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nyu_physics

Projects > Astroparticle Physics > Mock Catalogs for Ultrahigh Energy Cosmic Rays

Abstract: We provide realistic mock-catalogs of cosmic rays above 40 EeV, for a pure proton composition, assuming their sources are a random subset of ordinary galaxies in a simulated, volume-limited survey, for various choices of source density: 10-3.5 Mpc-3, 10-4 Mpc-3 and 10-4.5 Mpc-3. The spectrum at the source is taken to be E-2.3 and the effects of cosmological redshifting as well as photo-pion and e+ e- energy losses are included. The parent galaxy catalogs are two of the Las Damas "Carmen" catalogs with a number density of 4 10-4 Mpc-3 and extending to a redshift of z=0.165. We also provide mock galaxy catalogs in which both the true distances and redshifts including peculiar motion are given, generated from the Las Damas "Consuelo" simulation. The parent galaxy catalogs in this case extend to D = 290 Mpc or z = 0.07 and have an average number density of 0.02 Mpc-3. The catalogs are available for downloading from links herein.

In order to develop and test analysis tools for UHECR correlation studies, it is necessary to have mock catalogs of UHECRs under various realistic scenarios for the sources and magnetic deflections. There is no need at present to postulate a "new physics" origin for UHECRs, so the sources of UHECRs will be associated with the distribution of matter in the universe. The most popular types of source candidates reside in ordinary galaxies - for instance, AGNs and GRBs - and to first approximation these galaxies are a random subset of all galaxies. Here we provide mock UHECR catalogs assuming the sources are random galaxies. In this case, the key characteristic of a source population is its number density. The small number of doublets in the Auger events above 57 EeV leads to the lower bound of 61 on the number of sources producing them (Auger, 2008); this in turn leads to a lower bound on the source density of about 3 10-5 Mpc-3 (Farrar & Gruzinov,2009). Simulations of the spectrum suggest a density of 10-4 Mpc-3 (Takami et al, 2006). Therefore, we provide catalogs for the source density hypotheses 10-3.5 Mpc-3 ,10-4 Mpc-3 and 10-4.5 Mpc-3.

UHECR and source galaxy catalogs for E>40 EeV

To allow for a realistic treatment of CRs in the GZK transition region from 40-60 EeV, the galaxy catalog used to produce the UHECR mocks must be volume-limited to a much larger depth than is available in present-day "all sky" galaxy surveys, the best of which are 2MRS and PSCz. In particular, the galaxy catalog from which the source catalog is derived must be considerably denser than 10-3.5 Mpc-3 to simulate a scenario in which the source catalog has that density, and yet not every galaxy hosts a UHECR source. Therefore, we make use of the "Las Damas" mock galaxy catalogs (McBride et al, 2012, in preparation) which are created using LCDM simulations (Omega_M = 0.25, Omega_DE = 0.75, H0 = 70 km/s/Mpc , sigma_8 = 0.8 and n_s = 1) combined with an algorithm for populating the DM halos with galaxies, that is tuned to reproduce the SDSS observations. See http://lss.phy.vanderbilt.edu/lasdamas/ for full details.

We start with two Las Damas "Carmen" catalogs which are volume-limited for Mr < -21 (includes all galaxies with Mr = -21 and brighter) to a redshift z = 0.165, and have a number density of 4 10-4 Mpc-3 or log(n) = -3.38 . They are:

  • Carmen02_Mr21_Master.dat - 522769 galaxies

  • Carmen27_Mr21_Master.dat - 520277 galaxies

The local structure in the two catalogs can be seen in Fig. 1. The galaxies in each file are ordered by increasing redshift and each has a unique id with the format mgC<catID>_<N> where catID is either 02 or 27 and N is a unique integer that corresponds to the galaxy position in the redshift ordered list.

Fig 1: Local density of galaxies in Carmen02_Mr21_Master (left) and Carmen27_Mr21_Master (right) in a 4000 km/s slice centered on the origin.

Then, we randomly subsample each catalog to obtain sets of catalogs at lower densities. We create one catalog with log(n)=-3.5 for each of Carmen02 and Carmen27.

  • mockgalsCarmen02,3.5.dat

  • mockgalsCarmen27,3.5.dat

We create 3 independent mock UHECR-source catalogs with log(n) = -4 for each of Carmen02 and Carmen27:

  • mockgalsCarmen02,4.0,R<i>.dat where i=1,2,3

  • mockgalsCarmen27,4.0,R<i>.dat where i=1,2,3

We create 3 independent mock UHECR-source catalogs with log(n) = -4.5 for each of Carmen02 and Carmen27:

  • mockgalsCarmen02,4.5,R<i>.dat where i=1,2,3

  • mockgalsCarmen27,4.5,R<i>.dat where i=1,2,3

In all of these source catalogs, the file format is RA DEC z id. The id field gives the id of the galaxy to allow comparison with the relevant master catalog.

From these mock-source catalogs, we create mock UHECR catalogs from a given mock-source catalog by choosing a galaxy at random, with a probability pi = wijwj, with wi=ri-2, where ri is the distance of the ith galaxy. (Distance, not redshift, is used here because the effects of peculiar motion can lead to up to 20 Mpc shifts in the distance with respect to that calculated from the Hubble flow.) A CR from this galaxy is then assigned an energy according to an injection energy spectrum and propagated to Earth. Energy loss from redshifting as well as photo-pion and e+e- production is included. In the simulations presented here, the CR is assumed to be a proton; the injection spectrum is proportional to E-2.3 and ranges from 40 to 1000 EeV. If the energy after propagation is greater than 40 EeV, this proton is kept as an event. This procedure of source sampling and propagation is repeated until the desired number of events have been kept. Fig. 2 shows the final energy distribution as a function of redshift (actually, distance expressed as an equivalent redshift without peculiar motion).

Fig. 2: Distribution of energies at Earth, as a function of redshift of source.

The resulting catalogs are:

  • mockgalsCarmen02,3.5,CRs.dat

  • mockgalsCarmen27,3.5,CRs.dat

  • mockgalsCarmen02,4.0,R<i>,CRs.dat, i=1,2,3

  • mockgalsCarmen27,4.0,R<i>,CRs.dat, i=1,2,3

  • mockgalsCarmen02,4.5,R<i>,CRs.dat, i=1,2,3

  • mockgalsCarmen27,4.5,R<i>,CRs.dat, i=1,2,3

generated using the above mock-galaxy catalogs of the indicated source densities. Each file contains 100,000 mock cosmic rays. The file format is:

CRId E(EeV) srcID srcZ srcRA srcDec InjectionE Ra1Deg Dec1Deg ... Ra8Deg Dec8Deg

where:

  • CRId is an integer id

  • E is the energy of the CR at earth

  • srcID is the id of the source galaxy

  • srcZ, srcRA and srcDec are the redshift, RA and dec of the source galaxy

  • InjectionE is the energy at source for the CR (in eV)

  • Ra<i>Deg, Dec<i>Deg give smeared arrival directions for a smearing of i degrees (see below).

For each cosmic ray we provide the direction from which it would arrive if there were no deflection (srcRA and srcDec) as well as smeared arrival directions for an angular smearing of 1-8 degrees using a 2D Gaussian smearing. The Gaussian deflection is characterised by the angle σ, the spread of the 1D Gaussian distributions that combine to create the 2D Gaussian. 68% of the mass of the distribution is contained within an angle σ68=1.51σ. In each case the columns for the different deflections are labeled by σ

The full files can be downloaded here:

A full description of the catalogs can be found here.

Consuelo Catalogs with both distance and redshift (including peculiar motion)

To study possible sources of bias from peculiar velocity distortions, we provide galaxy catalogs with both true distances (RSpace), and redshifts including peculiar velocity distortions (ZSpace). The catalogs are constructed from the Las Damas "Consuelo" simulation. The large scale structure simulation is designed to accurately describe the clustering of SDSS galaxies down to an r-band magnitude of -17. Each galaxy has a luminosity associated with it that mimics the observed luminosity dependent clustering. As with the Carmen catalogs, two separate catalogs are generated from the same simulation by taking two different locations for the observer. The catalogs are volume limited out to z=0.07.

  • Consuelo_4005_Mr17 - 2240336 galaxies in RSpace, 2238387 galaxies in ZSpace.

  • Consuelo_4031_Mr17 - 2264943 galaxies in RSpace, 2277953 galaxies in ZSpace.

From these master catalogs we generate lower density subcatalogs by imposing luminosity thresholds that give subcatalogs with densities of 10-3.5 Mpc-3, 10-4.0 Mpc-3 and 10-4.5 Mpc-3.

For each density, and for both 4005 and 4031 master catalogs, we provide two galaxy catalog files:

  • RSpaceMock,<master catalog>,rho,<density>.data

  • ZSpaceMock,<master catalog>,rho,<density>.data

Each file has the format RA DEC z id. The z column in the RSpace mock is an effective redshift derived from the Hubble expansion and the true distance. In the ZSpace catalog, z includes a contribution from peculiar motion. Any blue shifted galaxies (z<0) are set to z=0 in the ZSpace mock catalogs. As the catalogs are cut-off at z=0.07, some galaxies that appear in the RSpace catalog do not appear in the ZSpace catalog and vice versa. The id field has the format mgC<catID>_R<N_R>_Z<N_Z> where catID is either 4005 or 4031 corresponding to the master catalog used, N_R is a unique integer that corresponds to the galaxy position in the redshift ordered master catalog in RSpace, N_Z is the integer id corresponding to the redshift ordered galaxy list in ZSpace.

We provide an accompanying set of mock proton cosmic rays that follow the format of the Carmen cosmic rays discussed above. For these cosmic rays we take an energy threshold of 60EeV. For these energies, 96% of cosmic rays are expected to originate within z=0.07, minimising the effect of the upper redshift limit on the cosmic ray production. The cosmic rays are generated using the RSpace mock catalogs in each case.

The full files can be downloaded here:

Deprecated Catalogs

Previous (deprecated) versions of the mock galaxy catalogs and cosmic rays can be downloaded here. These files have a different file structure to the current sets and do not contain multiple galaxy catalogs for the log(n) = -4, -4.5 samples.

Attribution

For proper attribution, we ask:

  • 1. Any use must credit the mock UHECR catalog project and cite Mock Catalogs for UHECR Studies, A. Berlind, N. Busca, G. R. Farrar, J. Roberts, arXiv:1112.4188 [astro-ph] and the Las Damas paper about the galaxy catalog from which it is derived: McBride et al, 2012, in preparation.

  • 2. If used in a publication, inform us about your work before submission.

  • 3. Let us know that you downloaded the catalogs, by sending an email to gf25@nyu.edu, so we can alert you if there are any problems discovered and about improvements implemented.

By downloading the mocks, you implicitly agree to these terms.