Relationships between Galactic Radio Continuum and H α Emission

Monthly Notices of the Royal Astronomical Society

2011

During a detailed search for optical counterparts of known Galactic supernova remnants (SNRs) using the Anglo‐Australian Observatory/United Kingdom Schmidt Telescope (AAO/UKST) Hα survey of the southern Galactic plane we have found characteristic optical Hα filaments and associated emission in the area of SNR G213.0−0.6. Although this remnant was previously detected in the radio as a non‐thermal source, we also confirm emission at 4850 MHz in the Parkes‐MIT‐NRAO (PMN) survey and at 1400 MHz in the NRAO/VLA Sky Survey (NVSS). There is an excellent match in morphological structure between the optical (Hα) and radio emission. We subsequently obtained optical spectroscopy of selected Hα filaments using the South African Astronomical Observatory 1.9‐m telescope which confirmed shock excitation typical of supernova remnants. Our discovery of Hα emission and the positional match with several radio frequency maps led us to reassign G213.0−0.6 as G213.3−0.4 as these coordinates more accurately reflect the actual centre of the SNR shell and hence the most probable place of the original supernova explosion. Support for this new SNR ID comes from the fact that the X‐ray source 1RXS J065049.7−003220 is situated in the centre of this new remnant and could be connected with the supernova explosion.

Section: Observationsmentioning

confidence: 97%

Optical detection and spectroscopic confirmation of supernova remnant G213.0−0.6 (now redesignated as G213.3−0.4)

Monthly Notices of the Royal Astronomical Society

2011

“…The optical study of Galactic SNRs permits a deeper understanding of the physical conditions in the remnant, such as density, kinematics and chemistry that is not possible with radio data alone. The optical data, when combined with radio, X‐ray and infrared data, are of particular value as the relationship between shock‐excited gaseous emission and synchrotron radio emission can be investigated (Cram, Green & Bock 1998). With SNR optical identification, we see a correlation between the shock wave and surrounding interstellar medium (ISM), especially if the supernova blast propagates into dense, cool regions where Hα emission is dominant.…”

Section: Optical Detection Of Snrsmentioning

confidence: 99%

First detection of optical light from SNR G279.0+1.1

Monthly Notices of the Royal Astronomical Society

2009

This is the initial paper in a series presenting the first optical detections and subsequent follow-up spectroscopy of known Southern Galactic supernova remnants (SNRs) previously discovered in the radio. These new detections come from the AAO/UKST HAlpha survey of the Southern Galactic plane which has opened up fresh opportunities to study Galactic remnants. Here we present the first optical imaging and follow-up spectra of Galactic SNR G279.0+1.1 where a series of 14 small-scale fragmented groups of HAlpha filaments have been discovered in a ~2.3 deg. area centred on G279.0+1.1. Individually they are somewhat inconspicuous but collectively they are completely enclosed within the overall radio contours of this known SNR. Three of these filamentary groupings are particularly prominent and optical spectra have been obtained across two of them. Their morphological structure and spectral characteristics are typical of optically detected SNR filaments. Very strong [S II] emission relative to H has been detected with [S II]/HAlpha 0.7 and 1.1, confirming strong, shock heated emission. This is sufficient to classify these filaments in the likely SNR domain and therefore indicating a direct connection with the radio remnant. Other typical SNR emission lines such as [O II] at 3727A, HBeta, [O III] at 4959 and 5007A, HAlpha and [N II] at 6548 and 6584A were also detected, lending strong support to an SNR origin of these optical filaments. The value and insights that these optical data can provide for known remnants are discussed along with their relevance to the Galactic nitrogen abundance. A serendipitous discovery of an adjacent H II region is also briefly described.Comment: 11 Pages. Accepted for publication in MNRA

“…However, only a very small component of Hα emission will be seen if the mechanical energy from the supernova explosion propagates into a very low density, hot ISM. At the same time non‐thermal emission will arise in different forms and instabilities will occur under the influence of magnetic fields (Cram, Green & Bock 1998). Hence, in order to see remnants in Hα, propagation of the blast wave should be into a cool and higher density ISM.…”

Section: Introductionmentioning

confidence: 99%

Catalogue of known Galactic SNRs uncovered in Hα light

Monthly Notices of the Royal Astronomical Society

2011

During detailed searches for new Galactic supernova remnants (SNRs) in the Anglo‐Australian Observatory/United Kingdom Schmidt Telescope (AAO/UKST) Hα survey of the southern Galactic plane, we also uncovered, for the first time, possible associated Hα emission in the vicinity of about 24 known Galactic SNRs previously known solely from radio or X‐ray observations. The possible optical counterparts to these known SNR were detected due to the 1‐arcsec resolution and 5 Rayleigh sensitivity of this Hα survey. The newly discovered emission frequently exhibits the typical filamentary form of other optically detected SNRs although sometimes the Hα emission clouds or fragmented filaments largely inside an SNR extend over the radio border. It is true that superposition of general diffuse and extended Galactic emission in the region of these remnants is a complicating factor, but for many optical candidates the Hα emission provides an excellent morphological and positional match to the observed radio emission so that an association seems clear. We have already published Hα images and confirmatory spectral observations for several of the best optical counterparts to known SNRs but for completeness and convenience we include them in our complete catalogue of previously known radio detected SNRs for which we have now uncovered Hα optical emission. For better visualization of the optical emissions from these faint supernova remnants and to enhance some low surface‐brightness features we also present quotient images of the Hα data divided by the accompanying broad‐band short‐red data. Out of 274 Galactic SNRs currently catalogued and detected in the radio only ∼20 per cent had previous optical counterparts. We may have now increased this by a further third by adding a further 24 candidate optical counterparts.