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Constrained Realization Images

These pages include:

• high resolution versions of figures published in the paper "Simulating the Formation of the Local Galaxy Population"
• high resolution versions of the figures published in the paper "Voids in the Simulated Local Universe"
• slices through the simulations
• images showing specific properties of the galaxies on top of the dark matter
• images from smoothed density fields
• and a movie showing the galaxy distribution on spherical shells.

Smoothed Density Fields

To get a more qualitative visual impression, we have smoothed the galaxy distribution with a gaussian filter, and then projected the resulting density field on the sky, in FK4 coordinates and on the supergalactic plane, in SG coordinates

FK4 projections of smoothed number density of galaxies

• slice within 4000 < cz < 8000 km/s, with smoothing centers at 6000 km/s
• 10 Mpc/h smoothing length
• first image: UZC at top, PSCZ at bottom
• second image: LCDM at top, TCDM at bottom : consistenty with both constrioned realizations sampling the same density field. Also compare LCDM,TCDM with PSCZ which was used to generate the IC field.

FK4 relative levels of smoothed number density of galaxies

• slice within 4000 < cz < 8000 km/s, with smoothing centers at 6000 km/s
• 10 Mpc/h smoothing length
• first picture : UZC at top, PSCZ at bottom
• 2nd picture : LCDM at top, TCDM at bottom

Overdensities in number of galaxies in SG plane for LCDM & TCDM

TCDM model at right, LCDM at left.

Smoothing radius of 5Mpc/h at top, 10Mpc/h bottom

The selected slice is [-50., 50.] Mpc/h in SGX & SGY

• [-20.,20.] Mpc/h in SGZ for 10 Mpc/h smoothing length
• [-10.,10.] Mpc/h in SGZ for 5 Mpc/h smoothing length

Overdense contours are full lines, underdense dash-dotted lines, labels display the overdensity / mean smoothing value over the selected region.

Click for larger image

Same data as before, now LCDM is at top, TCDM at the bottom.

Click for larger image

Click for larger image

Voids

Constrained crealizations of the Local Universe are also ideal to study the simulated population of galaxies in voids and to evaluate to which extent semi-analytic models (to their luminosity resolution limit) successfully reproduce voids as large and as empty as the nearby ones. We have checked (astro-ph/0201193) whether various galaxy and halo populations selected according to observationally relevant quantities could be considered to be homogeneously distributed with respect to the bright spirals.

Down to MB=-16.3, we came up wih negative conclusions for a possible homogeneous population.

Pictures are available here, and halo and galaxy catalogues used for the prospection of simulated voids can be downloaded from page 2, data download.

H. Mathis and S. D. M. White

High resolution Figure 1 (3 images) for astro-ph/0201193

In the Void region and the Virgo cluster, we show all galaxies down to M_B=-16.3 and M_B=-17 respectively. The latter is limited to avoid saturating the cluster region.

In the slice extracted from the "full simulation" (thickness 30 Mpc/h in the SGZ direction and centred on the SG plane), we only plot reference, L* spiral galaxies.

The colour and size of the symbols scale with the B-V index and the B-band luminosity of the galaxies.

download full-sized image (1036x1036 pixels)

download full-sized image (1036x1036 pixels)

download full-sized image (1036x1036 pixels)

Zoom out : 50 Mpc/h wide and 15 Mpc/h thick region centred on Figure 1

Click above the pictures to expand the image to full size : 1024x1024 pixels, in gif format. Note that the top right corners of the pictures extend to the low-resolution region of the simulation where we did not follow galaxy formation.

We caution that although we show the same galaxy population beyond the luminosity resolution limit as before, the colour scale for the symbols used in the following pictures has been modified with respect to the one used in the preprint, for better rendering of the population in the wider slice. We also provide below with a picture of the galaxy distribution in the 24 Mp/h cubic region discussed so far in that new colour scale, for meaningful comparison :

Image 1: Dark matter and galaxies brighter than the luminosity resolution limit (MB=-16.3) in a slice of thickness 15 Mpc/h and width 50 Mpc/h encompassing the SG plane and projected along SGZ. The slice is centred on the "void" shown in Section 2 of astro-ph/0201193.

download full-sized image (1024 x 1024 pixels)

Image 2: Distribution of the 70% least luminous galaxies brighter than the luminosity resolution limit in the same slice as above (open circles) compared to the distribution of the remaining most luminous objects (filled symbols).

download full-sized image (1024 x 1024 pixels)

Image 3: Distribution of galaxies in the 24 Mpc/h cube considered in Section 2 of astro-ph/0201193, but with a symbol colour scale similar to that used for the picture above (50x50x15 Mpc/h slice). Compare this image with the one below the title.

Probing the effect of the density of reference galaxies on nearest neighbour statistics

The next plots illustrate the effect of using a denser set of reference galaxies (new sample, with relaxed selection criteria) on the nearest neighbour statistics compared to the results obtained using the astro-ph/0201193 sample (initial sample). Recall that we are computing all statistics in real space.

Click the plots to view them in full extent (corresponding .ps.tar.gz files can then be downloaded).

• The first series of 4 panels below correspond to a new set of reference galaxies selected by their luminosity : -20.5 < M_B < -18.5 and the presence of a bulge, of any size. We find 26457 such galaxies in the high-resolution zone : comoving density 0.012 (h/Mpc)³. Note that at a factor of three down from the top of the distribution, the indices associated to the curves decrease monotonically from left (test sample #7) to right (test sample #1), as for the initial nearest neighbour statistics. We redirect to the preprint for the description of the test samples.

• The second series of 4 panels recall the nearest neighbour statistics for the initial set of reference galaxies used in the preprint : -21.8 < M_B < -19.8 and morphological type Sa/Sb/Sc as obtained with the Simien and de Vaucouleurs (1986) criterion : 1 < M_B,bulge-M_B,total < 2.2. We found 1471 such galaxies in the high-resolution zone : comoving density 0.00069 (h/Mpc)³.

download full-sized image

download full-sized image

We now focus on the samples associated with the two outermost galaxy property bins : samples #1 and #7, with the exception of the 6th "halo mass" sample for reasons of noise. We also plot the result of randomizing within the simulation the positions of one third of the test objects.

-The top (image 1) and bottom (image 2) pictures correspond to the new and old(initial) set of reference galaxies respectively.

-Let us compare nearest neighbour distances at a factor of three down from the top of the distribution in both samples. As expected, using more reference galaxies substantially reduces D_oo : at this population fraction :

• D_oo,new=2.5 Mpc/h
• D_oo,old=8.8 Mpc/h

-Distances from test samples to the nearest reference galaxy decrease as well, but the ratios D_to/D_oo increase. We quote D_to,new for the first sample of each set:

• D_{to,new,halo mass 1}= 3.1 instead of D_{to,old,halo mass 1}= 9.2 Mpc/h, and a 18% increase in the ratio D_to/D_oo
• D_{to,new,luminosity 1}= 2.8 instead of D_{to,old,luminosity 1}= 9 Mpc/h, and a 10% increase in the ratio D_to/D_oo
• Dto,new,colour 1= 3.3 instead of Dto,old,colour 1= 9.45 Mpc/h, and a 23% increase in the ratio Dto/Doo

Because our algorithm does not allow Dto=0, test samples overlapping in luminosity with the new reference sample will be biased toward higher distances. However, there is no overlap in luminosity between the new reference galaxies and the galaxies in our first, faintest luminosity test sample, where we will therefore gauge the effect of denser sampling (some 20 times denser).
In this case, the measured 10% increase in the ratio Dto/Doo proves that the effect is quite limited and does not change our conclusions that GL₁ does not constitute a homogeneous population with respect to the new reference objects. We stress that the new reference sample has 20 times more objects.

Note the sharp decrease in the plots for D_to in the right hand side windows of the plots with the new reference population. This is because a large faction of the test objects in the samples HM₆, GL₇ and GC₇ are galaxies in massive haloes. They find their nearest new reference galaxies as satellites or central objects within the same halo . The same trend was already apparent in the old sample of reference objects (compare to the corresponding plots in the Figure in image 2), but was much weaker. Recall that HM₆, GL₇ and GC₇ contain the most massive haloes, the brightest and the reddest galaxies respectively.

Image 1: The dashed line gives D_to for the extreme bins of each sample (1 and 7, with the exception of HM₆). The dash-dotted lines show the corresponding D_to after randomizing the positions of one third of the objects in each test sample, and the solid curve gives D_oo for the new set of reference galaxies. The dotted line is the same as in the Figures above.

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Image 2: Same as for the top picture, but with the initial set.

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Comments to: H. Mathis hmathis@mpa-garching.mpg.de