Repository logo
 

Thermal Pressure in the Cold Neutral Medium of Nearby Galaxies

Published version
Peer-reviewed

Type

Article

Change log

Authors

Herrera-Camus, R 
Bolatto, A 
Wolfire, M 
Ostriker, E 
Draine, B 

Abstract

Dynamic and thermal processes regulate the structure of the multiphase interstellar medium (ISM), and ultimately establish how galaxies evolve through star formation. Thus, to constrain ISM models and better understand the interplay of these processes, it is of great interest to measure the thermal pressure (Pth) of the diffuse, neutral gas. By combining [C ii] 158 μm, H i, and CO data from 31 galaxies selected from the Herschel KINGFISH sample, we have measured thermal pressures in 534 predominantly atomic regions with typical sizes of ~1 kiloparsec. We find a distribution of thermal pressures in the Pth/k103--105 K cm−3 range. For a sub-sample of regions with conditions similar to those of the diffuse, neutral gas in the Galactic plane, we find thermal pressures that follow a log-normal distribution with a median value of Pth/k ≈ 3600 K cm−3. These results are consistent with thermal pressure measurements using other observational methods. We find that Pth increases with radiation field strength and star formation activity, as expected from the close link between the heating of the gas and the star formation rate. Our thermal pressure measurements fall in the regime where a two-phase ISM with cold and warm neutral media could exist in pressure equilibrium. Finally, we find that the midplane thermal pressure of the diffuse gas is about ~30% of the vertical weight of the overlying ISM, consistent with results from hydrodynamical simulations of self-regulated star formation in galactic disks.

Description

Keywords

galaxies: ISM, galaxies: star formation, ISM: lines and bands, ISM: structure

Journal Title

Astrophysical Journal

Conference Name

Journal ISSN

0004-637X
1538-4357

Volume Title

835

Publisher

IOP Publishing
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)
R.H.C. acknowledges support from a Fulbright-CONICYT grant. A.D.B. acknowledges partial support from a CAREER grant NSF-AST0955836, from NSFAST1139998, from NASA-JPL 1373858, NSF-AST 1412419 and from a Research Corporation for Science Advancement Cottrell Scholar award. M.G.W. was supported in part by NSF grant AST-1411827. E.C.O. is supported by NSF grant AST-1312006. The work of A.K.L. is supported by the National Science Foundation under Grants No. 1615109 and 1615105. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS, and SPIRE consortia. This work is based (in part) on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.