suggest that ~2-4 are likely associated with the LMC. Furthermore, if several of these dwarfs nearby to the LMC are genuine members, then the LMC-group probably fell into the MW very recently, 2Gyr ago. If the connection with the LMC is established with the hope of the follow-up velocity measurements, these "satellites of satellites" represent prime candidates to study the affects of group pre-processing on lower mass dwarfs.
1504.04516
The clustering evolution of dusty star-forming galaxies
Cowley, Lacey, Baugh, Cole
Present predictions for the clustering of galaxies selected by their total L_IR, and their emission at FIR and sub-mm wavelengths. Combine a new version of the GALFORM SAM of galaxy formation, implemented in a Millennium-style N-body simulation utilizing the WMAP7 cosmology, with a self-consistent model for calculating the absorption and re-emission of stellar radiation by dust. In the model, galaxies selected at 850 um predominantly reside in DM haloes of mass 1e11.5-12 Msun/h, independent of z for 0.2<z<4 or flux (for 0.25<S_850um<4 mJy). Around the peak of their redshift distribution (z~2.5) the brightest galaxies (S_850um>4 mJy) exhibit a correlation length of r_0=5.5+0.3-0.5 Mpc/h, consistent with observations. Show further that these galaxies evolve into z=0 descendants with stellar mass ~1e11 Msun/h occupying haloes which span a broad range in mass ~1e12-14 Msun/h. The FIR emissivity at shorter wavelengths (250, 350, and 500 um) in the model is dominated by galaxies in the same halo mass range, again independent of z for 0.5<z<5. Compare the predictions of the angular power spectrum of Cosmic Infrared Background (CIB) anisotropies at these wavelengths with recent observations, and find that the model agrees with the observed power to within a factor of ~2 over all scales and wavelengths, an improvement over earlier versions of the model. Simulating sub-mm imaging at 850 um, show that source confusion due to the coarse angular resolution of single-dish telescopes at this wavelength can significantly bias angular clustering measurements severely complicating the interpretation of such observations.
Friday.
1504.04011
Constraints on the missing baryons from the kinetic Sunyaev-Zeldovich effect in Planck data
Hernández-Monteagudo, et al
Estimate the amount of the missing barons detected by Planck of kSZ effect around members of the Central Galaxy Catalogue (CGC) from SDSS DR7. Use 2 statistics yielding evidence for kSZ signal, namely the pairwise peculiar momentum and the correlation function of the kSZ temperature estimates and predicted line-of-sight peculiar velocities. Find that both statistics yields consistent measurements of the Thomson optical depth tau_T in the range of 0.5-1.4e-4 for angular apertures that, on average, correspond to a range of distances of >1 to almost 3 viral radii from the centers of the CG host halos. Find that, for the larger apertures for which we still have significant (2-2.5 sigma) kSZ detection, the regions probed around CGs contain roughly half the total amount of baryons present in the cosmological volume sampled by the Sloan footprint at z~0.12. Furthermore, under the assumption that baryons trace the DM distribution, the tau_T measurements are compatible with having detected all the missing baryons around the CGs. Finally, the kSZ measurements yields no evidence for a kSZ dipole on the positions of the CGs, providing the strongest constraints on the local bulk flow at a distance of 350 Mpc/h (below 290 km/s at 95% CL), and adding further evidence for the Copernican principle of homogeneity.
1504.04015
Beacons in the dark: using novae and supernovae to detect dwarf galaxies in the local universe
Conroy, Bullock
As the title says. Dwarf galaxies with M*<1e6 Msun beyond a few Mpc will likely be too faint and/or too low in surface brightness to be directly detected in upcoming large area ground-based photometric surveys, but novae can be detected. Depending on the form of the stellar mass-halo mass relation and the underlying SFHs of low mass dwarfs, the expected nova rates will be a few to ~100/yr and the expected NS rates will be ~1e2-4 within the observable volume. The transient rate associated with intrahalo stars will be comparably large, but these transients will be located close to bright galaxies, in contrast to the dwarfs, which should trace the underlying LSS of the cosmic web. Aggressive follow-up of hostess transients has the potential to uncover the predicted enormous population of low mass field dwarf galaxies.
1504.04025
The alignment and shape of dark matter, stellar, and hot gas distributions in the EAGLE and cosmo-OWLS simulations
Velliscig, Cacciato, et al
Report the alignment and shape of DM, stellar, and hot gas distributions in the EAGLE and cosmos-OWLS sims: 0<z<1, 11<log10(M200)<15. The shape parameters of the DM, stellar, and hot gas distributions follow qualitatively similar trends: they become more aspherical (and triaxial) with increasing halo mass, radius and redshift. Measure the misalignment of the baryonic components (hot gas and stars) of galaxies with their host halo as a function of halo mass, radius, z, and galaxy type (centrals vs satellites and early vs late-type). Overall, galaxies align well with local distribution of the total (most dark) matter. However, the stellar distributions on galactic scales exhibit a median misalignment of about 45-50 deg with respect to their host halos. This misalignment is reduced to 25-30 deg in the most massive haloes (13-15 log10(M200)). Halo of the disc galaxies in EAGL have a misalignment angle wrt their host halos larger than 40 deg. Present fitting functions and tabulated values for the probability distribution of galaxy-halo misalignment to enable a straightforward inclusion of the results into models of galaxy formations based on purely collisionless N-body sims.
1504.04088
Large-scale clustering of Lyman-alpha emission intensity from SDSS/BOSS
Croft et al
Consistent with LCDM with Omega_M=0.30+0.10-0.07. [...] 97% of the Lya emission in the universe at z<0.8 is therefore undetected in previous surveys of Lya emitters. [...] Also detect z-space anisotropy of the quasar-lay emission cross-correlation, finding evidence at the 3 sigma level that it is radially elongated, consistent with distortions caused by radiative-transfer effects. These measurements represent the first application of the intensity mapping technique to optical observations.
1504.04366
Equivalence principle and the Baryon Acoustic Peak
Baldauf et al
Study the dominant effect of a long wavelength density perturbation delta(lambda_L) on short distance physics. In the non-relativistic limit, the result is a uniform acceleration, fixed by the EP, and typically has no effect on statistical averages due to translational invariance. This same reasoning has been formalized to obtain a "consistency condition" on the cosmo correlation functions. In the presence of a feature, such as the acoustic peak at l_BAO, this naive expectations breaks down for lambda_L<l_BAO. Calculate a universal piece of the 3pt correlation function in this regime. The same effect is shown to underlie the spread of the acoustic peak, and is calculable to all orders in the long modes. This can be used to improve the result of perturbative calculations - a technique known as "IR resummation" - and is explicitly applied to the one-loop calculation of PS. Finally, the success of BAO reconstruction schemes is argued to be another empirical evidence for the validity of the results.
Thursday.
1504.03979
Do we need model-dependent covariances when we test cosmological models with galaxy power spectra?
Kalus, Percival, Samushia
Consider the shape of the posterior distribution to be used when fitting cosmo models to power spectra measured from galaxy surveys. At very large scales, Gaussian posterior distributions in the power do not approximate the posterior distribution P_R expected for a Gaussian density field delta_k, even if the covariance matrix is varied according to the model to be tested. Compare alternative posterior distributions with P_R, both mode-by-mode and in terms of expected f_NL-measurements. Marginalizing over a Gaussian posterior distribution P_f with fixed covariance matrix yields a posterior mean value of f_NL which, for a data set with the characteristics of Euclid, will be underestimated by Delta f_NL=0.4, while for SDSS DR9 BOSS it will be underestimated by Delta f_NL=19.1. The inverse cubic normal distribution (P_ICN) agrees very well with P_R at all scales and for all data sets, hence providing the same marginalized value. Adopting this likelihood function means that different covariance matrix for each model is not required to be tested: this dependence is absorbed into the functional form of the posterior. Thus, the computational burden of analysis is significantly reduced.
Tuesday. Wednesday.
1504.02777
The abundance of satellites depends strongly on the morphology of the host galaxy
Ruiz, Trujillo, Mármol-Queraltó
Using the spectroscopic catalogue of SDSS DR10, explore the abundance of satellites around a sample of 307 massive (M*>1e11 Msun) local (z<0.025) galaxies. Have divided the sample into 4 morphological group (E, S0, Sa, Sb/c). Find that the number of satellites with M*>1e9 Msun and R<300 kpc depends drastically on the morphology of the central galaxy. The average number of satellites per galaxy host (N_sat/N_host) down to a mass ratio of 1:100 is : 5.5±1.0 for E hosts, 2.7±0.4 for S0, 1.4±0.3 for Sa and 1.2±0.3 for Sb/c. The amount of stellar mass enclosed by the satellites around massive E-type galaxies is a factor of 2, 4, and 6 larger than the mass in the satellites of S0, Sa and Sb/c-types, respectively. If these satellites would eventually infall in to the host galaxies, for all the morphological types, the merger channel will be largely dominated by satellites with a mass ratio satellite-host mu<0.1. The fact that massive elliptical galaxies have a significant larger number of satellites than massive spirals could point out that elliptical galaxies inhabit heavier DM haloes than equal massive galaxies with later morphological types. If this hypothesis is correct, the DM haloes of late-type spiral galaxies are a factor ~3 more efficient on producing galaxies with the same stellar mass than those DM haloes of massive ellipticals.
1504.02778
Calibrated ultra fast image simulations for the Dark Energy Survey
Bruderer, Chang, Refregier, Amara, Berge, Gamper
To understand the measurement process of WL and associated systematic effects, image simulations are becoming increasingly important. Present a first implementation of Monte Carlo Control Loops (MCCL), a coherent framework for studying systematic effects in WL. It allows to model and calibrate the shear measurement process using image simulations from the Ultra Fast Image Generator (UFig). Apply this framework to a subset of the data taken during the SV of DES. Calibrate the UFig sims to be statistically consistent with DES images. Then perform tolerance analyses by perturbing the simulation parameters and study their impact on the shear measurement at the 1pt level. This allows determination of the relative importance of different input params to the simulations. For spatially constant systematic errors and 6 sim params, the calibration of the sims reaches the WL precision needed for the DES SV survey area. Furthermore, find a sensitivity of the shear measurement to the intrinsic ellipticity distribution, and an interplay between the magnitude-size and the pixel value diagnostics in constraining the noise model. This work is the first application of the MCCL framework to data and shows how it can be used to methodically study the impact of systematics on the cosmic shear measurement.
1504.02889
Stellar kinematics and metallicities in the ultra-faint dwarf galaxy reticulum II
Simon, et al (+70 others)
Present Magellan, VLT, Gemini South spectroscopy of the newly discovered MW satellite Reticulum II. Based on the spectra of 25 Reg II member stars selected from DES imaging, measure a mean heliocentric velocity of 62.8±0.5 km/s and a velocity dispersion of 3.3±0.7 km/s. The M/L ratio of Ret II within its halon-light radius is 470±210 Msun/Lsun, demonstrating that it is a strongly DM-dominated system. Despite its spatial proximity to the Magellanic clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28±0.09 dex, and identify several extremely metal-poor stars with [Fe/H]<-3. In combination with its luminosity, size and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H]=-2.65±0.07, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the 3rd closest dwarf galaxy to the MW, the LoS integral of the DM density squared is log J=18.8±0.6 GeV^2/cm^5 within 0.2 degrees, indicating that the predicted gamma-ray flux from DM annihilation in Ret II is lower than that of several other dwarf galaxies.
1504.02900
The dark energy camera
Flaughter et al (+117 others)
The DECam is a new imager with 2.2 deg diameter FoV mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by DES collaboration, and meets or exceeds the stringent requirements designed for the wide-field and SN surveys for which the collaboration uses it. The camera consists of a five element optical corrector, 7 filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises a 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs of guiding and focus. The CCDs have 15 microns x 15 microns pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation and current status.
1504.02932
Binary astrometric microlensing with Gaia
Sajadian
The Gaia efficiency for detecting the binary signatures in binary astrometric microlensing events is ~10-20 %. Microlensing binary events being observed wit Gaia with detectable binary signatures for the binary fraction about 0.1, is estimated as 6,11, 77, and 1306, respectively for (1) stellar mass BHs, (b) NSs, (c) WDs, and (d) MS stars as micro lenses. The efficiencies of measuring the mass of populations are 9.8, 2.9, 1.2 and 0.8 % respectively. The number of their astrometric microlensing events being observed in the Gaia era in which the lens mass can be inferred with the relative error less than 0.5 toward the Galactic bulge is estimated as 45, 34, 76 and 786 respectively.
1504.02936
Automated transient identification in the Dark Energy Survey
Goldstein, et al (+65 others)
Describe an algorithm for identifying point-source transients and moving objects on reference -subtracted optic mages containing artifacts of processing and instrumentation. The algorithm makes use of the supervised machine learning technique known as Random Forest. Present results from its use in the DES-SN program, where it was trained using a sample of 898k signal and background events generated by the transient detection pipeline. After reprocessing the data collected during the first DES-SN observing season (9/13 through 2/14) using the algorithm, the number of transient candidates eligible for human scanning decreased by a factor of 13.4, while only 1% of the artificial SNeIa injected into search images to monitor survey efficiency were lost, most of which were very faint events. Characterize the algorithm's performance in detail, and discuss how it can inform pipeline design decisions for future time-domain imaging surveys, such as the LSST and the Zwicky Transient Facility.
1504.02983
Galaxies in X-ray selected clusters and groups in dark energy survey data: stellar mass growth of bright central galaxies since z~1.2
Zhang, et al (+82 others)
Using the DES-SV data for a sample of 106 X-ray selected clusters and groups, study the stellar mass growth of BCGs since z=1.2. Compared with the expectation in a SAM applied to the MS, the observed BCGs become under-massive/under-luminous with decreasing redshift. Incorporate the uncertainties associated with cluster mass, z, and BCG stellar mass measurements into analysis of a z-dependent BCG-cluster mass relation, m*\propto (M200/1.5e14 Msun)^0.34±0.08(1+z)^-0.19±0.34, and compare the observed relation to the simulation prediction. Estimate the average growth rate since z=1.0 for BCGs hosted by clusters of M200,z=1e13.8Msun, at z=1.0: M*,BCG appears to have grown by 0.13±0.11 dex, in tension at ~2.5sigma significance level with the 0.4 dex growth rate expected in the simulation. Show that the buildup of extended ICL after z=1.0 may alleviate this tension in BCG growth rates.
1504. 1504.02996
DESAltert: enabling real-time transient follow-up with dark energy survey data
Poci, et al
DES is currently undertaking an observational program imaging 1/4 of the southern hemisphere sky with unprecedented photometric accuracy. In the process of observing millions of faint stars and galaxies to constrain the parameters of the DE EoS, the DES will obtain pre-discovery images of the regions surrounding an estimated 100 GRBs over 5 years. Once GRBs are detected by, e.g., the Swift satellite, the DES data will be extremely useful for follow-up observations by the transient astronomy community. Describe a recently-commissioned suite of SW that listens continuously for automated notices of GRB activity, collates useful information from archival DES data, and promulgates relevant data products back to the community in near-real-time. Of particular importance are the opportunities that DES data provide for relative photometry of GRBs or their afterglows, as well as for identifying key characteristics (e.g., photo-z) of potential GRB host galaxies. Provide the functional details of the DESAlert SW as it presently operates, as well as the data products that it produces, and show sample results from the application of DESAlert to several previously-detected GRBs.
1504.03002
Wide-field lensing mass maps from DES science verification data
Vikram, Chang, Jain, Bacon, ... et al
WL "mass maps" provide a powerful tool for studying cosmo as they probe both luminous and DM. In this paper, present a WL mass map constructed from shear measurements in a 139 deg.sq. area from DES SV data overlapping with the SPT survey. Compare the distribution of mass with that of the FG distribution of galaxies and clusters. The over densities in the reconstructed map correlated well with the distribution of optically detected clusters. Cross-correlating the mass map with the FG galaxies from the same DES SV data gives results consistent with mock catalogs that include the primary sources of statistical uncertainties in the galaxy, lensing, and photo-z catalogs. The statistical significance of the cross-correlation is at the 6.8 sigma level with 20' smoothing. A major goal of this study is to investigate systematic effects arising from a variety of sources, including PSF and photo-z uncertainties. Make maps derived from 20 variables that may characterize systematics and find the principle component. Find that the contribution of systematics to the lensing mass maps is generally within measurement uncertainties. Test and validate results with mock catalogs from N-body sims. In this work, analyze less than 3% of the final area that will be mapped by the DES; the tools and analysis techniques developed in this paper can be applied to forthcoming larger datasets from the survey.
1504.03039
OzDES multi-fibre spectroscopy for the dark energy survey: first-year operations and results
Yuan et al
OzDES is a five-year, 100-night, spectroscopic survey on AAT, whose primary aim is to measure redshifts of approximately 2500 SNeIa host galaxies over the redshift range 0.1<z<1.2, and derive reverberation-mapped BH masses for approximately 500 AGN and quasars over 0.3<z<4.5. This treasure trove of data forms a major part of the spectroscopic follow-up for the DES for which also galaxy clusters, radio galaxies, strong lensing and unidentified transients are targeted, as well as measuring luminous red galaxies and emission line galaxies to help calibrate photo-z. Present an overview of the OzDES program and the first-year results. Between 12/12 and 12/13, observed over 10k objects and measured more than 6k redshifts. The strategy of retargeting faint objects across many observing runs has allowed to measure redshifts for galaxies as faint as m_r=25 mag. Outline the target selection and observing strategy quantify the redshift success rate for different types of targets, and discuss the implications for the main science goals. Finally, highlight a few interesting objects as examples of the fortuitous yet not totally unexpected discoveries that can come from such a large spectroscopic survey.
1504.03044
Suzaku observations of subclass in the Coma cluster
Sasaki, Matsushita, Sato, Okabe
Observed 3 massive subclass in Coma with Suzaku (ID 1, 2, 32). Subhalos were detected with a WL survey from Suprime-cam, and are located 1.4, 1.2, and 1.6 r500 from the cluster center, respectively. ... Assuming an infall velocity of about 2000 km/s, at the boarder of the excess X-ray emission, the ram pressures for ID 1 and 32 are comparable to the gravitational restoring force per area. No significant excess X-ray emission in the ID 2 sub halo. Although X-ray clumps associated with the WL subhalos were found, their X-ray luminosities are much lower than the total ICM luminosity in the cluster outskirts.
1504.03264
DES J0454$-$4448: discovery of the first luminous z$\ge$ 6 quasar from the dark energy survey
Reed, et al
Present the first results of a survey for z>6 quasars using icy multicolor photometric observations from DES. Report the discovery and spectroscopic confirmation of the (z_AB, Y_AB) = (20.2, 20.2) (M1450=-26.5) quasar DES J0454-5558 with an emission line redshift of z=6.10±0.03 and a HI near zone size of 4.6±1.7 Mpc. The quasar was selected as an i-band dropout with i-z=2.46 and z_AB<21.5 from an area of ~300 sq deg. It is the brightest of the 43 candidates and was identified for follow-up spectroscopically solely based on the DES i-z and z-Y colors. The quasar is detected by WISE and has W1_AB=19.68. The discovery of one spectroscopically confirmed quasar with 5.7<z<6.5 and z_AB<20.2 is consistent with recent determinations of the LF at z~6. DES when completed will have imaged ~5000 deg sq to Y_AB=23.0 (5sigma point source) and expect to discover >50-100 new quasars with z>6 including 3-10 with z>7, dramatically increasing the numbers of quasars currently known that are suitable for detailed studies including determination of the neutral HI fraction of the IGM during the epoch of Hydrogen reionization.
1504.03290
Voids in Ly{\alpha} forest tomographic maps
Stark, Font-Ribera, White, Lee
Present a new method of finding cosmic voids using tomographic maps of Lya first flux. Identify cosmo voids with radii of 2-12 Mpc/h in large N-body sim at z=2.5, and characterize the signal of the high-z voids in density and Lya forest flux. The void properties are similar to what has been found at lower redshifts, but they are smaller and have steeper radial density profiles. Similarly to what has been found for low-z voids, the radial velocity profiles have little scatter and agree very well with the linear theory prediction. Run the same void finder on an ideal Lya flux field and tomographic reconstructions at various spatial samplings. Compare the tomographic map void catalogs to the density void catalog and find good agreement even with modest-sized voids (r>6 Mpc/h). Using the simple void-finding method, the configuration of the ongoing CLAMATO survey covering 1 sq deg would provide a sample of about 100 high-z voids. Also provide void-finding forecasts for larger area surveys, and discuss how these void samples can be used to test modified gravity models, study high-z void galaxies, and to make an Alcock-Paczynski measurement. To aid future work in the area, provide publid access to the simulation products, catalogs, and sample tomographic flux maps.
1504.03317
The dark matter profile of the Milky Way: a non-parametric reconstruction
Pato, Iocco
Present the results of a new, non-parametric method to reconstruct the Galactic dark matter profile directly from observations. Using the latest kinematic data to track the total gravitational potential and the observed distribution of stars and gas to set the baryonic component, infer the DM contribution to the circular velocity across the Galaxy. The radial derivative of this dynamical contribution is then estimated to extract the DM profile. The innovative feature of the approach is that it makes no assumption on the functional form nor shape of the profile, thus allowing for a clean determination with no theoretical bias. Illustrate the power of the method by constraining the spherical DM profile between 2.5 and 25 kpc away from the Galactic centre. The results show that the proposed method, free of widely used assumptions, can already be applied to pinpoint the DM distribution in the MW with competitive accuracy, and paves the way for future developments.
1504.03320
Spectroscopic confirmation of the existence of large, diffuse galaxies in the Coma cluster
van Dokkum, et al
Identified a population of low surface brightness objects in the field of the z=0.023 Coma cluster, using the Dragonfly Telephoto Array. Present Keck spectroscopy of one of the largest of these "ultra-diffuse galaxies" (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption features, including the CA II H+K lines and the G-band, and no detected emission lines. Its radial velocity of cz=6280±120 km/s is within the 1 sigma velocity dispersion of the Coma cluster. The galaxy has an effective radius of 4.3±0.2 kpc and a Sersic index of 0.89±0.06, as measured from Keck imaging. Find no indications of tidal tails or other distortions, at least out to a radius of ~2 r_e. Show that UDGs are located in a previously sparsely populated region of the size-magnitude plane of quiescent stellar systems, as they are ~6 mags fainter than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are needed to determine whether the dark matter haloes of UDGs are similar to those of galaxies with the same luminosity or to those of galaxies with the same size.
1504.03322
Position-dependent correlation function from the SDSS-III Baryon Oscillation Spectroscopic Survey Data Relase 10 CMASS sample
Chiang, Wagner, Sánchez, Schmidt, Komatsu
The new observable measures the correlation between 2pt functions of galaxy pairs within different sub volumes, xi(r,r_L), where r_L is the location of a sub volume, and the corresponding mean over densities, bar_delta(r_L). This correlation, dubbed the "integrated 3pt function", i zeta(r) = <xi(r, r_L) bar_delta(r_L)>, measures a 3pt function of 2 short- and one long-wavelength modes, and is generated by NL gravitational evolution and possibly also by the physics of inflation. The i zeta(r) measured from BOSS lies within the scatter of those from the mock galaxy catalogs in z-space, yielding a 10%-level determination of the amplitude of i zeta(r). The tree-level perturbation theory in z-space predicts how this amplitude depends on the linear and quadratic NL galaxy bias parameters (b1 and b2), as well as on the amplitude and linear growth rate of matter fluctuations (sigma_8 and f). Combining i zeta(r) with the constraints on b1 sigma8 and f sigma8 from the global 2pt correlation function and that on sigma8 from the WL signal of BOSS galaxies, measure b2=1.30±0.54 (68% CL).
1504.03388
The behavior of dark matter associated with 4 bright cluster galaxies in the 10kpc core of Abell 3827
Massey et al
Galaxy cluster A3827 hosts the stellar remnants of four almost equally bright elliptical galaxies within a core of radius 10 kpc. Such corrugation of the stellar distribution is very rare, and suggests recent f formation by several simultaneous mergers. Map the distribution of associated DM, using new HST imaging and VLT/MUSE IFS for a gravitationally lensed system threaded through the cluster core. Find that each of the central galaxies retains a DM halo, but that (at least) one of these is spatially offset from its stars. The best-constrained offset if 1.62±0.48 kpc, where the 68% CL includes both statistical error and systematic biases in mass modeling. Such offsets are not seen in field galaxies, but are predicted during the long infall to a cluster, if dark matter self-interactions generate an extra drag force. With such a small physical separation, it is difficult to definitively rule out astrophysical effects operating exclusively in dense cluster core environments - but if interpreted solely as evidence for self-interacting DM, this offset implies a cross-section sigma/m=(1.7±0.7)e-4 cm^2/g x (t/1e9 yrs)^-2, where t is the infall duration.
1410.0961
Type Ia supernovae yielding distances with 3-4% precision
Kelly, Filippenko, et al
The luminosities of SNIa, the thermonuclear explosions of WD stars, vary systematically with their intrinsic color and light-curve decline rate. These relationships have been used to calibrate their luminosities to within ~0.14-0.20 mag from broadband optical light curves, yielding individual distances accurate to ~7-10%. Identify a subset of SNIa that erupt in environments having high UV surface brightness and SF surface density. When a steep model extinction law is applied, these SN can be calibrated to within ~0.065-0.075 mag, corresponding to ~3-4% in distance -- the best yet in SN Ia by a substantial margin. The small scatter suggests that variations in only one or two progenitor properties account for their light-curve-width/color/luminosity relation.
1503.02632
Search for gamma-ray emission from DES dwarf spheroidal galaxy candidates with Fermi-LAT data
The Fermi-LAT Collaboration + the DES collaboration, Drlica-Wagner
Due to their proximity, high DM content, and apparent absence of non-thermal processes, MW dwarf spheroidal satellite galaxies are excellent targets for the indirect detection of dark matter. Recently, eight new dSph candidates were discovered using the first year of DES data. Searched for gamma-ray emission coincident with the positions of these new objects in 6 years of Fermi LAT data. Found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, compete individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses <20 GeV annihilating via the b-bbar or tau+tau- channels.
1504.02165
Identifying the source of preteens at the Parkes radio telescope
Petroff et al
"Perytons" are millisecond-duration transients of terrestrial origin, whose frequency-swept emission mimics the dispersion of an astrophysical pulse that has propagated through tenuous cold plasma. In fact, their similarly to FRB 010724 had previously cast a shadow over the interpretation of "fast radio bursts," which otherwise appear to be of extragalactic origin. Until now, the physical origin of the dispersion-mimicking perytons had remained a mystery. Identified a strong out-of-band emission at 2.3-2.5 GHz associated with several periton events. Subsequent tests revealed that a periton can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle. Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explain all of the observed properties of the peritonea signals. Now that the periton source has been identified, furthermore demonstrate that the microwaves on site could not have caused FRB 010724. This and there distinct observational differences show that FRBs are excellent candidates for genuine extragalactic transients.
1504.01734
Evidence for PopIII-like stellar populations in the most luminous Lyman-$\alpha$ emitters at the epoch of re-ionisation: spectroscopic confirmation
Sobral, et al
Faint Lya emitters become increasingly rarer towards the re-ionization epoch (z~6-7). However, observations from a very large (~5 sq deg) Lya survey at z=6.6 show that this is not the case for the most luminous emitters. Present follow-up observations of the 2 most luminous z~6.6 Lya candidates in the COSMOS field: 'MASOSA' and 'CR7'. Used X-SHOTTER, SINFONI and FORS2 (VLT), and DEIMOS (Keck), to confirm both candidates beyond any doubt. Find redshifts of z=6.541 and z=6.604 for MASOSA and CD7, respectively. MASOSA has a strong detection in Lya with a line width of 386±30 km/s (FWHM) and with high EW0 (>200 AA), but it is undetected in the continuum. CR7, with an observed Lya luminosity of 1e43.93±0.05 erg/s is the most luminous Lya emitter ever found at z>6. CR7 reveals a narrow Lya line with 266±15 km/s FWHM, being detected in the NIR (rest-frame UV, with beta=-2.3±0.1) with an excess in J, and also strongly detected IRAC/Spitzer. Detect a narrow HeII1640AA emission line (6sigma) which explains the excess seen in the J band photometry (EW0~80AA). Find no other emission lines from the UV to the NIR in the X-SHOOTER spectra, nor any signatures of SR stars. Find that CR7 is best explained by a combination of a PopIII-like population which dominates the rest-frame UV and the nebular emission, and a more normal stellar population which dominates the mass. HST/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Lya and HeII emission, and two red components (~5 kpc away), which dominate the mass. Findings are consistent with theoretical predictions of a PopIII wave, with PopIII SF migrating away from the original sites of SF.
