Unraveling the distribution of ionized gas in the Galactic plane with radio recombination lines.

Transcription

1 Unraveling the distribution of ionized gas in the Galactic plane with radio recombination lines. Jorge Pineda, Shinji Horiuchi, Tom Kuiper, Geoff Bryden, Melissa Soriano, and Joe Lazio Jet Propulsion Laboratory

2 Goal: Understand the lifecycle of the interstellar medium Far-IR tracers: [CII] 158um (Traces H 2, HI, and ionized gas ) [NII] 205 and 122um (Ionized gas) [OI] 145 and 63um (Dense and warm H 2 gas) Etc. ngvla tracers: High density molecular tracers. Radio Recombination Lines Radio Continuum

3 Goal: Understand the lifecycle of the interstellar medium Far-IR tracers: [CII] 158um (Traces H 2, HI, and ionized gas ) [NII] 205 and 122um (Ionized gas) [OI] 145 and 63um (Dense and warm H 2 gas) Etc. ngvla tracers: High density molecular tracers. Radio Recombination Lines Radio Continuum

4 Radio Recombination Line Survey of the Galactic Plane RRLs are spectrally resolved, unobscured tracers of ionized gas. Provide unambiguous determination of the emission measure EM=neN(H + )=ne 2 L. It allows us to study the electron density distribution. (Continuum has to be separated between thermal and non-thermal emission). Hydrogen RRLs are the brightest, but Helium and Carbon RRLs can be detected in bright sources. Line to continuum ratio gives the electron temperature (e.g. Quireza et al. 2006) They trace the number of Lyman continuum photons and thus they trace the Star Formation Rate. Observations with a broad instantaneous bandwidth can allow us to observe many RRLs simultaneously, thus significantly increasing the sensitivity (Balser 2006). Höglund and Mezger (1965)

5 Radio Recombination Line Survey of the Galactic Plane We will observe 112 GOT C+ lines-of-sight in RRL with the NASA DSS-43 70m telescope in K and X bands. (40 (K) and 110 (X) angular, <1 km/sec velocity resolution) Upcoming capabilities in of the DSS 43 will allow simultaneous observations of RRL between 18 and 24 GHz (2 pol x 8 RRLs) NASA DSS-43 Deep Space Network 70m antenna. Canberra, Australia.

6 GOT C+ [CII] 1.9 THz Survey GOT C+ is a volume weighted sample of 500 LOSs in the disk of the Milky Way. 7 LOS 10 LOS 11 LOS 11 LOS 11 LOS 6 LOS We sample the Galactic plane every one degree in the inner galaxy and every two in the outer galaxy. 6 LOS 7 LOS GOAL: Sample as many different clouds as possible over a wide range of physical conditions. This allow us to obtain statistical information about the clouds in the Milky Way.

7 The rotation of the Milky Way

8 The [CII] distribution of the Milky Way: Longitude-Velocity map The lines are projection of the Milky Way s spiral arms into the Longitude-Velocity map. Pineda et al. (2013) A&A 554, A103

9 Galactocentric Distribution To derive global properties of population of clouds in the Milky Way we divide it into a set of rings and calculate the radially average distribution of different tracers. Knowing the distribution of the ionized gas in the Galaxy is fundamental for the interpretation of [CII] observations.

10 Radio Recombination Line Survey of the Galactic Plane Science Objective #1: Follow techniques used in the GOT C+ survey to determine the distribution of ionized gas in the plane of the Milky Way. Determine the contribution from ionized gas to the observed [CII] emission.

11 Radio Recombination Line Survey of the Galactic Plane Science Objective #2: Derive the distribution of the Star Formation Rate in the plane of the Milky Way Compare the RRL derived SFR with other tracers such as [CII]. Pineda et al A&A 570, A121

12 Radio Recombination Line Survey of the Galactic Plane Science Objective #2: Derive the distribution of the Star Formation Rate in the plane of the Milky Way Compare the RRL derived SFR with other tracers such as [CII]. Pineda et al A&A 570, A121

13 Radio Recombination Line Survey of the Galactic Plane We will observe 112 GOT C+ lines-of-sight in RRL with the NASA DSS-43 70m telescope in K and X bands. (40 (K) and 110 (X) angular, <1 km/sec velocity resolution) Current status: 62 LOSs observed in X-band. NASA DSS-43 Deep Space Network 70m antenna. Canberra, Australia.

14 The RRL distribution of the Milky Way: Longitude-Velocity map The lines are projection of the Milky Way s spiral arms into the Longitude-Velocity map. Pineda et al. (2013) A&A 554, A103

15 The [CII] distribution of the Milky Way: Longitude-Velocity map The lines are projection of the Milky Way s spiral arms into the Longitude-Velocity map. Pineda et al. (2013) A&A 554, A103

16 The HI distribution of the Milky Way: Longitude-Velocity map The lines are projection of the Milky Way s spiral arms into the Longitude-Velocity map. Pineda et al. (2013) A&A 554, A103

17 The CO distribution of the Milky Way: Longitude-Velocity map The lines are projection of the Milky Way s spiral arms into the Longitude-Velocity map. Pineda et al. (2013) A&A 554, A103

18 Comparison between RRL, [CII] and [NII] lines in the MW. RRL tends to follow [NII] and [CII] emission. But [CII]/RRL and [NII]/RRL vary from place to place. Wide range of physical conditions in the observed clouds. Red: H91a and H92a Blue: [NII] 205um Black: [CII] 158um

19 [NII]/RRL ratio as a tracer of electron density. [NII] 205um intensity is proportional to the fractional population at the 3 P 1 level, f u (ne), which depends on the electron density, and the column density of N +. The RRL intensity is proportional to the electron density times the column density of H +. In LTE, the [NII]/RRL ratio is proportional to f u (ne)/ne times the nitrogen abundance. Correction needed for non-lte effects needed. We can use the [NII] 205um/RRL ratio to solve for the electron density of the gas.

20 [NII]/RRL ratio as a tracer of electron density. [NII] 205um intensity is proportional to the fractional population at the 3 P 1 level, f u (ne), which depends on the electron density, and the column density of N +. The RRL intensity is proportional to the electron density times the column density of H +. In LTE, the [NII]/RRL ratio is proportional to f u (ne)/ne times the nitrogen abundance. Correction needed for non-lte effects needed. We can use the [NII] 205um/RRL ratio to solve for the electron density of the gas.

21 [NII]/RRL ratio as a tracer of electron density. [NII] 205um intensity is proportional to the fractional population at the 3 P 1 level, f u (ne), which depends on the electron density, and the column density of N +. The RRL intensity is proportional to the electron density times the column density of H +. In LTE, the [NII]/RRL ratio is proportional to f u (ne)/ne times the nitrogen abundance. Correction needed for non-lte effects needed. We can use the [NII] 205um/RRL ratio to solve for the electron density of the gas.

22 [NII]/RRL ratio as a tracer of electron density. [NII] 205um intensity is proportional to the fractional population at the 3 P 1 level, f u (ne), which depends on the electron density, and the column density of N +. The RRL intensity is proportional to the electron density times the column density of H +. In LTE, the [NII]/RRL ratio is proportional to f u (ne)/ne times the nitrogen abundance. Correction needed for non-lte effects needed. We can use the [NII] 205um/RRL ratio to solve for the electron density of the gas. Average density in sample, 32 cm -3 Average density from 122um/205um, 44 cm -3 (Goldsmith et al. 2015) Next step: Derive ne as a function of velocity => determine the electron density distribution of the Milky Way. Pineda et al in preparation

23 Radio recombination line observations with the ngvla The large collecting area of the ngvla combined with large instantaneous bandwidths can provide extreme sensitive observations of RRLs. Our work in the Milky Way will pave the way for similar studies in external galaxies. We can learn about the properties of the ISM over different environmental conditions in galaxies as well as determine the star formation history of the universe. These data will have synergies with surveys of [CII] emission of high-z galaxies with ALMA and future Far-IR observatories.

24 Beyond the Milky Way The ngvla observations will complement current (SOFIA) and future (OST) Far-Infrared observatories. SOFIA is completing a full map of M51 in the [CII] 158um line. The ngvla will be able powerful tool to map nearby galaxies in RRLs revealing the properties of the ionized gas and star formation. Pineda, Stutzki et al in preparation