Tuesday.
1307.1135
LoCuSS: the steady decline and slow quenching of star formation in cluster galaxies over the last four billion years
Haines, Pereira, Smith, Egami, ... Finoguenov, et al
Analysis of the levels and evolution of SF activity in a representative sample of 30 massive galaxy clusters at 0.15<z<0.30 from LoCuSS, combining Spitzer 24um data with spectroscopy of cluster members. The sSFRs of massive (M>1e10 Msun) SF cluster galaxies within r200 are found to be systematically 28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7 sigma level. An unambiguous signature of SF in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their SFRs declining exponentially on quenching time-scales in the range 0.7-2.0 Gyr. Measure the MIR Butcher-Oemler effect [a hypothesis suggesting the cores of galaxies clusters at intermediate z (~0.3) contain a larger fraction of blue galaxies than do the cores of low redshift clusters] over the redshift range 0.0-0.4, finding rapid evolution in the fraction f_SF of massive M_K<-23.1 cluster galaxies within r200 with SFRs>3 Msun/yr, of the form f_SF(1+z)^7.6. Dissect the origins of the BO effect, revealing it to be due to the combination of a ~3x decline in the mean specific-SFRs of SF cluster galaxies since z~0.3 with a ~1.5x decrease in number density. 2/3s of this reduction in the sSFRs of SF cluster galaxies is due to the steady cosmic decline in the specific-SFRs among those field galaxies accreted into the clusters. The slow quenching of SF in cluster galaxies is consistent with a gradual shut down of SF in infalling spiral galaxies as they interact with the ICM via ram-pressure stripping or starvation mechanisms. Find no evidence for the build-up of cluster S0 bulges via major nuclear star-burst episodes.
1307.1155
Accurate weak lensing of standard candles, Part 2: measuring sigma8 with supernovae
Quartin, Marra, Amendola
Number of SNIa measurements will soon reach >100k. Understanding the effect of WL by matter substructures on the SNe brightness is important. Although SN lensing is usually seen as a source of systematic noise, will show that it can be turned into a signal. The non-Gaussianity introduced by lensing in the SN Hubble diagram dispersion depends rather sensitivity on the amplitude sigma8 of the matter PS. By exploiting this relation, able to predict constraints on sigma8 of 7% (3%) for a catalog of 100k (500k) SNe of average magnitude error 0.12 without having to assume that such intrinsic dispersion is known a priori. This method is independent of and complementary to the standard methods based on CMB, cosmic shear or cluster abundance observables.
1307.1232
Orientation of cosmic web filaments with respect to the underlying velocity field
Tempel, Libeskind, Hoffman, Liivamägi, Tamm
Suggested that the structure of cosmic web is dictated by the local velocity shear tensor, and in particular that the local direction of a filament should be strongly aligned with e3, the eigenvector associated with the smallest eigenvalue of the shear tensor. Aim is to test this conjecture on a high resolution cosmological simulation. Cosmic web delineated by DM halo distribution is probed by a marked point process with interactions (Bisous model) in order to detect filaments directly from the dark halo distribution (the P-web). IT is shown that the detected P-web filaments are strongly aligned with the local e3 eigenvector: the alignment is within 30 degree for ~80% of the detected elements. This result indicates that the large-scale filaments defined purely from the number density distribution of haloes (or galaxies) carry more than just morphological information, although the Bisous model does not make any prior assumption on the underlying shear tensor, nor does it make any use of it. The P-web filaments are also compared to the large scale structure revealed directly from an analysis of the velocity shear tensor (the V-web). In the densest regions, the P- and V-web filaments overlap well (90%), whereas in lower density regions, the P-web filaments preferentially mark regions which are collapsing in one dimension, defined to be sheets in the V-web. Further work is needed to inspect the causes and implications of the latter result.
1307.1366
Galaxies at z>1: shaping the Hubble sequence
Talia et al
Morphological properties of 494 galaxies at z>1 from the GMASS survey, in their optical rest-frame from HST/WFC3-IR images from CANDELS. Fractions of ellipticals and disks decline between z=1 to z=3, while at higher z the galaxy population is dominated by irregulars. Ellipticals have the highest concentration and Gini values, while irregulars assume the lowest ones. However, at 1<z<3, morphological parameters are not as effective in distinguishing the different Hubble types as they are at low z. No significant morphological k-correction was found to be required for the Hubble type classification. From a quantitative point of view, however, there are some differences between the optical and UV morphologies. Different morphological types occupy the two peaks of the (U-B) color distribution: the majority of irregulars are found in the blue peak, while ellipticals mainly populate the red one. Disks have a smoother color distribution. Also find that in an UVJ diagram, the quiescent region is inhabited mainly by ellipticals and, to a lesser extent, by disks. Only 33% of all ellipticals in our samples are red and passively evolving galaxies, a percentage that is consistent with results obtained at z<1. There is a remarkable structural similarity between red and blue ellipticials: they share the same Hubble type and have consistent distributions of all morphological parameters, except asymmetry, with blue ellipticals being less asymmetric than red ones. Compared morphological and spectroscopic classification; almost all irregulars have a SF spectrum. The majority of disks show signs of SF activity in their spectra, though in some cases their red continuum indicates the presence of older stellar populations. An elliptical morphology may be associated with either passively evolving or strongly SF galaxies.
1307.1467
The origin of physical variations in the universal star formation law
Federrath
SF laws: simple direct relations between the column density of SF and column density of available gas. One universal SF law in which Sigma_SFR is about 1% of the local gas collapse rate, Sigma_gas/t_ff. Find that the observed scatter in this universal law is primarily controlled by physical variations in the mach number of the turbulence and by differences in the SF efficiency. Secondary variations can be induced by changes in the turbulent driving and B-field in SF clouds. The model predictions are testable with observations that constrain both the Mach number and the SF efficiency in MW clouds, external disk and SB galaxies at low and high z. Also find that reduced telescope resolution does not strongly affect such measurement with Sigma-SFR is plotted against Sigma_gas/t_ff.
1307.1580
Search for impact craters in Iran: citizen science as a useful method
Pourkhorsandi
As the title says. 1 page paper.
1307.1702
Growth of brightest cluster galaxies via mergers since z=1
Burke, Collins
Hierarchical assembly within clusters of galaxies is tied directly to the evolution of the BCGs, which dominated the stellar light in the centers of rich clusters. In this paper, investigate the number of mergers onto BCGs in 14 X-ray selected clusters over the redshift range 0.8<z<1.4, using HST imaging data. Find significant differences in the numbers of companion galaxies to BCGs between the clusters in this sample, indicating that BCGs in similar mass clusters can have very different merging histories. Within a 50 kpc radius around the BCGs, find an average of 6.45 pm 1.15 companion galaxies with mass ratios (companion:BCG) between 1:1 and 1:20. The infalling companions show a 50/50 split between major (1:1-1:2) and minor (1:3-1:20) mergers. When compared to similar work using lower redshift clusters, these results demonstrate that both major and minor merging was more common in the past. Since the dynamical timescales for merging onto the BCG are relatively short compared with the look-back time to z~1 our results suggest that the BCG stellar mass may increase by as much as 1.8 times since z=1. However the growth rate of BCGs will be substantially less if stripped material from nearby companions ends up on the diffuse intracluster light.
1307.1706
A direct measurement of the linear bias of mid-infrared-selected quasars at z~1 using cosmic microwave background lensing
Geach, ... Holder, ... Holzapfel, et al
Measure the cross-power spectrum of the projected mass density as traced by the convergence of the CMB lensing field from the SPT and a sample of Type 1 and 2 (unobscured and obscured) quasars at z~1 selected with the Wide-field Infrared Survey Explorer, over 2500 deg^2. The cross-power spectrum is detected at ~7 sigma, and measure a linear bias b=1.67pm0.24, consistent with clustering analysis. Using and independent lensing map, derived from Planck observations, to measure the cross-spectrum, find excellent agreement with the SPT analysis. The bias of the combined sample of Type 1 and 2 quasars determined in this work is similar to that previously determined for Type 1 quasars alone; conclude that obscured and unobscured quasars must trace the matter field in a similar way. This result has implications for the understanding of quasar unification and evolution schemes.
1307.1712
The Jubilee ISW project I: simulated ISW and weak lensing maps and initial power spectra results
Watson et al
Present initial results, which models the expected LCDM ISW effect in the Jubilee simulation. Volume is (6 Gpc/h)^3, allowing power on very large-scales to be incorporated into the calculation. Haloes are resolved down to a mass of 1.5e12 Msun/h, which allows derivation of a catalogue of mock LRGs for cross-correlation analysis with the ISW signal. Find the ISW effect observed on a projected sky to grow stronger at late times with the evolution of the ISW PS matching expectations from linear theory. Maps of the gravitational lensing effect, including the convergence and defection fields, are calculated using the same potential as for the ISW. Calculate the redshift dependence of the ISW-LRG cross-correlation signal for a full sky survey with no noise considerations. For I<30, the signal is strongest for lower redshift bins (z~0.2 to 0.5), whereas for l>30 the signal is best observed with surveys covering z~0.6-1.0.
1307.1865
A "Light", centrally-concentrated Milky Way halo?
Rashkov, ... Madau, et al
Discuss a novel approach to "weighing" the WM DM halo, one that combines the latest samples of halo stars selected from SDSS with numerical sims of MW analogs. The fully cosmological runs employed in the present study include "Eris", one of the highest-resolution hydrodynamical simulations of the formation of a M_vir=8e11 Msun late-type spiral, and the DM only M_vir = 1.7e12 Msun "Via Lactea II" simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and successfully compare their density, velocity anisotropy, and radial velocity dispersion profiles with the observational data. Most mock SDSS realizations show the same "cold veil" recently observed in the distant stellar halo of the MW, with tracers as cold as sigma-los~50 km/s between 100-150 kpc. Controlled experiments based on the integration of the spherical Jeans equation as well as a particle tagging technique applied to Via Lactea II show that a "heavy" M_vir 2e12 Msun realistic host produces a poor fit to the kinematic SDSS data. Argue that these results offer added evidence for a "light", centrally-concentrated MW halo.
1307.1951
Quasar-galaxy clustering through project galaxy counts at z=0.6-1.2
Zhang et al
Investigate the spatial clustering of galaxies around quasars at redshifts from 0.6 to 1.2 using the photometric data from SDSS stripe 82. The quasar and galaxy cross-correlation functions are measured through the projected galaxy number density n(r_p) on scales 0.05<r_p<20 Mpc/h around quasars for a sample of 2300 quasars from Schneider+ (2007). Detect strong clustering signals at all redshifts, and find that the clustering amplitude increases significantly with redshift. Examine the dependence of the quasar-galaxy clustering on quasar and galaxy properties and find that the clustering amplitude is significantly larger for quasars with more massive BHs, or with bluer colors, while the dependence on quasar luminosity is absent. Also show that quasars have a stronger correlation amplitude with blue galaxies than with red galaxies. Discuss the implication of finding.
1307.2053
X-ray absorption of high redshift quasars
Eitan, Behar
Soft X-ray photoelectric absorption of high-z quasars has been known for two decades, but has no unambiguous astro-physical context. Construct the largest sample to date of 58 high redshift quasars (z>0.45) selected from the XMM-Newton archive based on a high photon count criterion (>1800). Measure the optical depth tau at 0.5 keV, and find that 43% of the quasars show significant absorption. Aim to find which physical parameters of the quasars drive their observed absorption, e.g., redshift, radio luminosity, radio loudness [what's the difference between loudness and luminosity?], or the X-ray luminosity. Compare the absorption behavior with redshift with the pattern expected if the diffuse IGM is responsible for the observed absorption, and with a comparison sample of GRB X-ray afterglows. Although the z>2 quasar opacity is consistent with diffuse IGM absorption, many intermediate z (0.45<z<2) quasars are not sufficiently absorbed for this scenario, and are appreciably less absorbed than GRBs. Only 10/37 quasars at z<2 are absorbed, and only 5/30 radio quiet quasars are absorbed. Find a weak correlation between tau and z, and even a weaker correlation between tau and radio luminosity, which leads to the conclusion that although a diffuse IGM origin for the quasar absorption is unlikely, optical depth does seem to increase with redshift, roughly as (1+z)^2.2pm0.6,tending at high-z to tau~0.4, similar to the high-z GRB values. This result can be explained by an ionized and clumpy IGM at z<2, and a cold, diffuse IGM at higher redshift. If, conversely, ascribed to local absorption at the quasar, and owing to the steep L_z~(1+z)^7.1pm0.5 correlation in the present sample, the host column density scales as N_H~L_x^0.7pm0.1.
1307.2068
A diversity of dusty AGN tori: data release for the VLTI/MIDI AGN large program and first results for 23 galaxies
Burtscher, ... Kishimoto, ... et al
The AGN-heated dust distributions (the "torus") is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear SMBH. Yet, even its most basic structural properties (e.g. extent, geometry and elongation) are unknown for all but a few archetypal objects. Since most AGNs are unresolved in the MIR, utilize the MID-IR interferometric instrument (MIDI) at the VLT interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds (has). Present here and extensive amount of new interferometric observations from the MIDI AGN Large program, and add data from the archive to give a complete view of the existing MIDI observations of AGNs. Additionally, obtain high-quality MIR spectra from VLT/VISIR. Present correlated and total flux spectra for 23 AGNs and derive flux and size estimates at 12 micron using simple axisymmetric geometrical models. Surprising result: relatively high level of unresolved flux and its large scatter: the median "point source fraction" is 70% for type 1 and 47% for type 2 AGNs, meaning that a large part of the flux is concentrated on scales smaller than about 5 mas (0.1-10 pc). Among sources observed with similar spatial resolution, it varies from 20%-100%. For 18 of the sources, two nuclear components can be distinguished in the radial fits. [cool! maybe spectra will show dual core.] While these models provide good first to all but the brightest sources, significant elongations are detected in eight sources. The half-light radii of the fainter sources are smaller than expected from the size~L^0.5 scaling of the bright sources and show a large scatter, especially when compared to the relatively tight size-luminosity relation in the NIR.
1307.2153
Cosmological magnetic fields
Kunze
B-fields are observed on nearly all scales in the universe, from stars and galaxies up to galaxy clusters and beyond. The origin of cosmic B-fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed B-field could explain the present day strength of the galactic B-field. However, it is still an open problem how and when this initial B-field was created. Observations of the CMB provide a window to the early universe and might therefore be able to tell us whether comic B-fields are of primordial, cosmological origin and at the same time constrain its parameters. Give an overview of the observational evidence of large scale B-fields, describe generation mechanisms of primordial B-fields and possible imprints in the CMB.
1307.2235
The influence of environment on the circumgalactic medium
Yoon, Putman
The effect of environment on the CGM is investigated through a comparison of Lya absorption line data in the Virgo cluster and the field. This paper uses the first systematic survey of background QSOs in and around the Virgo cluster and large existing surveys of galaxies at low redshift. While previous studies found denser gas (higher equivalent width) closer to a galaxy (lower impact parameter), this correlation disappears in the Virgo environment. In addition, the covering fraction of the CGM is lower in the cluster environment than in the circumcluster environment and field. The results indicate the CGM is suppressed for cluster galaxies while galaxies in the circumcluster environment have abundant CGM. The truncation of the CGM may result in the quenching of SF through starvation. Results show that CGM surveys need to consider the role of environment.
1307.2236
A megacam survey of outer halo satellites. II. Blue stragglers in the lowest stellar density systems
Santana, ... Geha, et al
A homogeneous study of blue straggler stars [what are these?] across ten outer halo globular clusters, 3 classical dSph and 9 ultra-faint galaxies based on deep and wide-field photometric data taken with MegaCam on CFHT. Find blue straggler stars to be ubiquitous among these MW satellites. Test the importance of primordial binaries or multiple systems on blue straggler SF in low density environments. For the outer halo globular clusters, find an anti-correlation between the specific frequency of blue straggler and absolute magnitude [so brighter = less frequent, or the other way around?], similar to that previously observed for inner halo clusters. When plotted against density and encounter rate [what is an "encounter rate"?], the frequency of blue stragglers are well fitted by single trends with smooth transitions between dwarf galaxies and globular clusters, which points to a common origin for their blue stragglers. The fraction of blue stragglers stays constant and high in the low encounter rate regime spanned by our dwarf galaxies, and decreases with density and encounter rate in the range spanned by the globular clusters. Find that young stars can mimic blue stragglers in dwarf galaxies only if their ages are 2.5pm0.5 Gyr and they represent ~1-7% of the total number of stars, which is deemed highly unlikely. These results point to mass-transfer or mergers of primordial binaries or multiple systems as the dominant blue straggler formation mechanism in low density systems.
* Blue straggler stars are MS stars in open or globular clusters that are more luminous and bluer than stars at the MS turn-off point for the cluster. Standard theories of stellar evolution hold that the position of a star on the HR diagram should be determined almost entirely by the initial mass of the star and its age. In a cluster, stars all formed at approximately the same time, and thus in an H-R diagram for a cluster, all stars should lie along a clearly defined curve set by the age of the cluster, with the positions of individual stars on that curve determined solely by their initial mass. With masses 2-3 times that of the rest of the MS cluster stars, blue stragglers seem to be exceptions to this rule. The resolution of this problem is likely related to interactions between 2 or more stars in the dense confines of the clusters in which blue stragglers are found. (from Wikipedia)
1307.2239
The chemical imprint of dust on the most metal-poor stars
Ji, Frebel, Bromm
Investigate the impact of dust-induced gas fragmentation on the formation of the first low-mass, metal-poor stars (<1M_sun) in the early universe. Previous work has posited the existence of a critical dust-to-gas ratio, below which dust thermal cooling is unable to cause fragmentation. Using Si-based (rather than C-based) dust compositions, compute such critical dust-to-gas ratios and associated critical silicon abundances. Evaluate the robustness of these critical values by considering variations in the dust chemical composition, grain size distribution, and star formation environment. Variations in the dust chemical composition are less important than variations in the size distribution, and the most likely environment where dust cooling becomes significant is in a rotationally supported protostellar disk. Test the dust cooling theory by comparing to Si abundances observed in metal-poor stars. Several stars have Si abundances low enough to rule out fragmentation induced by dust which follows a standard MW grain size distribution. Moreover, two of the most Fe-poor stars have such low Si abundances that even dust with a shocked grain size distribution [how does this distribution compare to MW grain size distribution?] cannot easily explain their formation. See evidence that stars with [Fe/H]<-4.0 exhibit either high C and low Si abundances or the reverse. This suggests that the earliest low-mass SF in the most metal-poor regime likely proceeded through two distinct pathways, one that relied on fine structure cooling and one that relied on dust cooling. This explains both the C-rich and C-normal stars at extremely low [Fe/H].
1307.2250
The extent of magnetic fields around galaxies out to z~1
Bernet, Miniati, Lilly
Radi quasar sightlines with strong MgII absorption lines display statistically enhanced Faraday Rotation Measures (RM) indicating the presence of additional magneto-active plasma with respect to sightlines free of such absorption. Use multicolor optical imaging to idenetify the likely galaxies hosting the magneto-active plasma, and to constrain the location of the latter with respect to the putative parent halo. Find that all of the sightlines with high RM pass within 50 kpc of a galaxy and that the RM distribution for low impact parameters, D<50kpc, is significantly different than for larger impact parameters. In addition, find a decrease in the ratio of the polarization at 21cm and 1.5cm, p_21/p_1.5 towards lower D. These two effects are most likely related, strengthen the association of excess RM with intervening galaxies, and suggest that intervening galaxies operate as inhomogeneous Faraday screens. These results are difficult to reconciliate with only a disk model for the B-field but are consistent with highly magnetized winds associated with MgII systems. Infer strong B-fields of a few tens of uG, consistent with values required by the lack of evolution of the FIR-radio correlation at high redshifts. Finally, these findings lends support to the idea that the small scale helicity bottleneck of alpha-Omega galactic dynamos can be significantly alleviated via galactic winds.
1307.2377
How real-time cosmology can distinguish between different anisotropic models
Amendola, et al
How to distinguish between isotropic and anisotropic cosmological models based on tracking the angular displacements of a large number of distant quasars over an extended period of time, and then performing a multipole-vector decomposition of the resulting displacement maps. Find that while the GAIA mission operating at its nominal specifications does not have sufficient angular resolution to resolve anisotropic universes from isotropic ones using this method within a reasonable timespan of ten years, a next-generation GAIA-like survey with a resolution 10 times better should be equal to the task. Distinguishing between different anisotropic models is however more demanding. Keeping the observational timespan to ten years, find that the angular resolution of the survey will need to be of order 0.1 micro-arcsecond in order for certain rotating anisotropic models to produce a detectable signature that is also unique to models of this class. However, should such a detection become possible, it would immediately allow us to rule out large local void models.
1307.2566
The effect of weak lensing on distance estimates from supernovae
Smith, et al
Using 608 SNIa from SDSS-II and BOSS surveys, combined with a sample of FG galaxies from SDSS-II, estimate the WL convergence for each SN LoS. Find that the correlation between this measurement and the Hubble residuals is consistent with the prediction from lensing (1.7 sigma significance). Strong correlations are also found between the residuals and SNe nuisance parameters after a linear correction is applied. When these other correlations are taken into account, the lensing signal is detected at 1.4 sigma. Show for the first time that distance estimates from SNe can be improved when lensing is incorporated by including a new parameter in the SALT2 methodology for determining distance moduli. The recovered value of the new parameter is consistent with the lensing prediction. Using WMAP7, HST and BAO data, find the best-fit value of the new lensing parameter and show that the central values and uncertainties on Omega_m and w are unaffected. The lensing of SNe, while only seen at marginal significance in this low z sample, will be of vital importance for the next generation of surveys, such as DES and LSST, which will be systematics dominated.
1307.2289
Anybody but Hubble!
Trimble
The question is: "who first recognized the expansion of the universe?"
1307.1135
LoCuSS: the steady decline and slow quenching of star formation in cluster galaxies over the last four billion years
Haines, Pereira, Smith, Egami, ... Finoguenov, et al
Analysis of the levels and evolution of SF activity in a representative sample of 30 massive galaxy clusters at 0.15<z<0.30 from LoCuSS, combining Spitzer 24um data with spectroscopy of cluster members. The sSFRs of massive (M>1e10 Msun) SF cluster galaxies within r200 are found to be systematically 28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7 sigma level. An unambiguous signature of SF in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their SFRs declining exponentially on quenching time-scales in the range 0.7-2.0 Gyr. Measure the MIR Butcher-Oemler effect [a hypothesis suggesting the cores of galaxies clusters at intermediate z (~0.3) contain a larger fraction of blue galaxies than do the cores of low redshift clusters] over the redshift range 0.0-0.4, finding rapid evolution in the fraction f_SF of massive M_K<-23.1 cluster galaxies within r200 with SFRs>3 Msun/yr, of the form f_SF(1+z)^7.6. Dissect the origins of the BO effect, revealing it to be due to the combination of a ~3x decline in the mean specific-SFRs of SF cluster galaxies since z~0.3 with a ~1.5x decrease in number density. 2/3s of this reduction in the sSFRs of SF cluster galaxies is due to the steady cosmic decline in the specific-SFRs among those field galaxies accreted into the clusters. The slow quenching of SF in cluster galaxies is consistent with a gradual shut down of SF in infalling spiral galaxies as they interact with the ICM via ram-pressure stripping or starvation mechanisms. Find no evidence for the build-up of cluster S0 bulges via major nuclear star-burst episodes.
1307.1155
Accurate weak lensing of standard candles, Part 2: measuring sigma8 with supernovae
Quartin, Marra, Amendola
Number of SNIa measurements will soon reach >100k. Understanding the effect of WL by matter substructures on the SNe brightness is important. Although SN lensing is usually seen as a source of systematic noise, will show that it can be turned into a signal. The non-Gaussianity introduced by lensing in the SN Hubble diagram dispersion depends rather sensitivity on the amplitude sigma8 of the matter PS. By exploiting this relation, able to predict constraints on sigma8 of 7% (3%) for a catalog of 100k (500k) SNe of average magnitude error 0.12 without having to assume that such intrinsic dispersion is known a priori. This method is independent of and complementary to the standard methods based on CMB, cosmic shear or cluster abundance observables.
1307.1232
Orientation of cosmic web filaments with respect to the underlying velocity field
Tempel, Libeskind, Hoffman, Liivamägi, Tamm
Suggested that the structure of cosmic web is dictated by the local velocity shear tensor, and in particular that the local direction of a filament should be strongly aligned with e3, the eigenvector associated with the smallest eigenvalue of the shear tensor. Aim is to test this conjecture on a high resolution cosmological simulation. Cosmic web delineated by DM halo distribution is probed by a marked point process with interactions (Bisous model) in order to detect filaments directly from the dark halo distribution (the P-web). IT is shown that the detected P-web filaments are strongly aligned with the local e3 eigenvector: the alignment is within 30 degree for ~80% of the detected elements. This result indicates that the large-scale filaments defined purely from the number density distribution of haloes (or galaxies) carry more than just morphological information, although the Bisous model does not make any prior assumption on the underlying shear tensor, nor does it make any use of it. The P-web filaments are also compared to the large scale structure revealed directly from an analysis of the velocity shear tensor (the V-web). In the densest regions, the P- and V-web filaments overlap well (90%), whereas in lower density regions, the P-web filaments preferentially mark regions which are collapsing in one dimension, defined to be sheets in the V-web. Further work is needed to inspect the causes and implications of the latter result.
1307.1366
Galaxies at z>1: shaping the Hubble sequence
Talia et al
Morphological properties of 494 galaxies at z>1 from the GMASS survey, in their optical rest-frame from HST/WFC3-IR images from CANDELS. Fractions of ellipticals and disks decline between z=1 to z=3, while at higher z the galaxy population is dominated by irregulars. Ellipticals have the highest concentration and Gini values, while irregulars assume the lowest ones. However, at 1<z<3, morphological parameters are not as effective in distinguishing the different Hubble types as they are at low z. No significant morphological k-correction was found to be required for the Hubble type classification. From a quantitative point of view, however, there are some differences between the optical and UV morphologies. Different morphological types occupy the two peaks of the (U-B) color distribution: the majority of irregulars are found in the blue peak, while ellipticals mainly populate the red one. Disks have a smoother color distribution. Also find that in an UVJ diagram, the quiescent region is inhabited mainly by ellipticals and, to a lesser extent, by disks. Only 33% of all ellipticals in our samples are red and passively evolving galaxies, a percentage that is consistent with results obtained at z<1. There is a remarkable structural similarity between red and blue ellipticials: they share the same Hubble type and have consistent distributions of all morphological parameters, except asymmetry, with blue ellipticals being less asymmetric than red ones. Compared morphological and spectroscopic classification; almost all irregulars have a SF spectrum. The majority of disks show signs of SF activity in their spectra, though in some cases their red continuum indicates the presence of older stellar populations. An elliptical morphology may be associated with either passively evolving or strongly SF galaxies.
1307.1467
The origin of physical variations in the universal star formation law
Federrath
SF laws: simple direct relations between the column density of SF and column density of available gas. One universal SF law in which Sigma_SFR is about 1% of the local gas collapse rate, Sigma_gas/t_ff. Find that the observed scatter in this universal law is primarily controlled by physical variations in the mach number of the turbulence and by differences in the SF efficiency. Secondary variations can be induced by changes in the turbulent driving and B-field in SF clouds. The model predictions are testable with observations that constrain both the Mach number and the SF efficiency in MW clouds, external disk and SB galaxies at low and high z. Also find that reduced telescope resolution does not strongly affect such measurement with Sigma-SFR is plotted against Sigma_gas/t_ff.
1307.1580
Search for impact craters in Iran: citizen science as a useful method
Pourkhorsandi
As the title says. 1 page paper.
1307.1702
Growth of brightest cluster galaxies via mergers since z=1
Burke, Collins
Hierarchical assembly within clusters of galaxies is tied directly to the evolution of the BCGs, which dominated the stellar light in the centers of rich clusters. In this paper, investigate the number of mergers onto BCGs in 14 X-ray selected clusters over the redshift range 0.8<z<1.4, using HST imaging data. Find significant differences in the numbers of companion galaxies to BCGs between the clusters in this sample, indicating that BCGs in similar mass clusters can have very different merging histories. Within a 50 kpc radius around the BCGs, find an average of 6.45 pm 1.15 companion galaxies with mass ratios (companion:BCG) between 1:1 and 1:20. The infalling companions show a 50/50 split between major (1:1-1:2) and minor (1:3-1:20) mergers. When compared to similar work using lower redshift clusters, these results demonstrate that both major and minor merging was more common in the past. Since the dynamical timescales for merging onto the BCG are relatively short compared with the look-back time to z~1 our results suggest that the BCG stellar mass may increase by as much as 1.8 times since z=1. However the growth rate of BCGs will be substantially less if stripped material from nearby companions ends up on the diffuse intracluster light.
1307.1706
A direct measurement of the linear bias of mid-infrared-selected quasars at z~1 using cosmic microwave background lensing
Geach, ... Holder, ... Holzapfel, et al
Measure the cross-power spectrum of the projected mass density as traced by the convergence of the CMB lensing field from the SPT and a sample of Type 1 and 2 (unobscured and obscured) quasars at z~1 selected with the Wide-field Infrared Survey Explorer, over 2500 deg^2. The cross-power spectrum is detected at ~7 sigma, and measure a linear bias b=1.67pm0.24, consistent with clustering analysis. Using and independent lensing map, derived from Planck observations, to measure the cross-spectrum, find excellent agreement with the SPT analysis. The bias of the combined sample of Type 1 and 2 quasars determined in this work is similar to that previously determined for Type 1 quasars alone; conclude that obscured and unobscured quasars must trace the matter field in a similar way. This result has implications for the understanding of quasar unification and evolution schemes.
1307.1712
The Jubilee ISW project I: simulated ISW and weak lensing maps and initial power spectra results
Watson et al
Present initial results, which models the expected LCDM ISW effect in the Jubilee simulation. Volume is (6 Gpc/h)^3, allowing power on very large-scales to be incorporated into the calculation. Haloes are resolved down to a mass of 1.5e12 Msun/h, which allows derivation of a catalogue of mock LRGs for cross-correlation analysis with the ISW signal. Find the ISW effect observed on a projected sky to grow stronger at late times with the evolution of the ISW PS matching expectations from linear theory. Maps of the gravitational lensing effect, including the convergence and defection fields, are calculated using the same potential as for the ISW. Calculate the redshift dependence of the ISW-LRG cross-correlation signal for a full sky survey with no noise considerations. For I<30, the signal is strongest for lower redshift bins (z~0.2 to 0.5), whereas for l>30 the signal is best observed with surveys covering z~0.6-1.0.
1307.1865
A "Light", centrally-concentrated Milky Way halo?
Rashkov, ... Madau, et al
Discuss a novel approach to "weighing" the WM DM halo, one that combines the latest samples of halo stars selected from SDSS with numerical sims of MW analogs. The fully cosmological runs employed in the present study include "Eris", one of the highest-resolution hydrodynamical simulations of the formation of a M_vir=8e11 Msun late-type spiral, and the DM only M_vir = 1.7e12 Msun "Via Lactea II" simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and successfully compare their density, velocity anisotropy, and radial velocity dispersion profiles with the observational data. Most mock SDSS realizations show the same "cold veil" recently observed in the distant stellar halo of the MW, with tracers as cold as sigma-los~50 km/s between 100-150 kpc. Controlled experiments based on the integration of the spherical Jeans equation as well as a particle tagging technique applied to Via Lactea II show that a "heavy" M_vir 2e12 Msun realistic host produces a poor fit to the kinematic SDSS data. Argue that these results offer added evidence for a "light", centrally-concentrated MW halo.
1307.1951
Quasar-galaxy clustering through project galaxy counts at z=0.6-1.2
Zhang et al
Investigate the spatial clustering of galaxies around quasars at redshifts from 0.6 to 1.2 using the photometric data from SDSS stripe 82. The quasar and galaxy cross-correlation functions are measured through the projected galaxy number density n(r_p) on scales 0.05<r_p<20 Mpc/h around quasars for a sample of 2300 quasars from Schneider+ (2007). Detect strong clustering signals at all redshifts, and find that the clustering amplitude increases significantly with redshift. Examine the dependence of the quasar-galaxy clustering on quasar and galaxy properties and find that the clustering amplitude is significantly larger for quasars with more massive BHs, or with bluer colors, while the dependence on quasar luminosity is absent. Also show that quasars have a stronger correlation amplitude with blue galaxies than with red galaxies. Discuss the implication of finding.
1307.2053
X-ray absorption of high redshift quasars
Eitan, Behar
Soft X-ray photoelectric absorption of high-z quasars has been known for two decades, but has no unambiguous astro-physical context. Construct the largest sample to date of 58 high redshift quasars (z>0.45) selected from the XMM-Newton archive based on a high photon count criterion (>1800). Measure the optical depth tau at 0.5 keV, and find that 43% of the quasars show significant absorption. Aim to find which physical parameters of the quasars drive their observed absorption, e.g., redshift, radio luminosity, radio loudness [what's the difference between loudness and luminosity?], or the X-ray luminosity. Compare the absorption behavior with redshift with the pattern expected if the diffuse IGM is responsible for the observed absorption, and with a comparison sample of GRB X-ray afterglows. Although the z>2 quasar opacity is consistent with diffuse IGM absorption, many intermediate z (0.45<z<2) quasars are not sufficiently absorbed for this scenario, and are appreciably less absorbed than GRBs. Only 10/37 quasars at z<2 are absorbed, and only 5/30 radio quiet quasars are absorbed. Find a weak correlation between tau and z, and even a weaker correlation between tau and radio luminosity, which leads to the conclusion that although a diffuse IGM origin for the quasar absorption is unlikely, optical depth does seem to increase with redshift, roughly as (1+z)^2.2pm0.6,tending at high-z to tau~0.4, similar to the high-z GRB values. This result can be explained by an ionized and clumpy IGM at z<2, and a cold, diffuse IGM at higher redshift. If, conversely, ascribed to local absorption at the quasar, and owing to the steep L_z~(1+z)^7.1pm0.5 correlation in the present sample, the host column density scales as N_H~L_x^0.7pm0.1.
1307.2068
A diversity of dusty AGN tori: data release for the VLTI/MIDI AGN large program and first results for 23 galaxies
Burtscher, ... Kishimoto, ... et al
The AGN-heated dust distributions (the "torus") is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear SMBH. Yet, even its most basic structural properties (e.g. extent, geometry and elongation) are unknown for all but a few archetypal objects. Since most AGNs are unresolved in the MIR, utilize the MID-IR interferometric instrument (MIDI) at the VLT interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds (has). Present here and extensive amount of new interferometric observations from the MIDI AGN Large program, and add data from the archive to give a complete view of the existing MIDI observations of AGNs. Additionally, obtain high-quality MIR spectra from VLT/VISIR. Present correlated and total flux spectra for 23 AGNs and derive flux and size estimates at 12 micron using simple axisymmetric geometrical models. Surprising result: relatively high level of unresolved flux and its large scatter: the median "point source fraction" is 70% for type 1 and 47% for type 2 AGNs, meaning that a large part of the flux is concentrated on scales smaller than about 5 mas (0.1-10 pc). Among sources observed with similar spatial resolution, it varies from 20%-100%. For 18 of the sources, two nuclear components can be distinguished in the radial fits. [cool! maybe spectra will show dual core.] While these models provide good first to all but the brightest sources, significant elongations are detected in eight sources. The half-light radii of the fainter sources are smaller than expected from the size~L^0.5 scaling of the bright sources and show a large scatter, especially when compared to the relatively tight size-luminosity relation in the NIR.
1307.2153
Cosmological magnetic fields
Kunze
B-fields are observed on nearly all scales in the universe, from stars and galaxies up to galaxy clusters and beyond. The origin of cosmic B-fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed B-field could explain the present day strength of the galactic B-field. However, it is still an open problem how and when this initial B-field was created. Observations of the CMB provide a window to the early universe and might therefore be able to tell us whether comic B-fields are of primordial, cosmological origin and at the same time constrain its parameters. Give an overview of the observational evidence of large scale B-fields, describe generation mechanisms of primordial B-fields and possible imprints in the CMB.
1307.2235
The influence of environment on the circumgalactic medium
Yoon, Putman
The effect of environment on the CGM is investigated through a comparison of Lya absorption line data in the Virgo cluster and the field. This paper uses the first systematic survey of background QSOs in and around the Virgo cluster and large existing surveys of galaxies at low redshift. While previous studies found denser gas (higher equivalent width) closer to a galaxy (lower impact parameter), this correlation disappears in the Virgo environment. In addition, the covering fraction of the CGM is lower in the cluster environment than in the circumcluster environment and field. The results indicate the CGM is suppressed for cluster galaxies while galaxies in the circumcluster environment have abundant CGM. The truncation of the CGM may result in the quenching of SF through starvation. Results show that CGM surveys need to consider the role of environment.
1307.2236
A megacam survey of outer halo satellites. II. Blue stragglers in the lowest stellar density systems
Santana, ... Geha, et al
A homogeneous study of blue straggler stars [what are these?] across ten outer halo globular clusters, 3 classical dSph and 9 ultra-faint galaxies based on deep and wide-field photometric data taken with MegaCam on CFHT. Find blue straggler stars to be ubiquitous among these MW satellites. Test the importance of primordial binaries or multiple systems on blue straggler SF in low density environments. For the outer halo globular clusters, find an anti-correlation between the specific frequency of blue straggler and absolute magnitude [so brighter = less frequent, or the other way around?], similar to that previously observed for inner halo clusters. When plotted against density and encounter rate [what is an "encounter rate"?], the frequency of blue stragglers are well fitted by single trends with smooth transitions between dwarf galaxies and globular clusters, which points to a common origin for their blue stragglers. The fraction of blue stragglers stays constant and high in the low encounter rate regime spanned by our dwarf galaxies, and decreases with density and encounter rate in the range spanned by the globular clusters. Find that young stars can mimic blue stragglers in dwarf galaxies only if their ages are 2.5pm0.5 Gyr and they represent ~1-7% of the total number of stars, which is deemed highly unlikely. These results point to mass-transfer or mergers of primordial binaries or multiple systems as the dominant blue straggler formation mechanism in low density systems.
* Blue straggler stars are MS stars in open or globular clusters that are more luminous and bluer than stars at the MS turn-off point for the cluster. Standard theories of stellar evolution hold that the position of a star on the HR diagram should be determined almost entirely by the initial mass of the star and its age. In a cluster, stars all formed at approximately the same time, and thus in an H-R diagram for a cluster, all stars should lie along a clearly defined curve set by the age of the cluster, with the positions of individual stars on that curve determined solely by their initial mass. With masses 2-3 times that of the rest of the MS cluster stars, blue stragglers seem to be exceptions to this rule. The resolution of this problem is likely related to interactions between 2 or more stars in the dense confines of the clusters in which blue stragglers are found. (from Wikipedia)
1307.2239
The chemical imprint of dust on the most metal-poor stars
Ji, Frebel, Bromm
Investigate the impact of dust-induced gas fragmentation on the formation of the first low-mass, metal-poor stars (<1M_sun) in the early universe. Previous work has posited the existence of a critical dust-to-gas ratio, below which dust thermal cooling is unable to cause fragmentation. Using Si-based (rather than C-based) dust compositions, compute such critical dust-to-gas ratios and associated critical silicon abundances. Evaluate the robustness of these critical values by considering variations in the dust chemical composition, grain size distribution, and star formation environment. Variations in the dust chemical composition are less important than variations in the size distribution, and the most likely environment where dust cooling becomes significant is in a rotationally supported protostellar disk. Test the dust cooling theory by comparing to Si abundances observed in metal-poor stars. Several stars have Si abundances low enough to rule out fragmentation induced by dust which follows a standard MW grain size distribution. Moreover, two of the most Fe-poor stars have such low Si abundances that even dust with a shocked grain size distribution [how does this distribution compare to MW grain size distribution?] cannot easily explain their formation. See evidence that stars with [Fe/H]<-4.0 exhibit either high C and low Si abundances or the reverse. This suggests that the earliest low-mass SF in the most metal-poor regime likely proceeded through two distinct pathways, one that relied on fine structure cooling and one that relied on dust cooling. This explains both the C-rich and C-normal stars at extremely low [Fe/H].
1307.2250
The extent of magnetic fields around galaxies out to z~1
Bernet, Miniati, Lilly
Radi quasar sightlines with strong MgII absorption lines display statistically enhanced Faraday Rotation Measures (RM) indicating the presence of additional magneto-active plasma with respect to sightlines free of such absorption. Use multicolor optical imaging to idenetify the likely galaxies hosting the magneto-active plasma, and to constrain the location of the latter with respect to the putative parent halo. Find that all of the sightlines with high RM pass within 50 kpc of a galaxy and that the RM distribution for low impact parameters, D<50kpc, is significantly different than for larger impact parameters. In addition, find a decrease in the ratio of the polarization at 21cm and 1.5cm, p_21/p_1.5 towards lower D. These two effects are most likely related, strengthen the association of excess RM with intervening galaxies, and suggest that intervening galaxies operate as inhomogeneous Faraday screens. These results are difficult to reconciliate with only a disk model for the B-field but are consistent with highly magnetized winds associated with MgII systems. Infer strong B-fields of a few tens of uG, consistent with values required by the lack of evolution of the FIR-radio correlation at high redshifts. Finally, these findings lends support to the idea that the small scale helicity bottleneck of alpha-Omega galactic dynamos can be significantly alleviated via galactic winds.
1307.2377
How real-time cosmology can distinguish between different anisotropic models
Amendola, et al
How to distinguish between isotropic and anisotropic cosmological models based on tracking the angular displacements of a large number of distant quasars over an extended period of time, and then performing a multipole-vector decomposition of the resulting displacement maps. Find that while the GAIA mission operating at its nominal specifications does not have sufficient angular resolution to resolve anisotropic universes from isotropic ones using this method within a reasonable timespan of ten years, a next-generation GAIA-like survey with a resolution 10 times better should be equal to the task. Distinguishing between different anisotropic models is however more demanding. Keeping the observational timespan to ten years, find that the angular resolution of the survey will need to be of order 0.1 micro-arcsecond in order for certain rotating anisotropic models to produce a detectable signature that is also unique to models of this class. However, should such a detection become possible, it would immediately allow us to rule out large local void models.
1307.2566
The effect of weak lensing on distance estimates from supernovae
Smith, et al
Using 608 SNIa from SDSS-II and BOSS surveys, combined with a sample of FG galaxies from SDSS-II, estimate the WL convergence for each SN LoS. Find that the correlation between this measurement and the Hubble residuals is consistent with the prediction from lensing (1.7 sigma significance). Strong correlations are also found between the residuals and SNe nuisance parameters after a linear correction is applied. When these other correlations are taken into account, the lensing signal is detected at 1.4 sigma. Show for the first time that distance estimates from SNe can be improved when lensing is incorporated by including a new parameter in the SALT2 methodology for determining distance moduli. The recovered value of the new parameter is consistent with the lensing prediction. Using WMAP7, HST and BAO data, find the best-fit value of the new lensing parameter and show that the central values and uncertainties on Omega_m and w are unaffected. The lensing of SNe, while only seen at marginal significance in this low z sample, will be of vital importance for the next generation of surveys, such as DES and LSST, which will be systematics dominated.
1307.2289
Anybody but Hubble!
Trimble
The question is: "who first recognized the expansion of the universe?"
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