The MROBS Project

- Help & HowTo -

Hi guest


Q: What is the Millennium Run Observatory?

We have developed the Millennium Run Observatory (MRObs), a theoretical virtual observatory framework which uses virtual telescopes to `observe' semi-analytic galaxy formation simulations based on the suite of Millennium Run (MR) dark matter simulations.

Q: What is the purpose of the MRObs?

Q: Where can I read more about the technical details?

Q: What is the history of the MRObs?

Q: What data products does the MRObs provide?

A detailed overview of the data products can be found here.

Q: How do I submit requests, feedback, comments, questions, bug reports?

Please contact Roderik Overzier (overzier /\T or Gerard Lemson (lemson /\T

Q: Can I request my own simulated survey?

Yes. We will do our best to act on requests as long as we have the manpower and resources available. Please contact Roderik Overzier (overzier /\T to discuss survey requests.

Q: How should I cite or acknowledge the MRObs in my own work?

The main reference to the MRObs methods and data products is Overzier et al. (2012). If the MRObs data was of use to you in your own work, we would appreciate an acknowledgment (e.g. "This work made use of data provided by the Millennium Run Observatory").


Q: Which simulations are used by the MRObs?

Q: Which cosmologies are available in the MRObs?

We use the native WMAP1 cosmology of the original MR simulation, as well as the more recent WMAP7 cosmology through use of the halo scaling technique developed by Angulo & White (2010).


Q: Which semi-analytic models are being used by the MRObs?

We currently use the Guo et al. (2010) and Guo et al. (2012) semi-analytic model parameters derived for the WMAP1 and WMAP7 cosmologies, respectively. We are open to implementing other semi-analytic models for comparison as well.

Q: Which stellar population libraries are available?

We have currently implemented two population synthesis models: BC03 and M05.

Q: How was dust taken into account?


Q: Where can I get the lightcone catalogs?

Coming soon.

Q: Where can I find the lightcone catalogs with structural properties?

Coming soon.

Q: Where can I find the IGM correction tables?

Coming soon.

Q: How do I apply the IGM corrections to the lightcone catalogs?

Coming soon.

Q: Where do I find the filter curves that were used?

Coming soon.


Q: What is being simulated?

Galaxy models: The MRObs is not in the business of just making pretty pictures. We strive to build mock images based solely on simulations predictions. Currently, the semi-analytic models and lightcone techniques provide the positions and multi-band fluxes of objects, the scale-lengths of their (assumed to be) exponential disks, the equivalent radius of the (assumed to be) spheroidal bulge component, the bulge-to-total light ratios, and the inclinations and position angles of the disks (the bulges are spherical). Because the model disks are currently considered to be infinitely thin, we have added a temporary constraint that the inclinations can not go within 10% of edge-on. This has the effect of simulating some scaleheight to highly inclined disks.
Telescope/instrument models:
Survey models:

Q: What is not being simulated?

Our semi-analytical models do not currently predict galaxy morphologies beyond the distinction between exponential disks and bulges. The galaxies in our simulations therefore do not contain any of the non-smooth components that real galaxies have, such as spiral arms, star clusters, or lumpy structures. Although dust is included in the photometric modeling of the galaxies, the dust distribution is assumed to be smooth, acting as a screen. Therefore, no dust lanes are present in our images. Although galaxies definitely do merge in the simulations, and objects in the images can be found in all stages of the merger process, no tidal features would be seen in the images.

Q: How accurate are the telescope, instrument, and survey models?

The MRObs aims to be a flexible, legacy facility that can handle a great many telescopes, instruments, and survey strategies in an efficient and manageble way. This means that we try to find balance between the quality of our methods and practicality.
Building a highly versatile virtual observatory while simultaneously taking into account the enormous range of details pertaining to each particular telescope, camera, site and survey would be cumbersome, and such a project is undoubtedly better handled by the relevant project teams. That said, our modular approach makes it straightforward to implement more sophisticated recipes in the future as the MRObs project expands. We also make available to the community all our input catalogs, pre-observation maps, and modeling methods, in the hope that they can serve as input for more specialized image simulation pipelines that want to benefit from our extensive underlying cosmological framework and physically-motivated parameter space.

Q: Where do I find an overview of the simulated surveys?

Please see the Surveys Overview Table on the MRObs welcome page.

Q: Where do I find the details of each simulation?

Because the exact modeling techniques used may vary from one survey to another, users should check the detailed descriptions given in the data sections for each particular simulated survey. For some surveys we provide data products that were derived using different, complementary techniques.

Q: How do I interpret the keywords in the FITS headers?

A description of keywords found in the FITS headers of the images created by the MRObs can (not yet) be found here.


Q: How do I cross-match objects found in the images with objects in the Millennium Database?

Coming soon.

Q: How do I cross-match objects in one image with those in another?

Coming soon.

Q: How do I cross-match objects in the SExtractor catalogs with those in the Millennium Database?

Coming soon.

Q: How do I get an account on the Millennium Database?

Interested users should send an email to Gerard Lemson (lemson /\T


Q: How does the MRObs browser work?

It just does.

Q: What is the difference between the static and the private MRObs browser?

Both the static and the private browser provide access to the deep-zoom RGB image pyramids that were made from the MRObs data sets. The static browser provides a convenient way of exploring different types of surveys, and how the observational predictions are affected by, for example, cosmic variance, the choice of stellar population synthesis model, IGM prescription, or cosmology.
The private browser is an enhanced version of the static browser that allows you to select galaxies in the images and query the Millennium Database for their properties. The query returns information on the photometric and structural properties of the object from the lightcone catalogues, physical properties from the semi-analytic catalogues the galaxy came from, and the properties of the dark matter halo of the galaxy as given by the dark matter catalogues. This information is displayed in a side panel of the browser. The private browser also allows one to link together and mark all objects belonging to the same friends-of-friends group associated with the selected galaxy. The display also shows which galaxies in the FoF group are central, satellite, and orphan galaxies (satellite galaxies that have lost their halo).

Q: How can I get an account for the private (interactive) version of the MRObs browser?

The private browser will be made available in a similar manner as the private MyMillennium Database. In order to streamline the anticipated load on the Millennium Database server due to the new querying functionality of the MRObs browser, the private browser has not yet been released to the community. Please check this webpage for updates.


Q: How can I make my own object list from the lightcones?

Object lists can be generated from lightcone catalogs in the Millennium Database by performing an SQL query. The query collects all the relevant information needed to define the position, flux, size and shape of each galaxy in the lightcone. For this to work, it is currently required that the lightcones already contain the structural information (inclinations and position angles) of the galaxies, as is the case for all lightcones that are part of the MRObs framework. The IGM corrections can be applied to the object fluxes "on-the-fly" as part of the same query, or can be performed afterwards as a separate step. The object lists related to the simulated surveys currently available in the MRObs can also be downloaded in the Data products section on this site, where we also provide the SQL queries that were used to generate all the object lists.

Q: How can I make my own pre-observation images from the object lists?

Users should be able to use any kind of profile modeling software capable of building fits images based on the parameters in the object lists. The MRObs object lists are used as input for a modified version of SkyMaker to generate the pre-observation images.

Q: How can I make my own simulated images from the pre-observation images?

The pre-observation images made available here can be seen as a perfect image of the sky, i.e. in the absence of sky background, sky and object noise, detector noise, and point spread function. This is useful for users who wish to perform their own telescope simulations but do not have the robust cosmological framework provided by the MRObs. Users should be aware that the properties of objects in the pre-observation image provided here still depend on the choice of filter, lightcone, stellar population model, IGM model, and some parameters of the instrument and survey, e.g. zeropoint, pixel scale and exposure time (although the latter three are easily rescaled). The pre-observation images are also useful for users who want to design their own survey composed of different numbers of sub-exposures, variable seeing and sky, or image dithering. In the future, more general pre-observation images may be made available for even greater flexibility.

Q: How can I make my own object catalogs from the science data?

The MRObs makes catalogs are made using Source Extractor. Users interested in making their own source catalogs using different detection and photometry algorithms, or using different Source Extractor parameter settings, are welcome to download the scientific FITS images and any supplementary material (e.g. weight maps) for custom processing.

Q: How can I make my own RGB color composites from the science data?

Users interested in making new or other color images from MRObs data products can download the scientific FITS images from the data release section on this web portal. A variety of software tools is available to make RGB color composites from these FITS images. The MRObs uses the highly efficient and versatile package STIFF.