Wine and Cheese Fall 2014
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8 Sept 2014
K.G. Lee
The First z>2 Large-Scale Structure Map with Lyman-Alpha Forest Tomography from LBGs
The hydrogen Lyman-alpha forest is a long-established probe of large-scale structure at z>2, but is typically limited to 1D investigations along individual quasar sightlines. However, by instead targeting LBGs as background sources, the transverse separation between sources is ~Mpc and it becomes possible to do a 3D 'tomographic' reconstruction of the intergalactic medium. I will describe pilot observations using this technique, which has produced the first map of 3D large-scale structure at z~2.3 within the COSMOS field. Comparisons with coeval galaxies and simulations indicate that our map is truly tracing large-scale structure. This motivates the CLAMATO survey, which will map out a volume of (100 Mpc/h)^3 at z~2.3 and allow us to search for galaxy protoclusters, study the effect of environment on galaxy evolution, and constrain cosmological parameters.
Peter Behroozi
Close Pairs: Observational Probes for how Halo Accretion Impacts Galaxy Star Formation
We present a simple observational method for selecting galaxies whose host dark matter haloes have had significantly higher-than-average accretion rates. The method relies on using close pairs of galaxies to preferentially identify major dark matter halo mergers. Applying the method to central L∗ galaxies in the Sloan Digital Sky Survey (SDSS) DR10, we find no evidence for enhanced average or median star formation accompanying as much as an 0.3 dex increase in average halo accretion rates. However, population subsamples do show enhancements. Most interestingly, star-forming L∗ galaxies show a double peak in star formation enhancements as a function of the distance to the close pair. The larger (factor of 2) enhancement occurs for close pairs within 30 kpc, and the smaller (factor of 40%) enhancement occurs for pairs separated by 100-200 kpc (i.e., just within the virial radius of the larger galaxy’s halo). We discuss implications for conditional abundance matching models; while galaxy quenchedness cannot depend only on halo mass and recent accretion, reproducing the full behaviour of star-forming galaxies requires more advanced models than currently exist.
15 Sept 2014
Dheeraj Pasham
A 400 solar mass black hole revealed while mimicking a stellar-mass black hole
The brightest X-ray source in M82 has been thought to be an intermediate-mass black hole (100-10,000 solar masses) because of its extremely high X-ray luminosity and variability characteristics, although some models suggest that its mass may be only of the order of 20 solar masses. The previous mass estimates were based on scaling relations which used low-frequency characteristic timescales which have large intrinsic uncertainties. In stellar-mass black holes we know that the high frequency quasi-periodic oscillations that occur in a 3:2 ratio (100-450 Hz) are stable and scale inversely with black hole mass with a reasonably small dispersion. The discovery of such stable oscillations thus potentially offers an alternative and less ambiguous mass determination for intermediate-mass black
holes, but has hitherto not been realized. I will discuss the discovery of stable, twin-peak (3:2 frequency ratio) X-ray quasi-periodic oscillations from M82 X-1 at the frequencies of 3.32 Hz and 5.07 Hz and how this helps overcome the systematic uncertainties present in previous studies. Assuming we can extend the stellar-mass relationship, we estimate its black hole mass to be 428+/-105 solar masses. (See also this paper for more information.)
Alex Mendez
AEGIS+PRIMUS: The Clustering of X-ray, mid-IR, and radio-selected AGN
We present a clustering study of X-ray, mid-IR, and radio-selected active galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7 separate fields spanning ~10 square degrees. Using the cross-correlation of AGN with dense galaxy samples, we measure the clustering scale length and slope, as well as the bias, of AGN selected at different wavelengths. We compare the clustering of each AGN sample with galaxy samples with the same stellar mass, star formation rate, and redshift distributions as the AGN host galaxies and find no significant difference in the clustering of AGN with matched galaxy samples. The observed differences in the clustering of AGN selected at different wavelengths can therefore be explained by the clustering differences of their host populations. We further find no significant difference between the clustering of obscured and unobscured AGN, using IRAC or WISE colors or X-ray hardness ratio.
22 Sept 2014
Yacine Ali-Haïmoud
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Jim Green
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29 Sept 2014
Remco van den Bosch
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Omer Bromberg
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6 Oct 2014
Matthias Bartelmann
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Elizabeth Fernandez
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13 Oct 2014
Jeff Cummings
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Nick Stone
Stellar Tidal Disruption: the Role of General Relativity
In tidal disruption events (TDEs), stars passing too close to supermassive black holes (SMBHs) are violently torn apart. I will discuss several recent findings about the light curves of these events, including the role of orbital pericenter, ways in which the spin of the SMBH can be imprinted into TDE light curves, and possible emission of high frequency gravitational waves. I will also discuss an ongoing project focused on how highly eccentric debris streams from a TDE can circularize into a luminous accretion disk. It appears likely that the circularization process is mediated by general relativistic effects: circularization is aided by apsidal precession and hindered by nodal precession due to Lense-Thirring torques.
20 Oct 2014
Roseanne Cheng
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27 Oct 2014
Sarah Hoerst
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3 Nov 2014
Chun Ly
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10 Nov 2014
Dominika Wylezalek
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Kevin Lewis
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The hydrogen Lyman-alpha forest is a long-established probe of large-scale structure at z>2, but is typically limited to 1D investigations along individual quasar sightlines. However, by instead targeting LBGs as background sources, the transverse separation between sources is ~Mpc and it becomes possible to do a 3D 'tomographic' reconstruction of the intergalactic medium. I will describe pilot observations using this technique, which has produced the first map of 3D large-scale structure at z~2.3 within the COSMOS field. Comparisons with coeval galaxies and simulations indicate that our map is truly tracing large-scale structure. This motivates the CLAMATO survey, which will map out a volume of (100 Mpc/h)^3 at z~2.3 and allow us to search for galaxy protoclusters, study the effect of environment on galaxy evolution, and constrain cosmological parameters.
The brightest X-ray source in M82 has been thought to be an intermediate-mass black hole (100-10,000 solar masses) because of its extremely high X-ray luminosity and variability characteristics, although some models suggest that its mass may be only of the order of 20 solar masses. The previous mass estimates were based on scaling relations which used low-frequency characteristic timescales which have large intrinsic uncertainties. In stellar-mass black holes we know that the high frequency quasi-periodic oscillations that occur in a 3:2 ratio (100-450 Hz) are stable and scale inversely with black hole mass with a reasonably small dispersion. The discovery of such stable oscillations thus potentially offers an alternative and less ambiguous mass determination for intermediate-mass black holes, but has hitherto not been realized. I will discuss the discovery of stable, twin-peak (3:2 frequency ratio) X-ray quasi-periodic oscillations from M82 X-1 at the frequencies of 3.32 Hz and 5.07 Hz and how this helps overcome the systematic uncertainties present in previous studies. Assuming we can extend the stellar-mass relationship, we estimate its black hole mass to be 428+/-105 solar masses. (See also this paper for more information.)
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In tidal disruption events (TDEs), stars passing too close to supermassive black holes (SMBHs) are violently torn apart. I will discuss several recent findings about the light curves of these events, including the role of orbital pericenter, ways in which the spin of the SMBH can be imprinted into TDE light curves, and possible emission of high frequency gravitational waves. I will also discuss an ongoing project focused on how highly eccentric debris streams from a TDE can circularize into a luminous accretion disk. It appears likely that the circularization process is mediated by general relativistic effects: circularization is aided by apsidal precession and hindered by nodal precession due to Lense-Thirring torques.
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