Tisková zpráva
VLT Studies a Moderately Distant Cluster of Galaxies
The FORS/ISAAC Cluster Deep Field
27. února 1999
Studies of "Deep Fields" are becoming common practice in astronomy. To mention a few: the two Hubble Deep Fields ( HDF-N and HDF-S , north and south of the celestial equator), the NTT Deep Field, the AXAF Deep Field , the FORS Deep Field. The latter will be observed during FORS1 "guaranteed time" that is available to astronomers from those institutes that built this instrument. All of these sky fields have been selected for being quite 'empty', in the sense that few brighter objects are seen in them. They are thus of the same type ('generic'), with the partial exception of HDF-S that contains a QSO (quasar).
A primary imaging programme for the FORS1 Science Verification programme aims at obtaining multicolour (UBVRI), deep images of a moderate redshift cluster seen in this direction and, if possible, complemented with infrared (JHK) images with ISAAC of the cluster core.
The scientific issues that may be addressed with such observational data are manifold, among others:
- Obtain photometric redshifts (and thus distances) by measuring accurate colours of all galaxies in the field;
- Construct gravitational shear maps , by studying systematic effects in the orientation of axes of the galaxies in the field;
- Measure the magnification effect , i.e. the rate by which the light of gravitationally lensed background objects is amplified by this effect;
- Construct models of the mass distribution in the cluster from these shear maps, the measured magnification and the observed gravitational arcs;
- Study the cluster galaxy population down to faint magnitudes, by means of observed colour-magnitude diagrammes;
- Search for high-redshift, lensed galaxies - this is an indirect method to find extremely distant objects;
- Identify interesting (peculiar) stars in the field.
For all of these scientific applications, ample expertise exists within the ESO community. This ensures a prompt, wide, and qualified exploitation of the data. If time allows, some multi-object spectroscopy (MOS) may also be attempted, including arclets and very red objects.
FORS observations of the cluster MS1008.1-1224
For preliminary test observations, a suitable galaxy cluster was selected according to the following characteristics:
- moderate redshift between 0.3 and 0.8 ;
- well observable in the middle of February (i.e. sky position in the interval R.A. = 6 - 10h);
- have a large velocity dispersion (larger than 1000 km/s) and/or Einstein radius (a measure of the size), and possibly with a known giant arc(s) ;
- not too high galactic latitude, in order to have enough stars to map the Point-Spread Function (PSF; the shape of the exposed image of a star) across the FORS field-of-view.
Several possible candidates were considered, and finally the cluster MS1008.1-1224 was selected. The redshift is z = 0.306; the velocity dispersion is 1054 km/sec, and many arclets are seen within the cluster area.
Many exposures were obtained during FORS Commissioning in January 1999, and were used to produce the colour images below.
The two photos show the intricate structure of this fine cluster and reveal the presence of a substantial number of gravitational effects. The strong gravitational potential of the cluster acts as a gravitational lens and distorts the images of several background galaxies, while magnifying their luminosity. The mapping of this "gravitational shear" and the study of the numerous "gravitational arclets" that are produced by the cluster will allow to determine its mass and mass distribution.
Some of the magnified galaxies may be very distant, lying at very high redshift. For them the cluster works as a "gravitational telescope", facilitating the study of these otherwise very faint primordial galaxies.
O zprávě
Tiskové zpráva č.: | eso9912 |
Legacy ID: | Photo 09a-b/99 |
Jméno: | MS 1008.1-1224 |
Typ: | Early Universe : Galaxy : Grouping : Cluster |
Facility: | Very Large Telescope |
Instruments: | FORS1, ISAAC |
Our use of Cookies
We use cookies that are essential for accessing our websites and using our services. We also use cookies to analyse, measure and improve our websites’ performance, to enable content sharing via social media and to display media content hosted on third-party platforms.
ESO Cookies Policy
The European Organisation for Astronomical Research in the Southern Hemisphere (ESO) is the pre-eminent intergovernmental science and technology organisation in astronomy. It carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities for astronomy.
This Cookies Policy is intended to provide clarity by outlining the cookies used on the ESO public websites, their functions, the options you have for controlling them, and the ways you can contact us for additional details.
What are cookies?
Cookies are small pieces of data stored on your device by websites you visit. They serve various purposes, such as remembering login credentials and preferences and enhance your browsing experience.
Categories of cookies we use
Essential cookies (always active): These cookies are strictly necessary for the proper functioning of our website. Without these cookies, the website cannot operate correctly, and certain services, such as logging in or accessing secure areas, may not be available; because they are essential for the website’s operation, they cannot be disabled.
Functional Cookies: These cookies enhance your browsing experience by enabling additional features and personalization, such as remembering your preferences and settings. While not strictly necessary for the website to function, they improve usability and convenience; these cookies are only placed if you provide your consent.
Analytics cookies: These cookies collect information about how visitors interact with our website, such as which pages are visited most often and how users navigate the site. This data helps us improve website performance, optimize content, and enhance the user experience; these cookies are only placed if you provide your consent. We use the following analytics cookies.
Matomo Cookies:
This website uses Matomo (formerly Piwik), an open source software which enables the statistical analysis of website visits. Matomo uses cookies (text files) which are saved on your computer and which allow us to analyze how you use our website. The website user information generated by the cookies will only be saved on the servers of our IT Department. We use this information to analyze www.eso.org visits and to prepare reports on website activities. These data will not be disclosed to third parties.
On behalf of ESO, Matomo will use this information for the purpose of evaluating your use of the website, compiling reports on website activity and providing other services relating to website activity and internet usage.
Matomo cookies settings:
Additional Third-party cookies on ESO websites: some of our pages display content from external providers, e.g. YouTube.
Such third-party services are outside of ESO control and may, at any time, change their terms of service, use of cookies, etc.
YouTube: Some videos on the ESO website are embedded from ESO’s official YouTube channel. We have enabled YouTube’s privacy-enhanced mode, meaning that no cookies are set unless the user actively clicks on the video to play it. Additionally, in this mode, YouTube does not store any personally identifiable cookie data for embedded video playbacks. For more details, please refer to YouTube’s embedding videos information page.
Cookies can also be classified based on the following elements.
Regarding the domain, there are:
- First-party cookies, set by the website you are currently visiting. They are stored by the same domain that you are browsing and are used to enhance your experience on that site;
- Third-party cookies, set by a domain other than the one you are currently visiting.
As for their duration, cookies can be:
- Browser-session cookies, which are deleted when the user closes the browser;
- Stored cookies, which stay on the user's device for a predetermined period of time.
How to manage cookies
Cookie settings: You can modify your cookie choices for the ESO webpages at any time by clicking on the link Cookie settings at the bottom of any page.
In your browser: If you wish to delete cookies or instruct your browser to delete or block cookies by default, please visit the help pages of your browser:
Please be aware that if you delete or decline cookies, certain functionalities of our website may be not be available and your browsing experience may be affected.
You can set most browsers to prevent any cookies being placed on your device, but you may then have to manually adjust some preferences every time you visit a site/page. And some services and functionalities may not work properly at all (e.g. profile logging-in, shop check out).
Updates to the ESO Cookies Policy
The ESO Cookies Policy may be subject to future updates, which will be made available on this page.
Additional information
For any queries related to cookies, please contact: pdprATesoDOTorg.
As ESO public webpages are managed by our Department of Communication, your questions will be dealt with the support of the said Department.