The Radio Sky at Meter Wavelengths:

Transcription

1 : Foregrounds for 21-cm Cosmology Michael W. Eastwood (Caltech) on behalf of the OVRO-LWA collaboration Cosmological Signals from Cosmic Dawn to the Present February 8, 2018 N 1 / 21

2 Caltech Gregg Hallinan Sandy Weinreb Stephen Bourke Chalmers Jake Hartman Google Harish Vedantham Jonathon Kocz Kate Clark Marin Anderson Ryan Monroe Devin Cody David Wang Harvard/SAO Lincoln Greenhill Ben Barsdell NVIDIA Danny Price Swinburne Hugh Garsden Gianni Bernardi SKA OVRO David Woody James Lamb OVRO staff JPL Larry D Addario Joe Lazio and the rest of the LWA team 2 / 21

3 The Owens Valley Radio Observatory Long Wavelength Array The OVRO-LWA Number of Antennas 288 (256 correlated) Core Diameter 200 m Maximum Baseline 1.5 km Resolution arcminutes Frequency Range MHz Frequency Resolution 24 khz Field of View Entire hemisphere Integration Time (this work) 28 hours 3 / 21

4 The Cosmic Dawn First generation of stars Formation and feedback Heating of the IGM Early X-ray sources See also Greenhill talk Transients Stellar flares Extrasolar planets SWIFT and LIGO follow-up See Anderson et al Space Weather Solar flares Jovian flares Cosmic Rays Real-time detection See Monroe et al. in prep. 4 / 21

5 21-cm Cosmology The 21-cm Power Spectrum 5 / 21

6 21-cm Cosmology Foregrounds in 21-cm Cosmology 6 / 21

7 Full Sky Maps The Venerable Haslam 408 MHz Map Haslam et al. (1981, 1982) 7 / 21

8 Full Sky Maps The Guzmán 45 MHz Map Guzmán et al. (2011) 8 / 21

9 Full Sky Maps The DRAO 22 MHz Map Roger et al. (1999) 9 / 21

10 Full Sky Maps LWA1 Sky Survey (35 80 MHz) Dowell et al. (2017) 10 / 21

11 Full Sky Maps OVRO-LWA Sky Maps (37 73 MHz) Eastwood et al. (2017) 11 / 21

12 Full Sky Maps Eight New Low-Frequency Sky Maps MHz MHz MHz MHz MHz MHz MHz MHz Eastwood et al. (2017) radio_maps_info.cfm N 12 / 21

13 Full Sky Maps Map Properties Frequency Bandwidth FWHM Noise # MHz khz arcmin K mjy/beam Eastwood et al. (2017) 13 / 21

14 visibility = m-mode Analysis Imaging and Cleaning (sky brightness) (beam) (fringe pattern) dω Shaw et al. (2014, 2015) 14 / 21

15 visibility = m-mode Analysis Imaging and Cleaning visibility (sky brightness) (beam) (fringe pattern) dω sidereal time Fourier transform m-mode Shaw et al. (2014, 2015) 14 / 21

16 visibility = m-mode Analysis Imaging and Cleaning. m-modes } {{ } v (sky brightness) (beam) (fringe pattern) dω sidereal time Fourier transform visibility m-mode.... = transfer matrix..... } {{ } B Shaw et al. (2014, 2015) a lm } {{ } a 14 / 21

17 visibility = m-mode Analysis Imaging and Cleaning. m-modes } {{ } v (sky brightness) (beam) (fringe pattern) dω sidereal time Fourier transform visibility m-mode.... = transfer matrix..... } {{ } B Shaw et al. (2014, 2015) a lm } {{ } a âââ = argmin { v Ba 2 + ε a 2} = (B B + εi) 1 B v Eastwood et al. (2017) 14 / 21

18 m-mode Analysis Dirty Map 15 / 21

19 m-mode Analysis Clean Map 16 / 21

20 Challenges Advantages and Disadvantages Advantages No gridding step No mosaicing step Exact treatment of widefield effects Optimal foreground filters (see Shaw et al. 2014, 2015) Disadvantages Matrix equation is block diagonal, but still large! 500 GB/frequency channel (!) Rapid ionospheric changes break assumptions 17 / 21

21 Challenges Sources of Error Bright point sources direction dependent calibration Variable ionospheric effects 10% errors within 1 RFI and common-mode pickup m = 0 discarded 18 / 21

22 Challenges Higher Resolution, Higher Sensitivity Eastwood et al. (2017) N 19 / 21

23 Challenges Higher Resolution, Higher Sensitivity Eastwood et al. (in prep.) N 20 / 21

24 Challenges Summary Foreground maps are going to be extremely important for 21-cm cosmology experiments going forward. Creating high-fidelity foreground maps is also challenging. These maps will be publicly availble online. radio_maps_info.cfm N 21 / 21

25 Backup Slides 22 / 26

26 Challenges Comparison with Haslam 408 MHz Eastwood et al. (2017) 23 / 26

27 Challenges Comparison with Haslam 408 MHz Haslam et al. (1981, 1982) 23 / 26

28 Challenges Comparison with Guzmán 45 MHz Eastwood et al. (2017) 24 / 26

29 Challenges Comparison with Guzmán 45 MHz Guzmán et al. (2011) 24 / 26

30 Challenges Comparison with DRAO 22 MHz Eastwood et al. (2017) 25 / 26

31 Challenges Comparison with DRAO 22 MHz Roger et al. (1999) 25 / 26

32 Challenges Comparison with Finkbeiner Hα Eastwood et al. (2017) 26 / 26

33 Challenges Comparison with Finkbeiner Hα Finkbeiner et al. (2003) 26 / 26