1308.5968
An 8 hour characteristic time-scale in submillimetre light curves of Sagittarius A*
Dexter, Kelly, Bower, Marrone, Stone, Plambeck, Doeleman
Compile and analyze ~10 year submillimetre (1.3, 0.87, 0.43 mm, submm) wavelength light curves of Sagittarius A*. Use Monte Carlo simulations to show that on minute to few hour time-scales the variability is consistent with a red noise process with 230 GHz PS slope of 2.3 pm 0.7 at 95 CL. The light curve is decorrelated (white noise) on very long (month to year) times. In order to identify the transition time between red and white noise, model the light curves as a stochastic damped random walk process. The models allow a quantitative estimate of this physical characteristic time-scale of 8pm3.5 hours at 230 GHz at 95% CL, with consistent results at 345 and 690 GHz. This corresponds to ~10 orbital times or ~1 inflow (viscous) time at R=3 Rs, a typical radius producing the 230 GHz emission as measured by very long baseline interferometry and found in theoretical accretion flow and jet models. This time-scale is significantly shorter (longer) than those measured at radio (NIR) wavelengths, and is marginally inconsistent with the same variability mechanism operating in the submm and NIR for the expected t~R^3/2 scaling. It is crudely consistent with the analogous time-scale inferred in studies of quasar optical light curves after the accounting for the difference in emission radius. Find evidence that the submm variability persists at least down to the ISCO [???], if not the event horizon. These results can be compared quantitatively with similar analysis at different wavebands to test for connections between the variability mechanisms, and with light curves from theoretical models of accreting black holes.
1308.5971
Precious metals in SDSS Quasar spectra II: tracking the evolution of strong, 0.4<z<2.3 MgII absorbers with thousands of systems
Seyffert, Cooksey, Simcoe, O'Maera, Kao, Prochaska
Performed an analysis of over 34,000 MgII doublets at 0.36<z<2.29 in SDSS DR7 quasar spectra; the catalog, advanced data products, and tools for analysis are publicly available. The catalog was divided into 14 small z bins with roughly 2,500 doublets in each, and from MC simulations, estimate 50% completeness at rest equivalent width W_r ~0.8A. The EW frequency distribution is described well by an exponential model at all redshifts, and the distribution becomes flatter with increasing redshift; i.e., there are more strong systems relative to weak ones. Direct comparison with previous SDSS MgII surveys reveal that at least 70% of the doublets in these other catalogs are recovered, in addition to detecting thousands of new systems. Discuss how these surveys come by their different results, which qualitatively agree but, due to the very small uncertainties, differ by a statistically significant amount. The estimated physical cross-section of MgII-absorbing galaxy haloes increased 3-fold, approximately, from z=0.4 -> 2.3, whie the W_r>= 1A absorber line density grew, dN_MgII/dX, by roughly 45%. [where do all these MgII go at low z? Do they collapse into something no longer in gaseous phase to be detected (maybe grains of dust or asteroids (I'm making stuff up)?] Explore the different evolution of various absorber populations -- damped Ly-a absorbers, Ly-limit systems, strong CIV absorbers, and strong and weaker MgII systems -- across cosmic time (0<z<6).
1308.5972
Cosmological information in the intrinsic alignments of luminous red galaxies
Chisari, Dvorkin
Explore the cosmological information encoded in the IA of red galaxies. Make forecasts for the ability of current and future spectroscopic surveys to constrain local primordial non-Gaussianity and BAO in the cross-correlation function of IA and the galaxy density field. For BAO surveys, find that the BAO signal in the IA is marginally significant with a S/N of 1.8 and 2.2 with the LOWZ and CMASS sample of galaxies, respectively, and increasing to 2.3 and 2.7 once the survey is completed. For the DE spectroscopic Instrument (DESI) and for a spectroscopic survey following the EUCLID redshift selection function, find S/N ratios of 12 and 15, respectively. Local type primordial non-Gaussianity, parameterized by fNL=10, is only marginally significant in the IA signal with S/N ratios < 2 for the 3 surveys considered.
1308.5978
Setting the stage for circumstellar interaction in core-collapse supernovae II: wave-driven mass loss in supernova progenitors
Shiode, Quataert
SNe powered by interaction with circumstellar material provide evidence for intense stellar mass loss during the final years leading up to core collapse. Argued that during and after core Ne burning, internal gravity waves excited by core convection can tap into the core fusion power and transport a super-Eddington energy flux out to the stellar envelope, potentially unbinding up to ~1 solar mass of material. In this work, explore the internal conditions of SN progenitors using the MESA 1-D stellar evolution code, in search of those most susceptible to wave-driven mass loss. Focus on simple, order of magnitude considerations applicable to a wide range of progenitors. Wave-driven mass loss during core Ne and O fusion happens preferentially in either lower mass (<~20 Msun ZAMS [??]) stars or massive, sub-solar metallicity stars. Roughly 20% of the SN progenitors surveyed can excite ~1e46-48 erg of energy in waves that can potentially drive mass loss within a few months to a decade of core collapse. This energy can generate a circumstellar environment with 1e-3 - 1 solar mass reaching ~100 AU before explosion. Predict a correlation between the energy associated with pre-SN mass ejection and the time to core collapse, with the most intense mass loss preferentially happening closer to core collapse. During Si burning, a ~5 day long phase for the progenitor models, wave energy may inflate ~1e-3 - 1 Msun of the stellar envelope to ~10-100s of solar radii. This suggests that some nominally compact SN progenitors (Type Ibc progenitors) will have a significantly different SN shock breakout signature than traditionally assumed. Discuss the implications of our results for the core-collapse SN mechanism, Type IIn SNe, Type IIb SNe from extended progenitors (e.g., SNe 1993j and 2011 dh), and observed pre-SN outbursts.
1308.5985
The changing Lya optical depth in the range 6<z<9 from MOSFIRE spectroscopy of Y-dropouts
Treu, Schmidt, Trenti, Bradley, Stiavelli
MOSFIRE spectroscopy of 13 candidate z~8 galaxies selected as Y-dropouts as part of the BoRG pure parallel survey. Detect no significant Lya emission (median 1-sigma rest-frame EW sensitivity is in the range 2-16A). Using the Bayesian framework derived in a previous paper, perform a rigorous analysis of a statistical subsample of non-detections for ten Y-dropouts, including data from the literature, to study the cosmic evolution of the Lya emission of Lyman break galaxies. Find that Lya emission is suppressed at z~8 by at least a factor of 3 with respect to z~6 continuing the downward trend found by previous studies of z-dropouts at z~7. This finding suggests a dramatic evolution in the conditions of the intergalactic or circumgalactic media in just 300 Myrs, consistent with the onset of reionization or changes in the physical conditions of the first generations of SF regions.
1308.6070
The synergy between weak lensing and galaxy redshift surveys
de Putter, Dore, Takada
Study the complementarity of WL and GC (spectroscopic) surveys, by forecasting DE and modified gravity constraints for 3 survey combinations: SuMIRe (Subaru Measurement of Images and Redshifts, the combination of Hyper Suprime-Cam lensing survey and the Prime Focus Spectrograph redshift survey), EUCLID and WFIRST. From the WL surveys, take in to account both the shear and clustering of the source galaxies and from the GC surveys, use the 3-dimensional clustering of spectroscopic galaxies, including redshift space distortions. A CMB prior is included in all cases. Focusing on the large-scale, two-point function information, find strong synergy between the two probes. The DE FoM from WL+GC is up to a factor ~2.5 larger than from either probe alone. Considering modified gravity, if the growth factor f(z) is treated as a free function, it is very poorly constrained by WL or GC alone, but can be measured at the few % level by the combination of the two. On the other hand, for cosmological constraints derived from (angular) PS and considering statistical errors only, it hardly matters whether the surveys overlap on the sky or not. For instance, the DE FoM for overlapping surveys is at most ~20% better than in the disjoint case. This modest gain can be traced to the fundamental fact that only a small fraction of the total number of modes sampled by the GC survey (or by the WL survey) contributes to the cross-correlations between WL and GC.
1308.6167
Analytic PSF correction for gravitational flexion studies
Levinson
Given a galaxy image, one cannot simply measure its flexion. An image's spin one and three shape properties, typically associated with F- and G-flexion, are actually complicated functions of the galaxy's intrinsic shape and the telescope's PSF, in addition to the lensing properties. The same is true for shear. In this work, create a completely analytic mapping from apparent measured galaxy flexions to gravitational flexions by (1) creating simple models for a lensed galaxy and for a PSF whose distortions are dominated by atmospheric smearing and optical aberrations, (2) convolving the two models, and (3) comparing the pre-and post-convolved flexion-like shape variations of the final image. For completeness, do the same for shear. As expected, telescope astigmatism, coma, and trefoil can corrupt measurements of shear, F-flexion, and G-flexion, especially for small galaxies. Additionally find that PSF size dilutes the flexion signal more rapidly than the shear signal. Moreover, mixing between shears, flexions, and asymmetric aberrations can create additive offsets in lensing measurements that vary with both galaxy size and galaxy ellipticity and flexion values. But all is not lost; by measuring the patterns, they can be corrected.
1308.6185
Interpreting the role of the magnetic field from dust polarization maps
Koch, Tang, Ho
Interpret the role of B-field in molecular clouds. B-field and dust emission gradient orientations are observed to show distinct patterns and features [??? like what kind of pattern?]. The angle delta between these orientations can be interpreted as a B-field alignment deviation, assuming the emission gradient orientation to coincide with the density gradient orientation in the MHD force equation. In SMA high-res (collapsing) cores, additional symmetry properties in delta can reveal accretion and outflow zones. All these observational findings suggest the angle delta to be a relevant quantity that can assess the role of the B-field. When comparing this angle with the (projection-free) B-field significance Sigma_B, it is demonstrated that |delta| yields an approximation to the change in Sigma_B. THus, changes in the B-field alignment deviation delta trace changes in the role of the B-field. The angle delta is observationally straightforward to determine, providing a tool to distinguish between zones of minor or significant B-field impact. This is exemplified by a few sources and by the SMA high-res data from a few other. Additional CSO sources are analyzed, providing further support of this result. Finally, based on the different features found in the sample of 31 sources in total, covering sizes from large-scale complexes to collapsing cores, a schematic evolutionary scenario is proposed.
1308.6200
The intrinsic shapes of dwarf irregular galaxies
Roychowdhury, et al
Find that the shapes of dIrr galaxies change systematically with luminosity, with fainter galaxies being thicker. In particular, most luminous dwarfs (-19.6<M_B<-14.8) have thin disks (thickness ~0.2), with the disc being slightly elliptical (axial ratio~0.8). At intermediate luminosity, -14.8<M_B<-12.6, the galaxies are still characterized by elliptical disks (axial ratio ~0.7), but the discs are somewhat thicker (thickness ~0.4). The faintest dwarfs, -12.6 to -6.7, are well described as being oblate spheroids with an axial ratio ~0.5. The increasing thickness of the stellar discs of dwarf irregulars with decreasing luminosity is compatible with the increasing ratio of velocity dispersion to rotational velocity with decreasing galaxy size.
1308.6215
High-n Hydrogen recombination lines from the first galaxies
Rule, Loeb, Strelnitski
Prospects of blind and targeted searches in the radio domain (10 MHz to 1 THz) for high-n H recombination lines from the first generation of galaxies, at z<10. The expected optically thin spontaneous alpha-line luminosities are calculated as a function of the absolute AB magnitude of a galaxy at 1500 A. For a blind search, semi-empirical luminosity functions are used to calculate the number of galaxies whose expected flux densities exceed an assumed detectability threshold. Plots of the minimum sky area, within which at least one detectable galaxy is expected at a given observing frequency, in the fiducial instantaneous passband of 1e4 km/s, allow to assess the blind search time necessary for detection by a given facility. Show that the chances for detection are the highest in the mm and submm domains, but finding spontaneous emission in a blind search, especially from z>>1, is a challenge even with powerful facilities, such as ALMA and SKA. The probability of success is higher for a targeted search of lines with principal quantum number n~10 in Ly-break galaxies amplified by gravitational lensing. Detection of more than one hydrogen line in such a galaxy will allow for line identification and a precise determination of the galaxy's redshift. [what are the rest frame wavelengths that we're talking about?]
Precious metals in SDSS Quasar spectra II: tracking the evolution of strong, 0.4<z<2.3 MgII absorbers with thousands of systems
Seyffert, Cooksey, Simcoe, O'Maera, Kao, Prochaska
Performed an analysis of over 34,000 MgII doublets at 0.36<z<2.29 in SDSS DR7 quasar spectra; the catalog, advanced data products, and tools for analysis are publicly available. The catalog was divided into 14 small z bins with roughly 2,500 doublets in each, and from MC simulations, estimate 50% completeness at rest equivalent width W_r ~0.8A. The EW frequency distribution is described well by an exponential model at all redshifts, and the distribution becomes flatter with increasing redshift; i.e., there are more strong systems relative to weak ones. Direct comparison with previous SDSS MgII surveys reveal that at least 70% of the doublets in these other catalogs are recovered, in addition to detecting thousands of new systems. Discuss how these surveys come by their different results, which qualitatively agree but, due to the very small uncertainties, differ by a statistically significant amount. The estimated physical cross-section of MgII-absorbing galaxy haloes increased 3-fold, approximately, from z=0.4 -> 2.3, whie the W_r>= 1A absorber line density grew, dN_MgII/dX, by roughly 45%. [where do all these MgII go at low z? Do they collapse into something no longer in gaseous phase to be detected (maybe grains of dust or asteroids (I'm making stuff up)?] Explore the different evolution of various absorber populations -- damped Ly-a absorbers, Ly-limit systems, strong CIV absorbers, and strong and weaker MgII systems -- across cosmic time (0<z<6).
1308.5972
Cosmological information in the intrinsic alignments of luminous red galaxies
Chisari, Dvorkin
Explore the cosmological information encoded in the IA of red galaxies. Make forecasts for the ability of current and future spectroscopic surveys to constrain local primordial non-Gaussianity and BAO in the cross-correlation function of IA and the galaxy density field. For BAO surveys, find that the BAO signal in the IA is marginally significant with a S/N of 1.8 and 2.2 with the LOWZ and CMASS sample of galaxies, respectively, and increasing to 2.3 and 2.7 once the survey is completed. For the DE spectroscopic Instrument (DESI) and for a spectroscopic survey following the EUCLID redshift selection function, find S/N ratios of 12 and 15, respectively. Local type primordial non-Gaussianity, parameterized by fNL=10, is only marginally significant in the IA signal with S/N ratios < 2 for the 3 surveys considered.
1308.5978
Setting the stage for circumstellar interaction in core-collapse supernovae II: wave-driven mass loss in supernova progenitors
Shiode, Quataert
SNe powered by interaction with circumstellar material provide evidence for intense stellar mass loss during the final years leading up to core collapse. Argued that during and after core Ne burning, internal gravity waves excited by core convection can tap into the core fusion power and transport a super-Eddington energy flux out to the stellar envelope, potentially unbinding up to ~1 solar mass of material. In this work, explore the internal conditions of SN progenitors using the MESA 1-D stellar evolution code, in search of those most susceptible to wave-driven mass loss. Focus on simple, order of magnitude considerations applicable to a wide range of progenitors. Wave-driven mass loss during core Ne and O fusion happens preferentially in either lower mass (<~20 Msun ZAMS [??]) stars or massive, sub-solar metallicity stars. Roughly 20% of the SN progenitors surveyed can excite ~1e46-48 erg of energy in waves that can potentially drive mass loss within a few months to a decade of core collapse. This energy can generate a circumstellar environment with 1e-3 - 1 solar mass reaching ~100 AU before explosion. Predict a correlation between the energy associated with pre-SN mass ejection and the time to core collapse, with the most intense mass loss preferentially happening closer to core collapse. During Si burning, a ~5 day long phase for the progenitor models, wave energy may inflate ~1e-3 - 1 Msun of the stellar envelope to ~10-100s of solar radii. This suggests that some nominally compact SN progenitors (Type Ibc progenitors) will have a significantly different SN shock breakout signature than traditionally assumed. Discuss the implications of our results for the core-collapse SN mechanism, Type IIn SNe, Type IIb SNe from extended progenitors (e.g., SNe 1993j and 2011 dh), and observed pre-SN outbursts.
1308.5985
The changing Lya optical depth in the range 6<z<9 from MOSFIRE spectroscopy of Y-dropouts
Treu, Schmidt, Trenti, Bradley, Stiavelli
MOSFIRE spectroscopy of 13 candidate z~8 galaxies selected as Y-dropouts as part of the BoRG pure parallel survey. Detect no significant Lya emission (median 1-sigma rest-frame EW sensitivity is in the range 2-16A). Using the Bayesian framework derived in a previous paper, perform a rigorous analysis of a statistical subsample of non-detections for ten Y-dropouts, including data from the literature, to study the cosmic evolution of the Lya emission of Lyman break galaxies. Find that Lya emission is suppressed at z~8 by at least a factor of 3 with respect to z~6 continuing the downward trend found by previous studies of z-dropouts at z~7. This finding suggests a dramatic evolution in the conditions of the intergalactic or circumgalactic media in just 300 Myrs, consistent with the onset of reionization or changes in the physical conditions of the first generations of SF regions.
1308.6070
The synergy between weak lensing and galaxy redshift surveys
de Putter, Dore, Takada
Study the complementarity of WL and GC (spectroscopic) surveys, by forecasting DE and modified gravity constraints for 3 survey combinations: SuMIRe (Subaru Measurement of Images and Redshifts, the combination of Hyper Suprime-Cam lensing survey and the Prime Focus Spectrograph redshift survey), EUCLID and WFIRST. From the WL surveys, take in to account both the shear and clustering of the source galaxies and from the GC surveys, use the 3-dimensional clustering of spectroscopic galaxies, including redshift space distortions. A CMB prior is included in all cases. Focusing on the large-scale, two-point function information, find strong synergy between the two probes. The DE FoM from WL+GC is up to a factor ~2.5 larger than from either probe alone. Considering modified gravity, if the growth factor f(z) is treated as a free function, it is very poorly constrained by WL or GC alone, but can be measured at the few % level by the combination of the two. On the other hand, for cosmological constraints derived from (angular) PS and considering statistical errors only, it hardly matters whether the surveys overlap on the sky or not. For instance, the DE FoM for overlapping surveys is at most ~20% better than in the disjoint case. This modest gain can be traced to the fundamental fact that only a small fraction of the total number of modes sampled by the GC survey (or by the WL survey) contributes to the cross-correlations between WL and GC.
1308.6167
Analytic PSF correction for gravitational flexion studies
Levinson
Given a galaxy image, one cannot simply measure its flexion. An image's spin one and three shape properties, typically associated with F- and G-flexion, are actually complicated functions of the galaxy's intrinsic shape and the telescope's PSF, in addition to the lensing properties. The same is true for shear. In this work, create a completely analytic mapping from apparent measured galaxy flexions to gravitational flexions by (1) creating simple models for a lensed galaxy and for a PSF whose distortions are dominated by atmospheric smearing and optical aberrations, (2) convolving the two models, and (3) comparing the pre-and post-convolved flexion-like shape variations of the final image. For completeness, do the same for shear. As expected, telescope astigmatism, coma, and trefoil can corrupt measurements of shear, F-flexion, and G-flexion, especially for small galaxies. Additionally find that PSF size dilutes the flexion signal more rapidly than the shear signal. Moreover, mixing between shears, flexions, and asymmetric aberrations can create additive offsets in lensing measurements that vary with both galaxy size and galaxy ellipticity and flexion values. But all is not lost; by measuring the patterns, they can be corrected.
1308.6185
Interpreting the role of the magnetic field from dust polarization maps
Koch, Tang, Ho
Interpret the role of B-field in molecular clouds. B-field and dust emission gradient orientations are observed to show distinct patterns and features [??? like what kind of pattern?]. The angle delta between these orientations can be interpreted as a B-field alignment deviation, assuming the emission gradient orientation to coincide with the density gradient orientation in the MHD force equation. In SMA high-res (collapsing) cores, additional symmetry properties in delta can reveal accretion and outflow zones. All these observational findings suggest the angle delta to be a relevant quantity that can assess the role of the B-field. When comparing this angle with the (projection-free) B-field significance Sigma_B, it is demonstrated that |delta| yields an approximation to the change in Sigma_B. THus, changes in the B-field alignment deviation delta trace changes in the role of the B-field. The angle delta is observationally straightforward to determine, providing a tool to distinguish between zones of minor or significant B-field impact. This is exemplified by a few sources and by the SMA high-res data from a few other. Additional CSO sources are analyzed, providing further support of this result. Finally, based on the different features found in the sample of 31 sources in total, covering sizes from large-scale complexes to collapsing cores, a schematic evolutionary scenario is proposed.
1308.6200
The intrinsic shapes of dwarf irregular galaxies
Roychowdhury, et al
Find that the shapes of dIrr galaxies change systematically with luminosity, with fainter galaxies being thicker. In particular, most luminous dwarfs (-19.6<M_B<-14.8) have thin disks (thickness ~0.2), with the disc being slightly elliptical (axial ratio~0.8). At intermediate luminosity, -14.8<M_B<-12.6, the galaxies are still characterized by elliptical disks (axial ratio ~0.7), but the discs are somewhat thicker (thickness ~0.4). The faintest dwarfs, -12.6 to -6.7, are well described as being oblate spheroids with an axial ratio ~0.5. The increasing thickness of the stellar discs of dwarf irregulars with decreasing luminosity is compatible with the increasing ratio of velocity dispersion to rotational velocity with decreasing galaxy size.
1308.6215
High-n Hydrogen recombination lines from the first galaxies
Rule, Loeb, Strelnitski
Prospects of blind and targeted searches in the radio domain (10 MHz to 1 THz) for high-n H recombination lines from the first generation of galaxies, at z<10. The expected optically thin spontaneous alpha-line luminosities are calculated as a function of the absolute AB magnitude of a galaxy at 1500 A. For a blind search, semi-empirical luminosity functions are used to calculate the number of galaxies whose expected flux densities exceed an assumed detectability threshold. Plots of the minimum sky area, within which at least one detectable galaxy is expected at a given observing frequency, in the fiducial instantaneous passband of 1e4 km/s, allow to assess the blind search time necessary for detection by a given facility. Show that the chances for detection are the highest in the mm and submm domains, but finding spontaneous emission in a blind search, especially from z>>1, is a challenge even with powerful facilities, such as ALMA and SKA. The probability of success is higher for a targeted search of lines with principal quantum number n~10 in Ly-break galaxies amplified by gravitational lensing. Detection of more than one hydrogen line in such a galaxy will allow for line identification and a precise determination of the galaxy's redshift. [what are the rest frame wavelengths that we're talking about?]
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