Future prospects for finding Milky Way satellites. Amit and Carl 31 March 2010

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1 Future prospects for finding Milky Way satellites Amit and Carl 31 March 2010

2 Where have all the satellites gone? The missing satellite problem! DM simulations (like Via Lactea) predict that there should be thousands of MW satellites, but only a few have been detected! Are our simulations wrong? Are the detections limited by biases? How many can we expect to find? Tollerud et al ) Asses current sample of MW satellites 2) Determine how badly this sample undercounts the actual # of MW satellites 3) Predict how man satellites future surveys will find.

3 The current sample of MW satellites

4 Approach The goal is to determine the total number of satellites brighter than Mv and within Router Ntot=c(r,Omega)Nobserved(<r,<Omega) Koposov et al determined a relation between Mv of a dsph galaxy and the completeness radius out two which SDSS DR5 could detect it. To determine the correction factor c, they will perform "observations" of Via Lactea Use the limits of DR5: Router = 417 kpc Omega = 8000 deg2

5 Via Lactea Highest resolution DM simulation of the MW like DM halo published. ~6553 sub-halos 2686 are within Router Diemand et al 2007 Radial correction cr = Ntot/N(<r)

6 Radial Correction Top: collor represents the fraction, f (<Omega), of subhalos with in 8000 deg2, centered at that point. Bottom: Distribution of correction factors, 1/f, that must be applied to return t Ntot within 417 kpc Average correction is 5.15 but can vary from ~3.5 to ~ 8.3 Solution to MSP? If within 23 kpc, ~15% of the sky has 1 or 0 subhalos visible to a SDSS sized survey.

7 Is this valid? Is the population/distribution of subhalos in Via Lactea consistent with the observed sample of galaxies? Make 1000 subsamples of 11 subhalos from Via Lactea and compare to the SDSS sample. Conclude that the observed sample is consistant with being a random subsample of the simulation.

8 The Corrected Luminosity Function Perform 18,576 mock surveys at 3096 different pointings on the sky, with the sun placed at 6 different positions in the Via Lactea grid to determine the correction factors. For each DR5 satellite they then determine the total number of satellites that should be detectable at that magnitude.

9 Dependance of correction on magnitude

10 Estimates of Satellites of the Milky Way

11 Possibilities...? - Its "just" a matter of looking everywhere! - The most conservative estimate suggests 5 times more satellites. - Various models suggest anisotropy in distribution All we need is surveying deeper and over more of the sky. - Ability to understand galaxy formation models - Compare with observations in other systems (M31 satellites) - A Larger statistical Sample is more dependable!

12 Next Steps - Future surverys like LSST, DES, PanSTARRS & SkyMapper - Estimate the completeness radius as: (assuming everything else SDSS like) - Detect objects over to Milky Way's virial radius that are as faint as the faintest galaxies observed today. - LSST will be able to detect objects L ~100Lsol upto ~200kpc

13 Predictions Maximum radius for detection of dsph's v/s Absolute Magnitude for DR5 (22.5) Compared to: - Single LSST (24.5) - Co-added LSST (27.5) - DES/ Single PanSTARRS (both 24) - SkyMapper & associated MSS (22.6). The data points are SDSS and classical satellites, as well as Local Group field galaxies.

14 Implications With the results so seen, lets consider a Milky Way halo filled Nsat ~ 400 What can we do with it? - Determine characteristic velocity scale in sub-halo distribution (Scenario 7) - Correlations on sub populations of Sub-Halos and Galaxies Consistency check for Mass-Luminosity relations (CDM Models) - Study Galaxy formations & discover Low Luminosity threshold for formation - Compare Luminosity functions & Distribution with other systems Constrain how dsph form - Further follow-ups will provide means to establish the particle nature of dark matter Small Scale Clustering characteristics of DM

15 Brief Intro to New Surveys Large Synoptic Survey Telescope (3200M pixels) : - Wide, Fast, Deep! Covers Half the sky. Incredible depth, Mag ~27. They claim to make the "Greatest Movie Ever", and they WILL have all the Stars :) Dark Energy Survey (500M pixels) : - Will map the galaxy distribution in the Universe. Chart Energy output and Distance measurement for clusters Influence of Dark Matter by measuring spacing b/w galaxies over history Panoramic Survey Telescope & Rapid Response System (1400M pixels): - Characterize Earth approaching objects. PS1working more to come. Also study Galaxy Clustering, Lensing, Ultra-deep surveys. Sky Mapper (268M pixels) : - SDSS's counterpart for the entire Southern Hemisphere.

16 Conclusions 1) Current detections of MW satellites are consistent with the Via Lactea simulation and VL can therefor be used for estimating the number of satellites detectable by future surveys. 2) The MSP may be simply a result of the observational biases of the survey's to date 3) Full sky surveys will detect hundreds of MW satellites and provide constraints on satellite formation and DM.