arXiv subjects

Justin Jonas

Publications and source records attributed to Justin Jonas.

3 recordsLinked to original sources

arXiv2016

An Improved Model of Diffuse Galactic Radio Emission from 10 MHz to 5 THz

We present an improved Global Sky Model (GSM) of diffuse galactic radio emission from 10 MHz to 5 THz, whose uses include foreground modeling for CMB and 21 cm cosmology. Our model improves on past work both algorithmically and by adding new data sets such as the Planck maps and the enhanced Haslam map. Our method generalizes the Principal Component Analysis approach to handle non-overlapping regions, enabling the inclusion of 29 sky maps with no region of the sky common to all. We also perform a blind separation of our GSM into physical components with a method that makes no assumptions about physical emission mechanisms (synchrotron, free-free, dust, etc). Remarkably, this blind method automatically finds five components that have previously only been found "by hand", which we identify with synchrotron, free-free, cold dust, warm dust, and the CMB anisotropy, with maps and spectra agreeing with previous work but in many cases with smaller error bars. The improved GSM is available online at github.com/jeffzhen/gsm2016.

astro-ph.CO↗

arXiv2013

Simultaneous VLBA polarimetric observations of the v={1,2} J=1-0 and v=1, J=2-1 SiO maser emission toward VY CMa: maser morphology and pumping

This paper presents a milliarcsecond-scale comparison of the polarised component-level v=1 J=1-0, v=2 J=1-0 and v=1 J=2-1 SiO maser emission toward the supergiant star VY CMa. These observations used the VLBA at λ=7mm and λ=3mm over two epochs. The goal is to use the relative characteristics and spatial distribution of the transitions in individual resolved maser components to provide observational constraints on SiO maser excitation and pumping models. We find that many v=1 J=1-0 and v=2 J=1-0 features overlap in the second observing epoch, at comparable sensitivity. The v=2 J=1-0 emission is primarily located within several v=1 J=1-0 regions, and has a high degree of morphological similarity in the northeastern envelope, supportive of local collisional pumping. We find significantly higher spatial overlap between v=1 J=1-0 and J=2-1 features than generally previously reported. However, the overlapping v=1 J=2-1 emission is usually weaker than predicted by hydrodynamical models, possibly due to low-density collisional pumping. The overall maser morphology contains several large-scale features that are persistent over multiple years and are likely associated with intrinsic physical circumstellar conditions. Our data cannot distinguish between competing near-circumstellar bulk kinematic models but do provide evidence for localized inhomogeneous mass-loss.

astro-ph.SR↗

arXiv2008

A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz

Understanding diffuse Galactic radio emission is interesting both in its own right and for minimizing foreground contamination of cosmological measurements. Cosmic Microwave Background experiments have focused on frequencies > 10 GHz, whereas 21 cm tomography of the high redshift universe will mainly focus on < 0.2 GHz, for which less is currently known about Galactic emission. Motivated by this, we present a global sky model derived from all publicly available total power large-area radio surveys, digitized with optical character recognition when necessary and compiled into a uniform format, as well as the new Villa Elisa data extending the 1.4 GHz map to the entire sky. We quantify statistical and systematic uncertainties in these surveys by comparing them with various global multi-frequency model fits. We find that a principal component based model with only three components can fit the 11 most accurate data sets (at 10, 22, 45 & 408 MHz and 1.4, 2.3, 23, 33, 41, 61, 94 GHz) to an accuracy around 1%-10% depending on frequency and sky region. Both our data compilation and our software returning a predicted all-sky map at any frequency from 10 MHz to 100 GHz are publicly available at http://space.mit.edu/home/angelica/gsm .

astro-ph↗