NATIONAL RADIO ASTRONOMY OBSERVATORY A New Detection of
NATIONAL RADIO ASTRONOMY OBSERVATORY A New Detection of Extragalactic AME Eric J. Murphy
20 cm/1. 4 GHz Radio-to-FIR Spectrum of a Galaxy M 51 Dumas et al. 2010 3. 6 cm/8. 3 GHz Hα ng. VLA 1. 4 GHz ~ν-0. 8 33 GHz ~ν-0. 1
How did I get here? ? ? The Star Formation in Radio Survey (SFRS) Studying the Astrophysics of Star Formation in Nearby Galaxies Ø Sample Derived From: SINGS/KINGFISH/GOALS Ø 3. 6 – 500μm imaging of 61+ nearby galaxies borne from SINGS sample Ø IRS/PACS spec-mapping for 118 Nucs (56) + enucs (62) Ø Additional ~68 LIRGs/ULIRGs from GOALS (Barcos, Evans, Leroy, Linden, EJM) See Evans talk & Linden Poster Ø SFRS: GBT/JVLA/ATCA/ALMA Ø GBT: Ka-band for >~100 SINGS/KINGFISH SF regions (EJM+11, 12) Ø JVLA: S-, Ku-, and Ka-band for >~112 SINGS/KINGFISH SF regions (EJM+18 a, b) + 88 local (U)LIRGs Ø ALMA: for dense gas tracers (e. g. , HCN, HNC, CS) for resolved SF Law work (EJM+15)
The Pilot: NGC 6946 – The First Detection of Extragalactic AME PACS 100μm Ka-band (26 -40 GHz) CCB on GBT CARMA (92 GHz) free-free Sync. Spinning Dust IR EJM+10 AMI (16. 5 GHz) (Scaife et al. 2010) GISMO (150 GHz) See Hensley, EJM, & Staugun (2015) for latest modeling
A new detection of AME: NGC 4725 B 1. 9 kpc 33 GHz Nucleus N=160 > 3σ EJM+18 b EJM+18 a 300 pc Radio Observations ν (GHz) 3 15 22 33 44 Date Obs. 11/13 11/14 7/17 3/13, 7/17
A new detection – NGC 4725 B (optically invisible) Optical (BVRI) Mid-IR Spitzer EJM+18 b
Comparison: N 6946 E 4 & N 4725 B 7
A new detection – NGC 4725 B • Similar 33 GHz thermal fraction and AME luminosity as N 6946 E 4 • No obvious optical or non-thermal component • Mid-IR counterpart (hot dust/small grains) • Unlikely background given what (little) is known about such sources (EJM+18 c). • Highly enshrouded, nascent star-forming region (<3 Myr). • Implications for observed AME? • Smallest grains not yet destroyed by SNe? EJM+18 b
Variations in Grain Distribution? Importance of MIR/FIR Spectral Maps A B Strength of 33 GHz AME/Excess Fe locked on grains Fe in gas phase A. Exposed to a near-average radiation field. B. Much less gas phase Fe+ (IP~7. 9 e. V) relative to Ne+ (IP~21. 9 e. V) Ø Fe locked up on grains that have not been processed by shocks? Ø Abundance of small grains (a < 10 -7 cm) present contributing to anomalous emission?
Summary/Future Outlook • 2/160 (~1%) sources have very large 33 GHz/24μm ratios & strong AME • 30 GHz (AME)/IR (dust) ~x 2 -3 larger in both N 6946 E 4 and N 4725 B compared to MW values – most favorable extreme from strong AME? • ALMA proposal to look at 90 GHz + CO emission from N 4725 B • JWST to map 3. 3/3. 4 μm PAH emission from both sources • written and ready for June 2020! • In process of looking at 3, 15, and 33 GHz spectra of sources for each region to help identify more candidates (EJM+18 d, in prep. ) • Candidates will require follow-up at 90 GHz 10
Prospects with the ng. VLA EJM+ng. VLA Science Book VLA would need >800 hr to deliver same sensitivity 1. 5 u. Jy/bm 1” beam 11 170 n. Jy/bm 1” beam
ngvla. nrao. edu www. nrao. edu science. nrao. edu public. nrao. edu The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. 12
- Slides: 12