# Copyright (c) 2016 Weitian LI # MIT license """ Diffuse Galactic free-free emission simulations. """ import os import logging from datetime import datetime, timezone import numpy as np from astropy.io import fits import astropy.units as au import healpy as hp from ..utils import read_fits_healpix, write_fits_healpix logger = logging.getLogger(__name__) class FreeFree: """ Simulate the diffuse Galactic free-free emission. The [Dickinson2003] method is followed to derive the free-free template. The H\alpha survey map [Finkbeiner2003] is first corrected for dust absorption using the infrared 100-\mu{}m dust map [Schlegel1998], and then converted to free-free emission map (brightness temperature). Parameters ---------- configs : ConfigManager object An `ConfigManager` object contains default and user configurations. For more details, see the example config specification. Attributes ---------- ??? References ---------- .. [Dickinson2003] Dickinson, C.; Davies, R. D.; Davis, R. J., "Towards a free-free template for CMB foregrounds", 2003, MNRAS, 341, 369, http://adsabs.harvard.edu/abs/2003MNRAS.341..369D .. [Finkbeiner2003] Finkbeiner, Douglas P., "A Full-Sky Hα Template for Microwave Foreground Prediction", 2003, ApJS, 146, 407, http://adsabs.harvard.edu/abs/2003ApJS..146..407F .. [Schlegel1998] Schlegel, David J.; Finkbeiner, Douglas P.; Davis, Marc, "Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds", 1998, ApJ, 500, 525, http://adsabs.harvard.edu/abs/1998ApJ...500..525S """ def __init__(self, configs): self.configs = configs self._set_configs() self._load_halphamap() self._load_dustmap() def _set_configs(self): """Load the configs and set the corresponding class attributes.""" self.halphamap_path = self.configs.get_path( "galactic/freefree/halphamap") self.halphamap_unit = au.Unit( self.configs.getn("galactic/freefree/halphamap_unit")) self.dustmap_path = self.configs.get_path( "galactic/freefree/dustmap") self.dustmap_unit = au.Unit( self.configs.getn("galactic/freefree/dustmap_unit")) # output self.prefix = self.configs.getn("galactic/freefree/prefix") self.save = self.configs.getn("galactic/freefree/save") self.output_dir = self.configs.get_path( "galactic/freefree/output_dir") self.filename_pattern = self.configs.getn("output/filename_pattern") self.use_float = self.configs.getn("output/use_float") self.clobber = self.configs.getn("output/clobber") # self.nside = self.configs.getn("common/nside") self.freq_unit = au.Unit(self.configs.getn("frequency/unit")) # logger.info("Loaded and set up configurations") def _load_halphamap(self): """Load the H{\alpha} map, and upgrade/downgrade the resolution to match the output Nside. """ self.halphamap, self.halphamap_header = read_fits_healpix( self.halphamap_path) halphamap_nside = self.halphamap_header["NSIDE"] logger.info("Loaded H[alpha] map from {0} (Nside={1})".format( self.halphamap_path, halphamap_nside)) # TODO: Validate & convert unit if self.halphamap_unit != au.Unit("Rayleigh"): raise ValueError("unsupported Halpha map unit: {0}".format( self.halphamap_unit)) # Upgrade/downgrade resolution if halphamap_nside != self.nside: self.halphamap = hp.ud_grade(self.halphamap, nside_out=self.nside) logger.info("Upgrade/downgrade H[alpha] map from Nside " "{0} to {1}".format(halphamap_nside, self.nside)) def _load_dustmap(self): """Load the dust map, and upgrade/downgrade the resolution to match the output Nside. """ self.dustmap, self.dustmap_header = read_fits_healpix( self.dustmap_path) dustmap_nside = self.dustmap_header["NSIDE"] logger.info("Loaded dust map from {0} (Nside={1})".format( self.dustmap_path, dustmap_nside)) # TODO: Validate & convert unit if self.dustmap_unit != au.Unit("MJy / sr"): raise ValueError("unsupported dust map unit: {0}".format( self.dustmap_unit)) # Upgrade/downgrade resolution if dustmap_nside != self.nside: self.dustmap = hp.ud_grade(self.dustmap, nside_out=self.nside) logger.info("Upgrade/downgrade dust map from Nside " "{0} to {1}".format(dustmap_nside, self.nside)) def _correct_dust_absorption(self): """Correct the H{\alpha} map for dust absorption using the 100-{\mu}m dust map. References: [Dickinson2003]: Eq.(1, 3); Sec.(2.5) """ if hasattr(self, "dust_corrected") and self.dust_corrected: return # logger.info("Correct H[alpha] map for dust absorption") # Effective dust fraction in the LoS actually absorbing Halpha f_dust = 0.33 logger.info("Effective dust fraction: {0}".format(f_dust)) # NOTE: # Mask the regions where the true Halpha absorption is uncertain. # When the dust absorption goes rather large, the true Halpha # absorption can not well determined. # Therefore, the regions where the calculated Halpha absorption # greater than 1.0 mag are masked out. halpha_abs_th = 1.0 # Halpha absorption threshold, unit: [ mag ] # Corresponding dust absorption threshold, unit: [ MJy / sr ] dust_abs_th = halpha_abs_th / 0.0462 / f_dust logger.info("Dust absorption mask threshold: " + "{0:.1f} MJy/sr ".format(dust_abs_th) + "<-> H[alpha] absorption threshold: " + "{0:.1f} mag".format(halpha_abs_th)) mask = (self.dustmap > dust_abs_th) self.dustmap[mask] = np.nan fp_mask = 100 * mask.sum() / self.dustmap.size logger.warning("Dust map masked fraction: {0:.1f}%".format(fp_mask)) # halphamap_corr = self.halphamap * 10**(self.dustmap * 0.0185 * f_dust) self.halphamap = halphamap_corr self.dust_corrected = True logger.info("Done dust absorption correction") def _calc_ratio_a(self, Te, nu_GHz): """Calculate the ratio factor a(T, nu), which will be used to transform the Halpha emission (Rayleigh) to free-free emission brightness temperature (mK). References: [Dickinson2003], Eq.(8) """ term1 = 0.366 * nu_GHz**0.1 * Te**(-0.15) term2 = np.log(4.995e-2 / nu_GHz) + 1.5*np.log(Te) a = term1 * term2 return a def _simulate_frequency(self, frequency): """Simulate the free-free map at the specified frequency. References: [Dickinson2003], Eq.(11) NOTE: [Dickinson2003], Eq.(11) may wrongly have the "10^3" term. """ # Correct for dust absorption first self._correct_dust_absorption() # Assumed electron temperature [ K ] Te = 7000.0 T4 = Te / 1e4 nu = frequency * self.freq_unit.to(au.GHz) # frequency [ GHz ] ratio_a = self._calc_ratio_a(Te, nu) # NOTE: ignored the "10^3" term in the referred equation ratio_mK_R = (8.396 * ratio_a * nu**(-2.1) * T4**0.667 * 10**(0.029/T4) * (1+0.08)) # Use "Kelvin" as the brightness temperature unit ratio_K_R = ratio_mK_R * au.mK.to(au.K) hpmap_f = self.halphamap * ratio_K_R return hpmap_f def _make_header(self): """Make the header with detail information (e.g., parameters and history) for the simulated products. """ header = fits.Header() header["COMP"] = ("Galactic free-free emission", "Emission component") header["CREATOR"] = (__name__, "File creator") # TODO: history = [] comments = [] for hist in history: header.add_history(hist) for cmt in comments: header.add_comment(cmt) self.header = header logger.info("Created FITS header") def output(self, hpmap, frequency): """Write the simulated free-free map to disk with proper header keywords and history. """ if not os.path.exists(self.output_dir): os.mkdir(self.output_dir) logger.info("Created output dir: {0}".format(self.output_dir)) # filename = self.filename_pattern.format(prefix=self.prefix, frequency=frequency) filename += ".fits" filepath = os.path.join(self.output_dir, filename) if not hasattr(self, "header"): self._make_header() header = self.header.copy() header["FREQ"] = (frequency, "Frequency [ MHz ]") header["DATE"] = ( datetime.now(timezone.utc).astimezone().isoformat(), "File creation date" ) if self.use_float: hpmap = hpmap.astype(np.float32) write_fits_healpix(filepath, hpmap, header=header, clobber=self.clobber) logger.info("Write simulated map to file: {0}".format(filepath)) def simulate(self, frequencies): """Simulate the free-free map at the specified frequencies.""" hpmaps = [] for f in np.array(frequencies, ndmin=1): logger.info("Simulating free-free map at {0} ({1}) ...".format( f, self.freq_unit)) hpmap_f = self._simulate_frequency(f) hpmaps.append(hpmap_f) if self.save: self.output(hpmap_f, f) return hpmaps