ALMA observations of molecular absorption in four directions toward the Galactic bulge

Abstract

Alma Cycle 3 observations showed strong absorption from diffuse molecular gas in the bulge at -200 \kms\ $<\mathrm{v}<-140$ \kms\ toward J1744-3116 (l,b)= (-2.13d,-1d) We aimed to test if bulge molecular gas could also be seen toward the three other sufficiently strong mm-wave sources seen toward the bulgeat $|b|<3$°We took absorption profiles of \hcop (1-0) and other species in ALMA Cy 4 toward J1713-3418, J1717-3341, J1733-3722 and J1744-3116. Strong molecular absorption from disk gas at $|\rmv| \la 30$ \kms\ was detected in all directions, and absorption from the 3 kpc arm was newly detected toward J1717 and J1744. However, only the sightline toward J1744 is dominated by molecular gas overall and no other sightlines showed molecular absorption from gas deep inside the bulge. No molecular absorption was detected toward J1717 where H I emission from the bulge was previously known. As observed in \hcop, HCN, \cch\ and CS, the bulge gas toward J1744 at $v<-135$ \kms\ has chemistry and kinematics like that seen near the Sun and in the Milky Way disk generally. We measured isotopologic ratios N(\hcop)/N(H${}^{13}$CO\p) $>51(3\sigma )$ for the bulge gas toward J1744 and $58\pm 9$ and $64\pm 4$ for the disk gas toward J1717 and J1744, respectively, all well above the value of 20-25 typical of the central molecular zone.} %conclusions heading (optional), leave it empty if necessary {The kinematics and chemistry of the bulge gas observed toward J1744 more nearly resemble that of gas in the Milky Way disk than in the central molecular zone.}

In press in Astronomy and Astrophysics

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