19 Feb
2019
19 Feb
'19
8:27 a.m.
*Speaker:* Shmuel Bialy (Center For Astrophysics)
*Date:* Thursday, February 21th
*Time:* 12:00-1:00 pm
Includes Pizza.
*Title: *The Multiphase HI Gas - from Solar to Low Metallicities
*Abstract: *The neutral atomic ISM is found to be multiphased, composed of
the cold neutral medium (CNM, T ~100 K) and the warm neutral medium (WNM, T
~ 10^4 K), which coexist at approximately the same thermal pressure. Such a
multiphase structure is predicted by models of heating-cooling thermal
balance, where heating is dominated by photoelectric heating from
dust-grains (and/or cosmic-ray heating), and cooling by Ly\alpha line
emission (for the WNN, T ~10^4 K) and [C II] and [O I] line-emission (for
the CNM, T ~100 K). Intermediate temperatures are thermally unstable. The
multiphase phenomena and the thermal instability zone, may play a key role
in regulating the star-formation properties in galaxies.
I will present recent results (Bialy & Sternberg, in prep) discussing the
thermal properties of HI gas, as functions of the UV intensity, the
cosmic-ray ionization rate, and gas metallicity, from solar to primordial
metallicities.I will discuss the importance of the residual H2 in controlling
the thermal structure of the predominantly HI gas. Despite its low
equilibrium abundance (H2/HI ~ 10^{-6}), we find that H2 cooling and
heating mechanisms (dominated by H2 ro-vibrational cooling, UV pumping
heating, and H2 formation heating) strongly affect (or totally dominate)
the phase structure at low metallicities and/or when the UV intensity to
cosmic-ray ionization rate ratio is low.
*Location: *B-106 @ Center for Astrophysics (60 Garden Street
<https://maps.google.com/?q=60+Garden+Street&entry=gmail&source=g>)
*Directions: *After entering the lobby of the CfA, turn right to enter the
hallway of the B building. In the hallway, turn right again, B-106 will be
at the end of the hallway on the left side.