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S3-SAX-Box is a simulation of galaxies in the cubic simulation box of the Millennium simulation. Each galaxy is specified by an array of intrinsic properties, which include detailed attributes of neutral atomic (HI) and molecular (H2) hydrogen and associated luminosities of HI and CO emission lines.

Simulation Method

The Millennium dark matter simulation (Springel et al., 2005) is a numerical simulation of the evolution of cosmic structure in a cubic simulation box with a constant comoving side length sbox. This simulation assumed a Lambda-Cold Dark Matter (ΛCDM) cosmology with the parameters ΩΛ = 0.75, Ωmatter = 0.25, Ωbaryon = 0.045, h = 0.73 (Hubble parameter), σ8 = 0.9. Using the evolving mass skeleton of the Millennium simulation, Croton et al. (2006) and De Lucia et al. (2007) simulated the formation and the cosmic evolution of galaxies in a semi-analytic way. The resulting galaxy simulation is available on the German Astrophysical Virtual Observatory under the name "DeLucia2006a".

In DeLucia2006a-simulation, the cold gas in galaxies was treated as a single component, hence masking the complexity of atomic and molecular phases. Obreschkow et al. (2009b) therefore post-processed the DeLucia2006-simulation to assign HI and H2 to galaxies, based on their total cold gas masses and a few additional galaxy properties. The method for this splitting relies on the empirical relation between the pressure of the Interstellar Medium (ISM) and the local H2/HI-ratio in galaxies. This approach permitted to (i) split total cold gas masses between HI, H2, and Helium, (ii) to assign realistic sizes to both the HI- and H2-disks, and (iii) to evaluate the corresponding velocity profiles and shapes of the characteristic radio emission lines. Detailed explanations and results were presented in Obreschkow et al. (2009b). Given an H2 mass for each galaxy Obreschkow et al. (2009c) further estimated the luminosities of various CO emission lines.

The figure below shows the local HI-mass function and the local CO(1-0)-luminosity function of this post-processed semi-analytic simulation (solid lines). The empirical data (dots and error bars) represent the inferences of the HI-Parkes All Sky Survey (HIPASS, Zwaan et al., 2005) and the FCRAO extragalactic CO survey (Keres et al., 2003, corrected for a variable CO/H2-conversion by Obreschkow et al., 2009a).


Data structure and access

According to the nomenclature of the DeLucia2006a-simulation, "one galaxy" means one galaxy at one specific time step in its cosmic evolution. In other words, progenitors and descendants of a galaxy at different discrete time steps in the simulation are called "different galaxies" and they are ascribed different galaxy identifiers ("galaxyid's"). This indexing is practical, when galaxies have complex merger histories, where progenitors are not unique. The DeLucia2006a-catalog contains about 1.1×109 galaxies, distributed over 64 discrete cosmic time steps. About 2.7×107 of those galaxies are at the last time step, corresponding to the redshift z = 0. In the classical nomenclature, where each "galaxy" is an evolving object, one could therefore say that the DeLucia2006a-simulation tackles the cosmic evolution of about 2.7×107 galaxies.

The 1.1×109 galaxies in the DeLucia2006a-catalog were stored in a table with exactly one row per galaxy. The columns of this table represent the different galaxy properties as described here. Using the post-processing summarized above (see also Obreschkow et al. 2009b, Obreschkow et al. 2009c), additional properties for HI, H2, and CO were assigned to each galaxy. These properties were stored in a second table, which lists the same galaxies in the same order as the DeLucia2006a-catalog. The columns of the second galaxy table are shown in the table below.

Both galaxy tables, i.e. the DeLucia2006a-catalog and the extended HI/H2/CO properties, can be accessed online via the structured query language (SQL) interface of the German Astrophysical Virtual Observatory (registration required to access the tables). This sophisticated interface allows the user to perform far more complex tasks than just downloading the tables. For example, it is possible to construct mass and magnitude limited samples, or to directly request the simulated HI-mass functions, H2-mass functions, and CO-luminosity functions at various redshifts. Such queries can be built using the sample queries G1−G6 on the query page.


1galaxyidBIGINTGalaxy identifier in the "DeLucia2006a" catalog of the Millennium database-
2hubbletypeFLOATNumerical Hubble type along the RC2 sequence −6,...,10-
3bulgetototalFLOATBulge-to-total mass ratio-
4rmolcFLOATH2/HI surface density ratio at the disk center-
5gasscaleradiusFLOATExponential scale radius of the cold gas disk (HI+H2+He)kpc
6coldgasmassFLOATCold gas of De Lucia et al. 2006a corrected by the factor zetaMsun
10hilumFLOATVelocity-integrated luminosity of HI-line at 1.42 GHz (rest frame)Jy km/s Mpc2
11colum_1_0FLOATVelocity-integrated luminosity of CO(1-0)-line at 115 GHz (rest frame)Jy km/s Mpc2
12colum_2_1FLOATVelocity-integrated luminosity of CO(2-1)-line at 231 GHz (rest frame)Jy km/s Mpc2
13colum_3_2FLOATVelocity-integrated luminosity of CO(3-2)-line at 346 GHz (rest frame)Jy km/s Mpc2
14colum_4_3FLOATVelocity-integrated luminosity of CO(4-3)-line at 461 GHz (rest frame)Jy km/s Mpc2
15colum_5_4FLOATVelocity-integrated luminosity of CO(5-4)-line at 576 GHz (rest frame)Jy km/s Mpc2
16colum_6_5FLOATVelocity-integrated luminosity of CO(6-5)-line at 692 GHz (rest frame)Jy km/s Mpc2
17colum_7_6FLOATVelocity-integrated luminosity of CO(7-6)-line at 807 GHz (rest frame)Jy km/s Mpc2
18colum_8_7FLOATVelocity-integrated luminosity of CO(8-7)-line at 922 GHz (rest frame)Jy km/s Mpc2
19colum_9_8FLOATVelocity-integrated luminosity of CO(9-8)-line at 1037 GHz (rest frame)Jy km/s Mpc2
20colum_10_9FLOATVelocity-integrated luminosity of CO(10-9)-line at 1153 GHz (rest frame)Jy km/s Mpc2
21inclinationFLOATInclination : 0=face-on, pi/2=edge-on (used for CO-self absorption)rad
22cofillingfactorFLOAT0..1 Filling factor of molecular gas in surface-velocity space-
23hiradius_msunpcFLOATHI-radius where Sigma_HI = 1 Msun/pc2kpc
24hiradius_maxFLOATHI-radius where Sigma_HI is maximal (is 0, if HI peaks at the disk center)kpc
25hiradius_50maxFLOATHI-radius where Sigma_HI is at 50% of its maximum (outer solution)kpc
26hiradius_10maxFLOATHI-radius where Sigma_HI is at 10% of its maximum (outer solution)kpc
27hiradius_halfmassFLOATHI-radius containing half of the HI-masskpc
28h2radius_msunpcFLOATH2-radius where Sigma_H2 = 1 Msun/pc2kpc
29h2radius_50maxFLOATH2-radius where Sigma_H2 is at 50% of its maximumkpc
30h2radius_10maxFLOATH2-radius where Sigma_H2 is at 10% of its maximumkpc
31h2radius_halfmassFLOATH2-radius containing half of the H2-masskpc
32balanceradiusFLOATRadius where Sigma_HI = Sigma_H2kpc
33hilumcenterFLOATNormalized central luminosity density at rest-frames/km
34hilumpeakFLOATNormalized peak luminosity density at rest-frames/km
35hiwidthpeakFLOATLine width between the two horns of the HI-line profilekm/s
36hiwidth50FLOATLine width at 50% of peak luminosity densitykm/s
37hiwidth20FLOATLine width at 20% of peak luminosity densitykm/s
38columcenterFLOATNormalized central luminosity density at rest-frames/km
39columpeakFLOATNormalized peak luminosity density at rest-frames/km
40cowidthpeakFLOATLine width between the two horns of the molecular line profilekm/s
41cowidth50FLOATLine width at 50% of peak luminosity densitykm/s
42cowidth20FLOATLine width at 20% of peak luminosity densitykm/s