126 research outputs found
Phase statistics of the WMAP 7 year data
We performed a comprehensive statistical analysis using complex phases of the
a_lm coefficients computed from the most recent data of the Wilkinson Microwave
Anisotropy Probe (WMAP). Our aim was to confirm or constrain the presence of
non-Gaussianities in the data. We found phase correlations - that suggest
non-Gaussianity - at high-l in a_lm coefficients by applying various
statistical tests. Most of all, we detected a non-Gaussian signal reaching a
significance of 4.7 sigma using random walk statistics and simulations.
However, our conclusion is that the non-Gaussian behavior is due to
contamination from galactic foregrounds that show up in small scales only. When
masked out the contaminated regions, we found no significant non-Gaussianity.
Furthermore, we constrained the f_NL parameter using CMB simulations that mimic
primordial non-Gaussianity. Our estimate is f_NL=40 +/- 200, in agreement with
previous measurements and inflationary expectations.Comment: 4 pages, 4 figures, Accepted for Publication in A
Semi-automatic Removal of Foreground Stars from Images of Galaxies
A new procedure, designed to remove foreground stars from galaxy profiles is
presented. Although several programs exist for stellar and faint object
photometry, none of them treat star removal from the images very carefully. I
present my attempt to develop such a system, and briefly compare the
performance of my software to one of the well known stellar photometry
packages, DAOPhot. Major steps in my procedure are: (1) automatic construction
of an empirical 2D point spread function from well separated stars that are
situated off the galaxy; (2) automatic identification of those peaks that are
likely to be foreground stars, scaling the PSF and removing these stars, and
patching residuals (in the automatically determined smallest possible area
where residuals are truly significant); and (3) cosmetic fix of remaining
degradations in the image. The algorithm and software presented here is
significantly better for automatic removal of foreground stars from images of
galaxies than DAOPhot or similar packages, since: (a) the most suitable stars
are selected automatically from the image for the PSF fit; (b) after
star-removal an intelligent and automatic procedure removes any possible
residuals; (c) unlimited number of images can be cleaned in one run without any
user interaction whatsoever.Comment: 20 pages, TeX, 4 PostScript figures. Accepted for publication in the
PASP. Figures 2, 3, and 4 can be obtained from the following WWW pages:
http://astro.princeton.edu/~frei/papers.html (fast from the US) or:
http://hercules.elte.hu/~frei/papers.html (European mirror
Cross-correlation of WMAP7 and the WISE Full Data Release
We measured the cross-correlation of the Wilkinson Microwave Anisotropy Probe
(WMAP) 7 year temperature map and the full sky data release of the Wide-field
Infrared Survey Explorer (WISE) galaxy map. Using careful mapmaking and masking
techniques we find a positive cross-correlation signal. The results are fully
consistent with a Lambda-CDM Universe, although not statistically significant.
Our findings are robust against changing the galactic latitude cut from |b|>10
to |b|>20 and no color dependence was detected when we used WMAP Q, V or W
maps. We confirm higher significance correlations found in the preliminary data
release. The change in significance is consistent with cosmic variance.Comment: 5 pages, 4 figures, Accepted for publication in MNRAS Letter
A Catalog of Digital Images of 113 Nearby Galaxies
We present a digital catalog of images of 113 galaxies in this paper. These
galaxies are all nearby, bright, large and well resolved. All images were
recorded with charge coupled devices (CCDs) at the Palomar Observatory with the
1.5 meter telescope and at the Lowell Observatory with the 1.1 meter telescope.
At Palomar we used the Thuan--Gunn g, r and i photometric bands to take 3
images each of 31 spiral galaxies; at Lowell we used the B_J and R bands (2
images per galaxy) of the photometric system by Gullixson et al. (1995) to
observe 82 spirals and ellipticals. The galaxies were selected to span the
Hubble classification classes. All data are photometrically calibrated with
foreground stars removed. Important data on these galaxies published in the
"Third Reference Catalog of Bright Galaxies" (RC3) are recorded in the FITS
file headers. All files are available through anonymous FTP from
ftp://astro.princeton.edu/, through WWW at
http://astro.princeton.edu/~frei/galaxy_catalog.html, and Princeton University
Press will soon publish the data on CD-ROM.Comment: uuencoded compressed tar archive of postscript files (paper + 2
tables + 7 figures) Accepted for publication in the Astronomical Journa
Időben változó finomszerkezeti állandó az asztrofizikában = Temporally varying fine-structure constant in astrophysics
Tanulmálnyoztuk a csillagokbeli szén- és oxigéntermelés 3-alfa-rátától való függését. A C-12 magbeli 0+_2 állapot energiáját változtatva meghatároztuk a kis-, közepes- és nagytömegű csillagokban termelődött szén és oxigén mennyiségét. Eredményeink azt mutatják, hogy a nagytömegű csillagokbeli szén- és oxigéntermelés erősen függ a kezdeti tömegtől, és alapvető fontosságú a teljes evolúciós folyamat végigkövetése. A finomszerkezeti állandónak a közelmúltban megfigyelt kozmológiai léptékű változása azt eredményezi, hogy a C-12 atommag 0+_2 energiaszintjének helye időben változik. Ez a fentiek szerint izotóparány-eltolódáshoz vezet. Ennek eredményeként például módosulhattak a korai, fémben szegény csillagok által létrehozott gázfelhők izotóparányai, illetve a kozmológiai távolságmérésben használt Ia-típusú szupernovák szén-oxigén törzse, és így fényessége. Kifejlesztettünk egy primordiális nukleoszintézist modellező programot, és vizsgáltuk a keletkező elemgyakoriságok fizikai konstansoktól való függését. Megállapítottuk, hogy a kvarktömegek változására a Li-7 gyakorisága a leginkább érzékeny, ami esetleg oka lehet a megfigyelt primordiális litium anomáliának. A primordiális magreakcióknak az erős kölcsönhatás csatolási állandójától való függését vizsgálva azt találtuk, hogy a kritikus d(t,alfa)n reakcióbeli rezonancia poziciójára a vártnál sokkal kevésbé érzékenyek a gyakoriságok. | We have studied the dependence of the stellar carbon and oxygen production on the triple-alpha rate. By varying the 0+_2 state of C-12, we determined the amounts of carbon and oxygen, produced in low-, medium-, and high-mass stars. Our results show that the carbon- and oxygen production in massive stars strongly depend on the initial mass, and the full description of the complete stellar evolution is essential. The recently observed variation of the fine structure constant on cosmological scales leads to a temporal variation of the position of the 0+_2 state of carbon. This results in changes in the stellar isotope ratios. This may lead to changes in the isotope ratios in gas clouds produced in early metal-poor stars, or in the core and thus the brightness of type Ia supernovae, used in cosmological distance measurements. We have developed a computer model of primordial nucleosynthesis, and studied the dependence of the produced elemental abundances on the physical constants. We found that the Li-7 abundance is the most sensitive to changes in the quark masses, which may help to explain the primordial lithium anomaly. By studying the dependence of the primordial nuclear reactions on the coupling constant of the strong interaction, we have found that the elemental abundances are much less sensitive to the resonance position of the critical d(t,alpha)n reaction than expected
Pre-Merger Localization of Gravitational-Wave Standard Sirens With LISA I: Harmonic Mode Decomposition
The continuous improvement in localization errors (sky position and distance)
in real time as LISA observes the gradual inspiral of a supermassive black hole
(SMBH) binary can be of great help in identifying any prompt electromagnetic
counterpart associated with the merger. We develop a new method, based on a
Fourier decomposition of the time-dependent, LISA-modulated gravitational-wave
signal, to study this intricate problem. The method is faster than standard
Monte Carlo simulations by orders of magnitude. By surveying the parameter
space of potential LISA sources, we find that counterparts to SMBH binary
mergers with total mass M~10^5-10^7 M_Sun and redshifts z<~3 can be localized
to within the field of view of astronomical instruments (~deg^2) typically
hours to weeks prior to coalescence. This will allow targeted searches for
variable electromagnetic counterparts as the merger proceeds, as well as
monitoring of the most energetic coalescence phase. A rich set of astrophysical
and cosmological applications would emerge from the identification of
electromagnetic counterparts to these gravitational-wave standard sirens.Comment: 29 pages, 12 figures, version accepted by Phys Rev
MEASURING SPIRAL ARM TORQUES: RESULTS FOR M100
Spiral arms, if they are massive, exert gravitational torques that transport
angular momentum radially within galactic disks. These torques depend not on
the pattern speed or permanence of the arms but only on the nonaxisymmetric
mass distribution. Hence the torques can be measured from photometry. We
demonstrate this using CCD data for M100 (NGC 4321). Since we find
consistency among the three bands, we believe that dust and young stars in the
arms do not seriously bias our results. If the present epoch is representative,
the timescale for redistribution of angular momentum in M100 is Gyr, the
main uncertainty being the mass-to-light ratio of the disk.Comment: Uuencoded compressed PostScript (300k) - 26 pages, figs. 3-9;
submitted to AJ. Full PostScript version (with all figures) is available
through anonymous ftp at ftp://astro.princeton.edu/ognedin/Torque/paper.ps or
ftp://astro.princeton.edu/library/preprints/pop613.ps.Z or through WWW
http://www.astro.princeton.edu/~library/prep.htm
Fotometriai vöröseltolódások és az SDSS adatbázis = Photometric redshifts and the SDSS Science Archive
A kitűzött célokat messzemenően teljesítettük. Az általunk folyamatosan fejlesztett fotometrikus vöröseltolódás becslésének technika az SDSS hivatalos módszerévé vált, ennek segítségével készítettük el a publikus adatkibocsátások katalógusait. A fotometrikus vöröseltolódás becslés felhasználásával MgII abszorberek távolságát határoztuk meg spektroszkópiai észlelések nélkül, LRG-MgII korrelációs függvényeket, és halo tömeget becsültünk. Kimutattuk, hogy az MgII felhők nem virializálódnak, melyből sejtéseket lehet felállítani keletkezésük körülményeire. Az adatbázis indexelési technológiákat fejlesztve kialakítottunk egy több-dimenziós (pl. fotometriai) térben hatékonyan kereső keretrendszert, melyet integráltuk az SDSS adatbázis architektúrájába, újfajta kereséseket lehetővé téve. Elkészültek prototípusok, amelyek az adatok 2 és 3 dimenziós, az adatbázissal közvetlenül kölcsönható vizualizációját szolgálják. Bekapcsolódtunk a nemzetközi Virtuális Obszervatórium munkájába, és büszkén mondhatjuk, hogy a valójában működő eszközök (Spectrum and Filter Services, Footprint Services, SkyServer, CasJobs, SDSS WorldWind) jelentős hányada elsősorban a pályázatban résztvevő kollégák munkájának eredménye. A pályázat lehetővé tette számos diák bekapcsolódását a nemzetközi kutatásokba, mely több diploma- és PhD munka alapját képezte, hozzájárult a témavezető MTA doktori disszertációjának elkészítéséhez valamint új alapkutatási és kutatás-fejlesztési pályázatok elnyeréséhez. | The goals of the proposal have been fulfilled. Our photometric estimation technique became the official method to estimate galaxy redshifts for the SDSS. With our algorithm we have created the public catalogs for the yearly data releases. With the help of the estimated photometric redshifts we were able to measure the distance of MgII absorbers without spectroscopic observations, and estimated the LRG-MgII correlation function and the mass of halos. We have shown, that the MgII clouds are not virialized, which fact contributes to the understanding of their formation. The development of new database indexing techniques resulted in a new multidimensional search method, which has been integrated into the SDSS archive to search the magnitude space. We have created prototypes for interactive data visualization in 2 and 3 dimensions. We have joined the International Virtual Observatory Alliance, and most of the flagship tools (Spectrum and Filter Services, Footprint Services, SkyServer, CasJobs, SDSS WorldWind) are results of mostly colleagues participating in this project. The support of the project made possible for several students to join the international astronomical research community, several theses were based on this research, and it was a solid base for further grant proposals, where the work can be continued
Prompt Shocks in the Gas Disk Around a Recoiling Supermassive Black Hole Binary
Supermassive black hole binaries (BHBs) produced in galaxy mergers recoil at
the time of their coalescence due to the emission of gravitational waves (GWs).
We simulate the response of a thin, 2D disk of collisionless particles,
initially on circular orbits around a 10^6 M_sun BHB, to kicks that are either
parallel or perpendicular to the initial orbital plane. Typical kick velocities
(v_k) can exceed the sound speed in a circumbinary gas disk. While the inner
disk is strongly bound to the recoiling binary, the outer disk is only weakly
bound or unbound. This leads to differential motions in the disturbed disk that
increase with radius and can become supersonic at ~700 Schwarzschild radii for
v_k ~500 km/s, implying that shocks form beyond this radius. We indeed find
that kicks in the disk plane lead to immediate strong density enhancements
(within weeks) in a tightly wound spiral caustic, propagating outward at the
speed v_k. Concentric density enhancements are also observed for kicks
perpendicular to the disk, but are weaker and develop into caustics only after
a long delay (>1 year). Unless both BH spins are low or precisely aligned with
the orbital angular momentum, a significant fraction (> several %) of kicks are
sufficiently large and well aligned with the orbital plane for strong shocks to
be produced. The shocks could result in an afterglow whose characteristic
photon energy increases with time, from the UV (~10eV) to the soft X-ray
(~100eV) range, between one month and one year after the merger. This could
help identify EM counterparts to GW sources discovered by LISA.Comment: 4 pages, 3 figures, submitted to ApJ
Can Virialization Shocks be Detected Around Galaxy Clusters Through the Sunyaev-Zel'dovich Effect?
In cosmological structure formation models, massive non-linear objects in the
process of formation, such as galaxy clusters, are surrounded by large-scale
shocks at or around the expected virial radius. Direct observational evidence
for such virial shocks is currently lacking, but we show here that their
presence can be inferred from future, high resolution, high-sensitivity
observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. We study
the detectability of virial shocks in mock SZ maps, using simple models of
cluster structure (gas density and temperature distributions) and noise
(background and foreground galaxy clusters projected along the line of sight,
as well as the cosmic microwave background anisotropies). We find that at an
angular resolution of 2'' and sensitivity of 10 micro K, expected to be reached
at ~ 100 GHz frequencies in a ~ 20 hr integration with the forthcoming ALMA
instrument, virial shocks associated with massive M ~ 10^15 M_Sun clusters will
stand out from the noise, and can be detected at high significance. More
generally, our results imply that the projected SZ surface brightness profile
in future, high-resolution experiments will provide sensitive constraints on
the density profile of cluster gas.Comment: 15 pages, submitted to Ap
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