Daisy Mak | University of Southern California (original) (raw)

Papers by Daisy Mak

We perform a Fisher matrix analysis to forecast the capability of ongoing and future Sunyaev-Zeld... more We perform a Fisher matrix analysis to forecast the capability of ongoing and future Sunyaev-Zeldovich cluster surveys in constraining the deviations from Gaussian distribution of primordial density perturbations. We use the constraining power of the cluster number counts and clustering properties to forecast limits on the fNL parameter. The primordial non-Gaussianity (NG) effects on the mass function and halo bias are considered. We adopt self-calibration for the mass-observable scaling relation and evaluate constraints for the South Pole Telescope, Planck, CCAT-like, South Pole Telescope polarization survey, and Atacama Cosmology Telescope polarization survey. We show that the scale dependence of the halo bias induced by the local NG provides strong constraints on fNL, while the results from number count are two orders of magnitude worse. When combining information from number counts and the power spectrum, the Planck cluster catalog provides the tightest constraint with σfNL=7 (68% C.L.) even for relatively conservative assumptions on the expected cluster yields and systematics. This value is a factor of 2 smaller than the 1σ error as measured by WMAP cosmic microwave background measurements and comparable to what is expected from Planck. We find that the results are mildly sensitive to the mass threshold of the surveys but strongly depend on the survey coverage; a full-sky survey like Planck is more favorable because it can probe longer wavelength modes that are most sensitive to NG effects. In addition, the constraints are largely insensitive to priors on nuisance parameters as they are mainly driven by the power spectrum probe, which has a mild dependence on the mass-observable relations.

Arxiv preprint arXiv: …, Jan 1, 2011

We investigate the constraining power of current and future Sunyaev-Zeldovich cluster surveys on ... more We investigate the constraining power of current and future Sunyaev-Zeldovich cluster surveys on the f (R) gravity model. We use a Fisher matrix approach, adopt self-calibration for the massobservable scaling relation, and evaluate constraints for the SPT, Planck, SPTPol and ACTPol surveys. The modified gravity effects on the mass function, halo bias, matter power spectrum, and mass-observable relation are taken into account. We show that, relying on number counts only, the Planck cluster catalog is expected to reduce current upper limits by about a factor of four, to σ f R0 = 2 × 10 −5 (68% confidence level) while SPT, SPTPol and ACTPol yield about 3 × 10 −5 . Adding the cluster power spectrum further improves the constraints to σ f R0 = 5 × 10 −6 for Planck and σ f R0 = 2 × 10 −5 for SPTPol, pushing cluster constraints significantly beyond the limit where number counts have no constraining power due to the chameleon screening mechanism. Further, the combination of both observables breaks degeneracies, especially with the expansion history (effective dark energy density and equation of state). The constraints are only mildly worsened by the use of self-calibration but depend on the mass threshold and redshift coverage of the cluster samples.

The Astrophysical Journal, Jan 1, 2011

We predict the performance of the Planck satellite in determining the bulk flow through kinetic S... more We predict the performance of the Planck satellite in determining the bulk flow through kinetic Sunyaev-Zeldovich (kSZ) measurements. As velocity tracers, we use ROSAT All-Sky Survey (RASS) clusters as well as expected cluster catalogs from the upcoming missions Planck and eRosita (All-Sky Survey: EASS). We implement a semi-analytical approach to simulate realistic Planck maps as well as Planck and eRosita cluster catalogs. We adopt an unbiased kinetic SZ filter (UF) and matched filter (MF) to maximize the cluster kSZ signal to noise ratio. We find that the use of Planck CMB maps in conjunction with the currently existing ROSAT cluster sample improves current upper limits on the bulk flow determination by a factor ∼ 5 (∼ 10) when using the MF (UF). The accuracy of bulk flow measurement increases with the depth and abundance of the cluster sample: for an input bulk velocity of 500 km/s, the UF recovered velocity errors decrease from 94 km/s for RASS, to 73 km/s for Planck and to 24 km/s for EASS; while the systematic bias decreases from 44% for RASS, 5% for Planck , to 0% for EASS. The 95% upper limit for the recovered bulk flow direction ∆α ranges between 4 • and 60 • depending on cluster sample and adopted filter. The kSZ dipole determination is mainly limited by the effects of thermal SZ (tSZ) emission in all cases but the one of EASS clusters analyzed with the unbiased filter. This fact makes the UF preferable to the MF when analyzing Planck maps.

The Astrophysical …, Jan 1, 2011

We have looked for bulk motions of galaxy clusters in the WMAP 7 year data. We isolate the kineti... more We have looked for bulk motions of galaxy clusters in the WMAP 7 year data. We isolate the kinetic Sunyaev-Zeldovich (SZ) signal by filtering the WMAP Q, V and W band maps with multifrequency matched filters, that utilize the spatial properties of the kinetic SZ signal to optimize detection. We try two filters: a filter that has no spectral dependence, and a filter that utilizes the spectral properties of the kinetic and thermal SZ signals to remove the thermal SZ bias. We measure the monopole and dipole spherical harmonic coefficients of the kinetic SZ signal, as well as the ℓ = 2 − 5 modes, at the locations of 736 ROSAT observed galaxy clusters. We find no significant power in the kinetic SZ signal at these multipoles with either filter, consistent with the ΛCDM prediction. Our limits are a factor of ∼ 3 more sensitive than the claimed bulk flow detection of Kashlinsky et al. (2009). Using simulations we estimate that in maps filtered by our matched filter with no spectral dependence there is a thermal SZ dipole that would be mistakenly measured as a bulk motion of ∼ 2000 − 4000 km/s. For the WMAP data the signal to noise ratio obtained with the unbiased filter is almost an order of magnitude lower.

The Astrophysical …, Jan 1, 2007

We report the identification of a recurrent ultraluminous X-ray source (ULX), a highly absorbed X... more We report the identification of a recurrent ultraluminous X-ray source (ULX), a highly absorbed X-ray source (possibly a background AGN), and a young supernova remnant near the center of the starburst galaxy M82. From a series of Chandra observations taken from 1999 to 2005, we found that the transient ULX first appeared in 1999 October. The source turned off in 2000 January, but later reappeared and has been active since then. The X-ray luminosity of this source varies from below the detection level (∼ 2.5 × 10 38 ergs s −1 ) to its active state in between ∼ 7 × 10 39 ergs s −1 and 1.3 × 10 40 ergs s −1 (in the 0.5-10 keV energy band) and shows unusual spectral changes. The X-ray spectra of some Chandra observations are best fitted with an absorbed powerlaw model with photon index ranging from 1.3 to 1.7. These spectra are similar to those of Galactic black hole binary candidates seen in the low/hard state except that a very hard spectrum was seen in one of the observations. By comparing with near infrared images taken with the Hubble Space Telescope, the ULX is found to be located within a young star cluster. Radio imaging indicates that it is associated with a H II region. We suggest that the ULX is likely to be a > 100M ⊙ intermediate-mass black hole in the low/hard state. In addition to the transient ULX, we also found a highly absorbed hard X-ray source which is likely to be an AGN and an ultraluminous X-ray emitting young supernova remnant which may be related to a 100-year old gamma-ray burst event, within 2 arcsec of the transient ULX.

HKU Theses Online (HKUTO), Jan 1, 2008

of thesis entitled X-RAY OBSERVATIONS OF THE STARBURST GALAXY IC 342