These data represent the complete EMPIRE survey public data release, which include data cubes, integrated intensity maps, velocity field maps (moment-1) and uncertainty maps.

CONTENTS

This release includes the following data, in FITS format, for each galaxy:

EMPIRE_NAME_LINE_RES.fits - data cube, resolution given in the file name
NAME_LINE_RES_mom0.fits - integrated intensity map
NAME_LINE_RES_emom0.fits - uncertainty map integrated intensity 
NAME_LINE_RES_mom1.fits - velocity field (moment 1)
NAME_LINE_RES_emom1.fits - uncertainty map velocity field (moment-1)

Here, NAME refers to each galaxy name (e.g. NGC2903), LINE stands for the spectral line (e.g. HCN), and RES refers to the resolution (e.g. 33as for 33 arcseconds).

We have tried to make the headers as informative as possible. These include the standard astrometry keywords, units (BUNIT), resolution (BMAJ, BMIN), line and rest frequency (LINE, RESTFREQ), and the telescope efficiency that we have already applied to place cubes on the "main beam brightness temperature" scale.

Note: This data release does not include 12CO and 13CO data for NGC5194. These data belong to the PAWS survey and are also publicly available.

UNITS

The data should be ready to use for science as are, without further processing. Data cubes are in units of "main beam" temperature scale (K) so that they represent our best estimates of the brightness temperature of our tracers. Moment maps are in units of K km/s (moment-0 and associated uncertainty maps) and km/s (moment-1).

METHOD

Data reduction of all data cubes is described in detail in Jimenez-Donaire et al. (2019). 

We constructed the integrated intensity (moment-0) maps by integrating the cubes along the velocity axis, using the HERACLES 12CO(2-1) maps as a prior for masking. These masks are constructed from identifying 4-sigma peaks in each spectrum (pixel) in the HERACLES CO cubes and are expanded to include all neighboring channels with emission >1-sigma. Moment-0 maps are then derived by integrating the cube along the velocity axis taking into account all channels included in this mask. The uncertainty maps are the product of the RMS scatter outside these spectral masks times the velocity-width per channel times the square root of the number of channels the mask is covering for each pixel.

The velocity fields (moment-1 maps) are derived only for the high signal-to-noise transitions 12CO(1-0) and 13CO(1-0) and represent the intensity weighted mean velocity using the same spectral mask as a prior as for the integrated intensity maps above. The moment-1 uncertainty maps are calculated by integrating the product of the RMS scatter (see above), the channel-width and delta-v (the distance in km/s of the given channel from the derived moment-1 value) and normalisation of the integral by the moment-0 value. 

QUESTIONS and ACKNOWLEDGMENTS

If you have any questions about the data, please do not hesitate to contact us (bigiel@astro.uni-bonn.de, mdonaire@cfa.harvard.edu). We would also like to hear about any scientific use of the data and would appreciate acknowledgment in publications or talks using EMPIRE data.