Tracing the Magnetic Field of IRDC G028.23-00.19 Using NIR Polarimetry

Abstract

The magnetic field (B-field) of the starless dark cloud L1544 has been studied using near-infrared (NIR) background starlight polarimetry (BSP) and archival data in order to characterize the properties of the plane-of-sky B-field. NIR linear polarization measurements of over 1700 stars were obtained in the H band and 201 of these were also measured in the K band. The NIR BSP properties are correlated with reddening, as traced using the Rayleigh-Jeans color excess (H-M) method, and with thermal dust emission from the L1544 cloud and envelope seen in Herschel maps. The NIR polarization position angles change at the location of the cloud and exhibit their lowest dispersion there, offering strong evidence that NIR polarization traces the plane-of-sky B-field of L1544. In this paper, the uniformity of the plane-of-sky B-field in the envelope region of L1544 is quantitatively assessed. This allows evaluation of the approach of assuming uniform field geometry when measuring relative mass-to-flux ratios in the cloud envelope and core based on averaging of the radio Zeeman observations in the envelope, as done by Crutcher et al. In L1544, the NIR BSP shows the envelope B-field to be significantly non-uniform and likely not suitable for averaging Zeeman properties without treating intrinsic variations. Deeper analyses of the NIR BSP and related data sets, including estimates of the B-field strength and testing how it varies with position and gas density, are the subjects of later papers in this series.

Multiwavelength Polarimetry of the Filamentary Cloud IC 5146. II. Magnetic Field Structures

“…The magnetic field regulated accretion mechanism also predicts an increase of the mass-to-flux ratio with density (Heitsch & Hartmann 2014). This is seen in some observations (e.g., Hoq et al 2017). However, here we do not find a significant correlation between the mass-to-flux criticality and density.…”

“…Compared to the indices of 0.75±0.02 and 0.73±0.06 toward GRSMC 45.60+0.30 (Marchwinski et al 2012) and IRDC G028.23-00.19 (Hoq et al 2017), we find a significantly shallower index, even though these other two studies also used near-infrared starlight polarization data, and probed parsec-scale clouds with a similar density range, 10-10 2 cm −3 for GRSMC 45.60+0.30 and 10 2 -10 3 cm −3 for G028.23-00.19. On the other hand, the index of 0.41±0.04 found by Li et al (2015a) in NGC 6334 is similar to our results, but their data trace the environments in denser regions (10 3 -10 7 cm −3 ) and on larger scales (10-0.1 pc).…”

Distortion of Magnetic Fields in a Starless Core. IV. Magnetic Field Scaling on Density and Mass-to-flux Ratio Distribution in FeSt 1-457

“…A similar value is obtained toward the filamentary cloud IRDC G28.23-00. 19 (κ = 0.73 ± 0.06, Hoq et al 2017). These studies support the conclusion by Crutcher et al (2010).…”

“…Ching et al (2017) obtained κ = 0.54 ± 0.30 toward the cores in the dense filamentary cloud DR21 based on the submillimeter (submm) dust emission polarimetry and the Chandrasekhar-Fermi method (Chandrasekhar & Fermi 1953). Hoq et al (2017) obtained κ = 0.73 ± 0.06 toward the filamentary infrared dark cloud (IRDC) G28.23-00.19 based on near-infrared (NIR) dust extinction polarimetry and the Chandrasekhar-Fermi method. Observations show a variety of κ values ranging from κ ≈ 1/2 to κ ≈ 2/3.…”

Understanding the Links among the Magnetic Fields, Filament, Bipolar Bubble, and Star Formation in RCW 57A Using NIR Polarimetry

“…Therefore, we exclude the pixels with n13,000cm −3 while estimating the mean volume densities in regions A, B, C, D, and E. The means and Poisson errors (standard deviation divided by the square root of the number of measurements) of the volume densities for the five regions (A, B, C, D, and E) are estimated and are listed in column 10 of Table 2. More details on producing the volume density map from the column density can also be found in Smith et al (2014) and Hoq et al (2017).…”