1308.6278
Probing the cosmic-ray content of galaxy clusters by stacking Fermi-LAT count maps
Huber et al
Galaxy clusters are giant reservoirs of CRs (shown in radio). A gamma-ray signal from the cluster volume is expected to arise through interactions of CR protons with the ambient plasma, but a confirming observation is still missing. Search for cumulative gamma-ray emission in direction of galaxy clusters by analysing a collection of stacked Fermi-LAT count maps. Also look at possible systematic differences in the emission between cool-core and non-cool core cluster populations. Making use of a sample of 53 clusters selected from the HIFLUGCS catalog, do not detect a significant signal from the stacked sample. The flux upper limit derived for the total stacked sample is at the level of a few 1e-11 ph cm^-2 s^-1 at 95% CL in the 1-300 GeV band, assuming power-law spectra with photon indices 2.0, 2.4, 2.8 and 3.2. Separate stacking of the cool core and non-cool core clusters in the sample lead to similar values around 5e-11 and 2e-11 ph/cm^2/s, respectively. Under the assumption that decaying \pi^0, produced in collisions between CRs and the ambient thermal gas, are responsible for the gamma-ray emission, set upper limits on the average CR content in galaxy clusters. For the entire cluster population, upper limit on the gamma-ray flux translates into an upper limit on the CR-to-thermal energy ratio of 4.6% for a photon index of 2.4. The 95% upper limits are at the level expected from numerical simulations, which likely suggests that the injection of CR at cosmological shocks is less efficient than previously assumed.
1308.6286
Are group- and cluster-scale dark matter haloes over-concentrated?
Auger et al
Investigate the relationship between the halo mass, M_200, and concentration, c, for a sample of 26 group- and cluster-scale strong gravitational lenses. In contrast with previous results, find that these systems are only ~0.1 dex more over-concentrated than similar-mass haloes from dark matter simulations; the concentration of a halo with M_200-1e14 Msun is log c = 0.78 pm 0.05, while simulations of haloes with this mass at similar redshifts (z~0.4) predict log c~0.56-0.71 [what dataset and analysis did they use?]. Also find that cannot make informative inference on the slope of the M_200-c relation in spite of the large sample size; note that the steep slopes found in previous studies tend to follow the slope in the covariance between M_200 and c, indicating that these results may be measuring the scatter in the data rather than the intrinsic signal. Furthermore, conclude that the inability to constrain the M_200-c slope is due to a limited range of halo masses, as determined by explicitly modeling the halo mass distribution, and suggest that other studies may be producing biased results by using an incorrect distribution for their halo masses.
1308.6294
Distribution function approach to redshift space distortions. Part V: perturbation theory applied to dark matter haloes
Vlah, Seljak, Okumura, Desjacques
Numerical simulations show that RSD introduce strong scale dependence in PS of haloes, with 10% deviations relative to linear theory predictions even on relatively large scales (k<0.1 h/Mpc) and even in the absence of satellites (which induce FoG effects). If unmodeled, these effects prevent one from extracting cosmological information from RSD surveys. In this paper we use perturbation theory (PT) and halo biasing model and apply it to the distribution function approach to RSD, in which RSD is decomposed into several correlators of density weighted velocity moments. Model each of these correlators using PT and compare the results to simulations over a wide range of halo masses and redshifts. Find that with an introduction of a physically motivated halo biasing, and using DM PS from simulations, can reproduce the simulation results at a % level on scale up to k~0.15 h/Mpc at z=0, without the need to have free FoG parameters in the model.
1308.6322
What do observations of the Lyman-alpha fraction tell us about reionization?
Taylor, Lidz
Measuring the z evolution of the Ly-a fraction to study the reionization history of the Universe is appealing, but this fraction is expected to fall-off towards high z as the intergalactic medium becomes significantly neutral, and the galaxies' Ly-a emission is progressively attenuated. Early measurements with this technique suggest a strong drop in the Ly-a fraction near z~7. Previous work concluded that this requires a surprisingly neutral IGM -- with neutral H filling more than 50% of the volume of the universe -- at this redshift. Model the evolving Ly-a fraction using cosmological simulations of the reionization process. Before reionization completes, the simulated Ly-a fraction has large spatial fluctuations owing to the inhomogeneity of the reionization. SInce existing measurements of the Ly-a fraction span relatively small regions on the sky, and sample these regions only sparsely, they may by chance probe mostly galaxies with above average Ly-a attenuation. Find that this sample variance is not exceedingly large for existing surveys, but that it does somewhat mitigate the required neutral fraction at z~7. Quantitatively, in a fiducial model calibrated to match measurements after reionization, find that current z=7 observations require a volume-averaged neutral fraction of x_HI>0.05 at 95% CL. Hence, find that the z~7 Ly-a fraction measurements do likely probe the universe before reionization completes but that they do not require a very large neutral fraction.
1308.6517
Evidence for a receding dust sublimation region around a supermassive black hole
Kishimoto, Hoenig, ... et al
The NIR emission in Type 1 AGN is though to be dominated by the thermal radiation from dust grains that are heated by the central engine in the UV/optical and are almost at the sublimation temperature. A brightening of the central source can thus further sublimate the innermost dust, leading to an increase in the radius of the NIR emitting region. Such changes in radius have been indirectly probed by the measurements of the changes in the time lag between the NIR and UV/optical light variation. Report direct evidence for such a receding sublimation region through the NIR interferometry of the brightest Type 1 AGN in NGC4151. The increase in radius follows a significant brightening of the central engine with a delay of at least a few years, which is thus the implied destruction timescale of the innermost dust distribution. Compiling historic flux variations and radius measurements, also infer the reformation timescale for the inner dust distribution to be several years in this galactic nucleus. More specifically and quantitatively, find that the radius at a given time seems to be correlated with a long-term average of the flux over the previous several (~6) years, instead of the instantaneous flux. Finally, also report measurements of three more Type 1 AGNs newly observed with the Keck interferometer, as well as the second epoch measurements for 3 other AGNs.
1308.6574
A hot Jupiter transiting a mid-K dwarf foundi n the pre-OmegaCam Transit Survey
Koppenhoefer et al
Pre-OmegaTranS project: A deep survey for transiting extra-solar planets in the Carina region of the Galactic disk. In 2006-2008 observed a single dense stellar field with a very high cadence of ~2 min using the ESO wide field imager at La Silla. Using the Astronomical Wide-field System for Europe and the Munich Difference Imaging Analysis pipeline, a module that has been developed for this project, created the light curves of 16000 stars with more than 4000 data points which have been searched for periodic transit signals using a box-fitting least-squares detection algorithm. All light curves are publicly available. In the course of the pre-OmegTranS project, identified two planet candidates - POTS-1b and POTS-C2b - which is presented here. With expensive follow-up observations, able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K dwarf. The planet has a mass of 2.31 pm 0.77 M_Jup and a radius of 0.94 pm 0.04 R_Jup and a period of P=3.16d. The host star POTS-1 has a radius of 0.59pm0.02 R_sun and a mass of 0.70pm0.05 M_sun. Due to its low apparent brightness of I=16.1 mag the follow-up and confirmation of POTS-1b was particularly challenging and costly.
1308.6577
On the influence of physical galaxy properties on Lyman-alpha escape in star-forming galaxies
Atek, .. Kneib, et al
Among the different observational techniques used to select high-z galaxies, the hydrogen recombination line Lya is of particular interest as it gives access to the measurement of cosmological quantities such as the SFR of distant galaxy populations. However, the interpretation of this line and the calibration of such observables is still subject to serious uncertainties. Therefore, it is important to understand under what conditions the Lya line can be used as a reliable SF diagnostic tool. Use a sample of 24 Lya emitter at z~0.3 with an optical spectroscopic follow-up to calculate the Lya escape fraction and its dependency upon different physical properties. Also examine the reliability of Lya as a SFR indicator. Combine these observations with a compilation of Lya emitters selected at z=0-0.3 to assemble a larger sample. The Lya escape fraction depends clearly on the dust extinction following the relation fesc(Lya)=C(Lya)x1e{-0.4 E(B-V) k(Lya)}, but with a shallower slope than previously reported, with k(lya)~6.67 and C(Lya)=0.22. However, the correlation does not follow the expected curve for a simple dust attenuation. Explore the various mechanisms that lead to fesc(Lya) values above and continuum extinction curve, i.e. to an enhancement of the Lya output. Also observe that the strength of Lya and the escape fraction appear unrelated to the galaxy metallicity. Regarding the reliability of Lya as a SFR indicator, show that the deviation of SFR (Lya) from the true SFR (as traced by the UV continuum) is a function of the observed SFR(UV), which can be seen as the decrease of fesc(Lya) with increasing UV luminosity. Moreover, observe a redshift-dependence of this relationship revealing the underlying evolution of fesc(Lya) with redshift.
1308.6818
Host galaxy spectra and consequences for SN typing from the SDSS SN survey
Olmstead, ... Sako, ... D'Andrea, et al
Spectra from 5254 galaxies that hosted SNe or other transient events in SDSS-II. This sample represents the largest systematic, unbiased, magnitude limited spectroscopic survey of SN host galaxies. Using the host galaxy redshifts, test the impact of photometric SN classification based on SDSS imaging data with and without using spectroscopic redshifts of the host galaxies. Following suggested scheme, there are a total of 1166 photometrically classified SNe Ia when using a flat z prior and 1126 SNe Ia when the host specz is assumed. For 1024 (87.8%) candidates classified as likely SNe Ia w/o z information, find that the classification is unchanged when adding the host galaxy redshift. Using photometry from SDSS imaging data and the host galaxy spectra, also report host galaxy properties for use in future analysis of SN astrophysics. Finally, investigate the differences in the interpretation of the light curve properties with and without knowledge of the redshift. When using the SALT2 light curve fitter, find a 21% increase in the number of fits that converge when using the spectroscopic redshift. Without host galaxy redshifts, find that SALT2 light curve fits are systematically biased towards lower photometric redshift estimates and redder colors in the limit of low S/N data. The general improvements in performance of the light curve fitter and the increased diversity of the host galaxy sample highlights the importance of host galaxy spectroscopy for current photometric SN surveys such as the DES and future surveys such as the LSST.
1309.0004
Surface brightness profiles of dwarf galaxies: I. profiles and statistics
Herrmann, Hunter, Elmegreen
Radial surface brightness profiles of spiral galaxies: (i) single exponential (ii) more steeply, (iii) less steeply. Profile breaks are also found in dwarf disks, but some dwarf Type IIs are flat or increasing out to a break before falling off. Re-examine the stellar disk profiles of 141 dwarfs: 96 dwarf irregulars (dIms), 26 blue compact dwarfs (BCDs), and 19 Magellanic-type spirals (Sms). Fit signle, double, or even triple exponential profiles in up to 11 passbands: GALEX FUV and NUV, ground-based UBV JHK and Halpha, and Spitzer 3.6 and 4.5 um. Find that more luminous galaxies have brighter centers, larger inner and outer scale lengths, and break at larger radii; dwarf trends with M_B extend to spirals. However, the V-band break surface brightness is independent of break type, M_B, and Hubble type. Dwarf Type II and III profiles fall off similarly beyond the breaks but have different interiors and IIs break ~twice as far as III's. Outer type II and III scale lengths may have weak trends with wavelength, but pure Type II inner scale lengths clearly decrease from the FUV to visible bands whereas Type III inner scale lengths increase with redder bands. This suggests the influence of the different SFHs on profile type, but nonetheless the break location is approximately the same in all passbands. Dwarfs continue trends between profile and Hubble types such that later-type galaxies have more Type II but fewer Type I and III profiles than early-type spirals. BCDs and Sms are over-represented as Type III and II, respectively, compared to dIms.
1309.0008
Encoding the infrared excess (IRX) in the NUVrK color diagram for star-forming galaxies
Arnouts, ... Ilbert, ... Capak, ... Scoville, McCracken, ... et al
Empirical method of assessing the SFR of SF galaxies based on their locations in the rest-frame color-color diagram (NUV-r) vs (r-K). By using the Spitzer 24 micron sample in the COSMOS field (~16400 galaxies with 0.2<z<1.3) and a local GALEX-SDSS-SWIRE sample (~700 galaxies with z<0.2), we show that the mean infrared excess <IRX>=<L_IR/L_UV> can be described by a single vector, NRK, that combines the two colors. The calibration between <IRX> and NRK allows recovery of the IR luminosity, L_IR, with an accuracy of ~0.21 dex for the COSMOS sample and ~0.27 dex for the local one. The SFRs derived with this method agree with the ones based on the observed (UV+IR) luminosities and on the SED fitting for the vast majority (~85%) of the SF population. Thanks to a library of model galaxy SEDs with realistic prescriptions for the SFH, show that inclusion of a 2-component dust model (i.e., birth clouds and diffuse ISM) is necessary, and a full distribution of galaxy inclinations in order to reproduce the behavior of the <IRX> stripes in the NUVrK diagram. In conclusion, the NRK method, based only on rest-frame UV and optical colors available in most of the extragalactic fields, offers a simple alternative of assessing the SFR of SF galaxies in the absence of FIR or spectral diagnostic observations.
1309.0009
Habitable planets around white dwarfs: an alternate mission for the Kepler spacecraft
Kilic, Agol, Loeb, Maoz, Munn, Gianninas, Canton, Barber
A large fraction of WDs may host planets in their habitable zones. These planets may provide best chance to detect bio-markers on a transiting exoplanet, thanks to the diminished contrast ratio between the Earth-sized WD and its Earth-sized planets. The JWST is capable of obtaining the first spectroscopic measurements of such planets, yet there are no known planets around WDs. Here we propose the take advantage of the unique capability of the Kepler spacecraft in the 2-wheels mode to perform a transit survey that is capable of identifying the first planets in the habitable zone of a WD. Propose to obtain Kepler time-series photometry of 10k WDs in the SDSS imaging area to search for planets in the habitable zone. Thanks to the large field of view of Kepler, for the first time in history, a large number of WDs can be observed at the same time, which is essential for discovering transits. Proposed survey requires a total of 200 days of observing time, and will find up to 100 planets in the WD habitable zone. This survey will maintain Kepler's spirit of searching for habitable Earths, but near new hosts. With few-day observations and minute-cadences per field, it will also open up a completely unexplored discovery space. In addition to planets, this survey is sensitive to pulsating WDs, as well as eclipsing short period stellar and substellar companions. These have important implications for constraining the double WD merger rate and their contribution to Type Ia SNe and the gravitational wave foreground. Given the relatively low number density of the targets, this program can be combined with other projects that would benefit from high cadence and many-fields observations with Kepler, e.g., a transit survey of a magnitude-limited, complete sample of nearby M dwarfs or asteroseismology of variable stars (e.g. RR Lyrae) in the same fields.
1309.0197
Counting gamma rays in the directions of galaxy clusters
Prokhorov, Churazov
Emission of AGNs and neutral pion decay - are the two most important natural mechanisms, that could make a galaxy cluster be a source of gamma-raysi n the GeV regime. Revisited this problem by using 52.5 month FERMI-LAT data above 10 GeV and stacking 55 lusters from the HIFLUGS sample of the X-ray brightest clusters. The choice of >10 GeV photons is optimal from the point of view of angular resolution, while the sample selection optimizes the chances of detecting signatures of the neutral pion decay, arising from hadronic interactions of relativistic protons with an intra-cluster medium, which scale with the X-ray flux. In the stacked data [how many clusters were stacked?], detected a signal for the central 0.25 deg circle at the level of 4.3 sigma. An evidence for a spatial extent of the signal is marginal. A subsample of cool-core clusters has higher count rate 1.9 pm 0.3 per cluster compared to the subsample of non-cool core clusters 1.3pm0.2. Several independent arguments suggest that the contribution of AGNs to the observed signal is substantial if not dominant. No strong support for the large contribution of pion decay was found. In terms of a limit on the relativistic protons energy density, got an upper limit of ~1.5% relative to the gas thermal energy density, provided that the spectrum of relativistic protons is hard (s=4.1 in dN/dp=p^-s). This estimate assumes that relativistic and thermal components are mixed. For softer spectra the limits are weaker.
1309.0329
Astrometric detection of exoplanets from the ground
Sahlmann, et al
As the title says. [How...?]
1309.0382
Planck 2013 results. XXX. Cosmic Infrared background measurements and implications for star formation
Planck Collaboration
Combine HFI with IRAS, the angular auto- and cross-frequency PS is measured from 143 to 3000 GHz, and the auto-bispectrum from 217 to 545 GHz. The total areas used to compute the CIB PS and bispectrum are about 2240 and 4400 deg^2, respectively. After careful removal of the contaminants, and a complete study of systematics, the CIB PS and bispectrum are measured with unprecedented S/N ratio from angular multipoles ell~150 to 2500, and ell~130 to 1100, respectively. Two approaches are developed for modeling CIB PS anisotropies. The first approach takes advantage of the unique measurements by Planck at larger angular scales, and models only the linear part of the PS, with a mean bias of DM haloes hosting dusty galaxies at a given redshift weighted by their contribution to the emissivities. The second approach is based on a model that associates SF galaxies with DM haloes and their subhaloes, using a parametrized relation between the dust-processed infrared luminosity and (sub-)halo mass. The two approaches simultaneously fit all auto- and cross-PS very well. Find that the SFH is well constrained up to z~2. However, at higher redshift, the accuracy of the SFH measurement is strongly degraded by the uncertainty in the SED of CIB galaxies. Also find that CIB galaxies have warmer temperatures as redshift increases. The CIB bispectrum is steeper than that expected from the PS, although well fitted by a power law; this gives some information about the contribution of massive halos to the CIB bispectrum.
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