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Tuesday.
1508.07369
Sub-kiloparsec imaging of cool molecular gas in two strongly lensed dusty, star-forming galaxies
Spilker, et al
Two objects at z=2.78 and 5.66, with effective source-plane resolution of less than 1kpc. The cold molecular gas as traced by low-J CO always has a larger half-light radius than the 870um dust continuum emission. ...
1508.07373
The most massive ultra-compact dwarf galaxy in the Virgo Cluster
Liu, et al
Report on the properties of the most massive UCD in the nearby Virgo Cluster of galaxies using imaging from the NGVS and spectroscopy from Keck/DEIMOS. This object (M59-UCD3) appears to be associated with the massive Virgo galaxy M59 (NGC 4621), has an integrated velocity dispersion of 78 km/s, a dynamical mass of 3.7e8 Mxun, and an effective radius (Re) of 25 pc. With an effective surface mass density of 9.4e10 Msun/kpc^2, it is the densest galaxy in the local Universe discovered to date, surpassing the density of the luminous Virgo UCD, M60-UCD1. M59-UCD3 has a total luminosity of M_g'=-14.2 mag, and a spectral energy distribution consistent with an old (14 Gyr) stellar population with [Fe/H]=0.0 and [alpha/Fe]=+0.2. Also examine deep imaging around M59 and find a broad low surface brightness stream pointing towards M59-UCD3, which may represent a tidal remnant of the UCD progenitor. This UCD, along with similar objects like M60-UCD1 and M59cO, likely represents an extreme population of tidally stripped galaxies more akin to larger and more massive compact early-type galaxies than to nuclear star clusters in present-day dwarf galaxies.
Monday.
1508.07012
Modelling galaxy clustering: halo occupation distribution versus subhalo matching
Guo, Zheng, Behroozi, Zehavi, et al
Model the luminosity-dependent projected and z-space 2PCFs of the SDSS DR7 Main galaxy sample, using the HOD model and the sub halo abundance matching (SHAM) model and its extension. All the models are built on the same high-res N-body sims. Find that the HOD model generally provides the best performance in reproducing the clustering measurements in both projected and z spaces. The SHAM model with the same halo-galaxy relation for central and satellite galaxies (or distinct haloes and sub haloes), when including scatters, has a best-fitting chi2/DOF around 2-3. Therefore extend the SHAM model to the sub halo clustering and abundance matching (SCAM) by allowing the central and satellite galaxies to have different galaxy-halo relations. Infer the corresponding halo/subhalo parameters by jointly fitting the galaxy 2PCFs and abundances and consider sub haloes selected based on three properties, the mass M_acc at the time of accretion, the maximum circular velocity V_acc at the time of accretion, and the peak maximum circular velocity V_peak over the history of the sub haloes. The 3 sub halo models work well for luminous galaxy samples (with luminosity above L*). For low-luminosity samples, the V_acc model stands out in reproducing the data, with the V_peak model slightly worse, while the M_acc model fails to fit the data. Discuss the implications of the modeling results.
1508.07220
Angular momentum evolution for galaxies in a Lambda-CDM scenario
Pedrosa, Tissera
Galaxy formation in the current cosmo paradigm is a very complex process in which inflows, outflows, interactions and mergers are common events. These processes can redistribute the angular momentum content of baryons. Recent observational results suggest that disc formed conserving angular momentum while elliptical galaxies, albeit losing angular momentum, determine a correlation between the specific angular momentum of the galaxy and the stellar mass. These observations provide stringent constraints for galaxy formation models in a hierarchical clustering scenario. Aim to analyze the specific angular momentum content of the disc and bulge components as a function of virial mass, stellar mass and redshift. Also estimate the size of the simulated galaxies and confront them with observations. Use cosmo hydrodynamical simulations that include an effective physically-motivated Supernova feedback which is able to regulate the SF in haloes of different masses. Analyse the morphology and formation history of a sample of galaxies in a cosmo sim by performing a bulge-disc decomposition of the analyse systems and their progenitors. estimate the angular momentum content of the stellar and gaseous discs, stellar bulges and total baryons. In agreement with recent observational findings, the simulated galaxies have disc and spheroid components whose specific angular momentum contents determine correlations with the stellar and DM masses with the same slope, although the spheroidal components are off-set by a fixed fraction.
Friday.
1508.06647
The proper motion of Palomar 5
Fritz, Kallivayalil
Pal 5 is a faint halo globular cluster associated with narrow tidal tails, a useful system to understand the process of tidal dissolution, as well as to constrain the potential of the MW. A well-determined orbit for Pal 5 would enable detailed study of these open questions. Present the first CCD-based proper motion measurement of Pal 5 obtained using SDSS as a first epoch and new LBT/LBC images as a second, giving a baseline of 15 years. Perform relative astrometry, using SDSS as a distortion-free reference, and images of the cluster and also of the Pal 5 stream for the derivation of the distortion correction for LBC. The reference frame is made up of background galaxies. Correct for differential chromatic refraction using relations obtained from SDSS colors as well as from flux-calibrated spectra, finding that the correction relations for stars and for galaxies are different. Obtain mu_alpha=-2.296±0.186 mas/yr and mu_delta=-2.257±0.181 mas/yr for the proper motion of Pal 5. Use this motion, and the publicly available code galpy, to model the disruption of Pal 5 in different MW models consisting of a bulge, a disk and a spherical DM halo. The fits to the observed stream properties (streak and radial velocity gradient) result in a preference for relatively large Pal 5 distance of around 24 kpc. A slightly larger absolute proper motion than what we measure also results in better matches but the best solutions need a change in distance. Find that a spherical MW model, with V0=220 km/s and V_(20kpc), i.e., approximately at the epicenter of Pal 5, of 218 km/s, can match the data well, at least for the choice of disk and bulge parameterization.
Thursday.
1508.06503
The foreground wedge and 21 cm BAO surveys
Seo, Hirata
Redshifted H 21cm emission from unresolved low-z LSS is a promising window for ground-based BAO observations. One of the major challenges for this method is separating the cosmic signal that contains the BAO from the FGs of Galactic and extra-Galactic origins that are stronger by many orders of magnitude than the former. The smooth frequency spectrum expected for the FGs would nominally contaminate only very small k_|| modes; however the chromatic response of the telescope antenna pattern at this wavelength to the FG introduces non-smooth structure, pervasively contaminating the cosmic signal over the physical scales of interest. Such contamination defines a wedged volume in Fourier space around the transverse modes that is inaccessible for the cosmic signal. In this paper, test the effect of this contaminated wedge on the future 21 cm BAO surveys using Fisher information matrix calculation. Include the signal improvement due to the BAO construction technique that has been used for galaxy surveys and test the effect of this wedge on the BAO reconstruction as a function of signal to noises and incorporate the results in the Fisher matrix calculation. Find that the wedge effect expected at z=1-2 is very detrimental to the angular diameter distances: the errors on angular diameter distances increased by 3-4.4x, while the errors on H(z) increased by a factor of 1.5-1.6. Meanwhile the BAO reconstruction is still valuable for constraining the Hubble parameter even in the near absence of the transverse information and even in this low signal to noise regime (i.e., S/N<1) of the 21 cm surveys: for H(z) precision, observed 10-40% improvement depending on redshift and the noise level.
Wednesday.
1508.06017
What drives the M*-SFR relation turning over at high masses? the role of bulges
Pan, et al
It is unclear whether bulge growth is responsible for the flattening of the SF MS at the high mass end. To investigate the role of bulges in shaping the MS, compare the NUV-r color between the central (r<R_50) and other regions for a sample of 6401 local SF galaxies. The NUV-r color is a good sSFR indicator. Find that at M*<1e10.2 Msun, the central NUV-r is on average only ~0.25 mag redder than the outer NUV-r. Above M*=1e10.2 Msun, the central NUV-r becomes systematically much redder than the outer NUV-r for more massive galaxies, indicating that the central bulge is more evolved at the massive end. When dividing the galaxies according to their Sersic index n, find that galaxies with n>2.0 tend to be redder in the central NUV-r color than those with n<2.0, even at fixed B/T and M*. This suggests that star formation in bulges is more strongly dependent on n (or central mass density) that on B/T. Finally, find that the fraction of galaxies with n>2.0 rapidly increases with M* at M*>1e10.2 Msun, which is consistent with the turning over of the MS at the same transition mass. Conclude that the increasing fraction of low-sSFR dense bulges in M*>1e10.2 Msun galaxies, rather than increasing B/T, is responsible for the flattened slope of the M*-SFR relation at high masses.
Tuesday.
1508.05388
Sussing merger trees: a proposed merger tree data format
Thomas et al
Propose a common terminology for use in describing both temporal merger trees and spatial structure trees for dark-matter haloes. Specify a unified data format in HDF5 and provide example I/O routines in C, FORTRAN and PYTHON.
1508.05393
Modeling galactic conformity with the color-halo age relation in the Illustris simulation
Bray et al
Comparisons between observational surveys and galaxy formation models find that the mass of DM haloes can largely explain galaxies' stellar mass. However, it remains uncertain whether additional environmental variables, generally referred to as assembly bias, are necessary to explain other galaxy properties. Use the Illustris Sim to investigate the role of assembly bias in producing galactic conformity by considering 18k galaxies with M*>2e9 Msun. Find a significant signal of galactic conformity: out to distances of about 10 Mpc, the mean red fraction of galaxies around redder galaxies is higher than around bluer galaxies at fixed stellar mass. DM haloes exhibit an analogous conformity signal, in which the fraction of haloes formed at earlier times (old haloes) is higher around old haloes than around younger ones at fixed halo mass. A plausible interpretation of galactic conformity can be given as a combination of the halo conformity signal with the galaxy color-halo age relation: at fixed stellar mass, particularly toward the low-mass end, Illustris' galaxy colors correlate with halo age, with the reddest galaxies (often satellites) being preferentially found in the oldest haloes. In fact, the galactic conformity effect can be explained with a simple semi-emprical model, by assigning stellar mass based on halo mass (abundance matching) and by assigning galaxy color based on halo age (age matching). Investigate other interpretations for the galactic conformity, particularly its dependence on the isolation criterion and on the central-satellite information. Regarding comparison to observations, conclude that the adopted selection/isolation criteria, projection effects, and stacking techniques can have significant impact on the measured amplitude of the conformity signal.
1508.05394
Evidence for two spatially separated UV continuum emitting regions in the Cloverleaf broad absorption line quasar
Sluse et al
Testing the standard Shakura-Sunyaev model of accretion is a challenging task because the central region of quasars where accretion takes place is unresolved with telescopes. The analysis of microlensing in gravitationally lensed quasars is one of the few techniques which can test this model, yielding to the measurement of the size and of the temperature profile of the accretion disc. Present spectroscopic observations of the gravitationally lensed broad absorption line quasar H1413+117, which reveal partial microlensing of the continuum emission that appears to originate from two separated regions, a micro lensed region corresponding the compact accretion disc, and a non-microlensed region, more extended and contributing to at least 30% of the total UV-continuum flux. Because this extended continuum is occulted by the broad absorption line clouds, it is not associated to the host galaxy, but rather to light scattered in the neighborhood of the central engine. Measure the amplitude of microlensing of the compact continuum over the rest-frame wavelength range 1000-7000AA. Following a Bayesian scheme, confront the measurements to microlensing simulations of an accreting disc with a temperature varying as T~R^{-1/nu}. Find a most likely source half-light radius of R_1/2 =0.61e16 cm (i.e., 0.002pc) at 0.18 um, and a most likely index of nu=0.4. The standard disc (nu=4/3) model is not ruled out by the data, and found within the 95% confidence interval associated to the measurements. Demonstrate that for H1413+117, the existence of an extended continuum in addition to the disc emission has only a small impact on the inferred disc parameters, and is unlikely to solve the tension between the microlensing source size and standard disc sizes as previously reported in the literature.
1508.05655
An accurate and practical method for inference of weak gravitational lensing from galaxy images
Bernstein, Armstrong, Krawiec, March
Demonstrate recovery of WL shear at parts-per-thousand accuracy using an implementation of the Bayesian Fourier Domain (BFD) method proposed by Bernstein+Armstrong (2014). The BFD formalism is rigourously correct for Nyquist-sampled, background-limited, uncrowded image of background galaxies. BFD does not assign shapes to galaxies, instead compression the pixel data D into a vector of moments M, such that there is an analytic expression for the probability P(M|g) of obtaining the observations with gravitational lensing distortion g along the LoS. Extend the BA14 formalism to include detection and selection of galaxies without inducing biases on the inferred g. Describe a practical algorithm for conducting BFD's integrations over the population of unlined source galaxies. The BFD implementation measures ~10 galaxies per second per core on current hardware, a speed that will be largely independent of the number of images taken of each target. Initial tests of this code on ~500 M simulated lensed galaxy images recover the simulated shear to a fractional accuracy of m=(2.2±0.6)e-3, substantially more accurate than has been demonstrated previously for any generally applicable method. The method is readily extended to use multiple exposures in multiple filters. Deep sky exposures generate a sufficiently accurate approximation to the noiseless, unused galaxy population distribution assumed as input to BFD. Describe the remaining challenges for applying the BFD method to current and future surveys, as well as potential further extensions, such as simultaneous measurement of magnification and shear; multi-band observations; and joint inference of photometric redshifts and lensing tomography.
Monday.
1508.05098
Supermassive black hole seed formation at high redshifts: long-term evolution of the direct collapse
Shlosman, CHoi, Begelman, Nagamine
Use cosmo AMR code Enzo zoom-in sims to study the long term evolution of the collapsing gas within DM haloes at high redshifts. This direct collapse process is a leading candidate for rapid formation of SMBH seeds at high z. To circumvent the Courant condition at small radii, use the sink particle method, and focus on the evolution on scales ~0.01-10pc. The collapse proceeds in two stages, with the secondary runaway happening within the central 10 pc, and with no detected fragmentation. The sink particles form when the collapsing gas requires additional refinement of the grid size at the highest refinement level. Their mass never exceeds ~1e3 Mo, with the sole exception of the central seed which grows dramatically to ~2e6 Mo in ~2 Myr, confirming the feasibility of this path to the SMBH. The time variability of angular momentum axis in the accreted gas results in the formation of two misaligned disks -- a small inner disk, and a more massive, outer disk which is inclined by ~45deg to the inner disk. The self-gravity of these disks is heavily diluted -- both disks lie within the Roche limit of the central seed. While the inner disk is geometrically thin and weakly asymmetric, the outer disk flares due to turbulent motions as a result of the massive inflow along a pair of penetrating filaments. The geometry of inflow via filaments determine the dominant and secondary Fourier modes in this disk -- these modes have a non-self-gravitational origin. Do not confirm that m=1 is a principal mode that derive the inflow in the presence of a central massive object. While the positions of the disks depend on the scale chosen to break the self-similar collapse, the overall configuration appears to be generic, and is expected to form when the central seed becomes sufficiently massive.
1508.05308
Statistical uncertainties and systematic errors in weak lensing mass estimates of galaxy clusters
Köhlinger, Hoekstra, Eriksen
Upcoming and ongoing large area weak lensing surveys will also discover large samples of galaxy clusters. Accurate and precise masses of galaxy clusters are of major importance for cosmology, for example, in establishing well calibrated observational halo mass functions for comparison with cosmo predictions. Investigate the level of statistical uncertainties and sources of systematic errors expected for WL mass estimates. Future surveys that will cover large areas on the sky, such as Euclid or LSST and to lesser extent DES, will provide the largest weak lensing cluster samples with the lowest level of statistical noise regarding ensembles of galaxy clusters. However, the expected low level of statistical uncertainties requires scrutinizing various sources of systematic errors. In particular, investigate the bias due to miscentering, i.e., the displacement between any observationally defined cluster centre and the true minimum of its gravitational potential. The impact of this bias might be significant with respect to the statistical uncertainties. However, complementary future missions such as eROSITA will allow definition of stringent priors on miscenetring parameters which will mitigate this bias significantly.
Friday.
1508.04771
Galaxy structure as a driver of the star formation sequence slope and scatter
Whitaker, Franx, et al
It is well established that (1) SF galaxies follow a relation between their SFR and stellar mass M*, the "star-formation sequence", and (2) the SFRs of galaxies correlate with their structure, where SF galaxies are less concentrated than quiescent galaxies at fixed mass. Here, consider whether the scatter and slope of the SF sequence is correlated with systematic variations in the Sersic indices, n, of galaxies across the SFR-M* plane. Use a mass-complete sample of 23,848 galaxies at 0.5<z<2.5 selected from the 3D-HST photometric catalogs. Galaxy light profiles parameterized by n are based on HST CANDELS NIR imaging. Use a single SFR indicator empirically-calibrated from stacks of Spitzer/MIPS 24um imaging, adding the unobscured and obscured SF. Find that the scatter of the SF sequence is related in part to galaxy structure; the scatter due to variations in n at fixed mass for SF galaxies ranges from 0.14±0.02 dex at z~2 to 0.30±0.04 dex at z<1. While the slope of the log(SFR)-log(M*) relation is of order unity for disk-like galaxies, galaxies with n>2 (implying more dominant bulges) have significantly lower SFR/M* than the main ridgeline of the SF sequence. These results suggest that bulges in massive z~2 galaxies are actively building up, where the stars in the central concentration are relatively young. At z<1, the presence of older bulges within star-forming galaxies lowers global SFR/M*, decreasing the slope and contributing significantly to the scatter of the SF sequence.
1508.04842
Is main sequence galaxy star formation controlled by halo mass accretion?
Rodriguez-Puebla, Primack, Behroozi, Faber
It is known that the galaxy stellar-to-halo mass ratio (SHMR) is nearly independent of redshift from z=0-4. This motivates to construct a toy model in which it is assumed that the SMHR for central galaxies measured at z~0 is independent of z, which implies that the SFR is determined by the halo mass accretion rate, a phenomenon termed Stellar-Halo Accretion Rate Coevolution (SHARC). Moreover, show here that the ~0.3 dex dispersion of the halo mass accretion rate (MAR) is similar to the observed dispersion of the SFR on the main sequence. In the context of bathtub-type models of galaxy formation, SHARC leads to mass-dependent constraints on the relation between SFR and MAR. The SHARC assumption is no doubt over-simplified, but it is expected to be possibly valid for central galaxies with stellar masses of 1e9-10.5 Msun that are on the SF MS. Such galaxies represent most of the life history of M* galaxies, and therefore most of the SF in the Universe. The predictions from SHARC agree remarkably well with the observed SFR of galaxies on the main sequence at low z and fairly well out to higher z, although the predicted SFR exceeds observations at z<4. Assuming that the interstellar gas mass is constant for each galaxy, equilibrium condition, the SHARC model allows calculation of mass loading factors for inflowing and outflowing gas. With assumptions about preventive feedback based on simulations, the model allows calculation of galaxy metallicity evolution. If the SFR in SF galaxies is indeed largely regulated by halo mass accretion, especially at low z, that may help to explain the success of models that tie galaxy properties to those of their host halos, such as age matching and the relation between two-halo galaxy conformity and halo mass accretion conformity.
1508.04901
Galaxy clustering using photometric redshifts
Soltan, Chodorowski
Investigate the evolution of the galaxy 2PCF over a wide redshift range, 0.2<z<3. For the first time the systematic analysis covers the redshifts above 1-1.5. The catalogue of ~250k galaxies with i+<25 and known photo-z in the Subaru Deep field is used. The galaxies are divided into 3 luminosity classes and several distance/redshift bins. First, the 2D CF is determined for each luminosity class and distance bin. Calculations are based on the quantitative differences between the surface distributions of galaxy pairs with comparable and distinctly different photometric redshifts. The power law approximation for the CF is used. A limited accuracy of photo-z as compared to the spectroscopic ones has been examined and taken into account. Then, the 3D functions for all the selected luminosities and distances are calculated. The power-law parameters of the CF, the slope and the correlation length, are determined. Both parameters do not show strong variations over the whole investigated redshift range. The slope of the luminous galaxies appears to be consistently steeper than that for the fainter ones. The linear bias factor, b(z), grows systematically with redshift; assuming the local normalization b(0)=1.1-1.2, the bias reaches 3-3.5 at the high redshift limit.
Thursday.
1508.04446
Unveiling the Milky Way: a new technique for determining the optical color and luminosity of our Galaxy
Licquia, Newman, Brinchmann
Demonstrate a new statistical method of determining the global photometric properties of the MW to an unprecedented degree of accuracy, allowing our Galaxy to be compared directly to objects measured in extragalactic surveys. Capitalizing on the high-quality imaging and spectroscopy dataset from the SDSS, exploit the inherent dependence of galaxies' luminosities and colors on their total stellar mass, M*, and SFR, dot(M*), by selecting a sample of MW analog galaxies designed to reproduce the best Galactic M* and dot(M*) measurements, including all measurement uncertainties. Making the Copernican assumption that the MW is not extraordinary amongst galaxies of similar stellar mass and SFR, analyze the photometric properties of this matched sample, constraining the characteristics of our Galaxy without suffering interference from interstellar dust. Explore a variety of potential systematic errors that could affect this method, and found that they are subdominant to random uncertainties. Present both SDSS ugriz absolute magnitudes and colors in both rest-frame z=0 and z0.1 passbands for the MW, which are in agreement with previous estimates but can have up to ~3x lower errors. Find the MW to have absolute magnitude ^0M_r-5 log h = -21.00±0.38 and integrated color ^0(g-r)=0.682±0.06, indicating that it may belong to the green-valley region in color-magnitude space and ranking it amongst the brightest and reddest of spiral galaxies. Also present new estimates of global stellar M/L ratios for our Galaxy. This work will help relate the in-depth understanding of the Galaxy to studies of more distant objects.
Wednesday.
1508.04138
The 21-cm BAO signature of enriched low-mass galaxies during cosmic reionization
Cohen, Fialkov, Barkana
Studies of the formation of the first stars have established that they formed in small haloes of ~1e5-6 Msun via molecular H cooling. Since a low level of UV radiation from stars suffices to dissociate H2, under the usually-assumed scenario this primordial mode of SF ended by z~15 and much more massive haloes came to dominate star formation. However, metal enrichment from the first stars may have allowed the smaller haloes to continue to form stars efficiently, a possibility that has been boosted by recent numerical simulations. In this Letter, explore the possible effect of SF in metal-rich low-mass haloes on the redshifted 21-cm signal of H2 from z=6-40. These haloes are significantly affected by the supersonic streaming velocity, with its characteristic BAO signature. Show that enrichment of low-mass galaxies can produce a strong signature in the 21-cm PS over a wide range of redshifts, and can allow the effect of the streaming velocity to survive until the midpoint of reoinization. The predictions, therefore, are relevant for current and upcoming radio telescopes.
1508.04143
Dark matter cores all the way down
Read, Agertz, Collins
Use high resolution sims of isolated dwarf galaxies to study the physics of DM cusp-core transformation at the edge of galaxy formation (Mvir=1e7-9 Msun). Work at a resolution (4pc) at which the impact from individual supernovae explosions can be resolved, becoming insensitive to even large changes in the numerical 'sub-grid' parameters. Find that the dwarf galaxies give a remarkable match to the stellar light profile; SFH; metallicity distribution function; and star/gas kinematics of isolated dwarf irregular galaxies. The key result is that DM cores of size comparable to the half light radius r_1/2 always form if SF proceeds for long enough. Cores fully form in less than 4 Gyrs for the Mvir=1e8Msun and 14 Gyrs for the 1e9 Msun dwarf. Provide a convenient two parameter 'coreNFW' fitting function that captures this DM core growth as a function of SF time and the projected HLR. The results have several important implications: (i) a strong prediction is made that if LCDM is correct, then 'pristine' DM cusps will be found either in systems that have truncated SF and/or at radii r>r_1/2; (ii) complete core formation lowers the projected velocity dispersion at r_1/2 by a factor ~2, which is sufficient to fully explain the 'too big to fail problem' (though it is stressed that a full solution likely also involves unmodelled environmental effects); and (iii) cored dwarfs will be much more susceptible to tides, leading to a dramatic scouring of the sub halo mass function inside galaxies and groups. Explore such environmental effects in a forthcoming paper.
1508.04149
Investigating galaxy-filament alignments in hydrodynamic simulations using density ridges
Chen, Ho, et al
Study the filamentary structures and the galaxy alignment along filaments at z=0.06 in the MassiveBlack-II simulation, a state-of-the-art, high-res hydro cosmo sims which includes stellar and AGN feedback in a volume of (100 Mpc/h)^3. The filaments are constructed using the subspace constrained mean shift (SCMS). First, show that reconstructed filaments using galaxies and reconstructed filaments using DM particles are similar to each other; over 50% of the points on the galaxy filaments have corresponding point on the DM filaments within distance 0.13 Mpc/h (and vice versa) and this distance is even smaller at high-density regions. Second, observe the alignment of the major principal axis of a galaxy with respect to the orientation of its nearest filament and detect a 2.5 Mpc/h critical radius for filament's influence on the alignment when the sub halo mass of this galaxy is between 1e9Msun/h and 1e12 Msun/h. Moreover, find the alignment signal to increase significantly with the sub halo mass. Third, when a galaxy is close to filaments (less than 0.25 Mpc/h), the galaxy alignment toward the nearest galaxy group depends on the galaxy sub halo mass. Finally, find that galaxies close to filaments or groups tend to be rounder than those away from filaments or groups.
Tuesday.
1508.03860
On methods of estimating cosmological bulk flows
Nusser
Explore similarities and differences between several estimators of the cosmo bulk flow, B, from the observed radial peculiar velocities of galaxies. A distinction is made between two theoretical definitions of B as a dipole moment of the velocity field weighted by a radial window function. One definition involves the 3D peculiar velocity, while the other is based on its radial component alone. Different methods attempt at inferring B for either of these definitions which coincide only for a constant velocity field. Focus on the Wiener Filtering (WF, Hoffmann+2015) and the Constrained Minimum Variance (CMB, Feldman+2010) methodologies. Both methodologies require a prior expressed in terms of the radial velocity correlation function. Hoffmann+ compute in Top-Hat windows from a WF realization of the 3D peculiar velocity field. Feldman+ infer B directly from the observed velocities for the second definition of B. The WF methodology could easily be adapted to the second definition, in which case it will be equivalent to the CMV with the exception of the imposed constraint. For a prior with vanishing correlations or very noisy data, CMV reproduces the standard Maximum Likelihood (ML, Kaiser 1988) estimation for B of the entire sample independent of the radial weighting function. Therefore, this estimator is likely more susceptible to observational biases that could be present in measurement of distant galaxies. Finally, two additional estimators are proposed.
1508.04121
Quasar classification using color and variability
Peters, Richards, Myers, Strauss, Schmidt, Ivezic, Ross, MacLeod, Riegel
Conduct a pilot investigation to determine the optimal combination of color and variability information to identify quasars in current and future multi-epoch optical surveys. Use a Bayesian quasar selection algorithm (Richards+ 2004) to identify 35,820 type 1 quasar candidates in a 239 sq deg field of SDSS Stripe 82, using a combination of optical photometry and variability. Color analysis is performed on 5-band single- and multi-epoch SDSS optical photometry to a depth of r~22.4. From these data, variability parameters are calculated by fitting the structure function of each object in each band with a power law model using 10 to >100 observations over timescales from ~1 day to ~8 years. Selection was based on a training sample of 13,221 spectroscopically-confirmed type-1 quasars, largely from SDSS. Using variability alone, colors alone, and combining variability and colors, achieve 91, 93, 97% efficiency respectively, with particular improvement in the selection of quasars at 2.7<z<3.5 where quasars and stars have similar optical colors. The 22,867 quasar candidates that are not spectroscopically confirmed reach a depth of i~22.0; 21876 (95.7%) are dimmer than coadded i-band magnitude of 19.9, the cut off for spectroscopic follow-up for SDSS on Stripe82. Brighter than 19.9, find 5.7% more quasar candidates without confirming spectra in sky regions otherwise considered complete. The resulting quasar sample has sufficient purity (and statistically correctable incompleteness) to produce a luminosity function comparable to those determined by spectroscopic investigations. Discuss improvements that can be made to the process in preparation for performing similar photometric selection nan science on data from post-SDSS sky surveys.
Monday.
1508.03336
Planet sensitivity from combined ground- and space-based microlensing observations
Zhu, Gould, et al
Present the first planet sensitivity analysis for microlensing events with simultaneous observations form space and ground. Present this analysis for 2 such events, which both show substantial planet sensitivity even though neither of them reached high magnification. Suggests an ensemble of low to moderate magnification events can also yield significant planet sensitivity and therefore probability to detect planets. The implications of the results to the ongoing and future space-based microlensing experiments to measure the Galactic distribution of planets are discussed.
1508.03375
Planck 2013 results. XXXI. Consistency of the Planck data
Planck Collaboration
The Planck design and scanning strategy provide many levels of redundancy that can be exploited to provide tests of internal consistency. One of the most important is the comparison of the 70 GHz and 100 GHz channels. Based on different instrument technologies, with feeds located differently in the focal plane, analyzed independently by different teams using different software, and near the minimum of diffuse foreground emission, these channels are in fact two different experiments. The 143 GHz channel has the lowest noise level on Planck, and is near the minimum of unresolved foreground emission. In this paper, analyse the level of consistency achieved in the 2013 Planck data. Concentrate on comparisons between the 70/100/143 GHz channel maps and power spectra, particularly over the angular scales of the first and second acoustic peaks, on maps masked for diffuse Galactic emission and for strong unresolved sources. Difference maps covering angular scales from 8 deg - 15 arcmin are consistent with noise, and show no evidence of CMB structure. Including small but important corrections for unresolved-source residuals, demonstrate agreement between 70 and 100 GHz power spectra averaged over 70<l<390 at the 0.8% level, and agreement between 143 and 100 GHz power spectra of 0.4% over the same ell range.
1508.03580
Impact of cosmological satellites on the vertical heating of the Milky Way disc
Moetazedian, Just
Present a high-res study of the impact of realistic satellite galaxies, extracted from cosmo sims of MW haloes including 6 Aquarius suites and Via Lactea II, on the dynamics of the galactic disc. The initial conditions for the multi-component NW galaxy were generated using the GalIC code, to ensure a system in real equilibrium state prior to addition of satellites. The candidate sub haloes that came closer than 25 kpc to the center of the host DM haloes, with initial mass M_tid>1e8=0.003 Mtid/Mdisc, were identified, inserted into the high res N-body sims and evolved for 2 Gyrs. Quantified the vertical heating due to such impacts by measuring the disc thickness, root-mean-square of z-coordinate, and vertical velocity dispersion sigma^2_z across the disc. According to the analysis the strength of the heating is strongly dependent on the high mass end of the sub halo distribution from the cosmo sims. The mean increase of the vertical dispersion is ~25 km^2/s^2/Gyr for R>4 kpc while, if the Aq-F-2 results are excluded, the mean heating is <12 km^2/s^2/Gyr. The observed vertical heating rate in the solar neighborhood has a value of 67 km^2/s^2/Gyr; taking into account the 1 sigma statistical dispersion around the mean, it lies just below the observed value of 144 km^2/s^2 after 2 Gyrs. Observed a general flaring of the disc height in the case of all 7 simulations in the outer disc where the thickness was increased by ~40% at 15 kpc. The 1 sigma cosmic variance corresponds to doubling the disc thickness in the outer region.
1508.03622
Eight ultra-faint galaxy candidates discovered in year two of the dark energy survey
The DES Collaboration
Report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the DES. Six of these candidates are detected at high confidence, while two additional lower-confidence candidates are identified in regions of incomplete or non-uniform survey coverage. The new stellar systems are found using three independent automated search techniques, and are identified as statistically significant over densities of individually resolved stars consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. the new systems are faint (Mv>-4.7 mag) and span a broad range of physical sizes (17 pc < r_1/2 < 181 pc) and heliocentric distances (25 kpc < D < 214 kpc). All of the new systems have central surface brightnesses (mu>27.5 mag arcsec^2) consistent with known ultra-faint dwarf galaxies. Roughly half of the DES candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known MW satellite galaxies, and would have had a low probability of detection if observed by SDSS. A large fraction of satellite candidates are found in the southern half of the DES footprint in proximity to the Magellanic Clouds. Find that the DES data alone exclude (p<0.001) a spatially isotropic distribution of MW satellites, and that this distribution can be well, although not uniquely, explained by a model in which several of the observed DES satellites are associated with the Magellanic system. Including the current sample, the model predicts that ~100 ultra-faint galaxies with physical properties comparable to the DES satellites might exist over the full sky and that 20-30% of these would be spatially associated wit the Magellanic Clouds.
Friday.
1508.03042
Reactivity and survivability of Glycolaldehyde in simulated meteorite impact experiments
McCaffrey, et al
Sugars of extraterrestrial origin have been observed in the ISM, in at least one comet spectrum, and in several carbonaceous chondritic meteorites that have been recovered from the surface of the Earth. To explore the possibility that sugars could be generated during shock events, this paper reports on the results of the first laboratory impact experiments wherein glycolaldehyde, found in the ISM, as well as glycolaldehyde mixed with montmorillonite clay, have been subjected to reverberated shocks from ~5 to >25 GPa. New biologically relevant molecules, including threes, erythrose and ethylene glycol, where identified in the resulting samples. These results show that sugar molecules can not only survive but also become more complex during impact delivery to planetary bodies.
1508.03043
SETI via leakage from light sails in exoplanetary systems
Guillochon, Loeb
The primary challenge of rocket propulsion is the burden of needing to accelerate the spacecraft's own fuel, resulting in only a logarithmic gain in maximum speed as propellant is added to the spacecraft. Light sails offer an attractive alternative in which fuel is not carried by the spacecraft, with acceleration being provided by an external source of light. By artificially illuminating the spacecraft with beamed radiation, speeds are only limited by the area of the sail, heat resistance of its material, and power use of the accelerating apparatus. In this paper, show that leakage from a light sail propulsion apparatus in operation around a solar system analogue would be detectable. To demonstrate this, model the launch and arrival of a microwave beam-driven light sail constructed for transit between planets in orbit around a single star, and find an optimal beam frequency on the order of tens of GHz. Leakage from these beams yields transients with flux densities of 0.1 Jy and durations of seconds at 100 pc. Because most travel within a planetary system would be conducted between the habitable worlds within that system, multiply-transiting explanatory systems offer the greatest chance of detection, especially when the planets are in projected conjunction as viewed from Earth. If interplanetary travel via beam-driven light sails is commonly employed in our galaxy, this activity could be revealed by radio follow-up of nearby transiting explanatory systems. The expected signal properties define a new strategy in the search for extraterrestrial intelligence (SETI).
1508.03046
Exploring the 2MASS extended and point source catalogs with clustering redshifts
Rahman, Ménard, Scranton
2MASS has mapped out the low-z Universe down to K_S~14 mag. As its NIR photometry primarily probes the featureless Rayleigh-Jeans tail of galaxy spectral energy distributions, color-based redshift estimation is rather uninformative. Until now, redshift estimates for this dataset have relied on optical follow-up suffering from selection biases. Here, use the newly-developed technique of clustering-based redshift estimation to infer the redshift distribution of the 2MASS sources regardless of their optical properties. Characterize redshift distributions of objects from the Extended Source Catalog as a function of NIR colors and brightness and report some observed trends. Also apply the clustering redshift technique to dropout populations, sources with non-detections in one or more NIR bands, and present their redshift distributions. Combining all extended sources, show that the z distribution of the sample extends up to z~0.3. Perform a similar analysis with the PSC and show that it can be separated into stellar and extragalactic contributions with galaxies reaching z~0.7. Estimate that the PSC contains 1.6 M extragalactic objects: as many as in the ESC but probing a cosmic volume ten times larger.
1508.03162
Improving the precision matrix for precision cosmology
Paz, Sanchez
The estimation of cosmo constraints from observations of the LSS of the universe, such as the power spectrum or the correlation function, requires the knowledge of the inverse of the associated covariance matrix, namely the precision matrix, Psi. In most analyses, Psi is estimated from a limited set of mock catalogues. Depending on how many mocks are used, this estimation has an associated error which must be propagated into the final cosmo constraints. For future surveys such as Euclid and DESI, the control of this additional uncertainty requires a prohibitively larger number of mock catalogues. In this work, test a novel technique for the estimation of the precision matrix, the covariance tapering method, in the context of BAO measurements. Even though this technique was originally devised as a way to speed up maximum likelihood estimations, our results show that it also reduces the impact of noisy precision matrix estimates on the derived confidence intervals, without introducing biases on the target parameters. The application of this technique can help future surveys to reach their true constraining power using a significantly smaller number of mock catalogues.
Thursday.
1508.02715
Comprehensive assessment of the Too-big-to-fail problem
Jiang, van den Bosch
"Too Big To Fail" problem: refers to the overabundance of massive, dense sub haloes predicted by CDM compared to the observed number of relatively luminous satellite galaxies of the MW or the LG. Use a SAM for the substructure of DM haloes to assess the TBTF problem. The model accurately reproduces the average sub halo mass and velocity functions, as well as their halo-to-halo variance, in N-body sims. Construct thousands of realizations of MW size host haloes, allowing investigation of the TBTF problem with unprecedented statistical power. Examine the dependence on host halo mass and cosmology, and explicitly demonstrate that a reliable assessment of TBTF requires large samples of hundreds of host haloes. Argue that previous statistics used to address TBTF suffer from the look-elsewhere effect and/or disregard certain aspects of the data on the MW satellite population. Devise a new statistic that is not hampered by these shortcomings, and using only data on the 9 known MW satellite galaxies with V_max>15 km/s, demonstrate that 1.4±3% of MW-size host halos have a sub halo population in statistical agreement with that of the MW. However, when using data on the MW satellite galaxies down to V_max=8km/s, this MW consistent fraction plummets to <5e-4 (at 68% CL). Hence, if it turns out that the inventory of MW satellite galaxies is complete down to 8 km/s, then the maximum circular velocities of MW satellites are utterly inconsistent with LCDM predictions, unless baryonic effects can drastically increase the spread in V_max values of satellite galaxies compared to that of their sub haloes.
Wednesday.
1508.02381
Digging deeper into the Southern skies: a compact Milky-Way companion discovered in first-year Dark Energy Survey data
Lique, et al
DES is a 5k sq deg survey in the southern hemisphere, which is rapidly reducing the existing north-south asymmetry in the census of MW satellites and other stellar substructure. Use the Y1 DES data down to previously unprobed photometric depths to search for stellar systems in the Galactic halo, therefore complementing the previous analysis of the same data carried out by the group earlier this year. The search is based on a matched filter algorithm that produces stellar density maps consistent with stellar population models of various ages, metallicities, and distances over the survey area. The most conspicuous density peaks in these maps have been identified automatically and ranked according to their significance and recurrence for different input models. Report the discovery of one additional stellar system besides those previously found by several authors using the same fist-year DES data. The object is compact, and consistent with being dominated by an old and metal-poor population. DES J0034-4902 is found at high significance and appears in the DES images as a compact concentration of faint blue point sources at ~87kpc. Its half-light radius of r_h=0.88±4.31 pc and total luminosity of M_V~=3.05±0.5 are consistent with it being a low mass halo cluster. It is also found to have a very elongated shape. In addition, the deeper probe of DES 1st year data confirms the recently reported satellite galaxy candidate Horologium II as a significant stellar overdensity. Also infer its structural properties and compare them to those reported in the literature.
1508.02469
Geometrical constraint on curvature with BAO experiments
Takada, Dore
The spatial curvature (K or Omega_K) is one of the most fundamental parameters of isotropic and homogeneous universe and has a close link to the physics of the early universe. Combining the radial and angular diameter distances measured via the baryon acoustic oscillation experiments allows us to unambiguously constrain the curvature. The method is primarily based on the metric theory, but not much on the theory of structure formation other than the existence of BAO scale and is free of any model of DE. In this paper, estimate a best-achievable accuracy of constraining the curvature with the BAO experiments. Show that an all-sky, cosmic-variance-limited galaxy survey covering the universe up to z>4 enables a precise determination of the curvature to an accuracy of sigma(Omega_K)~1e-3. When a model of dark energy is assumed, either the cosmo constraint or the (w0,wa)-model, it can achieve a precision of sigma(Omega_K)~a few 1e-4. These forecasts require a high sampling density of galaxies, and are degraded by up to a factor of a few for a survey with a finite number density of galaxies.
1508.02484
Exploring photometric redshifts as an optimization problem: an ensemble MCMC and simulated annealing-driven template-fitting approach
Speagle, Capak, Eisenstein, Masters, Steinhardt
Using a grid of ~2 million elements (Delta z = 0.005) adapted from COSMOS photo-z searches, investigate the general properties of template based photo-z likelihood surfaces. Find these surfaces are filled with numerous local minima and large degeneracies that generally confound rapid but "greedy" optimization schemes, even with additional stochastic sampling methods. In order to robustly and efficiently explore these surfaces, develop BAD-Z [Brisk Annealing-Driven Redshifts (Z)], which combines ensemble MCMC sampling with simulated annealing to sample arbitrarily large, pre-generated grids in approximately constant time. Using a mock catalog of 384k objects, show BAD-Z samples ~40 times more efficiently compared to a brute-force counterpart while maintaining similar levels of accuracy. The results represent first steps toward designing template-fitting photo-z approaches limited mainly by memory constraints rather than computation time.
1508.02654
The Mira-Titan Universe: Precision predictions for Dark Energy Surveys
Heitmann, et al
Ground band space-based sky surveys enable powerful cosmological probes based on measurements of galaxy properties an the distribution of galaxies in the Universe. These probes include WL, BAO, galaxy cluster abundance, and RSD; they are essential to improving our knowledge of the nature of DE. On the theory and modeling front, large-scale simulations of cosmic structure formation pay an important role in interpreting the observations and in the challenging task of extracting cosmological physics at the needed precision. These simulations must cover a parameter range beyond the standard six cosmological parameters and need to be run at high mass and force resolution. One key simulation-based task is the generation of accurate theoretical predictions for observables, via the method of emulation. Using a new sampling technique, explore an 8-D parameter space including massive neutrinos and variable DE EoS. Construct trial emulators using two surrogate models (the linear PS and an approximate halo mass function). The new sampling method allows us to build precision emulators from just 26 cosmo models and to increase the emulator accuracy by adding new sets of simulations in a prescribed way. This allows emulator fidelity to be systematically improved as new observational data becomes available and higher accuracy is required. Finally, using one LCDM cosmo as an example, study the demands imposed on a simulation campaign to achieve the required statistics and accuracy when building emulators for DE investigations.
Tuesday.
1508.01803
Disentangling redshift-space distortions and nonlinear bias using the 2d power spectrum
Jennings, Wechsler
Present the nonlinear 2d galaxy PS, P(k,mu), in redshift space, measured from the DarkSky simulations, using galaxy catalogs constructed with both HOD and sub halo abundance matching methods, chosen to represent an intermediate z sample of LRGs. Find that the information content in individual mu (cosine of the angle to the line of sight) bins is substantially richer than mutipole moments, and show that this can be used to isolate the impact of nonlinear growth and RSD effects. Using the mu<0.2 sim data, which is shown not to be impacted by RSD effects, NL bias can be successfully measured to an accuracy of ~5% at k<0.6h/Mpc. This use of individual mu bins to extract the NL bias successfully removes a large parameter degeneracy when constraining the linear growth rate of structure. Carry out a joint parameter estimation, using the low mu simulation data to constrain the NL bias, and mu>0.2 to constrain the growth rate and show that f can be constrained to ~26(22)% to a k_max<0.4(0.6) h/Mpc from clustering alone using a simple dispersion model, for a range of galaxy models. The analysis of individual mu bins also reveals interesting physical effects which arise simply from different methods of populating haloes with galaxies. Find a prominent turnaround scale, at which RSD damping effects are greater than the nonlinear growth, which differs not only for each mu bin but also for each galaxy model. These features may provide unique signatures which could be used to shed light on the galaxy-dark matter connection.
1508.01874
The distribution of galaxies gravitational field stemming from their tidal interaction
Stephanovich, Godlowski
Calculate the distribution function of astronomical objects (like galaxies and/or smooth haloes of different kinds) gravitational fields due to their tidal interaction. For that, apply the statistical method of Chandrasekhar (1943), used there to calculate famous Holtzmark distribution. Show that in the approach, the distribution function is never Gaussian, its form being dictated by the potential of interaction between objects. This calculation permits performing a theoretical analysis of the relation between angular momentum and mass (richness) of the galaxy clusters. To do so, follow the idea of Catelan & Theuns (1996) and Heavens&Peacock (1988). The main difference is that here, the problem is reduced to discrete many-body case, where all physical properties of the system are determined by the interaction potential V(r_ij). The essence of reduction is that the multipole is used (up to quadrupole here) expansion of Newtonian potential so that all hydrodynamic, "extended" characteristics of an object like its density mass are "integrated out" giving its "point-like" characteristics like mass and quadrupole moment. In that sense, make no difference between galaxies and smooth component like halos. Compare the theoretical results with observational data.
1508.02076
Galaxy and mass assembly (GAMA): Panchromatic data release (far-UV---far-IR) and the low-z energy budget
Driver, et al
Present the GAMA Panchromatic data release (PDR) constituting over 230 deg2 of imaging with photometry in 21 bands extending from the far-UV to the far-IR. These data complement the spectroscopic campaign of over 300k galaxies, and are compiled from observations with a variety of facilities including: GALEX, SDSS, VISTA, WISE, and Herschel, with the GAMA regions currently being surveys by VST and scheduled for observations by ASKAP. These data are processed to a common astrometric solution, from which photometry is derived for 221,373 galaxies with r<19.8 mag. Online tools are provided to access and download data cutouts, or the full mosaics of the GAMA regions in each band. Focus, in particular, on the reduction and analysis of the VISTA VIKING data, and compare to earlier datasets (i.e., 2MASS and UKIDSS) before combining the data and examining its integrity. Having derived the 21-band photometric catalogue, proceed to fit the data using the energy balance code MAGPHYS. These measurements are then used to obtain the first fully empirical measurement of the 0.1-500um energy output of the Universe. Exploring the Cosmic Spectral Energy Distribution (CSED) across three time-intervals (0.3-1.1 Gyr, 1.1-1.8 Gyr and 1.8-2.4 Gyr), find that the Universe is currently generating (1.5±0.3)e35 h_70 W Mpc^-3, down from (2.5±0.2)e35 h_70 W Mpc^-3 2.3 Gyr ago. More importantly, identify significant and smooth evolution in the integrated photo scale fraction at all wavelengths, with the UV escape fraction increasing form 27(18)% at z=0.18 in NUV(FUV) to 34(23)% at z=0.06. The GAMA PDR will allow for detailed studies of the energy production and outputs of individual systems, sub-populations, and representative galaxy samples at z<0.5. The GAMA PDR can be found at gama-psi.icrar.org.
1508.02346
Taking advantage of photometric galaxy catalogues to determine the halo occupation distribution
Rodriguez, Merchán, Sgró
Context: HOD is a powerful statistic that allows the study of several aspects of the matter distribution in the Universe, such as evaluating SAM of galaxy formation or imposing constraints on cosmo models. Consequently, it is important to have reliable method for estimating this statistic, taking full advantage of the available information on current and future galaxy surveys. Aims. The main goal of this project is to combine photometric and spectroscopic information using a discount method of background galaxies in order to extend the range of absolute magnitudes and to increase the upper limit of masses in which the HOD is estimated. Also evaluate the proposed method and apply it to estimating the HOD on SDSS DR7. Methods. Propose the background subtraction technique to mel information provided by spectra galaxy groups and photometric survey of galaxies. To evaluate the feasibility of the method, implement the proposed technique on a mock catalogue built from a SAM of galaxy formation. Furthermore, apply the method to DR7 using a galaxy group catalogue taken from spectra and the corresponding photometric galaxy survey. Results. Demonstrated the validity of the method using the mock catalogue. Applied this technique to obtain the DR7 HOD in absolute magnitudes raining from M=-21.5 to M=-16.0 and masses up to ~1e15 Msun throughout this range. On the brighter extreme, found that the results are in excellent agreement with those obtained in previous works.
Monday, @Leiden.
1508.01525
Large-scale mass distribution in the Illustris-Simulation
Haider, et al
Observations at low redshifts thus far fail to account for all the baryons expected the Universe according to cosmo constraints. A large fraction of the baryons presumably resides in a thin and warm-hot medium between the galaxies, where they are difficult to observe due to their low densities and high temperatures. Cosmo sims of structure formation can be used to verify this picture and provide quantitative predictions for the distribution of mass in different large-scale structure components. Study the distribution of baryons and dark matter at different epochs using data from the Illustris Sim. Identify regions of different DM density with the primary constituents of LSS, allowing measurements of mass and volume of haloes, filaments and voids. At redshift zero, find that 49% of the DM and 23% of the baryons are within haloes. The filaments of the cosmic web host a further 45% of the DM and 46% of the baryons. The feedback models used in Illustris have a significant impact on the baryon distribution at large scales, leading to 31% of the baryons residing in DM voids. Categorizing the baryons according to their density and temperature, find that 17.8% of them are in a condensed state, 21.6% are present as cold, diffuse gas, and 53.9% are found in the state of warm-hot intergalactic medium.
1508.01615
The relation between star formation rate and stellar mass of galaxies at z $\sim$ 1-4
Katsianis, Tescari, Wyithe
The relation between SFR and M* of galaxies represents a fundamental constraint on galaxy formation. However, the observed amplitude of the SFR - M* relation has not been successfully reproduced in sims, indicating either that the halo accretion history and baryonic physics are poorly understood or that observations contain biases. In this paper, examine the evolution of the SFR-M* relation of z~1-4 galaxies and display the inconsistency between observed relations that are obtained using different techniques. Employ cosmological hydrodynamic simulations from various groups and compare these with a range of observations. The comparison suggests that using SEDs to estimate SFRs, dust corrections and stellar masses produces the most reliable SFR-M* relations. On the contrary, the combination of IR and UV luminosities (UV+IR) over predicts the SFR and dust corrections at a fixed stellar mass almost by a factor of 5 for z~1.5-4. For z<1.5, the SED fitting technique and IR+UV conversion agree well. Find remarkable agreement between the numerical results from various authors who have employed different cosmo codes and run simulations with different resolutions. This is interesting for 2 regions. A) simulations can produce realistic populations of galaxies within representative cosmo volumes even at relatively modest resolutions. B) It is likely that current numerical codes that rely on similar subgrid multiphase ISM models and are tuned to reproduce statistical properties of galaxies, produce similar results for the SFR-M* relation by construction, regardless of resolution, box size and, to some extent, the adopted feedback prescriptions.
Friday.
1508.01203
Discovery of two gravitationally lensed quasars in the Dark Energy Survey
Agnello, Treu, ... et al
Present spectroscopic confirmation of 2 new lensed quasars via 6.5 Magellan/Baade Telescope. The lens candidates have been selected from DES and WISE based on their multi-band photometry and extended morphology in DES images. Images of DES J0115-5244 show 2 blue point sources at either side of a red galaxy. The long-slit data confirm that both point sources are images of the same quasar at z_s=1.64. The Einstein Radius estimated from the DES images is 0.51". DES J2200+0110 is in the area of overlap between DES and SDSS. Two blue components are visible in the DES and SDSS images. The SDSS fiber spectrum shows a quasar component at z_s=2.38 and absorption compatible with Mg II and Fe II at z_l=0.799, which is possibly associated with the foreground lens galaxy. The long-slit Magellan spectra show that the blue components are resolved images of the same quasar. The Einstein Radius is 0.68" corresponding to an enclosed mass of 1.6e11 Msun. Three other candidates were observed and rejected, two being low-z pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data-mining and model-based selection that is being applied to the entire DES data set.
1508.01204
The galaxy UV luminosity function before the epoch of reioinzation
Mason, Trenti, Treu
Present a model for the evolution of the galaxy UV LF across cosmic time where SF is linked to the assembly of DM halos under the assumption of halo mass dependent, but redshift independent, star formation efficiency. This model improves on previous work by introducing a new self-consistent treatment of the halo SF history, which allows making predictions at z>10 (loopback time <500 Myr), when growth is rapid. With a calibration at a single redshift to set the stellar to halo mass ratio, and no further degrees of freedom, the model captures the evolution of the UV LF over all the available observations (0<z<10). The significant drop in the luminosity density of currently detectable galaxies beyond z~8 is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, derive a reionization optical depth tau=0.056±0.01 fully consistent with the latest Planck measurement, and implying that the universe is fully recognized at z=7.84±0.98. In addition, the model naturally produces smoothly rising SFHs for galaxies with L<L* in agreement with observations and detailed hydro sims. Before the epoch of reionization at z>10, predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope (alpha~-3.5 at z~16). Finally, construct detailed forecasts with JWST and WFIRST, including the boost from gravitational lensing magnification bias in blank fields, and predict that galaxies out to z~14 will be observed. However, galaxies at z>15 will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.
Thursday.
1508.00895
Performance of internal covariance estimators for cosmic shear correlation functions
Friedrich, Seitz, Eifler, Gruen
Data re-sampling methods such as the delete-one jackknife are a common tool for estimating the covariance of LSS probes. In this paper, investigate the concepts of internal covariance estimation in the context of cosmic shear two-point statistics. Demonstrate how to use log-normal simulations of the convergence field and the corresponding shear field to carry out realistic tests of internal covariance estimators and find that most estimators such as jackknife or sub-sample covariance can reach a satisfactory compromise between bias and variance of the estimated covariance. In a forecast for the complete, 5-year DES survey, show that internally estimated covariance matrices can provide a large fraction of the true uncertainties on cosmological parameters in a 2d cosmic shear analysis. The volume inside contours of constant likelihood in the Omega_m-sigma8 plane as measured with internally estimated covariance matrices is on average >85% of the volume derived from the true covariance matrix. The uncertainty on the parameter combination Sigma8~sigma8Omega_m^0.5 derived from internally estimated covariances is ~90% of the true uncertainty.
1508.01034
Cosmic explotions, life in the universe and the cosmological constant
Piran, Jiminez, Cuesta, Simpson, Verde
Find that Lambda-dominated universes favor the survival of life against GRBs.
