Warm and diffuse gas in the CMZ revealed by infrared H 3 + spectrum

1. Warm and diffuse gas in the CMZrevealed by infrared H3+ spectrum Takeshi Oka (Chicago), Tom Geballe (Gemini),Miwa Goto (MPIA) Tomonori Usuda (Subaru), Nick Indriolo, Ben McCall (UIUC) with thanks to: Tetsuya Nagata (Kyoto), Tomoharu Oka (Keio) Farhad Yusef-Zadeh (Northwestern), Kazuo Makishima (Tokyo) Galactic center workshop 2009, Shanghai, October 19-23, 2009

2. H3+, the new probe of the CMZ 1975 H 1980 Laboratory Spectrum (IR) Oka, PRL. 45, 531 T.G. 1951 1996 Interstellar H3+, Discovery, Dense Clouds Geballe, Oka, Nature 384, 334 H2 1970 1973 • Surprise - H3+ in GC and diffuse clouds • Geballe et al., ApJ, 510, 251, McCall et al. Sci, 279,1910 1998 – 2002 (H3+/H2)diffuse ~ 10 (H3+/H2)dense McCall et al. ApJ, 522, 338 & 567, 391 H3+ 2002 Surprise - discovery of (3,3) metastable line in GC Gotoet al. PASJ, 54, 951 1996 + • 2003ζdiffuse ~ 10ζdenseMcCallet al. Nature 422, 500 • (2009 - can be explained by increasing low-energy c-r’s • Indriolo et al. ApJ, 694, 257) The three stable forms of hydrogenand their discovery dates in the ISM • Revelation of warm and diffuse gas in GC • Oka et al. ApJ 632, 882 2008 Probe central 30 pc sightlinesGoto et al. ApJ 688, 306 2009 Sightlines 140 pc W – 100 pc E Geballe, Oka

3. What do we learn from H3+ ? fundamental IR vib-rot transitions 3.5-4.0μm ζL ζ~ 10-17 s-1 for dense clouds in Gal. Disk ζ~ 10-16 s-1 for diffuse clouds in GD ζ ~ 10-15 s-1 for gas in the CMZ ζ ~ 10-14 s-1 for gas in the CND (?) H2 ioniz. rate, ζ J Path length, L CO → M H3+ → L (if we know ζ, or ζ if we know L ) 361 K above gnd 27 days K rotational levels in v=0 ortho Temperature, T, density, n para

4. Sightline to Quintuplet source GCS 3-2 (pencil-beam through foreground and CMZ) narrow components plus “trough” CMZ T ~ 250 K n≤ 100 cm-3 Spiral arms no CO trough This sightline has little or no CMZ CO.

5. Eight stars from the center to 30 pc East All show absorption trough in (3,3) level so H3+ ubiquitous warm and diffuse gas everywhere High values of ζL for trough (CMZ) high ionization rate long path length and volume filling factor ζL = 2keN(H3+)(nC/nH)SVRX /f (ζL)min = (1.3 – 4.3) ×105 cm/s For ζ ~ 3 ×10-16 s-1, L~ 150 – 500 pc clearly absurd ζ ~ 3× 10-15 s-1L~ 15 – 50 pc note: these assume solar interstellar C; for constant ζ, L increases as C increases But even these sightlines sample only a small fraction of the CMZ.

6. New sightlines by data-mining GLIMPSE and 2MASS for bright IR sources with smooth continua (i.e., not RGs) in or behind the CMZ. (also hope to use Mauerhan’s stars) 100 pc 140 pc CO H3+ GCS 3-2 α Sgr C two high vel. mol clouds, 3 kpc arm, low vel diffuse cl.- no CO Is it in the CMZ? ι Sgr B ~12 vel. components; largest N(H3+) ever; is any of it CMZ gas?

7. The new environment is incompatible with the previous concept of gas in the CMZ Previous New X-ray gas 80 % « 80 % (Chandra) Ionized gas 10 % 10 % Molecular gas 10 % few % AV~ 30 Diffuse gas 0% > 10%

8. CONCLUSION Not only is the average density of the CMZ ~ 100 cm-3 (Martin-Pintado – this meeting), but also a significant (and perhaps dominant) fraction of the CMZ’s volume actually is filled with warm gas at about that density! Spitzer+VLA

10. M. Schultheis et al., A&A, 495, 157 (2009)