1308.3496
Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey
Willett et al
Present data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304,122 galaxies drawn from SDSS [where does the 16M come from?]. Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with m_r>17, in addition to deeper images from SDSS Stripe 82. While the original Galaxy Zoo project identified galaxies as early-typs, late-types, or mergers, GZ2 measures finer morphological features. THese include bars, bulges, and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the ful public data release for the project, including measures of accuracy and bias. The majority (>90%) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars, and arm curvature. Both the raw and reduced data products can be obtained in electronic format at http://data.galaxyzoo.org.
1308.3551
Window effect in the power spectrum analysis of a galaxy redshift survey
Sato, et al
Investigate the effect of the window function on the multipole power spectrum in two different ways. Consider the convolved PS including the window effect, which is obtained by following the familiar (FKP) method developed by Feldman, Kaiser and Peacock. Show how the convolved multipole PS is related to the original PS, using the multipole moments of the window function. Second, investigate the deconvolved PS, which is obtained by using the Fourier deconvolution theorem. In the second approach, measure the multipole PS deconvolved from the window effect. Demonstrate how to deal with the window effect in these two approaches, applying them to the SDSS LRG sample.
1308.3617
The peculiar light curve of the Symbiotic Star AX Per of the last 125 years
Leibowitz, Formiggini
Analyze the last 125 years optical light curve of the symbiotic star AX Per through correlations discovered in its PS. The data were assembled from the literature and from the AAVSO database. A series of 6 major outbursts dominate the light curve. They are presented in the PS as 13 harmonics of the fundamental frequency fa=1/Pa=1/23172 day^-1. Refer to them as the "red" frequencies. Oscillations with the binary periodicity of the system Pb=1/fb=381.48d are also seen in the light curve, with particularly large amplitudes during outbursts. The fb peak in the PS is accompanied by 13 other peaks on each side, which is referred as the "blue" frequencies. A distinct structure in the frequency distribution of the blue peaks, as well as in their peak power are best interpreted as reflecting beating of the 13 "red" frequencies with the binary one. Suggest that the major outbursts of the system result from events of intense mass loss from the giant star. Mass accretion onto the hot component, partially through the L1 point of the system, took place in the last 125 years at a rate that oscillated with the 13 first harmonics of the fa frequency. The binary orbit is slightly eccentric and periastron passages induced modulation of the L1 accretion at the binary frequency. Hence the fb oscillations in the brightness of the star of amplitude that is modulated by the "red" frequencies of the system.
1308.3704
Searching for Oscillations in the primordial power spectrum: perturbative approach (Paper I)
Meerburg, Spergel, Wandelt
Present a new method for searching for oscillatory features in the primordial PS. A wide variety of models predict these features in one of two different flavors: logarithmically spaced oscillations and linearly spaced oscillations. The proposed method treats the oscillations as perturbations on top of the scale-invariant PS, allowing variation of all cosmological parameters. This perturbative approach reduces the computational requirements for the search as the transfer functions and their derivatives can be precomputed. Show that the most significant degeneracy in the analysis is between the distance to last scattering and the overall amplitude at low frequencies. For models with logarithmic oscillations, this degeneracy leads to an uncertainty in the phase. For linear spaced oscillations, it affects the frequency of the oscillations. In this paper (one out of two), test code on simulated Planck-like data, and show ability to recover fiducial input oscillations with an amplitude of a few times order 1e-2. Apply the code to WMAP9 data and confirm the existence of two intriguing resonant frequencies for log spaced oscillations. For linear spaced oscillations, find a single resonance peak. Use numerical simulations to assess the significance of these features and conclude that the data do not provide compelling evidence for the existence of oscillatory features in the primordial spectrum.
1308.3705
Searching for oscillations in the primordial power spectrum: constraints from Planck (Paper II)
Meerburg, Spergel
Continuation of the above. Log-spaced resonant features in WMAP9 has little to no significance. Confirm the presence of a several low frequency peaks earlier identified by the Planck team, but with a better improvement of fit (delta chi^2~12). Further investigate this improvement by allowing the lensing potential to vary as well, showing mild correlation between the amplitude of the oscillations and the lensing amplitude. Find that the improvement of the fit increases even more (~14) for the low frequencies that modify the spectrum in a way that mimics the lensing effect. Since these features were not present in the WMAP data, they are primarily due to better measurements of Planck at small angular scales. For linear spaced oscillations, find a maximum delta chi^2~13 scanning two orders of magnitude in frequency space, and the biggest improvements are at extremely high frequencies. Recover a best fit frequency very close to the one found in WMAP9, which confirms that the fit improvement is driven by low l. Further comparisons with WMAP9 show Planck contains many more features, both for linear and log space oscillations, but with a smaller improvement of fit. Discuss the improvement as a function of the number of modes and study the effect of the 217 GHz map, which appears to drive most of the improvement for log spaced oscillations. Conclude that none of the detected features are statistically significant.
1308.3707
Galaxy pairs in the Sloan digital sky survey - VIII: the observational properties of post-merger galaxies
Ellison, Mendel, Patton, Scudder
Present a study of 10,800 galaxies in close pairs and a sample of 97 post-mergers identified in SDSS. Find that the average central SFR enhancement (x3.5) and the fraction of starbursts (20%) peak in the post merger sample. The post-mergers also show a stronger deficit in gas phase metallicity that the closest pairs, being more metal-poor than their control by -0.09 dex. Combined with the observed trends in SFR and the timescales predicted in merger simulations, estimate that the post-mergers in sample have undergone coalescence iwthin the last few hundred Myr. In contrast with the incidence of SF galaxies, the frequency of AGN peaks in the post-mergers, outnumbering AGN in the control sample by a factor of 3.75. Moreover, amongst the galaxies that host an AGN, the black hole accretion rates in the closest pairs and post-mergers are higher by a factor of ~3 than AGN in the control sample. These results are consistent with a picture in the which star formation is initiated early on in the encounter, with AGN activity peaking post-coalescence.
Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey
Willett et al
Present data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304,122 galaxies drawn from SDSS [where does the 16M come from?]. Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with m_r>17, in addition to deeper images from SDSS Stripe 82. While the original Galaxy Zoo project identified galaxies as early-typs, late-types, or mergers, GZ2 measures finer morphological features. THese include bars, bulges, and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the ful public data release for the project, including measures of accuracy and bias. The majority (>90%) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars, and arm curvature. Both the raw and reduced data products can be obtained in electronic format at http://data.galaxyzoo.org.
1308.3551
Window effect in the power spectrum analysis of a galaxy redshift survey
Sato, et al
Investigate the effect of the window function on the multipole power spectrum in two different ways. Consider the convolved PS including the window effect, which is obtained by following the familiar (FKP) method developed by Feldman, Kaiser and Peacock. Show how the convolved multipole PS is related to the original PS, using the multipole moments of the window function. Second, investigate the deconvolved PS, which is obtained by using the Fourier deconvolution theorem. In the second approach, measure the multipole PS deconvolved from the window effect. Demonstrate how to deal with the window effect in these two approaches, applying them to the SDSS LRG sample.
1308.3617
The peculiar light curve of the Symbiotic Star AX Per of the last 125 years
Leibowitz, Formiggini
Analyze the last 125 years optical light curve of the symbiotic star AX Per through correlations discovered in its PS. The data were assembled from the literature and from the AAVSO database. A series of 6 major outbursts dominate the light curve. They are presented in the PS as 13 harmonics of the fundamental frequency fa=1/Pa=1/23172 day^-1. Refer to them as the "red" frequencies. Oscillations with the binary periodicity of the system Pb=1/fb=381.48d are also seen in the light curve, with particularly large amplitudes during outbursts. The fb peak in the PS is accompanied by 13 other peaks on each side, which is referred as the "blue" frequencies. A distinct structure in the frequency distribution of the blue peaks, as well as in their peak power are best interpreted as reflecting beating of the 13 "red" frequencies with the binary one. Suggest that the major outbursts of the system result from events of intense mass loss from the giant star. Mass accretion onto the hot component, partially through the L1 point of the system, took place in the last 125 years at a rate that oscillated with the 13 first harmonics of the fa frequency. The binary orbit is slightly eccentric and periastron passages induced modulation of the L1 accretion at the binary frequency. Hence the fb oscillations in the brightness of the star of amplitude that is modulated by the "red" frequencies of the system.
1308.3704
Searching for Oscillations in the primordial power spectrum: perturbative approach (Paper I)
Meerburg, Spergel, Wandelt
Present a new method for searching for oscillatory features in the primordial PS. A wide variety of models predict these features in one of two different flavors: logarithmically spaced oscillations and linearly spaced oscillations. The proposed method treats the oscillations as perturbations on top of the scale-invariant PS, allowing variation of all cosmological parameters. This perturbative approach reduces the computational requirements for the search as the transfer functions and their derivatives can be precomputed. Show that the most significant degeneracy in the analysis is between the distance to last scattering and the overall amplitude at low frequencies. For models with logarithmic oscillations, this degeneracy leads to an uncertainty in the phase. For linear spaced oscillations, it affects the frequency of the oscillations. In this paper (one out of two), test code on simulated Planck-like data, and show ability to recover fiducial input oscillations with an amplitude of a few times order 1e-2. Apply the code to WMAP9 data and confirm the existence of two intriguing resonant frequencies for log spaced oscillations. For linear spaced oscillations, find a single resonance peak. Use numerical simulations to assess the significance of these features and conclude that the data do not provide compelling evidence for the existence of oscillatory features in the primordial spectrum.
1308.3705
Searching for oscillations in the primordial power spectrum: constraints from Planck (Paper II)
Meerburg, Spergel
Continuation of the above. Log-spaced resonant features in WMAP9 has little to no significance. Confirm the presence of a several low frequency peaks earlier identified by the Planck team, but with a better improvement of fit (delta chi^2~12). Further investigate this improvement by allowing the lensing potential to vary as well, showing mild correlation between the amplitude of the oscillations and the lensing amplitude. Find that the improvement of the fit increases even more (~14) for the low frequencies that modify the spectrum in a way that mimics the lensing effect. Since these features were not present in the WMAP data, they are primarily due to better measurements of Planck at small angular scales. For linear spaced oscillations, find a maximum delta chi^2~13 scanning two orders of magnitude in frequency space, and the biggest improvements are at extremely high frequencies. Recover a best fit frequency very close to the one found in WMAP9, which confirms that the fit improvement is driven by low l. Further comparisons with WMAP9 show Planck contains many more features, both for linear and log space oscillations, but with a smaller improvement of fit. Discuss the improvement as a function of the number of modes and study the effect of the 217 GHz map, which appears to drive most of the improvement for log spaced oscillations. Conclude that none of the detected features are statistically significant.
1308.3707
Galaxy pairs in the Sloan digital sky survey - VIII: the observational properties of post-merger galaxies
Ellison, Mendel, Patton, Scudder
Present a study of 10,800 galaxies in close pairs and a sample of 97 post-mergers identified in SDSS. Find that the average central SFR enhancement (x3.5) and the fraction of starbursts (20%) peak in the post merger sample. The post-mergers also show a stronger deficit in gas phase metallicity that the closest pairs, being more metal-poor than their control by -0.09 dex. Combined with the observed trends in SFR and the timescales predicted in merger simulations, estimate that the post-mergers in sample have undergone coalescence iwthin the last few hundred Myr. In contrast with the incidence of SF galaxies, the frequency of AGN peaks in the post-mergers, outnumbering AGN in the control sample by a factor of 3.75. Moreover, amongst the galaxies that host an AGN, the black hole accretion rates in the closest pairs and post-mergers are higher by a factor of ~3 than AGN in the control sample. These results are consistent with a picture in the which star formation is initiated early on in the encounter, with AGN activity peaking post-coalescence.
No comments:
Post a Comment