============================================== Multi-wavelength coverage over the eROSITA sky Tom Dwelly (dwelly@mpe.mpg.de), 07/05/2013 ============================================== This document presents the calculation of how much of the German eROSITA sky is jointly covered by various existing and future large-area multi-wavelength surveys. Method ====== First I collect/construct footprints of various wide area sky surveys in the form of 'mangle' polygon mask files. mangle is the masking software used within the SDSS collaboration to define the footprint of the SDSS imaging and spectroscopic observations. See http://space.mit.edu/~molly/mangle/ for details of mangle. A Monte-Carlo approach is then used to calculate the areal overlap between various survey footprints. A wrapper script around the mangle task 'polyid' is used to determine what fraction of a large set of randomly distributed points lie within the bounds of a sequence of mangle mask(s). The script allows the joint area of any set of mangle masks to be evaluated (combined with logical AND or NAND). The sky area contained within those masks is then 4pi*Nin/Ntotal, where Nin is the number of trials within the mask, and Ntotal is the total number of trials. Note that the fractional uncertainty on the area estimate is approx sqrt(Nin*(1-Nin/Ntotal))/Ntotal. So for a total of 1e6 trials, and a region of interest subtending 20000 deg^2, we have an uncertainty of ~20deg^2. Large area surveys and details of their sky coverage ==================================================== eROSITA ------- I assume that German eROSITA sky covers 180deg < l < 360deg with no 'demilitarized zone' between the DE and RU sky areas. Extra-galactic sky is assumed to lie at |b| > 20deg. SDSS - (e)BOSS -------------- For this we use the SDSS-DR8 BOSS targeting footprint, which is essentially the extra-galactic part of the full SDSS imaging footprint (which includes connecting strips crossing the Galactic plane). It is my understanding that this can also be considered to be a superset of the eBOSS tiling area. The BOSS/eBOSS targeting footprint is supplied as a mangle polygon file: http://data.sdss3.org/sas/dr9/boss/lss/boss_survey.fits See description here: http://www.sdss3.org/dr9/algorithms/boss_tiling.php I have not accounted for areas affected by bad imaging, bright stars etc. The sky area covered by the above (e)BOSS targeting mask is 10778deg^2. UKIDSS ------ I use the UKIDSS-DR10 LAS K-band footprint to describe the area usefully covered by the UKIDSS survey. These mask are available from the WSA: http://surveys.roe.ac.uk/wsa/coverage-maps.html and specifically: http://surveys.roe.ac.uk/wsa/coverage-maps/UKIDSS/DR10/las-K-DR10.fits Unfortunately the UKIDSS coverage maps are supplied in HEALPIX MOC (Multi-order coverage) map format, but I've written a shell script to allow conversion from MOC to mangle polygon format. The sky area covered by the las-K-DR10.fits coverage mask is ~3600 deg^2. A straw-man UKIRT Hemisphere Survey (UHS) would complete (in J only) the remaining sky between 05.5deg. VISTA-VIKING - is assumed to cover the same sky area as VST-KIDS, see above. Dark Energy Survey (DES) ------------------------ I have built a mangle mask from the following DES survey description www.darkenergysurvey.org/survey/des-description.pdf‎ Table 1: Wide-Area Survey Boundaries: Sub-Area RA bounds(deg) Dec Bounds(deg) ---------------------------------------------------- SPT -60 < RA < 105 -65 < Dec < -40 Viking -30 < RA < 60 -40 < Dec < -25 Round 82 -3 < RA < 45 -25 < Dec < +3 Stripe 82 -43 < RA < -3 -1 < Dec < +1 PanSTARRS-1/2 ------------- I have assumed that the PanSTARRS 3pi survey will cover the whole sky North of Dec=-30deg. SkyMapper --------- I have assumed that the SkyMapper Southern Sky Survey will cover the whole sky South of Dec=0deg. 4MOST spectroscopic survey -------------------------- I have assumed that a 4MOST extra-galactic dark/grey time survey will cover the whole |b|>25deg sky between the limits -7025deg) sky North of Dec=+10deg (Total ~9440 deg^2) Further into the future ----------------------- LSST -> http://www.lsst.org/lsst/science/science-faq#q2 - All sky south of Dec=+10deg Euclid - (Rough guess) - all extra-galactic sky with |b|>35deg => 17000deg^2 Results ======= Here is a summary of the aforementioned survey regions and their areas. All numbers should be accurate to +-20deg^2 or better |--------------------------------------------------------------------| |Survey | Total | In eROSITA-DE sky | | | |------------------------------------| | | | any b | |b|>20deg | |b|<20deg | | | (deg^2) | (deg^2) | (deg^2) | (deg^2) | |--------------------------------------------------------------------| |eROSITA | 41000 20600 13550 7050 | |(e)BOSS footprint | 10780 3630 3550 80 | |UKIDSS-LAS-K-DR10 | 3600 1900 1890 10 | |UKIDSS-UHS-J | 17870 4780 3490 1290 | |VST-ATLAS | 4690 3280 3280 0 | |VST-KIDS | 1500 1120 1120 0 | |VISTA-VHS & VIKING | 18620 14220 10090 4230 | |VISTA-VIKING | 1500 1120 1120 0 | |DES | 5000 3470 3440 30 | |PanSTARRS | 30920 10930 8100 2830 | |SkyMapper | 20620 15850 10090 5760 | |4MOST-exgal | 16000 10020 10020 0 | |WEAVE-LOFAR | 9450 2080 2080 0 | |LSST | 24210 17510 11290 6220 | |Euclid | 17590 8780 8780 0 | |--------------------------------------------------------------------- Note that it would be very easy to use my script to evaluate compound queries such as: Calculate the sky area satisfying: (inside eROSITA-DE) AND (inside |b|>20deg) AND (inside eBOSS) AND (inside UKIDSS-LAS) AND (outside DES) Visibility of German eROSITA sky from leading observatory sites: ================================================================ For this exercise I have calculated the amount of eROSITA-DE sky which is visible (within reasonable airmass limits) from various famous observatory sites. I've used the same approach as before, and have constructed mangle masks for the potential sky visible from nominal observatory latitudes. I approximate AM = sec(Z), where Z is the zenith distance. Therefore, if AM<1.5 then Z<48.2deg, if AM<2 then Z<60.0deg. ----------------------------------------------- Optical/IR ----------------------------------------------- Site Name Latitude Telescopes SAAO, Sutherland -32d 23' SALT AAO,Siding Spring -31d 17' AAT Cerro Pachon -30d 15' Gemini-S,SOAR Cerro Tololo -30d 10' Blanco(DES) La Silla -29d 15' NTT,3.6m,MPG2.2m ... Las Campanas -29d 01' Magellans Paranal -24d 38' VLT,VST,VISTA Mauna Kea +19d 50' Keck,Subaru,Gemini-N,UKIRT,CFHT... La Palma +28d 46' GTC,WHT,TNG,INT... Kitt Peak +31d 57' WIYN Apache Point +32d 47' SDSS,ARC3.5m Xinglong +40d 24' LAMOST ----------------------------------------------- ----------------------------------------------- Radio/mm ----------------------------------------------- Site Name Latitude Telescopes Northern Cape -30d 50' MeerKat Murchison -26d 42' ASKAP Chajnantor -23d 01' ALMA, APEX, ACT Socorro +34d 05' VLA LOFAR +52d 54' LOFAR Westerbork +52d 55' WSRT-APERTIF ----------------------------------------------- Results ======= Here are the sky areas covered for a representative set of telescope latitudes. All sky areas should be accurate to +-20deg^2 or better |-------------|-----------------------------------------| | | Area in eROSITA-DE sky | | Telescope |-----------------------------------------| | latitude | any b | |b|>20deg | | |--------------------|--------------------| | | AM<1.5 | AM<2.0 | AM<1.5 | AM<2.0 | | (deg) | (deg^2) | (deg^2) | (deg^2) | (deg^2) | |-------------|-----------------------------------------| | -30deg | 18290 19970 11760 13000 | | -25deg | 18420 20280 11850 13240 | | +20deg | 10540 13300 7830 9510 | | +30deg | 8360 10960 6260 8120 | | +50deg | 4450 6670 3240 4930 | |-------------|-----------------------------------------| end ---