DHIGLS: DRAO H i INTERMEDIATE GALACTIC LATITUDE SURVEY

Abstract

Observations of Galactic H I gas for seven targeted regions at intermediate Galactic latitude are presented at 1 angular resolution using data from the DRAO Synthesis Telescope (ST) and the Green Bank Telescope (GBT). The DHIGLS data are the most extensive arcminute resolution measurements of the diffuse atomic interstellar medium beyond those in the Galactic plane. The acquisition, reduction, calibration, and mosaicking of the DRAO ST data and the cross calibration and incorporation of the short-spacing information from the GBT are described. The high quality of the resulting DHIGLS products enables a variety of new studies in directions of low Galactic column density. We analyze the angular power spectra of maps of the integrated H I emission (column density) from the data cubes for several distinct velocity ranges. Fitting power spectrum models based on a power law, but including the effects of the synthesized beam and noise at high spatial frequencies, we find exponents ranging from −2.5 to −3.0. Power spectra of maps of the centroid velocity for these components give similar results. These exponents are interpreted as being representative of the 3D density and 3D velocity fields of the atomic gas, respectively. We find evidence for dramatic changes in the H I structures in channel maps over even small changes in velocity. This narrow line emission has counterparts in absorption spectra against bright background radio sources, quantifying that the gas is cold and dense and can be identified as the cold neutral medium phase. Fully reduced DHIGLS H I data cubes and other data products are available at www.cita.utoronto.ca/DHIGLS.

Probing interstellar turbulence in cirrus with deep optical imaging: no sign of energy dissipation at 0.01 pc scale

“…The exponent found here is comparable to what was found earlier using 100 µm IRAS data, γ ∼ −2.9, (Gautier et al 1992;Miville-Deschênes et al 2007) or 250 µm Herschel-SPIRE data on a similar range of scales (down to 30 ), γ = −2.7 ± 0.1, (Miville-Deschênes et al 2010). Our results are also similar to what was found recently using 21 cm observations of diffuse high Galactic latitude fields (values ranging from −2.5 to −3.0) by Martin et al (2015) and Blagrave et al (2016).…”

Spatial power spectra of dust across the Local Group: No constraint on disc scale height

“…The power spectra we find here are consistently shallower than power spectra from Milky Way studies. Galactic H I power spectra typically have indices from 2.5-4 (Deshpande et al 2000;Dickey et al 2001;Miville-Deschênes et al 2003;Pingel et al 2013;Martin et al 2015;Blagrave et al 2017;Pingel et al 2018), with extreme values of 2.2 (Green 1993) to 4.9 (Kalberla et al 2017). Values from dust include 2.7 from extinction over the Perseus molecular cloud (Pingel et al 2018), 2.9 from diffuse galactic light in optical bands (Miville-Deschênes et al 2016), and 2.7 from Herschel SPIRE maps of the Polaris flare (Miville-Deschênes et al 2010).…”

“…One reason for the confusion may be that extragalactic power spectrum analyses use heterogeneous data and techniques. In general, extragalactic studes have also not corrected for steepening on small scales due to the PSF response (excepting Muller et al 2004), though this effect is commonly account for in Galactic power spectrum analyses (Miville-Deschênes et al 2003;Martin et al 2015;Blagrave et al 2017). This issue was also noted by Grisdale et al (2017) who found that the break points in H I power spectra in a few nearby galaxies are consistently limited by the PSF scale.…”

H i column density statistics of the cold neutral medium from absorption studies

“…In this work we are interested in cold neutral medium structures at length scales ranging sub parsecs to a few tens of parsecs. Recent works by Martin et al (2015); Kalberla & Kerp (2016); Kalberla et al (2017); Blagrave et al (2017) and Clark et al (2019) find the existence of anisotropic structures at scales of a few pcs to 100s of pcs in certain directions in the Galaxy with significant alignments along the magnetic field lines. Here, we restrict ourselves to the isotropic estimators of the two point correlation function and hence Ξ depends only on U = | U |.…”